Yoshiyasu Ueno

168-Gb/s all-optical wavelength conversion with a symmetric-Mach-Zehnder-type switch

Error-free all-optical wavelength conversion at 168 Gb/s, which is the highest repetition rate ever reported, has been achieved by using a symmetric-Mach-Zehnder (SMZ)-type switch. Low-power-penalty 84-Gb/s operation is also demonstrated. The push-pull switching mechanism of the SMZ switch enables such ultrafast operation based on cross-phase modulation associated with the carrier depletion in a semiconductor optical amplifier. The configuration of the delayed-interference signal-wavelength converter, which is a simplified variant of the SMZ switch, is used in this experiment.

Experimental and theoretical investigation of the impact of ultra-fast carrier dynamics on high-speed SOA-based all-optical switches.

The impact of ultra-fast carrier dynamics in semiconductor optical amplifiers (SOAs) on switches based on cross-gain and cross-phase modulation is analyzed theoretically and experimentally. We find that ultra-fast effects lead to additional spectral broadening, which improves the optical signal-to-noise ratio for switches based on an SOA and an optical filter. For such switches, the influence of ultra-fast effects on the so-called nonlinear patterning effect is analyzed for three filter configurations: the asymmetric Mach-Zehnder interferometer (AMZI), a band-pass filter (BPF), and a cascade of an AMZI and a BPF. We conclude that fast carrier dynamics dramatically reduces nonlinear patterning and that the successful high-speed (>100 Gb/s) demonstrations in the literature rely on these effects.

Ultrafast (200-fs switching, 1.5-Tb/s demultiplexing) and high-repetition (10 GHz) operations of a polarization-discriminating symmetric Mach-Zehnder all-optical switch

We demonstrate 200-fs switching and 1.5-Tb/s demultiplexing with a polarization-discriminating, symmetric Mach-Zehnder (PD-SMZ) all-optical switch. This switch is based on a highly efficient but slowly relaxing band-filling effect resonantly excited in a passive InGaAsP bulk waveguide. By using a mechanism that cancels out the effect of the slow relaxation, ultrafast switching is realized. The applicability of this mechanism to optical demultiplexing of well over 1 Tb/s is experimentally demonstrated for the first time. High-repetition operation at 10 GHz with the same nonlinearity used for the present ultrafast switching is also verified.

Novel Window-Structure AlGaInP Visible-Light Laser Diodes with Non-Absorbing Facets Fabricated by Utilizing GaInP Natural Superlattice Disordering

Window-structure AlGaInP visible-light ( λL=680 nm) laser diodes (LDs) have been fabricated, for the first time, by utilizing GaInP natural superlattice (NSL) disordering with selective Zn diffusion. The bandgap energy for the active layer near the mirror facets is increased by 70 meV by the NSL disordering. An 80 mW output power in a fundamental transverse-mode has been achieved for the uncoated window LDs under 1 µsec long pulsed operations. The maximum output power density for the window LDs is estimated to be 10 MW/cm2, which is five times higher than that for conventional LDs.

632.7 nm CW Operation (20?C) of AlGaInP Visible Laser Diodes Fabricated on (001) 6? off toward [110] GaAs Substrate

632.7 nm continuous wave operation was achieved at 20°C, by an AlGaInP visible laser diode (LD) with an AlGaInP quaternary active layer fabricated on a (001) GaAs substrate with a misorientation angle of 6° toward the [110] direction. The epitaxial layers for the laser structure are grown by metalorganic vapor phase epitaxy. The lasing wavelength is almost the same as that for He-Ne lasers. Lasing wavelengths for the LDs were also compared with wavelengths for those fabricated on an exact (001) orientation substrate.

Nonexistence of Long-Range Order in Ga0.5In0.5P Epitaxial Layers Grown on (111)B and (110)GaAs Substrates

It has been found that Ga0.5In0.5P layers grown at 700°C on (111)B and (110)GaAs substrates do not show {1/2, 1/2, 1/2} superlattice (SL) formation, in contrast to that for the layers grown on (001)GaAs. The band-gap energy for these layers, which show no SL and are lattice-matched to GaAs, was estimated to be 1.918±0.002 eV at room temperature.

Frequency-dependent electric dc power consumption model including quantum-conversion efficiencies in ultrafast all-optical semiconductor gates around 160 Gb/s

Based on nine up-to-date types of semiconductor-optical-amplifier (SOA) samples, we devised a power-consumption model of SOA-based all-optical gates as a tool to develop faster and more efficient OTDM systems for bitrates from 10 to 160 Gb/s and those over 160 Gb/s. The conventional effect of a continuous wave (cw) holding beam was included in the model. Furthermore, in this work we defined three step-wise quantum conversion efficiencies eta(1), eta(2), and eta(3) from current-injected carriers through photons. The dependence of each of the three efficiencies on the SOA-structure was studied. The total efficiency eta(T) observed for the nine SOAs ranged widely from 0.07 to 0.46. The validity of the power-consumption model was verified by systematically measuring the effective carrier recovery rate. According to our model, the power consumption of the best existing SOA-based gate for 160-Gb/s signals is 750 mW, and this increases at a rate approximately proportional to (bitrate)(2), and decreases proportionally to (1/etaT)(2).

Theoretical and experimental study of fundamental differences in the noise suppression of high-speed SOA-based all-optical switches.

We identify a fundamental difference between the ASE noise filtering properties of different all-optical SOA-based switch configurations, and divide the switches into two classes. An in-band ASE suppression ratio quantifying the difference is derived theoretically and the impact of the ASE filtering on the optical spectrum is verified experimentally using a hybrid DISC setup. ASE power suppression of around 3 dB over the total signal bandwidth is demonstrated.

Reduction of nonlinear patterning effects in SOA-based all-optical switches using optical filtering

We explain theoretically, and demonstrate and quantify experimentally, how appropriate filtering can reduce the dominant nonlinear patterning effect, which limits the performance of differential-mode SOA-based switches.

Spectral Phase-Locking in Ultrafast All-Optical Mach-Zehnder-Type Semiconductor Wavelength Converters.

We studied the spectrum-domain mechanism of the delayed-interference signal-wavelength converter (DISC) analytically and found that the role of the passive Mach-Zehnder interferometer in this converter differs completely from that of conventional spectrum filters: it converts the semiconductor-optical-amplifier-induced cross-phase-modulated spectrum phase from out-of-phase to in-phase (constant phase). This converter therefore efficiently generates ultrashort nearly transform-limited pulses having a broad phase-locked spectrum. These conclusions are consistent with the output pulse shapes and spectra measured in experiments in which the wavelength of 2-ps 42-GHz pulses was converted from 1560 nm to 1553 nm.