Large-scale programmable phononic integrated circuits

Abstract

Electronic and photonic chips revolutionized information technology through massive integration of functional elements, yet phonons as fundamental information carriers in solids remain underestimated. Here, we demonstrate large-scale programmable phononic integrated circuits (PnICs) for complex signal processing. We developed a comprehensive library of gigahertz-frequency phononic building blocks that control acoustic wave propagation, polarization, and dispersion. Combining these elements, we demonstrate an ultra-compact 1$\times$128 on-chip acoustic power splitter with unprecedented integration density of 3,000/cm$^2$, a 21-port acoustic frequency demultiplexer with 3.8~MHz resolution, and a four-channel reconfigurable frequency synthesizer. This work establishes scalable phononic integration as the third pillar of information processing alongside electronics and photonics, enabling hybrid chips that combine all three domains for advanced signal processing and quantum information applications.

Figures (5)

• Figure 1: Large-scale programmable phononic circuits.a-c, Schematics of conventional integrated acoustic devices: bulk acoustic wave (BAW) (a), surface acoustic wave (SAW) (b), and suspended phononic crystal structures (c). d, Schematic of large-scale programmable suspension-free phononic integrated circuits (PnICs) leveraging phononic refractive index contrast. The inset illustrates the confined phononic mode in the phononic waveguide. Through the combination of various phononic functional building blocks, including directional couplers, Y-splitters, polarization converters (PC), Mach-Zehnder interferometers (MZI), microring resonators, and phononic waveguide gratings, PnICs can achieve diverse phononic signal processing functionalities, such as multi-port acoustic power splitters, acoustic arrayed waveguide gratings (AAWG), and reconfigurable acoustic frequency synthesizer.
• Figure 2: Building blocks of the programmable PnICs.a, Scanning electron microscope (SEM) image of a dispersive phononic waveguide showing a group velocity of 3904 m/s. b-d, SEM images and the measured acoustic fields of a phononic waveguide directional coupler by home-built vibrometer (b), a Y-splitter (c), and a multi-mode interferometer for power splitting (d). e, An adiabatic polarization converter based on tapered waveguides. f, SEM image and transmission spectrum of a microring resonator showing resonances of two polarization modes (quasi-Love and quasi-Rayleigh). g, SEM image and transmission spectrum of a phononic waveguide grating structure with a 33 MHz bandgap. h, SEM image and the normalized output acoustic amplitude as a function of heater power for an MZI modulator.
• Figure 3: Phononic power splitter.a, SEM image of a 1$\times$128 phononic power splitter based on a cascaded network of Y-splitters. b, Measured normalized acoustic amplitude distribution in the white boxed region of a. c, Measured average acoustic amplitude of the 128 output ports in the yellow boxed region of a. d, Statistical analysis of the amplitude of the 128 output ports. Black curve: normal distribution fit with mean amplitude of 6.5 pm and standard deviation of 1 pm. e, Split ratio and insertion loss of the power splitter as a function of frequency. f, Insertion loss as a function of the layer $l$ with port number $2^l$ for different waveguide losses. The dashed lines indicate the result of extrapolations.
• Figure 4: Acoustic arrayed waveguide grating (AAWG).a,b, Schematic diagram and SEM image of the AAWG. c,d, SEM image and corresponding normalized acoustic amplitude distribution in the input free propagation region (FPR) of the AAWG. e,f, SEM image and normalized acoustic amplitude distribution at three frequencies in the output FPR: 1.416 GHz ($f_a$), 1.406 GHz ($f_b$), and 1.396 GHz ($f_c$). Acoustic waves of different frequencies converge at different output ports. g, Spectral responses of the 21 AAWG output ports, exhibiting a free spectral range of 81 MHz. h, Zoom-in view of the spectral responses showing a channel spacing ($\Delta f$) of 3.8 MHz between adjacent ports.
• Figure 5: Reconfigurable acoustic frequency synthesizer (RAFS).a, Schematic diagram of the RAFS, comprising an AAWG, four thermo-acoustically tunable acoustic MZIs, and a four-to-one acoustic combiner. The input radio frequency signal is converted to acoustic signals through the input IDT and then output from four different ports of the AAWG. The amplitude of the signal from each port is controlled by subsequent MZIs and then combined into a single output waveguide through an acoustic combiner. b, Optical image of the wire-bonded RAFS device. Inset: magnified view of the device. c, Experimentally measured transmission spectra at the four output ports of the AAWG. d, Normalized transmission of MZI3 with different driving voltages on its heater. e, Acoustic interference amplitude distribution at the output port of MZI3 corresponding to points $C$ and $C'$ in d. At point $C'$ (19 V), destructive interference causes acoustic energy to leak into the substrate. f, Normalized output amplitude of MZI1 and MZI3 as a function of heater power. g, Transmission ratio between MZI3 and MZI1 with simultaneous thermal tuning of their heaters. The white dashed line shows the evolution of the maximum output power position of MZI3 under different heater powers of MZI1. h, Demonstration of selective single channel activation by independent MZI control.