Xiaoqi Zhu

Wideband tunable optoelectronic oscillator based on a phase modulator and a tunable optical filter

A widely tunable optoelectronic oscillator (OEO) based on a broadband phase modulator and a tunable optical bandpass filter is proposed and experimentally demonstrated. A tunable range from 4.74 to 38.38 GHz is realized by directly tuning the bandwidth of the optical bandpass filter. To the best of our knowledge, this is the widest fundamental frequency tunable range ever achieved by an OEO. The phase noise performance of the generated signal is also investigated. The single-sideband phase noise is below -120 dBc/Hz at an offset of 10 KHz within the whole tunable range.

Tunable DC-60 GHz RF Generation Utilizing a Dual-Loop Optoelectronic Oscillator Based on Stimulated Brillouin Scattering

A dual-loop optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS) is experimentally demonstrated. Two lasers are utilized to realize the tunability of the OEO. One acts as the signal laser, the other is employed as the pump laser. By directly tuning the wavelength of the pump laser, a widely tunable range from dc to 60 GHz for the RF signal generation can be obtained. To the best of our knowledge, this is the widest fundamental frequency tunable range which has ever been achieved by an OEO. With dual-loop fiber lengths of 2 and 4 km, the single sideband (SSB) phase noise is measured to be -100 dBc/Hz at 10 kHz offset when the oscillation frequency is chosen as 5, 10, or 20 GHz. The side-mode suppression ratio (SMSR) is 35 dB when the oscillation frequency is 10 GHz. The stability of both frequency and power of the proposed OEO is improved with the dual-loop configuration when compared with the singleloop one. The Allan variances of the frequency fluctuation at 1-s average are 1.2 × 10-7 and 4.9 × 10-11 for the single-loop and dual-loop configurations, respectively. Furthermore, a phase noise model based on control theory to evaluate the SSB phase noise performance of the dual-loop OEO based on SBS is detailed for the first time. The experimental phase noise results agree well with the proposed phase noise model at an offset frequency range from 100 Hz to 100 MHz. Among different phase noise tests, the amplified spontaneous emission (ASE) noise induced by SBS is shown theoretically and experimentally to be the dominant source for the phase noise beyond 100-kHz frequency offset in the proposed OEO.

Orthogonal-band-multiplexed offset-QAM optical superchannel generation and coherent detection.

Nowadays the Internet not only has fast growing data traffic, but also has a fast growing number of on-line devices. This leads to high demand of capacity and flexibility of the future networks. The conventional Orthogonal Frequency Division Multiplexing (OFDM) and Nyquist pulse shaping signals have the advantage of high spectral efficiency when consisting of superchannels in the Wavelength-Division-Multiplexing (WDM) way. However, they face a cost issue when the spectral granularity of the superchannel is decreased to support more users. This paper proposes for the first time the scheme of Orthogonal-band-multiplexed offset-Quadrature Amplitude Modulation (OBM-OQAM) superchannel. OBM-OQAM superchannel provides large capacity and high spectral efficiency. Furthermore, it has the advantage of offering subbands of variable symbol rate without changing the system configuration. We provide a proof-of-principle demonstration of OBM-OQAM superchannel transmission. In our experiment, 400 Gbps 16 Quadrature Amplitude Modulation (QAM) OBM-OQAM superchannel transmission over 400 km Standard Single Mode Fiber (SSMF) is conducted. The experimental results show that the OBM-OQAM signal has low penalty in multi-band aggregation.

Wideband tunable optoelectronic oscillator based on the deamplification of stimulated Brillouin scattering

A wideband tunable optoelectronic oscillator (OEO) based on the deamplification of stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. A tunable single passband microwave photonic filter (MPF) utilizing phase modulation and SBS deamplification is used to realize the tunability of the OEO. Theoretical analysis of the MPF and phase noise performance of the OEO are presented. The frequency response of the MPF is determined by the + 1st sideband attenuation due to SBS deamplification and phase shift difference between the two sidebands due to chromatic dispersion and SBS. The close-in (< 1 MHz) phase noise of the proposed OEO is shown to be dominated by the laser frequency noise via phase shift of SBS. The conversion of the laser frequency noise to the close-in phase noise of the proposed OEO is effectively reduced compared with the OEO based on amplification by SBS. Tunable 7 to 40 GHz signals are experimentally obtained. The single-sideband (SSB) phase noise at 10 kHz offset is -128 dBc/Hz for 10.30 GHz signal. Compared with the OEO based on SBS amplification, the proposed OEO can achieve a phase noise performance improvement beyond 20 dB at 10 kHz offset. The maximum frequency and power drifts at 10.69 GHz are within 1 ppm and 1.4 dB during 1000 seconds, respectively. To achieve better close-in phase noise performance, lower frequency noise laser and higher pump power are preferred. The experimental results agree well with the theoretical models.

Coherent Detection-Based Automatic Bias Control of Mach–Zehnder Modulators for Various Modulation Formats

In this paper, a method to automatically control the bias voltages of LiNbO3 Mach-Zehnder modulator (MZM) is proposed and demonstrated experimentally. The automatic bias control (ABC) method is based on low cost coherent detection employing 3 × 3 optical coupler, which enhances the dither detection sensitivity. By minimizing the monitored dither frequency components which represents the residual carrier component in the optical signal, the modulator biases are optimized. A 0-π/2 square-wave phase modulation is introduced to mitigate the detection fluctuation induced by the imbalance of 3 × 3 coupler and improve the monitoring accuracy. Experiments show that the proposed method is universal for different modulation formats. High bias control precision is achieved for inner in-phase/quadrature (I/Q) branches and outer phase bias of optical quadrature modulator. The penalty caused by the proposed ABC is negligible for both single carrier (SC) modulation and optical orthogonal frequency division multiplexing modulation. The tolerance to temperature disturbance is also demonstrated.

Novel programmable microwave photonic filter with arbitrary filtering shape and linear phase

We propose and demonstrate a novel optical frequency comb (OFC) based microwave photonic filter which is able to realize arbitrary filtering shape with linear phase response. The shape of filter response is software programmable using finite impulse response (FIR) filter design method. By shaping the OFC spectrum using a programmable waveshaper, we can realize designed amplitude of FIR taps. Positive and negative sign of FIR taps are achieved by balanced photo-detection. The double sideband (DSB) modulation and symmetric distribution of filter taps are used to maintain the linear phase condition. In the experiment, we realize a fully programmable filter in the range from DC to 13.88 GHz. Four basic types of filters (lowpass, highpass, bandpass and bandstop) with different bandwidths, cut-off frequencies and central frequencies are generated. Also a triple-passband filter is realized in our experiment. To the best of our knowledge, it is the first demonstration of a programmable multiple passband MPF with linear phase response. The experiment shows good agreement with the theoretical result.

Tunable DC-40 GHz RF generation with high side-mode suppression utilizing a dual loop Brillouin optoelectronic oscillator

An agilely tunable DC to 40 GHz RF generation using a dual-loop optoelectronic oscillator based on Stimulated Brillouin Scattering is experimentally demonstrated. The side-mode suppression ratio is measured to be 43.1 dB at 20 GHz.

Microwave Photonic Down-conversion based on a Wideband Tunable Optoelectronic Oscillator

We present a novel microwave photonic down-conversion system based on a wideband tunable optoelectronic oscillator. Microwave signals from 14.8 to 31.0 GHz are down-converted to 1 GHz successfully. The conversion gain is about -55 dB.

Tunable-Bandwidth Optical Parametric Amplifier Based on Intermodal Four-Wave Mixing in a Few-Mode Fiber

An optical parametric amplifier based on intermodal four-wave mixing in few-mode fibers is proposed. The results show that tunable amplification bandwidth from 1GHz to 60GHz can be realized by changing the wavelength of the pumps.

Phase Noise Performance Improvement for EDFA-Based Coupled Optoelectronic Oscillator utilizing Balanced Detection

A coupled optoelectronic oscillator (COEO) utilizing balanced detection is proposed and experimentally demonstrated. A 10-dB improvement of phase noise performance at 10-kHz offset can be obtained compared to the traditional single detection.