Polarization characteristics of self-aligned stripe (SAS) laser diodes (LDs) and Ridge-LDs are investigated to realize highly efficient polarization beam combined (PBC) LD modules. Vertical layers of both lasers are designed identically. Near field patterns (NFP) of TM polarization for the Ridge-LD showed peaks at the side edges, as expected by the strain simulation. On the other hand, SAS-LD showed a relatively flat and weak profile. Polarization purity (ITE/ (ITE+ITM)) of SAS-LDs exceeds 99%, while those of the Ridge-LDs are as low as 96%. It is confirmed that our SAS-LDs are suitable sources for PBC with low power loss.
High-brightness and high-efficiency fiber-coupled pump module has been developed with newly designed laser diodes and improved spatial optical system. High-power operation was realized by widening laser stripe width. The optical system of the module consists of only spatial multiplexing, not using polarization or wavelength multiplexing technique. Therefore it has advantages that no power loss at a polarization beam combiner or gratings, low material costs of optics, and high excitation efficiency by single wavelength excitation for a fiber laser. The peak power conversion efficiency of the module is 65.6% at 120 W output power, and its efficiency maintains more than 60% up to 220 W at 19 A driving current, and the maximum output power is 252 W at 23 A, at 25 degrees C heat sink temperature. The fiber outside diameter of the module is conventional 125 μm. Center wavelength of the laser is 915 nm.
Design optimization of single emitter broad stripe 9xx-nm laser diodes was studied to achieve ultimate high power and high efficiency operation for a use in fiber laser pumping and other industrial applications. We tuned laser vertical layer design and stripe width in terms of optical confinement as well as electrical resistance. As a result, newly designed LDs with 4mm-long cavity and 220 μm-wide stripe successfully demonstrate maximum CW output power as high as 33 W and high efficiency operation of more than 60 % PCE even at 27 W output power. In pulse measurement, the maximum output of 68 W was obtained.
High-brightness laser diode module over 300 W with 100 μm core/NA 0.22 fiber has been developed by integrating the several tens of optimally designed single emitter laser diodes in a newly designed package. We employed the Asymmetric Decoupled Confinement Heterostructure (ADCH) and the wide strip width to increase the durability for the catastrophic optical damage. High fiber-coupling efficiency was obtained with the uniquely designed micro-optical system. In addition, low thermal resistance made it possible to operate higher power. As a result, 300 W power was achieved without thermal rollover at 15.5 A with significantly high reliability. The high-brightness modules have a great advantage for high power fiber lasers such as 10 kW and beyond.
915nm high-power and high-reliability single emitter laser diodes based on Asymmetric Decoupled Confinement
Heterostructure (ADCH) are demonstrated. Advantage of ADCH is that it can optimize active layer confinement () and
confinement ratio of p- to n-doped layer (p/n), independently, to manage large effective spot size and low internal loss
without any penalty in carrier confinement. 4mm-cavity, 100m wide stripe LDs with large effective spot size of 1.5m
demonstrates record high Catastrophic-optical-damage (COD) free operation over 42W output. Accelerated aging tests are
conducted for 325 devices in total with 1.8 million device hours. Mean time to failure of random failure mode is estimated
to be 1.1 million hours for 12W at room temperature.