Results for a new compact 488 nm solid-state laser for biomedical applications are presented. The architecture is based
on a multi-longitudinal mode external cavity semiconductor laser with frequency doubling in a ridge waveguide fabricated in periodically poled MgO:LiNbO3. The diode and the waveguide packaging have been leveraged from telecom packaging technologies. This design enables built-in control electronics, low power consumption (≤ 2.5 W) and a footprint as small as 12.5 x 7 cm. Due to its fiber-based architecture, the laser has excellent beam quality, M2 <1.1. The laser is designed to enable two light delivery options: free-space and true fiber delivered output. Multi-longitudinal
mode operation and external doubling provide several advantages like low noise, internal modulation over a broad frequency range and variable output power. Current designs provide an output power of 20 mW, but laser has potential for higher power output.
Fiber lasers products have been developed at JDS Uniphase with up to 25 Watt cw output power and diffraction limited beam. Similar fiber lasers have been demonstrated with over 100 Watt cw output power. The fiber laser is based on an all fiber optic cavity with no free alignments or possibility for contamination resulting in a reliable laser cavity. A distributed pump architecture based on an array of 3-5 Watt fiber coupled pumps provides redundancy for reliability. The unpolarized, fiber delivered, compact and direct modulated fiber laser sources are ideal for a range of applications including material processing, marking and reprographics. Moreover the pump source has applications in material processing as well. The advantages of the fiber laser are illustrated in marking system.
Multi-mode pumps based on single emitter diodes deployed in distributed pump architectures offer significant advantages in thermal management and reliability for pumping high-power fiber lasers and amplifiers. In a distributed architecture, while individual diode failures do not directly generate failures of other diodes in the distributed ensemble, failures do cause the rest of the sources to drive to higher power levels to compensate for the loss of power. A model of the ensemble lifetime based on module failure rates and power-scaling factors demonstrates that the distributed pump architecture requires random failure rates corresponding to better than 200,000 h mean time between failure (MTBF) to meet typical application requirements. A high power multi-mode pump module suitable for commercial aplications is shown. Critical elements are based on telecom architectures, including the optical train and the fiber alignment. The module has a low thermal resistance of 4 C/W from the laser diode junction to the external heat sink, couplng efficiency of over 80% into 0.2 NA, and demonstrated reliable output power of over 5W CW with peak wavelengths near 915 nm. Telecom qualified modules have random failure rates corresponding to better than 1,000,000 h MTBF. Stability of the critical fiber alignment joint for single mode packages has been demonstrated at elevated temperatures (e.g. 85 C) for thousands of hours. The reliability of the commercial multi-mode package can be estimated by similarity to the telecom package, and is verified by testing of conditions considered to be at risk based on the differences between the known telecom, and the new commercial package, designs. Test results are shown for temperature cycling, CW operation, and damp heat. The relationships between anticipated MTBF requirements, test duration and test population are shown.
We demonstrate the phase locking of a 12 X 12 two-dimensional surface emitting laser array to generate 1.4 W of output power in diffraction limited far-field. A phase contrast imaging system is used to measure array element phases and apply corrections to an intracavity liquid crystal array.
This paper describes phasing of semiconductor laser arrays placed in an external Talbot cavity for high coherent output power. The external Talbot cavity couples the light between many adjacent lasers such that all lasers operate at the same frequency and phase, resulting in a high power diffraction limited output beam. We first verified the concepts of the Talbot cavity exploiting a simple 1-D Talbot cavity with 20 elements and demonstrated over 600 mW cw total output power in a diffraction limited output beam. In order to fabricate a highly scalable 2-D phased array of lasers, a new type of monolithic 2-D surface emitter was developed for the 2-D Talbot cavity. We have demonstrated 50 W cw output power from a nonphased 2-D monolithic surface emitting laser array with 1500 laser elements. Finally, using a similar 2-D 12 by 12 element surface emitting laser array, we demonstrated 2-D coherence from a compact 2-D Talbot cavity which includes a GaP mass transport lens array, a liquid crystal array and a phase sensing and control system.
This paper describes semiconductor laser arrays placed in an external Talbot cavity. The external Talbot cavity couples the light between many adjacent lasers such that all lasers operate at the same frequency and phase, resulting in a high power diffraction limited output beam. We designed a compact cavity which is comprised of a 30 by 50 element monolithic 2-D laser array, a GaP mass transport lens array, a liquid crystal array, a phase sensing and control system and a waveguide. Initial results obtained from a 20 element linear Ta1bOt cavity with a calculated mode discrimination similar to the 2-D
cavity demonstrate in excess of 30 mW cw per laser element in a diffraction limited far field. In addition we have also demonstrated 50 Watt CW incoherent output power from a monolithic 2D laser array
A method was developed for sensing the phases of a two-dimensional array of coherent sources. The method is based upon phase contrast imaging and was developed to correct the phases of individual GaAlAs emitters in a two-dimensional external cavity laser array. This paper describes the method and presents results for an 18-element linear Talbot laser cavity and for an experimentally simulated 12 x 12 array. Phase correction was achieved using a nematic liquid crystal array.
The coherent operation of one-dimensional linear arrays of grating-coupled surface-emitting lasers is experimentally investigated, for different laser designs (gain lengths, grating parameters. For laser arrays with shallow grating teeth and strong interelement coupling, a diffraction-limited far field of 0.012 deg FWHM was obtained from up to six coupled lasers extending over a length of 3.5 mm.
The steady-state properties of a two-gain section/three-grating surface-emitting laser are studied theoretically as a function of length-induced phase variations. In particular, the optical length of one gain section is varied with respect to the other by up to one grating period. It is found that several mode hops occur. Although the number of these can be reduced by optimizing the design, stable single-mode laser operation requires control of the optical length of each gain and grating section to better than one wavelength.
A compact external cavity configuration consisting of a gain guided array, a graded index lens, and a mode selective mirror was investigated. Results obtained from this external cavity configuration show 410 mW total power (CW) with a diffraction limited far field pattern.