This PDF file contains the front matter associated with SPIE Proceedings Volume 11261, including the title page, copyright information, table of contents, and author and conference committee lists.

The use of photonic integrated circuits and components in many areas across the general area of laser systems is increasing. Example applications of such systems include free space optical communication, remote standoff sensing, solid state and fiber laser pumping, LIDAR for autonomous vehicles, and atomic laser systems for position, navigation, and timing. In this talk we will review the design, performance, and robustness of Freedom Photonics high performance integrated photonic components for these applications and others, focusing in particular on recent advancements in our products at 780 nm, 1060 nm, 1310 nm, and at 1550 nm.

The use of epoxies in space-based instruments is often unavoidable in situations where the bonding of dissimilar materials such as glass and metal is required. While there are epoxies that exhibit low total mass loss (TML) and collected volatile condensable materials (CVCM) in vacuum, in some applications they can still be a source of problematic contamination. Epoxies can also be incompatible with exposure to chemical environments some space instrumentation may be exposed to. In high power laser instruments such as LIDAR systems where optical components must be securely bonded to metal mounts, the impact of epoxy outgassing can be especially acute. Even with very low outgassing levels, the intense laser can break down the outgassed material and preferentially deposit it on optics that handle high optical power. This laser induced contamination in turn leads to laser induced damage, leading to degradation of optical components and reducing the reliability and operational lifetime of laser instruments [1-6]. Alternative bonding methods that avoid introducing additional contaminants could greatly improve reliability and operational lifetime of space instruments.

The use of additive manufacturing methods in research and industry has led to the possibility of designing more compact, light and low-cost assemblies. In the field of laser development, new opportunities resulting from additive manufacturing have rarely been considered so far. We present a compact, lightweight solid-state amplifier system for low-power applications where the optomechanical components are manufactured completely additive via Fused Filament Fabrication (FFF). The amplifier system is based on a Nd:YVO₄-crystal pumped with an external, fiber-coupled diode at a wavelength of 808nm and a maximum output power of 3 W. The seed source is a Nd:YVO₄-crystal based solid-state laser with an emission wavelength of 1064 nm. The commercial optical components, such as lenses and crystal, are firmly imprinted via FFF in the optomechanics and thus secured against misalignment. Additionally, sensor technology for temperature measurement is implemented into the devices. The use of FFF, in which the components are printed from polymers, results in a lightweight yet stable construction. We have shown, that optical components can be imprinted without adding mechanical stress. To increase the mechanical and thermal robustness of the system different types of polymers as well as post process treatments are tested and the use of Laser Metal Deposition for this application is investigated. The thermal stability of the printed structures is evaluated to determine the maximum power level of the system without damaging the polymer-optomechanics. Furthermore, output power, optical-to-optical efficiency, beam pointing, and beam shape are measured for several on- and off-switching processes as well as long-term operation.

The mid-infrared (MIR) molecular fingerprint region has gained great interest in the last past years thanks to development of semiconductor laser source like Quantum Cascade Lasers (QCL). Nevertheless, because of the small size of the waveguide of such devices (≈ 10μm), the beam at the output of such source has an extreme divergence (could be < 45 deg) which makes it difficult to use without specific optics. Several solutions, such as classical lens in chalcogenide glass or parabolic mirror, have been used to shape the laser beam. However, this kind of solution remain expensive and not always usable for small component. This paper present a new kind of lens for the collimation of MIR laser beam, very compact and with a focal length highly adjustable. The fabrication of this dielectric flat lens has the advantages of the semiconductor fabrication techniques and a single etch step on a wafer is sufficient to perform the lens. The main principle is to structure the wafer surface with sub wavelength pattern to induce a local variation of the refractive index. Then the mapping of this local index is the key to control the phase of an input beam and to perform the desired lens function. This works shows simulation results and demonstrate the first prototype of this device for wavelength close to 9μm with a focal length and numerical aperture of almost 150μm and 0, 5. This prototype is disc-shaped with a diameter of 100μm made on InP wafer.

Kylia’s main expertise is ultra-precise assembly of optical elements on glass breadboards, using 6D positioning. Thanks to its know how in assembly epoxies, Kylia can provide stable and robust devices, made to be used in extreme environment. Kylia’s technology is usually referred to as “free-space optics” . It consists in the 6-axis nano-positioning of micro optical elements (lenses, prisms, diffraction gratings…) and their bonding onto a reference surface. The wide scope of this technology and its flexibility enable low-cost and fast cutting edge components development. This technology can be used to design on-demand products including the following optical functionalities: laser cavity, optical interferometers, splitting or combining of polarized beams, wavelength multiplexing, and fiber coupling.

The safe and reliable transportation of human beings and goods using Lidar becomes possible in case of simultaneously illuminating the 360° field of view (FOV) around the vehicle with a constant power density in all directions. Conventionally, a rotating mirror is widely used to reorient a constant-power laser beam at the target direction but not simultaneously in a 360° FOV. The key challenge in this application is creating a constant light intensity in all detectable directions at the same time. This can be tackled by combining four laser sources and corresponding micro-optical components that shape the light within a rectangular 120°x20° (horizontal and vertical directions) FOV.

Laser systems provide unique thermal challenges due in large part to high levels of waste heat, heat flux and packaging constraints. ACT is a leader in developing innovative thermal designs to meet harsh operation and technical specifications. This presentation will dive into several solutions that are used to maintain safe operations of systems ranging from 10s of Watts to 10s of KiloWatts. This presentation will provide a combination of theoretical physics, practical application and design tools for engineers to work with potential solutions. We will focus on heat pipes, vapor chambers and pumped two-phase solutions; designed to meet the demands of high heat density applications.

Automated, ultra-precise packaging strategies reduce production time and costs while increasing yield, quantity, and precision, making them one of the main research and development questions in the field of production technology. Fraunhofer IPT develops sensor-guided assembly solutions for packaging and testing of optical and non-optical components to meet the demand. In this paper, we present a prototypical process for the automated, ultra-precise passive alignment using the assembly of a diamond engraving tool as an example. The challenge is to place a diamond measuring three millimetres in its largest dimension into a groove of similar size and to position the tip of the diamond within tolerances of a few micrometres and arcminutes. This six dimensional assembly problem is tackled by feeding live camera data to an image processing algorithm and by aligning the diamond using Fraunhofer IPT’s ultra-precise micromanipulator, collectively forming an automated, closed-loop assembly process. Thus, a fully automated packaging process with very high accuracy and reliability is proven to be technically possible.

The industrial assembly processes for fast axis collimation (FAC) lenses with high power laser diodes are continuously being improved and automated. The system requirements allow for various solutions for the attachment process of the micro-optic component, the standard being active assembly relative to the light emitting laser-diode facet with joining by a UV-curable glue at attachment positions outside of the laser beam-path. To facilitate higher degrees of freedom and to optimize the results in the joining process with tighter tolerances in some critical functions, the FAC mounted on tab is one of the possible solutions and a viable process option. We report the results of high accuracy preassembly of FAC on tab with respect to the specific requirement of a target assembly back focal length within tight tolerance values.

We have simulated and optimized a conductive cooling structure including the distribution of temperature in active layer, and the deformation of laser to achieve high power operation with low SMILE value. Unlike the traditional conductive cooling structure, our structure improves the heat dissipation efficiency from three aspects: with angle structure in the front of heat sink; double side heat dissipation and without submount packaging technology. In this report, an output power of more than 250W CW from a 4 mm long laser bar with a filling factor of 50% is shown at 240A driving current with a power conversion efficiency of 65%. The thermal rollover of this packaging conductive cooling device can reach 385W at 400A driving current.

Publisher’s Note: This conference presentation, originally published on 11 March 202, was withdrawn on 3 June 2020 per author request.

High power, high efficiency diode lasers operating in the 15xx nm wavelength range are needed for a variety of applications, including eye-safe infrared illuminators and resonant diode pumps for Erbium-based high energy laser systems. We have demonstrated high power, high efficiency lasers at 1532 nm with integrated wavelength control. We have engineered the epitaxial structure in InP to mitigate losses and to include a buried distributed feedback (DFB) grating layer for wavelength control. We have demonstrated 15xx nm lasers generating >3 W at 36% EO efficiency. We have also demonstrated multi-Watt DFB broad area lasers with >99% of the power concentrated in a narrow spectral width <1 nm. These lasers are being packaged into fiber-coupled modules.

Light absorption at the facet of a high power diode laser can lead to severe heating and catastrophic optical damage. In this work, a combination of high resolution thermoreflectance imaging and a detailed heat transport model of the diode chip are used to measure facet absorption in diode lasers. This approach permits a direct measurement of the effectiveness of passivation layers in improving facet robustness and device lifetime. The ability to quantify facet absorption is an essential step toward enabling rapid development of alternative passivation technologies and improving the reliability and maximum output power of diode laser systems.

Disk laser offers excellent scalability over a broad variety of average powers and pulse energies simply by changing the disk size and/or the number of disks in an amplifier. This makes the disk laser a leading candidate for applications ranging from industrial devices for material processing to drivers for laser acceleration of nuclear particles and inertial confinement fusion. This paper highlights key milestones in the evolution of disk lasers and it reports on recent developments of innovative designs offering high performance in compact and modular packaging.

High power laser systems require the use of optical isolators to prevent coupling of reflected light into the pump laser. Terbium Gallium Garnet (TGG) and Potassium Terbium Fluoride (KTF) are materials used as optical isolators and while they have been grown for many years, advances in crystal growth and processing make a new set of measurements of the Verdet coefficients of these materials desirable. We present new measurements of the Verdet coefficients of TGG and KTF from 0.405 μ to 1.55 μ and derive expressions for the spectral behavior of the Verdet coefficients.

Passively Q-switched solid-state laser is potentially a very advantageous light source for automotive LiDAR application. The key challenge is the ability of wide temperature range operation. In this work we investigated high-power diode laser bar pumped passively Q-switched Nd:YAG/Cr:YAG solid-state laser with a stable output over a wide temperature range. Firstly we studied the impact of the pump light wavelength and the laser crystal temperature on the pulse energy and threshold, and results showed that to obtain the stable output of a solid-state laser in a wide temperature range, both the diode output and the laser crystal temperature should be stabilized in a reasonable small range. Further we designed and fabricated solid-state laser modules with a single active temperature control for both laser diode and crystal, which had stable pulse energy of millijoules with a pulse width of about 2 ns and a repetition rate of 30 Hz over a wide temperature range from -30 oC to 90 oC.

Fibertek reports on the design and performance of two high power ruggedized Thulium fiber laser systems designed for spaceborne and airborne applications. The spaceflight system is a 100 W average power, linearly polarized, 1940 nm thulium doped fiber laser (TDFL) packaged in a hermetic 11-liter module. The airborne system is an all-fiber, narrowlinewidth, master oscillator power amplifier architecture with staged thulium fiber amplifiers with 80 W peak power and 20 W average power in a quasi-continuous temporal waveform. The airborne laser includes programmable digital phase codes with bit rates up to several GHz. We will discuss the overall system performance and environmental qualification testing of both systems.

We present recent developments regarding fiber Bragg gratings for kilowatt-level fiber lasers. First, we show that writing grating reflectors through the fiber coating using an ultrafast laser improves reliability and enables higher pump power handling. The use of ultrafast laser technology also offers more options to produce gratings in larger core fibers. Finally, we show that Raman suppression gratings are a good solution for SRS mitigation with their large (<20 dB) rejection over 15 nm and low reflectivity at Raman wavelengths, and negligible insertion loss at the laser wavelength.

Chirped Volume Bragg Gratings (CBGs) in photo-thermo-refractive (PTR) glass allow stretching and compression of ultra-short pulses with high pulse energy and power and minimal beam distortions. PTR glass based CBGs can stretch pulses up to 1 ns while the duration of the recompressed pulses is nearly transform limited. In this work we report for the first time on multiplexed chirped volume Bragg gratings in PTR glass. These novel optical elements allow shaping of an ultrashort pulse spectral profile with a Moire pattern. Such elements can be used for comb-generation, shaping of ultrashort pulses, and output couplers.

The cladding-pumping scheme has made the power scalability of rare-earth-doped fiber lasers up to record levels possible by distributing the pump absorption along much longer fiber lengths. However, in addition to increasing the fiber cost and the cavity losses, a longer cavity length leads to enhanced detrimental nonlinear effects such as stimulated Raman scattering. As a way to reduce the required length of such lasers, we propose here an all-fiber laser architecture that makes use of a femtosecond-written chirped inner-cladding Bragg grating (ICBG) as a residual pump reflector. We report a 73% reflectivity of the pump power propagating in the highly multimode 125 μm-diameter inner cladding of the fiber made out of pure silica. This component was inscribed by using 400 nm femtosecond pulses and the phase-mask technique. Such a reflectivity was reached by optimizing the chirp of the grating and by inserting the fiber inside a hollow capillary with an outside diameter of 1 mm during the inscription. The latter reduces greatly the impact of the fiber’s curvature on the refraction of the writing beam. A larger writing area and consequently a stronger reflectivity could therefore be reached. The presence of this component at the output of a 21 m long erbium-doped silica fiber laser operating at 1.6 μm increased its slope efficiency from 20.5 to 25.1 % with respect to the injected pump power and increased its output from 22.8 to 29 W at 115 W of pump power.

We present a novel approach for the inscription of nonlinearly chirped fiber Bragg gratings (N-CFBGs) using femtosecond laser pulses. This approach allows the efficient fabrication of N-CFBGs by partially tuning the average refractive index of an already inscribed linearly CFBG. No complex phase mask designs or further modifications of the inscription setup are necessary. This approach involves selectively modifying the average refractive index perturbation and the index offset of smaller sections of the grating and has the advantage of reproducibility and flexibility. It paves the way for N-CFBGs with tailored dispersion profiles used in fiber based CPA systems.

The use of optical fiber in a multitude of applications has been increasing for several decades. This increased use has thrown up some limitations particularly in area of high-power delivery where the low damage threshold of conventional AR coatings has become an issue. Various methods such as the use end caps have been used to reduce this problem, but the fundamental issue remains, AR coatings have a low damage threshold which makes them difficult to use for high power applications. As the demand for high power delivery by optical fibers increases there is a need for more robust AR coatings for fiber end faces. AR coatings have various limitations such as very narrow bandwidth, a relatively low damage threshold compared to that of glass etc. There is need for a better solution. In this paper, we describe the use of meta-surfaces on the end of fibers that can replace standard AR coatings. These surfaces or motheye structures impart AR properties to the end faces of the fibers that are superior in almost every way. They have superior damage threshold than coatings as well as working over a broad wavelength range with no angular dependence. We compare the performance and properties of these structures with that of AR coatings.

We report on the inscription of compact and highly efficient transmission fiber gratings by means of an amplitude mask and femtosecond laser pulses at 800 nm. With the approach, gratings with strong resonances could be realized where the total length as well as the polarization dependent loss could be significantly reduced compared to previous results. The fiber integrated component, shown in this contribution, could be an ideal candidate for the mitigation of nonlinear effects in fiber laser applications, such as stimulated Raman scattering.

An innovative hollow-core fiber with anti-resonant arches (HC-ARA) is designed and made of chalcogenide glass As₂S₃. The HC-ARA fiber has a single layer of eight non-touching curved arches, each one being solidly attached at two locations on the outer solid region to prevent any lateral displacement and to preserve the arches’ shape and uniformity during the fabrication process. The thickness and spacing between the arches are selected to minimize the fiber transmission loss <0.1 dB/m for CO₂ laser at 10.6 micron. Also the higher order modes of the HC-ARA fiber are more attenuated than the fundamental mode, so the fiber is effectively single mode after only a few meters. The HC-ARA preform is made by extrusion of chalcogenide glass through a die specifically designed to produce the anti-resonant arches. The extruded HC-ARA preform is pulled in a fiber using photonic crystal fiber draw techniques. Recent simulation and experimental results on the HC-ARA fiber are presented to illustrate a novel fiber solution for CO₂ laser transmission at 10.6 micron.

Multi-Stack IR diode laser sources in combination with micro-optics for beam forming allows the design and production of the most compact and efficient laser sources for high productive and selective heat treatment of surfaces and coatings in nearly all segments of industries. The direct diode approach without brightness destroying fiber delivery enables power densities above 10kW/cm² for high heating rates and accurate thermal envelopes with sub-second dwell times. Thanks to a special designed line beam profile the line length and related processed area per time can be scaled by putting several line segments together without any power or intensity drop at the stitching points of the line beam segments.

We have developed a multichannel output coupler enabling coherent beam combining in the two-micron spectral range. We demonstrate experimentally the combining of multiple beams utilizing a set of thulium-doped, double-clad, singlemode optical fibers. The fibers are pumped by fiber-pigtailed laser diodes at 793 nm via (4+1)x1 pump-signal combiners. The combiners are fabricated using vanishing-core technology, which allows for preservation of the mode field through the tapering process. The output of individual lasing channels is generated over a 20 nm spectral band at around 1970 nm without any spectrally selective elements. The slope efficiency of individual lasers is approximately 50% with respect to the pump power. All lasing channels are fused into a monolithic silica structure with channel spacing of 32 microns on a triangular lattice. The fused assembly is fabricated in a glass microforming tapering process with a draw ratio of 3.9. In the process, the mode field at 1970 nm expands slightly to about 15 microns at the end of the taper, while the outer diameter is reduced from 2.3 mm to approximately 590 microns. The tapered end is straight polished and fusion spliced to a 600- micron diameter silica glass rod. The rod is cleaved and optically polished at zero degrees. The length of the rod is one half of the Talbot distance for optimal coherent beam combining. In the experiment, an antiphase supermode is observed when only the seven inner channels are pumped, and an in-phase supermode is excited when the number of channels is nineteen or larger.

Successful commerce of science and technology requires standardization of measurement. Today more than ever, there is need for a new Optical Laser Damage standard to increase the efficiency of commerce in the optical industry. The current Laser Damage Standard, ISO 21254, is overly complicated for a general seller/buyer and can produce ambiguous results. To address the challenges to efficient commerce from ISO 21254, OEOSC Task Force 7 (TF7) is developing a new US laser damage standard. The new standard is based on a measurement theory approach and introduced and examined. The optical manufacturer (seller) directly benefits from an operationally effective means to determine acceptance criteria around the ability of categorizing optics that will meet customer’s requirements. OEOSC Task Group TF7 is seeking broad industry support to develop the most useful and robust standard possible. The new US Laser Damage Standard will benefit the optical manufacturing industry and customers alike that use optics susceptible to laser damage in their applications by providing a clear unambiguous pass or fail result. The paper will conclude with a discussion of the path forward in the development of the US laser damage standard.

Achromats are one of the most commonly used optical components in optical design and engineering. Historically, an achromat is composed of two lenses: a positive crown glass element and a negative flint glass element, cemented together. The compound lens brings at least two wavelengths of light to a common focus along the optical axis. Presented in this paper is the novel implementation of an achromatic singlet made of a single optical material, Zeonex E48R. A customized ray tracing algorithm was used to arrive at the solution while single point diamond turning is used to fabricate a series of prototypes. Axial MTF and chromatic focal shift data are presented alongside two similar comparison lenses: a plano-convex lens and a traditional cemented achromatic doublet. The test results illustrate achromatic performance can be achieved using a single optical material with axial performance that exceeds an incumbent cemented achromat with the same first order properties of focal length and lens diameter. Applications for the new singlet achromatic lens design form include broadband focusing, high laser power uses, and ultraviolet applications where optical cement is not desired. Keywords:

High-power diode lasers are widely used in solid-state and fiber laser pumping. The spectral power distribution (SPD) of diode lasers should be perfectly matched with the absorption peak of gain materials. Spectral broadening would lead to a low optical-optical efficiency for the pump lasers. In this paper, a mathematical model based on multiple Gaussian functions was introduced to characterize the SPD of high-power diode lasers. The effect of temperature and the distribution on laser spectrum was specially included in this model. Temperature distribution in high-power diode lasers was calculated via an analytical three-dimensional thermal model. The temperature difference within the active region for diode lasers with different package structures and under different heat dissipation conditions was demonstrated. The intrinsic SPD for diode lasers with uniform junction temperature distribution was obtained from the experimental measurements in which a cold pulse current was injected into the diode lasers. SPDs for diode lasers under different injected currents were illustrated by this spectrum model, and compared to the experimental results for model validation. SPDs for the diode lasers with different chip architectures and packaging structures was calculated by coupling the analytical temperature fields into the spectrum model. Laser spectrum was verified to be independent of current density, but mainly depend on the junction temperature distribution in the experiments by comparing the spectra of the epi-up and epi-down packaged F-Mount single-emitters at same injected current.

All-glass microstructured high-power cladding light strippers (CLSs) capable of handling hundreds of watts of cladding power or more are highly desired in cladding-pumped high power fiber laser systems. In this paper we demonstrate high strength, high efficiency CLSs with tensile strength more than 50 N, temporary bending diameter less than 6 cm and power stripping efficiency more than 7 dB/cm. These CLSs are fabricated by CO₂ laser ablation and their advantages and disadvantages are discussed. The all-glass CLSs possess outstanding heat-dissipating capability and do not require thermal management for up to a few kW of cladding power. Conventionally CLSs are fabricated by utilizing high-index polymer recoating, acid etching or CO₂ laser ablation, etc. CLSs with CO₂ laser ablation are highly preferred in many application due to their chemical free, contamination-free, noncontact manufacturing process. CLSs with CO₂ laser ablated transversal or spiral grooves have the advantages of high efficiency, short processing time. However, the fiber tensile strength is greatly reduced due to glass mini-fractures or cracks that may be introduced and propagate along the grooves. Creating holes on the optical fibers with CO₂ laser ablation is an alternative way to fabricate high efficiency CLSs. It provides greatly improved mechanical strength compared to CLSs with transversal or spiral grooves though it needs longer manufacturing time. In this paper we demonstrate high efficiency CLSs with spiral grooves and holes respectively and their optical, thermal performance and mechanical properties are discussed.

Diffractive optical elements with a large diffraction angle require feature sizes down to sub-wavelength dimensions, which require a rigorous electromagnetic computational model for calculation. However, the computational optimization of these diffractive elements is often limited by the large number of design parameters, making parametric optimization practically impossible due to large computation times. The adjoint method allows calculating the gradient of the target function with respect to all design variables with only two electromagnetic simulations, thus enabling gradient optimization. Here, we present the adjoint method for modeling wide-angle diffractive optical elements like 7×7 beam splitters with a maximum 53° diffraction angle and a non-square 5×7 array generating beam splitter. After optimization we obtained beam splitter designs with a uniformity error of 16:35% (7×7) and 6:98% (5×7), respectively. After reviewing the experimental results obtained from fabricated elements based on our designs, we found that the adjoint optimization method is an excellent and fast method to design wide-angle diffractive fan-out beam-splitters.

Miniaturized RGB-laser light sources could become an enabler for fashionable augmented and mixed reality glasses. Increased assembly productivity for these micro opto-electrical RGB-light sources and a further reduction in their package dimensions are mandatory. We present our new approach to build miniature RGB-light sources on structured silicon wafers. These are part of our optical packaging platform that enables efficient assemblies with controlled working environments for long term performance of semiconductor laser sources. The platform provides an optical bench with integrated heat spreader and emission windows enabling miniature hermet ic housing for laser diodes assemblies on 8” wafers or chip level.