Munefumi Tsurusawa

Mechanism for reducing recovery time of optical nonlinearity in semiconductor laser amplifier

We propose and demonstrate a novel scheme to reduce the recovery time of optical nonlinearity in a semiconductor laser optical amplifier driven under a loss condition for the signal light pulse. Additional light, which is set at a transparency wavelength in the active layer, promotes stimulated recombination of excess carriers induced by the absorption of the signal light. This scheme excludes any additional carrier transport mechanism and nonradiative recombination and hence generation of heat. The principle of operation is experimentally verified by measuring time-domain transmission variance using a pump–probe method. A drastic reduction of the excess-carrier lifetime to less than 70 ps was confirmed.

Novel scheme for reducing the pattern effect in 40 Gbps SOA based all-optical switch utilizing transparent CW assist light

We have successfully confirmed the reduction of the pattern effect in semiconductor optical amplifier (SOA)-based all-optical switches at 40 Gb/s operation, utilizing the transparent CW assist light which clamped the gain profile of the SOA. Error-free operation without an error floor was obtained with a power penalty of 1 dB compared with the input data stream. The receiver sensitivity improvement of 2.3 dB was confirmed at BER=10/sup -9/. The scheme for the reduction of the pattern effect is an attractive method for high-speed operation because the required signal powers can be small.

Patterning effect at 40 Gbit/s of wavelength converter utilizing cross-phase modulation in InGaAsP/InP electroabsorption modulator

Cross-absorption and cross-phase modulation in an InGaAsP/InP electroabsorption modulator (EAM) were experimentally analyzed. The patterning effect of the EAM-based delayed-interferometric wavelength converter was studied by numerical simulation based on the experimental results.

New method for reduction of carrier lifetime in semiconductor optical amplifier using assist light

We propose a novel method for reducing the absorption recovery time in a semiconductor optical amplifier driven under a loss condition for a signal pulse that acts as a saturable absorber. The reduction of the absorption recovery time was successfully demonstrated by stimulated recombination due to CW additional light (assist light) whose wavelength was longer than that of the signal. The injection current and the wavelength of the assist light for the reduction effect were optimized experimentally. The stimulated recombination process is ultrafast and generates little heat since the process does not involve carrier transport in the device. This technique can be applied to ultra high repetition rate optical processing. A minimum absorption recovery time of less than 50 ps was confirmed.

Experimental analysis of cross gain modulation and cross phase modulation in SOA with assist light injection

A simple analysis technique of cross gain modulation and cross phase modulation in SOA using delayed interferometer configuration was proposed. Recovery time and the amounts of XGM and XPM were measured in assist light injected SOA.

Demonstration of optical noise reduction using nonlinear absorption in a semiconductor laser amplifier

We propose a new way to use a semiconductor laser amplifier driven under a loss condition for a signal light that acts as an ultrafast noise reduction device using a nonlinear absorption effect. The absorption recovery time was reduced by stimulated recombination due to continuous-wave additional light (assist light) whose wavelength was longer than that of the signal. This simple method is an attractive technique to realize optical functional devices with an ultrahigh-repetition rate. We have successfully confirmed a receiver sensitivity improvement of 0.5 dB in a 5-Gb/s nonreturn-to-zero signal by using this principle. The improvement of the eye opening by passing through the noise reduction device was estimated theoretically to reveal design rules for an optimum optical noise reduction device.

First demonstration of 40 Gbps wavelength conversion with no pattern effect utilizing cross-phase modulation in an electroabsorption waveguide

Wavelength conversion utilizing cross-phase modulation in an electroabsorption waveguide (EA-WG) was investigated. An error-free wavelength conversion at 40 Gbps was confirmed with a negligibly small pattern effect due to a fast absorption recovery of the EA-WG for the first time.

Novel mechanism for ultrafast optical nonlinearity in semiconductor laser amplifier using assist light

We have proposed and first demonstrated a novel mechanism for ultrafast optical nonlinearity in semiconductor laser amplifiers as saturable absorbers. We have obtained the reduced carrier lifetime of less than 70 ps by stimulated recombination due to a novel assist light. The further reduction of lifetime can be expected for shorter devices. This novel mechanism is promising for ultra-high repetition-rate gate function and noise reduction function, because there is little heat generation process through this fast stimulated emission.

Device length dependency of cross gain modulation and gain recovery time in semiconductor optical amplifier

The cross gain modulation and its recovery time in the SOAs with the various lengths were experimentally investigated. It was found that these values strongly depended on the device length.

Optical 3R regeneration with single InGaAsP/InP electroabsorption modulator

A new optical 3R regeneration technique, which is referred to as RF-XAM 3R regeneration, that requires only one electroabsorption modulator (EAM) for both clock recovery and gating was proposed for the first time. The idea was experimentally verified at 20 Gbit/s and we have confirmed that the RF-XAM 3R regenerator possesses retiming function. The simple configuration of our proposed scheme is expected to contribute not only to reduction in size and power consumption, but also high stability and easy tunability.