Yoh Ogawa

Mode-locking at very high repetition rates more than terahertz in passively mode-locked distributed-Bragg-reflector laser diodes

We propose a technique for achieving mode-locking at very high repetition rates more than terahertz with high output power using a distributed-Bragg-reflector (DBR) laser, including an intracavity saturable absorber. This method is based on harmonic passive mode-locking at high gain levels and the selectivity of harmonic numbers related to the spectrum-filtering property of the intracavity Bragg reflector. Transform-limited pulses at repetition rates from 500 GHz to 1.54 THz were generated with an output power exceeding 15 mW. We studied stability of harmonic pulses by using conventional self-consistent mode-locking equations. We also discuss the effect of the spectrum-filtering properties of the intracavity Bragg reflector to the characteristics of mode-locked pulses.

Electrical characteristics of directly‐bonded GaAs and InP

The electrical characteristics of directly bonded GaAs/InP heterointerfaces have been investigated for the first time. The mirror‐polished surfaces of GaAs and InP wafers were put face to face and bonded by heat treatment at temperatures ranging from 450 to 700 °C. The wafers were successfully bonded without using any solders at all the temperatures tested. 1.3 μm InP/GaInAsP lasers were fabricated on GaAs substrates using direct bonding at 450 °C, and room‐temperature lasing operation has been achieved with the threshold current identical to that of conventional InP lasers.

Terahertz-rate optical pulse generation from a passively mode-locked semiconductor laser diode

We report what is to our knowledge the first demonstration of terahertz-rate optical pulse generation by harmonic passive mode locking in a distributed-Bragg-reflector laser diode. Along with the fundamental repetition rate of 38.8 GHz, we observed 400-GHz, 800-GHz, and 1.54-THz harmonics, depending on the bias condition of gain section. The pulse envelope for 1.54-THz pulses was in good agreement with a calculation from the Fourier transformation of the optical spectrum, indicating that the output pulses are transform limited.

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.

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>>

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.

Optical trapping of small particles using a 1.3-μm compact InGaAsP diode laser

We describe the noncontact optical trapping of small particles by a single-beam gradient force using a near-infrared InGaAsP diode laser operating at 1.33 μm. The feasibility and reliability of diode-laser trapping was confirmed with polystyrene latex and glass spheres as well as with yeast cells. By moving small particles vertically to the laser beam axis, we measured the horizontal component of the trapping force based on the Stokes law. Thus a linear relationship between the trapping laser power and the horizontal trapping force is demonstrated and compared quantitatively with that for the Ar laser.

All-optical 160-gb/s clock extraction with a mode-locked laser diode module

All-optical clock extraction at 160 Gb/s was successfully achieved using a monolithic colliding-pulse mode-locked laser diode module. Low excess timing jitter less than 0.1 ps was achieved at the injection power of data signal from -3.5 to 3 dBm without any degradation of the pulse characteristics of the output clock pulses.

Synchronous mode-locking in passively mode-locked semiconductor laser diodes using optical short pulses repeated at subharmonics of the cavity round-trip frequency

Synchronous mode-locking was achieved in passively mode-locked semiconductor lasers using optical pulses with repetition rates at subharmonics of the cavity round-trip frequency. Stable and continuous mode-locked pulses at 8.5 GHz were generated when the repetition rate of the control optical pulses was 4.25 GHz (2nd subharmonic). The timing jitter of the mode-locked pulses was reduced to 1 ps. The relationship between repetition rates of the control pulses and the realization of stable and continuous mode-locking was examined.