Wenhui Sun

Frequency-Doubling OEO Using the Polarization Property of LiNbO 3 Modulator

A frequency-doubling optoelectronic oscillator (OEO) has been proposed. In the proposed device, several passive components are introduced into the traditional OEO to handle the polarization state of the laser in the feedback loop. Making use of the polarization dependence of the LiNbO3 intensity modulator, a special double sidebands modulation is implemented where the polarization direction of the optical carrier is orthogonal with that of the first-order sidebands. Two polarizers are used to choose the specific optical components from the modulated light, which ensures that a microwave signal at the second-harmonic frequency outputs from the OEO when the fundamental frequency signal is self-oscillating in the loop. In the experiment, a 20-GHz frequency-doubled signal was generated, whose phase noise performance and immunity to the polarization drift were measured and evaluated.

Improved wavelength coded optical time domain reflectometry based on the optical switch

This paper presents an improved wavelength coded time-domain reflectometry based on the 2 × 1 optical switch. In this scheme, in order to improve the signal-noise-ratio (SNR) of the beat signal, the improved system used an optical switch to obtain wavelength-stable, low-noise and narrow optical pulses for probe and reference. Experiments were set up to demonstrate a spatial resolution of 2.5m within a range of 70km and obtain the beat signal with line width narrower than 15 MHz within a range of 50 km in fiber break detection. A system for wavelength-division-multiplexing passive optical network (WDM-PON) monitoring was also constructed to detect the fiber break of different channels by tuning the current applied on the gating section of the distributed Bragg reflector (DBR) laser.

Photonic-Assisted Wideband Phase Noise Analyzer Based on Optoelectronic Hybrid Units

We demonstrate a photonic-assisted wideband phase noise analyzer based on optoelectronic hybrid units comprising a microwave photonic phase shifter (MPS) and a microwave true time delayer. The MPS and the microwave true time delayer are achieved by a dual-drive Mach-Zehnder modulator (DMZM) incorporating with a broadband microwave frequency up-convertor (MFC) and an optical fiber delay line (ODL), respectively. Our scheme, which is analogous to the conventional microwave delayed homodyne self-reference method, can effectively improve its accuracy using longer time delay with minimum power consumption. In the scheme, the microwave signal is up-converted using the MFC and then down-converted using optical mixing in a photo-detector (PD). Meanwhile, the microwave signal is phase shifted using the MPS and time delayed using the ODL and are finally homodyne mixed with reference signals for converting phase fluctuations to voltage fluctuations. The motivation of this work lies in the fact that the previously reported phase noise measurement configurations based on photonic techniques are hard to accurately measure phase noise of microwave oscillators working at low frequencies. The microwave signals are phase tuned over 360° at frequency range of 0.5-9 GHz to achieve a photonic-assisted phase detector. Microwave signals at the frequency of 3-, 9-GHz are measured with a phase noise of -70.9 and -66 dBc/Hz at 1 kHz offset frequency, respectively.

Channelization Microwave Frequency Upconversion Based on Dual-parallel Optical Frequency Comb Generators

A multichannel frequency upconverter based on dual-parallel optical frequency comb generators (OFCGs) is proposed and demonstrated. Intermediate frequency (IF) microwave signals could be simultaneously upconverted into multiband over a frequency range from C-band to K-band.

Multi-microwave sources generation based on dual optical frequency combs

We proposed a scheme for multi-band microwave sources generation based on dual optical frequency combs (OFCs) in this paper. By optically channelizing the mixed OFCs, the heterodyned electrical signals in different bands can be obtained in different channels. Multiple microwave sources at 2.5GHz, 5GHz, 7.5GHz, 10GHz and 12.5GHz were generated, whose signal to noise ratio (SNR) between 38dB to 49dB in 1.4GHz bandwidth were obtained. The system has potential applications in satellite repeaters.

Frequency stability measurement of laser by using two independent tunable lasers

We demonstrate a novel scheme to measure frequency stability of laser by using two independent tunable lasers with the exactly same parameters. Due to the square relationship between the Allan variance of the beating tone and two laser sources, the frequency stability of the measured laser can be obtained through two steps. Thus, an optical reference source which is significantly more stable than the laser under test can eliminate the need. The frequency stability of the laser is 2.96×10-9.

Orthogonal polarization modulation based fully coherent self-heterodyne detection for future UDWDM-PON

A fully coherent optical communication link using orthogonal polarization modulation based self-heterodyne detection is proposed and experimentally demonstrated where the local oscillator optical source and phase estimation algorithm need not be employed at the receiver. OPM based self-heterodyne detection scheme for fully coherent optical communication link was proposed and experimentally demonstrated.

Reconfigurable microwave photonic filter based on Brillouin-assisted narrowband rectangular optical amplifier

A reconfigurable microwave photonic filter based on a Brillouin-assisted narrowband rectangular optical amplifier with a constant gain and a linear phase response is proposed. The optical amplifier is achieved by a joint use of two independent Brillouin pumps.

Narrow linewidth 1.55μm directly modulated distributed-feedback laser

We fabricated a narrow linewidth 1.55μm directly-modulated distributed-feedback (DFB) laser. The laser exhibits an output power of 14mW at 100mA, flat frequency response with -3 dB bandwidth of 18 GHz, the third-order intermodulation distortion (IMD3) with 39.8dBm, narrow optical linewidth with 181kHz, and RIN below -135.7dB/Hz in the 0.1-10GHz range along with the high side-mode suppression ratio (<52dB). We also experimentally verified the modulation bandwidth, linearity, and linewidth is related to the bias current. The characteristics of the laser, namely sufficient modulation bandwidth, high linearity, low relative intensity noise (RIN) and narrow linewidth, make it the perfect candidates for high dynamic directly modulated analog optical link.

An ultra-wide-band optical frequency comb generator based on semiconductor quantum dot F-P cavity

An ultra wideband optical frequency comb (OFC) generator based on semiconductor Quantum dot F-P cavity is packaged by our group. The free spectral rage (FSR) of the OFC can be tunable from 97GHz to 100GHz and the pulse width of the 100GHz OFC is 1.2ps.The full span of the OFC spectra is 80nm with a Gaussian shaped, and in span of 10nm, the flatness of the OFC can be limited to 1.7dB. The OFC has the advantages of small volume, simple and compact structure, low power dissipation, and has an ultra-wide bandwidth and flat spectrum, which can be used in the field of arbitrary waveform generation, channel information processing, and optical frequency division multiplexing.