This PDF file contains the front matter associated with SPIE Proceedings Volume 12614, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In this paper, an underwater visible light communication (UVLC) system is set up to simulate the nonlinear noise channel. Then we adopted Levin-Campello (LC) bit-load algorithm to make the system adaptively modulate input signals according to sub-channel gains and signal noise ratio. The bitrate and bit error rate (BER) are utilized as the main indexes to quantize the performance of amplitude phase shift keying (APSK) and the square geometrical shaping (QAM) modulation format in both linear and nonlinear operating range. Experimental results show that particularly in nonlinear operation range. The result indicates that APSK modulation format can achieve the higher bitrate than that with QAM modulation format, and with LC bit-load algorithm APSK can achieve a 3.18Gbps transmission rate below 3.8 x 10^-3 BER threshold.

We experimentally demonstrate a method for predicting and compensating the system error of a 3×3 on-chip microring resonator (MRR) weight bank using a pre-designed back propagation (BP) neural network. The system error can be quickly predicted and well compensated to improve the computation precision of optical matrix-vector multiplication (MVM), without bulky experimental devices. The results show that the computation precision can be increased from 5- bit to 7-bit. This work provides a weight accuracy improvement method for MRR-based photonic integrated chips for applications such as optical computing and optical communication.

Broad-spectrum light sources are widely used in optical fiber sensing and spectral analysis. At present, the supercontinuum spectrum generated by photonic crystal fiber nonlinearity covers a wide range of wavelengths, while it is a challenge to make the spectral flat, especially in 1000-1200nm range. In comparison, ultra-broadband light sources generated by doped fibers have better flatness. Bi-doped glass and optical fibers have attracted much attention in the field of ultra-broadband light sources and optical amplifiers due to their ultra-broadband spontaneous emission. We prepared Bi-doped quartz glass by glass phase separation method, and synthesized Bi active center-Al (BAC-Al) in glass by controlling the valence state of Bi by sintering atmosphere, which possess luminescence at 1120nm. Yb and Bi were simultaneously incorporated into glass for achieving combined BAC-Al and Yb luminescence. The combined spectrum covers 1000-1250nm, and the half maximum full width can reach 150nm. Various properties of the glass are tested, and the luminescence of bismuth and ytterbium in the glass are studied. The energy transfer between Bi and Yb was discovered, which can help to infer the energy level of BAC-Al. This work not only provides new materials and methods for ultra-broadband light sources, but also provides new ideas for exploring the near-infrared luminescence principle of Bi.

An algorithm based on the Manhattan algorithm is developed to solve the equal-length waveguide (WG) problem in silicon photonics (SiPh) layout. The method is applicable to complex photonic circuits.

Dispersion management is highly desired in various applications such as microwave photonics and optical communication, helping reduce the delay disorder and modulate the pulse profiles. In this paper, we propose a new concept of digitally-tunable dispersion management. and a digitally-tunable dispersion controller (DTDC) on silicon composed of optical switches and chirped multimode waveguide gratings (CMWGs) is demonstrated for the first time. All the CMWGs are identical and have the same dispersion value of D₀ and dispersion ranging from 0 to (2^N-1)D₀ can be tuned with a step of D₀ by switching the propagation path of light. More importantly, the DTDC is circulator-free. finally, a DTDC is realized with four stages of 2-mm-long CMWGs, enabling the dispersion tuning from 0 to 42.8 ps/nm with a step of 2.82 ps/nm.

With the expansion of human activities underwater, such as environmental monitoring, underwater exploration, and scientific data collection, there is an urgent need for a secure, reliable, and high-speed underwater wireless communication technology. Visible light communication technology, as a necessary path for future 6G high-speed wireless communication, has the advantages of high bandwidth, high confidentiality, lightweight equipment size, as well as meets the concept of carbon neutrality. With the rapid development of LED industry, LED-based visible light communication technology has also been widely used and developed, only that most of the researches are established under short distance and high-speed laboratory conditions. In view of the integration requirements of lighting and communication, as well as the serious attenuation of radio frequency communication in water that causes the limited transmission distance, and the low bandwidth of underwater acoustic communication, this paper demonstrates underwater audio transmission over 10 m distance, exploiting four blue (454 nm) LEDs at the transmitter and a photodiode at the receiver. The system uses STC15W4K60S4 microcontroller as the main control chip. The transmitter conducts low-pass filtering and signal amplification through MAX9813L and AD828, and drives LEDs to realize the conversion and transmission of electro-optic signals. The receiver uses photodiode to convert the received optical signal into an electrical signal, and generates the output signal of the audio playback device through transimpedance amplification and filter circuits. Underwater test results prove that the proposed communication system can achieve high audio transmission quality.

Due to the growing demand for devices supporting the Internet of Things (IoT), it’s necessary to develop integrated chips with small size, fast response and high robustness to provide the application of the IoT. In addition to light emission, GaN-based quantum well diodes (QWDs) can convert light into electricity via the photovoltaic effect, simultaneously exhibiting inherent light emission and detection functionalities. Here, we report a LED with automatic brightness control utilizing the dual function of simultaneous light emission and detection, which is implemented on an III-nitride-on-silicon. Due to the inherent rapid photoelectric conversion of MQW diode, the diode is able to communicate with another. Using one MQW diode as the emitter, and another MQW diode as receiver, a visible light communication link was established. The overlap between the emission and detection spectra demonstrated that simultaneous emission-detection phenomenon also exists in MQW diodes. When the LED is modulated to emit light and we shine it with another modulated light beam at the same time, the LED operates under the simultaneous emissiondetection mode. The MQW diode converted external light into photocurrent as feedback to control circuit, by programming in one-chip computer, we can control the feedback circuit to turn the diode brighter or darker according to our willing. Utilizing the dual function of simultaneous light emission and detection of the MQW diode, the proposed MQW diode on its own can achieve real-time regulation of brightness without an external photodetector by integrating a programmed circuit.

In this work, we demonstrate a green light in-plane communication system at 557 nm through a monolithic integration of two same structure MQWs devices-LED and PD, and waveguides on a GaN-on-Si wafer with InGaN/GaN superlattice layer. The MQW structures are responsible for the emission in the LED and photodetection in the PD. In addition, the device have the ability of luminescing and detecting simultaneously in quantum wells. The front side of device is completed by using e-beam evaporation, photolithography, etching. Since Si substrate is unfavorable for optical transmission due to strong visible light absorption. One last step is stripping of the Si substrate to increase the signal intensity received at the receiving side. As on-chip free-space transmission is hard to achieve due to the omnidirectional emission of LED, the installation of waveguides between LED and PD is beneficial for efficient transmission of optical signals. The optical and electrical properties of this communication system are characterized through series of measurement. To practically cognize the ability of transmission of the communication system, we use the system achieveing an in-panle transmission of PRBS signals modulated by non-return-to-zero on-off-keying (NRZ-OOK) at the speed of 10 Mbps, then analyze the result and the influence of other system factors such as resistive-capacitive (RC) time constant and junction capacitance of the receiver. According to the analysis of results, the system is able to transmitted and received PRBS signals at a rate of 10 Mbps.

The presence of quantum correlations in composite quantum systems is one of the main features of quantum mechanics. However, by now, all known quantifications of this correlation for continuous-variable systems are very difficult to compute. Therefore, it makes sense to find simpler and computable quantifications of Gaussian quantum correlations. Recently, a computable Gaussian quantum correlation M is proposed, which can be obtained based on the covariance matrix. Here, we experimentally demonstrate the Gaussian quantum correlation 𝑀 based on the two-mode entangled state carrying orbital angular momentum (OAM) generated from a four-wave mixing process in a hot Cesium atom vapor cell and investigate the evolution of such correlation in the lossy channel. Our results show that quantum correlation 𝑀 is robust in the lossy channel.

Quartz has the characteristics of piezoelectricity, insulation, light transmission, high hardness, etc., and has great potential for development, especially devices based on single crystal quartz materials are widely used in various sensors. The development of quartz MEMS devices in the direction of miniaturization and high integration puts forward higher requirements for the micro-nano processing technology of quartz. The main processing techniques of quartz MEMS devices are mechanical processing, dry etching and wet etching; mechanical processing is difficult to break through the bottleneck of accuracy and size; dry etching requires a thick enough mask and is difficult to prepare; wet etching rate High, the process is simple and easy to control, and the cost is low, especially for the processing of irregular and complex three-dimensional structures such as cavities, sharp corners, high aspect ratio sidewalls, cantilever beams, etc., especially for anisotropic wet etching. At the same time, the interface will not cause physical damage to the material itself, which can ensure the stability of the quartz MEMS device. This paper focuses on the wet etching process of Z-cut quartz to optimize the wet etching rate and surface roughness for MEMS devices.

The actual trunk multi-core fiber (MCF) splicing is studied by a 7-core fiber for long-distance transmission. The results show that the splicing quality is influenced by fusion splicing parameters mostly, such as Including fiber separation distance and electrode spacing. It is influenced by the mismatch of the mode field and other factors. By improving the process of the fiber end-face treatment, programming the end-face alignment and using the axis algorithm to optimize the fusion splicing parameters automatically, the low-loss optical fiber fusion is achieved. The typical value of splicing point loss can be less than 0.35dB, which can better meet the requirements of application for engineering wiring.

We investigate theoretically and experimentally anomalous spectral holes, i.e. the cancellations of certain frequency modes inside a wide frequency comb, in a fiber-loop circuit with an incorporated phase modulator (PM). During the process of phase modulation, the frequency modes couple between each other accompanying with a nonreciprocal phase, which mimics an artificial gauge potential for photons. As the light circulates in the fiber loop, coherent interference effects occur between frequency modes in distinct circulations, which are highly influenced by the artificial gauge potential. By carefully choosing the gauge potential via adjusting the modulation phase, we can coherently suppress a series of frequency components within a broad spectrum and flexibly manipulate the positions, widths and depths of these drops. In the experiment, we achieved a hole position shift with ~50 GHz and a hole width with ~30 GHz while the extinction ratio reaches ~15 dB. For even higher modulation depth beyond the experiment range, the simulation shows that the width of main spectral hole will grow linearly with the increase of modulation depth while the position and depth tend to be stable. The study reveals the anomalous cancellation of frequency modes in a fiber loop, which holds great promises for potential applications in optical communications and signal processing.

Optical fiber composite overhead ground wire (OPGW), which consists of ground wire and optical fibers, plays an important role at electric power communication system. In daily operation, due to bad low temperature, OPGW will be covered by ice, which will lead to OPGW galloping and sleet jump of the wire. Meanwhile, OPGW icing can also make the wire with strain, which has the possibility of fiber fracture. Therefore, it is very important to judge and predict the state of OPGW icing. In this paper, a prediction model of ice coating thickness of OPGW based on multi-class Support Vector Machine (SVM) is proposed. In this model, the optical cable icing data measured in actual operating environment and laboratory simulation experiments are used as the data set to construct the prediction model.

We numerically and experimentally demonstrated a low different modal gain (DMG) 4-LP modes L-band few-mode fiber amplifier by using an extremely simple fiber structure. The optimization effect of FM-EDF core radius on DMG performance and gain was numerically studied. An FM-EDF was fabricated by modified chemical vapor deposition (MCVD), for which the NA was improved to 0.25 and the core radius was properly selected to 8.1 μm. In the case of core pumping of the LP₁₁ mode at 1480 nm, an e DMG of ~0.7 dB and the gain of <17 dB was obtained for all four modes at 1570 nm. The results suggested that our proposed erbium-doped fiber amplifier has great potential for large-capacity long-haul mode division multiplexing (MDM) transmission system.

The nanoporous silica with silica content more than 96% can be obtained, which based on the glass phase separation technology, the boron rich phase can be removed by acid leaching which according to control the stable and uniform phase separation of borosilicate glass (SiO₂-B₂O₃-Na₂O). The porous glass has strong adsorption capacity and large surface area, in particular, the abundant broken bonds on the surface of porous glass channels provide enough non-bridging oxygen bonds. So that a new active fiber with high gain and uniformity can be obtained by drawing the rare earth doped nanoporous glass which is potential for fiber amplifiers and fiber lasers. However, nanoporous glass is doped in solution, hydroxyl groups will be retained after the sintering, which will increase the background loss of the material. Because Si-F bond energy is greater and bonding is stronger than Si-OH, F-bonds with Si replaced OH- by fluoride doping so as to reduce the loss caused by hydroxyl. In this paper, nanoporous glass is soaked in the solution with a certain concentration of fluoride, and sintered it at high temperature in helium atmosphere to reduce loss. The experimental results show that the hydroxyl content in porous glass gradually decreases with the increase of fluoride concentration, the raman peak at 935 cm-1 in the raman spectrum also confirms the existence of Si-F bond, and the lowest hydroxyl content is only 3.31ppm. In this case, the refractive index of glass will decrease uniformly with the increase of fluoride doping concentration, which provides a new method for preparing low loss nanoporous glass fiber materials.

In the aviation field, the instrument must be small, light, and vibration resistant. A Fiber Bragg Grating (FBG) sensor interrogator with a linear variable filter (LVF) can be well suited for the requirements in the aviation field, due to its special optical structure. Moreover, it has a great prospect of applications in the aviation field. An error model is established and the simulation results show that the inhomogeneous illumination of the incident light has an impact on the sensitivity of the interrogator. This paper defines the degree of inhomogeneity to describe the effect of inhomogeneous illumination. Using this model, the design of the interrogator can be optimized to improve its sensitivity.

Phase-sensitive optical time-domain reflectometry (φ-OTDR) is highly sensitive to strain changes of sensing fiber caused by external vibration, by which we are able to locate the vibration. In practice, interference fading will inevitably occur in backscattered Rayleigh traces of φ-OTDR due to the use of highly coherent light source, which increase the possibility of failure detection. In order to reduce the influence of interference fading on vibration detection, both frequency-division multiplexing (FDM) and rotated-vector-sum (RVS) over both time-and frequency-domain are employed in our method. Based on the method, we perform φ-OTDR experiment to locate vibrations. By extracting 3 frequency components of the beating signals (~200 MHz) and carrying out dual rotation, interference fading can be suppressed to a large extent, the vibration-induced phase changes are precisely recovered. One point should be noted is that we found that there is a certain correlation between each frequency component extracted from the beating signal, resulting in interference fading points cannot be completely removed.

Reducing false alarming of vibration and shortening data processing time are one of the key problems of phase sensitive optical time-domain reflectometer (φ-OTDR). Generally speaking, there are two demodulation methods to locate vibrations: phase demodulation and amplitude demodulation. At present, an often-used method is phase-based crosscorrelation, which shows a comparatively reliable detection performance. Compared with phase cross-correlation, energy/power cross-correlation between different positions is simpler and has certain advantages in practical applications. In this paper, we use φ-OTDR to collects periodic vibration signals (power signals) and transient vibration signals (energy signals). Amplitude differentiation is firstly calculated along slow time axis for the Rayleigh backscattering trajectories. For periodic vibration, power spectrum is then obtained at each position, and cross-correlation coefficients between any two spectrums are computed. If the vibration is transient, average energy is calculated along fast time axis and average energy cross-correlation is performed between any two locations. With the cross-correlation values, we are able to determine whether there is vibration on the optical fiber. In the experiment, periodic vibration is simulated by a sine-driven PZT and transient vibration is mimicked by pencil-break. These results demonstrate that power (energy) cross-correlation coefficients work well to locate periodic (transient) vibrations.

Distributed vibration sensors by amplitude-demodulated phase sensitive optical time-domain reflectometers (φ-OTDR) have been widely used in many applications like safety monitoring of large-scale infrastructures and fence security. In order to locate vibrations, every two Rayleigh backscattering traces (RBTs) spaced apart by a certain interval (i.e., differential step k) are traditionally subtracted over a certain measurement time, and then all the subtractions are summed together and used to detect external vibration events. This method is denoted as amplitude-based accumulative differential method (ADM). Yet, the ADM has been demonstrated that the superimposing differential signal shows highly dependent on k which is closely related to vibration frequency (i.e., fs). Inappropriate k values would fail to locate the vibration. It is thus possible to envisage measuring f_s by taking advantage of this strong dependence of the ADM on f_s. In this manuscript, a simple method of estimating f_s is proposed by measuring the relationship between the ADM signal and k. The validity of this method is demonstrated by our experiment, in which a vibration event induced by a sinusoidal-driven PZT is detected.

In this article, a long period fiber grating (LPFG) based on femtosecond laser irradiation is proposed to generate the third order Orbital Angular Momentum (OAM) mode. With the advantage of lower heat absorption efficiency, lower power and small focused spot size，this method is more reliable ,repeatable and promising compared with the traditional method based on carbon dioxide laser. The experiments results demonstrated that the fundamental mode can be converted to the linear polarization mode LP₃₁ mode even OAM_±3 modes with 98% mode conversion efficiency near 1550nm. The proposed method has the potential to generate higher order mode.

Phase-sensitive optical time domain reflectometer (φ-OTDR) has been extensively investigated in fields of intrusion detection and structural health monitoring. It should be noted that phase noises would keep accumulating during pulse transmission. By subtracting an initial phase at the input point from demodulated phases at other positions, the noises related to the laser itself except random noises can be considerably reduced. In order to further decrease the impact of random noises on waveform retrieval of external vibrations, it is necessary to eliminate the accumulated noises before vibration position as much as possible. In this work, a sliding root mean square method (SRMS) is firstly applied to locate vibration events. By the SRMS, the demodulated phase at ~10 m before vibration point is regarded as the modified reference. Then, the vibration waveform can be retrieved after phase subtraction. For comparison purpose, both the input and modified references are employed to retrieve temporal vibration signals. Experimental results show that the SRMS shows good noise performance for vibration location. In terms of signal retrieval, the vibration waveform can be recovered with better noise suppression by the modified reference compared to the input one.

Surface plasmon resonance (SPR) sensors show great potential in practical applications of concentration and temperature measurement due to their high sensitivity and fast response speed. However, the cumbersome probe preparation process is still a significant problem faced by fiber SPR technology. Here, we propose a simple and rapid method for the fabrication of sensing probes. In this study, the silver mirror reaction was used to coat the silver film on the surface of a core mismatch fiber structure formed by a single-mode fiber (SMF) and two multimode fibers (MMF) to excite the SPR, The core mismatch sensing element is prepared by cleaving and fusion splicing, and the coating of the sensing film adopts a simple silver mirror reaction, so the preparation process is extremely simple. After the silver film is uniformly coated on the single-mode fiber sensing unit, the sensing unit was immersed in polydimethylsiloxane (PDMS) and cured by heating for temperature sensing measurement. Thanks to the higher thermo-optic coefficient, the refractive index of PDMS on the sensor probe will also change when the external temperature changes, so the surface plasmon resonance dip underwent a noticeable wavelength shift. Further, the cured PDMS can also enhance the stability of the probe structure. The results show that in the temperature range of 20℃ to 80℃, the maximum temperature sensitivity is -1.66nm/℃, with good stability, accuracy and repeatability. In addition, the sensor has the advantages of simple structure, convenient fabrication, good reversibility and strong stability. The temperature sensor based on core mismatch is expected to be used in the temperature detection of fields such as biology, medical treatment, and aerospace.

Optical fiber has become a very important optical transmission medium due to its excellent anti-interference ability, longdistance transmission and low loss characteristics, which is widely used in signal transmission, remote sensing, optical imaging fields. In order to obtain the specific image spot shape and size, the research of optical output and imaging performance of fiber is gradually increasing. At present, common optical fibers have weak imaging regulation ability, most of the optical fiber imaging probes mainly use light regulation ability of photonic crystal fiber or add microlens on the fiber end face to realize the regulation of light output and imaging ability, which used to light collimate, light focus and control the wavelength of light. However, photonic crystal fibers have the disadvantages of difficult preparation, high equipment requirements and high cost, the method of adding microlens on the fiber end face will cause the probe to be oversize. Here, we propose a simple-fast and cost-effective preparation method for beveled fiber, which can be prepared by beveling and grinding simply. The beveled angle of fiber is closely related to the incident angle and exit angle of the light, different bevel angles will have a huge impact on the propagation path of light and lead to different degrees of total internal reflection of light on the end face of fiber, which will ultimately affect the shape of image spot. The imaging performance of fiber is simulated and analyzed by Zemax software, results show that the shape of image can be control by changing the beveled angle of fiber end face. The experiments show that the actual effect of beveled fiber is consistent with the simulation results, specific imaging requirements can be met by optimizing beveled angle, which is expected to be combined with optical elements to build a compact optical path.

In-situ and real-time particle size measurements are necessary in many industrial fields, such as real-time monitoring of particle manufacturing process and intermediate process analysis of chemical reactions. Currently, most of the traditional laser particle size analyzers are bulky, not suitable for in-situ measurement in narrow space. Fiber-optic particle size analyzers based on white-light scattering usually have a slow detection rate and cannot meet the needs of real-time measurement. In this report, a fiber-optic particle sizer based on multi-spectral scattering for in-situ rapid measurement of particle size distribution is proposed. The particle size distribution is measured by a variety of light sources with different spectra based on the Mie scattering theory. We theoretically analyzed the feasibility of this technology and demonstrated in polystyrene microsphere suspensions. The results show that the fiber-optic particle sizer can achieve a measurement accuracy of 0.5μm in the measurement range of 3-15μm, with the measurement speed of 1kHz.

In this paper, a optical fiber magnetic field sensor with the tapered twin-core photonic crystal fiber coupling structure has been presented and experimentally demonstrated. The magnetic fluid(MF) was injected into the air hole between two parallel fiber cores of the photonic crystal fiber, and then the two fiber cores of the twin-core photonic crystal fiber infiltrated with MF were tapered horizontally. A total reflection film was plated on the end face of the fusion cone of the twin-core photonic crystal fiber. The guided light was transmitted from the input port to the pull-cone area of the fiber, reflected by the reflection end face after mode coupling, and finally reflected from the output port to the output fiber. According to the above light transmission mode of reflective fiber coupler, The magnetic field measurement principle was studied, which the coupling region of twin-core photonic crystal fiber had been injected MF. The change of the effective refractive index will lead to the central wavelength shift of the fiber magnetic field coupler, and the magnetic field is measured by inquiring the wavelength shift of the transmission spectrum. The magnetic field response characteristics of the sensor were studied and analyzed through experiments. The experimental results show that the sensitivity of this method can reach 116pm/Oe. The fiber magnetic field sensor has the advantages of miniaturization, high sensitivity, and no electromagnetic interference. The magnetic field sensor can be widely used in the field of aviation, military, transportation, medicine and other fields of magnetic field accurate measurement.

We demonstrate the capability of the multimode fiber and photonic time-stretch based compressive sampling scheme to detect chirp radio frequency signals, with the advantages of fast speed, high accuracy, less complexity and low cost.

Pico projector has the advantages of small size, large field of view, and wide color gamut, suitable in AR or VR displaying. In this study, we reported a single-fiber scanning projector, which can sweep a modulated laser beam to form an image via a PZT tube. However, PZT is sensitive to environmental temperature, the change of temperature will lead to the unexpected shifts of optical fiber scanning trajectory and finally affect the quality of the projection. In order to solve this problem, proposed a self-calibration system which can automatically adjust the PZT drive signal and achieve constant fiber scanning trajectory under different ambient temperatures by combining piezoelectric self-induction and reinforcement learning (RL).

Oscillating-amplifying integrated fiber laser (OAIFL) can take into account the advantages of fiber laser oscillators and amplifiers, including well anti-back reflected light ability, high conversion efficiency, good nonlinear suppression capability and compact structure. In this work, based on the steady-state rate equations of the fiber laser, combined with the special boundary conditions of OAIFL, the rate equation model of the OAIFL is established. Based on this model, the effects of the pump configuration, the fiber length ratio of the oscillating section and the amplifying section, and the reflectivity of the output coupler fiber Bragg grating on the output characteristics of the OAIFL are theoretically studied. In addition, experiments are carried out to verify the reliability of the pump control logic of the laser under different pump configurations. The results show that OAIFL can maintain a safe working state when using the pump control sequence that inevitably causes laser burnout in conventional fiber laser amplifiers.

In the optical fiber sensor, the signal light output from the silica fiber is transmitted to the detector, which usually needs to be coupled through the lens focusing. However, this often destroys the compactness and flexibility of the optical fiber sensor system structure. Therefore, this article proposes a hydrogel fiber optic lens solution, that is, a method that can directly focus the signal light output from the quartz fiber to the photodetector. Its bottom-up photochemical fixation method determines its flexible sexual characteristics and can meet individual needs. In this article, according to the size of the image distance, that is, the distance from the silica fiber to the detector (image distance), and the size of the spot on the detector (focal point), the radius of curvature of the polyethylene glycol diacrylate (PEGDA)-based hydrogel fiber lens and the distance from its apex to the silica fiber end face (object distance) are optimized. Through simulation, it is found that as the radius of curvature decreases, the diameter of the spot increases, and the increase of the object distance also increases the diameter of the spot, while the size of the central bright spot decreases with the decrease of the radius of curvature and the increase of the object distance. Consistent with the variation trend of the Airy disk in the simulation, it is proved that a smaller radius of curvature and a larger object distance can improve the focusing effect of the hydrogel fiber. The simulation based on ZEMAX verifies the application feasibility of this hydrogel fiber lens, which is expected to realize the integration of optical fiber sensor structure and has the potential to be applied to some fields such as industry, biology and medicine.

Fluorescence sensors have been defined as an important detection method due to their high sensitivity, low detection limit, strong intuition, simple operation, and wide application range. This detection method has wide application value in the detection of various ions and molecules. However, the current fluorescence sensors require complex optical components and systems, which make them expensive and bulky. Here, we propose a portable fluorescence sensor. The sensor mainly consists of two modules: fluorescence excitation and fluorescence signal acquisition. The excitation light is generated by a small laser, and the transmission of excitation light and fluorescence is realized by a Y-type optical fiber coupler. Finally, the signal is collected by the smartphone. The visualization operation is realized by building a smartphone APP, the fluorescent image is processed by digital image processing technology, and the biochemical quantitative detection is realized by calculating the gray value change of the fluorescent signal. Hypochlorite is the most active and widely used chlorine compound in chlorides. It can effectively inactivate microbial cells suspended in water, thereby achieving sterilization of water. Therefore, hypochlorite is widely used as a water bactericide, but too much hypochlorite will cause certain damage to cells and tissues in the human body. As a commonly used fluorescent dye, coumarin has a wide range of applications in biochemical detection due to its good fluorescence spectrum. Among them, 7-diethylamino-4 methyl coumarin will react with hypochlorite to produce fluorescence quenching. Therefore, it can be used for quantitative detection of hypochlorite content in water. Experiments show that the sensor can quickly detect the concentration of hypochlorite, not only has high sensitivity and low detection limit, but also has good accuracy. Because of its small size, simple operation, cost-effectiveness, and on-site detection, the instrument is expected to be used in the detection of in vivo cells and has a good development prospect.

We propose a joint pre-compensation method based on digital resolution enhancer (DRE) and Tomlinson-Harashima precoding (THP) for low-resolution data center optical interconnect. DRE is utilized to reduce the quantization noise of the digital-to-analog converter (DAC), while THP is utilized to fall off the frequency fading caused by the system bandwidth limitation and chromatic dispersion. By combining THP and DRE, we can achieve a 112-Gb/s PAM4 system over a 40-km standard single-mode fiber with a physical number of bits (PNOB) = 4 DAC on the transmitter side Moreover, using THP in bandwidth-constrained systems can increase the transmission capacity by 26.15%.

Based on the combination of cascaded spectral broadening induced by self-phase modulation and offset spectral filtering effect, Mamyshev oscillators have been regarded as convenient test beds for exploring complex nonlinear dynamical behaviors, including stable pulses and pulsations. Here, we demonstrate the experimental observation of bound-state pulses and period-doubling pulsations in a self-starting Yb-doped Mamyshev oscillator. The bound-state pulses operate stably in period-1 as an envelope or two envelopes with different intensities, or operate in pulsating process with period doubling. Thanks to the emerging dispersive Fourier transform technique, the transient spectra of the pulsating boundstate pulse are measured. It is shown that bound-state pulsation pulses of adjacent periods have periodic changes in the pulse shape and energy but the same spectral modulation period from one round trip to another. To our knowledge, this work provides the first observation of period-doubling bound-state pulses in a self-starting Mamyshev oscillator.

With the rapid development and breakthrough of semiconductor laser technology, the quality of semiconductor laser products, wavelength ranges and output power are rapidly improving, and the product range is becoming increasingly rich. Semiconductor lasers have the advantages of small size, light weight, high electro-optical conversion efficiency, stable performance, high reliability and long life, etc., and have revealed their dominant position in the field of lasers At present in the semiconductor laser research, semiconductor lasers are prone to defects under the influence of various environmental factors. In the traditional way, manual miscopy is a commonly used method of detecting surface defects. However, because of its low sampling rate, poor accuracy, low efficiency and large labor costs, manual microscopy cannot meet the needs of quality inspection. In order to solve the problem of high quality control and production costs in the microscopy process, we designed a trouble shooting method for convolutional neural networks. This paper attempts to implement a single-conductor laser radiation fault diagnosis system based on memristor convolutional neural network, and studies the integrated diagnosis system of integrated circuit electrical faults and radiation faults. Firstly, we should classify the problems that often arise in semiconductor lasers. Then the data in the fault state is collected through modeling simulation to form a data set. Finally, the dataset is classified and diagnosed by writing program. After training, the neural network fully realizes the classification diagnosis of radiated fault data and normal working data. The accuracy of the program is up to 95% or more.

In order to solve the problems of slow response of the Selective Area Growth – Double Stack Active Laser-Electro-absorption Modulated Laser (SAG-DSAL-EML) in high frequency modulation and catastrophic optical damage (COD) caused by the sharp rise of cavity surface temperature when working at high temperature, a new type of SAG-DSAL-EML is designed, In this paper, the InGaAsP/InP material with 1.31 um iron-doped buried structure is used. The active region of the new SAG-DSAL-EML becomes mesa structure, and the iron-doped InP layer is grown on its two layers of epitaxy, and the cavity surface is coated with Al₂O₃ ,in the meantime the heat insulation structure is added. Firstly, ALDS and HFSS are used to analyze the laser and modulator of the designed iron-doped buried structure EML, the threshold current of SAG-DSAL laser is reduced by 13% , the lateral limiting ability of iron-doped buried structure is increased by 52% , the difference of far-field transverse and longitudinal angles is reduced by 40% , and the far-field divergence angle is smaller than the traditional ridge waveguide structure Compared with the traditional PNPN burying structure, the response band width of the iron-doped burying structure modulator is improved by about 24% at -3 dB, which meets the basic requirements of high-speed laser communication. Then, the solid heat transfer of the laser model is analyzed numerically and simulated by COMSOL. At 550K,the temperature of the cavity surface is simulated when there is no heat-insulating structure, no heat-insulating structure, no heat-insulating structure and no heat-insulating structure. The experimental results show that the laser with coating and heat insulation can effectively prevent COD at 550K and prolong its service life.

Mamyshev oscillators (MOs) are characterized by high energy output, but the complex structure and the difficulty of the start-up have hindered their application. A temperature-boosted MO is demonstrated here, which has an extremely simple all-fiber structure with only one passive arm. The self-starting process is achieved by precisely adjusting two filters containing cascaded long-period fiber gratings (CLPFGs). The variation of the filter spacing is tuned by changing the filter heating controller. The wavelength-tunable procedure of the MO is also realized by simultaneously controlling the temperature of the two filters. The novel structure combined with the flexible CLPFGs filters provides an attractive way to explore the nonlinear dynamics in MO.

We report on the multiple wavelengths Raman laser output, the laser wavelength span from violet to mid-infrared, 359nm～9.2μm have been detected and recorded on spectrum and energy meter. In this investigation, 222mJ Q-switch Nd:YAG 1064nm laser set as pump laser, 737/770nm and 1.1/1.7/1.9/2.1/2.4/9.2μm Raman laser is high gained and takes a measure of the energy. 1.9μm laser maximum 28mJ, 2.1μm laser maximum 30mJ, laser pulse width is 4ns. And 9.2μm mid-infrared laser gets 0.8mJ. The pressurized hydrogen is pumped by a 1064nm laser and 737/770nm anti-Stokes Raman laser are generated. The 737nm laser is generated by stimulated vibrational Raman Scattering (SVRS); while the 770nm laser is generated by the combination processes of SVRS and stimulated rotational Raman scattering (SRRS). The maximum pulse energies of 6.42mJ at 737nm and 4.42mJ at 770nm are achieved by the optimization of anti-Stokes Raman laser. The energy efficiency is 2.6% at 737nm and 1.8% at 770nm.

In the era of Big Data, Cold data devours a large amount of storage volume and consumes power that cannot be ignored. Optical storage, as one of the cold data storage solutions, featuring with better unit bit cost, excellent reliability, and less power consumption, comes back to the spot of storge arena. To realize its potential, the actuators implementing high precision focusing and tracking in optical disk drives should be proved capable for high density recording. The traditional actuator performance testing is carried out by laser Doppler vibrometers (LDV), which not suitable for online inspection. Therefore, we propose a convenient and low-cost method for actuator dynamic performance testing for online inspection. By exciting coils and then analyzing certain signals from PDICs we can determine the dynamic characteristics of the actuator under testing, both in manufacturing and/or daily operating.

With the rapid deployment of 5G communication facilities, cloud computing, artificial intelligence, etc., the amount of data is growing explosively. According to International Data Corporation(IDC), the total amount of data in 2018 is 32ZB, and it is expected to reach 175ZB by 2025, of which 10%~15% is cold data. Cold data features as infrequent access and rare modification, but great longevity. Taking the cost of storing cold data into consideration, optical storage, especially, the write once read many recording media(WORM) become one of the most appropriate candidates for this scenario. To accelerate developing drive techs for new generation WORM, we choose the heterogeneous platform, upon which FPGA and DSP are resided, to develop servo and RF channels, in order to provide agility and flexibility in both modeling and tuning.

In the paper, we discuss the field enhancement effect in terahertz nano metasurfaces. The unit cell of the metasurfaces consists of a metallic split ring resonator (SRR) connecting with a wire. When the gap of SRR varies from micron-scale to nano-scale, the field enhancement factor in the gap achieves an order-of-magnitude increase in nano metasurfaces compared to that of micron metasurfaces. We then apply the nano metasurfaces to electric field sensing by assembling a layer of graphene film. In the simulation, the conductivity of graphene is tuned by varying the scattering time (relaxation time) corresponding to the varying external voltage. Compared to the structure without graphene film, the transmission of the graphene-based metasurfaces will be modulated by graphene conductivity. And the conduction effect of the graphene-based metasurfaces with nanogap under the same voltage is much better than that of the structure with micron gap, due to the extreme high field enhancement of the former. Based on this study, we can further optimize the nano metasurfaces for high sensitivity sensing, which can be applied in biological/chemical sensors or nonlinear devices.

A method is proposed to evaluate the interference of ultrawideband (UWB) signals to other systems outside its frequency band, by introducing two critical parameters W_ob and P_ob. These two parameters represent the total bandwidth and total power of the UWB signal to be evaluated exceeding the frequency mask, respectively. W_ob is the bandwidth out of the frequency mask limit and P_ob is the signal power exceeding the frequency mask. At last, the derivatives of the Gaussian pulse are evaluated up to third order, i.e. monocycle, doublet and triplet, when the original Gaussian pulse width varies from 60 to 350 ps. The results show that the interference introduced to outside band by the UWB signal decreases at first and then increases and finally decreases again, when the original Gaussian pulse width increases. To evaluate an optical UWB signal, this evaluation method should be applied after a simple photoelectric conversion.

We proposed and demonstrated a photonic integrated sensing and communication (ISAC) system with multi-target detection capability. In addition to wireless communication, the proposed system implements accurate range and Doppler measurements with the help of polarization-multiplexing, frequency-doubling, and other optical methods. Besides, a frequency-domain method is applied to decouple range and Doppler frequencies. Thus, the system has the advantages of high resolution, real-time processing, and less calculation.

A photonic-assisted multi-functional system that can implement simultaneous distance, velocity and frequency measurement is proposed and experimentally demonstrated. The distance and the radial velocity of a moving target are measured by transmitting a complementarily (V-shaped) linear-frequency-modulated microwave waveform, and by mixing the reflected microwave waveform with the transmitted microwave waveform, two de-chirped waveforms with different carrier frequencies are generated. The distance and the radial velocity are measured by analyzing the de-chirped microwave waveforms. Frequency measurement can also be performed by the system which is done by modulating a received unknown signal on an optical carrier which is mixed with a frequency-sweeping light. By passing the mixed signal through an electrical bandpass filter, short electrical pulses are generated. By measuring the time delay difference between adjacent pulses, the frequency of the unknown signal is measured. The operation of the proposed system is evaluated experimentally. The results show that the distance and velocity can be measured with mean absolute errors of 2.95 cm and 6.09 cm/s, respectively, with a range resolution better than 5.5 cm. The frequency measurement function with the capability of implementing single-tone, multi-tone and broadband signals is verified for an input signal with a frequency ranging from 1 to 20 GHz. The mean absolute error of the frequency measurement is 34.22 MHz.

As a new pulse compression signal, the phase-coded linearly frequency modulated (LFM) signal is proposed to faciliate multi-purpose radars. Here, we propose and demonstrate a phase-coded LFM signal generator, whose center frequency and bandwidth can be both adjusted. The phase-coded LFM signal generator is realized by feeding a phase-modulated optical signal into an optoelectronic oscillator (OEO). When the Fourier domain mode-locking is achieved, a phasecoded LFM signal is successfully generated. The center frequency and bandwidth of the generated microwave signal can be adjusted by changing the wavelength of the tunable laser source (TLS) and the peak-to-peak voltage of the driving signal, respectively. Experiment results show that a phase-coded LFM microwave signal with a center frequency of 9.5 GHz and a bandwidth of 5 GHz is successfully generated, whose TBWP is 5.6×10⁵. To demonstrate the flexibility of the proposed scheme, the center frequency and bandwidth of the generated phase-coded LFM signal are adjusted to 12.4 and 2.6 GHz, respectively. The signal generator can be used in pulse compression radar in the future.

We have proposed and experimentally demonstrated optical fiber strain sensor with a extended dynamic range based on a coupled optoelectronic oscillator (COEO). The oscillation frequency equals to the mode spacing of the laser that is affected by the axial strain applied to the cavity. Thus, we can evaluate the strain by measuring the oscillation frequency shift. A proof-of-concept experiment is carried out. The dynamic range is up to 10000 με. The sensitivity is 13.8 Hz/με for 2700 MHZ. The COEO has a maximum frequency drift range of ±303.907 Hz for 2700 MHz within 90 minutes, and the corresponding measurement error is ±20 με . The scheme has the advantages of high precision and high speed.

In order to realize multi-function, the radar has wide instantaneous bandwidth and working bandwidth. Unfortunately, the traditional phased array radar antenna by microwave phase shifter in the way of phasing. This paper presents a kind of wideband phased array antenna based on array element micro-ring resonator delay and subarray optical switch, and performance simulation to the proposed antenna system. The simulation results shows that the proposed antenna system can be more effectively satisfied with requirement of wideband and wide-angle scanning of phased array radar.

We numerically generate the one-dimensional terahertz quasi-perfect vortex beam arrays by using encoding holographic grating. Further, we use a focal hyperbolic lens to detect the topological charge of these vortex beam arrays.

Optical metasurfaces, i.e., consisting of subwavelength meta-atoms, have emerged as a versatile platform for shaping light in both linear and nonlinear regimes. However, rare researches have focused on their saturable absorption properties and corresponding applications. Here we report a Q-switched polarization-maintaining fiber laser working at 1 μm based on double-rod gold metasurface as an SA. The periodic double-nanorod gold metasurface can provide a strong field enhancement by introducing Fano resonance and surface lattice resonance simultaneously, which is of benefit to significant nonlinear effects. Experimental results successfully confirm that the proposed gold metasurface can be implemented as a saturable absorber in a polarization-maintaining fiber laser for Q-switching operation. Typically, the passively Q-switched fiber laser could give output pulses at 1031.4 nm with a repetition rate of 34.1 kHz and a pulse width of 2.12 μs when pumped by a 976 nm laser diode of 155 mW. The repetition rate increases from 21.82 kHz to 35.76 kHz and the pulse width decreases from 3.38 μs to 1.92 μs when the pump power ranges from 105 mW to 160 mW.

This paper firstly gives a detailed description of the equivalent iterative method and the transfer matrix method for calculating the transmittance of a multi-layer membrane structure, and then uses these two methods to simulate the transmittance characteristics of a single cavity all-dielectric thin film Fabry-Perot filter. By comparison, the equivalent iterative method can generate a similar distribution of optical intensity transmittance for TE and TM plane waves with that for the transfer matrix method. The optical intensity transmittance for the equivalent iterative method is just a little lower than that for the transfer matrix method. Besides, for either the TE or the TM plane wave, the distributions of phase variation between the two methods are different.

Structural colors can be generated by metasurfaces with the capability of spectrum manipulation at subwavelength. In general, the optimization of specific color designs and iterative geometric parameters is computationally time-consuming, so obtaining thousands of different structural colors can be challenging. Deep learning methods offer a new approach to the efficient design of nanophotonic devices, as it revolutionizes the way nanophotonic devices are designed. Here, we trained a deep learning method, which can predict the colors by random geometries in the forward modeling process. The forward design model is good at processing data, which is an effective way to design nanophotonic devices.

Because of the special diffraction characteristic of sub-wavelength grating structures, light energy with different polarization states will distribute in different diffraction orders. These gratings can obtain a high polarization extinction ratio with an appropriate set of parameters of grating structures and the incidence angle. The polarization beam splitters with different operating modes (reflective) was designed, and the finite-difference time-domain (FDTD) method was used to simulate the intensity of each diffraction order. The rigorous coupled wave analysis (RCWA) method was applied to analyze the spectral characteristics and the fabrication tolerance. The effects of the errors are clarified. In this paper, a polarization beam splitter based on grating with binary sub-wavelength structures is proposed. The ridges or grooves can be etched directly on the substrate instead of the dielectric layer. The split gratings work with an oblique incidence angle, and the waves with different polarization are distributed in different diffraction orders in the reflection or transmission area.

High-performance optical absorbers have garnered great interest because of their wide applications in solar thermophotovoltaic systems, sensors, photo-thermal modulators, etc. In this work, we experimentally realize an omnidirectional ultra-broadband metamaterial absorber with a 90% absorption bandwidth from 440-2124 nm and an average absorption higher than 95%. The peak absorption reaches up to 99.57%. Apart from multiple substructures in the pattern layer, which preliminarily broadens the absorption bandwidth due to the corresponding multiple resonance modes, a silica anti-reflection layer is additionally coated on the top to manipulate the impedance of the nanostructure to match that of the air. Physical mechanism is discussed in detail in the paper. With the assistance of the anti-reflection coating, the proposed nanostructure exhibits an increase of the absorption bandwidth by more than 590 nm while maintains high average absorptance. The anti-reflection layer can be replaced with silicon nitride to broaden the absorption bandwidth further. Nearly angle-independent spectral performance for both TE and TM polarizations are observed in both case. Moreover, for the fabrication, only one electron beam lithography is required to construct the metasurface atoms, eliminating the process of multiple lithography or pattern alignment. The proposed absorber shows a promising prospect in versatile utilizations such as solar energy harvesting, thermal emitters, photodetectors, and so on.

We propose a design of a bandpass-filter-integrated metalens for the gas sensing. A device with both filtering and focusing functions is designed, by integrating a one-dimensional photonic crystal and a metalens. It has a great filtering effect for one absorption peak (1650 nm) of the target gas (the methane). The transmission rate of the target wavelength is 89% and the relative intensity of the light field is up to 135. Our device has the function of focusing the light onto the photodetector (PD). The response of PD has been greatly improved. Meanwhile, the device can be fabricated into a photonic integrated chip. We provide a new scheme of the photonic integration chip for the multiple gas sensing.

Exciton-polaritons, hybrid particles composed of photons and excitons, have been identified as a potential solution for the control of light at the nanoscale. This is due to their unique combination of the controllability of excitons and the fast propagation velocity of photons, which enables Bose-Einstein condensation to occur at room temperature. Excitonpolaritons have also been shown to be capable of generating entangled states through parametric scattering, an important aspect for quantum communication and detection. However, conventional resonant pump techniques for generating entangled exciton-polaritons have limitations. In this work, it reports a successful demonstration of inter-band parametric scattering of exciton-polaritons in quasi-one-dimensional ZnO system through the use of an improved angle-resolved fluorescence spectroscopy system. This observation holds significant implications for the study and application of exciton-polaritons in the field of quantum communication and quantum technology.

There are obvious moiré fringes in the naked-eye 3D images light-emitting diode(LED) display based on a conventional lenticular lens grating. To weak moiré fringes, we proposed 1D unequal distance metagrating inclined to the display. Based on convolution with superposition of intensity profile which is transmitted from the metagrating and bidirectional array pixels of display and the spread function, firstly, we simulate moiré fringes on unequal distance and inclined metagraing with display respectively, meanwhile, main moiré pitch were extract from moiré fringes. Comparison with conventional lenticular lens grating shows that the slanted metagrating could make moiré fringes sparsely, and the unequal distance metagrating make the moiré fringes intensity contrast ratio weaken. The above combination of slant and unequal distance can achieve the purpose of weakening the moiré fringes and crosstalk also reduced simultaneously.

The efficient combination of multiple functions through a single, planar and compact metastructure has become an emerging research area, offering the possibility to design and realize highly integrated and miniaturized multifunctional devices in photonics, but Huge challenges still need to be solved, especially in the visible wavelengths. Here, we design the metasurface structure by means of unit structure addition, allowing the linear polarization to be effectively separated into x-polarized and y-polarized components at normal incidence, and achieve anomalous reflection of light waves and unidirectional excitation of Surface Plasmon Polaritons (SPPs). The structure can locally propagate the energy of SPPs more efficiently, or reflect more energy out through the phase gradient. When linearly polarized light of 1200 nm is incident vertically, two different linear phase gradients are generated along the same direction, resulting in the realization of the same metasurface distinctly different functions. Among them, by analyzing the local electric field distribution caused by the interaction between the incident light and the structure, it can be clearly found that the x-polarized light effectively excites surface plasmons (SPPs), and most of the energy propagates to the right along the surface of the structure. The y-polarized light achieves an abnormal reflection of 30°, and it is verified that the large-angle deflection characteristic of 20°-60° can be achieved in the wavelength range of 1000nm-1500nm. The bifunctional metasurface developed in this study can provide ideas and methods for the study of photonic integrated devices in the optical band.

Silica nanospheres have special optical properties such as relatively stable chemical property, high temperature resistance and corrosion resistance, so they can be widely used in Chemistry, biomedical and materials science fields. However, many existing preparation methods of silica nanospheres not only rely on expensive instruments, but also have long preparation cycles. Here, we propose an optimized Stӧber method to prepare silica nanospheres, which is simple, efficient and low-cost. Silica nanospheres with different sizes can be obtained by repeatedly adding the tetraethoxysilane (TEOS) solution dropwise at a constant speed. The characterizations by transmission electron microscope (TEM) and zeta potential meter reveal that the size of silica nanospheres gradually increases with the increase of the amount of TEOS. In addition, different concentrations of ammonia affect not only the rate of reaction, but also the final particle size of the microspheres. Afterwards, the silica nanospheres with sizes of 190 nm, 235 nm, and 284 nm were prepared into colored photonic crystal thin films by chemical self-assembly, and they appeared blue, green and red under the reflection of natural light. Finally, their reflection spectra were measured using a selfbuild characterization system, and found that their peak reflection wavelengths were 427 nm, 511 nm, and 622nm. These results indicate that the reflection peaks of the films gradually red-shift with increasing silica nanosphere size. The proposed optimized Stӧber method for preparing silica nanospheres is simple and efficient, which can greatly expand their application in various fields. For example, the surface of silica nanospheres can be linked to various chemical groups by silanization, which can be used for biochemical sensing. Colored films prepared from silica nanospheres also have potential applications in decoration and other fields.