107 research outputs found

    A Linearized Analog Microwave Photonic link with an Eliminated Even-order Distortions

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    International audienceAn improved linearized analog microwave photonic link (AMPL) with significant multioctave bandwidth performance is experimentally presented. The proposed AMPL configuration is based on a double dual-parallel Mach-Zehnder modulator and a differential balanced photodetector (BPD). Explicitly, a gallium arsenide (GaAs)-based modulators are used as opposed to the commonly known lithium niobate (LiNbO3) modulators, due to its robustness in the harsh environment. The system configuration is designed to process a carrier suppressed double-sideband signal through the link, and then at the receiver, a carrier suppressed double-sideband signal is combined with an unmodulated optical carrier, which is transmitted through a polarization maintained (PM) optical fiber. In our experiment, only PM-based optical components are used for better system stability. The developed theoretical model of the proposed system illustrates the elimination of even-order distortions and a high suppression to the third-order intermodulation distortions at the BPD. Consequently, the fundamental signal to interference ratio of 60 dB was experimentally achieved. Furthermore, experimental results, simultaneously, demonstrate a significant increase of second-order spurious-free dynamic range and third-order spurious-free dynamic range by 19.5 and 3.1dB, respectively, compared to the previously reported AMPL performances based on polarization multiplexing dual-parallel Mach-Zehnder modulator. To the best of our knowledge, this is the highest dynamic range AMPL system performance deploying GaAs electro-optic modulator which has most significant capabilities in managing RF signals and exhibits excessive performance in harsh operating environment in terms of thermal stability, power-handling, radiation resistance and longevity for aerospace, defense, and satellite-to-ground downlink communication system applications

    Fifth-order Polynomial Predistortion for Mach-Zehnder Modulator Linearization

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    Modern wireless applications require access to ultra-wide instantaneous RF bandwidths to provide frequency agility and multi-band RF processing. Wireless communications, radar and electronic warfare are examples of applications that will benefit from wideband multi-function transceivers. The role of the front-end filtering is critical in order for the multi-function transceiver to achieve adequate RF performance. Integrated electric filters are unable to achieve the required frequency selectivity and tuning range mainly due to low Q of on-chip inductors. This renders a complete integrated solution impractical. Normally, high frequency and high selectivity filters are achieved with off-chip bulky SAW filters. The limitation of electrical filters has motivated the employment of RF photonic receivers. The main issue with photonics is the cost but in recent times the emergence of silicon photonics has enabled the potential of RF photonics receivers to be implemented at a low cost. The use of photonics gives access to devices that can achieve really high Q and high integration at high frequencies. At the heart of the photonic receiver is the Mach-Zehnder modulator (MZM). It modulates the received signal from the antenna to the optical carrier. The major issue with the MZM is: it is non-linear and wideband. The MZM is placed before the photonic filter and right after the antennae so interferers received with the desired RF signal generate intermodulation products at the output of the MZM. The intermodulation products can be very close to the desired RF signal so they cannot be filtered out by the photonic filter and may corrupt the desired RF signal. To curtail the effects of the MZM non-linearity, linearization schemes are implemented to reduce the amplitude of the intermodulation products generated when the MZM receives interferers. This thesis work focuses on two main issues, Firstly, analysis of the intermodulation products generated by the MZM when a two tone RF signal is applied. Secondly, a literature review is done to examine the existing linearization schemes. Based on the predistortion linearization scheme, a new fifth-order predistortion is proposed. The proposed fifth-order predistortion is fabricated in GP 65nm TSMC CMOS process. The proposed fifth-order linearization achieves high IM3 suppression~ 20dB at high modulation index ~49.7% with 49.2mW of power consumed

    Techniques for nonlinear distortion suppression in radio over fiber communication systems

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    Radio over fiber (RoF) is a promising technology that will indisputably compete as a viable solution for future wireless, cellular and broadband networks. RoF, when combined with dense wavelength division multiplexing (DWDM), such as SONET/SDH, it can become a complete flexible and cost effective solution to the global telecommunication network, where asynchronous and synchronous communications may be efficiently supported. Subcarrier modulation (SCM) is utilized to modulate a RF signal on light, which in turn will be transmitted by fiber. Unfortunately, the transmission in most cases may become corrupted by nonlinear distortion that is induced by the nonlinear response of the optical transmitter, optical receiver and chromatic dispersion of the single mode fiber (SMF). The nonlinear distortion degrades the receiver sensitivity, which leads to a poor bit error rate (BER) and spurious free dynamic range (SFDR). Ultimately, this will increase RoF system costs and render it impractical. The objective of this thesis is to develop linearization methods that reduce the nonlinear distortion, increase receiver sensitivity and increase SFDR. The designs should also address the entire RoF system by combating the optical power fading issue that will be discussed in Chapter 2 without significantly adding great expense and complexity to the RoF system. Four optical linearization methods are proposed and shown through extensive simulation and/or experimentation to outperform similar existing linearization systems described in literature. The proposed single wavelength balanced system is shown to improve the suppression of 2nd order distortion over the dual wavelength balanced system, thereby leading to greater improvement in receiver sensitivity and BER. Furthermore, the design also suppresses relative intensity noise (RIN). The proposed tunable fiber Bragg grating (FBG) balanced system is capable of suppressing both 2 nd and 3 rd order distortions despite which RF carrier that is used. Furthermore, it was shown to outperform the conventional RoF system in terms of receiver sensitivity and BER. The proposed asymmetric Mach-Zehnder modulator (MZM) has been shown to generate optical single sideband (OSSB) transmissions and outperform the dual-parallel modulator, by improving 3rd order intermodulation distortion (3IMD) suppression and increasing SFDR. The final proposed linearization method is the mixed-polarization MZM, where OSSB is also generated and outperforms the conventional OSSB RoF system in terms of 3IMD suppression and SFDR. Furthermore, close form expressions for SFDR are developed for the final two designs, which is crucial in study of their stability and performance

    Injection-locked Semiconductor Lasers For Realization Of Novel Rf Photonics Components

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    This dissertation details the work has been done on a novel resonant cavity linear interferometric modulator and a direct phase detector with channel filtering capability using injection-locked semiconductor lasers for applications in RF photonics. First, examples of optical systems whose performance can be greatly enhanced by using a linear intensity modulator are presented and existing linearized modulator designs are reviewed. The novel linear interferometric optical intensity modulator based on an injection-locked laser as an arcsine phase modulator is introduced and followed by numerical simulations of the phase and amplitude response of an injection-locked semiconductor laser. The numerical model is then extended to study the effects of the injection ratio, nonlinear cavity response, depth of phase and amplitude modulation on the spur-free dynamic range of a semiconductor resonant cavity linear modulator. Experimental results of the performance of the linear modulator implemented with a multi-mode Fabry-Perot semiconductor laser as the resonant cavity are shown and compared with the theoretical model. The modulator performance using a vertical cavity surface emitting laser as the resonant cavity is investigated as well. Very low VÏ€ in the order of 1 mV, multi-gigahertz bandwidth (-10 dB bandwidth of 5 GHz) and a spur-free dynamic range of 120 dB.Hz2/3 were measured directly after the modulator. The performance of the modulator in an analog link is experimentally investigated and the results show no degradation of the modulator linearity after a 1 km of SMF. The focus of the work then shifts to applications of an injection-locked semiconductor laser as a direct phase detector and channel filter. This phase detection technique does not iv require a local oscillator. Experimental results showing the detection and channel filtering capability of an injection-locked semiconductor diode laser in a three channel system are shown. The detected electrical signal has a signal-to-noise ratio better than 60 dB/Hz. In chapter 4, the phase noise added by an injection-locked vertical cavity surface emitting laser is studied using a self-heterodyne technique. The results show the dependency of the added phase noise on the injection ratio and detuning frequency. The final chapter outlines the future works on the linear interferometric intensity modulator including integration of the modulator on a semiconductor chip and the design of the modulator for input pulsed light

    Performance improvement and cost reduction techniques for radio over fiber communications

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    Advanced cost reduction and performance improvement techniques conceived for Radio Over Fiber (ROF) communications are considered. ROF techniques are expected to form the backbone of the future 5G generation of wireless networks. The achievable link performance and the associated deployement cost constitute the most salient metrics of a ROF architecture. In this paper, we commence by providing a rudimentary overview of the ROF architecture and then elaborate on ROF techniques designed for improving the attainable system performance. We conclude by describing the ROF techniques conceived for reducing the ROF system installation costs

    True linearized intensity modulation for photonic analog to digital conversion using an injection-locked mode-locked laser

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    A true linearized interferometric intensity modulator for pulsed light has been proposed and experimentally presented in this thesis. This has been achieved by introducing a mode-locked laser into one of the arms of a Mach-Zehnder interferometer and injection-locking it to the input light (which is pulsed and periodic). By modulating the injection-locked laser, and combining its output light with the light from the other arm of interferometer in quadrature, one can achieve true linearized intensity modulator. This linearity comes from the arcsine phase response of the injection-locked mode-locked laser (as suggested by steady-state solution of Adler\u27s equation) when it is being modulated. Mode-locked lasers are fabricated using a novel AlGaInAs-InP material system. By using the BCB for planarization and minimizing the metal pad size and directly modulating the laser, we have achieved very effective fundamental hybrid mode-locking at the repetition rate of ~ 23 GHz. This laser also provided the short pulses of 860 fs and 280 fs timing jitter integrated from 1 Hz- 100 MHz. The linearized intensity modulator has been built by using two identical two-section mode-locked lasers with the same length, one as the slave laser in one of the arms of the Mach-Zehnder interferometer injection-locked to the other one as the master which is the input light to the modulator. A low V? of 8.5 mV is achieved from this modulator. Also the current of the gain section or the voltage of the saturable absorber section of the slave laser has been used to apply the modulation signal. A spur free dynamic range of 70 dB.Hz2/3 is achieved when modulating the modulator through the saturable absorber. Modulating the saturable absorber provides a reduced third-order intermodulation tone with respect to modulating the gain. This is simply because of the unwanted amplitude modulation created when modulating the gain section current. Finally an improved design is proposed and demonstrated to improve the modulator performance. This is achieved by introducing a third section to the laser. Using the impurity free vacancy disordering technique the photoluminescence peak of this section is blue-shifted selectively and therefore there would not be any absorption in that passive section. By applying the modulation signal to this passive section rather than applying it to the gain section or saturable absorber section, the amplitude and phase modulation could be decoupled. The experimental results have presented here and an almost six-fold reduction in V? and 5 dB improvement in spur free dynamic range have been achieved. The proposed and demonstrated configuration as an analog optical link has the potential to increase the performance and resolution of photonic analog-to-digital converters

    Orthogonal frequency division multiplexing for optical access networks

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    Orthogonal Frequency Division Multiplexing (OFDM) is a modulation scheme with numerous advantages that has for years been employed as the leading physical interface in many wired and wireless communication systems. Recently, with advancements made in digital signal processing, there has been a surge of interest in applying OFDM techniques for optical communications. This thesis presents extensive research on optical OFDM and how it is being applied in access networks. With the aid of theoretical analysis, simulations and experiments, it is shown that the system performance of direct-detection optical OFDM (DD-OOFDM) in the presence of MZM non-linear distortion can be improved by proper biasing and selection of appropriate drive to the MZM. Investigations are conducted to illustrate how a variation in the number of subcarriers and the modulation format influences the sensitivity of the DD-OOFDM system to the MZM non-linear distortion. The possibility of improving the spectral efficiency by reduction of the width of the guard band is also investigated. This thesis also looks into the radio-over-fibre (RoF) transmission of Multiband OFDM UWB as a transparent and low-cost solution for distributing multi-Gbit/s data to end-users in FTTH networks. Due to relaxed regulatory requirements and the wide bandwidth available, UWB operation in the 60-GHz band is also considered for this FTTH application scenario. Four techniques for enabling MB-OFDM UWB RoF operation in the 60-GHz band are experimentally demonstrated. The impacts of various parameters on the performance of the techniques as well as the limitations imposed by fibre distribution are illustrated. Finally, a digital pre-distorter is proposed for compensating for the MZM non-linearity. Experimental demonstration of this digital pre-distortion in an UWB over fibre transmission system shows an increased tolerance to the amplitude of the driving OFDM signal as well as an increase in the optimum modulation index of the OFDM signal

    Optical single-sideband modulation with tunable optical carrier to sideband ratio in radio over fiber systems

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    Radio over fiber (RoF) has been considered as a promising technology for the distribution of the future high capacity wireless signals such as ultra-wideband and millimeter-wave signals. In RoF systems, optical subcarrier modulation (SCM) is commonly used, such as optical double sideband (ODSB) modulation, and optical single sideband (OSSB) modulation. However, ODSB modulation will introduce RF signal power fading due to the fiber chromatic dispersion. To evade this problem, conventional optical single sideband (OSSB) modulation was proposed and demonstrated. Unfortunately in the conventional OSSB, the modulation efficiency, defined as optical carrier-to-sideband ratio (OCSR) in optical power, is extremely low for small modulation index, i.e. low driven voltage used. On the other hand, when high voltage is applied to the modulator, i.e. high modulation index used, the nonlinear distortion will be induced due to the nonlinearities of the optical modulator response, which will degrade the receiver sensitivity and lead to a poor bit error rate (BER) and spurious free dynamic range (SFDR). Eventually, this will increase RoF system cost and render it impractical. So far, suppressing the OCSR has become a popular way to improve the modulation efficiency. Lots of related techniques have been proposed and demonstrated. The objective of this thesis is to develop a simple modulation technology that OSSB modulation and tunable OCSR are obtained simultaneously only by adjusting the direct current (DC) bias of two parallel non-ideal Mach-Zehnder Modulators (MZMs). In this thesis, the theoretical analyses to prove the functions of this modulation technique are given out first. Then by comparing the theoretical analyses with simulation results, it is found that the results are well matched. Here the impacts of imperfect situations are concerned: bias voltage drift, phase imbalance of the two parallel MZMs, mismatch of splitting and combining coupler's factors, MZM extinction ratio imbalance, inter-modulation distortions (IMDs), high order distortions and chromatic dispersion. The functions and reliability of this modulation technique are deeply discussed. Furthermore, some methods to compensate the impacts due to the non-ideal situations are also considered. Finally, the experimental results are presented to validate the proposed techniqu

    Feed-forward linearisation of a directly modulated semiconductor laser and broadband millimetre-wave wireless over fibre systems.

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    This thesis is concerned with reduction of non-linear distortion in a directly modulated uncooled semiconductor laser using feed-forward compensation and investigating the performance of broadband millimetre-wave wireless over fibre systems. One of the key elements that determine the performance in a fibre optic link is the linearity of the optical source. Direct modulation of an uncooled semiconductor laser diode is a simple and cost effective solution. However, the distortion and noise generated by the laser limit the achievable dynamic range and performance in a system. Feed-forward linearisation is demonstrated at 5 GHz, the highest operating frequency reported, with 26 dB third order intermodulation distortion suppression and simultaneous noise reduction leading to enhanced spurious free dynamic range of 107 dB (1Hz). The effectiveness of feed-forward in a multi-channel system is investigated. Laser non-linearity can cause spectral re-growth and interchannel distortion that can completely mask the adjacent channel. A significant 11 dB interchannel distortion suppression and 10.5 dB power advantage is obtained compared to the non-linearised case. These results suggest that feed-forward linearisation arrangement can make a practical multi-channel or multi-operator wireless over fibre system. In the second part of this thesis the first experimental transmission of wireless data over fibre with remote millimetre-wave local oscillator delivery using a bi-directional semiconductor optical amplifier in a full duplex system with 2.2 km coarse wavelength division multiplexing fibre ring architecture is demonstrated. The use of bi-directional SOAs in place of unidirectional erbium doped fibre amplifier or unidirectional SOAs, together with the use of CWDM and optical distribution of the local oscillator signal allow substantial reduction in overall complexity and cost. Successful transmission of data over 12.8 km fibre is achieved with clear and well defined constellations and eye diagrams as well as 10.5% and 7.8 % error vector magnitude values for the downlink and uplink directions, respectively. The thesis also presents an implementation and performance of a millimetre-wave gigabit wireless over fibre system. CWDM devices such as uncooled laser diodes and passive components are used for the first time in a gigabit system allowing cost savings compared to dense WDM. This makes such solutions more attractive for millimetre-wave access systems. Optically modulated gigabit wireless data signals to and from the base stations are distributed at 5 GHz and up-converted using a remotely delivered LO source. Eye diagrams and bit error rate are measured to assess the system performance
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