Masashi Usami

Experimental analysis of cross-phase modulation and cross-gain modulation in SOA-injecting CW assist light

Cross-phase modulation (XPM) and cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) pumped by assist light were experimentally analyzed. A simple analysis technique for evaluating the XPM separately from the XGM was proposed utilizing a polarization-discriminating delayed interferometer. An initial phase deviation and a gain recovery time in SOA with injecting assist light were quantitatively estimated.

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.

Operational design on high-speed semiconductor optical amplifier with assist light for application to wavelength converters using cross-phase modulation

Using the newly developed time-dependent transfer matrix method with nonlinear effects, we analyzed the characteristics of cross-phase modulation (XPM), cross-gain modulation and gain recovery time of a semiconductor optical amplifier (SOA) with an assist light injection, which is introduced to speed up the gain recovery of the SOA. Particularly for the application to high-speed wavelength converters using XPM with an interferometer structure where /spl pi/-phase change is required, various parameters such as SOA lengths, wavelengths and powers of injected lights, and their propagation directions are designed via numerical simulation. Discussions concerning the conditions of an SOA structure and the parameters of injected lights for high-speed operation are described to show the potential of fast gain recovery with a response time as low as 25 ps.

Bidirectional Data Injection Operation of Hybrid Integrated SOA–MZI All-Optical Wavelength Converter

A bidirectional data signal input scheme of a semiconductor optical amplifier--Mach-Zehnder interferometer (SOA-MZI) wavelength converter was proposed and experimentally verified for a nonreturn-to-zero (NRZ)-format signal. Theoretical analyses reveal that it is possible to mitigate the patterning effect induced by cross-gain modulation (XGM) by utilizing the difference of the ratio between the XGM and cross-phase modulation on the injection directions of data signals. A hybrid integrated SOA-MZI all-optical wavelength converter, in which the coupling loss between the SOA and the silica waveguide was as small as 1 dB owing to a unique active alignment technique, was used for the experiment. We have verified the superior characteristics of the proposed operation scheme for the first time. Error-free wavelength-conversion operation for an NRZ signal at 40 Gb/s was confirmed

5-Gb/s performance of integrated light source consisting of lambda /4-shifted DFB laser and EA modulator with SI InP BH structure

The fabrication process and characteristics, including 5-Gb/s transmission, of an integrated light source consisting of a lambda /4-shifted distributed feedback laser and an electroabsorption (EA) modulator are discussed. By introducing a semi-insulating (SI) InP on the butt-joint region, both the large electrical isolation resistance (>10 M Omega ) between the laser and the modulator and a high optical coupling efficiency (>80%) between them are achieved. A typical threshold current was 50-70 mA, and single-mode operation at 1.576 mu m was maintained up to 5.5-mW output power. The modulation voltage to swing between 90% transmission and 10% transmission was 6.2-12 V, depending on the modulator length in the range 1000-400 mu m. The 3-dB bandwidth is 7.7 GHz and a linewidth enhancement factor ( alpha ) of 0.9 is estimated from the sideband-to-carrier ratio of the spectra. >

All-optical wavelength conversion by electroabsorption modulator

All-optical wavelength conversion using an electroabsorption modulator (EAM) in conjunction with delayed interferometer (DI) is investigated. The optical nonlinearities induced in an EAM were experimentally characterized. High bit-rate wavelength conversion at 100 Gb/s was demonstrated by an EAM-DI wavelength converter with required optical pulse energy of 1.5 pJ. It was verified that the operable bandwidth of the EAM-DI wavelength converter at 40 Gb/s covered almost full range of C-band without tuning operation conditions. These results indicate that the EAM-based wavelength converter is capable for ultrafast wide-band wavelength conversion.

Analysis of negative group delay response of all-pass ring resonator with Mach-Zehnder interferometer

The chromatic dispersion characteristics of waveguide all-pass filters were theoretically analyzed, in which the round-trip loss of a ring resonator was taken into account. Although an all-pass filter based on a ring resonator is lossless in principle, a finite round-trip loss of an actual filter changes an amplitude response and a group delay response drastically. The negative group delay resonance peak was confirmed both theoretically and experimentally.

Optical clock recovery circuits using traveling-wave electroabsorption modulator-based ring oscillators for 3R regeneration

We describe an optical clock recovery circuit that employs a traveling-wave electroabsorption modulator-based ring oscillator. This approach provides synchronized optical clock and the original optical data signal from the same output at separate wavelengths, eliminating additional timing adjustments for the subsequent nonlinear decision gate for reamplifying, reshaping, and retiming (3R) regeneration. Furthermore, additional retiming and lateral reshaping of the original data signal can be realized along with optical clock recovery by synchronized modulation. We present a general model of jitter transfer and locking dynamics for the clock recovery circuit and compare with experimental results. Theoretical results indicate that by using hybrid integration to shorten the cavity length, nanosecond-order locking time can be achieved, which is critical for a variety of applications such as protection switching, optical burst and optical packet switching. Experimental demonstrations of 40-Gb/s optical clock recovery and its application for optical 3R regeneration are presented. The recovered 40-GHz optical clock has 500-fs timing jitter and 8-ps pulsewidth, and within 0.3 /spl mu/s locking time. 3R experiment is implemented by using the OCR combined with a subsequent regenerative wavelength converter, which provides vertical reshaping function. 3R regeneration is demonstrated with a reduced timing jitter.

Tunable chromatic dispersion compensator utilizing silica waveguide ring resonator having Mach-Zehnder interferometric variable coupler eliminating crossing point of waveguides

A new configuration for an all-pass filter-based tunable chromatic dispersion compensator utilizing silica waveguide ring resonators having a Mach-Zehnder interferometer without a crossing point was proposed and fabricated. FSR of 24 GHz and tuning range of +/-1280 ps/nm was confirmed.

40-Gb/s optical packet clock recovery with simultaneous reshaping using a traveling-wave electroabsorption modulator-based ring oscillator

An injection-locking traveling-wave electroabsorption modulator-based ring oscillator is demonstrated to perform optical clock recovery and simultaneous reshaping of 40-Gb/s optical packets. The transient response analysis and experimental results show strong injection and short loop length reduce the locking time to within 0.3 /spl mu/s. The recovered packet optical clock has 532-fs timing jitter.