Optical Communication

Optical communication is very much useful in telecommunication systems, data processing and networking. It consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its desired destination, and a receiver that reproduces the message from the received optical signal. It presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. The chapters cover general concepts of optical communication, components, systems, networks, signal processing and MIMO systems. In recent years, optical components and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on optical devices, networking, signal processing, and MIMO systems and other enhanced functions for optical communication. This book is targeted at research, development and design engineers from the teams in manufacturing industry, academia and telecommunication industries

Optoelectronic Frequency Stabilization Techniques in Forced Oscillators

Forced frequency stabilization techniques of self-injection locking (SIL) and self-phase locked loop (SPLL) have been demonstrated to be effective for phase noise reduction. In SIL scheme, a portion of the oscillator output is directly injected back to the oscillator after passing through a long delay while in SPLL, the delayed signal is used to compare against a non-delayed signal to generate an error signal which will be used to control the oscillator frequency. The published literature and reported patent investigations has revealed that SIL and SPLL are only being used independently, whereas in this thesis SILPLL is introduced for the first time by simultaneously combining of SIL and SPLL; the control theory based modeling of SIL, SPLL, and SILPLL techniques are developed and the simulation results have indicated that phase noise of the oscillation signal is enhanced as injection locking removes phase noise in far-out offset frequency, while phase locking effectively reduces the close-in to carrier phase noise. Optimum delay length and delay parameters are identified for the most effective performance. Both SIL and SPLL techniques require a low noise figure and long fiber optic delay lines to provide substantial phase noise reduction, but the long delay generates undesirable sidemodes that are seen within 20kHz to 200kHz offset to carrier for fiber optic delays from 10km to 1km and are difficult to be filtered out by electrical filters. Therefore, forced oscillation technique employing short and long delay is proposed to suppress these sidemodes. In this dissertation, experimental results of a dual self-injection locking (DSIL) and dual self-phase locked loop (DSPLL) employing short and long delays have been proposed for this sidemode suppression, while maintaining same amount of phase noise reduction provided by the long delay. As an example of DSIL, sidemode suppression of more than 20dB for fiber delay links of 1km and 5km have been experimentally achieved compared to a single 5km long SIL with a phase noise reduction of 40dB (in reference to free running oscillator) at 10kHz offset from carrier for both standard OEO and a self-seeded structure with electrical 3 port oscillator at 10GHz; for a DSPLL fiber delay lines of 3km and 5km, a sidemode suppression of 29dB have also been experimentally achieved compared to SPLL of 5km with a phase noise reduction of 30dB (in reference to free running oscillator) at 10kHz offset from carrier. For the case of SPLL, phase locking performance of a 10GHz oscillation signal are experimentally evaluated as various methods of phase locking are compared. Experiment results that demonstrate the benefit of SILPLL incorporating dual delays have been reported for the first time corroborating analytical predictions. A dual SILPLL (DSILPLL) system with 3km and 5km fiber delay has been implemented, and measured phase noise reduction of 40dB provided by DSILPLL is the same as DSIL at 10kHz offset. However, at 1kHz offset, DSILPLL provides a phase noise reduction of 52dB which is 11dB better than DSIL; at 300Hz offset, DSILPLL provides 70dB reduction while DSIL provides only 42dB reduction. In summary, DSILPLL is effective for sidemode suppression and phase noise reduction, where SPLL using tunable MZM with DSIL of a VCO provides the best performance improvement over other investigated topologies. Due to the advances in low noise electronics and broad bandwidth of the optical components used in the DSILPLL system, the DSILPLL technique has the potential to create highly stable RF oscillators approaching 100GHz.Ph.D., Electrical Engineering -- Drexel University, 201

Generation of Frequency Tunable and Low Phase Noise Micro- and Millimeter-Wave Signals using Photonic Technologies

The concept of generating micro- and millimeter-wave signals by optical means offers a variety of unique features compared to purely electronics such as high frequency tunability, ultra-wideband operation and the possibility to distribute micro- and millimeter-wave signals over kilometers of optical fiber to a remote site. These features make the photonic synthesizer concept a very interesting alternative for several applications in the micro- and millimeter-wave regime. This thesis focuses on the realization and characterization of different photonic synthesizer concepts for the optical generation of frequency tunable and low phase noise micro- and millimeter-wave signals. Advanced microwave photonic approaches utilizing external optical modulation and optical multiplication will be presented, offering high frequency optical millimeter-wave generation up to 110 GHz with superior performances in terms of maximum frequency tuning ranges and phase noise characteristics. In addition, the concept of a novel dual-loop optoelectronic oscillator will be presented that enables optical millimeter-wave signal generation without the need of any electronic reference oscillator. By using the developed dual-loop optoelectronic oscillator, microwave signal generation with tuning ranges in the gigahertz regime has been experimentally demonstrated for the first time.Das Konzept der optischen Mikro- und Millimeterwellen-Generation bietet gegenüber rein elektronischen Konzepten eine Vielzahl einzigartiger Möglichkeiten, bedingt durch die hohe Frequenzabstimmbarkeit, die extrem hohe Bandbreite sowie die Möglichkeit, Mikro- und Millimeterwellen-Signale über optische Fasern kilometerweit zu einer entfernten Station zu übertragen. Diese Eigenschaften machen das Konzept des photonischen Synthesizers zu einer sehr interessanten Alternative für viele Applikationen im Mikro- und Millimeterwellen-Bereich. Diese Arbeit beschäftigt sich mit der Realisierung und Charakterisierung verschiedener photonischer Synthesizer-Konzepte zur optischen Generation von frequenzabstimmbaren Mikro- und Millimeterwellen-Signalen mit geringem Phasenrauschen. Fortschrittliche photonische Konzepte unter Ausnutzung externer optischer Modulation sowie optischer Multiplikation werden vorgestellt. Diese Konzepte ermöglichen die optische Generierung hochfrequenter Millimeterwellen bis zu 110 GHz mit ausgezeichneter Performance in Bezug auf maximale Frequenzabstimmbarkeit sowie Phasenrauschen. Des Weiteren wurde ein neuartiges Konzept des optoelektronischen Oszillators, bestehend aus zwei Faserringen, vorgestellt, welches die Generierung von Millimeterwellen-Signalen ohne die Notwendigkeit eines elektronischen Referenzoszillators ermöglicht. Mit Hilfe des entwickelten optoelektronischen Oszillators wurde erstmals ein Mikrowellen-Signal mit einer Frequenzabstimmbarkeit im Gigahertz-Bereich experimentell erreicht

Photonic Technologies for Millimeter- and Submillimeter-wave Signals

[EN] Fiber optic components offer a competitive implementation for applications exploiting the millimeter-wave and THz regimes due to their capability for implementing broadband, compact, and cost-effective systems. In this paper, an outline of the latest technology developments and applications of fiber-optic-based technologies for the generation, transmission, and processing of high-frequency radio signals is provided. © 2012 B. Vidal et al.B. Vidal would like to thank the Spanish Ministerio de Economia y Competitividad for its support through Project TEC2009-08078. T. Nagatsuma would like to acknowledge the financial support provided by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (A) 23246067, 2011 and the JST-ANR WITH program.Vidal Rodriguez, B.; Nagatsuma, T.; Gomes, NJ.; Darcie, TE. (2012). Photonic Technologies for Millimeter- and Submillimeter-wave Signals. Advances in Optical Technologies. 2012:1-17. doi:10.1155/2012/925065S117201

Sub-femtosecond precision timing distribution, synchronization and coherent synthesis of ultrafast lasers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 180-189).In this thesis, we present a complete set of techniques for sub-femtosecond measurement, control and distribution of ultrafast optical pulse trains, with respect to pulse timing and phase. First, analytical analysis of the balanced optical cross-correlator (BOC) for attosecond precision pulse timing measurement is presented for both short and long crystal devices. It is found that the sensitivity of the long crystal BOC is independent of pulse duration, to first order. In addition, analytical noise models predict 13 as rms resolution, within a 1 MHz bandwidth, for optical pulses consistent with a practical fiber optic timing link. This analysis aids the widespread adoption of the BOC technique for other wavelengths and implementations. Secondly, long term timing distribution of a 200 MHz ultrafast optical pulse train over 340 m of single mode optical fiber is demonstrated, using the BOC. In this way, the group delay of the fiber link is directly stabilized with unprecedented precision and longterm stability. In addition, by distributing the entire optical pulse train, all optical and RF harmonics are provided at the remote location for direct synchronization of remote ultrafast lasers and microwave electronics. Over 168 hours of continuous, unaided operation, a drift of 5 fs rms is achieved, with less than 1.5 fs rms drift at timescales up to 10,000 seconds. Additional analysis of factors effecting performance, such as polarization mode dispersion and fiber nonlinearity is studied through experiment and simulations. It is found that nonlinear-origin drifts can be avoided for pulse energies below 40 pJ. A chirped pulse method could be implemented to distribute pulses of higher energy. Thirdly, the first quantum-resolution timing jitter measurement of ultrafast laser timing jitter for passively mode-locked lasers up to the Nyquist frequency is presented. The total jitter from for a 79.4 MHz stretched pulse erbium fiber laser is found to be 2.6 fs rms [10 kHz, 39.7 MHz]. It is found that the timing jitter power spectral density scales with frequency according to that expected for a white noise source, in agreement with theory. However, unexpected spurious jitter at high frequencies can occur for some mode-locked states, adding up to 5.5 fs rms jitter. Similar measurements of a 200 MHz erbium fiber soliton laser reveal the decay time of center frequency fluctuations to be 17 ns, with a predicted excess noise of approximately ten. These measurements suggest that timing jitter can be decreased through improved amplifier design. Finally, the synchronization of a 8 fs fiber supercontinuum at 1200 nm to a 7 fs Ti:Sapphire laser pulse train at 800 nm is achieved for both pulse timing and phase with attosecond precision. This achievement is enabled by the development of a novel scheme for stabilization of the carrier envelope offset of the entire optical bandwidth of an octave spanning supercontinuum, without introducing excess timing jitter. In particular, by implementing an acousto-optic frequency shifting (AOFS) feedback system within a fiber supercontinuum source, carrier envelope phase locking, to the Ti:Sapphire laser, is demonstrated to within 200 mrad rms [100 Hz, 5 MHz]. Previous techniques lack the high-speed, orthogonal control of CEP and pulse timing and broad optical bandwidth for synthesizing few-cycle optical pulses. Furthermore, timing synchronization of 280 as rms is achieved through combined piezoelectric and electro-optic feedback on the fiber supercontinuum, as measured with the BOC. This work enables the synthesis of a frequency comb spanning 650 to 1400 nm, resulting in a 3.5 fs transform limited pulse duration-assuming ideal spectral phase compression. To date, the spectrum has been successfully compressed to 4.7 fs, as measured with two-dimensional spectral shearing interferometry (2DSI). Moreover, by stabilizing a fiber supercontinuum source to a low-noise Ti:Sapphire laser, the ultra-high stability of the Ti:Sapphire laser is fully transferred to the octave spanning supercontinuum.by Jonathan A. Cox.Ph.D

Versatile femtosecond optical parametric oscillator frequency combs for metrology

This thesis addresses the development of broadly tunable, high repetition rate frequency combs in the mid-IR region. A novel PPKTP crystal design was used to provide phasematching for parametric oscillation and simultaneously give efficient pump+idler sum-frequency generation (SFG). This innovation enabled a fully stabilized idler comb from a 333-MHz femtosecond optical parametric oscillator to be generated in which the carrier envelope offset frequency fCEO together with the repetition frequency fREP were stabilised. This OPO platform was then extended to demonstrate, via harmonic pumping, a fully stabilized 1-GHz OPO frequency comb from a 333-MHz pump laser. Next, an alternative route to a 1-GHz OPO comb was investigated by synchronously pumping an OPO directly with a 1-GHz Ti:sapphire laser. Here the comb was fully stabilized for the signal, idler and pump pulses by using a narrow linewidth CW diode laser developed for the project and whose design is also presented. A further increase in the comb mode spacing was performed with a Fabry-Pérot cavity. A stabilised cavity was used to filter 1.5 m signal pulses from a 333-MHz repetition rate OPO frequency comb to yield a 10-GHz comb. The length of the Fabry-Pérot cavity was dither locked to a single-frequency ECDL and later on directly to the OPO frequency comb. Finally the 333-MHz OPO comb was demonstrated in an optical frequency metrology experiment. The frequency comb mode number and the absolute frequency of a narrow-linewidth CW laser were measured and the performance of the OPO comb was found to be comparable to that of a commercial fibre laser comb used as a benchmark in the experiment

Semiconductor Optical Amplifiers and mm-Wave Wireless Links for Converged Access Networks

Future access networks are converged optical-wireless networks, where fixed-line and wireless services share the same infrastructure. In this book, semiconductor optical amplifiers (SOA) and mm-wave wireless links are investigated, and their use in converged access networks is explored: SOAs compensate losses in the network, and thereby extend the network reach. Millimeter-wave wireless links substitute fiber links when cabling is not economical

Photonic Technologies for Radar and Telecomunications Systems

The growing interest in flexible architectures radio and the recent progress in the high speed digital signal processor make a software defined radio system an enabling technology for several digital signals processing architecture and for the flexible signal generation. In this direction wireless radar\telecommunications receiver with digital backend as close as possible to the antenna, as well as the software defined signal generation, reaches several benefits in term of reconfigurabilty, reliability and cost with respect to the analogical front-ends. Unfortunately the present scenario ensures direct sampling and digital downconversion only at the intermediate frequency. Therefore these kinds of systems are quite vulnerable to mismatches and hardware non-idealities in particular due to the mixers stages and filtering process. Furthermore, since the limited input bandwidth, speed and precision of the analog to digital converters represent the main digital system‘s bottleneck, today‘s direct radio frequency sampling is only possible at low frequency. On the other hand software defined signals can be generated exploiting direct digital synthesizers followed by an up-conversion to the desired carrier frequency. State-of-the-art synthesizers (limited to few GHz) introduce quantization errors due to digital-to-analog conversion, and phase errors depending on the phase stability of their internal clock. In addition the high phase stability required in modern wireless systems (such as radar systems) is becoming challenging for the electronic RF signal generation, since at high carrier frequency the frequency multiplication processes that are usually exploited reduce the phase stability of the original RF oscillators. Over the past 30 years microwave photonics (MWP) has been defined as the field that study the interactions between microwave and optical waves and their applications in radar and communications system as well as in hybrid sensor‘s instrumentation. As said before software defined radio applications drive the technological development trough high speed\bandwidth and high dynamic range systems operating directly in the radio frequency domain. Nowadays, while digital electronics represent a limit on system performances, photonic technologies perfectly engages the today‘s system needs and offers promising solution thanks to its inherent high frequency and ultrawide bandwidth. Moreover photonic components with very high phase coherence guarantees highly stable microwave carriers; while strong immunity to the electromagnetic interference, low loss and high tunability make a MWP system robust, flexible and reliable. Historical research and development of MWP finds space in a wide range of applications including the generation, distribution and processing of radio frequency signals such as, for example, analog microwave photonic link, antenna remoting, high frequency and low noise photonic microwave signal generation, photonic microwave signal processing (true time delay for phased array systems, tunable high Q microwave photonic filter and high speed analog to digital converters) and broadband wireless access networks. Performances improvement of photonic and hybrid devices represents a key factor to improve the development of microwave photonic systems in many other applications such as Terahertz generation, optical packet switching and so on. Furthermore, advanced in silicon photonics and integration, makes the low cost complete microwave photonic system on chip just around the corner. In the last years the use of photonics has been suggested as an effective way for generating low phase-noise radio frequency carriers even at high frequency. However while a lot of efforts have been spent in the photonic generation of RF carriers, only few works have been presented on reconfigurable phase coding in the photonics-based signal generators. In this direction two innovative schemes for optically generate multifrequency direct RF phase modulated signals have been presented. Then we propose a wideband ADC with high precision and a photonic wireless receiver for sparse sensing. This dissertation focuses on microwave photonics for radar and telecommunications systems. In particular applications in the field of photonic RF signal generation, photonic analog to digital converters and photonic ultrawideband radio will be presented with the main objective to overcome the limitations of pure electrical systems. Schemes and results will be further detailed and discussed. The dissertation is organized as follows. In the first chapter an overview of the MWP technologies is presented, focusing the attention of the limits overcame by using hybrid optoelectronic systems in particular field of applications. Then optoelectronic devices are introduced in the second chapter to better understand their role in a MWP system. Chapters 3,4, and 5 present results on photonic microwave signal generation, photonic wideband analog to digital converters and photonic ultrawideband up\down converter for both radar and telecommunications applications. Finally in the chapter 6 an overview of the photonic radar prototype is given