Atsuo Kozen

A high-efficiency 50 GHz InGaAs multimode waveguide photodetector

A side-illuminated p-i-n photodetector with a multimode waveguide structure is proposed. Numerical and experimental results show that higher-order mode lights greatly enhance the coupling efficiency between the waveguide photodetector (WGPD) and a fiber, which leads to a high external quantum efficiency. The multimode WGPD has the major advantage that the external quantum efficiency and bandwidth can be derived independently of each other because the multimode waveguide structure can be designed without deteriorating electrical properties. The fabricated WGPD has an external quantum efficiency of 56% without AR coating and 68% with AR coating, and an electrical frequency 3 dB greater than 50 GHz at a 1.55- mu m wavelength. >

Improvement of kink-free output power by using highly resistive regions in both sides of the ridge stripe for 980-nm laser diodes

Suppressing the lateral expansion of driving current by forming highly resistive regions at both sides of the ridge stripe in ridge-waveguide-type 980-nm laser diodes leads to an enhanced kink-free output power. The highly resistive regions are formed by hydrogen passivation of p-type carrier (Zn) on the plasma exposure in a mixture gas of methane and hydrogen. A simulation predicted a decrease in local gain in the lateral direction at both sides of the ridge stripe. Fabricated laser diodes with the highly resistive regions exhibit kink-free output power of over 500 mW, showing an increase in kink-free power of 85 mW on average with an increase of slope efficiency of about 10% compared to those without highly resistive regions.

High-responsivity and low-operation-voltage edge-illuminated refracting-facet photodiodes with large alignment tolerance for single-mode fiber

We demonstrate a novel edge-illuminated refracting-facet photodiode (RFPD), in which the incident light parallel to the up-side surface is refracted at an angled facet and absorbed in a thin absorption layer. Although the absorption layer is thin, the absorption length is effectively increased by making the light transit at a certain angle to the absorption layer, resulting in an increase in internal quantum efficiency. The fabricated RFPDs with an absorption layer thickness of 1.5 /spl mu/m have a responsivity as high as 0.95 A/W even at a bias voltage of 0.5 V for a flat-ended single-mode fiber. The 1-dB-down misalignment tolerances for vertical and horizontal directions are as large as 9.5 and 33 /spl mu/m, respectively. A 3-dB bandwidth of more than 6 GHz is obtained.

Ultrafast monolithic receiver OEIC composed of multimode waveguide p-i-n photodiode and HEMT distributed amplifier

A multimode waveguide p-i-n photodiode (WGPD) and a distributed baseband amplifier consisting of high-electron mobility transistors (HEMTs) were monolithically integrated on InP substrate using a stacked layer structure for both components. The multimode WGPD has a 3-dB bandwidth of 49 GHz. The distributed baseband amplifier has a 3-dB bandwidth of 47 GHz, though its 0.5-/spl mu/m gate-length HEMTs have modest cutoff frequencies f/sub T//f/sub max/ of 47/100 GHz. The receiver optoelectronic integrated circuit has a bandwidth of 46.5 GHz. It was packaged into a fiber-pig-tailed module, and the WGPD in the module has a high responsivity of 0.62 A/W for 1.55-/spl mu/m wavelength. The module achieves a sensitivity of -22.7 dBm at 40 Gb/s and exhibits a clear eye-opening at 50 Gb/s.

Sensitivity limits of long-wavelength monolithically integrated p-i-n JFET photoreceivers

Noise characteristics and factors which limit the sensitivity of long-wavelength monolithically integrated photoreceivers using InGaAs p-i-n photodiodes (PD) and InGaAs junction-held-effect transistors (JFETs) were analyzed with regard to the input-noise current and the open-loop gain. Effects of the JFET gate length and the parasitic capacitance on the sensitivity were also clarified. Three types of photoreceivers were fabricated by using metal organic vapor phase epitaxy (MOVPE)-grown crystals and Be-ion implantation technology. The receiver using a cascode input stage had an extremely high sensitivity (-35.4 dBm) for a 622-Mb/s NRZ, 13-/spl mu/m-wavelength signal. The sensitivity of the other two receivers using an inverter input stage was moderate, -33.6 dBm for a multipower supply input stage and -31.4 dBm for a single power supply input stage.