Academic literature on the topic 'All-optical regeneration'

All-optical signal processing techniques for phase-shift keyed (PSK) systems were developed theoretically and demonstrated experimentally. Nonlinear optical effects in fibers, in particular four-wave mixing (FWM) that occurs via the ultra-fast Kerr nonlinearity, offer a flexible framework within which numerous signal processing functions can be accomplished. This research has focused on the regenerative capabilities of various FWM configurations in the context of processing PSK signals. Phase-preserving amplitude regeneration, phase regeneration, and phase-regenerative wavelength conversion are analyzed and demonstrated experimentally. The single-pump phase-conjugation process was used to regenerate RZ-DPSK pulse amplitudes with different input noise distributions, and the impact on output phase characteristics was studied. Experiments revealed a limited range over which amplitude noise could effectively be suppressed without introduction of phase noise, particularly for signals with intensity pattern effects. Phase regeneration requires use of phase-sensitive amplification (PSA), which occurs in nonlinear interferometers when the pump and signal frequencies are degenerate (NI-PSA), or in fiber directly through single-stage (degenerate) or cascaded (non-degenerate) FWM processes. A PSA based on a Sagnac interferometer provided the first experimental demonstration of DPSK phase and amplitude regeneration. The phase-regenerative capabilities of the NI-PSA are limited in practice by intrinsic noise conversion (amplitude to phase noise) and to a lesser extent by the requirement to modulate the pump wave to suppress stimulated Brillouin scattering (SBS). These limitations are relaxed in novel materials with higher SBS thresholds and nonlinearities. Degenerate FWM provides PSA in a traveling-wave configuration that intrinsically suppresses the noise conversion affecting the NI-PSA, while providing stronger phase-matched gain. Experiments confirmed superior phase-regenerative behavior to the NI-PSA with simultaneous reduction of amplitude noise for NRZ-DPSK signals. Phase-regenerative wavelength conversion (PR-WC) provides the regenerative properties of PSA at a new wavelength, and was proposed and demonstrated for the first time in this research. The parallel implementation of two FWM processes, phase-conjugation and frequency conversion, provides two idlers which exhibit interesting and useful regenerative properties. These were investigated theoretically and experimentally. Ideal phase-regenerative behavior is predicted when the contributing FWM processes are equally phase-matched, which can be maintained over any interaction length or wavelength shift provided the pump powers are properly adjusted. Depleted-pump regime PR-WC provides simultaneous phase and amplitude regeneration. Experiments confirmed regenerative behavior for wavelength shifts of the idlers up to 5 nm. Two techniques for phase regeneration of 4-level PSK signals were developed and evaluated. The first is based on parallel operation of PSAs suitable for processing 2-level PSK signals, where phase projection and regeneration are combined to recover the input data. Analysis of this scheme outlined the conditions required for effective phase regeneration and for practical implementation using known PSAs. A novel process based on FWM (parallel phase-conjugation followed by PSA) was developed and analyzed, and demonstrated using numerical simulations. These studies provide a basis for further work in this area.<br>Ph.D.<br>Optics and Photonics<br>Optics and Photonics<br>Optics PhD

All-optical signal processing schemes are being studied as promising candidates for adoption in future optical transmission systems, where they are hoped to offer benefits such as ultra-fast signal processing, reduced energy consumption and in some cases, multi-channel processing, supporting the deployment of new techniques such as optical burst switching and software defined networks. The topic of this thesis is the all-optical phase and amplitude regeneration of complex signals using four-wave mixing (FWM). Many schemes for all-optical signal regeneration which have so far been demonstrated expose a signal to some undesirable concomitant distortion during regeneration, grossly limiting their practicability. Therefore, the work in this thesis focuses upon eliminating these undesirable effects and pursuing the development of regenerators possessing more ideal performance. To this end, an amplitude preserving phase regenerator is ?first demonstrated using a phase sensitive amplifier (PSA) which functions through the use of an additional phase harmonic beyond that commonly used. The conclusions of this are extended to show that, given a means to coherently add a large number of phase harmonics of a signal, the phase transfer function of a PSA may be tailored exactly as pleased using a method similar to Fourier analysis. Adoption of an exact solution to degenerate FWM allows for the demonstration of phase preservation in a saturated, pump-degenerate FWM-based amplitude regenerator, enabled by adopting a high pump to signal power ratio. Understanding of the phase noise processes present in this amplitude regenerator leads to an alternative scheme for phase preservation being demonstrated, which functions by predistorting the signal using optical nonlinearities, before amplitude squeezing. This technique is then combined with a novel, single stage, wavelength converting idler-free PSA, to realise a system which is capable of regenerating both the phase and amplitude of a signal, and, by making use of the conjugating nature of both stages, allows for the negation of nonlinearity induced phase distortion between the two stages to realise a system which is greater than the sum of its two parts.

Recentemente è stata notata una crescita dei servizi multimediali richiesti dagli utenti finali; in tal modo numerose soluzioni sono state implementate per garantire elevati bit rate e qualità del servizio necessari per questo tipo di applicazioni. Le reti completamente ottiche sono state stese in molte nazioni (Giappone, Corea, Cina) per fornire servizi a banda larga fino a casa dell'utente. Conseguentemente, sono richiesti dispositivi in grado di operare nel dominio ottico in modo tale da evitare il noto “collo di bottiglia” derivante dalle conversioni di formato O/E/O (ottico/elettrico/ottico). In questo modo, nuovi tipi di sistemi (per esempio: optical processing e passive optical network) in grado di operare nel dominio completamente ottico sono richiesti poiché solo questo tipo di soluzione è la miglior strada per offrire alte prestazioni in termini di servizi, rate e riduzione dei costi per bit. Il lavoro eseguito durante questo dottorato di ricerca è stato incentrato sull'evoluzione di dispositivi per la rigenerazione ottica in grado di operare al contempo una Ri-amplificazione e Ri-sagomatura (2R) dei segnali ottici. Studi ed esperimenti sono stati effettuati nei laboratori dell’ ISCOM sfruttando la possibilità di rigenerazione completamente ottica di un dispositivo 2R multi-canale in grado di lavorare e gestire più clients nel medesimo istante temporale. Il sistema è stato implementato in uno scenario DWDM (Dense Wavelegth Division Multiplexing); inoltre, lavorando nel dominio completamente ottico sono state eliminate le conversioni di formato (O/E/O). Il sistema di rigenerazione è basato sulla modulazione di fase presente all'interno della fibra ottica usata per ottenere, sotto particolari condizioni, la generazione di nuove repliche del segnale originario che si vuole rigenerare. Queste nuove repliche, essendo posizionate a nuove lunghezze d’onda, possono essere usate sia per ottenere una conversione di lunghezza d’onda sia per ottenere una rigenerazione ottica dei segnali. Ciascuna replica, infatti, è caratterizzata dall’ avere un andamento simile alle funzioni di Bessel in grado di eliminare il rumore accumulatosi durante la trasmissione dei segnali. L’idea di questo lavoro è basato su un approccio multi-lunghezza d’onda in modo tale da poter usare un solo dispositivo per fornire una rigenerazione 2R completamente ottica ai numerosi utenti operanti a 10 Gbps. La capacità dei sistemi, implementati nei laboratori ISCOM, di risagomare i segnali, è stata confermata sperimentalmente in termini di misurazioni di diagramma ad occhio dei segnali di uscita e dalle curve di BER (Bit Error Rate).<br>A recent increase of multimedia service demand from end-users has been noticed, thus several solutions have been implemented to guarantee the high rate and relative QoS (Quality of Service) needed for these kind of services. All optical networks have been deployed in many countries (Japan, Korea, China, at all) in order to supply broadband services to the home. Consequently, devices able to operate in optical domain are requested in order to avoid the so called “bottle-neck” coming from the O/E/O data conversion format. Thus, new kind of systems (optical processing and passive optical networks, at all) able to operate in photonic domain are requested because only this kind of solution is the better way to offer high performances in term of services, rate and low cost per bit. The work performed during this PhD program has been focused on the evolution of regeneration devices able to perform Re-amp and Re-shaping also know as 2R. Studies and experiments have been carried out at the ISCOM labs exploiting the possibility to a multi-channel 2R all optical regeneration device which is able to work with different client signals at the same time. The system has been implemented in a dense WDM (Wavelength Division Multiplexing) scenario. Moreover, working completely in optical domain, the format conversion (O/E/O) is avoided. The regeneration system is based on phase modulation present in the fiber and used to obtain, under particular conditions, the generation of new signal replica. These new replica, being placed at new different wavelengths can be used both to reach a wavelength conversion and to obtain an all optical regeneration effect. Each replica, in fact, is characterized by a Bessel like transfer function able to clean the noise accumulated along the signal transmission. The idea of this work is based on a multi-wavelength approach, thus only one device can be used to provide all optical 2R regeneration to several client signals at 10 Gbps at the same time. The ability of the systems, implemented at the ISCOM labs, to reshape the signals, has been experimentally confirmed in terms of eyes diagrams and BER (Bit Error Rate) measurements.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.<br>Includes bibliographical references.<br>In the thirty years since the installation of the first fiber optic data link, data rates in installed fiber links have risen from a few Mb/s to tens of Gb/s. In the laboratory, data rates in a single optical fiber have already reached tens of Tb/s. These data rates greatly exceed electronic processing rates, so researchers have turned to all-optical signal processing to achieve many basic network tasks, like wavelength conversion, packet switching, and data regeneration. As data rates increase, the impairments caused by propagation through the glass of optical fiber become worse. Chromatic dispersion causes the temporal broadening of optical bits during propagation, leading to interference between neighboring bits. Nonlinear effects, like the nonlinear index of refraction and four-wave mixing, can cause interference between neighboring wavelength channels. The interaction of dispersion and nonlinearities can lead to variations in the timing of bits and the appearance of optical energy where there had been none. All these effects make 1-bits and 0-bits difficult to distinguish. Today, these distortions are overcome by electronic regenerators. Optical data streams are converted to electrical signals, processed electronically, converted back to an optical signal, and returned to the optical network. In this way, regenerators prevent the accumulation of noise and prevent noise from contributing to the production of more noise. The electronic solution is costly because of the extra hardware required for optical to electrical to optical conversions and performs poorly because of the losses incurred by those conversions. In this thesis, we investigate two regenerators that restore the data quality of ON/OFF keyed data without a conversion of the data to the electrical domain.<br>(cont..) Both regenerators are based on all-optical switches that take two inputs: the data pulses from the network, and a locally generated clock-pulse train. The all-optical switches then modulate the data pattern onto the clock-pulse train, which becomes the new data stream. The first switch we consider, the WMFUNI, uses the nonlinear properties of fiber to produce the switching action. Using the WMFUNI regenerator, we demonstrate the propagation of 10 Gb/s data over 20,000 km of commercial optical fiber. We also demonstrate the WMFUNI's ability to operate on 40-Gb/s data. Unfortunately, fiber has only a weak nonlinearity, so the WMFUNI is large (~40 cmx40 cm). The second switch uses the much stronger nonlinearity of a semiconductor optical amplifier (SOA). SOA-based switches can be integrated onto chip-scale optics. The switch we test, the SOA-MZI, fits on a ~0.5 cmxl cm chip. Using the SOA-MZI regenerator, we demonstrate the propagation of 10 Gb/s data over 10,000 km of commercial optical fiber. We also show in simulation that the SOA-MZI's operation may be extended to 40 Gb/s.<br>by Shelby Jay Savage.<br>Ph.D.

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.<br>Includes bibliographical references (leaves 105-110).<br>by Shelby Jay Savage.<br>M.Eng.

In this dissertation I investigated a multi-channel and multi-bit rate all-optical clock recovery device. This device, a birefringent Fabry-Perot resonator, had previously been demonstrated to simultaneously recover the clock signal from 10 wavelength channels operating at 10 Gb/s and one channel at 40 Gb/s. Similar to clock signals recovered from a conventional Fabry-Perot resonator, the clock signal from the birefringent resonator suffers from a bit pattern effect. I investigated this bit pattern effect for birefringent resonators numerically and experimentally and found that the bit pattern effect is less prominent than for clock signals from a conventional Fabry-Perot resonator.I also demonstrated photonic balancing which is an all-optical alternative to electrical balanced detection for phase shift keyed signals. An RZ-DPSK data signal was demodulated using a delay interferometer. The two logically opposite outputs from the delay interferometer then counter-propagated in a saturated SOA. This process created a differential signal which used all the signal power present in two consecutive symbols. I showed that this scheme could provide an optical alternative to electrical balanced detection by reducing the required OSNR by 3 dB.I also show how this method can provide amplitude regeneration to a signal after modulation format conversion. In this case an RZ-DPSK signal was converted to an amplitude modulation signal by the delay interferometer. The resulting amplitude modulated signal is degraded by both the amplitude noise and the phase noise of the original signal. The two logically opposite outputs from the delay interferometer again counter-propagated in a saturated SOA. Through limiting amplification and noise modulation this scheme provided amplitude regeneration and improved the Q-factor of the demodulated signal by 3.5 dB.Finally I investigated how SPM provided by the SOA can provide a method to reduce the in-band noise of a communication signal. The marks, which represented data, experienced a spectral shift due to SPM while the spaces, which consisted of noise, did not. A bandpass filter placed after the SOA then selected the signal and filtered out what was originally in-band noise. The receiver sensitivity was improved by 3 dB.