Satoko Kutsuzawa

30-GHz bandwidth 1.55-μm strain-compensated InGaAlAs-InGaAsP MQW laser

High-speed 1.55 /spl mu/m laser diodes with a 3-dB modulation bandwidths of 30 GHz were fabricated by using short-cavity mushroom structures with undoped, strain-compensated InGaAlAs-InGaAsP twenty-quantum-well active regions. The bandwidths were achieved at low bias current of 100 mA. The laser exhibited a high differential gain of 1.54/spl times/10/sup -15/ cm/sup 2/ and a small K factor of 0.135 ns. These results were achieved by using an In/sub 0.386/Ga/sub 0.465/AlAs barrier with 0.83% tensile strain to reduce the thermal emission time of holes from wells and hence the hole transport time.

Repetition-frequency multiplication of mode-locked pulses using fiber dispersion

In this paper, we describe a novel method for generating a highly repetitive optical pulse train using mode-locked pulses and the group-velocity dispersion (GVD) of optical fiber. An optical pulse train at a multiplied repetition frequency oscillation of an initial mode-locked pulse train is obtained by adjusting waveform fiber length in accordance with the mode-locking frequency and the fibers GVD. A subterahertz optical pulse train (98-196 GHz) was successfully generated with low pulse intensity fluctuation.

Generation of wavelength tunable gain-switched pulses from FP MQW lasers with external injection seeding

High-repetition rate (20 GHz), wavelength tunable (40 nm) optical pulses have been generated by gain switching of 1.55-/spl mu/m Fabry-Perot (FP) multiple-quantum-well (MQW) lasers using continuous-wave (CW) light injection for longitudinal mode selection. After fiber compression, a pulse duration shorter than 5.8 ps was obtained over the entire wavelength tuning range. The pulsewidth, chirping characteristics and side-mode suppression ratio were investigated as functions of the seeding power and wavelength. In addition, we report on the observation of chaos and period doubling for a gain-switched laser without injection seeding, and show that irregular behavior can be suppressed by injection seeding of the laser.

Bifurcation in 20-GHz gain-switched 1.55-/spl mu/m MQW lasers and its control by CW injection seeding

A gain-switched laser operating at a 20-GHz repetition rate exhibited chaos and period-doubling depending on the bias condition, which was the first observation for 1.55-/spl mu/m strain-compensated InGaAlAs-InGaAsP multiple-quantum-well (MQW) lasers. Unlike the case previously reported for bulk lasers, the irregular behavior was set over wide bias current conditions for the MQW laser. We show that the instability is attributable to a small gain compression factor of the MQW laser and a high-repetition frequency of the gain-switching operation. Further, we report that the irregular behavior can be successfully suppressed by seeding the laser with external coherent-light injection. The numerical simulations of a set of rate equations using parameters extracted from small-signal modulation characteristics were carried out in order to clarify the conditions for the stabilization of the gain-switching operation. The scenario behind the inhibition of irregular behavior was due to the enhanced damping phenomena of a nonlinear oscillator induced by the injection seeding light. The influence of the /spl alpha/ parameter on the optical pulse distortion under the external seeding and the parametric dependence for a single-period operation were investigated based on numerical simulation.

Extreme timing jitter reduction of a passively mode-locked laser diode by optical pulse injection

Reduction of the timing jitter to less than that of the master laser pulses was achieved for a passively mode-locked laser diode stabilized by subharmonic-frequency optical pulse injection. Detailed investigation revealed that this phenomenon originates from the short-term stability of the mode locking frequency under passively mode-locking operation with suitable bias conditions of the saturable absorber and the gain sections.

Experimental demonstration of performance improvement of 127-chip SSFBG en/decoder using apodization technique

We present the experimental result of apodiz 127-chip 160-Gchip/s superstructured fiber Bragg grating (SSFBG) en/decoder with Gold code in bipolar phase-shift key coherent time-spreading optical code-division multiple-access system. Compared with uniform SSFBGs, the apodized SSFBG demonstrates the overall performance improvements, including a high reflectivity and a good peak-to-wing ratio of autocorrelation as well as a good bit-error-rate performance.

Generation of synchronized subterahertz optical pulse trains by repetition-frequency multiplication of a subharmonic synchronous mode-locked semiconductor laser diode using fiber dispersion

We describe the generation of a synchronized, low-jitter, subterahertz optical pulse train by repetition-frequency multiplication of a subharmonic synchronous mode-locked semiconductor laser diode using the group-velocity dispersion (GVD) of optical fiber. A 49-196 GHz optical pulse train was generated with low intensity fluctuation and with low timing jitter, by adjusting fiber length in accordance with the mode-locking frequency and the fibers GVD.

10 Gb/s x 2 ch signal unrepeated transmission over 100 km of data rate enhanced time-spread/wavelength-hopping OCDM using 2.5-Gb/s-FBG en/decoder

We developed data rate enhanced time-spread/wavelength-hopping optical code-division multiplexing using 2.5-Gb/s fiber Bragg grating encoder/decoder and achieved 10 Gb/s /spl times/ 2 ch signal unrepeated transmission over 100 km distance. Five-chip multiwavelength prime hop code in the 1550.4-1553.6-nm region with spacing of 0.8 nm was used.

Demonstration of 10 Gbit/s-Based Time-Spreading and Wavelength-Hopping Optical-Code-Division-Multiplexing Using Fiber-Bragg-Grating En/Decoder

We studied 10Gbit/s-based time-spreading and wavelength-hopping (TS-WH) optical code division multiplexing (OCDM) using fiber Bragg gratings (FBGs). To apply it to such the high bit rate system more than ten gigabit, two techniques are adopted. One is encoding with the maximum spreading time of 400 ps, which is four times as data bit duration, to encode without shortening chip duration. Another is encoder design. The apodized refractive index profile to the unit-gratings composing the encoder is designed to encode the pulses with 10-20ps width at 10Gbit/s rate. Using these techniques, 2 × 10Gbit/s OCDM is demonstrated successfully. In this scheme, transmission distance is limited due to dispersion effect because the signal has wide bandwidth to assign a wavelength-hopping pattern. We use no additional devices to compensate the dispersion, in order to construct simple and cost-effective system. Novel FBG encoder is designed to incorporate both encoding and compensating of group delay among chip pulses within one device. We confirm the extension of transmission distance in the TS-WH OCDM from the demonstration over 40 km-long single mode fiber.

Field trial of time-spreading and wavelength-hopping OCDM transmission using FBG en/decoders.

In this paper, field trial on optical code division multiplexing through the commercial-used fiber line is presented. We fabricated fiber Bragg grating en/decoders with time-spreading and wavelength-hopping scheme, considering environmental fluctuation of transmission fiber. 200 km-long transmission of 2-channel x 10 Gb/s signals was achieved on the field photonic network test bed of JGN II. Error free transmission was demonstrated in real field deployed single-mode transmission fiber.