We investigated the temperature characteristics of a modularized semiconductor optical amplifier (SOA) utilizing InAs/AlGaAs quantum dot (QD) in the active layer operating at C-band (1.53μm–1.56μm). It has been reported by many literatures on physics that QDs are superior at energy efficiency and leads to less thermal energy generation. By changing the temperature of the Peltier element inside the module from 20℃ to 80℃, we measured the difference in the gain at each input power and injection current. The QD-SOA we measured was utilizing InAs QD in active layer and the laminated structure had 20 layers having 20nm of intermediate layers which refers to the width between QDs. When the input power was -50 dBm, we successfully confirmed more than 10 dB at the Peltier element temperature of 70℃ by injecting a current larger than 400 mA. In addition, we obtained a maximum gain of 20.68 dB at the center wavelength and a constant gain of approximately 15 dB at other Peltier element temperatures. It can be concluded from the output of the experiment that this QD-SOA can be put to use in optical communication in several situations where the temperature ranges between 20℃ to 80℃. This involves a new approach towards the application of QD amplifiers in the field of optical fiber communications.
Optical power-delivery systems are applied to distribute electrical power over optical fibers for systems such as remote wireless radio heads. Typically, the electrical voltage at the receiver side is low, around 1.0 V, owing to the use of a long-wavelength carrier. Consequently, we recently proposed a light-wave-modulation method for increasing the received electrical voltage. A 940-nm high-power laser was directly modulated to form a modulated light wave. We also used a small inductor to generate an induced electromotive force from the modulated light wave. We successfully obtained a peak voltage over 18 V using this simple technique.
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.
A 100-GHz narrowband photoreceiver module integrated with a zero-bias operational uni-traveling-carrier photodiode (UTC-PD) and a GaAs-based pseudomorphic high-electron-mobility transistor (pHEMT) amplifier was fabricated and characterized. Both devices exhibited flat frequency response and outstanding overall performance. The UTC-PD showed a 3-dB bandwidth beyond 110 GHz while the pHEMT amplifier featured low power consumption and a gain of 24 dB over the 85-100 GHz range. A butterfly metal package equipped with a 1.0 mm (W) coaxial connector and a microstrip-coplanar waveguide conversion substrate was designed for low insertion loss and low return loss. The fabricated photoreceiver module demonstrated high conversion gain, a maximum output power of +9.5 dBm at 96 GHz, and DC-power consumption of 0.21 W.
Short-range interconnection and/or data center networks require high capacity and a large number of channels in order to support numerous connections. Solutions employed to meet these requirements involve the use of alternative wavebands to increase the usable optical frequency range. We recently proposed the use of the T- and O-bands (Thousand band: 1000–1260 nm, Original band: 1260–1360 nm) as alternative wavebands because large optical frequency resources (>60 THz) can be easily employed. In addition, a simple and compact Gb/s-order high-speed optical modulator is a critical photonic device for short-range communications. Therefore, to develop an optical modulator that acts as a highfunctional photonic device, we focused on the use of self-assembled quantum dots (QDs) as a three-dimensional (3D) confined structure because QD structures are highly suitable for realizing broadband optical gain media in the T+O bands. In this study, we use the high-quality broadband QD optical gain to develop a monolithically integrated QD optical gain modulator (QD-OGM) device that has a semiconductor optical amplifier (QD-SOA) for Gb/s-order highspeed optical data generation in the 1.3-μm waveband. The insertion loss of the device can be compensated through the SOA, and we obtained an optical gain change of up to ~7 dB in the OGM section. Further, we successfully demonstrate a 10-Gb/s clear eye opening using the QD-OGM/SOA device with a clock-data recovery sequence at the receiver end. These results suggest that the monolithic QD-EOM/SOA is suitable for increasing the number of wavelength channels for smart short-range communications.
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.