Chie Fukuda

Compact and low power DP-QPSK modulator module with InP-based modulator and driver ICs

A compact 128 Gbit/s DP-QPSK modulator module including driver ICs and polarization multiplexing micro-optics is demonstrated. A dissipation power of only 3.2 W was achieved with a low differential driver output voltage of 2.5 Vpp.

Facet Passivation of GaInAsP/InP Edge-Emitting Laser Diode by Aluminum Ultrathin Layer Insertion

We investigated the suppression of facet degradation in GaInAsP/InP edge-emitting laser diodes (LDs). And we demonstrated that facet degradation is successfully suppressed using facet passivation by inserting an aluminum thin layer to the interface between the semiconductor facet and the facet coating film. The ultrathin aluminum layer was approximately 20 A thick. From photoelectron spectroscopy analysis of the passivated surface, it was found that this passivation is effective in reducing surface recombination. This reduction effect is caused by the suppression of both phosphorus shortage and oxidation. To investigate the passivation effect, we evaluated the tolerance to facet degradation by high-current injection test up to 600 mA and electrostatic discharge test up to 1.2 kV. Although about half of the tested LDs without passivation were degraded, all the LDs with passivation survived. This facet passivation method can suppress facet degradation markedly and it can be applied to not only GaInAsP/InP LD but also other InP-based LDs.

Low driving voltage InP-based Mach-Zehnder modulators for compact 128 Gb/s DP-QPSK module

We demonstrated the InP-based DP-QPSK modulator monolithically integrated with four Mach-Zehnder modulators planarized by the benzocyclobutene polymer. Clear eye-opening under 32 Gb/s operation was successfully achieved in all of four Mach-Zehnder modulators at a low driving voltage of 1.8 Vpp.

GaInNAs Distributed Feedback (DFB) Laser Diode

First successful operation of a buried-ridge-type GaInNAs-DFB laser was realized. Under CW condition, it oscillated with a threshold current of 18 mA at 25degC, and it could oscillate up to 110degC with good I-L linearity and with SMSR > 40 dB.

GaInNAs Electroabsorption Modulated Laser

We for the first time fabricated an electroabsorption modulated laser (EML) with a GalnNAs multiple quantum well (MQW) active layer using the butt-joint regrowth technique. Single longitudinal mode operation with side-mode suppression ratio (SMSR) of more than 45 dB up to 120degC and the extinction ratio of more than 15 dB up to 100degC were obtained. The 2.5-Gb/s uncooled operation from 25degC to 100degC was successfully demonstrated by changing the EA bias voltage.

Dependence of facet stress on reliability of AlGaInAs edge-emitting lasers

The relationship between facet stress and reliability of AlGaInAs edge-emitting lasers is unclear despite it being an important issue. We prepared two 1.3 μm AlGaInAs Fabry–Perot buried-heterostructure (BH) lasers that were identical except that they had tensile and compressive stress at the facet. The magnitude of the facet stress was controlled to be approximately 200 MPa in both lasers. We performed three reliability tests. In forward-biased electrostatic discharge tests, which can evaluate the resistance to optical damage, the cumulative degradation ratio of the compressive stressed laser was 33% lower than that of the tensile stressed laser. This result indicates a reduction in the optical absorption due to enlargement of the energy band gap at the facet. In the long-term aging of the light output power of 8 mW at 85 °C over 5 000 h, no dependence of the facet stress on the lifetime was observed. Since a major limitation of InP-based BH lasers is the BH interface, the aging results are reasonable. In...

Improvement in electrostatic-discharge tolerance of 1.3µm AlGaInAs/InP buried heterostructure laser diodes

This is the first report on electrostatic discharge (ESD)-induced degradation of AlGaInAs/InP buried heterostructure laser diodes. We found that the dominant degradation mechanism was melting of the active layer due to light absorption. We successfully improved ESD tolerance by facet passivation. The cumulative degradation ratio at 1.0kV ESD tests was decreased from 40 to 0%.