Photonic Signal Processing Research Articles

Photonic-Assisted Microwave Frequency and Phase Shifter for Deception Jamming

A new microwave photonic signal processing structure that has the ability to realise frequency and phase shifting operation is presented. The proposed structure uses Serrodyne phase modulation in a dual-polarisation binary phase shift keying (DP-BPSK) dual-drive Mach Zehnder modulator to shift the frequency of an input microwave signal. This has the advantage over the conventional frequency mixers that the unwanted frequency components adjacent to the frequency translated microwave signal can be largely suppressed. It is suitable for use in deception jamming in electronic countermeasures systems. The phase shifting operation is realised by controlling the bias voltages of the DP-BPSK modulator. The dual-function microwave photonic signal processor has a simple structure and a wide bandwidth. The structure enables commercial modulator bias controllers to be used to provide long-term stable performance. Experimental results are presented that demonstrate a wide operating frequency range of 3 to 16 GHz, an over 35 dB suppression on the spurious signals and 0° to 360° phase shift on the frequency translated microwave signal. Using bias controllers to maintain a large spurious suppression ratio of around 35 dB is also demonstrated.

Wideband Anti-Jamming Based on Free Space Optical Communication and Photonic Signal Processing.

We propose and demonstrate an anti-jamming system to defend against wideband jamming attack. Free space optical communication is deployed to provide a reference for jamming cancellation. The mixed signal is processed and separated with photonic signal processing method to achieve large bandwidth. As an analog signal processing method, the cancellation system introduces zero latency. The radio frequency signals are modulated on optical carriers to achieve wideband and unanimous frequency response. With wideband and zero latency, the system meets the key requirements of high speed and real-time communications in transportation systems.

Photonic RF and Microwave Fractional Differentiation, Integration, and Hilbert Transforms With Kerr Optical Micro-Combs

Integrated Kerr micro-combs are a powerful source of multiple wavelength channels for photonic radio frequency (RF) and microwave signal processing, particularly for transversal filter systems. They offer significant advantages featuring a compact device footprint, high versatility, large numbers of wavelengths, and wide Nyquist bands. We present our recent progress on photonic RF and microwave high bandwidth temporal signal processing based on Kerr micro-combs with comb spacings from 49GHz to 200GHz. We focus on integral and fractional Hilbert transforms, differentiators as well as integrators. The future potential of optical micro-combs for RF photonic applications in terms of functionality and ability to realize integrated solutions is also discussed.

Novel microwave photonic applications based on integrated microcombs (Invited)

Microresonator-based frequency combs (microcombs) are very promising for microwave photonic applications for their advantages including wide bandwidth, large line spacing, and compact volume. Recently, various microcomb-based microwave photonic systems have been reported such as high-spectral-purity microwave generation, microwave photonic signal processing, true-time-delay beamforming, etc. Outstanding performances including low phase noise, high reconfigurability, and large Nyquist bandwidth have been demonstrated, showing a bright future of microcomb-based microwave photonics.

A novel wideband radio frequency measurement based on photonic signal processing

AbstractPhotonic signal processing is a suitable alternative of electronics based processing for wideband frequency detection. We propose a novel technique for the detection of a wide range of frequencies based on photonic signal processing. The unknown frequency to be measured is used to modulate a tunable optical source by implementing single sideband suppressed carrier modulation. The modulated signal is combined with two fixed frequency optical carriers to perform heterodyne detection. The frequency of the tunable laser source is swept until significant power of the beat signal is observed after photodetection. A mathematical expression is presented that can be used to measure the frequency of the unknown electrical signal based on value of the center frequency of tunable laser source. The effect of increasing laser linewidth up to 100 MHz and instantaneous shift in laser center frequency up to 200 MHz has also been demonstrated. It has been shown that the proposed technique can measure almost any radio frequency by simply varying the frequency of the tunable laser source.

Dispersion-tailored few-mode fiber design for tunable microwave photonic signal processing

Dispersion-tailored few-mode fiber design for tunable microwave photonic signal processing

Dispersion-tailored few-mode fiber design for tunable microwave photonic signal processing.

We present a novel double-clad step-index few-mode fiber that operates as a five-sampled tunable true-time delay line. The unique feature of this design lies in its particular modal chromatic dispersion behavior, which varies in constant incremental steps among adjacent groups of modes. This property, which to the best of our knowledge has not been reported in any other few-mode fiber to date, is the key to tunable operation of radiofrequency signal processing functionalities implemented in few-mode fibers. The performance of the designed true-time delay line is theoretically evaluated for two different microwave photonics applications, namely tunable signal filtering and optical beamforming networks for phased array antennas. In the 35-nm optical wavelength tuning range of the C-band, the free spectral range of the microwave filter and the beam-pointing angle in the phased array antenna can be continuously tuned from 12.4 up to 57 GHz and 12.6° up to 90°, respectively.

On-chip high-sensitivity photonic temperature sensor based on a GaAs microresonator.

We demonstrate an on-chip high-sensitivity photonic temperature sensor based on a GaAs microdisk resonator. Based on the large thermo-optic coefficient of GaAs, a temperature sensitivity of 0.142 nm/K with a measurement resolution of 10 mK and low input optical power of only 0.5 µW was achieved. It exhibits great potential for chip-scale biological research and integrated photonic signal processing.

Lithium niobate photonic-crystal electro-optic modulator

Modern advanced photonic integrated circuits require dense integration of high-speed electro-optic functional elements on a compact chip that consumes only moderate power. Energy efficiency, operation speed, and device dimension are thus crucial metrics underlying almost all current developments of photonic signal processing units. Recently, thin-film lithium niobate (LN) emerges as a promising platform for photonic integrated circuits. Here, we make an important step towards miniaturizing functional components on this platform, reporting high-speed LN electro-optic modulators, based upon photonic crystal nanobeam resonators. The devices exhibit a significant tuning efficiency up to 1.98 GHz V−1, a broad modulation bandwidth of 17.5 GHz, while with a tiny electro-optic modal volume of only 0.58 μm3. The modulators enable efficient electro-optic driving of high-Q photonic cavity modes in both adiabatic and non-adiabatic regimes, and allow us to achieve electro-optic switching at 11 Gb s−1 with a bit-switching energy as low as 22 fJ. The demonstration of energy efficient and high-speed electro-optic modulation at the wavelength scale paves a crucial foundation for realizing large-scale LN photonic integrated circuits that are of immense importance for broad applications in data communication, microwave photonics, and quantum photonics.

Time-Stretched Femtosecond Lidar Using Microwave Photonic Signal Processing

A real-time ranging lidar with 0.1 Mega Hertz update rate and few-micrometer resolution incorporating dispersive Fourier transformation and instantaneous microwave frequency measurement is proposed and demonstrated. As time-stretched femtosecond laser pulse passing through an all-fiber Mach-Zehnder Interferometer, where the detection light beam is inserted into the optical path of one arm, the displacement is encoded to the frequency variation of the temporal interferogram. To deal with the challenges in storage and real-time processing of the microwave pulse generated on a photodetector, we turn to all-optical signal processing. A carrier wave is modulated by the time-domain interferogram using an intensity modulator. After that, the frequency variation of the microwave pulse is uploaded to the first order sidebands. Finally, the frequency shift of the sidebands is turned into transmission change through a symmetric-locked frequency discriminator. In experiment, A real-time ranging system with adjustable dynamic range and detection sensitivity is realized by incorporating a programmable optical filter. Standard deviation of 7.64 {\mu}m, overall mean error of 19.10 {\mu}m over 15 mm detection range and standard deviation of 37.73 {\mu}m, overall mean error of 36.63 {\mu}m over 45 mm detection range are obtained respectively.

Repetition-Frequency-Doubled Transform-Limited Optical Pulse Generation Based on Silicon Modulators

Compact and integrated optical pulse generation with a high repetition rate and a small duty cycle can benefit various applications such as integrated microwave photonics. In this work, a method to generate a repetition-frequency-doubled narrow optical pulse train based on two cascaded silicon Mach–Zehnder modulators is proposed and demonstrated. The generated frequency comb has even-order sidebands with linear phase and suppressed odd-order sidebands, which results in the transform-limited pulses in the time domain. The tunability of the repetition rate from 4.0 to 6.6 GHz and the duty cycle from 10.6% to 14.0% has been achieved. An analytic model that considers the non-ideal properties of the silicon modulators is also established and is able to reproduce the key features in the experiment. Our work shows the potential of an integrated silicon chip to generate high-speed optical pulse trains with tunable duty cycles demanded in integrated microwave photonics and integrated photonic signal processing.

Mesh-Structure-Enabled Programmable Multitask Photonic Signal Processor on a Silicon Chip

Photonic integrated circuits (PICs) have recently attracted extensive attention in advanced photonic signal processing to meet the ever-increasing demands on high-speed and ultracompact data signal...

Multitasking and Cascadable Microwave Photonic Signal Processing Topologies with Silicon Photonic Technologies

ABSTRACT Microwave photonics (MWPs) is an emerging interdisciplinary field, where photonics technologies are adopted to facilitate the generation, transmission, detection, and processing of signals at radio-wave, microwave, and millimeter-wave frequencies. Recently, the integrated photonic technology has demonstrated its capability to miniaturize photonic circuits on a single chip, which paves the way for next-generation integrated MWP signal processing systems having reduced size, weight, and power consumption (SWaP) specifications. In particular, by means of incorporating complementary metal-oxide-semiconductor (CMOS) electronic, optical, and optoelectronic components on a single integrated chip, silicon photonic circuits have brought new architectures and functionalities for MWP signal processing. This accelerates the evolution of MWPs from a single-use microwave signal processor toward a multitasking and cascadable MWP system, which is readily adaptable for a wide variety of uses and applications. In this review article, we provide an overview of the fundamental principle of the MWP signal processing topology. Developments in the microwave filtering technologies are reviewed with a focus on the integrated microwave filtering enhanced by optical phase equalization. We also review the recent progress and give an outlook for the future trend in MWP signal topologies, exploring the realization of multitasking and cascadable microwave signal processing systems based on silicon photonics.

Self-Configuring and Reconfigurable Silicon Photonic Signal Processor

Photonic signal processing is essential in the optical communication and optical computing. Numerous photonic signal processors have been proposed, but most of them exhibit limited reconfigurability and automaticity. A feature of fully automatic implementation and intelligent response is highly desirable for the multipurpose photonic signal processors. Here, we report and experimentally demonstrate a fully self-learning and reconfigurable photonic signal processor based on an optical neural network chip. The proposed photonic signal processor is capable of performing various functions including multichannel optical switching, optical multiple-input-multiple-output descrambler and tunable optical filter. All the functions are achieved by complete self-learning. Our demonstration suggests great potential for chip-scale fully programmable optical signal processing with artificial intelligence.

Few-Mode Fibers With Uniform Differential Mode Group Delay for Microwave Photonic Signal Processing

We present a novel design of few-mode fiber (FMF) with a uniform differential mode group delay (U-DMGD) among propagating modes and apply the FMF to a single-fiber delay line module for implementing microwave photonic finite impulse response (FIR) filters. By optimizing key parameters such as the core grading exponent and the dimension of the trench of FMF, a U-DMGD between adjacent modes among four modes (LP 01 , LP 11 , LP 02 and LP 31 ) over the entire C band is achieved. Wavelength dependence is entirely removed. An FIR microwave photonic filter (MPF) implemented using the designed 1-km FMF is investigated through numerical simulations. The free spectral range (FSR) of the MPF is 5.7 GHz, the 3-dB bandwidth is 1.26 GHz, and the main lobe-to-side lobe ratio (MSR) is 10.42 dB. Discussions on fabrication aspects have also been presented. The proposed single-fiber delay line structure based on FMF can significantly reduce the system complexity of microwave photonic signal processing.

Fully Reconfigurable Waveguide Bragg Gratings for Programmable Photonic Signal Processing

Fiber Bragg gratings have been invented for over three decades now and have been intensively employed in optical communication and sensor systems. The key limitation of a fiber Bragg grating is that once fabricated, it is hard to be tuned or with very limited tunability via thermal or mechanical tuning. Recently, great efforts have been directed into the study of realizing Bragg gratings on silicon-on-insulator (SOI) platform. The key advantage of Bragg gratings based on SOI is that the gratings can be fast and electrically reconfigured with the use of free-carrier plasma dispersion effect in silicon, which can be employed for fast programmable photonic signal processing. In this article, Bragg gratings based on SOI that are electrically programmable will be reviewed and their use for advanced programmable optical and microwave signal processing will be discussed.

Microcomb-Based Photonic RF Signal Processing

Microcombs are powerful tools as sources of multiple wavelength channels for photonic RF signal processing. They offer a compact device footprint, large numbers of wavelengths, and wide Nyquist bands. Here, we review recent progress on microcomb-based photonic RF signal processors, including true time delays, reconfigurable filters, Hilbert transformers, differentiators, and channelizers. The strong potential of optical micro-combs for RF photonics applications in terms of functions and integrability is also discussed.

Large on-chip Brillouin net amplification in silicon-based nano-photonics

Recent developments in on-chip forward Brillouin scattering open up potential applications such as RF photonic signal processing, on-chip Brillouin amplification, and on-chip Brillouin lasers. The stimulated Brillouin scattering gain coefficients become significant with a small optical mode area, and the Brillouin net amplification has been believed to be strong with a small mode area, too. However, here, we present a theoretical study of higher net amplification with a large optical mode area than that with a small mode area and explain this counter-intuitive phenomenon by examining the contribution of various optical forces to Brillouin gain coefficients for various optical waveguide dimensions. The simulation results show that a waveguide with large optical waveguide dimensions can yield significant net amplification by high Brillouin gain coefficients and low optical losses at high pump power even if the Brillouin gain coefficients are lower than that with a small waveguide dimension. Therefore, it is necessary to optimize the optical waveguide dimensions to achieve maximum net amplification for the development of Brillouin lasers and amplifiers in silicon-based nanophotonics.

Ring-core few-mode fiber for tunable true time delay line operation.

We propose, for the first time to our knowledge, tunable true time delay line operation for radiofrequency signals on a few-mode fiber link. In particular, the custom design of a 7-LP-mode ring-core few-mode fiber together with a set of 5 broadband long period gratings inscribed at the proper positions along the fiber allows 4-sample true time delay line tunability over a 20-nm optical wavelength range. We study the performance of the designed true time delay line in the context of reconfigurable microwave photonics signal processing by theoretically evaluating microwave signal filtering and optical beamforming networks for phased array antennas.

Bending and twisting effects on multicore fiber differential group delay.

In this paper we provide the theoretical and experimental evaluation of fiber bending and twisting effects on the group delay performance of a homogeneous 7-core fiber. We have experimentally evaluated the differential group delay between the central and outer cores for different curvature radii and twisting conditions, demonstrating that fiber twisting counteracts the degradation introduced by the curvature itself. These findings are generally applicable to time-sensitive application areas such as radio-over-fiber distribution and microwave photonics signal processing in fiber-wireless access networks, as well as high-capacity long-haul digital communications where digital multiple-input multiple-output processing may be required.