Saeko Oshiba

Transform-limited optical short-pulse generation at high repetition rate over 40 GHz from a monolithic passive mode-locked DBR laser diode

The fabrication of monolithic InP-based passively mode-locked distributed-Bragg-reflector (DBR) laser is reported. An optical short-pulse train with a duration of 3.5 ps was generated at a repetition rate of over 40 GHz. The time-bandwidth product was 0.43, and it was very close to the transform-limited value of a Gaussian waveform. Peak power of 60 mW has been achieved. This laser is promising as an optical source for a high-bit-rate soliton transmission system.<<ETX>>

Picosecond pulse generation from a 1.3 mu m distributed feedback laser diode using soliton-effect compression

An experimental demonstration of the soliton-effect pulse compression with a 1.3- mu m distributed feedback (DFB) semiconductor laser, a compression fiber, two traveling-wave optical amplifiers, and a soliton-effect compression fiber is presented. The experimental configuration and the details of the pulse generation from a gain-switched 1.3- mu m DFB laser diode are described. Results of temporal compression using a fiber of normal dispersion are presented where reduction of the pulsewidth to 2.45 ps is realized. The pulse amplification characteristics of a two-stage traveling-wave semiconductor laser amplifier are discussed with emphasis on the observed temporal broadening and spectral narrowing. After a brief description of the soliton-effect compression in an optical fiber, details of the experimental realization are given. >

Low-drive-voltage MQW electroabsorption modulator for optical short-pulse generation

This paper reports on InGaAsP-InGaAsP tensile strained MQW electroabsorption (EA) modulators with a high modulation efficiency of 35 GHz/V that generate optical short pulses. We studied and optimized the multiple-quantum-well (MQW) structural parameters, barrier height, and well number, thickness, and strain in the absorption layer to ensure high attenuation efficiency and generate low duty cycle pulses. Low TE/TM polarization sensitivity was obtained by controlling strain. Stable, nearly transform-limited optical pulse trains with a narrow pulsewidth of 3.6 ps are generated by applying a 20-GHz sinusoidal modulation voltage (6 V/sub pp/) to the EA modulator. This achieves a very small pulse duty cycle of 7.2%.

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.

Experimental study on time-spread/wavelength-hop optical code division multiplexing with group delay compensating en/decoder

10-Gb/s time-spread/wavelength-hop optical code generation and decoding were performed by group delay compensating fiber Bragg grating (FBG) en/decoder pair. A 10-km single-mode fiber (SMF) transmission of 10-Gb/s optical code division multiplexing (OCDM) was experimentally demonstrated.

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.

Accessible Optical Wireless Pedestrian-Support Systems for Individuals with Visual Impairment

We construct a pedestrian support system using visible-light communication with self-illuminated bollards. The system is designed for the requirements of people with weak eyesight and the elderly to notify them of danger and obstacles such as steps and signals. The luminescent color that the color temperature of 2000 K, that is orange, is suitable for communication. And we demonstrate prototype models of visible-light communication with 4PPM modulation format. Moreover, we carry out evaluation experiments with visually impaired people to determine the best distance for danger notification.

RZ pulse-width dependence of impulse radio UWB over combined fiber and wireless link

We demonstrated the dependence of IR-UWB signal waveform on the RZ pulse width, and made it clear that optical RZ pulse width of 12.5 to 90 ps is necessary in combined 1.25 Gbps 10 km SMF and wireless link with UWB band of 7.25–10.25GHz. The 10Gbps (1.25 Gbps × 8TDM) IR signal transmission in optical fiber link is also demonstrated using 29 ps optical pulse. The system satisfies the communication quality in the wireless transmission range of 0.5 m–2.5 m.

All-optical arbitrary wavelength conversion with signal regeneration based on slicing of supercontinuum spectrum

Signal regeneration was demonstrated with a wavelength conversion in a wide wavelength range (±20 nm from an input signal) using a highly nonlinear fiber (HNLF) at normal dispersion. At the optimum pumping condition, Q-factor of converted signals can be increased up to 15.

Phase-coding OCDM using fiber-Bragg-grating with enlarged signal pulse width

We evaluate correlation characteristics for phase-coding scheme utilizing fiber-Bragg-gratings as encoder/decoder. From the results, we confirmed that channel discrimination is sufficiently capable with the enlarged pulse width 4 times longer than chip duration.