Optical buffer memory for 10-Gb/s data signal is demonstrated experimentally using a polarization bistable vertical-cavity surface-emitting laser (VCSEL). The optical buffer memory is based on an optical AND gate function and the polarization bistability of the VCSEL. Fast AND gate operation responsive to 50-ps-width optical pulses is achieved experimentally by increasing the detuning frequency between an injection light into the VCSEL and a lasing light from the VCSEL. A specified bit is extracted from the 10-Gb/s data signal by the fast AND gate operation and is stored as the polarization state of the VCSEL by the polarization bistability. The corresponding numerical simulations are also performed using two-mode rate equations taking into account the detuning frequency. The simulation results confirm the fast AND gate operation by increasing the detuning frequency as well as the experimental results.

Ultrafast all-optical switching was experimentally demonstrated using four-wave mixing in an SOA. Two pump pulses with different wavelengths and timings were used for 12 switching. The cross-correlation measurements of FWM signals using a short reference pulse show the high-speed switching capability for wavelength routing in OTDM networks.

An 80 Gbit/s conventional and carrier-suppressed return-to-zero optical time-division multiplexing signal transmission over a 208 km standard single-mode fiber was experimentally demonstrated. This was achieved by using mid-span optical phase conjugation based on four-wave mixing in semiconductor optical amplifiers. In addition, it was confirmed that the transmitted carrier-suppressed return-to-zero optical signal's carrier phase-relation was held.

We numerically investigated the optical output characteristics in two kinds of optical waveguide coupled high-index-contrast subwavelength grating VCSELs (HCG-VCSELs) that couple the laser output to the in-plane waveguide, operating at a 1.55-µm region. One is the transverse electric (TE) HCG, and the other is the transverse magnetic (TM) HCG. In a waveguide coupled HCG without a cavity structure, the out-coupling efficiency to the waveguide strongly depends on the intensity of the incident light at the starting edge of the waveguide. In a waveguide coupled HCG-VCSEL, the ratio of the waveguide output to the optical power inside the active region is determined also by the intensity of the resonant mode at the waveguide edge. The TE-HCG-VCSEL exhibited an almost 30 times larger waveguide output power while the quality factor of the laser cavity is 1/3, compared to those in the TM-HCG-VCSEL. The single mode condition was satisfied for the waveguide of the TE-HCG-VCSEL while the first order mode was allowed for that of the TM-HCG-VCSEL. Positioning the mesa edge at the waveguide edge within 1-µm accuracy results in waveguide outputs of about 0.7 and 0.02% of that inside the active region for TE- and TM-HCG-VCSEL, respectively.