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Non-reciprocal optical components such as isolators and circulators are crucial for preventing catastrophic backreflection and controlling optical cross talk in photonic systems. While non-reciprocal devices based on Brillouin intermodal transitions have been experimentally demonstrated in chip-scale platforms, harnessing such interactions has required a suspended waveguide structure, which is challenging to fabricate and is potentially less robust than a non-suspended structure, thereby limiting the design flexibility. In this paper, we numerically investigate the performance of a Brillouin-based isolation scheme in which a dual-pump-driven optoacoustic interaction is used to excite confined acoustic waves in a traditional ridge waveguide. We find that acoustic confinement, and therefore the amount of Brillouin-driven mode conversion, can be enhanced by selecting an appropriate optical mode pair and waveguide geometry of two arsenic-based chalcogenide platforms. Further, we optimize the isolator design in its entirety, including the input couplers, mode filters, the Brillouin-active waveguide as well as the device fabrication tolerances. We predict such a device can achieve 30 dB isolation over a 38 nm bandwidth when 500 mW pump power is used; in the presence of a ± 10 n m fabrication-induced width error, such isolation can be maintained over a 5–10 nm bandwidth.

Electrodes in close proximity to an active area of a device are required for sufficient electrical control. The integration of such electrodes into optical devices can be challenging since low optical losses must be retained to realise high quality operation. Here, we demonstrate that it is possible to place a metallic shallow phosphorus doped layer in a silicon micro-ring cavity that can function at cryogenic temperatures. We verify that the shallow doping layer affects the local refractive index while inducing minimal losses with quality factors up to 10$^5$. This demonstration opens up a pathway to the integration of an electronic device, such as a single-electron transistor, into an optical circuit on the same material platform., Comment: 6 figures

We present the first demonstration of backward stimulated Brillouin scattering between distinct guided optical spatial modes in an integrated multi-modal photonic circuit. This unique opto-acoustic process enables new opportunities for on-chip Brillouin signal processing technology.

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 demonstrate a microwave photonic spectral shaper in a silicon chip enabling distinct phase and amplitude modulation transformation. We show unprecedented RF filtering through monolithic integration of the spectral shaper with tunable ring resonators.

Recent advances in design and fabrication of photonic-phononic waveguides have enabled stimulated Brillouin scattering (SBS) in silicon-based platforms, such as under-etched silicon waveguides and hybrid waveguides. Due to the sophisticated design and more importantly high sensitivity of the Brillouin resonances to geometrical variations in micro- and nano-scale structures, it is necessary to have access to the localized opto-acoustic response along those waveguides to monitor their uniformity and maximize their interaction strength. In this work, we design and fabricate photonic-phononic waveguides with a deliberate width variation on a hybrid silicon-chalcogenide photonic chip and confirm the effect of the geometrical variation on the localized Brillouin response using a distributed Brillouin measurement., 5 pages, 4 figures

Integrated silicon microwave photonics offers great potential in microwave phase shifter elements, and promises compact and scalable multi-element chips that are free from electromagnetic interference. Stimulated Brillouin scattering, which was recently demonstrated in silicon, is a particularly powerful approach to induce a phase shift due to its inherent flexibility, offering an optically controllable and selective phase shift. However, to date, only moderate amounts of Brillouin gain has been achieved and theoretically this would restrict the phase shift to a few tens of degrees, significantly less than the required 360 degrees. Here, we overcome this limitation with a phase enhancement method using RF interference, showing a 360 degrees broadband phase shifter based on Brillouin scattering in a suspended silicon waveguide. We achieve a full 360 degrees phase-shift over a bandwidth of 15 GHz using a phase enhancement factor of 25, thereby enabling practical broadband Brillouin phase shifter for beam forming and other applications., Comment: \copyright 2019 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved

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 present a novel measurement technique to perform full phase-sensitive tomography on the joint spectrum of photon pair sources, using stimulated four-wave mixing and phase-sensitive amplification. Applying this method to an integrated silicon nanowire source with a frequency chirped pump laser, we are able to observe a corresponding phase change in the spectral amplitude that would otherwise be hidden in standard intensity measurements. With a highly nonlinear fiber source, we show that phase-sensitive measurements have superior sensitivity to small spectral features when compared to intensity measurements. This technique enables more complete characterization of photon pair sources based on nonlinear photonics.

We demonstrate a compact silicon-on-sapphire (SOS) strip waveguide sensor for mid-IR absorption spectroscopy. This device can be used for gas and liquid sensing, especially to detect chemically similar molecules and precisely characterize extremely absorptive liquids that are difficult to detect by conventional infrared transmission techniques. We reliably measure concentrations up to 0.25% of heavy water (Dsub2/subO) in a Dsub2/subO-Hsub2/subO mixture at its maximum absorption band at around 4 μm. This complementary metal-oxide-semiconductor (CMOS) compatible SOS Dsub2/subO sensor is promising for applications such as measuring body fat content or detection of coolant leakage in nuclear reactors.

Wavelength-scale SBS waveguides are enabling novel on-chip functionalities. The micro- and nano-scale SBS structures and the complexity of the SBS waveguides require a characterization technique to monitor the local geometry-dependent SBS responses along the waveguide. In this work, we experimentally demonstrate detection of longitudinal features down to 200$\mu$m on a silicon-chalcogenide waveguide using the Brillouin optical correlation domain analysis (BOCDA) technique. We provide simulation and analysis on how multiple acoustic and optical modes and geometrical variations influence the Brillouin spectrum., Comment: 8 pages, 6 figures

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 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 record high Brillouin gain in a silicon chip through hybrid integration. Negligible nonlinear losses lead to a net gain amplification of 18.5 dB in a compact (0.3 mm2) 5.7cm As2S3 spiral.

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.

Integrated sources of indistinguishable photons have attracted a lot of attention because of their applications in quantum communication and optical quantum computing. Here, we demonstrate an ultracompact quantum splitter for degenerate photon pairs based on a monolithic silicon chip. It incorporates a Sagnac loop and a microring resonator with a total footprint of 0.011 mm2, generating and deterministically splitting indistinguishable photon pairs using two-photon interference. The ring resonator provides an enhanced photon generation rate, and the Sagnac loop ensures the photons travel through equal path lengths and interfere with the correct phase to enable the reversed Hong–Ou–Mandel (HOM) effect to take place. In the experiment, we observed a HOM dip visibility of 94.5±3.3%, indicating the generated photons are in a suitable state for further integration with other components for quantum applications, such as controlled-NOT gates.

The mobile nature of fluids is fully exploited in planar photonic crystals to not only tune and reconfigure in situ optical microcavities, in a continuous and reversible manner, but also to create "a posteriori" spatially programmable cavities. Both the amount of liquid and the location of the selectively infiltrated area can be accurately controlled either mechanically, using a microfiber manipulator, or optically, using a laser-controlled evaporation and recondensation scheme. The wide applicability is illustrated by tuning a cavity resonance over 50¿nm, adjusting the frequency splitting of an originally degenerate cavity mode, and by freely moving a liquid-induced cavity through dragging a microdroplet.

We demonstrate the first, to the best of our knowledge, functional signal processing device based on stimulated Brillouin scattering in a silicon nanowire. We use only 1 dB of on-chip stimulated Brillouin scattering gain to create an RF photonic notch filter with 48 dB of suppression, 98 MHz linewidth, and 6 GHz frequency tuning. This device has potential applications in on-chip microwave signal processing and establishes the foundation for the first CMOS-compatible high-performance RF photonic filter.

Instantaneous frequency measurement (IFM) of microwave signals is a fundamental functionality for applications ranging from electronic warfare to biomedical technology. Photonic techniques, and nonlinear optical interactions in particular, have the potential to broaden the frequency measurement range beyond the limits of electronic IFM systems. The key lies in efficiently harnessing optical mixing in an integrated nonlinear platform, with low losses. In this work, we exploit the low loss of a 35 cm long, thick silicon waveguide, to efficiently harness Kerr nonlinearity, and demonstrate the first on-chip four-wave mixing (FWM) based IFM system. We achieve a large 40 GHz measurement bandwidth and record-low measurement error. Finally, we discuss the future prospect of integrating the whole IFM system on a silicon chip to enable the first reconfigurable, broadband IFM receiver with low-latency., 13 pages, 7 figures

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 generate a 1.9-4.9 µm supercontinuum in dispersion engineered silicon waveguides with a sapphire substrate. The sapphire substrate allows for extension of the long wavelength edge into the mid-IR by ~1000 nm over silicon-on-silica waveguides.

We theoretically investigate non-reciprocal mode-conversion arising from Stimulated Brillouin Scattering (SBS) in sub-micron nanophotonic waveguides. We find that hybrid acoustic modes can be efficiently generated via radiation pressure, leading to enhancement of SBS-based mode conversion.

We fabricated a relative humidity sensor based on a selectively infiltrated photonic crystal. We demonstrate how the reversible hydroscopic behavior of the embedded liquid into the air micropores impacts the photonic crystal waveguide cut-off frequency.

We experimentally demonstrate dispersion engineering of slow light photonic crystal (PhC) waveguides using selective infiltration of the first two rows of air holes with high index ionic liquids. The infiltrated PhC waveguide exhibits a dispersion window of 3 nm with a nearly constant group velocity of ~c/80 that depends on the liquid physical properties. We investigate how the effective refractive index changes in time due to the dynamics of the liquids in the holes. This demonstration highlights the versatility, flexibility, and tunability offered by optofluidics in PhC circuits.

We present a new method to create a coupled waveguide array via tapering a seven-core telecommunications fiber. The fiber based waveguide array is demonstrated to exhibit the novel physics associated with coupled waveguide arrays, such as discrete diffraction and discrete self-focusing. The saturable absorber characteristics of the device are characterized and an autocorrelation measurement reveals significant single-pass pulse reshaping.

We demonstrate, experimentally, slow light dispersion engineering of photonic crystal waveguides using a selective liquid infiltration. We highlight how the amount of fluid infiltrated into the periodic air micropores critically influences the waveguide dispersion

We present a method to create coupled waveguide arrays via tapering 7-core germanosilicate fiber. Using an ultrashort pulse laser system the device is shown to exhibit nonlinear waveguide array physics, including nonlinear optical pulse chopping.

We present a new method to create a coupled waveguide array via tapering a multi-core telecommunications fiber. This device exhibits the novel physics associated with coupled waveguide arrays: Discrete self-focusing and nonlinear pulse chopping.

Silicon has attracted great interest as a platform for both linear and nonlinear integrated photonics for over 15 years. While its primary applications have been in the telecom window (near 1.5 μm), the capability of exploiting its full transparency window to 8 μm in the mid-IR is highly attractive, since this will open it up to entirely new applications in fields such as spectroscopy, chemical and biological sensing, and free-space communications. However, while silicon-on-insulator has shown great promise just beyond the telecommunications window [to the shortwave IR band (2.5 μm)], its wavelength range has been limited to < 4 μm by absorption in the silica cladding layer. Here, we demonstrate octave-spanning supercontinuum generation in silicon, covering a continuous spectral range from 1.9 to beyond 6 μm in dispersion-engineered silicon-on-sapphire (SOS) nanowires. This represents both the widest spectrum and longest wavelength generated to date in any silicon platform, and establishes SOS as a promising new platform for integrated nonlinear photonics in the mid-IR.

The new CO2 laser constructed in Cali Colombia was characterized. Include power vs. pressure, for a constant voltage and constant pressure, spectrum visible for mixture, stability of the power, wavelength measurement, polarization, and mixture optimization.

Using a single-beam, compact interferometer, we measure the refractive index of liquids in the near IR. This highly compact device relies on a silica capillary with a 50 μm inner diameter: it uses a minimal volume of test liquid, isolates the liquid from the humid atmosphere, has broadband operation, and is inherently mechanically stable. These characteristics, in combination with straightforward data acquisition, make it particularly well-suited for measuring the optical properties in the near IR of a wide range of liquids. Using this refractometer, we measure the refractive index of high-index liquids that are expected to be hydroscopic. The accuracy of the refractometer (±0.1%) is demonstrated through measuring the indices of air and pure water. We show that the hydroscopic behavior of the probed liquids has little influence on their optical properties in the near IR.

We report a distributed Brillouin scattering measurement in a silicon-chalcogenide hybrid platform with a controlled width variation. We confirm 2 mm spatial resolution using Brillouin optical correlation domain analysis (BOCDA) technique in the waveguide.

This paper gives an overview of the applications of on-chip stimulated Brillouin scattering (SBS) in RF photonic signal processing, including for high extinction notch filtering, tunable phase shifter, instantaneous frequency measurement, and bandwidth-reconfigurable signal processing.

Low phase noise lasers are used throughout many applications including precision metrology [1], and pure microwave synthesis [2], among others. Stimulated Brillouin scattering (SBS), a coherent interaction between photons and phonons, is capable of spectrally purifying optical sources to sub-Hz levels [3]. Previous demonstrations of Brillouin lasers have been limited to fiber based systems or micro-resonators which use tapered fibers or prisms to couple to external setups, preventing wafer scale integration and mass production.

Optical modulation plays arguably the utmost important role in microwave photonic (MWP) systems. Precise synthesis of modulated optical spectra dictates virtually all aspects of MWP system quality including loss, noise figure, linearity, and the types of functionality that can be executed. But 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 versatile RF photonic spectrum synthesis in an all-integrated silicon photonic circuit, enabling electrically-tailorable universal analog modulation transformation. We show a series of unprecedented RF filtering experiments through monolithic integration of the spectrum-synthesis circuit with a network of reconfigurable ring resonators.

We demonstrate the first tunable microwave photonic filter based on stimulated Brillouin scattering in a silicon nanowire. We use the low on-chip SBS gain to create a notch with 48dB of suppression and 98MHz linewidth.