K. Akahane

Zero-bias operational ultra-broadband UTC-PD above 110 GHz for high symbol rate PD-array in high-density photonic integration

We have successfully developed a zero-bias operational ultra-broadband uni-traveling-carrier photodiode (UTC-PD) with a frequency bandwidth above 110 GHz using a low carrier concentration of 3 × 10¹⁴ cm^-3 in the carrier collection layer.

1-μm- band transmission by use of a wavelength tunable quantum-dot laser over a hole-assisted fiber

An injection-seeding bandwidth of 4 THz (1042-1057 nm) was successfully obtained for a quantum-dot (QD) Fabry- Perot laser diode operating in a 1-μm optical waveband. The operation of a fabricated laser was investigated for transmission through a 1-km hole-assisted fiber (HAF), and clear eye-openings and almost power-penalty-free transmission were successfully demonstrated with respect to 2.5 Gbps for various wavelengths in the 1-μm band.

Bias free operational 107-Gbaud ultra-fast photodetector

We designed a high-baud-rate UTC photodetector without a bias circuit for the first time. The photodetectors wideband frequency response over 100 GHz and clear eye diagrams up to 107 Gbaud were confirmed at 0 V. Bit error rate is discussed for 56 Gbaud and 107 Gbaud.

31-GHz single-carrier, 44.6-Gbps photonic wireless transmission using a wide-bandwidth high power photodetector and a pre-distortion technique

Single-carrier photonic wireless transmission at 31 GHz and 8.0 Gbaud with 64QAM is successfully achieved with error-free operation. A newly developed wide bandwidth high power photodetector and a pre-equalizing subsystem are presented.

Photonic integrated device of highly-stacked quantum dot using quantum dot intermixing by ion implantation

We studied the photonic integrated device of highly-stacked quantum dot (QD) on InP(311)B substrates using quantum dot intermixing (QDI) technique. A photoluminescence (PL) spectral blue-shift by about 190 nm was observed for the QDI process with B+ implantation and rapid thermal annealing (RTA) at 620°C. A QD laser integrated with two micro-ring-resonators (MRRs) was successfully fabricated with the QDI technique to show a large output of >20mW and a wavelength selective characteristic associated with MRRs.

High conversion gain, low power consumption W-band photoreceiver integrated with UTC-PD and InP-PHEMT amplifier

In this study, we successfully fabricated a W-band high-power photoreceiver with high output power and low power consumption. This W-band photoreceiver was integrated with a bias-free uni-travelling carrier photodetector (UTC-PD) and an InP high electron mobility transistor (PHEMT) amplifier for the first time. An ultrabroad 3 dB bandwidth beyond 110 GHz in an UTC-PD and maximum oscillation frequency of 320 GHz in a PHEMT low-noise amplifier were used for this hybrid integration. At 109 GHz, a high radio frequency output power of +10 dBm, high transimpedance gain of 828 □, and low power consumption of 67 mW was achieved in an optical-electrical converting process.

Ultra-broadband UTC-PD beyond 110 GHz at 0 v for future photonic integration

We have successfully realized the non-bias operation of an ultra-wide bandwidth uni-traveling-carrier photodetector (UTC-PD) using a low carrier concentration of 3 × 1014 cm-3 in the carrier collection layer for future high-density photonic integration. A 3-dB bandwidth above 110 GHz was confirmed without a bias circuit. In this paper, we discuss the proposed design and the experimental results obtained for the frequency response and maximum RF output power.

High-responsivity 100GHz waveguide UTC photodetector

We present a double cladding, high-mesa-type waveguide UTC photodetector with an improved the responsivity. In this device structure, an InGaAs thin core layer was sandwiched by p-InP/InGaAsP and n-InP/InGaAsP cladding layers, including a UTC structure, in order to obtain a good optical coupling between the waveguide and the fiber. By comparing the resulting mode field with that obtained with a single cladding layer structure, we confirmed that the vertical mode field was enlarged. Without a spot size converter, the measured responsivity was as high as 0.6 A/W at 1550 nm, which suggests a responsivity three times higher than that of back-illuminated structures, and higher responsivity than that of previous reports. A high frequency performance (f3dB = 100 GHz) was also measured. The device structure, including the layer, doping level conditions, and optical fiber coupling results are discussed, and its performance is characterized in detail.

Ar implantation-induced quantum dot intermixing technique for 1550 nm-band highly stacked QD photonic integrated circuit

We studied an Ar-implantation-induced quantum dot intermixing (QDI) technique and its physical mechanism, and demonstrate an almost equal performance of the QDI used 120 nm shifted laser diode compared to the performance without the technique.

High-performance PIN photodetector at 67 GHz and beyond for radio over fiber applications

High-performance photodetectors (PDs) for radio over fiber (RoF) applications over 60 GHz were designed and fabricated. The RF output was investigated while a high linearity was observed for two designs: a low carrier concentration InGaAs absorption layer in a PIN structure and a low carrier concentration collection layer in a unitravelling- carrier (UTC) structure. The RF output performances of both PIN and UTC structures were studied at 67 GHz and 100 GHz respectively. High photocurrent densities could be obtained from both structures (21.7 kA/cm2 in the PIN structure and 35.4 kA/cm2 in the UTC structure). The PIN structure exhibited a slightly higher current density of 1.6 times than the UTC structure. The frequency response of the UTC-PD exhibited excellent flatness up to 110 GHz, with a 3 dB bandwidth beyond 110 GHz. In addition, maximum RF output powers of +6.8 dBm at 67 GHz and -5 dBm at 100 GHz was successfully obtained. The space charge effect could be ruled out for the output linearity, but avoiding overheating in the p-contact metal had to be considered. By modifying impedance matching circuit designs, the maximum RF output power level of 3 dB can be improved.