Takeshi Nakata

High-speed, high-reliability planar-structure superlattice avalanche photodiodes for 10-Gb/s optical receivers

This paper reports the planar-structure InAl-GaAs-InAlAs superlattice avalanche photodiodes (SL-APDs) with a Ti-implanted guard-ring, which were developed for a compact and high-sensitivity 10-Gb/s optical receiver application. The design and fabrication of the novel concept planar-structure including the Ti-implanted guard-ring are described. The characteristics of the planar APDs are 0.36 /spl mu/A dark current at a multiplication factor of 10, 67% quantum efficiency, 110-GHz gain-bandwidth (GB) product, 15-GHz top-bandwidth, and - 27.2-dBm sensitivity at 10 Gb/s. The reliability was preliminary tested and the lifetime of longer than 10/sup 7/ h at 50/spl deg/C was estimated. The dark current characteristics including its temperature dependence and the excess noise characteristics are also analyzed. All the obtained characteristics exhibit the practical availability of the planar SL-APDs in the 10-Gb/s trunk line optical receiver uses.

High-reliability and low-dark-current 10-Gb/s planar superlattice avalanche photodiodes

For compact and high-sensitivity 10 Gb/s optical receiver applications, we have developed low-dark-current planar-structure InAlGaAs-InAlAs superlattice avalanche photodiodes with a Ti-implanted guard-ring. The APDs exhibited dark current as low as 0.36 /spl mu/A at a gain of 10. The temperature dependence of the dark current was confirmed to be in a sufficient level for practical 10-Gb/s applications. The APDs also exhibited a quantum efficiency of 67%, a gain-bandwidth-product of 110 GHz, a top 3-dB bandwidth of 15.2 GHz, and a minimum gain for 10-GHz bandwidth of 1.6. Preliminary aging test also showed a stable dark current operation after aging of over 2200 h at 200/spl deg/C. These high-reliability, low-dark-current, high-speed, and wide-dynamic-range characteristics are promising for 10-Gb/s high-sensitivity optical receiver use.

High-power and high-efficiency photodiode with an evanescently coupled graded-index waveguide for 40 Gb/s applications

High-power evanescently coupled pin photodiodes with external efficiencies of as high as 0.96 A/W, enabled by the graded index configuration of the waveguide, have been developed for 40 Gb/s applications.

High-speed and high-sensitivity waveguide InAlAs avalanche photodiodes for 10-40 Gb/s receivers

We have developed APDs designed for 10 Gb/s and 40 Gb/s receivers. A multimode waveguide structure and a very thin InAlAs multiplication layer enable high quantum efficiency, a high bandwidth, and low-voltage operation. Therefore, the waveguide structure is suitable for 10 Gb/s or higher bit rate APD receivers. In this paper, an InAlAs multiplication layer thickness is optimised so as to achieve low dark current and high GB product for 10-40 Gb/s high-sensitivity receivers.

40-Gbps waveguide avalanche photodiodes

Thin multiplication waveguide avalanche photodiodes have been developed for use in 40-Gbit/s receivers. High responsivity of 0.73-0.88 A/W, wide bandwidth of 30-35 GHz, and gain-bandwidth product of 140-180 GHz have realized the receiver sensitivity of -19 dBm at 40 Gbit/s.

Multiplication Noise Characterization of InAlAs-APD With Heterojunction

The excess noise and ionization coefficient ratio of InAlAs avalanche photodiodes (APDs) with heterojunctions has been measured. To obtain these values accurately, we used a differential amplifier and determined the optical current at which the avalanche multiplication equals 1. These made it possible to conduct measurements on excess noise including that in the low multiplication region. Measured ionization coefficient ratios at M=10 were 0.18 and 0.17 with multiplication layer widths of 0.2 and 0.7 ¿m , respectively. Excess noise was reduced with an increase in the optical input power. This tendency appeared more prominently in APDs with a thin multiplication layer.

An ultra high speed waveguide avalanche photodiode for 40-Gb/s optical receiver

We have developed an ultra high speed InAlAs-WG-APD with a 30-GHz bandwidth. We fabricated well defined small mesa APDs using dry-etching to reduce the capacitance of the APD. By combining this WG-APD and a GaAs-based preamplifier, we achieved a 30-GHz bandwidth APD receiver at M=2. This front end shows the possibility of applying the APDs to 40-Gb/s optical receivers for the first time.

Superlattice avalanche photodiodes for optical communications

This paper reviews the research into and development trends to date of high-speed high-sensitivity semiconductor superlattice (SL) avalanche photodiodes (APDs) for use in 1.3 to 1.55μm wavelength optical communications. We focus on three types of SL-APDs based on an InAlGaAs-well/InAlAs-barrier structure. The first is an InAlGaAs/InAlAs polyimide-coated mesa-structure SL-APD with a high gain-bandwidth product of over 120GHz and a low multiplied dark current of a few tens of nano-amperes. Its reliability has been measured to be over 105h at 50°C. The second is a planar-structure SL-APD with a new titanium-implanted guard-ring; this structure has a longer lifetime than the mesa structure. The third is a large-receiving-area SL-APD integrated with a monolithic lens for eye-safety 1.5μm wavelength optical measurement systems.

Theoretical and Experimental Study on Waveguide Avalanche Photodiodes With an Undepleted Absorption Layer for 25-Gb/s Operation

Waveguide avalanche photodiodes (WG-APDs) have been developed for a 25-Gb/s operation. The waveguide structure was adopted for the APDs in order to achieve both high-speed performance and high responsivity. First, the dependence of the multiplication and absorption layer thickness on the 3-dB bandwidths of the WG-APDs was theoretically clarified. It was found that introducing an undepleted absorption layer was effective in improving the 3-dB bandwidth without reducing efficiency. The 3-dB bandwidth of the fabricated WG-APD based on the calculation results was over 20 GHz up to a multiplication factor of 7. The responsivities were 0.6 A/W for 1.31 m and 0.75 A/W for 1.55 m wavelength. High reliability of the WG-APDs was also demonstrated.

Over-Gb/s Mesa-structure APDs with High Reliability

We have developed mesa-structure avalanche photodiodes (MS-APDs) for Gb/s application. These MS-APDs combine high-speed peformance with the potential for low-cost productivity. Additionally, we realized high reliability of the mesa-structure APDs for the first time.