Programmable Optical Processor Research Articles

Microwave photonic I/Q mixer for wideband frequency downconversion with serial electro-optical modulations.

In this paper, we propose a serial electro-optical (EO)-modulation-based microwave photonic in-phase and quadrature (I/Q) mixer and investigate its performance for wideband frequency downconversion. The proposed I/Q mixer uses two EO modulators and a programmable optical processor in a serially cascaded structure, which ensures good phase stability and flexibility to achieve high-performance broadband frequency downconversion. A proof-of-concept experiment is carried out in which the frequency downconversion of the RF signals in the range from 10 to 40 GHz is demonstrated with an average image rejection ratio of 38.66 dB. The spurious-free dynamic range (SFDR) measured at around 15 GHz is 86 dBc·Hz2/3. Based on this microwave photonic I/Q mixer, a broadband radar receiver is established and de-chirping of linearly frequency modulated (LFM) radar echoes with an instantaneous bandwidth of 8 GHz (10-18 GHz) is achieved. The results verify its feasibility for high-performance I/Q mixing in practical applications.

On-chip Optical Phase Monitoring in Multi-Transverse-Mode Integrated Silicon-based Optical Processors

We design a Multi-Transverse-Mode Optical Processor (MTMOP) on 220 nm thick Silicon Photonics exploiting the first two quasi-transverse electric modes (TE0 and TE1). The objective is to measure the optical phase, required for programming the optical processor, without use of conventional optical phase detection techniques (e.g., coherent detection). In the proposed design, we use a novel but simple building block that converts the optical phase to optical power. Mode TE0 carries the main optical signal while mode TE1 is for programming purposes. The MTMOP operation relies on the fact that the group velocity of TE0 and TE1 propagating through a mode-sensitive phase shifter are different. An unbalanced Mach-Zehnder interferometer (MZI) consists of a mode-sensitive and mode-insensitive phase shifters in the two arms. We set the bias of the phase shifters so that TE0 propagating in the two arms constructively interfere while this will not be the case for TE1. Hence, we detect the phase shift applied to TE0 by measuring the variation in the optical power of TE1. To the best of our knowledge, this design is the first attempt towards realizing a programmable optical processor with fully integrated programming unit exploiting multimode silicon photonics.

Optical Implementation of 2 × 2 Universal Unitary Matrix Transformations

AbstractUnitary operations are a specific class of linear transformations that have become an essential ingredient for the realization of classical and quantum information processing. The ability of implementing any n‐dimensional unitary signal transformation by using a reconfigurable optical hardware has recently led to the pioneering concept of programmable linear optical processor, whose basic building block (BB) must be correctly designed to guarantee that the whole system is able to perform universal (i.e., arbitrary) unitary matrix transformations. Here, it is demonstrated that the present architectures of the BB do not fulfil the universal unitary property (at least) in optical processors, limiting the number of unitary matrix transformations that may be generated. Aiming to solve this fundamental constraint, the theoretical tools required to analyze and design universal unitary optical circuits and their corresponding BBs are presented. The consequences of this mathematical framework are explored, obtaining a simple route to implement different BB architectures, all of them guaranteeing a true universal unitary functionality in the resulting optical processors. These findings may pave the way to revisit the design of high‐dimensional unitary optical processors, unleashing the potential of programmable integrated photonics technology.

Chip-Scale Reconfigurable Optical Full-Field Manipulation: Enabling a Compact Grooming Photonic Signal Processor

Waveshaper, a programmable optical processor providing a variety of optical filtering and switching functions, has attracted great attention in the past decade, especially in optical communications...

Ultrahigh-resolution and wideband optical vector analysis for arbitrary responses.

An ultrahigh-resolution and wideband optical vector analyzer (OVA) with the simplest architecture, to the best of our knowledge, is proposed and demonstrated based on chirped optical double-sideband (ODSB) modulation in a single-drive Mach-Zehnder modulator (MZM). To distinguish the magnitude and phase information carried by the two sidebands in the ODSB signal, a two-step measurement, in which biasing, respectively, the MZM at two different points is applied. Because no optical filtering is required in the scheme, the optical carrier can be located at any wavelength that is suitable for accurate measurement, e.g., close to the notch of a notch response or within the passband of a bandpass response, so the proposed OVA has the capability to measure an arbitrary response. An experiment is carried out, which achieves the magnitude and phase responses of a programmable optical processor with bandpass, notch, or falling-edge responses. The measurement bandwidth is 134GHz, and the measurement resolution is 1.12MHz.

Programmable optical processor chips: toward photonic RF filters with DSP-level flexibility and MHz-band selectivity

AbstractIntegrated optical signal processors have been identified as a powerful engine for optical processing of microwave signals. They enable wideband and stable signal processing operations on miniaturized chips with ultimate control precision. As a promising application, such processors enables photonic implementations of reconfigurable radio frequency (RF) filters with wide design flexibility, large bandwidth, and high-frequency selectivity. This is a key technology for photonic-assisted RF front ends that opens a path to overcoming the bandwidth limitation of current digital electronics. Here, the recent progress of integrated optical signal processors for implementing such RF filters is reviewed. We highlight the use of a low-loss, high-index-contrast stoichiometric silicon nitride waveguide which promises to serve as a practical material platform for realizing high-performance optical signal processors and points toward photonic RF filters with digital signal processing (DSP)-level flexibility, hundreds-GHz bandwidth, MHz-band frequency selectivity, and full system integration on a chip scale.

High-frequency reverse-time chaos generation using an optical matched filter.

The optical reverse-time chaos is realized by modulating a binary pseudo-random bit sequence onto an optical carrier, and then driving an optical matched filter. The filter is demonstrated experimentally by using two fiber Bragg gratings and a Fourier-domain programmable optical processor. The complexity relationship between the binary input sequence and the output chaos signal is studied. This approach could be a novel way to generate a high speed repeatable and controllable optical chaos signal, which has the potential to be used in optical secure communication systems.

Highly reconfigurable microwave photonic single-bandpass filter with complex continuous-time impulse responses

We propose a novel structure of complex-tap microwave photonic filter (MPF) employing an incoherent broadband optical source (BOS) and a programmable optical spectrum processor. By tailoring the optical spectral amplitude and phase, arbitrary complex continuous-time impulse responses of the MPF can be constructed. Frequency responses with a single flat-top, highly chirped, or arbitrary-shape passband are demonstrated, respectively. The passband center can also be tuned in a wide range only limited by the opto-electrical devices. To the best of our knowledge, it is the first demonstration of an incoherent-BOS-based MPF which is single-bandpass, widely tunable, and highly reconfigurable with complex taps.

A Study on LCoS-Based Remote Nodes for 60 GHz Fiber-Wireless Links

In this paper, we investigate and study the performance of a WDM-based 60 GHz mm-wave fiber-wireless link incorporating a liquid-crystal-on-silicon (LCoS)-based programmable optical processor (POP) in the remote node (RN) for demultiplexing and processing of multiple channels. To ensure that the fiber-wireless link is compatible with existing WDM optical backbones, we have evaluated the performance of the 60 GHz link using a typical WDM channel plan with 100 GHz spacing. A number of different filter profiles are investigated for the POP within the RN and the link performance is quantified and fully characterized. To demonstrate the robustness and flexibility of the POP as a RN, we also investigate wavelength-interleaved 60 GHz fiber-wireless link which requires a more complex filter profile for channel demultiplexing. Our results demonstrate that the POP allows error-free reception of demultiplexed channels, though the performance depends on the type of profile used to process the individual channels.

Photonic Generation of Frequency-Tunable Microwave Signals Using an Array of Uniformly Spaced Optical Combs

We show analytically as well as experimentally a photonic technique for generation of frequency-tunable microwave signals. The technique involves propagating an array of uniformly spaced optical combs with identical comb profile into a length of dispersive single-mode fiber (SMF) prior to photodetection. A new scheme that involves a supercontinuum source and a Fourier-domain programmable optical processor as a spectral filter is proposed to generate the required array of optical combs. For an initial optical comb with a fixed repetition rate and a given length of standard SMF, our scheme shows that by choosing appropriate values of the number of optical combs, the number of comb lines in each optical comb, as well as the frequency spacing between the adjacent optical combs, we can generate a microwave signal whose frequency can be tuned to any integer multiple of the optical comb's repetition frequency that lies within the bandwidth of the photodetector. Based on the proposed scheme, using a 2 GHz supercontinuum source as an initial optical comb, we demonstrate the generation of stable microwave signals tunable to 8, 10, and 12 GHz.

Flexible OTDM to WDM converter enabled by a programmable optical processor

We propose an OTDM to WDM converter which enables wavelength tunability, flexible OTDM tributary to WDM channel mapping and modulation format transparency. The converted signals are obtained by four-wave mixing (FWM) the input 160 Gb/s OTDM signal with a multi-wavelength sampling pulse train (SPT). The generation of the multi-wavelength SPT starts by multicasting an optical clock signal. The multicast pulses are then individually delayed and reshaped by a programmable optical processor (POP), resulting in flexible generation of the SPT. Error-free performance was achieved in different OTDM tributary to WDM channel mappings. In addition, intermediate rate conversion (2x80 Gb/s) was also achieved simply by reconfiguring the POP.

Time-resolved chirp measurement for 100GBaud test systems using an ideal frequency discriminator

In this paper we present multi-channel chirp measurements of wide-band sources, using a programmable Fourier-domain optical processor (FDOP) as a near-perfect linear frequency discriminator element followed by a fast photodiode and electrical sampling oscilloscope. The electric field of a 10.7Gbit/s phase-encoded data source and a directly modulated laser diode are simultaneously interrogated with this measurement system. The constellation diagram of the phase-encoded data source is demonstrated, and a comparison with another phase-sensitive measurement technique is performed. Additionally, an extension to this technique is demonstrated in which the time-resolved chirp of a picosecond-duration mode-locked laser diode with a 260GHz spectral bandwidth is characterised using the FDOP and a high-bandwidth optical sampling oscilloscope. This measurement ensemble has sufficient temporal resolution to characterise random or repetitive data signals up to 100GBaud.

Microwave photonic quadrature filter based on an all-optical programmable Hilbert transformer

A microwave photonic quadrature filter, new to our knowledge, based on an all-optical Hilbert transformer is presented. It is based on mapping of a Hilbert transform transfer function between the optical and electrical domains, using a programmable Fourier-domain optical processor and high-speed photodiodes. The technique enables the realization of an extremely wide operating bandwidth, tunable programmable bandwidth, and a highly precise amplitude and phase response. Experimental results demonstrate a microwave quadrature filter from 10 to 20 GHz, which achieves an amplitude imbalance of less than ±0.23 dB and a phase imbalance of less than ±0.5°.

Reconfigurable Optical Pulse Generator Employing a Fourier-Domain Programmable Optical Processor

This paper demonstrates a reconfigurable optical pulse generator based on the creation of a high-quality flat continuum that covers the C-band, followed by the tailoring of the spectral amplitude and phase of the continuum using a commercially available reconfigurable programmable optical processor in order to provide an arbitrary picosecond pulse shape or width. The highly efficient continuum is achieved by seeding a highly nonlinear fiber with transform-limited 4 ps parabolic-shaped pulses. A 20 nm 3 dB continuum at the very high repetition rate of 40 GHz is generated. Fourier-domain pulse shaping techniques are then applied to this continuum via the programmable optical processor to generate any arbitrary pulse shape. We present two specific pulse shaping examples suitable for a variety of high-bit-rate applications. The first example shows the improvement in pulse quality using tailored compression techniques over conventional methods and the second example presents multiwavelength pulse generation, which demonstrates the flexibility and range of pulse shapes that can be achieved using this system. Experimental findings are supported with theoretical results.

Repetition-rate-selective, wavelength-tunable mode-locked laser at up to 640 GHz

We demonstrate a tunable passively mode-locked fiber laser with a selectable repetition rate of up to 640 GHz. The mode-locking mechanism is based on dissipative four-wave mixing in combination with a programmable optical processor as the spectral filter. We achieve up to 20 nm wavelength tunability and present mode-locked operation at repetition rates between 40 and 640 GHz. Measurements of the power spectra using a cross-phase modulation technique confirm the mode locking.

Optical triple-in digital logic using nonlinear optical four-wave mixing

A new programmable optical processor is proposed for implementing triple-in combinatorial digital logic that uses four-wave mixing. Binary-coded decimal-to-octal decoding is experimentally demonstrated by use of a photorefractive BaTiO(3) crystal. The result confirms the feasibility of the proposed system.

General-purpose optical pattern recognition image processors

A general-purpose programmable optical image processor architecture is described. A correlator architecture is used with different filter functions employed to implement a variety of different operations required in the different levels of computer vision. We consider input scenes with a number of objects present in clutter with a number of different object classes, distortions, and contrasts. The system locates all objects and identifies the class of each. The optical image processing operations performed include morphological low-level nonlinear functions, detection of candidate regions of interest, fusion of correlation outputs to reduce false alarms, image enhancement, and feature extraction. The optical correlation filters to realize each operations, examples of each, and real-time optical correlator hardware are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Programmable optical parallel processor based upon polarization modulation: cascade operations

The architectural considerations and experimental results of a new optical parallel are presented. An array logic concept is introduced as the building blocks of the processor. The processor performs programmable logic operations. Polarization modulation and spatial separation of the modulated light, together with the operation kernel, are keys to programmability for any Boolean logic operation. The operation kernel determines the logic operation to be executed according to instructions simply by spatially filtering encoded light. Real-time programmable cascade logic operations for three patterns are demonstrated experimentally using a liquid crystal spatial light modulator as the operation kernel.

Programmable optical processor based on symbolic substitution

Faster computing requires not only faster gates and faster interconnections but also a modified architecture. The requirements of such architectures favor an optical implementation. This paper presents a programmable optical processor based on symbolic substitution logic.

Digital analysis of optical transforms and correlations

Hardware, applications and experimental results for an interface from an optical processor to a digital computer are described. The interface analyzes the contents of the Fourier transform and correlation planes of an optical processor displays and stores various representations of the data in these planes, controls the format and contents of the input and matched spatial filter planes of the optical processor, and by digital feedback controls the throughput and operation of the optical processor. A hybrid optical/digital processor and a programmable optical processor result. Much of the interface is constructed from existing computer modules.