Photonic Signal Processing Research Articles

Microwave Photonic Signal Processing

This paper reviews the recent advances in the field of radio frequency signal processing using photonic devices and subsystems or microwave photonic (MWP) signal processing. We focus our attention on the results reported during the last six years, as previous work has been adequately addressed in previous review papers. After a brief introduction to the basic concepts involved in MWP signal processing, we focus our attention on the most significant advances reported by different research groups in overcoming their main limitation factors. Recent advances in the emergent topic of integrated MWP signal processors are also covered and the novel approaches toward the evaluation of the main figures of merit are discussed. New proposed applications and future directions of work are also considered.

All-Optical Techniques Enabling Packet Switching with Label Processing and Label Rewriting

Scalability of packet switched cross-connects that utilize all-optical signal processing is a crucial issue that eventually determines the future role of photonic signal processing in optical networks. After reviewing several labeling techniques, we discuss label stacking and label swapping techniques and their benefits for scalable optical packet switched nodes. All-optical devices for implementing the packet switch based on the labeling techniques will be described. Finally, we present a 1×4 all-optical packet switch based on label swapping technique that utilizes a scalable and asynchronous label processor and label rewriter. Error-free operation indicates a potential utilization of the swapping technique in a multihop packet-switched network.

New multiple-tap, general-response, reconfigurable photonic signal processor

A new photonic signal processor structure that can realize multiple-taps, with a general response capability, low-noise and widely tunable processor operation, is presented. It is based on a novel concept of employing positive and negative group delay slopes simultaneously by means of a dual-fed chirped fiber Bragg grating, and a new wavelength mapping scheme that enables wavelength re-use. The technique offers scalability, arbitrary responses with both positive and negative taps, tunability, and high frequency operation. Experimental results demonstrate widely tunable filters, with arbitrary bipolar tap generation, no PIIN noise, and with high FSR.

All-optical high-speed signal processing with silicon–organic hybrid slot waveguides

Integrated optical circuits based on silicon-on-insulator technology are likely to become the mainstay of the photonics industry. Over recent years an impressive range of silicon-on-insulator devices has been realized, including waveguides1,2, filters3,4 and photonic-crystal devices5. However, silicon-based all-optical switching is still challenging owing to the slow dynamics of two-photon generated free carriers. Here we show that silicon–organic hybrid integration overcomes such intrinsic limitations by combining the best of two worlds, using mature CMOS processing to fabricate the waveguide, and molecular beam deposition to cover it with organic molecules that efficiently mediate all-optical interaction without introducing significant absorption. We fabricate a 4-mm-long silicon–organic hybrid waveguide with a record nonlinearity coefficient of γ ≈ 1 × 105 W−1 km−1 and perform all-optical demultiplexing of 170.8 Gb s−1 to 42.7 Gb s−1. This is—to the best of our knowledge—the fastest silicon photonic optical signal processing demonstrated. A silicon–organic hybrid slot waveguide with a strong optical nonlinearity is demonstrated to perform ultrafast all-optical demultiplexing of high-bit-rate data streams. The approach could form the basis of compact high-speed optical processing units for future communication networks.

All-Optical Label Swapping of Scalable In-Band Address Labels and 160-Gb/s Data Packets

Scalability and photonic integration of packet switched cross-connect nodes that utilize all-optical signal processing is a crucial issue that eventually determines the future role of photonic signal processing in optical networks. We present a 1times4 all-optical packet switch based on label swapping technique that utilizes a scalable and asynchronous label processor and label rewriter. By combining N in-band labels at different wavelengths (within the bandwidth of the payload), up to 2N possible addresses can be encoded. The proposed label processor requires only N active devices to process the 2N addresses that makes this label processing technique scalable with the number of addresses. Experimental results showed error-free packet switching operation at 160 Gb/s. The label erasing and new label insertion operation introduces only 0.5 dB of power penalty. These results indicate a potential utilization of the presented technique in a multi-hop packet switched network.

A New Optical Phase Modulator Dynamic Response Measurement Technique

A new technique for measuring the dynamic response of optical phase modulators is presented. It is based on a photonic signal processor principle, in which the phase modulator is inserted in a Sagnac loop, and coherent summation of the counter-propagating phase modulated signals converts the off-loop-center phase modulation into intensity modulation, so that modulator response can be measured on a network analyzer from the envelope of the resulting microwave photonic filter response. Experimental results demonstrate that this technique is applicable for both polarizing and nonpolarizing waveguide optical phase modulators, and that it has wideband measurement capabilities with swept frequency response characterization features.

All‐optical reconfigurable microwave photonic signal processor

AbstractAn all‐optical reconfigurable high resolution microwave photonic signal processor is presented. It is based on a 2 × 1 electro‐optic modulator and an active‐fiber Bragg‐grating‐pair filter. Experimental results demonstrate a sharp bandpass filter response and a narrow stopband notch filter response which can be obtained by controlling the optical sources. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1989–1991, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23557

Design tool and its experimental validation for SOA-based photonic signal processing

This paper reports a unified, accurate and fast simulation tool, able to describe photonic SOA-based digital processing schemes. The model exploits cross gain modulation in SOAs in time resolved analysis in which each amplifier can be thought of as a point amplifier. Simulation and experimental comparisons of the steady state and dynamic amplified spontaneous emission noise behaviour of SOA are carried out. Details of multistage modelling useful for long nonlinear SOA has been described. Implementation of schemes such as combinatorial logic functions may require many cascading SOAs and contribution of ASE noise from each amplifier also been taken into account. A procedure of the extraction of parameters from the commercial SOA utilised in the experiment is laid down. Various sources of degradation have been identified and the method for evaluation of bit error rate for complex SOA based combinatorial network has been outlined. The tool is validated through the implementation of a photonic bit comparator. Important design guidelines are extracted by the proposed tool.

Switching Energy and Device Size Limits on Digital Photonic Signal Processing Technologies

The relationship between device size and power consumption of photonic signal processing devices is derived using device-specific models for photonic signal processing using semiconductor optical amplifiers, periodically poled lithium niobate, and highly nonlinear fibers. The results are then compared with the power-length characteristics of CMOS digital devices. The general conclusion is that photonic signal processing technologies demand significantly larger space and/or power than CMOS technologies.

10 Gb/s Reconfigurable Optical Logic Gate Using a Single Hybrid-Integrated SOA-MZI

A novel reconfigurable Boolean device based on a single Mach-Zehnder interferometer with semiconductor optical amplifiers is demonstrated at 10 Gb/s using intensity return-to-zero modulated signals. The experimental results show that the device can be dynamically reconfigured to operate as a logic XOR, AND, OR, and NOT gate using optical switches. By properly adjusting the input powers, an extinction ratio higher than 10 dB may be obtained. The potential of integration of this architecture makes it an interesting approach in photonic computing and optical signal processing.

Fourier information optics for the ultrafast time domain

Ultrafast photonic signal processing based on Fourier optics principles offers exciting possibilities to go beyond the processing speeds of electronics technologies for applications in high-speed fiber communications and ultrawideband wireless. I review our recent work on processing of ultrafast optical signals via conversion between time, space, and optical frequency (Fourier) domains. Specific topics include optical arbitrary waveform generation, application of optical pulse shaping technologies for wavelength-parallel compensation of fiber transmission impairments and for experimental studies of optical code-division multiple-access communications, and application of photonic methods for precompensation of dispersion effects in wireless transmission of radio-frequency signals over ultrawideband antenna links.

A novel high-order FIR photonic signal processor

A new topology for realizing a high-order FIR RF photonic filter is presented. It is based on a novel structure that uses wavelength conversion and a routing technique to enable a multiple-pass transmission of the signal to be obtained through a single photonic sub-filter. The sub-filter can be of low order, however the routing of the output of the sub-filter back to itself several times together with some additional coefficients, realizes a high-order filter. Experimental results are presented which demonstrate a high-order FIR photonic filter realization comprising 39 taps.

Arbitrary Optical Waveform Generation Using Planar Lightwave Circuits

We provide an overview of the direct temporal domain approach for designing optical fllters for ultrafast photonic signal processing applications. We discuss difierent fllter designs, including lattice-form Mach-Zehnder interferometers and two-dimensional ring resonator arrays, to perform pulse repetition rate multiplication and arbitrary optical waveform generation. Simulation and experimental results are presented. 1. INTRODUCTION Techniques for the generation, control, and manipulation of optical pulses attract considerable interest for numerous applications and have become increasingly important in many scientiflc areas. Of speciflc interest are techniques for pulse repetition rate multiplication (PRRM), which are used to obtain ulrafast optical pulse trains from a lower repetition rate input pulse train, as well as for arbitrary optical waveform generation (AOWG). Traditional pulse shaping methods are based on frequency domain processing (i.e., spectral flltering) in which we speciflcally manipulate the difierent spectral components of the input pulse in amplitude and/or phase. However, the relationship between the input pulse spectrum and the target temporal waveform is not always straightforward, especially for phase-only flltering processes. In this paper, we present an overview of our recently developed direct temporal domain approach for designing optical fllters to achieve PRRM and AOWG. 2. THEORY

Noise Mitigation in Spectrum Sliced Microwave Photonic Signal Processors

A new noise mitigation design strategy for spectrum sliced microwave photonic filters is presented. It is based on making the spectral slice bandwidths narrower than the modulation frequency and making the spacing between slices larger than the photodetector bandwidth. Advantages of this approach are that it is particularly simple, it does not require additional components, and it does not distort the signal. A detailed theoretical model of the relative intensity noise in spectrum sliced photonic signal processors is presented, including the effects of modulation, dispersion, and multislice stochastic sources. The phenomenon of modulation-induced noise translation in spectrum-sliced photonic signal processors is also reported for the first time. Results show that the new design strategy for noise mitigation can realize a significant increase in the SNR for a filter operating at 6.3 GHz

Novel photonic recursive signal processor with reduced phase-induced intensity noise

A new technique to reduce the dominant phase-induced intensity noise (PIIN) in active high-Q recursive photonic signal processors is presented. This is based on using cross-gain-modulation effects in a semiconductor optical amplifier in the recursive loop of the processor. Two different laser sources are used, and no recombination of the optical power from the same laser source occurs in the optical domain, hence, PIIN generation is suppressed. The processor structure also features the advantage that it does not require an incoherent light source. Hence, the free spectral range of the processor is not limited by the coherence of the laser source, as in existing incoherent approaches. Experimental results for the new processor demonstrate a more-than-30-dB reduction in PIIN level for a high-Q bandpass filter, compared to the conventional approach for the same filtering parameters.

A new technique for generating negative coefficients in photonic signal processors based on dual-input and dual-output intensity modulator sagnac interferometers

New structures that can realize bias drift-free dual-input and dual-output intensity modulators, and which can generate negative coefficients in photonic signal processors, are presented. They are based on a Sagnac loop comprising a travelling-wave optical phase modulator, together with a routing structure that gives outputs with opposite radio-frequency phases. Results using the dual-input mode of operation demonstrate a new technique for generating negative coefficients in an all-optical microwave photonic filter

Novel approach to RF photonic signal processing using an ultrafast laser comb modulated by traveling-wave tunable filters

The analogy between optical frequencies and RFs leads to a novel technique for RF photonic signal processing using a femtosecond laser comb modulated by a traveling-wave tunable filter, such as an acoustooptic tunable filter (AOTF) or a novel electrooptic tunable filter (EOTF). In this new scheme, the recent history of an applied RF waveform to-be-processed slides into the tunable filter and a femtosecond pulse train diffracts off the moving acoustooptically or electrooptically induced dielectric grating, producing a shaped optical pulse train with each shaped pulse as a compressed replica of the RF waveform contained within the device aperture that is sped up by the ratio between the center optical and RF frequency. For a CW RF tone input, only a narrowband group of the frequency comb lines in the incoming laser comb is spectrally filtered and modulated due to the phase-matching condition in the filter and is simultaneously Doppler shifted by that RF due to the traveling-wave grating obeying the conservation of energy. This allows us to use the traveling-wave tunable filter as a spectrally mapped Doppler-shifted modulator that encodes different RF components onto the corresponding optical frequency comb lines. RF signal processing can then be performed by using optical techniques to manipulate the spectrally modulated laser comb. To reconstruct the processed RF signal, the Doppler-shifted and optically processed pulse train is heterodyne detected by beating with a reference femtosecond pulse train from the same laser source. A high repetition rate femtosecond laser comb is modulated by an AOTF to experimentally demonstrate this novel RF photonic signal processing technique. We demonstrate an RF tunable bandpass/notch filter, an RF down-converter, and an RF jammer nuller as novel applications of ultrafast lasers.

Photonic signal processing of microwave signals

Photonic signal processing offers the prospect of realizing extremely high multigigahertz sampling frequencies, overcoming inherent electronic limitations. This stems from the intrinsic excellent delay properties of optical delay lines. These processors provide new capabilities for realizing high time-bandwidth operation and high-resolution performance. In-fiber signal processors are inherently compatible with fiber-optic microwave systems and can provide connectivity with built-in signal conditioning. Fundamental principles of photonic signal processing, including sampling, tuning, and noise, are discussed. Structures that can extend the performance of photonic signal processors are presented, including methods for improving the filter shape characteristics of interference mitigation filters, techniques to increase the stopband attenuation of bandpass filters, and methods to achieve large free spectral range. Several photonic signal processors, including high-resolution microwave filters, widely tunable filters, arbitrary waveform generators, and fast signal correlators, are discussed. Techniques to solve the fundamental noise problem in photonic signal processors are described, and coherence-free structures for few-tap notch filters are discussed. Finally, a new concept for realizing multiple-tap coherence-free processor filters, based on a new frequency-shifting technique, is presented. The structure not only eliminates the phase-induced intensity noise limitation, but can also generate a large number of taps to enable the achievement of processors with high performance and high resolution.

Suppression of phase-induced intensity noise in optical delay-line signal processors using a differential-detection technique

A new technique that can suppress the dominant phase-induced intensity noise (PIIN) in photonic signal processors is presented. It is based on a novel topology for the processor structure that enables bi-directional operation to be obtained, which enables the use of differential detection to be employed for suppressing the PIIN. This technique is simple and it does not affect the signal-processor RF response. Experimental results demonstrate a large phase-noise reduction of 36.7 and 16.5 dB in the passive and active recirculating delay-line filters, respectively. This is the first demonstration of PIIN reduction in multiple-tap recirculating delay-line signal processors.

Lithium niobate optical modulators: Devices and applications

Optical modulators, using acousto-optic, magneto-optic or electro-optic effects, as the principal components for external modulation of lightwaves, have presently played the important role in modern long-haul ultra-high speed optical communications and photonic signal processing systems. LiNbO 3 is an ideal host material for such modulators. In this paper we present: (i) a brief overview the electro-optic interaction in LiNbO 3 optical waveguides and the travelling electric waves for modulation; (ii) fabrication techniques of optical waveguides and electrodes for the excitation of microwave and millimeter waves, including the prospects of the uses of ultra-thick “brick-wall like” type by synchrotron deep X-ray LIGA process; (iii) a comprehensive modelling of the travelling wave electrodes for the design of interferometric optical modulators, including different electrode structures. Tilted and thick and “brick-wall” like electro-plated electrodes are modelled and confirmed with implemented modulators operating up to 26 GHz in diffused LiNbO 3 optical interferometric waveguide structures; (iv) the design and implementation of LiNbO 3 single or dual drive as modulators for modulating lightwaves in modern transmission systems as ultra-high speed pulse carvers, generators of modulation formats (NRZ, RZ, CS-RZ, DPSK, DQPSK, etc.) and photonic signal processors.