We report the development of fused-fiber pump and signal combiners. These combiners are enabling components of a ytterbium fiber-laser emitting 4 kW of 1080-nm radiation. The fiber-laser system consists of seven fiber laser modules and a 7:1 signal combiner. The laser modules are end-pumped by 90 915-nm JDSU L4 diode-lasers, yielding a nominal pump power of 900 W. The diode laser radiation is coupled into the laser fiber through a 91:1 fused-fiber pump combiner. The input fibers of this pump combiner are standard 105/125-um multimode fibers with an NA of 0.22. These fibers form a hexagonally packed fused-fiber bundle, which is tapered to match the cladding diameter of the laser fiber. Eighty-six percent of the light exiting the pump-combiner is emitted within an NA of 0.32, and all measurable power is emitted within an NA of 0.45. The typical insertion loss of the pump combiners is <1%. The high-brightness radiation of seven laser modules is combined into a single output fiber using a 7:1 fused-fiber signal combiner providing a total power of >4 kW in the single output beam. The beam parameter product of the combined output was 2.5 mm-mrad. The low insertion loss of < 2% indicates that the signal combiner is suitable to handle even higher laser powers.
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:LiNbO<sub>3</sub>. 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, M<sup>2</sup> <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.
We have developed a single-emitter multi-mode laser-diode-pump platform for high efficiency, brightness and high
reliability in a small form factor. This next-generation package is scalable to higher optical power and offers a low-cost
solution for industrial applications, such as fiber lasers, graphic arts and medical. The pump modules employ high
coupling efficiency, >90%, high power-conversion efficiency, >50%, and low thermal resistance, 2.2°C/W, in an
electrically-isolated package. Output powers as high as 18W have been demonstrated, with reliable operation at 10W
CW into 105μm core fiber. Qualification results are presented for 0.15NA and 0.22NA fiber designs.
Developers building high-power fiber lasers and diode pumped solid state lasers can receive significant benefits in thermal management and reliability by using single emitter multi-mode diodes in distributed pump architectures. This proposed distributed architecture relies on independent single emitter pump lasers and a modest level of pump redundancy. Driving the remaining diodes slightly harder componensates individual diode failures. 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 200,000h mean time between failure (MTBF), which meets typical industrial requirements. A high power, pigtailed, multi-mode pump module suitable for commercial applications is created through this model. 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 chip-on-sub-mount to the external heat sink, coupling efficiency of over 80% into 0.2 NA, and demonstrated reliable output power of over 5W cw with peak wavelengths near 915 nm. Individual pump modules are predicted to produce 5W cw output power with an MTBF of more than 400,000h. The relationship between anticipated MTBF requirements, test duration and test population is shown.
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 have successfully fabricated optically pumped semiconductor micro-disk and micro-ring lasers under the InGaAsP/InGaAs system at the 1.5 micrometers wavelength and under the InGaP/InGaAlP system at the 0.66 micrometers wavelength. The spontaneous emission factor (beta) of these micro-lasers is estimated directly from their output-pump curves and its dependence on the cavity volume is verified. Interesting phenomena regarding the far-field emission pattern and lasing linewidth of these micro-cavity lasers are experimentally observed and theoretically studied.
A single narrow-linewidth quantum-well absorption peak is coupled to the single-mode resonance of a moderately high reflectivity microcavity, resulting in an anticrossing curve as a function of relative detuning. For zero detuning, two cavity peaks and two photoluminescence peaks are seen. Two quantum wells with different resonant energies result in a system of three coupled oscillators. Nonlinear studies include determination of the nonlinearities of the quantum wells, observation of optical bistability, and saturation of the microcavity transmission.
Instability in the output of dc-biased surface emitting lasers due to an external cavity effect was observed. The output power spectrum exhibited multiple peaks with spacing corresponding to exactly the round-trip delay in silica fibers with length ranging from 2 m to 2 km. The magnitude of the peaks was enhanced in the spectral region centered at the laser relaxation frequency. With increased feedback, the background of the output spectrum was found to increase, indicating the presence of optical chaos. Numerical simulation based on the rate equation analysis was found to agree with the experiment, indicating the surface emitting lasers are well described by the rate equation and are susceptible to feedback as the edge emitting lasers.
Vertical cavity surface emitting lasers (VCSELs) were realized in MBE-grown GaAS/A1GaAS and
MOVPE-grown InGaAsPf.EnP material systems with emission wavelengths near 0.87 and 1.3 p.m.
respectively. The GaAS/A1GaAS VCSELs incorporating epitaxially grown DBR mirrors on both sides of
the cavities were operated at room temperature cw condition with maximum output power greater than 1
mW. The InGaAsP/InP VCSEL, which employed a much simpler cavity structure containing metal and
dielectric mirrors, operated up to 220 K with a threshold current as low as 5 mA at 77K, indicating that
improvements on the cavity design should yield room temperature lasing operation. Single longitudinal
mode emission and circular near- and far-field patterns were observed for the two VCSEL structures.
SC403: DWDM Components: Circulators, WDMs, and Interleavers
This course introduces the basic theories and technology behind fundamental components for WDM architectures. These include the circulator, WDM elements like mux/demux, and interleavers. In addition to the inner working of these components, the various technology choices for WDM are compared and it is shown where each best fits into the different applications. Concepts include polarization, birefringence, thin films, planar waveguides, and fiber Bragg gratings, with an emphasis on the thin film technology. Novel experiments using the disruptive technology of the interleaver are described.