Hengyun Jiang

All-Optical Signal Processing for UltraHigh Speed Optical Systems and Networks

With high-bandwidth and on-demand applications continuing to emerge, next-generation core optical networks will likely require significant improvements in reconfigurability and ultra-fast operations. Optical signal processing overcomes the electronic bandwidth limitations with the advantages in terms of transparency and scalability. We review recent progresses in all-optical signal processing potentially for ultrahigh speed systems and networks. Starting from a brief overview of optical signal processing in high-speed optical systems and networks, we highlight a few key network functionalities, including optical logic operations, reconfigurable add/drop multiplexing, optical regeneration, wavelength conversion, format conversion, and phase-sensitive amplification. Different techniques are investigated and discussed, employing a wide range of devices and various nonlinearities. Some of experimental results are presented in both single polarization systems and polarization-division multiplexing systems.

SFDR enhancement in analog photonic links by simultaneous compensation for dispersion and nonlinearity

A method to improve the spurious-free dynamic range (SFDR) of analog photonic links has been proposed and experimentally demonstrated, which only consists of a phase modulator (PM), a polarizer and an optical filter. Such structure could compensate for the chromatic dispersion and the nonlinearity of the modulator simultaneously. In addition, by adjusting the states of polarization (SOPs) launching into the PM and the polarizer, the proposed scheme could also be reconfigured to mitigate the second harmonic nonlinearity induced by the photodetector. Experimental results show that the suppressions of the second-order and third-order intermodulation distortions (IMD2 & IMD3) are larger than 14-dB and 25.4-dB, respectively. Furthermore, the SFDR can achieve ~110-dB · Hz(4/5) for 40-km fiber transmission, which is 26-dB higher than that of the link without compensation.

Photonic arbitrary waveform generation based on crossed frequency to time mapping

Microwave photonic arbitrary waveform generation based on incoherent frequency-to-time-mapping (FTTM) accompanied by intersymbol interference, so called crossed FTTM (CFTTM). The pulse shape can be defined and tuned by properly adjusting the spectrum shaper (symbol shape) and the degree of intersymbol interference. UWB-, triangular-, rectangle-, comb- and user-defined pulse shapes are experimentally obtained.

Photonic generation of phase-coded microwave signals with tunable carrier frequency

A photonic scheme to generate a phase-coded microwave signal with tunable carrier frequency based on a simple single-trip and two-pass structure is proposed. Facilitated by the fiber Bragg grating and phase modulator along the trip, both frequency doubling and signal phase coding could be achieved simultaneously. Phase-coded microwave signals at 20 and 22 GHz are experimentally generated.

Comb filter with independently tunable wavelength spacing and bandwidth using cascaded variable differential group delay elements

An all-optical comb filter with independently tunable wavelength spacing and bandwidth (BW) is proposed. Using three cascaded variable differential-group-delay elements, we demonstrate theoretically and experimentally the tunability of the comb filter with >10 dB sidelobe reduction by adjusting three elements. The wavelength spacing is determined by the first filter module, while the sidelobe suppression ratio and the BW are defined by the middle and the last one, respectively.

Transmission of multi-polarization-multiplexed signals: another freedom to explore?

We propose a configuration of signal multiplexing with four polarization states, and investigate its transmission performance over single-mode-fiber links. Assisted by coherent detection and digital signal processing (DSP), the demodulation of four-polarization multiplexed (4PM) on-off-keying (OOK) and phase-shift-keying (PSK) signals are achieved. We then discuss the impact of the crosstalk from polarization mode dispersion (PMD) on 4PM systems. The transmission distance is extended from ~50-km to ~80 km by employing feedback-decision-equalizers. We also compare the back-to-back characteristics of the 40-Gbit/s 4PM-OOK system and 40-Gbit/s PDM-QPSK system with the same spectral efficiency. The results show that the performance of 4PM systems is comparable to that of PDM-QPSK systems, which indicates that the proposed scheme is a potentially promising candidate for future optical networks.

Pre-Distortion Compensation of Dispersion in APL Based on DSB Modulation

A simplified pre-distortion compensation scheme for dispersion-induced power fading in double-sideband analog photonic links is experimentally demonstrated. By properly tuning the bias of the dual-electrode Mach-Zehnder modulator and the relative phase difference between two input RF signals, the frequency response of a dispersive link can be controlled. Experimental results show that the power fading occurred at 13 and 15 GHz over SMF is fully compensated with an enhancement of ~15 dB in spurious-free dynamic range.

A Tunable Microwave Photonic Filter With a Complex Coefficient Based on Polarization Modulation

A tunable microwave photonic filter with a complex coefficient based on polarization modulation and a single laser source is proposed and demonstrated. Two out-of-phase microwave signals with orthogonal polarization states are generated using a polarization modulator and then combined into one special polarization state to introduce certain phase shifts after filtering out one sideband. The tunability of the filter with the complex coefficient is achieved by adjusting the phase shifts between two taps. In addition, the frequency response of the proposed filter from 10 to 11 GHz with FSR of 400 MHz is measured.

A Photonic Comb Filter With Independently and Digitally Tunable Bandwidth and Frequency Spacing

A photonic comb filter with digitally tunable bandwidth and frequency spacing is proposed. Using cascaded differential-group-delay (DGD) element and polarization switch based filters, we demonstrate independent tunability of both parameters with >; 12-dB first-sidelobe reduction for a 6-bit configuration. Limitations of such an approach are also discussed.

Photonic generation of impulse ultrawideband signals with switchable shapes and polarities based on frequency-to-time mapping.

A photonic approach to generate impulse ultrawideband (UWB) signals with switchable shapes and polarities based on the frequency-to-time mapping technique is proposed and demonstrated. UWB monocycle, doublet, and triplet signals with two polarities can be obtained by adjusting the switchable spectrum shaper.