Haruhisa Takiguchi

Suppression of feedback-induced noise in short-cavity V-channeled substrate inner stripe lasers with self-oscillation

Self‐oscillations of V‐channeled substrate inner stripe (VSIS) lasers with index guiding and the influence of external feedback on low‐frequency noise generation are presented. The self‐oscillation is induced by means of shortening a cavity length of VSIS laser to 110 μm. VSIS lasers with self‐oscillation have the fundamental linewidth of 0.56 A below 3 mW and are not sensitive to both phase and amplitude of the externally reflected light. Signal to noise ratio of short‐cavity VSIS laser at 1 MHz with a 10‐KHz bandwidth was 97 dB at 0.05% optical feedback.

Room‐temperature cw operation of InGaPAs/GaAlAs visible light double heterojunction lasers

InGaPAs/GaAlAs double heterojunction (DH) lasers operated continuously at room temperature in the spectral range of 720–730 nm. The DH structure was grown on a GaAs substrate by liquid phase epitaxy, and the laser diode fabrication was the same as V‐channeled substrate inner stripe lasers. The lowest values of a threshold current (Ith) were 145 and 186 mA under pulsed and cw operation, respectively. The characteristic temperature T0 of the Ith was typically 120 K. It was confirmed that the InGaPAs/GaAlAs system has sufficient band‐gap energy difference between the active layer and the cladding layer. Multiple longitudinal and fundamental transverse modes were obtained.

Integrated optic disc pickup

The present status of waveguide-type integrated-optic disc pickups are reviewed. The authors have proposed and fabricated several types, and have demonstrated their fundamental functions. For the ROM pickup, they successfully reduced the focused spot to a diameter that is slightly larger than the diffraction-limited value, and confirmed capability of the focusing/tracking error signal detection. The pickup was extended to that for magneto-optical (MO) disc system, and the MO pickup was found experimentally to detect a polarization rotation as small as one contained in the signal beam reflected from MO medium. The pickup for parallel-data cards was also fabricated with photodiode array, and seven-track parallel readout was demonstrated. It was found by theoretical analysis that the waveguide-FGC combined type pickup has the possibility of super-resolution readout.

Low noise characteristics of V-channeled substrate inner stripe laser in single-longitudinal-mode operation

Stabilization of the single-longitudinal mode of the V-channeled substrate inner stripe (VSIS) laser is attained by coating multidielectric films with high reflectivity on both facets. VSIS lasers with high-reflectivity mirrors are confirmed to have stable spectral characteristics and low noise characteristics. Consequently, in these lasers, the ratio of the lasing mode to the strongest nonlasing mode intensity is ~1250:1, and mode competition noise is suppressed at a temperature of more than 75°C; feedback-induced noise is also repressed up to 0.5% feedback at 3-mW constant output power by automatic power control. A SNR of 110 dB is attained at 1 MHz with 10-kHz bandwidth.