Minyu Yao

All-Optical Analog-to-Digital Conversion Based on Polarization-Differential Interference and Phase Modulation

A novel approach of an all-optical analog-to-digital converter is proposed and demonstrated. One single-phase modulator and a continuous-wave laser diode are used to quantize the sinusoidal tone analog signal. Software sampling measurements yielded an effective number of bits of 4.1. Benefits of the proposed setup are its simple design, high bandwidth, and stability. The scheme is primarily limited in the optical domain by the speed of the phase modulator and in electronic domain by electrical comparators and logic devices

Improvement of flatness of optical frequency comb based on nonlinear effect of intensity modulator

Optical frequency comb (OFC) generated using cascaded intensity and phase modulators was experimentally demonstrated. Very flat OFC can be achieved by cascading intensity and phase modulators driven directly by sinusoidal waveform, where chirped fiber Bragg grating or specially tailored radio frequency waveforms are not required. It is found that the spectral flatness of OFC is related to direct current (DC) bias of intensity modulator and the optimum ratio of DC bias to half-wave voltage is 0.35. In the experiment, 15 comb lines within 1 dB spectral power variation are obtained at 10 GHz microwave frequency. The experimental results agree well with the simulation.

Generation of Flat Optical-Frequency Comb Using Cascaded Intensity and Phase Modulators

A scheme using one intensity modulator and two phase modulators driven directly by sinusoidal waveform to generate an optical-frequency comb (OFC) is experimentally demonstrated. It is relatively simple, where Bragg grating or specially tailored waveforms are not used. By setting the ratio of direct-current bias to half-wave voltage and phase shifts between sinusoidal waveform applied on the intensity and two phase modulators at appropriate values, 29 comb lines with spectral power variation less than 1.5 dB at 10 GHz are obtained. And the scheme has adjustability; a flat-top OFC with frequency spacing of 9.5-10 GHz is achieved.

All-Optical Analog-to-Digital Conversion Using Inherent Multiwavelength Phase Shift in LiNbO

All-optical analog-to-digital conversion utilizing inherent multiwavelength phase shift in lithium niobate phase modulator is proposed. In the experimental demonstration, a wavelength-tunable continuous-wave laser diode and a lithium niobate phase modulator are used to quantize the sinusoidal tone electrical analog signal. Using 16 different wavelengths, an effective number of bits of 4.3-bit has been obtained after software sampling measurement. Benefits of the presented approach in this letter are its simple realization of the phase shift and high stability.

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Detailed analyses of the short-term stability of the semiconductor fiber ring laser (SFRL) are presented. Analysis with rate equations shows that the relaxation oscillation effect does not exist in the SFRL. With a frequency-domain model, the mode competition in the SFRL is shown to be suppressed by the gain saturation effect of the semiconductor optical amplifier. Thus the observed good short-term stability of SFRL is theoretically explained. The analyses are verified in experiments.

Phase Modulator

A novel photonic digital-to-analog converter (PDAC) scheme based on summing of serial weighted multiwavelength pulses is proposed and experimentally demonstrated. The weighted multiwavelength pulses are delayed and summed in time domain through dispersion, and each weighted pulse with specific wavelength corresponds to a bit of input digital data. Regardless of the resolution, this scheme only requires one electrooptic modulator (EOM). In the experiment, a 3-bit PDAC with a sample rate of 2.5 GS/s is realized, and the input digital signal is mapped to an analog output linearly by a transfer function. This simple and compact setup could reduce the system complexity and avoid the synchronization of multiple EOMs.

Theoretical analyses on short-term stability of semiconductor fiber ring lasers

In this paper, an interferometric autocorrelator based on two-photon-absorption (TPA) detector is demonstrated. It can be used in the measurement of ultrashort pulse at 1.55 um wavelength region. From the second order autocorrelation trace of optical field, we can infer the pulse width. Accompanied with a linear detector, we can fully characterize the optical pulse, including intensity and phase profiles. A novel phase retrieval algorithm is proposed. It is a combination of an iterative loop and an evolution process. Simulation results show that our algorithm converges stably and can give a better approximation of the optical field than traditional algorithm.

Photonic Digital-to-Analog Converter Based on Summing of Serial Weighted Multiwavelength Pulses

We propose an asymmetrical interferometer to compensate the pattern effect in semiconductor optical amplifier (SOA) as an inline amplifier in dense wavelength-division-multiplexing (DWDM) system. Experiments are demonstrated with a commercial integrated Mach-Zehnder interferometer (MZI)-SOA. The experiments showed that in a 16/spl times/10-Gb/s DWDM system, the power penalty induced by the SOA decreased from 6.8 to 0.9 dB by the interference at 1 mW input power, and the input power dynamic range of the SOA was efficiently extended.

Ultrashort pulse measurement using interferometric autocorrelator based on two-photon-absorption detector at 1.55-μm wavelength region

A theoretical assessment of the interferometric noise in the optical time division multiplexing (OTDM) transmission system is presented. The impact of such noise on the system performance were investigated in detail. The corresponding system requirements were also revealed by the calculation results. Recommendations on the use of prechirping to reduce the interferometric noise in the OTDM system are given.

Experimental demonstration of pattern effect compensation using an asymmetrical Mach-Zehnder interferometer with SOAs

The performance of optical time division multiplexing (OTDM) system is limited by a complex combination of noise. In this paper we present a theoretical framework for the optical receiver in OTDM system based on the moment generation function. The proposed receiver model is showed to be more accurate in predicting the bit error rate (BER) performance than the former ones. Its validity is also verified by the experimental results.