Hiroyasu Mawatari

Linewidth enhancement factor in InGaAsP/lnP modulation-doped strained multiple-quantum-well lasers

Reduction of the linewidth enhancement factor /spl alpha/ is studied in InP-based strained multiple-quantum-well (MQW) lasers. Theoretical analysis shows that the /spl alpha/-parameter is greatly reduced in modulation-doped strained MQW lasers and may be zero while keeping positive gain. The experimental evaluation exhibits a very small /spl alpha/-parameter of around 1 in InGaAsP/InP modulation-doped strained MQW lasers. As a result of the small /spl alpha/-parameter, the linewidth-power product is effectively reduced in 1.5-/spl mu/m DFB lasers with the modulation-doped strained MQW structure. A narrow spectral linewidth around 100 kHz was also obtained reproducibly in 1.5-/spl mu/m modulation-doped strained MQW DFB lasers. >

Monolithically integrated eight-channel WDM modulator with narrow channel spacing and high throughput

We demonstrate an eight-channel wavelength division multiplexing (WDM) modulator module that monolithically integrates arrayed waveguide gratings and semiconductor optical amplifiers and electroabsorption optical modulators arrays. The compact module can generate individual optical signals for each WDM channel with low optical and electrical crosstalk. We show two configurations for the narrow channel spacing of 25 GHz and high throughput of beyond 80 Gb/s. Combining this WDM modulator with a multi-wavelength light source is a promising approach to creating a compact WDM optical transmitter.

Lasing wavelength changes due to degradation in buried heterostructure distributed Bragg reflector lasers

Changes in the wavelength and lamp characteristics due to the degradation of distributed Bragg reflector (DBR) lasers are investigated and the lasers are confirmed to be reliable enough for application as the light sources in WDM systems. The change in wavelength characteristics is due to degradation of the DBR or phase control region and the change in lamp characteristics is due to the degradation of active region. These changes in the characteristics are caused by diminished recombination carrier lifetime. The wavelength stability is strongly correlated with the injected current density. The lamp characteristics is confirmed to be almost as stable as in conventional Fabry-Perot lasers. The applicability of DBR lasers as the light source for wavelength division multiplexing (WDM) systems is demonstrated for actual-use conditions.

Demonstration of 50 Gbit/s 16QAM signal generation by novel 16QAM generation method using a dual-drive InP Mach-Zehnder modulator

We propose a novel 16QAM signal generation method using a single Mach-Zehnder modulator. We successfully demonstrate 50 Gbit/s 16QAM signal generation with a dual-drive npin InP Mach-Zehnder modulator using amplitude control by electro-absorption.

Transmitter Optical Subassembly Using a Polarization Beam Combiner for 100 Gbit/s Ethernet over 40-km Transmission

A transmitter optical subassembly (TOSA) has been developed for a 100-Gbit/s Ethernet system for a long optical transmission distance over a 40-km single-mode fiber (SMF). To obtain a high optical output power and a high dynamic extinction ratio, the TOSA consists of two two-channel distributed feedback laser diode array chips integrated with electro-absorption modulators (EADFB laser array chips) with a 2 × 1 multimode interference (MMI) optical coupler and a polarization beam combiner for wavelength multiplexing. The TOSA is 8.7 mm × 28.7 mm × 6.5 mm including an LC-type receptacle. The TOSA has a twin collimator path for two EADFB laser array chips. The wavelength multiplexer consists of a mirror, a half-wavelength plate, and a polarization beam combiner. The TOSA could improve the optical output power by around 2 dB compared with a TOSA with a four-channel EADFB laser array chip and a 4 × 1 MMI optical coupler. An optical modulation amplitude of over 0.5 dBm and a mask margin exceeding 21% were obtained for each lane when all lanes were operated simultaneously with an EA modulator driving voltage of 1.5 V at a bit rate of 25.78125 Gbit/s, which fully satisfies the 100GBASE-ER4 specifications. We demonstrated error-free operation for an SMF transmission of over 40 km. Moreover, we confirmed that the TOSA was capable of error-free SMF transmission over 60 km with a power penalty of less than 1.4 dB.

Electrical Evaluation of Dry Etching Damage on the Side Wall of Mesa Structure.

We propose a method for evaluating the electrical properties of damage on the sidewalls of mesa structures. In the method, current flowing through the mesa sidewalls (Imesa) is obtained from the forward current-voltage (IF-V) characteristics for Schottky barriers formed on both the sidewalls of the mesa structures and (100) surface. In applying the method to evaluate the damage on the sidewalls of InP mesa structures fabricated by reactive ion etching (RIE) with methane (CH4)/hydrogen (H2), we found that Schottky barrier height on the mesa sidewalls is increased by RIE. This suggests that an n-type damage layer is induced by RIE on the sidewalls. We also found that the damage could be induced on the mesa-sidewall at least with comparable density to that on the (100) surface, and to a depth less than that on the (100) surface.

Spectral linewidth and linewidth enhancement factor in 1.5-μm modulation-doped strained multiple-quantum-well lasers

A study of the linewidth enhancement factor (a-parameter) of 1.5-μm modulation-doped strained multiple-quantum-well (MQW) lasers is reported. The a-parameter was effectively decreased with increasing negative detuning. At a detuning of -30 nm, the a-parameter can be reduced to less than 1 by 1×10 18 cm -3 p-type modulation doping and 1.4% compressive strain in a Fabry-Perot laser. Applying this structure to a distributed feedback (DFB) laser, we investigate the dependence of the linewidth characteristics on the a-parameter. Finally, in the DFB laser with the cavity length of 1500 μm, the minimum spectral linewidth is lowered to 80 kHz at an output power of 40 mW

Wavelength chirping in wavelength conversion of 10 Gb/s signal with semiconductor laser converter

The chirping effects of wavelength converted 10 Gb/s signals in semiconductor wavelength converter on the waveform degradation after optical fiber transmission are investigated. The 10 Gb/s converted signal can be transmitted over 100 km with less than 2 dB power penalty in the converted wavelength region of 1.524 to 1.564 /spl mu/m when a broadly tunable SSG-DBR laser wavelength converter and a dispersion shifted fiber are used. It is also discussed how waveform degradation can be reduced when linewidth enhancement factor (/spl alpha/-parameter) of semiconductor laser wavelength converter is reduced by using modulation-doped strained MQW DFB lasers.

Modulation‐doped GaInAs/GaInAsP strained multiple‐quantum‐well lasers grown by chemical beam epitaxy

We report the characteristics of Be‐modulation‐doped strained multiple‐quantum‐well (MQW) buried heterostructure lasers grown by chemical‐beam epitaxy. Secondary ion mass spectroscopy revealed that the Be‐modulation‐doping profile was fabricated and maintained even after annealing at 620 °C for 30 min, which is the same condition used to fabricate the buried heterostructure. A linewidth enhancement factor (α parameter) of only 0.8 was obtained in 3×1018 cm−3 Be‐modulation‐doped strained MQW Fabry–Perot lasers at a wavelength of 35 nm shorter than the gain peak.

Clarification of the degradation modes of an InP-based semiconductor MZ modulator

We clarified the degradation modes of an InP-based semiconductor optical Mach-Zehnder modulator (MZM) using high-power light-injected accelerated aging tests. Degradation clearly occurred at the light injected side of the edge on the electric field applied region. We found that the degradation threshold depends strongly on temperature, wavelength and bias voltage. By correlating these parameters, we propose a degradation model based on the concentration of the optical absorption current, which depends on the optical absorption coefficient. By employing the degradation model, we obtained the degradation activation energy for a semiconductor MZM for the first time, and the value was 0.45 eV. These results indicate that a semiconductor MZM is sufficiently reliable for use in actual optical communication systems.