All-optical format conversion of NRZ-OOK to QPSK and 16QAM signals via XPM in a SOA-MZI

Abstract

This letter proposes a scheme for the format conversion of on-off keying (OOK) signal to quadrature phase-shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM) signals via cross-phase modulation (XPM) in a semiconductor optical amplifier (SOA). Theoretical and experimental analyses of the format conversion scheme are conducted to validate its feasibility. The phase changing is obtained because of the XPM in the SOA. The QPSK and 16QAM signals are converted from the OOK signal. The performance of the 10 Gb/s format conversion system is evaluated and discussed. The receiver sensitivities of the converted QPSK and 16QAM signals after detection are -27.25 and -23.5 dBm, respectively, at a bit error rate (BER) of 10 −9 . OCIS codes: 060.2330, 230.4480, 070.4340. doi: 10.3788/COL201311.030604.All-optical signal processing is a promising technology for future optical transparent networks because it helps reduce implementation costs and removes the bottleneck in ultrafast signal processing without requiring costly optical-electrical-optical equipment [1,2] . Optical format conversion, one of the key optical signal processing technologies, has been extensively studied. Researchers have mainly focused on the conversion between conventional on-off keying (OOK) and binary phase shift keying (BPSK) [3−6] . By contrast, the multiple-OOK to M -ary phase-shift keying and/or quadrature amplitude modulation (QAM) conversion is rarely demonstrated. The OOK to BPSK conversion can be conducted in commercially available semiconductor optical amplifier (SOA) because of the simplicity of the BPSK format. However, the conversion of multiple OOK signals to higher order constellation signals is more difficult to achieve and requires a more flexible device approach than that of a single SOA. Based on previous reports, schemes are usually complex and costly, such as cascaded Mach-Zehnder modulators (MZMs) followed by a phase modulator [7] , dual-parallel MZM [8] , dual-drive MZM [9] , and parallel SOA Mach-Zehnder interferometer (MZI) [10] . In this letter, a novel scheme for the format conversion of nonreturn to zero (NRZ)-OOK signal to QPSK or 16-ary QAM (16QAM) signal via cross-phase modulation (XPM) in a SOA based MZI (SOA-MZI) is proposed and verified. The return to zero (RZ) pulse and dual NRZ-OOK signals are injected into a SOA, and the quadrature phase-shift keying (QPSK) signal is converted from an OOK signal via the XPM in the SOA. The dual NRZ-OOK signals are then injected into the SOAs located at the upper and lower MZI arm. Therefore, the dual QPSK signal is converted at the lower and upper arm via the XPM in the SOA-MZI. The 16QAM signal can then be converted by coupling the double QPSK signals. The scheme is simpler, more compact, and cost-efficient than traditional schemes. Our format conversion scheme is entirely in the optical domain and reduces the unstable factors in the electrical domain. The feasibility of this technique is evaluated through theoretical and experimental analyses. Figure 1 shows the th...

RZ-OOK to NRZ-OOK format conversion based on a single fiber Bragg grating

“…All-optical format conversion is an important interface technology for future optical transparent networks that will include different formats [1,2] . For instance, with the conversion between return-to-zero (RZ) and nonreturn-to-zero (NRZ) formats, the optical communication system will be more robust and more flexible for use in different networks such as optical time division multiplexing and wavelength division multiplexing networks [3,4] .…”

All-Optical OOK -to-QPSK Modulation Format Conversion With Wavelength Multicasting Based on Cascaded SOA Configuration

“…Based on the cross phase modulation (XPM) effect in SOA, various conversions between conventional OOK and binary phase shift keying (BPSK) have been reported [15], [16]. The QPSK signal can be converted from two OOK signals via the XPM in semiconductor optical amplifier (SOA) [17], however, the output optical power is hard to equalize by using this scheme due to that the two OOK signals are injected into the SOA simultaneously, so there will be a crosstalk between the signals when it is used for signal multicasting. In order to receive constant power of the converted QPSK signal, the XPM process in SOA is properly controlled by an assistant light [18], consequently if multi-channel probe lights are injected into SOA for signal multicasting, the crosstalk between signals is still inevitable.…”

Theoretical study of all-optical RZ-OOK to NRZ-OOK format conversion in uniform FBG for mixed line-rate DWDM systems

“…These approaches could be classified as nonlinear and linear. Modulation format conversion with nonlinear signal processing include use of semiconductor optical amplifiers (SOAs)/Mach-Zehnder interferometer (MZI) [7] , nanoporous silicon waveguide [8] , nonlinear optical loop mirror [9] , and stimulated Brillouin scattering [10] . Methods which include linear optical signal processing are mainly based on the spectral shaping of the input optical signal.…”