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We experimentally demonstrate a new kind of integrated Si 3 N 4 microwave photonic (MWP) signal processor that combines a programmable modulation transformer (MT) with a versatile double-injection ring resonator (DI-RR). With this circuit we show an array of MWP filtering functions unmatched by traditional MWP circuits.

Microwave signal filtering is a fundamental and central functionality in radio-frequency (RF) systems. Underpinned by advanced integrated photonics technologies, emerging integrated microwave photonic (IMWP) filter platforms enable reconfigurable and widely tunable RF signal filtering functionalities that were unattainable using conventional electronics while also exhibiting superior features in terms of compactness, light weight, stability, low power consumption, and low latency. This paper presents a comprehensive review of the principles, architectures, and performance of IMWP filters. We highlight recent advances of IMWP filters enabled by on-chip nonlinear optics, RF-interference technology and emerging integration platforms, with an emphasis on the RF performance which is critical for their usability in real-world applications. We conclude with a perspective on future research challenges and new possibilities for IMWP filters.

One of the key functionalities in microwave photonics is to be able to define controllable time delays during the signal processing. Optical fibers are often used to achieve this functionality, especially when a long delay or a widely-tunable delay is needed. However, the stability of this delay in the presence of environmental changes (e.g., temperature) has not, to the best of our knowledge, been reviewed yet. Here, we firstly discuss the impact of temperature-induced variations on the signal propagation time in optical fibers and its implications in microwave photonics. We compare the impact of the thermal sensitivity of various delay lines for applications in which the signal is transported from point A to point B, as well as for applications in which the propagation time through a fiber or the fiber dispersion is used to create a fixed or tunable delay. In the second part of the article we show the impact of fiber thermal sensitivity on a narrow-band microwave photonics filter made of standard single mode fiber (SSMF) and a hollow core fiber (HCF), which has significantly lower thermal sensitivity of propagation time to temperature. The central frequency of the band-pass filter changes almost 16 times more in the filter made of SSMF as compared to that of HCF, dictating very tight (0.05 °C) temperature stabilization for SSMF-based filters. On the basis of our thermal sensitivity analysis we conclude that HCFs are very promising for environmentally stable microwave photonics applications.

Optical modulation plays arguably the utmost important role in microwave photonic (MWP) systems. Precise synthesis of modulated opti- cal spectra dictates virtually all aspects of MWP system quality including loss, noise figure, linearity, and types of functionalities that can be executed. However, for such a critical function, the versatility to generate and transform analog optical modulation is severely lacking, blocking the pathways to truly unique MWP functions including ultra-linear links and low-loss high rejection filters. Here, we demonstrate a versatile radiofrequency (RF) photonic spectral shaper integrated in a silicon photonic circuit. The spectral shaper controls the two modu- lation bands generated from an electro-optic modulation process in their relative amplitude and phase, offering an enhanced versatility for microwave-photonic modulation applications. Using the spectral shaper, we show electrically tailorable modulation transformations. Fur- thermore, we show a series of unprecedented RF filtering experiments through monolithic integration of the spectral shaper with a network of reconfigurable ring resonators.

A silicon nitride chip-based tunable microwave photonic notch filter based on phase-to-intensity modulation conversion with dual-sideband processing is proposed. Furthermore, an integrated optical carrier filtering is added to enhance the noise performance of the filter.

We discuss a new concept in integrated microwave photonics (MWP) aiming at complex phase and amplitude tailoring of RF modulated spectrum for advanced functionalities including modulation transformation and all-optimized MWP filtering.

An overview of the most recent developments and improvements to the low-loss TriPleX Si3N4 waveguide technology is presented in this paper. The TriPleX platform provides a suite of waveguide geometries (box, double stripe, symmetric single stripe, and asymmetric double stripe) that can be combined to design complex functional circuits, but more important are manufactured in a single monolithic process flow to create a compact photonic integrated circuit. All functionalities of the integrated circuit are constructed using standard basic building blocks, namely straight and bent waveguides, splitters/combiners and couplers, spot size converters, and phase tuning elements. The basic functionalities that have been realized are: ring resonators and Mach–Zehnder interferometer filters, tunable delay elements, and waveguide switches. Combination of these basic functionalities evolves into more complex functions such as higher order filters, beamforming networks, and fully programmable architectures. Introduction of the active InP chip platform in a combination with the TriPleX will introduce light generation, modulation, and detection to the low-loss platform. This hybrid integration strategy enables fabrication of tunable lasers, fully integrated filters, and optical beamforming networks.

Processing of microwave signals using photonics has several key advantages for applications in wireless communications. However, to bring photonic-based microwave signal processing to the mainstream requires a reduction of the form factor. Integration is a route for achieving high-performance, low-cost, and small-footprint microwave photonic devices. A high on-chip stimulated Brillouin scattering (SBS) gain is essential for synthesizing several key functionalities for advanced integrated microwave signal processing. We have optimized our on-chip SBS platform to achieve a record on-chip gain of 52 dB. In this paper, we discuss the implications of this giant gain from the viewpoint of new enabled technologies. The giant gain can be distributed over wide frequencies, which can be exploited for the realization of reconfigurable microwave bandpass, bandstop, and multiband filters. High gain also enables the demonstration of low-threshold on-chip lasers, which can be of relevance for a low-noise radio-frequency signal generation. These wide ranges of functionalities are made possible by the breakthrough on-chip gain makes Brillouin-based microwave photonic signal processing a promising approach for real-world implementation in the near future.

Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth as well as compatibility for embedding into integrated photonic circuits are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si3N4 in SiO2) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around 1.55 um wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser., 25 pages, 16 figures

Signal processing using on-chip nonlinear or linear optical effects has shown tremendous potential for RF photonic applications. Combining nonlinear and linear elements on the same photonic chip can further enable advanced functionality and enhanced system performance in a robust and compact form. However, the integration of nonlinear and linear optical signal processing units remains challenging due to the competing and demanding waveguide requirements, specifically the combination of high optical nonlinearity in single-pass waveguides, which is desirable for broadband signal processing with low linear loss and negligible nonlinear distortions required for linear signal processing. Here, we report the first demonstration of integrating Brillouin-active waveguides and passive ring resonators on the same integrated photonic chip, enabling an integrated microwave photonic notch filter with ultradeep stopband suppressions of >40 dB, a low filter passband loss of

On-chip stimulated Brillouin scattering (SBS) that results from enhanced light–sound interactions, has recently demonstrated great applicability and versatility for signal generation and manipulation. Progress toward realizing fully integrated Brillouin photonic circuits is promising; however, the control and routing of on-chip optical waves requires non-reciprocal elements such as circulators, which is challenging and adds complexity. Here, a circulator-free Brillouin photonic planar waveguide circuit which eliminates the need for separate non-reciprocal elements is demonstrated. Backward inter-modal Brillouin scattering (BIBS) is used in a planar photonic integrated circuit, for the first time, to provide Brillouin processing capability in a multi-modal waveguide, conveniently allowing for the separation of counter-propagating pump and signal using passive integrated mode-selective filters. Using an As2S3–Si hybrid multi-modal photonic circuit, inter-optical-mode energy transfer with a Brillouin gain coefficient of 280 m−1W−1 is experimentally demonstrated, representing two orders of magnitude enhancement compared to conventional optical fibers. This on-chip BIBS circuit allows for independent routing of pump and signal waves, showing resilience to the cross talk. The experimental demonstrations provide an important basis for achieving fully integrated Brillouin photonic circuits without requiring on-chip circulators and fine spectral filtering, opening a new dimension for studying spatial-dependent photon–phonon nonlinear dynamics.

The last few years have seen major progress in harnessing on-chip photon-phonon interactions, leading to a wide range of demonstrations of new functionalities. Utilizing not only the optical response of a nonlinear waveguide - but also acoustic resonances - enables the realization of microwave devices with unprecedented performance, otherwise hard to achieve in all-optical processing schemes or electronically. Here, we overview on-chip stimulated Brillouin scattering (SBS) with special emphasis on microwave sources and microwave signal processing schemes. We review the different material platforms and structures for on-chip SBS, ranging from chalcogenide rib waveguides to hybrid silicon/silicon-nitride structures, high-Q photonic-phononic silica microresonators, and suspended silicon nanowires. We show that the paradigm shift in SBS research - from long length of fibers to chip-scale devices - is now moving toward fully integrated photonic-phononic CMOS chips.

We present a high-performance, low-noise figure tunable microwave photonic bandpass filter based on stimulated Brillouin scattering (SBS) loss responses. The bandpass filter response is formed by suppressing the out-of-band signal using multiple broadened SBS loss responses on a high-performance MWP link without introducing additional noise in the passband. A noise figure of 20 dB and -17 dB link gain of 100 MHz passband bandwidth at 14 GHz with spurious free dynamic range of 105 dB.Hz$^{2/3}$ are obtained. Multi-bandpass response, bandwidth reconfigurability from 100 MHz to 1 GHz and center frequency tunability up to 16 GHz are also demonstrated.

In this paper we present high stimulated Brillouin scattering (SBS) gain in a chip-scale device. Narrowband gain of >50 dB is achieved in a chalcogenide waveguide with a bandwidth of ~10 MHz. Such a large gain is promising for on-chip amplification for the realization of integrated structures with many optical components, as well as for RF photonic and optical signal processing applications. We harness the highly efficient SBS interaction in the photonic chip to realize low-power RF filters, phase shifters and delay lines. Through the concept of RF interference an enhancement in the delay by almost a factor of 6 compared to pure SBS-based slow light is observed, making this technology promising for lowpower-budget RF photonic systems.

We overview our recent progress in Si 3 N 4 -photonic-chip-based microwave photonic filters, with demonstrations of optimized link-performance, advanced functionalities and compactness which are crucial properties for practical employment in future and existing radio-frequency (RF) signal processing systems.

We report a silicon nitride chip-based radio-frequency photonic notch filter with an unprecedented performance including an RF gain of 8 dB, a record-low noise figure of 15.6 dB, and a spurious-free dynamic range of 116 dB·Hz2/3, with a stop band rejection of 50 dB. This level of performance is achieved by using on-chip resonators’ unique phase responses, and thorough optimizations of the photonic link. These record results will potentially stimulate future implementations of integrated microwave photonic subsystems for real-world applications.

We present our recent results on harnessing the nonlinear stimulated Brillouin scattering effect on a photonic chip for coherent optical communications. At the transmitter-end, an optical frequency comb was regenerated through on-chip Brillouin scattering for 64-level QAM communications. At the receiver-end, low-latency self-homodyne reception was achieved through Brillouin-assisted carrier recovery.

We present a microwave photonic notch filter based on a Si 3 N 4 photonic chip, with a noise figure of less than 20 dB, a positive link gain and an ultra-deep rejection beyond 50 dB in the stopband. This level of performance is achieved by using on-chip resonators' unique phase responses, and thorough optimizations of the photonic link.

Integrated microwave photonics has strongly emerged as a next-generation technology to address limitations of conventional RF electronics for wireless communications. High-resolution RF signal processing still remains a challenge due to limitations in technology that offer sub-GHz spectral resolution, in particular at high carrier frequencies. In this paper, we present an on-chip high-resolution RF signal processor, capable of providing high-suppression spectral filtering, large phase shifts and ns-scale time delays. This was achieved through tailoring of the Brillouin gain profiles using Stokes and anti-Stokes resonances combined with RF interferometry on a low-loss photonic chip with strong opto-acoustic interactions. Using an optical power of

We report a silicon nitride RF photonic notch filter with unprecedented performance including 8 dB of RF gain, record-low noise figure of 15.6 dB, and spurious-free dynamic range of 116 dB while achieving an ultra-deep rejection of beyond 50 dB in the stopbands., Presented as a post deadline paper at CLEO Pacific Rim 2017

We demonstrate the first all-optical carrier recovery of coherent signals using on-chip Brillouin gain, replacing digital techniques, with sub-nanosecond latency. This demonstration serves as a proof-of-concept for integrated photonic carrier recovery chips for coherent communications.

We for the first time, study the effect of signal power variations on the extinction ratio and bandwidth of on-chip Brillouin filters for applications in RF photonics and coherent optical communications. The passband extinction reduces from 35 dB to 25 dB on increasing the input signal power by 36 dB, while the bandwidth increased from 13 MHz to 30 MHz.

A range of unique capabilities in optical and microwave signal processing and generation have been demonstrated using stimulated Brillouin scattering (SBS). The need to harness SBS in mass-manufacturable integrated circuits has led to a focus on silicon-based material platforms. Remarkable progress in silicon-based Brillouin waveguides has been made, but results have been hindered by nonlinear losses present at telecommunications wavelengths. Here, we report on a new approach to surpass this issue through the integration of a high Brillouin gain material, As2S3, onto a silicon-based chip. We fabricated a compact spiral device within a silicon circuit, achieving an order-of-magnitude improvement in Brillouin amplification. To establish the flexibility of this approach, we fabricated a ring resonator with free spectral range precisely matched to the Brillouin shift, enabling the first demonstration, to our knowledge, of Brillouin lasing in a planar integrated circuit. Combining active photonic components with the SBS devices shown here will enable the creation of compact, mass-manufacturable optical circuits with enhanced functionalities.

We demonstrate a technique that enables three-fold enhancement of time delay and seamless delay switching for RF signals at gigahertz speed from optical ring resonators on an integrated Si 3 N 4 chip, solely by optical power control.

Incorporation of photonic integration in microwave signal processing is one of the fastest growing fields. This technology is expected to underpin ultra-high-speed wireless communications. Here we review the latest advancements in integrated microwave photonics.

We present an integrated RF photonic notch filter on a Si 3 N 4 chip, with tunable bandwidth (150–300 MHz), high rejection (>50 dB), tuning range of 1–12GHz and negligible RF insertion loss, using resonators' unique phase responses.

We discuss the recent advances of on-chip stimulated Brillouin scattering for signal processing, including for tunable RF filtering, regeneration of optical frequency combs, and for generation of narrow linewidth laser on a hybrid silicon chip.

Demonstration of continuously tunable delay, low- noise lasers, dynamically controlled gratings, and optical phase shifting using the stimulated Brillouin scattering (SBS) process has lead to the emergence of SBS as a promising technology for microwave photonics. On-chip realization of SBS enables photonic integration of microwave photonic signal processing and offers significantly enhanced performance and improved efficiency. On-chip stimulated Brillouin scattering is reviewed in the context of slow-light based tunable delay, low-noise narrow linewidth lasers and filtering for integrated microwave photonics. A discussion on key material and device properties, necessary to enable on-chip Brillouin scattering using both the single-pass and resonator geometry, is presented along with an outlook for photonic integration of microwave signal processing and gener- ation in other platforms.

Microwave photonic bandpass filters (MPBPFs) are important building blocks in radio-frequency (RF) signal processing systems. However, most of the reported MPBPFs fail to satisfy the stringent real-world performance metrics, particularly low RF insertion loss. In this paper we report a novel MPBPF scheme using two cascaded integrated silicon nitride (Si3N4) ring resonators, achieving a high link gain in the RF filter passband. In this scheme, one ring operates at an optimal over-coupling condition to enable a strong RF passband whilst an auxiliary ring is used to increase the detected RF signal power via tuning the optical carrier-to-sideband ratio. The unique combination of these two techniques enables compact size as well as high RF performance. Compared to previously reported ring-based MPBPFs, this work achieves a record-high RF gain of 1.8 dB in the passband, with a high spectral resolution of 260 MHz. Furthermore, a multi-band MPBPF with optimized RF gain, tunable central frequencies, and frequency spacing tunability is realized using additional ring resonators, highlighting the scalability and flexibility of this chip-based MPBPF scheme.

We present a high link-performance multi-band microwave photonic filter based on stimulated Brillouin scattering (SBS) loss responses. The bandpass filter response is formed by suppressing the out-of-band signal using multiple broadened SBS loss responses, which avoids introducing additional noise in the passband. The low-noise SBS bandpass filter is implemented in an optimized high-performance MWP link, which enabled the demonstration of filter functionalities with a low noise figure, reconfigurability, and high resolution. A noise figure of 18.9 dB is achieved in the passband with a filter bandwidth of 0.3 GHz at a central frequency of 14 GHz, with a link gain of −13.9 dB and a spurious free dynamic range of 106 dB.Hz2/3. Bandwidth reconfiguration from 0.1 GHz to 1 GHz and multi-bandpass responses are also demonstrated.

Microwave photonics (MWP) is an emerging field in which radio frequency (RF) signals are generated, distributed, processed and analyzed using the strength of photonic techniques. It is a technology that enables various functionalities which are not feasible to achieve only in the microwave domain. A particular aspect that recently gains significant interests is the use of photonic integrated circuit (PIC) technology in the MWP field for enhanced functionalities and robustness as well as the reduction of size, weight, cost and power consumption. This article reviews the recent advances in this emerging field which is dubbed as integrated microwave photonics. Key integrated MWP technologies are reviewed and the prospective of the field is discussed.

We present the first demonstration of a broadband and continuously tunable integrated optical beamforming network (IOBFN) capable of providing continuously tunable true-time-delay up to 236 ps over the entire DVB-S band (10.7–12.75 GHz), realized with a CMOS compatible process. The tunable delays are based on reconfigurable optical ring resonators in conjunction with a single optical sideband filter integrated on the same optical chip. The delays and filter responses are software programmable. Four tunable delay lines are integrated on a single chip and configured to feed a 16-element linear antenna array. The broadband beam steering capability of the proposed IOBFN is demonstrated by the squint-free antenna pattern generated from the measured RF amplitude and phase responses of the optical delay line.

Microwave photonic filters tunable up to 30 GHz are realized on a chip using stimulated Brillouin scattering. Tailoring of the pump allows bandwidth reconfigurability from 50MHz to 440MHz with a pass band ripple of

We present the first functional signal processing device based on stimulated Brillouin scattering from a silicon nanowire. We use only 0.98dB SBS gain to create a tunable RF notch filter with an ultrahigh 48dB suppression.

A rectangular microwave photonicfilter is proposed using on-chip silicon nitride ring resonators. The bandwidth of such filter can be largely adjusted from 1GHz to 13GHz in a very simple scheme.

Dynamic optical tuning of a Si3N4 ring resonator RF photonic delay line is experimentally demonstrated. Tunable delay and advancement of microwave pulses were achieved solely by controlling the power of an additional out-of-phase optical signal.

UltraNarrow RF bandpass filters with a high extinction of up to 45 dB have been demonstrated by shaping the Brillouin gain and through destructive signal interference at the tail of the Brillouin response.

We fabricated a nonlinear loss engineered silicon-chalcogenide hybrid waveguide and experimentally demonstrated TPA reduction. Additionally, we showed a five-fold improvement in the figure of merit compared to standard silicon nanowire.

We discuss the processing of RF signals using integrated stimulated Brillouin scattering. Bandpass and bandstop filters with wide reconfigurability and tuning are demonstrated. Furthermore, through the concept of RF interferometry, lossless phase amplification is demonstrated.

We show the first functional signal processing device based on forward stimulated Brillouin scattering from a silicon nanowire. We harness 1dB of SBS gain to create a high performance, energy efficient microwave photonic notch filter. The filter possess 48dB of suppression, 98 MHz linewidth, and is tunable within a 6 GHz bandwidth. This demonstration represents a significant advance in integrated microwave photonics with potential applications in on-chip microwave signal processing and establish the foundation towards the first CMOS-compatible high performance RF photonic filter.

Harnessing nonlinear optical effects in a photonic chip scale has been proven useful for a number of key microwave photonic applications. Here we look at a number of material platforms that can serve as the ideal platform for nonlinear integrated microwave photonics.

A photonic scheme of instantaneous multiple microwave frequencies measurement is realized using a narrow-band tunable notch filter based on stimulated Brillouin scattering. Using this technique, estimation of multiple GHz microwave frequencies with errors lower than 250 kHz is achieved.

In this paper we consider two new topologies of a tunable microwave photonic phase shifter using stimulated Brillouin scattering. In the first topology, independent phase and amplitude control of an optical carrier was achieved by controlling two SBS pumps in an optical fiber leading to a record demonstration of 360° continuously tunable phase shift, with less than 0.25 dB output power fluctuations, over a frequency band from 1.5 to 31 GHz. In the second topology, the first integrated phase shifter using SBS on chip was demonstrated. We highlight an advantage of a shorter integrated platform compared to a long length of optical fibers, which is a higher pump depletion threshold that leads to a greater potential for reducing the phase shifter insertion loss.

Photonic chip based time-bin entanglement has attracted significant attention because of its potential for quantum communication and computation. Useful time-bin entanglement systems must be able to generate, manipulate and analyze entangled photons on a photonic chip for stable, scalable and reconfigurable operation. Here we report the first time-bin entanglement photonic chip that integrates time-bin generation, wavelength demultiplexing and entanglement analysis. A two-photon interference fringe with an 88.4% visibility is measured (without subtracting any noise), indicating the high performance of the chip. Our approach, based on a silicon nitride photonic circuit, which combines the low-loss characteristic of silica and tight integration features of silicon, paves the way for scalable real-world quantum information processors., 4 pages, 5 figures

Here we show the first chip-based RF photonic band-stop filter with ultra-high suppression, high resolution, and 1-30 GHz frequency tuning. This record performance was achieved using an ultra-low Brillouin gain from a compact photonic chip

We present the first functional signal processing device based on stimulated Brillouin scattering from a silicon nanowire. We use only 0.98dB SBS gain to create a tunable RF notch filter with an ultrahigh 48dB suppression.

We demonstrate a scheme for minimising the insertion loss of an RF photonic filter, by exploiting the phase response of stimulated Brillouin scattering. We achieve a filter with high suppression, tunable bandwidth and low loss.

We report a technique to simultaneously optimize the peak rejection and the resolution of a radiofrequency photonic notch filter based on a silicon nitride ring resonator.