Pengbo Shen

Efficient generation of guided millimeter-wave power by photomixing

A 70-GHz bandwidth commercial photodiode has been coupled to W-band waveguide and used as a photomixing source from 75 to 170 GHz. Maximum power conversion efficiency of 1.8% was obtained at 75 GHz, where an optical input of +10 dBm yielded a nonsaturated millimeter-wave (mm-wave) power of -7.5 dBm. Optimizing the photomixer backshort tuning at individual frequencies showed that the mm-wave power decreased with frequency to a level of -30 dBm at 170 GHz. Fixed tuning allowed the generation of power across the full waveguide band from 75 to 110 GHz, with a variation within 5 dB across the majority of the band.

High-purity millimetre-wave photonic local oscillator generation and delivery

Tunable millimetre wave generation by spectrally slicing a phase modulated lightwave is demonstrated. The low phase noise signal (-95 dBc/Hz at 100 kHz offset) can be delivered through a 9 km fibre link, with no noticeable power penalty.

Nonlinearity and Noise Effects in Multi-Level Signal Millimeter-Wave Over Fiber Transmission Using Single and Dual Wavelength Modulation

We transmit multilevel quadrature amplitude modulation (QAM) data-IEEE 802.16 schemes-at 20 MSps and an orthogonal frequency-division multiplexing (OFDM) 802.11 g signal (54 Mbps) with a 25 GHz millimeter-wave over fiber system, which employs a dual wavelength source, over 20 km of single mode fiber. Downlink data transmission is successfully demonstrated over both optical and wireless (up to 12 m) paths with good error vector magnitude. An analysis of two different schemes, in which data is applied to one (single) and both (dual) of the wavelengths of a dual wavelength source, is carried out. The system performance is analyzed through simulation and a good match with experimental results is obtained. The analysis investigates the impact of Mach-Zehnder modulator (MZM) and RF amplifier nonlinearity and various noise sources, such as laser relative intensity noise, amplified spontaneous emission, thermal, and shot noise. A comparison of single carrier QAM IEEE 802.16 and OFDM in terms of their sensitivity to the distortions from MZM and RF amplifier nonlinearity is also presented.

Analysis and Demonstration of a Fast Tunable Fiber-Ring-Based Optical Frequency Comb Generator

Fiber-ring-based optical frequency comb generators are analyzed to understand their behavior and limitations. A numerical frequency-domain model is described for studying dispersion and other phase mismatch causing effects in the fiber ring cavity, as well as for predicting the spectral and temporal evolutions of the comb in time. The results from this analysis are verified with experimental measurements. A flat optical comb, with a terahertz span within a 6-dB power envelope and containing 100 comb lines, with a suppressed central comb line, is demonstrated. The comb shows an excellent coherence dependent on the phase noise from the radio frequency synthesizer that drives the comb generator. Improvement in the error correction loop also enables the comb spacing to be set at precise 12.5-MHz intervals without having to adjust the system. Fast frequency switching of the comb line spacing is demonstrated for the first time. The comb line spacing can be switched to any operation frequency with a resolution of 12.5 MHz between 6 and 12.5 GHz, as limited only by the microwave circuit used. The switching time is less than 1 s, and the spectral profile of the comb is maintained.

Multilevel Modulated Signal Transmission Over Serial Single-Mode and Multimode Fiber Links Using Vertical-Cavity Surface-Emitting Lasers for Millimeter-Wave Wireless Communications

Quadrature phase-shift keying, 16 quadrature amplitude modulation (QAM), and 64-QAM data transmission - Worldwide Interoperability for Microwave Access modulation schemes - at 6 and 20 MS/s is demonstrated for a link that emulates a cost-effective 1.55 mum vertical-cavity surface-emitting laser based radio over fiber millimeter-wave indoor picocellular system. The system consists of a concatenation of 20-km single-mode fiber and 300-m multimode fiber links between a central office and remote antenna unit and employs remote 30-GHz local oscillator delivery. Successful transmission over both optical and wireless paths is achieved with good error vector magnitude performance recorded for both uplink and downlink. The performance is compared to other demonstrations of multilevel signal transmission in millimeter-wave over fiber systems.

Millimetre wave generation using an optical comb generator with optical phase-locked loops

We report the generation of millimetre wave signals to 158 GHz with phase noise better than 75 dBC/Hz at 100 kHz offset, by heterodyning of two lasers which are optically phase locked through an optical comb generator.

Multilevel modulated signal transmission for millimeter-wave radio over fiber system

quadrature phase-shift keying (QPSK), 16 quadrature amplitude modulation (QAM), and 64-QAM data transmission at 6 MS/s are successfully demonstrated in a 60 GHz millimeter-wave over fiber system with good error vector magnitude performance recorded for the downlink. The system utilizes a photonic method to produce the 60 GHz carrier by employing a dual wavelength source consisting of an optical phase modulator and DWDM filter. The transmission of the data over a 20 km span of fiber has been performed with very good stability over a measurement period of 128 minutes.

The Temporal Drift Due to Polarization Noise in a Photonic Phase Reference Distribution System

The temporal drift due to the polarization noise in an ultralow temporal drift photonic phase reference distribution system is analyzed. The temporal drift is shown to be associated with the polarization changes, the differential group delay of the subsequent parts, and, the state of polarization dispersion of the photonic local oscillator signal. Such temporal drift cannot be corrected by line length correction schemes. As an example, polarization changes from a fiber stretcher are presented, discussed, and identified as one of the major contributors to the system temporal drift. A numerical model is developed. The magnitude and statistical distribution (based on random coupling) of the temporal drift excited by the polarization change of the fiber stretcher are investigated. Experimental work demonstrates that reduction in the polarization change successfully reduces the temporal drift, as predicted by the theory and simulation.

Low-Cost, Continuously Tunable, Millimeter-Wave Photonic LO Generation Using Optical Phase Modulation and DWDM Filters

We report on a low-cost technique for the photonic generation of wideband continuously tunable millimeter-wave local oscillator signals. It is based on sideband filtering using an optical phase modulator and thin-film dense wavelength- division-multiplexing filters. The generated millimeter-wave signal exhibits low phase noise, and its frequency covers the W - and F -bands, from 75 to 140 GHz.

Millimeter-Wave Wireless Local Area Network Over Multimode Fiber System Demonstration

A radio over fiber system using millimeter-wave for downlink (DL) and intermediate frequency for uplink (UL) transmission, that includes a wireless path and uses multimode fiber (MMF), is investigated by throughput measurements. Live wireless local area network transmissions (IEEE 802.11g, 54 Mbps), are upconverted to 25.2 GHz for the DL by using an optical phase modulator and optical filter millimeter-wave generation approach. Both DL and UL data were successfully transmitted between a mobile unit (MU) and commercial access point (AP), via a remote antenna unit connected to the AP by a 300-m MMF link. The measurements, for the full link using omni-directional antennas at the MUs, demonstrate good signal coverage throughout an office area of 12.8 × 7.2 m2 and indicate that a coverage area four times this size would be possible if the antenna were placed in the center of a room.