Guanghui Ren

Compact Brillouin devices through hybrid integration on silicon

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.

Design and analysis of a cascaded microring resonator-based thermo-optical tunable filter with ultralarge free spectrum range and low power consumption

A thermo-optical tunable filter based on the Vernier effect of cascaded microring resonators, which can expand the free spectrum range (FSR) and the tuning range, has been designed and simulated. The FSR of the filter with a radius of 48 μm for the first stage and 50 μm for the second stage microring can be expanded to 75.6 nm, which is, at present, the largest FSR to our best knowledge. A tuning range covering all of the above mentioned FSR can be reached under 103.1 mW heating power, which is also the largest one for silicon-based thermo-optical tunable microring resonator filters. The response time, calculated by solving the two-dimensional heat conduction equation with finite element method, of the designed tunable filter with 48/50 μm radius rings is 3.5 μs for the rise edge and 0.8 μs for the fall edge, which is much quicker than most of the reported silicon microring-based thermo-optical tunable filters.

Micro-ring resonator quality factor enhancement via an integrated Fabry-Perot cavity

We propose and experimentally demonstrate the enhancement in the filtering quality (Q) factor of an integrated micro-ring resonator (MRR) by embedding it in an integrated Fabry-Perot (FP) cavity formed by cascaded Sagnac loop reflectors. By utilizing coherent interference within the FP cavity to reshape the transmission spectrum of the MRR, both the Q factor and the extinction ratio (ER) can be significantly improved. The device is theoretically analyzed and practically fabricated on a silicon-on-insulator wafer. Experimental results show that up to 11-times improvement in the Q factor, together with an 8-dB increase in the ER, can be achieved via our proposed method. The impact of varying structural parameters on the device performance is also investigated and verified by the measured spectra of the fabricated devices with different structural parameters.We propose and experimentally demonstrate the enhancement in the filtering quality (Q) factor of an integrated micro-ring resonator (MRR) by embedding it in an integrated Fabry-Perot (FP) cavity formed by cascaded Sagnac loop reflectors (SLRs). By utilizing coherent interference within the FP cavity to reshape the transmission spectrum of the MRR, both the Q factor and the extinction ratio (ER) can be significantly improved. The device is theoretically analyzed, and practically fabricated on a silicon-on-insulator (SOI) wafer. Experimental results show that up to 11-times improvement in Q factor, together with an 8-dB increase in ER, can be achieved via our proposed method. The impact of varying structural parameters on the device performance is also investigated and verified by the measured spectra of the fabricated devices with different structural parameters.

Precise, reproducible nano-domain engineering in lithium niobate crystals

We present a technique for domain engineering the surface of lithium niobate crystals with features as small as 100 nm. A film of chromium (Cr) is deposited on the lithium niobate surface and patterned using electron beam lithography and lift-off and then irradiated with a wide diameter beam of intense visible laser light. The regions patterned with chromium are domain inverted while the uncoated regions are not affected by the irradiation. With the ability to realize nanoscale surface domains, this technique could offer an avenue for fabrication of nano-photonic and phononic devices.

Spectrum reshaping of micro-ring resonator via an integrated Fabry-Perot cavity

We investigate the enhancement in the filtering quality (Q) factor of an integrated micro-ring resonator (MRR) by embedding it in an integrated Fabry-Perot (FP) cavity formed by cascaded Sagnac loop reflectors (SLRs). By using coherent interference within the FP cavity to reshape the transmission spectrum of the MRR, both the Q factor and the extinction ratio (ER) can be greatly improved. The device is theoretically analyzed, and practically fabricated on a silicon-on-insulator (SOI) platform. Experimental results show that up to 11-times improvement in Q factor and an 8-dB increase in ER can be achieved via our proposed method. The impact of varying structural parameters on the device performance is also investigated and verified.

Brillouin lasing in a hybrid silicon chip

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.

Micro-ring resonator quality factor and extinction ratio enhancement via integrated Fabry-Perot cavity

We propose and experimentally demonstrate the enhancement of filtering quality factor (Q) and extinction ratio (ER) of an integrated micro-ring resonator through the use of an integrated Fabry-Perot cavity. Up to 11-times improvement in Q, together with an 8-dB increase in ER, are experimentally achieved.

Experimental demonstration of two-dimensional hybrid waveguide-integrated plasmonic crystals on silicon-on-insulator platform

Nanoscale plasmonic structures can offer unique functionality due to extreme sub-wavelength optical confinement, but the realization of complex plasmonic circuits is hampered by high propagation losses. Hybrid approaches can potentially overcome this limitation, but only few practical approaches based on either single or few element arrays of nanoantennas on dielectric nanowire have been experimentally demonstrated. In this paper, we demonstrate a two dimensional hybrid photonic plasmonic crystal interfaced with a standard silicon photonic platform. Off resonance, we observe low loss propagation through our structure, while on resonance we observe strong propagation suppression and intense concentration of light into a dense lattice of nanoscale hot-spots on the surface providing clear evidence of a hybrid photonic plasmonic crystal bandgap. This fully integrated approach is compatible with established silicon-on-insulator (SOI) fabrication techniques and constitutes a significant step toward harnessing plasmonic functionality within SOI photonic circuits.

Nonlinear Loss Engineering in a Silicon-Chalcogenide Hybrid Optical Waveguide

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.

Sub-micron domain engineering in lithium niobate by laser light irradiation of patterned chromium

We report the generation of sub-micron domains in lithium niobate crystals by irradiating a patterned chromium layer with focused laser light. The generated surface domain pattern follows the Cr pattern, which was predefined by photolithography or electron beam lithography and a lift-off process. A 2D surface domain pattern with a period of 600 nm has been realized.