Study On All-optical Wavelength Conversion

All-optical wavelength converter is one of the key components in wavelength division multiplexing optical networks. It can efficiently solve the wavelength blocking problem in the networks, increase the utilization ratio of wavelengths, simplify the management of the networks, and enhance the adaptability to failure of the networks. Wavelength conversion based on semiconductor optical amplifier has become a research hot-spot recently because of its low power consumption and high conversion bit rate.In this paper, wavelength conversion based on cross phase modulation (XPM) in SOAs was studied theoretically and experimentally. ⑴: The conversion characteristics of SOA-XPM converter were theoretically simulated by using the SOA gain and noise model and noise analysis method. The influences of input power, injection currents of the SOAs, spontaneous emission factors of the SOAs, and extinction ratio of input signal on inverted and non-inverted conversion characteristics were studied. ⑵: By using the 6 cascaded SOAs, dynamic XPM wavelength conversion at 2.5 Gbit/s bit rate was achieved with quite small power penalty which was nearly 0 dB on optimum condition. ⑶: XPM wavelength conversion at 10 Gbit/s bit rate was achieved over 40 nm wavelength range by using asymmetric Mach-Zehnder interferometer (MZI) structure. Two arms of the MZI are fiber-air-gap and SOAs, respectively. 3 SOAs with different gain peak wavelengths are cascaded in the SOA arm.Wavelength conversion based on cross polarization modulation (CPM) in SOA was also studied in this paper. ⑴: In the simulation of SOA-CPM wavelength conversion, the "polarization distance" was defined to quantize the state of polarization (SOP) change induced by signal light. The relationship of polarization distance with probe light SOP, signal light and SOA injection current was studied. The influences of polarization controller and polarizer on SOP were calculated using Stokes vector and Mueller Matrix method. Inverted and non-inverted CPM wavelength conversions were simulated theoretically and chirp and transmission characteristics of converted light were studied. ⑵: Inverted and non-inverted CPM wavelength conversions were achieved at 10 Gbit/s bit rate, and the pattern effect of the converted light was significantly reduced. The converter can be switched between inverted and non-inverted conversion state by simply change the settings of the PCs on the same input power and injection current condition. Error-free wavelength conversion was achieved over 25 nm wavelength range.