SOA is the key device for burst-mode upstream transmission of 40 Gb/s access network to extend distance and increase users. We evaluate two conventional SOAs and our QD-SOA in networks, consisting of 20-km Single Mode Fiber (SMF) and splitters (1:8, 1:16 & 1:32). First, their characteristics are reported: 3-dB bandwidth & peak wavelength of Amplified Spontaneous Emission (ASE) spectra, gain, saturation output & input, and Noise Figure (NF). QD-SOA gives the lowest NF of 4.59 dB at -20-dBm input due to its highest Optical Signal to Noise Ratio (OSNR). It also has the fastest response time (70 ps) with less data pattern effect when operating in saturation region. Besides the measurement of Input Power Dynamic Range (IPDR) of 3 SOAs, their performances of single versus two-cascaded SOA transmissions are evaluated by Bit Error Rate (BER) in many combinations of SMF and splitters. In case of inserting 1:8 splitter between two-cascaded SOAs, the performance of 2 nd -stage QD-SOA has lower BERs than 2 nd -stage conventional SOA due to its higher saturation output and less pattern effect when operating at high input power. Finally, both experimental and computed BERs are plotted versus SOA's input to confirm the OSNR degradation and data pattern effect.
This thesis presents the characteristics improvement and performance evaluation of Quantum Dot Semiconductor Optical Amplifier (QD SOA) in an access network. There are 3 parts: 1) improvement of internal quantum efficiency, 2) increase of chip gain and 3) implementation of QD SOA in 40 Gb/s access network. The first part, Rapid Thermal Annealing (RTA) is applied to improve internal quantum efficiency to be 1.4 times higher than without RTA and low optical loss. The second part, strain compensation technique is applied to increase the chip gain of QD SOA. Considering the design of Quantum Dot Laser Diode with optimized stacked QD layers and threshold current, then the same design is applied to QD SOA having 25-stacked QD layers and 2 mm long. It can achieve the maximum chip gain of 35 dB at 400-mA bias current. The last part of thesis, the performances of two conventional SOAs and one QD SOA are evaluated in 40 Gb/s access network. Starting from the characteristics between conventional SOAs and QD SOA are compared. QD SOA gives the lowest Noise Figure of 4.59 dB because of its highest Optical Signal to Noise Ratio (OSNR). Plus, QD SOA has the fastest response time of 70 ps with the lowest data pattern effect when operating in saturation region, which is suitable for burst-mode transmission. Next, the performance of single SOA transmission is evaluated, and the Input Power Dynamic Ranges (IPDR) of 3 SOAs are measured. Finally, the two-cascaded SOA is experimented to raise power budget of a network to successfully support 128 users and 20-km distance. Consequently, installing QD-SOA as 2nd-stage SOA following a conventional SOA provides lower Bit Error Rates (BERs) than two-cascaded conventional SOAs because QD SOA has higher saturation output power and lower data pattern effect when operating at high input power. Additionally, the BERs are computed by substituting all parameters from experiments into theoretical equations. They are compared to experimental BERs to confirm the root cause of OSNR degradation and data pattern effect.
This paper experimentally demonstrates the 10 Gb/s optical access network with downstream transmission at 1550-nm wavelength through a commercial EDFA in order to accomplish the maximum distance of 62 Km over SSMF and 256 subscribers. The theoretical analysis of three effects are considered: (1) link power budget from insertion loss of optical components, fiber's attenuation and an EDFA's gain, (2) pulse broadening due to Chromatic Dispersion (CD), and (3) added noises from APD and EDFA. The BER (Bit Error Rate) curves are computed in MATLAB and compared with experimental results when using two optical modulators: (1
) EML (Electroabsorption Modulated Laser) with a fixed 8.69-dB Extinction Ratio (ER) and (2) Lithium-Niobate Mach-Zehnder Modulator (MZM) with an adjustable ER between 11.18 -15.17 dB. Both computed and experimental BER curves prove that a higher ER via MZM gives a better BER than a lower ER fixed byEML. The experimental BER curves of full setup using EML shows its power penalty at BER 10 -12 due to CD and ASE noise to be 0.34 dB and 0.38 dB respectively, whereas the full setup using MZM gives a slightly larger penalty of 0.69 dB and 0.56 dB respectively. Finally, when two TOBPFs (Tunable Optical Band Pass Filter) with 1-nm and 0.25-nm spectral widths are inserted after EDFA, the experimental BER curves show a slight improvement in power penalties of 0.03 dB and 0.15 dB respectively. Evidently, the narrower spectral width can remove ASE noise more effectively.
Keywords-XG-PON, Optical Splitter, Erbium Doped-Fiber Amplifier, Bit Error RateI.
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