KEYWORDS: Optical amplifiers, Polarization, Signal attenuation, L band, Fiber amplifiers, Passive optical networks, Semiconductor optical amplifiers, Variable optical attenuators, Communication and information technologies, Optical networks
This research experimentally measured the characteristic parameters of 10 Gb/s bidirectional optical amplifier: (1) operating wavelength range, (2) small signal gain, (3) Polarization Dependent Loss (PDL), and (4) power consumption. Bidirectional amplifiers are the key component to extend coverage area as well as increase a number of users in Passive Optical Networks (PON). According to 10-Gigabit-capable PON or XG-PON standard, the downstream and upstream wavelengths are 1577 nm and 1270 nm respectively. Thus, our bidirectional amplifier consists of an Erbium Doped Fiber Amplifier (EDFA) and a Semiconductor Optical Amplifier (SOA) for downstream and upstream wavelength transmissions respectively. The operating wavelengths of EDFA and SOA are measured to be from 1570 nm to 1588 nm and 1263 nm to 1280 nm respectively. To measure gain, the input wavelengths of EDFA and SOA were fixed at 1577 nm and 1271 nm respectively, while their input powers were reduced by a variable optical attenuator. The small signal gain of EDFA is 22.5 dB at 0.15 Ampere pump current, whereas the small signal gain of SOA is 7.06 dB at 0.325 Ampere pump current. To measure PDL, which is a difference in output powers at various State of Polarization (SoP) of input signal, a polarization controller was inserted before amplifier to alter input SoP. The measured PDL of EDFA is insignificant with less than 0.1 dB. In contrast, the measured PDL of SOA is as large as 33 dB, indicating its strong polarization dependence. The total power consumptions were measured to be 1.5675 Watt.
We investigated the effect of Rapid Thermal Annealing (RTA) process on Quantum Dot Semiconductor Optical Amplifiers (QD SOAs). The devices are composed of 30-layer stacks of InAs quantum dot by using strain compensation method. The lateral size and height of QD are 30 nm and 4 nm, respectively. Our QD SOAs have emission wavelengths within 1.5 μm-band. We applied RTA process to improve the characteristics of internal quantum efficiency (ηi ) and optical loss (αi ) of ridge laser diode for QD SOAs. In this case, the operating temperatures of RTA process were set at 600°C, 620°C, 640°C and 660°C for 30 seconds each. In addition, the devices are cleaved to form a cavity length at 0.06 cm, 0.08 cm, 0.10 cm, 0.12 cm and 0.14 cm. According to the L-I characteristic result of ridge laser diode structure for QD SOAs at 640°C, the best minimum threshold current ( Ith ) is 47.93 mA. Moreover, according to the plot between 1 ηd−1 (external quantum efficiency) and cavity length, we can optimize the internal quantum efficiency and optical loss for a ridge laser diode structure to be 66.39% and 9.87 cm-1 respectively at 640°C RTA’s temperature. Finally, The RTA process helps to achieve 1.4 times higher in internal quantum efficiency as well as a minimal increase in internal optical loss comparing to without RTA.
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