Jinye Zhang

Class-B Microwave-Photonic Link Using Optical Frequency Modulation and Linear Frequency Discriminators

A class-B optical link is demonstrated as a means to provide high spur-free dynamic-range (110.4 dBmiddotHz2/3) with a minimum average received power associated with the optical carrier. The link uses optical frequency modulation, linear fiber-Bragg-grating frequency discriminators, and balanced detection to provide high linearity and maximum signal power. Shot and intensity noises are minimized by the low total average received photocurrent (0.88 mA) that results from class-B operation

Analysis of a Class-B Microwave-Photonic Link Using Optical Frequency Modulation

A class-B microwave-photonic link using optical frequency modulation (FM) and fiber-Bragg gratings (FBGs) is analyzed and results verified with measurements. Input voltage is converted linearly to FM, and this FM is converted by each FBG to intensity modulation. For small FM index beta, the signal increases as beta3, becoming linear in beta with a frequency offset or carrier leakage, and third-order distortion resulting from the detection process is shown to be worse than that obtained using a Mach-Zehnder intensity modulator at the same modulation index. For large beta( > 10), third-order distortion approaches zero and ideal class-B operation is predicted, and the only shot noise and relative intensity noise (RIN) added is that which arises from the detected signal power.

Low-biased microwave-photonic link using optical frequency or phase modulation and fiber-Bragg-grating discriminator

A linear microwave-photonic link is presented in which a fiber Bragg grating converts phase modulation into intensity modulation. DC-bias-related noise is reduced using a grating response that provides linear intensity modulation with low DC bias.

Broadband class-AB microwave-photonic link using polarization modulation

A novel broadband class-AB (CAB) microwave-photonic link is demonstrated using an AlGaAs-GaAs electrooptic mode-converter-based polarization modulator (PolM). The polarization-modulated signal is split into two paths, each independently optically biased to provide two electrooptic transfer functions operating close to, but on opposing sides of, their nulls. Experimental results at 2 and 4 GHz confirm that detection of the transfer functions in a differential detector provides excellent cancellation of second-order distortion and recreates the same third-order distortion as a quadrature-biased Mach-Zehnder modulator. Biasing the operating points near the null reduces optical carrier power, and hence, carrier-related noise, thereby increasing achievable spur-free dynamic range. The use of the PolM allows the CAB link to be implemented with a single modulator, reducing the matching requirements of dual modulator schemes and allowing third-order distortion-limited broadband operation.

Phase-Modulated Microwave-Photonic Link With Optical-Phase-Locked-Loop Enhanced Interferometric Phase Detection

We demonstrate a novel approach for coherently detecting microwave-modulated optical phase through interferometric phase detection and an optical phase-locked loop (OPLL). An asymmetric interferometer converts phase modulation into intensity modulation for direct detection. The optical phase in the interferometer is modulated by the detected signal through an OPLL. Balanced detection is achieved by biasing the interferometer at its quadrature point to cancel common-mode intensity noise and even-order nonlinear distortions. The concept was validated experimentally at a frequency of 25.7 MHz, limited by the large loop delay associated with discrete optical components. A numerical simulation is used to project system operation beyond the limitations of the experiment, showing that the linearity performance of the interferometric phase detector may be significantly improved by signal feedback.

Demonstration of a class-B microwave-photonic link using optical frequency modulation and complementary fiber-Bragg-grating discriminators

A high-dynamic-range (110.4 dB · Hz2/3) class-B optical link is demonstrated using optical frequency modulation, linear Bragg-grating frequency discriminators, and balanced detection to eliminate the optical carrier. A total average received photocurrent of only 0.88 mA minimizes shot noise and intensity noise.

High-performance microwave-photonic links

Microwave links have become key components in many communications, defense, and scientific optical system applications. Therefore work continues to devise new link technologies and system concepts that maximize link performance. In this paper we review recent progress towards high spur-free dynamic range links, comparing the most attractive new approaches, those using optical phase modulation (PM), with the well-established reference standard - the Mach-Zehnder-modulator based link. It becomes evident that links using differential PM offer some practical advantages, but with only modest performance improvements. In contrast, PM using coherent detection can offer very high performance, but large technical barriers remain.

Microwave Photonic Signal Detection Using Phase-Matched Optical Rectification in an AlGaAs Waveguide

We demonstrate a novel approach for detecting microwave-modulated optical signals through velocity-matched optical rectification in second-order optical nonlinear materials. Optical intensity modulation is down-converted to microwave frequency (5-20 GHz) using a traveling-wave GaAs electrooptic modulator as an optical square-law detector. Phase matching between microwave and optical waves is achieved through a velocity-matched slow-wave asymmetric coplanar-strip electrode structure.

Two-Tone Analysis of Distortion Suppression in Microwave-Photonic Links Using Phase Modulation and Fiber-Bragg Grating Filters

In this paper, we present a theoretical model of a microwave-photonic link using phase modulation and fiber-Bragg grating optical filter, based on two-tone analysis. The calculation supports the merit of the link by showing optical carrier suppression and third-order intermodulation distortion (IM3) cancellation for small-signal modulation and substantial suppression of IM3 even at high modulation levels. Ideally, the IM3 power decreases more than 75 dB than that without suppression at modulation depth up to 0.5.

THz Field Enhancement by Antenna Coupling to a Tapered Thick Slot Waveguide

We demonstrate experimentally the coupling of a THz beam into a laser-machined double-tapered thick slot waveguide operating between 0.3 and 2 THz. Simulation reveals that the THz field generated by a standard photoconductive antenna coupled to an undoped aspheric HRFZ-silicon focusing lens can be enhanced by 30 dB in the 40 μm taper waist, relative to a traditional Gaussian beam waist (at 1 THz). Analysis of the 8 dB insertion loss reveals positive implications for coupling between THz transceivers and in-plane-emitting antennas or low-loss THz waveguides.