X.S. Yao

Optoelectronic oscillator for photonic systems

We describe a novel photonic oscillator that converts continuous-light energy into stable and spectrally pure microwave signals. This optoelectronic oscillator (OEO) consists of a pump laser and a feedback circuit including an intensity modulator, an optical-fiber delay line, a photodetector an amplifier, and a filter. We present the results of a quasi-linear theory for describing the properties of the oscillator and their experimental verifications. Our findings indicate that the OEO can generate ultrastable, spectrally pure microwave-reference signals up to 75 GHz with a phase noise lower than -140 dBc/Hz at 10 KHz. We show that the OEO is a special voltage-controlled oscillator with an optical-output port and can be synchronized to a reference source by means of optical injection locking, electrical injection locking, and a phase-locked loop. Other OEO applications include high-frequency reference regeneration and distribution, high-gain frequency multiplication, comb frequency and pulse generation, carrier recovery, and clock recovery.

Multiloop optoelectronic oscillator

We describe and demonstrate a multiloop technique for single-mode selection in an optoelectronic oscillator (OEO). We present experimental results of a dual loop OEO, free running at 10 GHz, that has the lowest phase noise (-140 dBc/Hz at 10 kHz from carrier) of all free-running room-temperature oscillators to date. Finally, we demonstrate the first fiber-optic implementation of the carrier suppression technique to further reduce the close-to-carrier phase noise of the oscillator by at least 20 dB.

DUAL MICROWAVE AND OPTICAL OSCILLATOR

We describe and demonstrate a novel device in which a microwave oscillation and an optical oscillation are generated and directly coupled with each other. With the mutual influence between the microwave and the optical oscillations, we project that this device is capable of simultaneously generating stable optical pulses down to the subpicosecond level and spectrally pure microwave signals at frequencies greater than 70 GHz.

Coupled optoelectronic oscillators for generating both RF signal and optical pulses

We present experimental results of coupled optoelectronic oscillators (COEO) constructed with a semiconductor optical amplifier-based ring laser and a semiconductor colliding pulse mode-locked laser. Each COEO can simultaneously generate short optical pulses and spectrally pure radio frequency (RF) signals. With these devices, we obtained optical pulses as short as 6.2 ps and RF signals as high, in frequency, as 18.2 GHz with a spectral purity comparable with an HP83731B synthesizer. These experiments demonstrate that COEOs are promising compact sources for generating low jitter optical pulses and low phase noise RF/millimeter wave signals.

Coupled opto-electronic oscillators

We present experimental results of coupled optoelectronic oscillators (COEO) constructed with a semiconductor optical amplifier based ring laser and a semiconductor colliding pulse mode-locked laser. Each COEO can simultaneously generate short optical pulses and spectrally pure RF signals. With these devices, we obtained optical pulses as short as 6.2 picoseconds and RF signals as high, in frequency, as 18 GHz with a spectral purity comparable with a HP8561B synthesizer. These experiments demonstrate that COEOs are promising compact sources for generating low jitter optical pulses and low phase noise RF/millimeter wave signals.

Brillouin selective sideband amplification of microwave photonic signals

We introduce a powerful Brillouin selective side-band amplification technique and demonstrate an important application for achieving gain in photonic signal up- and down-conversions in microwave photonic systems, We show that systems employing such a scheme is also automatically immune to the fiber dispersion effect.

A high-speed photonic clock and carrier recovery device

We present the experimental results of a high-speed clock and carrier recovery device based on a novel oscillator called a optoelectronic oscillator (OEO). Such a device can recover a clock signal or carrier with a frequency up to 75 GHz and can be interfaced with a photonic communication system both electronically and optically.

Programmable group-delay module using binary polarization switching

We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.

A novel 2-D programmable photonic time-delay device for millimeter-wave signal processing applications

We describe a novel programmable photonic true time-delay device that has the properties of low loss, inherent two dimensionality with a packing density exceeding 25 lines/cm/sup 2/, virtually infinite bandwidth, and is easy to manufacture. The delay resolution of the device is on the order of femtoseconds (microns in space) and the total delay exceeds one nanosecond (30 cm in space).<<ETX>>

Practical Solutions to Polarization-Mode-Dispersion Emulation and Compensation

Polarization-mode dispersion (PMD) still remains a challenge for high-data-rate optical-communication systems. Practical solutions are desirable for PMD emulation, monitoring, and compensation. The authors review and compare various techniques for PMD emulation and compensation, with an emphasis on the application of programmable differential-group-delay (DGD) elements for manipulating PMD effects. The authors pay special attention to advanced emulation techniques, such as importance sampling and the hinge model, for practical applications. The tunability of programmable DGD elements proves to be attractive for both system performance evaluation and overall optimization