Using integrated acousto-optic cavities on thin-film lithium niobate, we demonstrate efficient conversion of GHz microwaves to 1.5 pm wavelength light via the piezoelectric effects and the optomechanical interactions

Chia, Cleaven

Lai, Keji

Lončar, Marko

Maity, Smarak

Shams-Ansari, Amirhassan

Shao, Linbo

Sinclair, Neil

Wang, Cheng

Yu, Mengjie

Zhang, Mian

Zheng, Lu

English

Caltech Authors - Main

FM2R.1.pdf CLEO 2020 © OSA 2020
Integrated Lithium Niobate Acousto-optic Cavities for 
Microwave-to-optical Conversion 
 
Linbo Shao1, Mengjie Yu1, Smarak Maity1, Neil Sinclair1,2, Lu Zheng3, Cleaven Chia1,  
Amirhassan Shams-Ansari1, Cheng Wang1,4, Mian Zhang1, Keji Lai3, and Marko Loncar1 
1John A. Paulson School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA 
2Division of Physics, Mathematics and Astronomy, and Alliance for Quantum Technologies (AQT), California Institute of Technology, 1200 E. 
California Blvd., Pasadena, California 91125, USA 
3Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA and 
4Department of Electrical Engineering & State Key Lab of THz and Millimeter Waves, City University of Hong Kong, Kowloon, Hong Kong, 
China 
Email: shaolb@seas.harvard.edu 
 
Abstract: Using integrated acousto-optic cavities on thin-film lithium niobate, we demonstrate 
efficient conversion of GHz microwaves to 1.5 μm wavelength light via the piezoelectric effects 
and the optomechanical interactions.  © 2020 The Author(s). 
 
1. Introduction 
Efficient microwave-to-optical converters and filters are desired for microwave photonic signal processing and long-
distance data transmission [1-3]. They could also be used as quantum transducers enabling coherent transfer of 
quantum information from electrical to optical domains, thus enabling efficient optical links between cryogenic 
quantum computers. Integrated lithium niobate photonics has emerged as a promising platform for realization of 
microwave-to-optical converters. Examples include efficient electro-optic modulators with bandwidth above 100 GHz 
[4], and optomechanical crystals that benefit from materials strong piezoelectric and photoelastic effects [5]. Here, we 
demonstrate an alternative approach based on integrated acousto-optic cavities realized in integrated lithium niobate 
photonic platform [6]. A high-quality (Q) acoustic resonator [7, 8] is used as a bridge since it can couple to microwave 
signals by piezoelectric effect and to optical signals by moving boundaries, photoelasticity, and electro-optics. we also 
demonstrate a microwave photonic link with unitary gain, which refers to a 0-dB microwave power transmission over 
an optical channel.  
2. Lithium niobate acousto-optic cavities 
Our device consists of an optical racetrack cavity partially embedded within an acoustic resonator, fabricated in 
suspended thin-film lithium niobate (Fig. 1a). The optical cavity, with loaded optical Q factor exceeding 2×106, is 
coupled by on-chip waveguide (Fig. 1b), and the acoustic resonator, with loaded acoustic Q factors of 3,600 is 
electrically excited by using interdigital transducers (IDTs) (Fig. 1c). Due to strong piezoelectric effect of lithium 
niobate, acoustic waves generate microwave electric fields, which in turn couple to optical waves via strong electro-
optic effect. This effect enhances the overall acousto-optic coupling mediated by photo-elastic and moving boundary 
effects. Numerical simulations reveal that this effect contributes constructively to the moving boundaries and 
photoelastic components, resulting in large acousto-optic effect (Fig. 1d). We note that in our devices the contribution 
of the moving boundary component is an order of magnitude weaker than the other two effects.  
3. Experimental characterization 
The characterization setup used in our experiments is shown in Fig. 2a and consists of vector network analyzer 
(VNA), a tunable telecom laser, Erbium-doped fiber amplifier (EDFA), and a photodiode (Finisar Ultra-High-Power 
Photodetector VPDV2120). When microwave signal is applied to resonantly excite the acoustic cavity, the sidebands 
(additional transmission dips) are observed in the optical transmission spectra. Second-order sideband dips could be 
generated with microwave power as low as 10 dBm, indicating a strong modulation of the optical cavity by the acoustic 
modes (Fig. 2b). To investigate the potential of our acousto-optic cavities in microwave photonics, we measure the S 
parameters of our system by sweeping the frequency of input microwave signal (Fig. 2c). The microwave photonic 
link is measured to be a unitary gain at 1.57 GHz frequency, which is achieved without the need of an optical amplifier 
within the link (after acousto-optic device). In these experiments, about 500 mW of optical power was delivered to 
the device with overall optical insertion loss of 10 dB, resulting in as little as 50 mW of optical power on the detector. 
4. Conclusion  
We demonstrate integrated acousto-optic cavities on thin-film lithium niobate platform. Unitary gain microwave 
photonic link is achieved by high-Q acoustic resonators and acousto-optic interactions in lithium niobate. Potential 
applications include microwave-to-optical quantum coherent converters, where mechanical resonance promotes 
Authorized licensed use limited to: CALIFORNIA INSTITUTE OF TECHNOLOGY. Downloaded on September 22,2020 at 00:39:44 UTC from IEEE Xplore.  Restrictions apply. 
FM2R.1.pdf CLEO 2020 © OSA 2020
conversion efficiency, and radar systems [9], where a spectral bandwidth of the pulse repetition frequency is enough 
to get information of moving targets. 
 
 
 
 
Fig. 1 Lithium niobate acousto-optic cavities. a, Microscopic image of optical racetrack cavity with thin-film 
acoustic resonators. The acoustic resonator is excited by the IDT. The zoom-in region is marked in the dash box. b, 
Optical transmission spectrum of a high-Q optical mode. c, Electrical S11 measurements of an acoustic mode. d, 
Acousto-optic simulation of the cross-section (marked in red line in inset in a) showing coupling between optical and 
acoustic modes via combined photoelastic and electro-optic effect.  
 
 
 
Fig. 2 Measurements of the acousto-optic RF link. a, Schematic of the experimental setup used for device 
characterization. b, The optical transmission spectrum showing optical sidebands due to a 10 dBm resonant acoustic 
wave driving. c, Microwave S parameter spectra of the acousto-optic microwave photonic link. 
 
Acknowledgment 
This work was supported by National Science Foundation (DMR-1707372, DMR-1231319, ECCS-1740296, ECCS-1810233); Office of Naval 
Research (N00014-15-1-2761); Natural Sciences and Engineering Research Council of Canada; U.S. Department of Energy (DE-SC0019219), 
Natural Sciences and Engineering Research Council of Canada (NSERC), the AQT Intelligent Quantum Networks and Technologies (INQNET) 
research program, and by the DOE/HEP QuantISED program grant, QCCFP (Quantum Communication Channels for Fundamental Physics). 
References  
1. D. Marpaung, et al., "Integrated microwave photonics," Nat. Photonics 13, 80-90 (2019). 
2. J. S. Fandiño, et al., "A monolithic integrated photonic microwave filter," Nat. Photonics 11, 124-129 (2016). 
3. D. Marpaung, et al., "Low-power, chip-based stimulated Brillouin scattering microwave photonic filter with ultrahigh selectivity," Optica 2, 
76-83 (2015). 
4. C. Wang, et al., "Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages," Nature 562, 101-104 (2018). 
5. W. Jiang, et al., "Lithium Niobate Piezo-optomechanical Crystals," arXiv preprint, arXiv:1903.00957 (2019). 
6. L. Shao, et al., "Microwave-to-optical conversion using lithium niobate thin-film acoustic resonators," Optica 6, 1498-1505 (2019). 
7. Y. Yang, et al., "1.7 GHz Y-Cut Lithium Niobate MEMS Resonators with FoM of 336 and fQ of 9.15×10^12," in 2018 IEEE/MTT-S 
International Microwave Symposium - IMS(2018), pp. 563-566. 
8. L. Shao, et al., "Phononic Band Structure Engineering for High-Q Gigahertz Surface Acoustic Wave Resonators on Lithium Niobate," Physical 
Review Applied 12, 014022 (2019). 
9. J. Capmany, et al., "A tutorial on microwave photonic filters," J. Lightwave Technol. 24, 201-229 (2006). 
 
Authorized licensed use limited to: CALIFORNIA INSTITUTE OF TECHNOLOGY. Downloaded on September 22,2020 at 00:39:44 UTC from IEEE Xplore.  Restrictions apply. 


Integrated Lithium Niobate Acousto-optic Cavities for Microwave-to-optical Conversion

https://authors.library.caltech.edu/105559/1/09192761.pdf

Integrated Lithium Niobate Acousto-optic Cavities for Microwave-to-optical Conversion

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main