Xiaofan Zhao

Switchable single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser incorporating a semiconductor optical amplifier

We propose and demonstrate a novel single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber ring laser incorporating a semiconductor optical amplifier. The SOA biased in its low-gain regime greatly reduces the gain competition of the two wavelengths. The stable SLM operation is guaranteed by a passive triple-ring cavity and a fiber Fabry-Perot filter. The dual-wavelength output with a 40 GHz wavelength spacing is switchable in the range of 1533-1565.4 nm.

Optical regenerative NRZ to RZ format conversion based on cascaded lithium niobate modulators

Optical regenerative nonreturn-to-zero (NRZ) to return-to-zero (RZ) format conversion using a lithium niobate phase modulator and a lithium niobate intensity modulator is proposed and demonstrated. The key advantage of the proposed format converter is that the converted RZ signal has a very small pulse width, which can be multiplexed to a higher bit rate using optical time division multiplexing technology. The operation can greatly reduce the timing jitter of the degraded NRZ signal due to the regenerative property of the proposed scheme. Besides, the format converter can also support multi-channel operation. An experiment is performed with the feasibility of the scheme demonstrated.

40 Gbits/s all-optical clock recovery for degraded signals using an amplified feedback laser.

All-optical clock recovery for the return-to-zero modulation format is demonstrated experimentally at 40 Gbits/s by using an amplified feedback laser. A 40 GHz optical clock with a root-mean-square (rms) timing jitter of 130 fs and a carrier-to-noise ratio of 42 dB is obtained. Also, a 40 GHz optical clock with timing jitter of 137 fs is directly recovered from pseudo-non-return-to-zero signals degraded by polarization-mode dispersion (PMD). No preprocessing stage to enhance the clock tone is used. The rms timing jitter of the recovered clock is investigated for different values of input power and for varying amounts of waveform distortion due to PMD.

Investigation of all-optical nonreturn-to-zero-to-return-to-zero format converter based on a semiconductor optical amplifier and a reconfigurable delayed interferometer

A simple and robust all-optical nonreturn-to-zero to return-to-zero (RZ) format converter is demonstrated and investigated using a semiconductor optical amplifier (SOA) and a reconfigurable delayed interferometer. The scheme can be used to convert input signals at different bit rates and obtain converted signals with tunable duty cycles. Format conversion at 10 Gb/s is achieved with a negative power penalty of -4.9 dB at a bit-error rate of 10(-9). Transmission of the converted RZ signal over a dispersion-managed fiber link of 80 km results in only a small power penalty of 0.9 dB. In addition, the format converter is found to be insensitive to the power fluctuation of the optical clock, as the SOA works in the saturation regime.

40-Gb/s all-optical 3R regeneration with semiconductor devices

In this paper, 40-Gb/s all-optical 3R regeneration has been experimentally demonstrated based on semiconductor devices. The 3R regenerator incorporates an amplified feedback laser (AFL) for all-clock recovery and a semiconductor optical amplifier delayed interferometer as the optical decision gate. 40-GHz optical clock with low timing jitter and uniform amplitude is successfully recovered from the degraded signal by the AFL. The degraded signal is restored by the 3R regenerator with the Q-factor improved.

Simultaneous multichannel NRZ-to-RZ format conversion of 4-ASK signal based on phase-intensity hybrid modulation and dispersion compensation fiber

We propose and investigate a novel technique to realize non-return-to-zero (NRZ) to return-to-zero (RZ) format conversion of a multichannel 4-ary amplitude shift keying (4-ASK) signal. The proposed format converter composed of two modulators and a dispersion compensating fiber (DCF) is theoretically investigated using numerical simulation as basis. Research shows that a 4-channel 20-Gb/s NRZ-4-ASK signal can be converted to a RZ-4-ASK signal simultaneously without wavelength shifting and signal quality degradation, with the converted signal multiplexed to 40 Gb/s.

Switchable single-longitudinal-mode dual-wavelength fiber ring laser using hybrid gain medium

We propose and demonstrate a novel single-longitudinal-mode dual-wavelength erbium-doped fiber ring laser incorporating a semiconductor optical amplifier. The dual-wavelength output with 40-GHz wavelength spacing is switchable in the range of 1533 nm-1565 nm.

Fractional frequency multiplication by using optically injection locked optoelectronics oscillator

Fractional frequency multiplication is demonstrated based on an optoelectronics oscillator. A multiplication ratio of 4/3 is realized by injecting an optical signal modulated by 7.5GHz RF clock into an optoelectronics oscillator to obtain 10-GHz clock.

Demonstration of two efficient optical 3R data regenerators at 40 Gb/s using EAM or SOA as all-optical decision gate

In this report, we experimentally demonstrate efficient optical 3R regeneration of 40-Gb/s degraded data signals by using two schemes. The first 3R regenerator incorporates a dual-ring injection mode-locked fiber ring laser as the clock recovery module and an electro-absorption modulator (EAM) as the decision gate and the other 3R regenerator consists of an amplified feedback laser (AFL) for all-clock recovery and a semiconductor optical amplifier delayed interferometer (SOA-DI)as the optical decision gate. Optical clock with low timing jitter and uniform amplitude are successfully extracted with the use of the clock recovery units and significant improvement of the signal quality are obtained from 40-Gb/s RZ data signals degraded by polarization mode dispersion(PMD), chromatic dispersion or noise of amplified spontaneous emission (ASE).

Optical subharmonic sideband injection locking of an optoelectronic oscillator

Synchronization of an optoelectronic oscillator (OEO) was realized by using the modulation sideband of an injected subharmonic optical signal. A stable 10 GHz microwave output with side mode suppression ratio (SMSR) of 57dB was obtained from a 1/3 harmonic injection at 3.3 GHz.