Kazutoshi Kato

110-GHz, 50%-efficiency mushroom-mesa waveguide p-i-n photodiode for a 1.55-/spl mu/m wavelength

A mushroom-mesa structure is proposed to reduce the CR-time constant which originates from the waveguide photodiode structure. Experimental results at a 1.55-/spl mu/m wavelength show that the multimode waveguide p-i-n photodiode with mushroom-mesa structure has an electrical 3-dB bandwidth of more than 75 GHz in the frequency domain and an electrical 3-dB bandwidth of 110 GHz in the time domain. The external quantum efficiency is 50% or 0.63 A/W, which leads to a record bandwidth-efficiency product of 55 GHz for long wavelength p-i-n photodetectors.<<ETX>>

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. >

Multichip optical hybrid integration technique with planar lightwave circuit platform

A two-step bonding technique for optical device assembly on a planar lightwave circuit platform was developed, which consists of a chip-by-chip thermo-compression prebonding step and a simultaneous reflow bonding step. The technique was used to realize multichip optical integration on the platform. The characteristics of the bonding technique were examined by investigating its strength and accuracy. The bonding accuracies in the horizontal and vertical directions were 1.1 and 0.8 /spl mu/m, respectively, with high bonding strength. The technique was first applied to a 3 chip integrated transceiver module and the 136 fabricated modules exhibited good performance. The average coupling loss between the laser diodes and the waveguide was estimated to be 4.1 dB and stable characteristics were observed during 1200 cycle thermal shock tests between -40 and 85/spl deg/C. Next, the two-step bonding technique was used for a 4 channel laser diode module on which 8 optical device chips were integrated and a low coupling loss was achieved of better than 4.2 dB which is as good as that of the 3 chip integrated optical modules.

A Burst-Mode 3R Receiver for 10-Gbit/s PON Systems With High Sensitivity, Wide Dynamic Range, and Fast Response

The burst-mode 3R receiver using monolithic ICs for 10-Gbit/s-class optical access networks is reported. In a point-to-multipoint access system like a passive optical network (PON), the receiver at the optical line terminal (OLT) must be able to handle burst-mode optical packets with significantly different powers and phases. An OLT receiver with high sensitivity with instantaneous response to burst inputs is desired for widening the accommodation area and for high efficiency in PON uplinks. Currently, the diffusion of high-speed Internet connection services represented by fiber to the home services at 1.25 Gbit/s is remarkable and the standardization of the next-generation system operating at 10 Gbit/s has started in IEEE. We first discuss the issues in the implementation of 10-Gbit/s-class PON systems, focusing on securing the accommodation area and the quality of the service comparable with those of the deployed system. Against that background, we propose target specifications for sensitivity, a dynamic range and response speed of the 10-Gbit/s-class burst-mode receiver so as to secure the power budget and the upstream efficiency comparable with those of the already-installed systems. Our burst-mode 3R receiver was designed to meet the above requirements and developed using monolithic ICs of transimpedance amplifier, limiting amplifier, and clock and data recovery circuit fabricated by using SiGe BiCMOS technologies along with a p-i-n photodiode. High sensitivity of , a wide dynamic range of over 16.5 dB, and quick response time of 75 ns were confirmed for burst inputs with extremely different powers.

New Beam Scanning Model for High-Speed Operation Using KTa1-xNbxO3 Crystals

We propose a new beam scanning model that is applicable to electrooptic materials with electron traps. With this model, we can achieve both high-speed operation and wide-angle scanning, because the operating speed is limited not by the electron mobility but by the frequency limit of the electrooptic effect of the materials. The voltage dependence of the scanning angle at 100 kHz using a KTa1-xNbxO3 crystal is consistent with the property predicted by the proposed model.

46.5-GHz-bandwidth monolithic receiver OEIC consisting of a waveguide p-i-n photodiode and a HEMT distributed amplifier

A large bandwidth monolithically integrated photoreceiver for 1.5-/spl mu/m wavelength operation was fabricated using a stacked structure of waveguide p-i-n photodiode layers and InAlAs-InGaAs high-electron mobility transistor (HEMT) layers grown using a single-step metal-organic vapor-phase epitaxy. The monolithic receiver optoelectronic integrated circuit (OEIC) consists of a waveguide p-i-n photodiode with a high responsivity of 0.5 A/W and a HEMT distributed amplifier. It has a bandwidth of 46.5 GHz, which is the largest yet reported for a long-wavelength receiver OEIC, and exhibits a clear eye opening at 40 Gb/s. This excellent performance is very attractive for use in high-speed optical transmission systems and millimeter-wave fiber-radio systems.

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.

Highly efficient 40 GHz waveguide InGaAs p-i-n photodiode employing multimode waveguide structure

The authors describe the design procedure of a highly efficient waveguide p-i-n photodiode. The efficiency of the waveguide InP/InGaAsP ( lambda /sub g/=1.3 mu m)/InGaAs/InGaAsP ( lambda /sub g/=1.3 mu m)/InP p-i-n photodiode is calculated using the step-segment method and overlap-integral between the optical field of a fiber and that of the photodiode. A remarkably high coupling efficiency to a fiber can be obtained by using a multimode waveguide structure. The fabricated device has an external quantum efficiency of 68% as well as 3 dB bandwidth of higher than 40 GHz at a 1.55 mu m wavelength.<<ETX>>

High-speed 32-channel optical wavelength selector using PLC hybrid integration

We have developed a new high-speed 32-channel optical wavelength selector (OWS) with gate drivers using PLC hybrid integration. It has excellent characteristics consisting of a low insertion loss of 2.3 dB, a low cross talk of -46 dB and the error-free optical wavelength selection of 10-Gbit/s optical signal.

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.