Cavity Enhancement of Anti-Stokes Scattering via Optomechanical Coupling with Surface Acoustic Waves

Ayato Okada, Fumikazu Oguro, Atsushi Noguchi, Yutaka Tabuchi, Rekishu Yamazaki, Koji Usami, and Yasunobu Nakamura

Phys. Rev. Applied 10, 024002 – Published 2 August 2018

Abstract

We report the development of an electro-optomechanical system based on surface acoustic waves (SAWs), where a piezoelectric material with a large optoelastic susceptibility is used for the coupling of both radiowaves and optical light to the SAW. In the optical domain, we exploit the tensorial nature of the optoelastic effect to show the polarization dependence of the photon-SAW interaction. We demonstrate increased coupling both by a two-dimensional SAW-focusing circuit and by the optical cavity enhancement of the photon-phonon scattering. We evaluate the optomechanical coupling rate of the system and discuss the future direction for the improvement of the coupling strength.

Received 31 May 2017
Revised 16 April 2018

DOI:https://doi.org/10.1103/PhysRevApplied.10.024002

Physics Subject Headings (PhySH)

Acoustic wave phenomena Light-matter interaction Optomechanics Quantum information with hybrid systems

Cavity resonators Microwave techniques Optical techniques Surface acoustic wave

Condensed Matter, Materials & Applied PhysicsQuantum Information, Science & TechnologyAtomic, Molecular & Optical

Authors & Affiliations

Ayato Okada^1,*, Fumikazu Oguro¹, Atsushi Noguchi^1,2, Yutaka Tabuchi¹, Rekishu Yamazaki^1,2, Koji Usami¹, and Yasunobu Nakamura^1,3

¹Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, Meguro-ku, Tokyo 153-8904, Japan
²PRESTO, Japan Science and Technology Agency, Kawaguchi-shi, Saitama 332-0012, Japan
³Center for Emergent Matter Science (CEMS), RIKEN, Wako, Saitama 351-0198, Japan

^*okada@qc.rcast.u-tokyo.ac.jp

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Vol. 10, Iss. 2 — August 2018

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Images

Figure 1
Two-dimensional SAW resonator. (a) Design of the SAW-focusing circuit. The outer (blue) and inner (green) patterns form a concentric Bragg mirror and an interdigitated transducer (IDT), respectively. (b) Magnified view of the center part. The width and spacing of the electrodes are $10 μ m$ . In order to map out the spatial variation of the optoelastic effect, a laser beam is scanned across the central region free from electrodes. (c) Photograph of a SAW resonator. Aluminum electrodes are evaporated on Y- and $128^{\circ}$ Y-cut $Li Nb O_{3}$ substrates. The chip is mounted on a sample holder and wire bonded to the SMA connectors. (d) Radio-frequency transmission spectrum from port 1 to port 2 through the SAW resonator. A clear SAW resonance peak is observed at 87 MHz (red arrow) with a linewidth of 1.7 MHz. A dip around 105 MHz is attributed to a leaky SAW mode (green arrow). Other spurious spikes are the overtones of the longitudinal and shear modes of the bulk waves. All the materials shown in (a)–(d) are of the Y-cut sample.
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Figure 2
Experimental setup for probing the optical modulation imparted by the SAW-induced optoelastic effect. A rf signal at around 87 MHz is applied to the device for the SAW excitation. A focused laser beam is sent through the SAW device. The heterodyne signal with a local oscillator (LO) laser is detected and demodulated with a lock-in amplifier to observe the phase modulation. The laser beam width at the SAW device is estimated to be $3.5 μ m$ , much smaller than the SAW wavelength of $40 μ m$ . The SAW device is attached to an $X Y Z$ -stage, which allows observation of the spatial distribution of the phase modulation.
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Figure 3
Upper panel: Spatial distribution of the laser phase modulation imparted by the SAW on the Y-cut $Li Nb O_{3}$ sample. Color maps show the normalized power of the generated sideband signal for the input laser of (a) $Z$ and (b) $X$ polarizations, respectively. Coordinates are aligned to the crystal axes of the sample. Lower panel: Cross sections (blue) attained by summing up the signal in (a) along the (c) $X$ and (d) $Z$ direction. Gaussian fitting (red) to the data yields effective radii of (c) $R_{Z} = 100 μ m$ and (d) $R_{X} = 80 μ m$ as the $1 / e$ decay length of the fitted Gaussian.
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Figure 4
Polarization dependence of the SAW-induced laser phase modulation. (a) Spatial distribution of the SAW resonator mode near its center, probed with the $Z$ -polarized laser light. Position A, indicated by the red circle, corresponds to the center antinode of the SAW resonator, where the maximum modulation is observed. Position B (yellow circle) is one of the nodes. (b) Power spectra of the sideband generated by the $X$ - (red) and $Z$ - (blue) polarized light at position A. (c) The same spectrum taken at position B. (d) Ratio of the sideband power generated by the $X$ and $Z$ polarization light at position B. The black dashed lines in (b)–(d) indicate the SAW excitation frequency used in (a). All the materials shown in (a)–(d) are of the Y-cut sample. The acoustic excitation power is $- 5 dBm$ for (a) and $- 9.3 dBm$ for (b)–(d).
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Figure 5
(a) Experimental setup for the measurement of the cavity-enhanced anti-Stokes scattering. The SAW resonator is inserted at the waist of a Fabry-Perot cavity. A reference laser (blue arrow) is used for the stabilization of the cavity spacing. While exciting the SAW resonator by a rf signal, detuned pump laser (solid red arrow) is injected from the opposite side of the cavity, from which the anti-Stokes scattering is observed (dotted red line). It is detected through the heterodyne measurement using the reference laser reflected back from the cavity. PD, photo detector; PBS, polarizing beamsplitter; PZT, piezoelectric actuator; EOM, electro-optic modulator; $λ / 4$ , quarter-wave plate. (b) Frequency diagram of the measurement. The pump laser frequency is set on the red side of the cavity resonance. Anti-Stokes scattering of the pump laser is enhanced by the optical cavity mode when the detuning $δ$ is close to zero. (c) Cavity-enhanced spectrum. The scattered light power shows a peak when the pump laser is swept across $δ = 0$ . The observed linewidth of 3.6 MHz is consistent with the cavity linewidth measured independently. The result is obtained for the $128^{\circ}$ Y-cut $Li Nb O_{3}$ sample. The acoustic excitation power is $- 5 dBm$ .
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