Showing papers by "Alwyn J. Seeds published in 2006"

Microwave Photonics

Abstract: The low-loss wide bandwidth capability of opto-electronic systems makes them attractive for the transmission and processing of microwave signals, while the development of high-capacity optical communication systems has required the use of microwave techniques in optical transmitters and receivers. These two strands have led to the development of the research area of microwave photonics. This paper reviews the development status of microwave photonic devices, describes their systems applications, and suggests some likely areas for future development

A high responsivity, broadband waveguide uni-travelling carrier photodiode

Abstract: A 02 A/W responsivity waveguide-uni-travelling carrier photodiode with a -3 dB electrical frequency response > 108 GHz is demonstrated Up to -5 dBm electrical power at 110 GHz, and 28 mA photocurrent (DC excitation) were detected The photodiode was also integrated with an antenna to permit a record breaking emission of up to 148 μW at 457 GHz and 25 μW at 914 GHz

Full-duplex DOCSIS/WirelessDOCSIS fiber-radio network employing packaged AFPM-based base-stations

Abstract: The simultaneous wireline (600 MHz) and wireless (5.5 GHz) transmission of data over cable service interface specification (DOCSIS) signals in a hybrid fiber-radio access network is presented. The DOCSIS signal wireless replica is generated by means of an optical harmonic up-conversion technique based on a dual-drive Mach-Zehnder modulator. The optical signal is fed to a base station (BS) where a packaged asymmetric Fabry-Pe/spl acute/rot modulator/detector acts simultaneously as a photodetector and an optical modulator. At the BS, the DOCSIS signals can be fed either to a wireline or a wireless access network, in a highly flexible approach. Full-duplex operation has been demonstrated for both access types, including indoor wireless transmission.

Wideband fibre-agnostic DAS using pluggable analogue optical modules

Abstract: We report a wideband (370?2500MHz) distributed antenna system (DAS) which uses pluggable analogue optical transceivers based on the industry standard small form-factor pluggable (SFP) format. The use of pluggable optics has a number of advantages such as hot-swappability, upgradeability and low initial cost, which has been exploited in the digital world for several years but has not been investigated to the same extend for analogue applications. In addition to the wideband system being RF signal agnostic, the system can also operate over different types of fibre, both SMF and MMF, or coaxial cable, by simply changing the transceiver module.

Broadband access using wireless-over-fibre technologies

Abstract: This paper describes a number of wireless-over-fibre technologies for broadband access which are being investigated in the Photonics Group at University College London (UCL). In particular, the paper will report the asymmetric Fabry-Perot modulator/detector (AFPM), functioning not only as an optical modulator in the uplink direction, but also as a conventional photodetector in the downlink direction in a single device. Compared to the existing waveguide type electro-absorption modulator, the AFPM is polarisation-insensitive to light, simpler to fabricate and uses only a single optical fibre for both uplink and downlink transmissions, and therefore has the potential to lower the costs of future picocell deployments. Direct modulation of a semiconductor laser is the simplest way to generate modulated optical signals. In the presence of multiple large modulation signals, however, intermodulation or inter-channel distortion can easily be generated in the semiconductor laser and affect other lower power neighbouring channels. A feed-forward linearisation technique for directly modulated semiconductor lasers, capable of operating at frequencies above 5 GHz, has been developed and will be described in detail in this paper. Most modern commercial buildings already have a multimode optical fibre (MMF) infrastructure for carrying the Ethernet data. To provide cost-effective and reliable indoor cellular and wireless local area network (WLAN) coverage without dependence on the radio penetration from outside base-stations, it is highly desirable that the same MMF infrastructure be used to carry these additional services between the equipment room and the remote antenna units around the building. Although not previously regarded as having sufficient bandwidth, it has now been shown that MMF can successfully carry microwave modulated optical signals, including GSM1800 and UMTS cellular radio. Use of MMF for multiservice, multioperator in-building radio coverage has been demonstrated in a collaboration between UCL and the University of Cambridge and will be described in this paper. As the number of cellular and broadband WLAN devices increases, the lower parts of the radio spectrum are becoming more and more congested. To meet the demand for ever higher data transmission rates, other parts of the radio spectrum are being considered for these applications, particularly the millimetre-wave region (30 GHz and above). One of the challenges facing such systems is the generation and delivery of a low phase noise precisely synchronised local oscillator signal. In this paper, a simple optical heterodyne source with two injection locked slave lasers and a more environmentally robust source using an optical injection phase lock loop will be described, together with signal distribution using a bidirectional semiconductor optical amplifier in a coarse wavelength division multiplex fibre ring architecture. Finally it will be argued in the conclusions that future broadband wireless-over-fibre access networks will be required to provide multiservice and multi-operator coverage for buildings, and having the required technologies at sufficiently low cost will be the key factor to success.

Signal stability in periodically amplified fiber transmission systems using multiple quantum well saturable absorbers for regeneration

Abstract: The use of multiple quantum well (MQW) saturable absorbers (SAs) for signal regeneration in periodically amplified fiber transmission systems is explored. A systematic study of signal destabilization resulting from incomplete saturation of MQW SAs used for regeneration, and of means of overcoming such destabilization, is presented. A computer model for MQW SAs, which considers the asymmetric Fabry-Pe/spl acute/rot (AFP) cavity structure commonly employed to increase the contrast of such devices, is presented. The model is used to simulate nitrogen-implanted MQW SAs with 7000 km when the two components are combined.

Photonic synthesis of THz signals

Abstract: In this paper we present a review of our work on photonic synthesis of high spectral purity THz signals. This work includes novel developments on optical frequency comb generation (integrated, 2THz span, 25 GHz spacing), frequency locking of semiconductor lasers (1kHz channel stability, 10 ns switching time) and high speed photodetectors integrated with antennas (3dB bandwidth > 108 GHz, 0.2 A/W responsivity , 148 muW output power at 457 GHz)

A Monolithic MQW InP/InGaAsP-Based Comb Generator

Abstract: We report a monolithic optical frequency comb generator using quaternary/quaternary multiple quantum well InP/InGaAsP material as phase modulator and gain medium in a Frequency Modulated (FM) laser design. The modulation was generated by quantum confined Stark effect to achieve a comb-line spacing of 24.4 GHz. The laser was fabricated using a single epitaxial growth step and quantum well intermixing to realize low loss phase and modulation sections. The resulting comb generator produces lines with a spacing exactly given by the modulation frequency, differential phase noise between adjacent lines of ?82 dBc/Hz at 1 kHz offset and a comb spectrum width of up to 2 THz.

Enhanced linear dynamic range of asymmetric Fabry-Pe/spl acute/rot modulator/detector

Abstract: An InGaAsP multiple-quantum-well asymmetric Fabry-Pe/spl acute/rot modulator/detector has been developed for radio-over-fiber systems. The measured bandwidth is more than 6 GHz and the total insertion loss is 7.1 dB. The property of nonlinearity and spurious-free dynamic range (SFDR) has been studied theoretically. By optimizing the operation optical wavelength and bias voltage based on the numerical simulation, fifth-order nonlinearity dominates the intermodulation distortion and an SFDR of 101 dB/spl middot/Hz/sup 4/5/ has been achieved experimentally.

A novel pulse source for low jitter optical sampling : a rugged alternative to mode-locked lasers

Abstract: A novel low jitter optical pulse source for applications including optical sampling has been modelled and experimentally verified using commercially available photonic components. Dispersion and non-linear fibre effects were utilised to compress a periodic optical waveform to generate pulses of the order of 10-15 picoseconds, via soliton-effect compression. Modelling of variable dispersion fibre indicates that future work will enable pulse compression to sub-picosecond durations. Attractive features of this new pulse source include electronically tuneable repetition rates over a continuous range at frequencies above ~1.5 GHz, ultra-short pulse duration (10-15 ps now, 100's fs planned), and low timing jitter as consistently measured by both harmonic analysis and single-sideband (SSB) phase noise measurements. In addition, the system is inherently robust to thermal effects unlike some low jitter pulse source alternatives, and does not require precise optical alignment. Timing jitter analysis reveals that the optical pulse timing jitter is currently limited by the mid-range specification microwave source used to create the initial periodic waveform. In order to overcome stimulated Brillouin scattering at high launch powers into the compression fibre, phase modulation was applied to the pulse train, and the timing jitter implications of this are discussed. It is believed that this is the first time that detailed timing jitter analysis has been performed on a soliton-effect compression scheme.

100 GHz spaced 10 Gbit/s WDM over 10 /spl deg/C to 70 /spl deg/C using an uncooled DBR laser

Abstract: 100 GHz spaced 10 Gbit/s (NRZ, PRBS 2/sup 31/-1) WDM transmission is demonstrated with an uncooled DBR laser. The wavelength of the laser was stabilised within 2 GHz from 10 /spl deg/C to 70 /spl deg/C using a predicting algorithm.

100 GHz Spaced 10 Gbit/s WDM over 10 oC to 70 oC Using an Uncooled DBR Laser

Abstract: 100 GHz spaced 10 Gbit/s (NRZ, PRBS 231-1) WDM transmission is demonstrated with an uncooled DBR laser. The wavelength of the laser was stabilised within 2 GHz from 10 oC to 70 oC using a predicting algorithm.

Monolithically integrated QCSE-tuned InGaAsP MQW ridge waveguide DBR laser

Abstract: The first QCSE-tuned ridge waveguide InGaAsP MQW DBR laser monolithically integrated with QW-intermixed tuning sections is demonstrated. QCSE is used for tuning with minimal thermal effects over /spl sim/7 nm for <2.5 V applied voltage change.

10 Gb/s noise suppression using an ion implanted waveguide saturable absorber

Abstract: Noise suppression of 3 dB per pass is demonstrated using a top-implanted passive InGaAsP/InGaAsP multiple quantum well ridge waveguide saturable absorber. The contrast ratio and recovery time are 3 dB and ~16 ps respectively.

Low cost packaging of a reflective electro-absorption modulator/detector with optimized spurious free dynamic range

Abstract: A packaged high speed reflective electroabsorption transceivers for radio-over-fiber applications is demonstrated. The transceiver, an AFPMD (Asymmetric vertically addressed Fabry-Perot Modulator/Detector), is successfully packaged into a standard module, originally intended for 10 Gbit/s Ethernet detectors. The packaging process and the electrical, optical and thermal performance of the packaged component are presented. A bandwidth of 6 GHz, a total reflective optical coupling loss of 7.1 dB and a responsitivity of 0.14 mA/mW are accomplished. By optimizing the operation optical wavelength and bias voltage, fifth-order nonlinearity dominates the intermodulation distortion and a spurious free dynamic range (SFDR) of 101dB center dot Hz(4/5) at 5.554GHz can be achieved experimentally.

Intermodulation Distortion Suppression in a Full-Duplex Radio-over-Fibre System Employing Asymmetric Fabry-Perot Modulator/Detector

Abstract: The property of intermodulation distortion in a full-duplex radio-over-fibre system with Asymmetric Fabry-Perot Modulator/Detector was investigated. By employing the balanced RF input powers, intermodulation distortion was suppressed and a SFDR of 99dB. Hz2/3 has been achieved.

Experimental Demonstration of Full-Duplex DOCSIS Signal Transmissions over a Wireline/Wireless-Fibre Access Network

Abstract: A fibre-radio access network architecture for simultaneous wireline and wireless transmissions of Data Over Cable Service Interface Specification (DOCSIS) signals is presented. An all-optical harmonic up-conversion technique using a dual-drive Mach-Zehnder modulator (DD-MZM) is employed at the central station while an InGaAsP/InGaAsP multiple quantum well (MQW) Asymmetric Fabry-Perot Modulator/Detector (AFPM) functions as a single optical/electrical transducer performing optical intensity modulation and photodetection simultaneously at the base station. Full-duplex operation is demonstrated for both access types in an indoor laboratory environment as well as in a small-scale outdoor field trial.