Yoshifumi Muramoto

High-speed and high-output InP-InGaAs unitraveling-carrier photodiodes

The unitraveling-carrier photodiode (UTC-PD) is a novel photodiode that utilizes only electrons as the active carriers. This unique feature is the key for its ability to achieve excellent high-speed and high-output characteristics simultaneously. To date, a record 3-dB bandwidth of 310 GHz and a millimeter-wave output power of over 20 mW at 100 GHz have been achieved. The superior capability of the UTC-PD for generating very large high-bit-rate electrical signals as well as a very high RF output power in millimeter/submillimeter ranges can lead to innovations in various systems, such as broadband optical communications systems, wireless communications systems, and high-frequency measurement systems. Accomplishments include photoreceivers of up to 160 Gb/s, error-free DEMUX operations using an integrated UTC-PD driven optical gate of up to 320 Gb/s, a 10-Gb/s millimeter-wave wireless link at 120 GHz, submillimeter-wave generation at frequencies of up to 1.5 THz, and photonic frequency conversion with an efficiency of -8 dB at 60 GHz. For the practical use, various types of modules, such as a 1-mm coaxial connector module, a rectangular-waveguide output module, and a quasi-optic module, have been developed. The superior reliability and stability are also confirmed demonstrating usefulness of the UTC-PD for the system applications.

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>>

Terahertz wireless communication link at 300 GHz

We present a terahertz wave wireless link operating at 300 GHz which has a potential for use in ultra fast future wireless services in short range. Terahertz wave was generated and modulated with photonic technologies in the transmitter, allowing us to use radio on fiber system concept as well. For the receiver, we used a Schottky barrier diode detector integrated with a planar antenna. With the link, error free data transmission at 12.5 Gbps was experimentally demonstrated. Taking the performance margin of the transmitter and receiver into consideration, we believe that even up to 20-Gbps data can be transmitted.

Unitraveling-Carrier Photodiodes for Terahertz Applications

Device design for unitraveling-carrier photodiodes (UTC-PDs) and their derivative structures is reconsidered from the point of view of terahertz (THz) applications. A key design procedure for maximizing their bandwidth is optimization by incorporating hybrid absorbers. The effect of quasi-field in p-type absorber is carefully examined. It has been shown that the initial velocity transient must be taken into account to evaluate the effective average velocity. Photomixers integrating a hybrid-absorber UTC-PD and a bow-tie antenna were fabricated and characterized. THz-wave generation by the photomixers in a frequency range of up to around 2.5 THz was confirmed. The observed THz-wave output exhibits significant changes with bias voltage, where the decrease in the output with increasing negative bias voltage is more pronounced at higher frequencies. This output behavior is due to the change in electron velocity in the diode depletion layer associated with the overshoot effect. From the dependence of the output power on frequency, effective electron velocity is found to be as high as

Rectangular waveguide output unitraveling-carrier photodiode module for high-power photonic millimeter-wave generation in the F-band

6 \times 10^{7}

Uni-Travelling-Carrier Photodiode Module Generating 300 GHz Power Greater Than 1 mW

cm/s at optimum bias voltage of -0.4 V.

High-power and broadband sub-terahertz wave generation using a J-band photomixer module with rectangular-waveguide output port

A compact unitraveling-carrier photodiode (UTC-PD) module with a WR-8 rectangular waveguide output port for operation in the F-band (90-140 GHz) has been developed. A resonating matching circuit integrated with a UTC-PD and a microstrip-line-to-rectangular-waveguide transformer are designed to have high output powers with a wide bandwidth covering the F-band. The module size and configuration are equivalent to those of conventional optoelectronic devices, which enables the use of standard assembly technology. The fabricated module exhibits a record millimeter-wave output power of 17 mW at 120 GHz for a bias voltage of -3 V. The 3-dB bandwidth is as wide as 55 GHz, which fully covers the F-band. An optical input stress test at a photocurrent of 10 mA performed to confirm the long-term stability of the module showed that the dark current stays below 1 /spl mu/A for more than 4000 hours.

Measurement of intermodulation distortion in a unitraveling-carrier refracting-facet photodiode and a p-i-n refracting-facet photodiode

In this letter, we demonstrate over 1 mW power generation at 300 GHz with a uni-travelling-carrier photodiode (UTC-PD) packaged in a WR-3 waveguide module. To increase the maximum power, two identical UTC-PDs were monolithically integrated along with a T-junction to combine the power from the two PDs. The UTC-PD module exhibited peak saturated output power of approximately 1.2 mW at 300 GHz with photocurrent of around 20 mA per PD and bias voltage of -3.9 V. In addition, 3 and 10 dB bandwidths were measured to be around 70 GHz or 23% and over 150 GHz or 50%, respectively.

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

A high-output-power photomixer module operating at 200-500 GHz has been developed. The module consists of a uni-traveling-carrier photodiode, a PD-waveguide mode-conversion coupler, and a compact metal package with a rectangular-waveguide that outputs sub-terahertz wave. The fabricated module exhibits a 10- dB down bandwidth of about 300 GHz and an output power as high as -2.7 dBm at 350 GHz. This is the highest value ever reported for a photomixer module operating at 350-GHz band.

Triple-mesa Avalanche Photodiode With Inverted P-Down Structure for Reliability and Stability

In this letter, we present an experimental characterization of third-order intermodulation distortion (IM3) at 5.8 GHz in a unitraveling-carrier refracting-facet photodiode (UTC-RFPD) and a p-i-n refracting-facet photodiode (pin-RFPD). The IM3 in the pin-RFPD is considerably reduced compared to the waveguide-type p-i-n photodiode. The third-order intercept point (IP3) of the UTC-RFPD does not decrease as the photocurrent increases, indicating that space-charge-induced nonlinearity is well suppressed in this photodiode. The two-tone IP3 of the UTC-RFPD estimated from the measurement reaches a very high level of 40.5 dBm.