Enze Yang

Tunable Microwave Frequency Multiplication by Injection Locking of DFB Laser With a Weakly Phase Modulated Signal

We have demonstrated in this paper a novel tunable microwave frequency multiplication by injecting a weakly phase-modulated optical signal into a DFB laser diode. Signals with multiple weak sidebands are generated by cross-phase modulation of a continuous wave (CW) with short pulses from mode-locked fiber laser. Then, frequency multiplication is achieved by injection and phase locking a commercially available DFB laser to one of the harmonics of the phase modulated signal. The multiplication factor can be tuned by changing the frequency difference between the CW and the free oscillating wavelength of the DFB laser. The experimental results show that, with an original signal at a repetition rate of 1 GHz, a microwave signal with high spectral purity and stability is generated with a multiplication factor up to 60. The side-mode suppression ratio over 40 dB and phase noise lower than -90 dBc/Hz at 10 kHz are demonstrated over a continuous tuning range from 20 to 40.

A Novel Optoelectronic Oscillator Based on Wavelength Multiplexing

A novel dual-loop optoelectronic oscillator (OEO) with different wavelengths is demonstrated. The principle of OEO is analyzed theoretically. There is almost no beating noise due to the optical domain dual-loop with different wavelengths. In our experiment, a 20-GHz radio frequency (RF) with high quality is obtained. The phase noise of the microwave signal is measured to be -120.6 dBc/Hz at 10 kHz. The loop drift of the OEO is compensated by a fiber stretcher using phase-loop locked technology and the stability of the RF has been improved greatly. The frequency drift of the OEO system is <; ± 92.5 mHz within 3 h. A 70-dB side-mode suppression ratio is achieved. In addition, the measured linewidth is better than 2.9 mHz and the Q-factor is on the order of 1012, which confirms the high spectral purity.

Pulse source based on directly modulated laser and phase modulator

We propose the simple pulse source, in which the pulses generated by large-signal directly modulated laser diode are phase-modulated, and then compressed into short pulses by an optimized length of DCF. On the one hand, phase modulator is used to enhance the negative chirp of large-signal directly modulated pulses. On the other hand, the largesignal directly modulated pulses are used to suppress the pedestal produced by the phase modulator. Using this technique, highly stable 10-GHz 5.5-ps optical pulses are obtained, which suppress pedestal up to 20dB and have a low timing jitter of 184fs.

40-Gb/s All-Optical Serial-to-Parallel Conversion Based on a Single SOA

An all-optical serial-to-parallel converter (AOSPC) was experimentally demonstrated. It could potentially be used to process variable-length optical packets. This scheme mainly consists of wavelength interleaved pulse generation and the sequential multiwavelength conversion (SMWC). The SMWC is based on a single semiconductor optical amplifier. In this research, a 40-Gb/s serial optical signal was converted into four-channel 10-Gb/s parallel optical signals. This scheme has the advantages of a simple system configuration, integration potential, and polarization independency. In addition, the AOSPC is suitable for an input signal with a low optical signal-to-noise ratio and at the same time can regenerate degraded serial signals.

Single Longitudinal Mode Brillouin Fiber Laser With Cascaded Ring Fabry–Pérot Resonator

A novel single longitudinal mode (SLM) Brillouin fiber laser (BFL) with cascaded ring (CR) Fabry-Pérot resonator is proposed and demonstrated. By optimizing the CR length of the single mode fiber cavity at 100 m (or 50 m) and 10 m, stable SLM operation is obtained. Therefore, the threshold power is lower and linewidth is narrower than that of previously reported BFL with 10 m (or 20 m) single cavity. Additionally, there is no additional attenuation except intrinsic loss of optical devices. The measured linewidth with 60 dB (or 45 dB) improved value of side mode suppression ratio is 0.41 kHz (or 3.23 kHz), which is three (or two) orders of magnitude than that of the pump. Using a stabilizing feedback loop based on autotracking technique with polarization maintaining fiber-based optical delay line, the SLM BFL exhibits good performance with 6% power fluctuation in 1 h.

Phase-modulator-based optoelectronic oscillator for generating short optical pulse and microwave signal

A phase-modulator-based optoelectronic oscillator (OEO) is utilized to implement a self-starting optical pulse and microwave signal source. This system is able to simultaneously generate a 9.8-GHz optical pulse stream with 141-fs (over 100 Hz to 1 MHz) timing jitter and 6.5-ps pulse width, along with a high spectral purity electrical signal that is locked to the repetition rate of the optical pulses. The measured phase noise is −112 dBc/Hz at 10 kHz away from carrier, and the side modes are perfectly suppressed.

A Novel and Tunable Frequency-Upconversion Based on FP-LD Injection of One Low Bit-Rate Signal Without Any RF Local Oscillator

An all-optical frequency-upconversion is presented by injecting a low bit rate signal into a Fabry-Pérot laser diode (FP-LD) without any radio-frequency local oscillator. One of the FP-LD lasing modes is locked by generated sideband through four-wave-mixing effect in FP-LD. The generated microwave subcarrier could be tunable by varying the power and polarization of the injected signal. The input signal at the data rate of 1.25, 2.5, and 2.7 Gb/s with nonreturn-to-zero format are upconverted to a subcarrier modulation signal at upcoversion frequencies of 20, 10, and 16.2 GHz, respectively. The single sideband phase noise of -81.2 and -87.7 dBc/Hz (10-kHz frequency deviation) at 16.2-GHz subcarrier are demonstrated. The difference of sidemode suppression ratio at the FP-LD output point is also analyzed.

Millimeter-wave subcarrier generation utilizing four-wave mixing and dual-frequency Brillouin pump suppression

A novel photonic technique of 60-GHz millimeter-wave subcarrier generation base on four-wave mixing effect in a semiconductor optical amplifier (SOA) and a dual-frequency Brillouin fiber laser configuration is proposed. In this system, two new harmonic components with six times spacing of the microwave source frequency are created when an optical signal, generated by carrier-suppressed intensity modulation, is launched into the SOA. The two residual modulation sidebands are then suppressed by stimulated Brillouin scattering process, and the leaved idlers provide an millimeter-wave subcarrier signal.

Simultaneous Dual-Channel Retiming and Reshaping Using Two Independent Phase Clocks in Fiber-Optic Parametric Amplification

We propose a novel scheme for simultaneous retiming and reshaping of two wavelength-division-multiplexing channels using two independent phase clock pump and polarization multiplexing in fiber-optic parametric amplification, with the benefits of suppressing the interchannel cross-phase-modulation effect induced by the clock pumps and four-wave-mixing crosstalk. Operation of two 10-Gb/s channels is demonstrated experimentally. In both single- and dual-channel operation, eye diagrams after regeneration are significantly cleared with pulsewidth narrowed, and the nonlinear interferences are effectively reduced. An average 2-dB power penalty improvement at a bit-error rate of 10-9 is obtained in both single- and dual-channel operation.

Investigation of a Rate-Selectable All-Optical Packet Clock Recovery System

This letter presents the experimental performance of a rate-selectable all-optical packet clock extractor using a Fabry-Perot (F-P) filter, a semiconductor optical amplifier (SOA), and polarization interferometers (PIs). The F-P filter with a low finesse and a free-spectral range (FSR) equal to the lowest packet data rate was used to directly extract the packet clock from the packet data stream, which ensures that the clock locks fast and vanishes quickly. Different PIs, in conjunction with the F-P filter, were used to form comb filters with different FSRs in order to suppress the undesired subharmonic frequencies. The clock then goes into SOA to reduce the low-frequency amplitude noise. We demonstrate packet clock extraction at 10, 20, and 40 Gb/s with the combination filter.