We demonstrate a single high-order transverse mode surface emitting laser (VCSEL) with narrow trenches formed on a top surface. The design and the fabrication of a single high-order mode 850 nm GaAs VCSEL with micromachined surface relief are presented. Stable single-mode operation with a side-mode suppression ratio of over 40 dB was obtained in an entire measured current range. We obtained the maximum single mode power of over 3.5 mW and a record low series resistance of below 50 Ω. In addition, a single-lobe far field pattern is demonstrated even under high-order transverse mode operation by loading phase-shift on the top surface. A coupling efficiency with optical fibers is dramatically improved.

We demonstrate heteroepitaxial growth of GaAs/Ge buffer layers for fabricating 1.3-µm range metamorphic InGaAs-based multiple quantum well (MQW) lasers in which the Ge buffer layer is grown using a metal-organic Ge precursor, iso-butyl germane, in a conventional metal-organic vapor phase epitaxy reactor. This enables us to grow Ge and GaAs buffer layers in the same reactor seamlessly. Transmission electron microscopy and X-ray diffraction analyses indicate that dislocations are well confined at the Ge/Si interface. Furthermore, thermal-cycle annealing significantly improves crystalline quality at the GaAs/Ge interface, resulting in higher photoluminescence intensity from the MQWs on the buffer layers.

We have demonstrated a dynamically stable polarization operation of GaInAs/GaAs vertical-cavity surface-emitting laser (VCSEL) array grown on a GaAs (311)B substrate. A fabricated 3 3 VCSEL array consists of devices with an oxide aperture of 3.4 µm 3.4 µm. The threshold current was 0.61 0.05 mA and the threshold voltage was 1.79 0.03 V. All of the devices exhibited single-transverse mode operation with an injection current up to three times the threshold. The side-mode suppression ratio (SMSR) is larger than 30 dB. The array also exhibited stable-polarization operation with an orthogonal polarization suppression ratio (OPSR) of over 25 dB. We measured the time-resolved OPSR under square-wave direct modulation. It was found that the orthogonal non-lasing mode was suppressed even at the first peak of relaxation oscillation with OPSR > 17 dB. In an experiment of 5 Gb/s non-return-to-zero (NRZ) pseudo-random bit sequence (PRBS) modulation, the OPSR was maintained being greater than 27 dB. These observed stable and single polarization characteristics were originated from the anisotropic optical gain of strained GaInAs/GaAs quantum wells formed on (311)B substrate. We also carried out an intensity noise measurement under single-transverse and stable polarization operation for the first time. The relative intensity noise (RIN) of -140 dB/Hz was obtained. In addition, we achieved 2.5 Gb/s data transmission through a 100 m multi-mode fiber. No error floor was observed at -20 dBm of received power level. The minimum received power is determined by the thermal noise.