All-optical modulation format conversion from NRZ-OOK to RZ-QPSK using parallel SOA-MZI OOK/BPSK converters

Abstract

A novel all-optical modulation format conversion from non-return-to-zero on-off-keying (NRZ-OOK) to return-to-zero quadrature-phase-shift-keying (RZ-QPSK) is proposed and experimentally demonstrated. The proposed format conversion scheme is based on parallel Mach-Zehnder interferometric (MZI) OOK/binary-PSK (BPSK) converters, consisting of integrated semiconductor optical amplifiers (SOAs). We experimentally demonstrate that in both decoded channels of the converted RZ-QPSK signal bit error rate (BER) curves show almost the same receiver sensitivity at a symbol-rate of 10.7 Gsymbol/s. In addition, a reasonable dispersion tolerance of the converted signal up to +295 ps/nm is observed. The numerical simulation based upon carrier rate equation verifies the experimental results.

Advanced optical modulation and format conversion

“…For example, as shown in Figure 2.18, all-optical OOK to QPSK converter can be constructed with nested OOK to BPSK converter pairs [87]. QPSK is generated when the overall phase difference between the two nested MZI-SOA pairs is set to ⇡/2 rad.…”

“…This topic is subject of further research in Chapter 5 of this thesis. An integrated triple arm MZI-SOA was proposed by Nissanka et al [89], to achieve lower power consumption as well as simplicity in operation compared to the solution reported in [87]. An experimental demonstration of format conversion was achieved for two NRZ-OOK signals to one QPSK at 10.7 Gsymbols/s.…”

Generation of 21.3 Gbaud 8PSK Signal Using an SOA-Based All-Optical Phase Modulator

“…For example, DPSK and QPSK signals were generated with on-off keyed (OOK) input signals in [11] using cross-phase modulation in highly nonlinear fiber. Semiconductor optical amplifier (SOA)-based MZI devices fabricated using monolithic [12] and hybrid integration [13] technologies have also been utilized to all-optically produce QPSK.…”

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

“…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 nonlinear phase change, arising from the carrier density-induced changes in the refractive index, is given by [10,11] …”