Surface acoustic microwave photonic filters in standard silicon-on-insulator

Abstract

The processing of analog microwave-frequency signals using optical means becomes increasingly important as part of advanced cellular networks. Chip-level integration of microwave photonic filters, particularly in silicon, is considered necessary for their large-scale deployment. Discrete-time, delay-and-sum filters are widely used to select narrow spectral bands out of broad optical bandwidths. However, the long delays that are required to obtain narrowband filters are difficult to accommodate in integrated optic waveguide paths. In this work, we report discrete-time, integrated microwave photonic filters on standard silicon-on-insulator. Long delays are realized through the conversion of incoming radio-frequency modulation to the form of slow-moving surface acoustic waves. Conversion relies on thermo-elastic expansion of metallic gratings and does not involve piezoelectricity. Information is recovered in the optical domain via photoelastic modulation of probe light in a resonator waveguide. The resonator is patterned to support multiple delayed modulation events. Filters having up to 12 taps are demonstrated, with 175 ns-long delays and passbands as narrow as 5 MHz. The magnitude and radio-frequency phase of each filter tap are designed arbitrarily, independent of those of all others. The coherent summation of delayed waveform replicas is free of environmental phase drifts. Surface acoustic wave modulation of a compact, defect grating waveguide is demonstrated as well. Surface acoustic wave devices can significantly extend the signal-processing capabilities of silicon photonics.

Light Modulation in Silicon Photonics by PZT Actuated Acoustic Waves

“…Thermoelastic actuation of a SAW has been shown, ,,− but in general, electromechanical actuation is preferred due to its convenience and efficieny. In this method, an IDT consisting of a periodic electrode pattern is deposited on a piezoelectric material.…”

“…37,38 Recently, thermoelastic actuation of acoustic waves on SOI was reported. 39,40 However, such a scheme is power-hungry due to the need of a high power modulated pump source and is costly, as they need separate electro-optic modulators. Therefore, a more promising route involves the direct integration of piezoelectric materials on the SOI platform.…”

Coherent optical coupling to surface acoustic wave devices

“…However, without optomechanical phase matching, efficient SAW confinement, and modal size matching between optical and acoustic fields, the system is limited to lower phonon frequencies, mechanical quality factors, and coupling strengths. Optomechanical coupling to SAW whispering gallery modes in microresonators 52 , 53 , travelling-wave SAWs within tapered-optical fibers 54 , and SAWs driven by optical absorption and thermal relaxation of metallic electrodes 55 , 56 also enable several new possibilities. However, these devices will be challenging to integrate with a range of qubit systems, which require specific geometries and minimal heating.…”

Thin-Film Lithium Niobate Based Acousto-Optic Modulation Working at Higher-Order TE1 Mode

“…Recently, various materials such as aluminum nitride (AlN) [11,12], gallium arsenide (GaAs) [13,14], gallium phosphide (GaP) [15,16], silicon [17,18], and lithium niobate Photonics 2022, 9, 12 2 of 14 (LN) [19,20] have been adopted for AOM. Among them, LN is the most promising candidate especially for the thin-film LN (TFLN) or LN-on-insulator (LNOI) owing to its wide transparent window (from 400 nm to 5 µm), high refractive index contrast (∆n > 0.7), large piezoelectric, electro-optic, photo-elastic, and nonlinear coefficients, as well as stable physical and chemical properties [1,[19][20][21][22][23][24].…”