Jizong Peng

On-Chip Tunable Second-Order Differential-Equation Solver Based on a Silicon Photonic Mode-Split Microresonator

We propose and experimentally demonstrate an on-chip all-optical differential-equation solver capable of solving second-order ordinary differential equations (ODEs) characterizing continuous-time linear time-invariant systems. The photonic device is implemented by a self-coupled microresonator on a silicon-on-insulator platform with mutual coupling between the cavity modes. Owing to the mutual mode coupling within the same resonant cavity, the resonance wavelengths induced by different cavity modes are self-aligned, thus avoiding precise wavelength alignment and unequal thermal wavelength drifts as in the case of cascaded resonators. By changing the mutual mode coupling strength, the proposed device can be used to solve second-order ODEs with tunable coefficients. System demonstration using the fabricated device is carried out for 10-Gb/s optical Gaussian and super-Gaussian input pulses. The experimental results are in good agreement with theoretical predictions of the solutions, which verify the feasibility of the fabricated device as a tunable second-order photonic ODE solver.

Silicon photonic bandpass filter based on apodized subwavelength grating with high suppression ratio and short coupling length

A compact silicon bandpass filter with high sidelobe suppression is proposed and experimentally demonstrated using an apodized subwavelength grating (SWG) coupler. The device is implemented by placing a SWG waveguide next to a strip waveguide, and apodization is employed with a Gaussian profile to taper the gap between the two waveguides. A high sidelobe suppression ratio of 27 dB can be obtained with a 3-dB bandwidth of 8.8 nm and an insertion loss of 2.5 dB. Owing to the large optical phase mismatch between the two waveguides and the presence of the SWG waveguide, the coupling length of the device is reduced to 100.3 μm. The experimental results validate our proposed apodized-SWG-based contradirectional coupler (contra-DC) as a promising device in suppressing out-of-band components in coarse wavelength division multiplexed (CWDM) optical communication systems.

SQNR Improvement Enabled by Nonuniform DAC Output Levels for IM-DD OFDM Systems

We propose and demonstrate via both simulation and experiment a scheme for a low-bit resolution digital-to-analog convertor (DAC) to improve the signal-to-quantification noise ratio (SQNR) of an intensity-modulated direct-detection (IM-DD) orthogonal frequency division multiplexing (OFDM) signal. In this scheme, the discrete output levels of a DAC are nonuniform and properly assigned based on the distribution of the OFDM signal. Such nonuniformity allows a better exploitation of output levels for the OFDM signal so that low-level waveforms that appear much more frequently experience mitigated quantization noise. To calculate these optimized output levels with the distribution of an OFDM signal, a numerical algorithm is proposed and verified. Our proposed scheme is proven effective in the simulations for Gaussian-distributed signals and brings over 3.6-dB and ∼2.5-dB improvements on SQNR and receiver sensitivity, respectively. The feasibility is also verified by a proof-of-concept experiment with ∼7.4-Gbps quadrature phase shift keying (QPSK)-modulated OFDM signals output by a 3-bit DAC. Our scheme enables transmission of such signals with no further optimization with ∼−25-dBm receiver sensitivity, while it is impossible using a conventional way. Both simulation and experimental results validate our scheme as a promising way to be implemented in low-bit resolution DACs for IM-DD OFDM applications.

Spectrally-efficient direct detection of QAM signal by orthogonal carrier interleaving

We propose and numerically demonstrate a scheme that enables the direct detection of QAM signals by a single photodetector. 40-Gb/s 16-QAM signal over 22-km fiber transmission is recovered without sacrificing optical spectral efficiency.

Multiband Ultra-Wideband Signal Generation With Quadrupled Capacity by a Single Modulator

We propose and experimentally demonstrate a photonic generation scheme for multiband ultra-wideband (MB-UWB) signal by employing a dual-drive Mach-Zehnder modulator (DDMZM). In this scheme, four electrical binary pulse streams with different bit rates are combined to drive one radio frequency (RF) port of the DDMZM, while the other RF port is modulated by the sum of their 1-b delayed duplicates. By properly adjusting the bit rate and the amplitude of each pulse stream, as well as the bias voltage of the DDMZM, an MB-UWB signal with four sub-bands can be obtained and the transmission capacity can be quadrupled. The feasibility of the proposed scheme is verified by a system demonstration, where the signal modulated by amplitude-phase-shift-key format reaches a high bit rate of 2 Gb/s.

Efficient Out-of-Band Spectrum Suppression in WDM-OFDM Systems

We propose and experimentally demonstrate a new scheme for orthogonal frequency division multiplexing (OFDM) sidelobe suppression by inserting sidelobe suppression prefix (SSP) ahead of cyclic prefix (CP). The feasibility of the proposal is verified by both simulation and experiment.

Energy-efficient optical network units with simplified FFT operation in direct-detection OFDM PON

We propose and experimentally demonstrate simplified FFT operation to improve the energy efficiency of ONUs in OFDM PON. Our proposal can achieve an energy saving of 14.6% compared to the conventional OFDM PON.

PAPR Reduction and Nonlinear Impairment Mitigation by Frequency Guard Band-Tone Reservation for DD-OFDM

A novel OFDM PAPR reduction scheme by exploiting frequency guard band (FGB) is proposed and experimentally demonstrated. Effective mitigation of nonlinear impairments is validated and BER improvement of 2.6 dB is achieved over 50-km fiber transmission without sacrificing data rate.