Bindong Gao

Phase-coded microwave signal generation based on a single electro-optical modulator and its application in accurate distance measurement

A novel scheme for photonic generation of a phase-coded microwave signal is proposed and its application in one-dimension distance measurement is demonstrated. The proposed signal generator has a simple and compact structure based on a single dual-polarization modulator. Besides, the generated phase-coded signal is stable and free from the DC and low-frequency backgrounds. An experiment is carried out. A 2 Gb/s phase-coded signal at 20 GHz is successfully generated, and the recovered phase information agrees well with the input 13-bit Barker code. To further investigate the performance of the proposed signal generator, its application in one-dimension distance measurement is demonstrated. The measurement accuracy is less than 1.7 centimeters within a measurement range of ~2 meters. The experimental results can verify the feasibility of the proposed phase-coded microwave signal generator and also provide strong evidence to support its practical applications.

Optical Pulse Generation by an Optoelectronic Oscillator With Optically Injected Semiconductor Laser

A frequency tunable short optical pulse generation scheme based on a self-starting optoelectronic oscillator (OEO) with an optically injected semiconductor laser is proposed and investigated. The generation of optical pulses with a repetition rate coarsely tuned from 6.5 to 15 GHz are demonstrated. Phase noise of the electrical clock signal from the OEO is below -101 dBc/Hz at 10 kHz within the whole tuning range, which leads to a very small timing jitter of the generated optical pulses. Assisted by optical pulse compression technique in the OEO, the full-width-at half-maximum of the generated optical pulses is narrower than 20 ps.

Triangular Pulse Generation by Polarization Multiplexed Optoelectronic Oscillator

A novel triangular pulse generator is proposed based on a polarization multiplexed optoelectronic oscillator (OEO). Employing a dual-polarization modulator, the proposed OEO can simultaneously oscillate at two frequencies of f and 3 f along the two orthogonal polarizations of the same optical carrier. Thanks to the harmonic injection coupling between the two OEO oscillations, the generated two signals have an exact frequency ratio of 1:3 and can be tuned to be in phase with each other. By properly setting the amplitudes of the two signals, a triangular pulse train can be generated. The generation of a 4.44-GHz triangular pulse train is experimentally demonstrated. A very clean electrical spectrum incorporating the 4.44and 13.32-GHz components is obtained, and the two tones have good phase noises of -100.6 dBc/Hz at 10 kHz and -99.2 dBc/Hz at 10 kHz, respectively. The generated triangular waveform is very close to an ideal waveform, and the root-meansquare error between the generated and the ideal waveforms is 5.145 × 10-4.

Simplified 2-bit photonic digital-to-analog conversion unit based on polarization multiplexing

Abstract. A 2-bit photonic digital-to-analog conversion unit is proposed and demonstrated based on polarization multiplexing. The proposed 2-bit digital-to-analog converter (DAC) unit is realized by optical intensity weighting and summing, and its complexity is greatly reduced compared with the traditional 2-bit photonic DACs. Performance of the proposed 2-bit DAC unit is experimentally investigated. The established 2-bit DAC unit achieves a good linear transfer function, and the effective number of bits is calculated to be 1.3. Based on the proposed 2-bit DAC unit, two DAC structures with higher (>2) bit resolutions are proposed and discussed, and the system complexity is expected to be reduced by half by using the proposed technique.

A Frequency-tunable Two-tone RF Signal Generator by Polarization Multiplexed Optoelectronic Oscillator

A two-tone radio frequency (RF) signal generator realized by a polarization multiplexed optoelectronic oscillator (OEO) is proposed and demonstrated. The OEO employs a dual-polarization modulator and can simultaneously generate two frequency tones through OEO oscillations in two orthogonal polarizations of the same optical carrier. Frequencies of the two tones can be tuned independently by adjusting the electrical filters. Advantage of the proposed system is that, the optical interference between two-tone oscillations is effectively suppressed by polarization isolation and the multi-frequency intermodulation in a single modulator is avoided, which leads to the generation of a high quality two-tone RF signal. In the experiment, a two-tone signal at 9.95GHz and 10.66 GHz is generated with a phase noise (@10kHz) of −105.06 dBc/Hz and −104.43 dBc/Hz, respectively. The frequency tunability of the two-tone signal generator is also demonstrated in a range from 4 GHz to 12 GHz.

Frequency tunable two-tone signal generation based on polarization multiplexed optoelectronic oscillator

A frequency tunable two-tone radio frequency (RF) signal generator is proposed based on a polarization multiplexed optoelectronic oscillator (OEO). The proposed system has a simple structure using one laser source and one integrated modulator. Frequencies of the generated two tones can be independently tuned by simply adjusting the electrical filters. Besides, the optical interference as well as gain competition between the two oscillating frequencies can be well suppressed to achieve a stable operation. An experiment is carried out. A two-tone signal is successfully generated at 9.95 GHz and 10. 66 GHz with the phase noise at 10 kHz frequency offset reaching -105.12 dBc/Hz and -107.91 dBc/Hz, respectively. The frequency tunability is also demonstrated in a tunable range of about 4-14 GHz.

Time-Domain Waveform Synthesis Using a Dual-Polarization Modulator

This letter proposes a time-domain waveform synthesis based on a dual-polarization modulator that is driven by single-frequency radio frequency signals. This is achieved by applying a dual-polarization modulator to generate a polarization multiplexed optical signal. By controlling the parameters of the driving signals, multiple waveforms can be generated by synthesizing optical intensity profiles along two orthogonal polarization states. Compared with previously reported signal generators, the proposed time-domain waveform synthesizer is simple, compact, and easy to implement. The generation of triangular, flat-top, and sawtooth pulse trains with 5- and 10-GHz repetition rates are demonstrated in this letter. The results indicate that the proposed system is feasible and would find applications in optical signal processing and microwave photonic signal processing systems.

Serial photonic digital-to-analog converter based on time and wavelength interleaving processing

A serial photonic digital-to-analog converter (PDAC) is proposed based on optical time and wavelength interleaving processing. In the proposed system, an intensity weighted, time and wavelength interleaved optical pulse train is generated by optical phase modulation and fiber dispersion. The obtained optical pulses are on-off keying modulated by the input serial digital bit stream. After dispersion compensation, an optical signal with the power proportional to the weighted sum of the input bits stream is obtained, and digital-to-analog conversion is implemented. Compared with the previous PDACs, the system complexity and cost are reduced. The system stability is also enhanced thanks to the compact configuration. A 4-bit 10GSa/s PDAC is experimentally demonstrated. The results can verify the feasibility of the proposed PDAC, which has the potential to realize high speed and high resolution digital-to-analog conversions in further communication and radar systems.

Multi-frequency optoelectronic oscillators: Realization and applications

Optoelectronic oscillator (OEO) is a promising technique with various applications for high quality microwave generation and signal processing in electro-optical systems. Traditional OEOs are mainly focused on single-frequency oscillation and its applications, while OEOs with the agility of multi-frequency oscillation are rarely reported. In this report, we concentrate on the realization and application of multi-frequency OEOs, which can simultaneously oscillate at multiple frequencies within a single OEO system. Compared with multi-frequency signal generation by multiple individual single-frequency OEOs, the multi-frequency OEO has apparently reduced complexity and cost. Whats more, the multi-frequency signals generated by a multi-frequency OEO can have supernormal performance, such as good phase coherence and accurate frequency relations between different frequencies. In this talk, we first propose the possible solutions for establishing a multi-frequency OEO and discuss the related technical problems. Then, several experimental demonstrations of dual-frequency OEOs are provide based on our previous works, where the multi-frequency oscillations are established based on multi-channel microwave photonic filters or based on polarization multiplexing. Performance of the established multi-frequency OEO is evaluated regarding on the frequency-tunability, phase noise and long term stability, etc.. After that, the potential applications of multi-frequency OEOs in radar, communication and sensing systems are proposed. Two specific applications of the multi-frequency OEO are introduced in detail. One example is arbitrary RF waveform generation realized by controlling the amplitude and phase of different oscillating frequencies. The other example is a sensing system based on frequency beating of two signals from a dual-frequency OEO, which has a high reliability and a high measurement accuracy.

Phase stable radio distribution over optic cable by phase conjugation using an optical frequency comb

A phase stable radio frequency (RF) distribution technique is proposed and experimentally demonstrated. The system transmits optical frequency comb lines through an optic cable with multiple fibers. At the receiver, RF phase variation is removed by frequency mixing based on phase conjugation. In the proposed system, round-trip transmission is implemented through different fibers, thus the signal degradation due to bidirectional fiber transmission is eliminated. Besides, electrical frequency manipulations are not required because different frequency components can be generated by beating the comb lines at a photodetector, which leads to a simplified structure and alleviated signal distortion. Another advantage of the proposed scheme is that a series of phase stabilized frequencies at In times (n is a positive integer) of the comb spacing can be obtained simply by tuning the electrical filters. In the experiment, phase stable distribution of a 5 GHz signal and a 10 GHz signal over a 1.5 km optic cable is successfully demonstrated in a temperature varying environment. The residual delay variation of the 5 GHz signal is confined within ±1.1 ps, and the phase noise of the signal is well preserved after fiber distribution.