Fast Axis Collimation Lenses Research Articles

The SMILE Effect in the Beam Propagation Direction Affects the Beam Shaping of a Semiconductor Laser Bar Array

Near-field bending of a laser diode bar (i.e., the SMILE effect) degrades the laser beam brightness, adversely affecting optical coupling and beam shaping. Previous reports mainly focused on the two-dimensional near-field bending of a laser diode bar. However, the near-field bending of a laser diode bar not only occurs in the laser bar growth direction, but also in the beam propagation direction. The present article proposes the three-dimensional near-field bending of a laser diode array, which is commonly known as the three-dimensional spatial SMILE effect. Through theoretical and simulated investigations, it has been found that a laser bar array not only deforms in the fast axis direction to cause the traditional two-dimensional SMILE effect but also experiences an additional deformation of approximately 2 μm in the laser emission direction simultaneously. Due to the SMILE effect in the beam propagation direction, not all emitters are aligned in a straight line, and some emitters experience defocusing during collimation. Consequently, there is an increase in the residual divergence angle and beam width, resulting in a degradation of the laser bar array’s beam quality. According to the theoretical calculations, ZEMAX simulations, and experimental results, for a FAC (fast axis collimation) with a focal length of 300 μm, the divergence angle of single emitter after collimating in the fast axis increases from 4.95 mrad to 6.46 mrad when the offsetting of the working distance between the incident beam waist and FAC lens increases from 0 μm to 2 μm.

Inhomogeneous thermal analysis of microlayer mold for glass molding of fast-axis collimation lens array

Fast-axis collimation (FAC) lens arrays play a crucial role in laser systems, offering precise beam shaping and focusing for applications such as laser marking, and optical communication. Achieving high precision in these applications requires a FAC lens array with a long Rayleigh range. While precision glass molding with nickel-phosphorus (Ni-P) microlayer molds has revolutionized the mass production of FAC lens arrays, the extreme conditions during the molding process can lead to poor profile accuracy. To address this issue, we developed an optical collimation system to derive the final characteristic parameters and obtain the beam waist radius and Rayleigh range of the collimated laser. Additionally, we conducted a thorough analysis of the inhomogeneous thermal expansion process of the microlayer mold and established a mathematical solution for thermal compensation to modify the mold's shape. We validated the proposed method by fabricating an FAC lens array mold and measuring the profile error and waist radius of a molded FAC lens array. We also calculated the profile error of this method using a finite element (FE) model in ABAQUS. The results indicate that incorporating the inhomogeneous thermal expansion reduces the shape error of the FAC lens array from 0.577 μm to 0.135 μm. Moreover, using inhomogeneous thermal compensation significantly improves the Rayleigh range of the FAC lens array from 1.285 μm to 9.8 × 104 μm.

Pulsed Diode Laser Minibars for Pumping Space-Borne Solid-State Lasers

Laser diode benches (LDBs) with lasing wavelength of 808 nm were developed, manufactured and endurance-tested for utilization as pump lasers for the Nd:YAG oscillator in the climate satellite MERLIN. The LDBs combine customized TE-polarized GaAs-based 5-mm minibars with fast axis collimation lenses to produce a reliable, space qualified component at optical power of 63 W per minibar. Accelerated life tests of 20 LDBs are presented. Except for a small increase in threshold current, no wear out in operating current or sudden failures were observed, and reliable operation over the full mission time of >4 gigashots was confirmed. The electro-optical characteristics remain in the specified ranges after exposure to the total operational load of the mission.

GPU-accelerated wave-optical model for external-cavity diode lasers.

The spatial distribution of the optical feedback field in an external-cavity diode laser (ECDL) is an important parameter influencing its lifetime and filamentation. From a modeling point of view, the evaluation of the full diffraction integral is required to calculate the propagation of light through thick lenses such as fast axis collimation lenses or beam transformation systems used for high-power diode lasers. In this Letter, we illustrate an algorithm for the accelerated computation of the Rayleigh-Sommerfeld diffraction integral on a graphics processing unit. We further show a validation of the results by measurements on an ECDL.

Fast-axis collimating lens recognition algorithm based on machine vision

In order to solve the problem of low efficiency and low accuracy of manually picked fast shaft collimation lens in actual production, the method of recognition of fast shaft collimation lens based on machine vision is studied. Using industrial camera to achieve image acquisition, using HALCON software to pre-process the image of fast-axis collimated lens, edge detection and other aspects of research, through the platform verification, the results show that the processed image is clear and easy to identify. In the lens placement is not accurate, the background is dirty can still ensure a better positioning effect, This study has some reference significance for visual recognition in the actual production of fast-axis collimation lens.

Automated UV-Epoxy-Based Micro-Optic Assembly for Kilowatt-Class Laser-Diode Arrays and Modules

This paper outlines the numerous interdisciplinary activities required to implement two ultraviolet (UV) epoxy-based automated micro-optic assembly tools within a “smart factory” for high-power semiconductor laser manufacturing. After a brief overview of the motivation and approach, two examples of automated micro-optic assembly tools [e.g., fast-axis collimation (FAC) lens attach and mirror stripe alignment] for kilowattclass laser-diode arrays and modules are given that demonstrate the breadth of automation activities required within a modern factory. For each system, the complete assembly sequence is outlined, and the steps that presented fully automated challenges are highlighted. In contrast, to the previous published results that focused on the details of the automated micro-optic alignment, the largest challenges primarily involved automation and repeatability of the UV-epoxy dispense and attach processes for these high-power semiconductor devices. These were solved by precise and stable mechanical design, customized lighting, and machine vision solutions. Finally, the complete integration of the tools into a “smart-factory” system is outlined.

High-power direct diode laser output by spectral beam combining

We demonstrate a spectral beam combining scheme based on multiple mini-bar stacks, which have more diode laser combining elements, to increase the combined diode laser power and realize equal beam quality in both the fast and slow axes. A spectral beam combining diode laser output of 1130 W is achieved with an operating current of 75 A. When a 9.6X de-magnifying telescope is introduced between the output mirror and the diffraction grating, to restrain cross-talk among diode laser emitters, a 710 W spectral beam combining diode laser output is achieved at the operating current of 70 A, and the beam quality on the fast and slow axes of the combined beam is about 7.5 mm mrad and 7.3 mm mrad respectively. The power reduction is caused by the existence of a couple resonator between the rear facet of the diode laser and the fast axis collimation lens, and it should be eliminated by using diode laser chips with higher front facet transmission efficiency and a fast axis collimation lens with lower residual reflectivity.

High power high efficiency fiber coupled diode laser module

The high coupling-efficiency fiber coupled diode laser module is obtained by beam shaping. The wavelength of the CW diode laser bar is 976 nm, and five bars are collimated by a fast axis collimation lens. Then the beams are transformed and collimated by slow axis collimation optics. Then all the beams are combined in space, and focused into a multimode fiber (400 m core diameter, the numerical aperture (NA) is 0.22). Experimental results show that the laser output from fiber could reach 327 W, and the coupling-efficiency is more than 93.6%. Experimental results demonstrate that this module lays a foundation for multi-wavelength, polarization beam combining and the high beam quality, high coupling efficiency diode laser module with CW thousands watts class output power can be developed.

Spectral linewidth narrowing and tunable two-color laser operation of two diode laser arrays

We propose and implement a common external cavity to narrow spectral linewidth of two broad-area laser diode arrays (LDAs) and align their center wavelengths. The locked center wavelength of two LDAs can be tuned in the range of ~10 nm by tuning the tilted angle of the diffraction grating. The output beams of two LDAs are spatially overlapped through the polarization beam splitter of the common external cavity, and the total output power equals the power of two LDAs. The center wavelength of each LDA can be independently tuned by shifting the corresponding fast-axis collimation lens. As a result, the high-power two-color LDA operation is demonstrated with the tunable wavelength difference of up to 2 nm (~1 THz).

Focus on lasers and imaging

Focus on lasers and imaging

Conductively Cooled 1 kW—QCW Diode Laser Stacks Enabling Simple Fiber Coupling

A new mini-bar design densely packed with 13 emitters in a 1.6 mm aperture has been developed. These mini-bars deliver >200 W output. With a very low divergence of 95% power enclosed in 25° they are suitable for fast axis collimation (FAC) lenses with large working distance. The mini-bars are mounted on compact CuW carriers, which are further integrated into a custom stack assembly where they are conductively cooled from both sides. This completely AuSn soldered stack consists of only coefficient of thermal expansion matched materials and was 100 times temperature cycled from -40°C to 85°C, without any change in the PUI characteristic, the spectrum and the far field. The beam propagation factor M 2 of a 12-layer stack is ?130 in the vertical direction (after FAC) and ?210 in the lateral direction. Thus, the stack can be coupled to a 1.2 mm multi-mode fiber (M 2 = 260) with a coupling efficiency of 90% using only low-cost lenses.