This PDF file contains the front matter associated with SPIE Proceedings Volume 10899, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

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Heat conduction is of great importance in thermal design for high power diode lasers. In this paper, an analytical, threedimensional, steady-state, multilayered, thermal model for a high power diode laser is derived. The temperature and heat flux distribution are discussed for an epi-down bonded broad-area diode laser, and it is found that heat spreading within laser chip contributes 6.8% to total heat dissipation. Further discussion is carried out on heat flow in the submount to show the submount size requirement for which this model can be used. Simulation result based on finite element method (FEM) is employed to confirm the calculation accuracy from this analytical model.

We introduce a toolbox for modelling laser diode operation over a large temperature range, as is encountered in long-pulse hair removal, and in mobile applications such as LiDAR. Power-to-current characteristics and lifetime estimations are sought for arbitrary pulse patterns in quasi-continuous-wave (QCW) operation. Our model is based on (1) the Z_th-representation of the package thermal transient, (2) a temperature-dependent family of diode characteristics replacing the insufficient T₀,T₁-approach, and (3) the assumption that the device lifetime depends on the maximum junction temperature. The simulated evolution of output power and temperature is experimentally verified. Using our model, we assess the influence of the package geometry on the diode temperature and on the efficiency of diode-pumped solid state lasers. We also re-assess lifetime data, and derive safe operating parameters for an arbitrary pulse length.

Several holographic and interferometric applications would benefit significantly from a diode laser based coherent light source near 633 nm. For this purpose a miniaturized master-oscillator power-amplifier (MOPA) was developed. The MOPA is integrated in a sealed package together with a custom-built micro-optical isolator to shield the MO from optical feedback. The MOPA reaches an optical output power of up to 70 mW near 633 nm. The power is boosted by a second, external amplifier to more than 500 mW. The package offers space for the future integration of the second amplifier stage.

High power, high efficiency diode lasers operating in the 15xx nm wavelength range are required for many applications, both in the military and in the commercial domains. Applications include eye-safe infrared illuminators, free-space optical (FSO) communication transmitters, LIDAR and range finder sources, as well as resonant pumping of Erbium-doped fiber or solid-state lasers for high energy lasers. In this paper, we will discuss our recent progress in developing high power, high efficiency stripe geometry and Master Oscillator Power Amplifier (MOPA) lasers operating at 1550 nm. MOPA lasers are fabricated in a monolithic platform in which we have engineered the epitaxial structure to mitigate Auger and other loss mechanisms. This device structure includes a single mode seed laser that feeds a tapered power amplifier. We have demonstrated single spatial mode performance of over 1 W output power (CW) and Electro-Optic (EO) power conversion efficiency of 44%. This EO efficiency is significantly higher than what is available today for 15xx nm lasers. The single spatial mode nature of these lasers has been verified through M^2 measurements. The MOPA shows a small-signal bandwidth >2GHz under direct modulation, offering a unique capability for free-space optical link applications. Stripe geometry lasers have been demonstrated generating in excess of 3 W output power (CW) with high EO efficiency (36%). While custom packaging is available, the MOPA lasers have been packaged into TO cans with collimating optics to enable easy integration into existing system architectures.

Quantum Technologies (QT) hold the promise of a step-change improvement in many high-impact applications, such as ultra-stable clocks and extremely sensitive gravity and acceleration sensors for financial transaction timestamping, satellite-free navigation, oil and gas prospecting, land-surveying, secure communications and scientific research. The underpinning scientific principles of QT systems are largely developed, but for QT to fulfill its potential then orders of magnitude reduction in size, cost and power consumption of the enabling technologies is required. Stabilized laser systems are key ingredients of many quantum sensors. In many cases multiple lasers, each with specific wavelength, power and linewidth requirements, are needed for cooling, trapping, imaging and the clock references. In this paper we describe the design and packaging of a compact, frequency-stabilized 780nm laser module with integrated vapor reference cell. This stabilized source addresses the D2 transition of 87Rb that connects the ground and excited states, which is used for laser cooling, trapping and repumping in a rubidium interferometer. Component packaging techniques more normally employed in telecoms component packaging are utilized to minimize size and maximize stability. The resulting laser module lends itself to usage in applications in portable instruments outside of the lab.

Highly complex optical fiber networks are the physical backbone of the internet today. For about two decades, the amount of data transferred through the optical networks keeps rising with no end being in sight. To fully use the capacity of the available optical mesh networks, more and more complex optoelectronic devices like Optical Cross-Connects, Wavelength Selective Switches and highly integrated Transceivers are being established. State of the art devices, e.g. WSS (Wavelength Selective Switch) can have 20 or more optical components, which is challenging and time consuming for conventional alignment routines. While these alignment routines are based on a stepwise alignment of single optical components, we propose a novel approach by simultaneously aligning pre-analyzed components and subgroups. The alignment strategy follows the optical functionality of the components being aligned: Prior to the assembly the module and each component once is being examined regarding their function and influence on the optical properties of the module being assembled. Functional sub-groups of components are investigated in the same manner. With this knowledge of each component’s influence on the optical properties of the module, it is possible to perform the simultaneous alignment with different alignment goals. Usually, it is desirable to minimize losses, but in some cases, the wavelength-dependent loss or the polarization-dependent loss can be of greater interest. In optical devices with dispersive elements like gratings and prisms, this approach can be applied to directly tailor the wavelength range or the wavelength resolution to the customer needs, while other properties are kept constant. In general, this approach allows adjusting optical properties independently from each other and can drastically reduce assembly times.

High power QCW diode laser stacks have been widely used in pumping applications for years. Different package structures of diode laser stacks are applied for pumping the cylindrical rod crystal, such as modular G-Stack, horizontal, vertical and annular arrays. Annular array is preferred in pumping of QCW mode with low duty cycle and short pulse width, due to the advantage of compact structural size, uniform light beam distribution and convenient electric connection. However, the development of annular diode laser array using hard solder is difficult because of the complex bonding process of diode laser on annular heatsink with conventional bonding fixture. Furthermore the stress and thermal behavior is yet to be well studied on the annular diode laser array. In this work, a sophisticated annular diode laser array was developed using hard solder. Optimized structure and thermal design were conducted to achieve uniform light beam distribution and good heat dissipation. Stress release structure of diode laser stack is applied to reduce the risk of chip crack and deviation of spatial spectrum. The annular diode laser array consists of 44 bars in a ring, with the peak output power of each bar over 500W. The maximum output power of each bar reaches 673 W.

The divergence of laser diodes is asymmetric and must be collimated in the fast-axis and slow-axis to reach an adequate beam shape for most applications. The most common technical solution is a combination of a Fast Axis Lens (FAC) and a Slow Axis Lens (SAC). These optical components are usually made of glass in combination with an anti-reflective optical coating tuned for a specific wavelength range. During the last decade, high power lasers have become more and more powerful and the requirements for specific collimation optics continuously increased. The FAC beam shaping performance is dependent mostly on the lens design and achieved surface quality, while the thermal behavior of the FAC is dependent on the laser power and the optical absorption within the lens. The solution for a low absorption lens for a high power blue laser diode presented in this paper, is a fused silica FAC. It shows excellent thermal properties and reduces heat generation rate by a factor approximately corresponding to the extinction value ratio when compared to other high refractive glass solutions optimized for blue applications.

Compact and robust external-cavity diode laser (ECDL) systems are a mandatory requirement for many next-generation quantum technology applications, e.g. quantum communication and quantum sensors. Today’s commercially available ECDLs are used for proof-of-principle demonstrations of such applications, however do not meet the requirements for the use in real-world environments. We investigate a novel design for a compact and robust ECDL suitable for the integration into first quantum technology applications. Experimental results of first prototypes are presented and compared to a commercially available ECDL and numerical simulations.

NASA is working with US industry and academia to develop Photonic Integrated Circuits (PICs) for: (1) Sensors (2) Analog RF applications (3) Computing and free space communications. The PICs provide reduced size, weight, and power that is critical for space-based systems. We describe recent breakthrough 3D monolithic integration of photonic structures, particularly high-speed graphene-silicon devices on CMOS electronics to create CMOS-compatible highbandwidth transceivers for ultra-low power Terabit-scale optical communications. An integrated graphene electro-optic modulator has been demonstrated with a bandwidth of 30 GHz. Graphene microring modulators are especially attractive for dense wavelength division multiplexed (DWDM) systems. For space-based optical communication and ranging we have demonstrated generating a variable number of channels from a single laser using breadboard components, using a single-sideband carrier-suppressed (SSBCS) modulator driven by an externally-supplied RF tone (arbitrary RF frequency), a tunable optical bandpass filter, and an optical amplifier which are placed in a loop. We developed a Return--to-Zero (RZ) Differential Phase Shift Keying (DPSK) laser transmitter PIC using an InP technology platform that includes a tunable laser, a Semiconductor Optical Amplifier (SOA), high-speed Mach-Zehnder Modulator (MZM), and an electroabsorption (EAM) modulator. A Silicon Nitride (SiN) platform integrated photonic circuit suitable for a spectrally pure chip-scale tunable opto-electronic RF oscillator (OEO) that can operate as a flywheel in high precision optical clock modules, as well as radio astronomy, spectroscopy, and local oscillator in radar and communications systems is needed. We have demonstrated a low noise optical frequency combs generation from a small OEO prototypes containing very low loss (~1 dB) waveguide couplers of various shapes and sizes integrated with an ultrahigh-Q MgF2 resonators. An innovative miniaturized lab-on-a-chip device is being developed to directly monitor astronaut health during missions using ~3 drops of body fluid sample like blood, urine, and potentially other body fluids like saliva, sweat or tears. The first-generation system comprises a miniaturized biosensor based on PICs (including Vertical Cavity Surface Emitting Laser – VCSEL, photodetector and optical filters and biochemical assay that generates a fluorescent optical signal change in response to the target analyte.

Fibertek has designed and is building a spaceflight (TRL 5-6) high-efficiency, high reliability (97.2% for 5-year mission) 100 W average, 1940 nm thulium doped fiber laser (TDFL) meeting all requirements for a NASA Earth Science spaceflight 2 μm Ho:YLF pump laser. These include polarization extinction ratio <16dB, diffraction limited beam quality, narrow linewidth (0.35nm) and >50% optical to optical efficiency. High reliability laser package, optimized for space environment and SWAP has size 10.6”x13.8”x4.4”and weight 30lbs. A summary of laser package design is presented, including structural and thermal analysis. Preliminary environmental testing results of the space laser are also presented. A spaceflight 100 W PM Tm laser provides a path to space for a pulsed, Q-switched 2 μm Ho:YLF laser with ~80 mJ/pulse at 100-200 Hz.

The optical characteristics and long-term stability are the key criteria to select glass for a wide range of optical applications. Nevertheless, current challenges in e.g. smart consumer applications and autonomous transportation are cost driven and polymer optics are the first choice for ten to hundred million pieces applications, so far. In combination with diode laser sources polymer optics can be used only for low power and low value applications. For a few Watts CW or 100 Watts QCW and more the safe and reliable operation even in a harsh environment has still a need for optics made of glass. Therefore, LIMO developed a non-sequential cold processing and polishing technology for cylindrical lenses with glass wafer that can reduce cost per processed mm² down to the polymer optics level. Similar like in microelectronics production, the use of large glass wafer in combination with simultaneous processing of all cylinder lenses increases productivity and reduces cost per mm². Beam shaping and collimation optics for edge emitter diodes and VCSEL can be produced now on the generation 5 substrate size of 300mm x 300mm. In addition, the development of higher grinding rates with constant geometrical shape was the key to scale the wafer size and reducing the turnaround times simultaneously. The resulting productivity went up more than ten times in comparison with the current generation 4 wafer. LIMO will present the production flow and high-speed grinding and polishing process in combination with wafer level testing and quality mapping processes to confirm the optical performance.

The market of Photonic integrated circuits (PICs) has risen significantly in the previous decade. One of the major challenges to SMEs is to reduce cost and effort of packaging and pre-package testing. The PIXAPP pilot line aims to address these challenges and fill missing links in the technology chain in the context of photonics pilot manufacturing. As part of the PIXAPP pilot line, we enable time-efficient PIC characterization and validation, which is indispensable for a cost-effective manufacturing chain. A fast alignment process of optical in- and outputs to the PIC is critical to reduce the cycle times for testing. There are many underlying factors that influence achievable alignment times, such as mode field diameter, mode mismatch between waveguide and fiber, available optical power, measurement noise, the mechanical properties of the setup, controller environment, strategies used to find first light, alignment algorithms and parallelization by employing fiber arrays. We discuss a selection of these factors. Among the covered topics are the available acceleration of the mechanical axes, fiber holder stiffness, motion controller frequency and parallelization by Periscope arrays for edge coupling on the wafer scale. We demonstrate the applicability of our findings by a double sided fiber alignment in 1.7s.

In micro-assembly of optical systems, active alignment can help to relax tolerances and guarantee optimal results for individual units by evaluating the actual system performance or suitable key-performance-indicators. Combined with capable micromanipulator technology bonding becomes the limiting factor in the overall assembly process. Due to unpredictable properties of the individual adhesive gap, volumetric shrinkage during curing is not sufficiently predictable for a robust compensation. In the past, Fraunhofer IPT presented curing-in-the-loop as a solution for increased precision in the bonding process. The measurement information from a preceding active alignment control loop can also serve as input during the bonding process. The observed and quantified shrinkage in the first moments of the curing process allows predicting the entire displacement due to volumetric shrinkage. A last correction step before the final curing dose leads the remaining shrinkage to approach the target pose. This curing-in-the-loop-strategy provides several parameters for tuning, which directly affect the achievable bonding strength. The segmentation in initial and final curing phase, the UV-doses, the time window to measure and evaluate and the amount of correction are just some examples. In this paper, we will present the bonding strategy and its parameters in detail and investigate the effects on the bonding strength of UV-cured adhesives. Especially the amount of correction during the curing process is an unknown process parameter.

ALPhANOV has developed expertise around the interfacing and integration of specialty optical fibers. We propose to present new developments concerning 100W-class fiber laser based on Yb-doped Large Mode Area fiber amplifier and a new plug-and-play connector for ultrashort pulse beam delivery by using Hollow Core Photonic Crystal Fibers. In terms of high power fiber amplifier, we recently developed a high performance, fully monolithic PCF amplifier module. The module is based on the DC-200/40-PZ-Yb of NKT Photonics and on a homemade fiber fused component allowing us to couple up to 6 pumps of 50 W at 976 nm together with 5 W of signal, leading to an achieved power of 210 W at 1064 nm, which is to the best of our knowledge the highest power ever delivered by a fully monolithic PCF amplifier. The module is entirely thermally controlled in a rugged package and has run more than 100 days at > 100W average power with an excellent power stability < 1%. Concerning fiber beam delivery solution, hollow core photonic crystal fiber has shown great potential for an industrial solution. To penetrate the industry, high power femtosecond lasers need low-loss stable and plug-and-play connectors to couple light into hollow-core single-mode fibers and carry it to the target. We recently developed such connector and tested it on different industrial femtosecond laser, 50W and 100W class. The new design of the connector compatible with vacuum or noble gas and 300W class femtosecond laser will also be presented.

Double-clad fibers (DCF) found in kilowatt-class fiber lasers typically have a second cladding made of fluoroacrylate. At high power, thermal damage or accelerated aging of this material becomes an issue. The operating temperature of the fluoroacrylate coating is found to be highly sensitive to the numerical aperture (NA) distribution of the pump light flowing through the fiber. Characterization of this effect with an optical loss measurement is impractical as this loss remains typically very low. Measurement of the coating temperature for a given input power and far-field distribution is much more sensitive. Furthermore, it directly gives the parameters that are key to the design of a high-power fiber laser. A system for the measurement of the thermal slope of DCF fibers and high-power fiber components has been built and tested. This system allows varying the input power and the source NA under high power with a unique splice to the device being tested. To achieve this, different types of fiber-coupled pump diodes are spliced to the inputs of a pump combiner. Fiber tapers are used to fine tune the sources’ NA. By turning on different diodes, the NA of the injected pump light can be varied. The thermal slope for a given NA can then be measured with a thermal camera and a power meter. Measurements show differing thermal slopes of DCF measured before and after a damp heat tests. These thermal slope variations are stronger when operating at a high numerical aperture.

Measuring the profile of a laser beam is of critical importance, especially for high power laser systems. Although different techniques exist to measure the beam profile, owing to the use of optoelectronic detectors or cameras, they primarily work at lower powers and require tapping and attenuating the beam. In this process, there is potential for the diagnostic system affecting the beam quality. In this work, we propose a simple technique which can measure the beam profile at full power using a thermal imager without the need for additional optical components. The method involves taking a thermal image of the beam while it is incident on an absorptive surface such as a thermopile head which is used to measure optical power. In addition, a second image is taken using a focused incidence on the surface at low powers. The second image which is reused provides the point spread function. We then make use of the linearity of the heat equation which allows the deconvolution of the point spread function from the original image to obtain the actual beam profile. In this work, we utilized the technique to directly analyze the beam profile at full power of a 100 W class fiber laser and analyzed deviations from single-modedness. In addition, we utilized offset splices to few-mode fibers to launch higher order modes at the 100W level and demonstrate their direct characterization of multimode nature of the profile. This technique provides a simple alternative, using instruments present in most laser labs for direct, high power laser beam profiling.

We report on a commercial laser system based on a Yb fiber oscillator with cross-filter mode lock (CFML) mechanism that is integrated with a programmable pulse shaper. The laser is self-starting and stable in a wide temperature range, 15- 50°C, resilient to vibrations and shock. It can serve as a seed for high-power femto- and pico- second systems or be implemented as a standalone unit, as illustrated in this paper. The master oscillator is outputting strongly chirped pulses, with the spectrum centered at 1030 nm and having the full bandwidth of up to 90 nm. It operates at 11 MHz repetition rate, with the pulse energy of at least 10 nJ at the output. When equipped with an additional power amplification module, the oscillator yields the same spectral output and repetition rate, but the pulse energy can be increased up to 400 nJ. The laser output is fully coherent, and pulses are compressible down to the transform limit (TL). For demanding femtosecond applications, the laser system is being configured with a static grating compressor and a compact spectral phase shaper. The pulse shaper utilizes a liquid-crystal spatial light modulator for active phase control which enables high-finesse pulse compression as well as arbitrary manipulation of the pulse waveform. With the use of the pulse shaper, the oscillator output is compressed down to 57 fs, which is within 7% from the TL pulse duration, 53 fs, calculated from the experimental laser spectrum.

We report on several ultra-short pulse compression schemes based on hollow-core photonic crystal fiber filled with a chosen gas-phase medium and undertaken in a versatile module coined “FastLas”. The scheme relies on dispersion management by both fiber design and gas pressure management to offer a highly versatile pulse compressor. Furthermore, the gas is also used to set the required optical nonlinearity. This type of hollow fiber based compressor is scalable with the laser wavelength, pulse energy and initial pulse-width. Among the achieved pulse compression, we list a self-compression of 500-600 fs ultra-short pulse Yb-laser and with energy range of 10-500 μJ. By simply scaling the fiber length we demonstrated pulses as short as ~20 fs for the whole energy range. Here, the self-compression is achieved through solitonic dynamic. Conversely, we demonstrated pulse compression based on self-phase modulation by adjusting the fiber and gas dispersion. Among the pulse compressors we have developed, based on self-phase modulation, we cite the compression of a frequency-tripled micro-Joule pulse-energy Yb-laser with a pulse width of 250 fs. The results show compressed UVpulses with temporal width in the range of 50-60 fs.

High-power pulsed lasers are widely used in scientific and industrial applications, and control of irradiance distribution using beam shaping optics is important to increase efficiency of laser techniques. A popular approach of building optical systems is use of a refractive beam shaper and imaging optics afterwards to create resulting spot of required intensity profile and size in a working plane. Important feature of imaging optical systems is creating the image after the paraxial focal plane – this means focusing of a high energy pulse before the image plane and probable air break down disturbing the intensity distribution in image and reducing performance of entire system. This problem becomes especially actual with modern ultrashort pulse lasers which pulse energy is constantly rising. Specific requirements to beam shaping optics in these laser systems are providing variable irradiance distributions, saving of beam consistency and flatness of phase front, capability to work with TEM00 and multimode lasers, resistance to high peak power radiation. Among various refractive and diffractive beam shaping techniques only refractive field mapping beam shapers like piShaper meet these requirements. The operational principle of these devices presumes almost lossless transformation of laser beam irradiance from Gaussian to flat-top, super-Gauss or inverse-Gauss through controlled wavefront manipulation inside a beam shaper using lenses with smooth optical surfaces. To overcome the problem of eventual air break down by imaging after a beam shaper it is suggested to apply optical systems with field lenses, which main function is changing the focusing conditions without change of the system transverse magnification. This approach allows to “move” the point of pulse energy concentration from the image zone and increase the focus spot size in order to reduce probability of air break down or avoid it at all. This paper will describe some design basics of refractive beam shapers of the field mapping type and optical layouts of their applying in optical systems of high-power lasers. Examples of real implementations and experimental results will be presented as well.

>2 PW/sr-cm2 highly brightness Micro-MOPA was achieved. This Micro-MOPA can generate 100 mJ-class and PW/sr-cm2-class pulse with the A3 paper size footprint.100 Hz operation of the Micro-MOPA with over 2 PW/sr/cm2 was achieved. Micro-MOPA system can generate 100 mJ-class and PW/sr/cm2-class pulse with paper size footprint. However, previous repetition rate is limited to 10 Hz in spite of the oscillator and the amplifier design for 100Hz operation due to its thermal problem. However, current repetition rate is limited to 10 Hz in spite of the oscillator and amplifier design for 100Hz operation, because tThe laser diode side-pumped Nd:YAG rod of the amplifier for Micro-MOPA causes lens effect in high brightness beam operation and the focused beam from the rod causes damage to optics. We measured the thermal lens effect of the amplifier Nd:YAG rod to optimize the design of 100 Hz and PW/sr-cm2 class Micro-MOPA. Measured thermal lens focal length at 100 Hz is 0.5 m, and we found thermal lens have no significant time dependence in spite of its QCW pumping. From this result, we insert the optics with composite focal length of 0.45 m to cancel thermal focusing. On the other hand, such the optics is designed on the assumption of thermal lensing, therefore, we have to align optics with pumped amplifier. However, unaligned pumped beam already has 100mJ class energy and it is easy to break optics. To keep thermal lensing constant and to avoid this difficulty, we focused that thermal lensing have no significant time dependence and propose procedure for alignment and amplified energy control by using pumping delay timing shift between oscillator and amplifiere. From these improvements, we have demonstrated the 100 Hz operation of the Micro-MOPA with over 2 PW/sr-cm2.

The ongoing increase of peak and average power of diode lasers makes the consideration of thermo-optical effects due to absorption in the optical system necessary. Otherwise, this local increase in temperature might lead to a significant reduction of the entire functionality or a complete failure. Here, we consider this issue in volume Bragg gratings (VBG) as they are typically used for wavelength stabilization of the laser diodes. Conventionally, these gratings are fabricated very effectively by inscription using ultraviolet light into special photosensitive glasses. However, the use of these special glasses might compromise the transmission and, thus, limit the application. As an alternative, we inscribe VBGs in pure fused silica using ultrashort laser pulses and the phase mask scanning technique. Applying these gratings for external stabilization of high power diode lasers already demonstrated an outstanding performance in sense of spectral drift due to load change compared to conventional VBGs. Here, we present investigations to further optimize the residual absorption of the gratings especially in the NIR. Apart from analyzing the influence of the processing parameters on the residual absorption, we also studied the possibility for a thermal post-processing to anneal absorbing defects. The resulting gratings exhibit a residual absorption close to the intrinsic absorption of fused silica, making them ideally suited for high power applications. Further applications in ultrashort pulse laser systems for pulse stretching and compression are discussed.

In the high-power laser system, intensity and phase fluctuations in laser beam induced by dust, defects on optical elements will grow rapidly during the propagation in laser mediums, and further lead to the small-scale self-focusing (SSSF). The traditional pinhole spatial filter is usually used to suppress SSSF effect by filtering most medium and high frequencies in the laser beams. In recent years, the angular filter based on volume Bragg gratings (VBGs) has been proposed to improve the uniformity of laser beam in near field. However, this angular filter cannot be used in plug-and-play scheme since the output beam is efficiently diffracted and the optical axis of output beam deflects compared to the incident beam through the VBGs, which will bring difficulty to the alignment of laser systems. Besides, all the medium and high frequencies over the cut-off frequency will be cleaned up and too much loss of medium and high frequencies in the filtering process may cause the decline in effective fill factor in the amplifier, leading to the reduction of energy extraction efficiency in laser amplification. To solve the problems, a band-stop angular filter (BSF) based on VBGs and hump volume Bragg gratings was proposed. The band-stop filtering in a two-stage amplifier laser system was discussed and simulated. Simulation results show that the small-scale self-focusing effect in the laser system can be effectively suppressed with the BSF due to the control of fast nonlinear growth in the specific range of spatial frequencies in laser beams. The near-field modulation of output beam from the laser system was decreased from 2.69 to 1.37 by controlling the fast nonlinear growth of the spatial frequencies ranging from 0.6 mm-1 to 1.2 mm-1 with BSF. Besides, the BSF can be used in plug-and-play scheme and has potential applications in high power laser systems.

High power laser systems operating at mid IR wavelengths are required for medical applications, environmental monitoring, and military applications. All of these systems require optical isolators to avoid feedback into the pump laser cavity. We present measurements of the Verdet coefficient of germanate glass with Dy concentrations varying from 20-50% at wavelengths between .4 and 1.5 microns. The results indicate a linear increase of the Verdet coefficient with impurity concentration and a Sellmeier like dependence on wavelength.

Multi-kW combiner is a key component to achieve very high-power fiber laser. In this study, of interest for various industrial applications, two different optical designs were investigated for high brightness 6+1 to 1 KW-class combiners using 30/200 LMA output fiber. The first one is a co-pumped combiner, which consists in making a bundle with 105/125 (0.22NA) multimode fibers with a 10/125 (0.1NA) signal fiber. This latter is tapered down to the output fiber diameter. An excellent multimode transmission up to 97% and a low single insertion loss below 0.5dB have been demonstrated. The second one is a counter-pumped combiner, based on the development of a special technology to overcome the tapering of the 30/200 input signal fiber. We demonstrate the same specification concerning multimode transmission and signal insertion loss below 0.2dB. The main issue consists of the reduction of the thermal heating, particularly for the counter pumped combiner, greatly dependent upon seeding and wavelengths operating conditions. To define power scaling limitations of the component, we have investigated the thermal effects origins and evolutions. These effects mainly depend on the type of loss along the optical structure, polymer absorption or contamination. We will discuss on a process optimization, of packaging and CO2-laser-based processing machine to reach KW-class level fiber combiners. To the best of our knowledge, our component presents record performances, in term of high brightness conservation for 200µm LMA fibers, power handling, insertion loss and thermal optimization leading to a rise of 10°C/kW pumping at 976m.

The mid-infrared molecular fingerprint region has gained great interest in the last decade thanks to development of on-chip semiconductor lasers and mid-IR optical fibers. For integrated-optic devices and optical sensors based on interferometric techniques, versatile and easy handling devices can be required. In this context, low-loss single-mode chalcogenide microstructured optical fibers (MOF)[1] which presents an antireflection coating have been elaborated in order to be connected to a Distributed Feedback Quantum Quantum Cascade Laser (DFB-QCL). In addition, another original design of a chalcogenide MOF has been also realized in order to obtained high birefringence properties that can permit to maintain the polarization of the QCL at the output of the fiber. Finally, the fiber properties have been evaluated using a DFB-QCL emitting at 7.4 µm and the polarization maintaining of the chalcogenide fiber has been demonstrated[2]. The combination between a DFB-QCL with such non-conventional fibers has led to the development of single-mode fibered Mid IR lasers. [1] J. Troles, L. Brilland, C. Caillaud, J.-L. Adam, Advanced Device Materials, 3 (2017) 7-13. [2] C. Caillaud, C. Gilles, L. Provino, L. Brilland, T. Jouan, S. Ferre, M. Carras, M. Brun, D. Mechin, J.-L. Adam, J. Troles, , Optics Express, 24 (2016) 7977-7986.

We designed a high-efficient acousto-optic Q-switch based on a potassium yttrium tungstate crystal (KY(WO₄)₂), or KYW. Isotropic acousto-optic interaction along N_mN_g plane of dielectric axes of the crystal was used. The Q-switch operated at the wavelength of 2.1 μm of a Ho:YAG laser with the diffraction efficiency over 60% at the RF driving power of 20 W. No laser damage of the crystal with antireflection coatings was observed at 12 J/cm² fluence for nanosecond pulses.

Tailored laser illumination systems play a major role in various industrial applications, ranging from laser-beam splitting and diffusing to generate signal patterns with large fields of view for face and movement recognition, to shaping the wavefront of a laser beam using freeform surfaces. Several design concepts are based on topology control of the shaping element to avoid strong phase jumps or to minimize phase vortices and control the speckles of the illumination pattern at the signal plane. Other techniques follow a local shaping approach of the phase to control the wavefront, either over the whole element or in specific regions, with said regions arranged periodically to generate e.g. micro-lens arrays or randomly to generate diffusers of continuous surface topology. In particular, we show how these techniques are related to each other and how they can be used to improve maximum efficiency, uniformity of the intensity distribution and to minimize the zeroth order for non-paraxial illumination by laser beams.

High-energy, high-power laser system for inertial confinement fusion (ICF), such as National Ignition Facility (NIF), is large in size and expensive in construction. The multi-pass amplifier (MA) with the large aperture amplifiers is widely used in high-power laser systems, such as ICF drivers. The systems with MA usually have four features: square beam, single aperture, single pulse and unidirectional propagation, and the expensive preamplifier systems are required to compensate for the limited gain of the main amplifiers. The gain and the extraction efficiency are limited in part by the number of passes that the beam can make through the amplifiers. Besides, the laser system in the multi-pass amplifier should operate at much higher fluence to achieve high extraction efficiency, which results in a technical challenge in the damage of optical components under high-power lasers irradiation. To efficiently extract the stored energy with low injection energy at low laser fluence operation and make the system compact and reliable, a bidirectional ring amplifier (BRA) with twin pulses is proposed and discussed. The structure of the bidirectional ring amplifier is described. The characteristics of the bidirectional ring amplifier on extraction efficiency and output energy capability are simulated and discussed. The simulation results show that an extraction efficiency of 62.3% and the output energy of 13.4 kJ per pulse at the B integral limit can be obtained at low average fluence of 10.3 J/cm2 and the low injection energy of 3.9 mJ in the bidirectional ring amplifier. Compared with the multi-pass amplifier, the bidirectional ring amplifier is more compact and the extraction efficiency is much higher at low laser fluence operation, which is beneficial to reduce the effects of nonlinear phase shift. Furthermore, the preamplifier system for the bidirectional ring amplifier is simple, only a fiber oscillator and a regenerative amplifier can work.

Optical components consisting of hybrid elements (reflective, refractive and diffractive elements) are widely used in modern optical applications. Diffractive lenses as an example play an important role in imaging systems, laser-beam shaping, integration systems in optical communications, etc. Recently, due to the advances in modern fabrication technologies, meta-lenses also start to draw attention. We propose methods for the modeling and design of diffractive and meta-lenses based on the concept of the fast-physical-optics approach. A diffractive or meta-lens can be modeled as a series of structures functioning locally (e.g. local gratings) on a base interface. Each local structure introduces a certain local phase modulation, and by putting all of them together, the lens functionality can be achieved. In our approach, the rigorous Fourier modal method (FMM) is applied for the analysis of the local micro-/nanostructures, with all vectorial effects and possible higher-order effects taken into consideration; then the phase modulations can be collected for the lens function modeling. In this manner, a multi-scale simulation becomes feasible and efficient in most cases. The design of diffractive/meta-lenses follows an inverse concept—starting with a functional description of the whole lens, and then searching for suitable local structures which realize the desired phase modulation with high efficiency. Depending on the working diffraction order of the local structures, either a diffractive or a meta-lens can be constructed.

We examine the radiation-induced properties changes of evanescent-field-interacting type graphene-saturable absorbers (SAs). The graphene-SA inserted to the mode-locked laser was exposed to ₆₀Co gamma-ray radiation up to 1.02 kGy at a 50 Gy/hr dose rate. To see how the graphene-SA affects to the laser performance, the graphene-SA-based mode-locked laser was also monitored simultaneously. The mode-locking was broken at 0.75 kGy irradiation dose, which corresponds to 15.6 years operation in low-earth orbit satellites. The optical properties of the graphene-SA was also compared before and after radiation.

We report the femtosecond laser inscription of fiber Bragg gratings (FBGs) in an Er-doped fluoride glass fiber used for lasing at a mid-infrared wavelength of 2.8 μm. FBG reflectivity and laser output power are observed with varying the index change of grating plane. We have tried to create high-index-contrast grating planes worked as Bragg reflector. The index change was estimated by fitting experimentally obtained reflectivity to its calculation. When using laser fluences of 25 and 40 J/cm², the index change was found to be 0.7×10^-3 and 1.1×10^-3, respectively. When using laser fluence of 25 J/cm², FBG reflectivity increases up to 95% at the grating length of 4.0 mm. The case of using 40 J/cm² shows 97% at the grating length of 2.5 mm. These results are in agreement with the reflectivity calculation. The investigation of lasing evolution will contribute to more efficient fabrications of FBG and fiber laser system.

Fiber lasers have attracted great attention in recent decades due to their high efficiency, low cost, compactness, and excellent beam quality. To achieve high power single-mode beam in fiber lasers, mode field adapters (MFAs) are usually required as they can significantly reduce the detrimental nonlinear effects. Traditionally a combination of thermally expanded core (TEC) technique and fiber tapering is used to fabricate MFAs. Due to narrow heating zones or short lifetime of electrodes and filaments, it is not very practical to directly expand the mode field diameter (MFD) of the single-mode fiber (SMF) to match that of the large mode area (LMA) fiber. Thus a combination of TEC and fiber tapering is needed to obtain matched MFDs between the two fibers. In this paper we present a very simple method for fabricating MFAs with CO₂ laser splicer. The wide heating zone provided by CO₂ laser splicer is ideal for TEC process. The MFD of the SMF can be easily expanded to around 20 μm, which is sufficient to match the MFDs of many commonly used LMA fibers. The SMF with TEC is directly spliced to the LMA fiber. Low insertion loss less than 0.2 dB and high beam quality with M² < 1.1 are achieved. The highly reliable and repeatable fabrication process may only take a few minutes, which is vital for volume production.