On-chip stimulated Brillouin scattering[SBS]has attracted extensive attention by introducing acousto-optic coupling inter-actions in all-optical signal processing systems.A series of chip-level applications such as Brillouin lasers,amplifiers,gyro-scopes,filters,and nonreciprocal devices are realized based on Brillouin acousto-optic interaction.Here,we first introduce the fundamental principle of SBS in integrated photonics and a method for calculating Brillouin gain;then we illustrate the Brillouin effect on different material platforms with diverse applications.Finally,we make a concise conclusion and offer prospects on the future developments of on-chip SBS.

On-chip stimulated Brillouin scattering (SBS) has attracted extensive attention by introducing acousto-optic coupling interactions in all-optical signal processing systems. In this article, we demonstrate stimulated intermodal Brillouin scattering (SIMBS) through a hybrid photonic-phononic silicon waveguide on the silicon-on-insulator (SOI) platform. The designed photonic-phononic waveguide can independently control the optical and acoustic fields by introducing the ridge waveguide as a line defect into the honeycomb lattice phononic crystal slab. Small-signal Stokes gain of 0.7 dB is achieved in a 1-cm long straight waveguide device with an on-chip pump power of 42.5 mW. Positive net Brillouin amplification is also expected by effectively reducing the linear loss. Our proposed device offers a potential approach to implementing Brillouin amplifiers, nonreciprocal devices, and signal processing in planar photonic integrated circuits.

We propose an integrated acousto-optic device with compact interdigital transducers (IDTs) design on aluminum nitride (AlN) platform for intramodal acousto-optic modulation. The designed suspended AlN-based acousto-optic devices are fabricated, which achieves maximum −34 dB double-sideband scattering, 3-dB RF modulation bandwidth up to 100 MHz, and optical operational bandwidth wider than 25 nm with stimulating acoustic wave frequency of 5.07 GHz in merely 560 × 65 μm 2 device footprint area. This device offers new opportunities for achieving efficient microwave-to-optical conversion for enhancing Brillouin lasers, nonreciprocal isolators and other multiple acousto-optic interaction applications.

Based on the parallelism and large bandwidth, photonic neural networks have achieved large-scale matrix multiply-accumulate with strong computing capability. We propose a novel integrated photonic neural network architecture based on stimulated Brillouin scattering to implement the next generation reservoir computing. The architecture provides a new approach to artificial intelligence enabled by integrated photonics.

Transferring completed electronic devices onto curvilinear surfaces is popular for fabricating three-dimensional curvilinear electronics with high performance, while the problems of conformality between the unstretchable devices and the surfaces need to be considered. Prior conformability design based on conformal mechanics model is a feasible way to reduce the non-conformal contact. Former studies mainly focused on stretchable film electronics conforming onto soft bio-tissue with a sinusoidal form microscopic morphology or unstretchable film conforming onto rigid sphere substrate, which limits its applicability in the aspect of shapes and modulus of the substrate. Here, a conformal mechanics model with general geometric shape and material is introduced by choosing a bicurvature surface as the target surface, and the conformal contact behavior of film electronics is analyzed. All eight fundamental local surface features are obtained by adjusting two principal curvatures of the bicurvature surface, and the conformal performance is simulated. A dimensionless conformal criterion is given by minimizing the total energy as a function of seven dimensionless parameters, including four in geometric and three in the material. Thickness-width ratio and length-width ratio of flexible electronics are two key geometric parameters that decide the conformal behavior, and smaller thickness-width ratio and length-width ratio are favorite for conformal contact. The model and analysis results are verified by the finite element analysis, and it can guide the prior conformability design of the curvilinear electronic devices during the planar manufacturing process.

We design and fabricate the suspended silicon microring with racetrack and spiral structure to exploit the resonantly enhanced stimulated Brillouin scattering (SBS). The designed photonic-phononic waveguide can provide the independent control on the optical and acoustic modes by introducing the silicon ridge waveguide into the phononic crystal slab as a line defect. We demonstrate efficient forward SBS in the two kinds of microrings and extract the characteristic Brillouin parameters through the heterodyne four-wave mixing measurement. The stronger inhomogeneous broadening effect in the spiral microring due to the structural variations is also observed. In addition, our microrings show the single mode transmission spectrum and high quality factor, which is beneficial to the enhanced intramodal forward SBS. This design can readily extend to other silicon-based platforms and paves the way toward on-chip photonic-phononic signal processing and Brillouin amplifier technologies.

Aluminum scandium nitride (AlScN) has attracted extensive attention for its excellent piezoelectric properties in the micro‐electromechanical system applications. In this work, AlScN is demonstrated to be a promising candidate for on‐chip acousto‐optic coupling interactions with outstanding piezoelectric properties as well. Based on piezoelectric Al 0.6 Sc 0.4 N film deposited on silicon‐on‐insulator platform, the proposed devices exhibit impressive acousto‐optic coupling performances over a short interaction length of 210 µm with surface acoustic waves actuated by interdigital transducers. Meanwhile, the acousto‐optic coupling performances are further improved in a compact spiral waveguide with eight interaction segments, where the measured modulation efficiency is enhanced from −21.5 to −12.5 dB and the radiofrequency (RF) 3‐dB bandwidth is narrowed from 4 to 3.1 MHz at central frequency of 3.044 GHz with RF drive power of 18.6 dBm. The measured modulation efficiency is proportional to the incident RF drive power, depicting a linear increasing trend with a slope of one as the RF power increases up to 24.6 dBm. Such acousto‐optic devices are capable of achieving broadband acousto‐optic modulation and narrow‐band microwave photonic filtering. Besides, the designed device structure provides a prospect in single‐sideband modulation, acousto‐optic frequency shift, and nonreciprocal light propagation.

We analyze theoretically and verify experimentally an effective approach to detect slight wavelength shift based on stimulated Brillouin scattering (SBS) effect. The concerned wavelength variation in an actively mode-locked fiber laser (MLFL) is caused by a π-phase-shifted fiber Bragg grating (π-PSFBG) under different temperatures. Based on the microwave photonics technology, the weak variations of the MLFL wavelength are converted into the amplitude changes of the beat signal generated by the mode-locked fiber laser. With the aid of the SBS effect, the beat signal is amplified larger than 20 dB, enhancing the measurement sensitivity. Through seeking the maximum beat signal, approximately 359.6 MHz modulation frequency shift of pump light with 0.2 °C temperature raise, corresponding to 2.876 pm wavelength shift in the 1550 nm band, is experimentally realized. Our proposed scheme achieves detection of minute wavelength shift with ultrahigh accuracy and convenient operation, which has potential applications for optical spectrum analysis of silicon-based integrated chips, biomedical fields and high sensitive optical sensing.

We experimentally demonstrate the enhanced four-wave mixing (FWM) by harnessing the forward stimulated Brillouin scattering (FSBS) within a silicon-based cascaded racetrack microring resonator (MRR). The frequency spacing of the split resonant peaks is precisely designed to match the Brillouin frequency shift (BFS). The cooperative interaction of the FSBS resonance and cascaded MRR resonance achieves an FWM enhancement of 2.97 and 2.43dB for anti-Stokes and Stokes sidebands under the launched pump power of 35.48 mW and probe power of 17.78 mW. The BFS from 3.34 to 7.13GHz is demonstrated by changing the waveguide width. Moreover, we show that this same system behaves as a single-sideband modulator, providing more than the 17dB single-sideband rejection ratio under the condition that the probe light and Stokes are resonant in the cascaded MRR. Building on these results, this device opens the door to new types of all-silicon Brillouin laser, amplifier, isolator, and single-sideband modulator.

We propose and demonstrate a notch filter on a silicon chip and apply it to a photonic microwave frequency measurement system with high precision and adjustable wide measurement range. The on-chip notch filter is implemented by embedding a serially coupled double microring resonator in a Fabry-Perot cavity consisting of two circular Bragg gratings with high reflectivity. The notch filtering with high quality factor and high rejection ratio is obtained by reconstructing the power transmission spectrum of the double microring resonator through the coherent interference within the Fabry-Perot cavity. The proposed notch filter is fabricated on a silicon-on-insulator wafer and the rejection ratio of the notch filter is measured to be 33.54 dB and the quality factor is 3.93×104. Based on the notch filter, a photonic microwave frequency measurement system is presented where the unknown radio frequency signal is detected by the variation of the output optical power from the notch filter through sweeping reference frequency. The measurement bandwidth of the system can be flexibly adjusted by tuning the output wavelength of the laser source. Broad measurement range of 0-26.62 GHz with a low error of ±0.25 GHz are obtained in a proof-of-concept experiment.

A hybrid silicon/aluminum nitride waveguide on the silicon-on-insulator platform is proposed to achieve an efficient Brillouin optomechanical interaction. Both intra-optical-mode and inter-optical-mode Brillouin scattering can be achieved. The novel arrangement of symmetric electrodes provides out-of-plane electric fields for piezoelectric materials and the possibility of suspended waveguides and cavities. The piezomechanical interaction coupling strength and the Brillouin optomechanical interaction coupling strength are numerically calculated. The simulation results show that near-unity internal conversion efficiency from the microwave domain to the optical domain can be achieved. Relatively low microwave power can be used to produced up to 5 order sidebands acousto-optical modulation. The proposed scheme paves the way for efficient classical and quantum application in integrated silicon photonics.

Brillouin lasing featured by narrow linewidth and wide tunability has been applied to sensing, coherent communication and microwave photonics. Here, we demonstrate a cascaded Brillouin lasing in the integrated silicon racetrack micro-ring pumped by the external fiber loop. The elaborate micro-ring can tightly confine both optical and acoustic fields, and enable the efficient generation of cascaded forward stimulated Brillouin scattering. Under the high external pump power, we observe the cascaded Brillouin lasing up to 3 Stokes order and 3 anti-Stokes order. Our experiment provides a new method to realize a cascaded Brillouin lasing in on-chip platform.

Stimulated Brillouin scattering in whispering gallery resonators has numerous potential applications. However, previously reported approaches are difficult to integrate and the Brillouin gain coefficient is small. We propose here a new approach to achieve giant forward stimulated Brillouin scattering (FSBS) and lasing on chip with double-disk microcavities made of silica glass. By considering the thickness of air gap to tailor optical forces especially radiation pressure in these double-disk microcavities, giant Brillouin gain enhancement can be realized in the intermode FSBS. The numerical simulation results indicate that for double-disk microcavity within the radius range of 50 mu m, stimulated Brillouin scattering gain is ten times larger than that of single-disk microcavity up to 74.3 m- 1W-1 with Rayleigh acoustic mode and 102 to 103 times larger up to 6361.19 m- 1W-1 with symmetric Lamb acoustic mode. Correspondingly, the on-chip pump power threshold of Brillouin lasing can be reduced to 55 mu W with the slope efficiency of 8.0%. Our proposed double-disk microcavities offer an effective and simple method to implement Brillouin lasing and can find versatile applications of acousto-optic interaction on all-integrated CMOS compatible chip.

Silicon-based stimulated Brillouin scattering (SBS) promotes the on-chip all-optical signal processing network by interfacing silicon photonic and phononic technologies. Controllable and strong Brillouin coupling in silicon is a key requirement for this purpose. Here, we demonstrate traveling-wave forward SBS and Brillouin gain through a class of hybrid photonic-phononic silicon waveguides on the silicon-on-insulator (SOI) platform. This design combines the advantages of a silicon ridge waveguide and phononic crystal slab, allowing the independent control on the confined optical and acoustic modes. The strong and tailorable Brillouin nonlinearity is demonstrated via the heterodyne four-wave mixing spectroscopy. Three-tone gain experiment reveals a small-signal Stokes gain of 0.9 dB in a 1.085 cm length straight waveguide device at moderate pump power. The limiting factors and further improvements of net Brillouin amplification in our system are also discussed. This design can also be applied to the intermodal SBS as well as other silicon-based material platforms, and thus it offers the pathway toward on-chip microwave photonic filters, Brillouin amplifiers, and nonreciprocal devices.

We design a partially suspended silicon nitride (Si3N4) slot waveguide on silica to realize efficient on-chip forward stimulated Brillouin scattering (FSBS). The slot waveguide can intensify radiation pressure close to the slot and simultaneously confine both optical and acoustic modes, resulting in an enhanced FSBS gain on the order of 300 W-1m-1. The acoustic radiation loss is significantly suppressed due to the strong acoustic coupling in the narrow slot waveguides. We analyze the impacts of structural parameters on the SBS properties, which produces the optimal parameters for maximum SBS gain. Based on the nonlinear coupled-mode equations, we compare the performance of Stokes amplification between the Si3N4 slot waveguides and the silicon nanowires. Simulation results indicate that the Si3N4 slot waveguides with low linear loss can offer a larger net Stokes amplification than silicon waveguides under moderate pump power. Such approach enables efficient on-chip SBS devices in CMOS-compatible Si3N4 platform.

We propose and design SiGe strip waveguides and silicon waveguides with SiGe cover layers to tailor optical forces. The forward stimulated Brillouin scattering (FSBS) in these SiGe waveguides are analyzed by considering the effects of SiGe concentration on the optical forces. In the radiation-enhanced configuration, electrostrictive forces can constructively add to or destructively interfere with radiation pressure, depending on the concentration. The silicon waveguides with graded-varying cover layers provide a means of enhancing photon-phonon interaction and rewriting the selection rule of excited acoustic modes. The numerical simulation results indicate that SiGe strip waveguides can realize the largest net Stokes' amplification up to 10.32 dB. Compared to traditional pure silicon waveguides, the silicon waveguides with graded-varying cover layers have an improvement of about 40% on Brillouin gain and at least 2.5 dB on net Stokes' amplification. Our proposed SiGe waveguides offer an effective approach to implement flexible FSBS in silicon-based chip.

We experimentally demonstrate the forward cascaded Brillouin lasing exploiting a silicon-based rectangular spiral microring resonator assisted by an erbium-doped fiber amplifier. To realize the enhanced Brillouin nonlinearity, the optical and acoustic fields are effectively confined by partly suspending the spiral resonator. The free spectral range is precisely designed to match the half of the Brillouin frequency shift to guarantee Brillouin laser oscillation. The fabricated spiral resonator is incorporated in a fiber loop to serve as not only a resonance-enhanced element to generate the internal pump lasing for Brillouin scattering but also a Brillouin gain medium to excite Brillouin lasing. The spiral structure allows a 0.6368 cm long resonator waveguide to be enclosed in a small footprint of 250 × 330 μm2. Four anti-Stokes and three Stokes lasing lines are obtained with the Brillouin frequency shift of about 12.0463 GHz. The proposed approach provides a potential way to implement Brillouin lasing on a silicon-based chip.

We demonstrate the forward stimulated Brillouin scattering (FSBS) in a partly suspended silicon nanowire racetrack resonator. To realize the tight confinement of the transverse acoustic modes in the nanoscale silicon core, the racetrack resonator is supported by the tiny pillar. The Brillouin amplification of 2.25 dB is achieved with the resonator radius of 100 μm under a low-power pump laser of 8 mW. The influences of the waveguide width and the top width of the tiny pillar on the Brillouin frequency shift and Brillouin gain are presented and analyzed. The Brillouin frequency shift is conveniently manipulated by the changes in waveguide widths. Our proposed approach furnishes an alternative towards harnessing FSBS in integrated photonic circuits.