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-/spl mu/m-thick DH laser is clarified to be between 0.30 and 0.35 /spl mu/m, since the 0.30- and 0.35-/spl mu/m-wide DH lasers lase in the TM mode and TE mode, respectively. The polarization-insensitive width of the fabricated 0.3-/spl mu/m-thick LDSW is estimated to be about 0.32 /spl mu/m 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 /spl mu/m. A 0.35-/spl mu/m-wide, 300-/spl mu/m-long LDSW module has lossless gain in the wavelength range of 1.31 to 1.36 /spl mu/m 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.