Chaotic optical communications provide high security for physical layer encryption. We propose a chaotic laser communication system based on a balanced detection optoelectronic delayed feedback system, which has a higher performance compared with one based on single-photodiode detection. Our numerical analysis proves that dynamic behaviors are achieved at only half feedback gain, and the safety hazard chaotic dead zone is eliminated. The generated chaos features high pseudo-randomness and a good capacity to conceal time-delay signatures, which makes it hard for an unauthorized party to remove the chaotic carriers. 10 Gbps message hidden in wideband chaotic carries is transmitted back-to-back, and the BER 10−1 of the eavesdropper achieved at a low feedback gain β=3.2 proves its high confidentiality. Our proposed system has the potential to promote chaotic laser systems to practical appliances with simple structure and high performance.
Fiber optic current sensors (FOCSs) are prone to environmental disturbances and have to be calibrated before going into service. A commonly adopted scheme is the single dimensional calibration method based on temperature. In this work, we propose a multi-dimensional FOCS calibration method based on the extreme gradient boosting (XGBoost) algorithm. Six operating parameters of the FOCS are chosen as the input of the calibration model, including the drive current of the light source, the average optical power of the photo detector (PD), the second harmonic of the PD output, the drive voltage of the piezoelectric transducer, the measured current, and the ambient temperature. The ratio error is acquired as the output. Temperature cycling experiments on three finished sensors in an environment of −40°C to 72°C are conducted. The experimental results show that the max absolute ratio error after multi-dimensional calibration based on XGBoost is 0.031% and the mean absolute ratio error is 0.003%, both of which are much lower than the single-dimensional calibration method based on temperature. It can be concluded that the proposed multi-dimensional calibration method based on XGBoost can effectively improve the accuracy and stableness of FOCSs.
To evaluate the effect of crosstalk caused by wavelength deviation of reconstruction-equivalent-chirp (REC) integrated multi-wavelength laser arrays (MWLAs) on an optical free-space communication system in which wavelength division multiplexing (WDM) is applied, we derive the model of power penalty caused by the wavelength deviation of REC-MWLAs and the bit error rate (BER) of the system under atmospheric turbulence and conduct a numerical simulation. The two adjacent channels in arranged REC laser arrays are defined as the analysis scope. We find that the power penalty is more sensitive to the deviation of the channel itself than the adjacent channel as the frequency shift increases from 0 to 50 GHz. The numerical relationship between the BER and power penalty is drawn to further investigate the tolerance for wavelength deviation under the requirements of BER < 10 − 6 and BER < 10 − 9. In addition, for a smaller deviation of 5 GHz of the analyzed channel, the linewidth compression of the REC laser can decrease the power penalty from 1.3 to 0.7 dB, improving the system performance and moderating the demands for deviation of REC-MWLAs, and the gemination of channel spacing does not evidently reduce the requirement for deviation. The results of this work demonstrate the feasibility of REC-MWLAs as the light source of WDM free-space communication systems under atmospheric turbulence and provide an effective reference for the allowable deviation in the design and testing of MWLAs.
Spun fiber has been used for current-sensing applications for decades. However, in actual situation, disturbance like squeezing or bending of spun fibers often causes evolution of polarization and eventually causes Faraday phase shift error. In this paper, we try to find out how bending will influence the polarization state of propagating light in spun fiber. We use a big bending spun fiber coil (50 cm in diameter) with a small disturbance coil (2-3cm in diameter) to easily simulate and quantify the magnitude of fiber bending. We calculate the polarization states of the left-hand and right-hand circular polarizations by solving differential equation of a spun fiber coil placed in the magnetic field generated by a current. Our results show that fiber bending will weaken the polarization-maintaining ability of spun fiber, causing polarization state oscillates periodically.
In this paper we propose a method for analyzing the operation health of a large number of all-fiber optical current transformers used in UHV converter stations by studying the correlations of their operating parameters. This method firstly realizes automatic data sampling of operation parameters of all-fiber optical current transformers by building a monitoring network. Then the method calculates the deviations of the operating conditions from their ideal values and the correlations between the relative parameters, thus achieves the operation health condition of the main functional modules in optical current transformers. Finally, through big data analysis, the comprehensive health index and service life of each optical current transformer are predicted. The proposed method can realize the health monitoring of all optical current transformers, which will guarantee their reliable operations and decrease the potential faults.
In this paper, we demonstrate a novel Fano resonance optical filter based on thin fiber taper coupled whispering gallery mode (WGM) liquid core microcapillary resonator, and such the filter comes from the narrow band transmission spectrum of Fano resonance. Due to the large thermos-optical coefficient of the liquid core, slight temperature change will greatly change the resonant wavelength. In addition, high order resonant modes are generated through thin fiber taper coupling. With their large intensity fraction in the liquid core, these modes achieve high sensitivity to refractive index change or temperature change of the liquid core. So this tunable filter has very large temperature tunable coefficient of about 0.4nm/K, which is far larger than other traditional methods.
Based on electromagnetic eigenequation in silver-coated microcylinder, we study its mode characteristics and sensing characteristics, including dispersion relation, quality factor (Q factor), sensitivity (S) and detection limit (DL). We find hybrid WGM-SPPs modes in energy distribution and mode coupling phenomenon in dispersion curve. In the vicinity of mode coupling point, hybrid TM-SPPs modes (or supermodes) have both high Q factor and high surface enhancement factor. Meanwhile the hybrid modes have high refractive sensitivity and figure of merit (FoM), which enables potential applications in chemical and biological sensing.
Based on weak fluctuation theory, the expression of bit-error rate (BER) of Multiple Quadrature Amplitude Modulation (MQAM) with the consideration of detector noise in the downlink of space communication system is discussed in this paper. According to the expression, the performance of three typical modulation schemes, which are 4QAM, 16QAM, 64QAM, are specially analyzed. It is known that the higher the order of the modulation scheme is, the more bits of information per symbol can carry. However, when the transmission power is 1 W and the receiver diameter Dr is 1 m, the BER is 2.12×10-13 for 4QAM, 5.98×10-8 for 16QAM and 6.22×10-5 for 64QAM, which means that a higher order modulation scheme shows a higher bit-error rate (BER). Thus considering bandwidth efficiency as well as bit error rate, 16QAM is highly recommended in the real space optical communication system. In addition, the relationships between BER and optimum divergence angle, transmitter beam radius, receiving aperture for downlink are also suggested respectively in this paper, which has important reference significance for the design of the ground-to-satellite laser communication system.
Space optical communication technique is attracting increasingly more attention because it owns advantages such as high security and great communication quality compared with microwave communication. As the space optical communication develops, people have already achieved the communication at data rate of Gb/s currently. The next generation for space optical system have goal of the higher data rate of 40Gb/s. However, the traditional optical communication system cannot satisfy it when the data rate of system is at such high extent. This paper will introduce ground optical communication system of 40Gb/s data rate as to achieve the space optical communication at high data rate. Speaking of the data rate of 40Gb/s, we must apply waveguide modulator to modulate the optical signal and magnify this signal by laser amplifier. Moreover, the more sensitive avalanche photodiode (APD) will be as the detector to increase the communication quality. Based on communication system above, we analyze character of communication quality in downlink of space optical communication system when data rate is at the level of 40Gb/s. The bit error rate (BER) performance, an important factor to justify communication quality, versus some parameter ratios is discussed. From results, there exists optimum ratio of gain factor and divergence angle, which shows the best BER performance. We can also increase ratio of receiving diameter and divergence angle for better communication quality. These results can be helpful to comprehend the character of optical communication system at high data rate and contribute to the system design.
For a space downlink laser communication system with an EDFA as a power amplifier, the
performance of its BER deteriorates because the EDFA’s characteristics are badly impacted by space
radiation. As is investigated in this paper, small divergence-angle, lower than 30μrad, assures that the
BER is lower than10-20 although the increase of radiation dose from 0Gy to 250Gy leads to 20 orders of
magnitude increase of the BER. Such perfection results from our selection of optimal parameters. In
the case of zenith angle, the BER increases smoothly when the zenith angle is lower than 10 degrees.
After the point of 10 degrees, however, the BER starts its linearly fast increase. Increasing the radiation
dose makes the BER increase and such evolution trend more smooth. Moreover, the increase of
receiving diameter leads to linear reduce of BER. It is interesting to note that the evolution becomes
nonlinear in region of low receiving diameter when we change the divergence-angle to a higher value
60μrad. Besides, suffering radiation makes the non-linearity mentioned above more apparent. Another
try to change the zenith angle to higher value 45° does not show obvious nonlinear effect but it worsens
the performance of BER quite a lot. Commonly, the impact of radiation will reach its saturation when
the dose of radiation continues to increase. The work will benefit the design of practical space laser
communication system with EDFAs.
Factors that affect the transient effect on small duty-cycle pulse in a cascaded erbium-doped fiber amplifier (EDFA) system are studied in simulation and experiment. The considered factors consist of the numbers of cascaded EDFAs, the peak power and the extinction ratio of optical pulse, with results showing that the optical pulse will be severely distorted by the transient effect of EDFA. The distortion becomes more serious with the increase of the three parameters. To avoid or mitigate the transient effect, a method of adding another optical signal with a different wavelength to the objective pulse is employed in the experiment. The experimental results show that this method could effectively restrain the transient effect in a cascaded EDFA system.
KEYWORDS: Phase modulation, Time division multiplexing, Iterated function systems, Heterodyning, Reflectometry, Digital signal processing, Modulation, Signal processing, Modulators, Pulse generators
A time division multiplexing optical time domain reflectometry (TDM-OTDR) based on multi-frequency probe
light and directly synthesizing heterodyne intermediate frequencies (IFs) is proposed and experimentally demonstrated.
Five time division multiplexing probe frequencies are obtained by synchronous control of an arbitrary waveform
generator and a phase modulator. Experimental results achieve 6.5dB dynamic range enhancement, compared with
conventional coherent OTDR.
We demonstrate the high power low RIN Brillouin fiber laser source with stimulated Brillouin scattering. Brillouin fiber laser and high quality RF are generated simultaneously in Brillouin optoelectronic oscillator. Brillouin fiber laser with 104mW power and -154dB/Hz RIN is generated. RIN of Brillouin fiber laser is 8dB lower than RIN of EDFA-amplified DFB.
We have proposed and demonstrated a novel multiwavelength Brillouin-erbium fiber laser (BEFL) with a linear cavity, in which, the Brillouin pump is self-excited within the cavity, doesn't require the injection from the external cavity or direct generation within the intracavity. In this scheme, more than 115 Stokes lines with relatively uniform amplitudes have been generated. The experiment also demonstrates that such a self-seeded BEFL performs good repetition and stability for both the operating wavelengths and the output power of each Stokes line. Meanwhile, the effect of the 980nm pump on the performance of the laser is investigated.
In the paper, the supercontinuum generation in the normal dispersion shifted fiber is investigated using the single-pass and double-pass configurations. The spectral bandwidth of supercontinuum is enhanced from the 90nm with single pass configuration to127nm using the double pass configuration. The enhanced broadening mechanism is mainly due to the collision interaction between counter- traveling pulses, as well as the doubled length of fiber.
We propose a general routine, Genetic-Simulated Annealing method (GSA) for the optimal design of quasi-phase matched (QPM) non-uniform grating. Here this method is applied to the design of the flat broadened wavelength conversion bandwidth of 40-mm aperiodically poled lithium niobate (APLN) based on difference-frequency generation (DFG). The flat conversion bandwidth of APLN is broadened from the original 65nm in a 40-mm periodically poled lithium niobate (PPLN) to the pre-designated 130 nm in a 40-mm APLN, which conversion efficiency is 6.7 dB higher than that of 12.4-mm PPLN under the same conversion bandwidth.
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