LD optical switch with polarization insensitivity over a wide wavelength range

A double-heterostructure (DH) laser with TM mode lasing has been achieved with a narrow active-layer width, and a laser-diode optical switch (LDSW) module with less than a 0.35-dB gain difference between the TE and TM modes over a wide wavelength range has been constructed by introducing a square bulk active layer formed by dry etching and regrowth. The polarization-insensitive width of a 0.3-μm-thick DH laser is clarified to be between 0.30 and 0.35 μm, since the 0.30- and 0.35-μm-wide DH lasers lase in the TM mode and TE mode, respectively. The polarization-insensitive width of the fabricated 0.3-μm-thick LDSW is estimated to be about 0.32 μm for the fabricated LDSW with a trapezoidal active layer by measuring the single-pass gain and the gain difference between the TE and TM modes. This must be to within 0.01 μm. A 0.35-μm-wide, 300-μm-long LDSW module has lossless gain in the wavelength range of 1.31 to 1.36 μm at 20 mA. The gain difference between the TE and TM modes is as low as 0.35 dB, The rise and fall times are 1.0 and 0.55 ns, respectively. The bulk active-layer LDSW module is promising for use as a polarization-insensitive optical-gate switch in optical information systems