One of cost-effective ways to increase the transmission capacity of current standard wavelength division multiplexing (WDM) transmission systems is to use a wavelength band other than the C-band to transmit in multi-band. We proposed the concept of multi-band system using wavelength conversion, which can simultaneously process signals over a wide wavelength range. All-optical wavelength conversion could be used to convert C-band WDM signals into other bands in a highly nonlinear fiber (HNLF) by four-wave mixing and allow to simultaneously transmit multiple WDM signals including other than the C-band, with only C-band transceivers. Wavelength conversion has been reported for various nonlinear waveguide materials other than HNLF. In such nonlinear materials, we noticed the possibility of wideband transmission by dispersion-tailored silicon-on-insulator (SOI) waveguides. Based on the CMOS process has high accuracy, it is expected that the chromatic dispersion fluctuation could be reduced in mass production. As a first step in the investigation of the broadness of wavelength conversion using SOI-based waveguides, we designed and fabricated dispersion-tailored 12 strip waveguides provided with an edge coupler at both ends. Each of the 12 waveguides having different widths and lengths and is connected to fibers via lensed fibers or by lenses. In order to characterize each waveguide, the pump-probe experimental setup was constructed using a tunable light source as pump and an unmodulated 96-ch C-band WDM test signal. Using this setup, we evaluate insertion loss, input power dependence, conversion bandwidth and conversion efficiency. We confirmed C-band test signal was converted to the S-band and the L-band using the same silicon waveguide with 3 dB conversion bandwidth over 100-nm. Furthermore, an increased design tolerance of at least 90 nm was confirmed for C-to-S conversion by shortening the waveguide length. It is confirmed that the wavelength converters using the nonlinear waveguide has sufficiently wide conversion bandwidth to enhance the multi-band WDM transmission system.

Using wavelength conversion of our fabricated SOI strip waveguide, we compared experimentally the polarization-insensitive configuration toward S-band real-time transmission. It is found that parallel configuration is 3dB superior in in-out conversion efficiency to loop configuration.

In0.056Ga0.944P0.975N0.025/GaP lattice-matched single quantum wells (SQWs) have been grown on GaP (001) substrates by metalorganic vapor phase epitaxy (MOVPE). Low-temperature (10K) photoluminescence (PL) and PL excitation (PLE) measurements for the varied well widths (LZ=1.6, 2.4, 3.2 and 6.4nm) have been revealed to confirm the quantum confinement by the well. Comparing with the bulk layer, the PL peak position blue shift amounts to 76meV for the narrowest well of LZ=1.6nm. On the other hand, the PLE spectra have shown the blue shift of the fundamental absorption edge to 2.17eV for LZ=1.6nm from 2.06eV for the bulk. The blue shift is about 110meV. In these samples, the PL and PLE blue shifts are believed to be predominantly determined by the quantum confinement effect to the well. Further results show a high-temperature PL has been far more enhanced than in the bulk due to the large conduction band offset ΔEc.

We report on the investigation of the effects of rapid thermal annealing (RTA) on the optical and structural properties of InxGa1−xP1−yNy alloys (x=0.176 and 0⩽y⩽0.087) on GaP grown by metalorganic vapor phase epitaxy (MOVPE). Photoluminescence (PL) and PL excitation (PLE) spectroscopies were carried out to measure the energy positions of the near band edge excitonic emission. The high-resolution X-ray diffraction (HRXRD) measurements were carried out to examine the changes in the N concentration after RTA at 750°C for 30s. For y<0.074, the RTA treatment induces a large blue-shift of the PL peak energy and the absorption edge of PLE, which indicates some structural modification of these alloy films. On the other hand, for y⩾0.074, both the PL and PLE spectral features remain qualitatively identical after RTA, suggesting the unchanged recombination mechanism. Furthermore, HRXRD results confirmed that the InxGa1−xP1−yNy closely lattice-matched films are thermally more stable against the N out diffusion.

InGaPN alloy films were grown on GaP (001) substrates by metalorganic vapor phase epitaxy (MOVPE) at 635°C using trimethylgallium (TMGa), trimethylindium (TMIn), PH3 and 1,1-dimethylhydrazine (DMHy) as the precursors of Ga, In, P and N, respectively. For the fixed combination of TMGa, PH3 and TMIn flows, the composition control of InxGa1−xP1−yNy was achieved simply by changing the molar flow ratio of DMHy to the total group V sources, giving y=0–8.7% and x=17.6%. The grown films show a systematic red shift of the photoluminescence (PL) peak energy with increasing N content. On the other hand, with increasing the TMIn molar flow while the other flows were fixed, the N incorporation is much affected by the TMIn flow due to some reaction kinetics. In fact, the N content was decreased from y=2.6% to 1.6% while the In content was increased from x=0 to 10.9%. As a result, the apparent blueshift of the PL peak energy for this growth series is due to the reduction of N incorporation with increasing TMIn flow. The lattice-matched InxGa1−xP1−yNy (x=17.6%, y=7.4%) film showed an excellent structural and optical quality in spite of the relatively high N content.