An all-optical aggregation and de-aggregation scheme between one 8-ary quadrature amplitude modulation (8QAM) signal and three binary phase shift keying (BPSK) signals is proposed and theory simulated based on nonlinear effects in high nonlinear fiber (HNLF). In this scheme, the input 8QAM signal is de-aggregated into three BPSK signals by deploying self-phase modulation (SPM), cross-phase modulation (XPM), four wave mixing (FWM) and parameter amplification (PA) effect. Firstly, an improved amplitude compression loop (ACL) is designed based on SPM effect to convert 8QAM signal into quadrature phase shift keying (QPSK) signal. A degenerate phase sensitive amplifier (PSA) based on FWM effect is used to decompose QPSK signal into the first two BPSK signals (BPSK-1 and BPSK-2). The third BPSK signal (BPSK-3) can be extracted from the probe light modulated in its phase by the input 8QAM signal thanks to XPM and PA effect. Secondly, BPSK-3 is converted into an atypical on-off keying (OOK) signal through a 1-bit delay interference (DI). BPSK-1 and BPSK-2 are recombined into one QPSK signal through a coupler. Finally, the recombined QPSK signal and the atypical OOK signal are aggregated into one 8QAM signal by using XPM and PA effect. The error vector magnitude (EVM) and bit error ratio (BER) of the 8QAM and BPSK signal before and after de-aggregation and aggregation are calculated to analyse the performance of the scheme. The scheme can be applied in the network node to connect different networks which explore to use 8QAM and BPSK signal respectively.

An all-optical format conversion (AOFC) scheme for star-octal quadrature amplitude modulation (star-8QAM) signals is proposed and numerically simulated based on nonlinear effects in the high nonlinear fiber (HNLF). In the first stage AOFC processing, the input 30 Gbit/s star-8QAM signal is firstly de-aggregated into one 20 Gbit/s quadrature phase shift keying (QPSK) signal and one 10 Gbit/s typical on-off keying (OOK) signal by deploying the self-phase modulation (SPM), cross-phase modulation (XPM) and parametric amplification (PA) effects. In the second stage AOFC processing, the 20 Gbit/s QPSK signal and the 10 Gbit/s typical OOK signal are aggregated into one 30 Gbit/s star-8QAM signal again by utilizing the XPM and PA effects. Moreover, the amplitude ratio (AR) between the outer ring and inner rings of the aggregated star-8QAM signal can be adjusted flexibly by changing the QPSK and OOK signals power. Other octal modulation formats can also be generated through changing the QPSK and OOK signals power, including the rectangular 8QAM signals, $\pi$ /4-8QAM signals and 8-ary phase shift keying (8PSK) signals. Error vector magnitude (EVM) and bit error ratio (BER) for star-8QAM signals before and after AOFC are measured to analyse the scheme performance. The AOFC scheme provides the flexibility to adopt the appreciate modulation formats at the optical nodes to connect different optical networks.

A flexible all-optical format interconversion scheme based on a pump assisted nonlinear optical loop mirror (NOLM) is proposed and numerically simulated for the first time to our knowledge. In this scheme, input multi-Gbps 8QAM signals are divided into clockwise (CW) and counter-clockwise (CCW) components by a 3-dB optical coupler (OC), which also couples light from the input pump into the NOLM from the CCW direction. The numerical model of the pump assisted NOLM with CW and CCW optical paths is simplified using a nonlinear Mach-Zehnder interferometer (MZI). Optical signals in the upper MZI arm will be mainly affected by the self-phase modulation (SPM) effect when traversing the highly nonlinear fiber (HNLF) and those in the lower MZI arm are impacted by cross-phase modulation (XPM) in addition to SPM when they experience the HNLF with the input pump light. When the upper-arm optical signal with SPM phase shift and the lower arm optical signal with SPM and XPM phase shifts are coherently mixed, a new converted 8QAM signal can be obtained. The power transfer function (PTF) of the pump assisted NOLM and the relative phase shift (RPS) between the input and the output optical signals are theoretically provided and verified. By only changing the input power of the 8QAM signal and the pump light, all-optical format interconversion of square-, standard- and star-shaped 8QAM signals can be achieved. Furthermore, the proposed scheme can achieve format conversion from the 30 Gbps square-shaped 8QAM signal to a 20 Gbps quadrature phase shift keying (QPSK) signal. The scheme performance is analyzed via constellation diagrams, eye diagrams, the error vector magnitude (EVM) and the bit error rate (BER) of the optical signals. The scheme developed can be deployed in optical gateways to connect different optical networks by dynamically selecting their appropriate modulation formats.

An all-optical format conversion scheme of 2-dimensional multiple-quadrature amplitude modulation (MQAM) to multiple-phase shift keying (MPSK) signals is proposed and numerically simulated by using the nonlinear Mach-Zehnder interferometer (MZI) configuration with wavelength preservation. The input octal-quadrature amplitude modulation (8QAM) signal is generated through the phase modulator (PM) and amplitude modulator (AM) and injected into the nonlinear MZI configuration. The designed nonlinear MZI configuration includes two 3 dB optical couplers (OCs), a piece of high nonlinear fiber (HNLF) and a variable optical attenuator (VOA) in the upper interfering arm and a piece of standard single mode fiber (SSMF) or tunable optical delay line (TODL) and a variable phase shifter (VPS) in the lower interfering arm. The converted octal-phase shift keying (8PSK) signal can be obtained from the nonlinear MZI configuration through vector superposition between the input optical signal and itself with some nonlinear phase shift. The needed asymmetric nonlinear phase shift is mainly induced by the big nonlinear index difference between HNLF and SSMF. The error vector magnitude (EVM) and bit error rate (BER) performance of the scheme are calculated before and after format conversion with the different input and receiver optical-signal-noise-ratios (OSNRs). The scheme can be used in the intermediate node to connect the different networks which adopt 8QAM and 8PSK signals, respectively.

We propose and demonstrate a highly efficient photonic-assisted microwave signal harmonic frequency down-conversion using four-wave mixing (FWM) in a silicon waveguide with a reverse-biased P-i-N junction. In the proposed method, two Mach-Zehnder modulators (MZMs) are driven by a radio frequency (RF) signal and a low-frequency local oscillation (LO) signal, separately. Then, the modulated LO signal is injected into the silicon waveguide. Besides, the FWM phenomenon occurred in the integrated waveguide due to the doped regions of the junction can increase the efficiency of free carrier removal from the waveguide region. As the applied bias voltage on the silicon waveguide is increased, the generated harmonic sidebands are further enlarged. Correspondingly, the conversion efficiency is up to 12.8 dB with the bias voltage of 30 V. The silicon waveguide is fully packaged with a grating coupling fiber array and a wire-bonded printed circuit board (PCB) to make the module stable and compact. By simply adjusting the low-frequency electrical LO, the down converter based on FWM can realize accurate tunable and ultra-wide frequency operation. Due to the strengths of silicon integrated waveguide doped with reverse-biased P-i-N junction, the high-order LO modulated optical sidebands can be generated and used to down-conversion high-frequency RF microwave signal. This scheme can significantly reduce the high-frequency demand for LO source. In the experiment, the RF signals ranging from 8 GHz to 31 GHz are all down converted within 2 GHz by utilizing the 5.8 – 8.2 GHz LO signals, and signal-to-noise ratios (SNRs) larger than 50 dB are achieved. Moreover, the phase noise of the intermediate frequency (IF) signal is as low as -80.12 dBc/Hz at an offset frequency of 10 kHz and spurious free dynamic range (SFDR) is 105.5 dB · Hz ^2/3 with 3 ^rd -order FWM effect for the LO signal and 103.8 dB · Hz ^2/3 with 4 ^th -order FWM effect for the LO signal. This shows that the down conversion signal is reliable to further use in modern electrical systems such as microwave photonic radar.

An all-optical format conversion (AOFC) scheme of star-m-ary quadrature amplitude modulation (star-mQAM) based on a nonlinear Mach-Zehnder interferometer (MZI) with nested-pump assisted nonlinear optical loop mirror (nested-PA-NOLM) is proposed and numerically simulated. In this scheme, input multi-Gbps star-8QAM signals can be converted into three quadrature phase shift keying (QPSK) signals (namely QPSK-A, -B and -C) through the PA-NOLM under different input power of the signal and the pump. The nonlinear MZI is formed by two PA-NOLMs of the upper and the lower arms, the former and the latter 3-dB optical couplers (OCs), a directional variable optical attenuator (VOA) in the upper arm and a directional variable phase shifter (VPS) in the lower arm. A VOA and a VPS are used to adjust the power ratio (PR) and relative phase shift (RPS) between any two of QPSK-A, -B and -C. When any two adjusted signals in QPSK-A, -B and -C are coherently superposed, the aggregated star-8QAM signal can be extracted again. Furthermore, the proposed scheme can also be used to convert the 20 Gbps bipolar 4-ary pulse amplitude modulation (PAM4) signal into two 10 Gbps BPSK signals and a 20 Gbps QPSK signal. When the proposed scheme is combined with the phase-sensitive amplification (PSA), it can also be used to convert one 16QAM into two QPSK signals. The scheme performance is analyzed via constellation diagrams, power waveforms, the error vector magnitude (EVM) and the bit error rate (BER) of the optical signals. The scheme can not only be deployed in optical gateways to connect optical networks using different modulation formats, but also has a potential applied advantage in security information transmission between different optical networks.