Lithium Niobate Resonators Research Articles

High-Q lithium niobate microdisk resonators on a chip for efficient electro-optic modulation.

Lithium niobate (LN) microdisk resonators on a LN-silica-LN chip were fabricated using only conventional semiconductor fabrication processes. The quality factor of the LN resonator with a 39.6-μm radius and a 0.5-μm thickness is up to 1.19 × 10(6), which doubles the record of the quality factor 4.84 × 10(5) of LN resonators produced by microfabrication methods allowing batch production. Electro-optic modulation with an effective resonance-frequency tuning rate of 3.0 GHz/V was demonstrated in the fabricated LN microdisk resonator.

Fabrication of high-Q lithium niobate microresonators using femtosecond laser micromachining.

We report on fabrication of high-Q lithium niobate (LN) whispering-gallery-mode (WGM) microresonators suspended on silica pedestals by femtosecond laser direct writing followed by focused ion beam (FIB) milling. The micrometer-scale (diameter ~82 μm) LN resonator possesses a Q factor of ~2.5 × 105 around 1550 nm wavelength. The combination of femtosecond laser direct writing with FIB enables high-efficiency, high-precision nanofabrication of high-Q crystalline microresonators.

Lithium Niobate on Silicon Dioxide Suspended Membranes: A Technology Platform for Engineering the Temperature Coefficient of Frequency of High Electromechanical Coupling Resonators

This paper presents a new class of laterally vibrating resonators (LVRs) based on Y-cut ion-sliced lithium niobate (LN) thin films on silicon dioxide (SiO 2 ). The SiO 2 layer is used to engineer the temperature coefficient of frequency (TCF) of the LN resonator. The LN LVR is built on top of a SiO 2 layer and released from the underlying silicon wafer by dry etching in Xenon difluoride (XeF 2 ). For a given sample having an LN layer thickness of 420 nm and SiO 2 thickness of 1600 nm, this paper demonstrated resonators with TCF of +17 ppm/°C, and +18 ppm/°C for devices vibrating at 460 and 420 MHz, and, respectively, oriented at 10° and 30° to the x-axis. TCF of +24.1 ppm/°C and +27.7 ppm/°C were recorded for devices vibrating at 720 MHz, respectively, oriented at 40° and 50° to the x-axis. These results correspond to a 4-5 X reduction in the TCF of standalone LN resonators. The positive TCF clearly indicates the effect of the SiO 2 layer, and its value matches with what is predicted analytically by finite element method simulations and nonlinear analysis of the resonator amplitude-frequency response. This demonstration offers evidence that TCF engineering of LN LVRs is possible. Most importantly, these LN LVRs still exhibited high values of electromechanical coupling, k 2 t , around 9% at 723.7 MHz, and Q in excess of 1320 in air at 419.3 MHz. By optimizing the relative values of the LN and SiO 2 thickness, it is ultimately possible to attain devices with zero first order TCF.

Electro-optic effect of lithium niobate in piezoelectric resonance

The electro-optic (EO) effect of a lithium niobate (LN) single crystal was analyzed around a piezoelectric resonance frequency. The EO-coefficient of the LN resonator was measured as a function of frequency. The EO-coefficient around piezoelectric resonance frequency varied with a maximum and a minimum in the frequency dependence. To explain the frequency dependence of the EO-coefficient, three effects were considered: (1) the intrinsic EO-effect excluding the effect of piezoelectric resonance, (2) the change of optical pass length due to piezoelectric displacement, and (3) the photo-elastic effect due to piezoelectric strain. The maximum of the EO-coefficient corresponded to the maximum of piezoelectric displacement at the resonance frequency, while the minimum was caused by the phase-lag between applied sinusoidal electric field and piezoelectric displacement. A new equation including the three effects as well as the phase-lag was formulated to represent the EO-effect of piezoelectric crystals. The equation gave a good agreement in the fitting of calculation to the observation.

Continuous-wave, all-solid-state, single-frequency 400-mW source at 589 nm based on doubly resonant sum-frequency mixing in a monolithic lithium niobate resonator

Sum-frequency mixing of two cw single-mode Nd:YAG lasers in a doubly resonant congruent lithium niobate resonator generated two TEM(00) beams of single-frequency 589-nm radiation. The primary beam had a power of 400 mW and the secondary beam of approximately 15 mW by use of 320 mW of 1319-nm and 660 mW of 1064-nm Nd:YAG radiation incident on the lithium niobate resonator. This corresponds to an optical power conversion efficiency of more than 40%.

High-frequency surface acoustic wave devices at very low temperature: Application to loss mechanisms evaluation

Previous work on high-performance bulk wave resonators in the frequency range of 5 to 25 MHz has shown that, by cooling to liquid helium temperature, acoustic losses become negligible. Therefore other sources of losses can be precisely measured. A similar approach is followed in the present work for high-frequency surface wave resonators. Experiments have been performed at 416 MHz on quartz devices. It is shown that for surface waves propagating in a good surface acoustic wave (SAW) resonator an important source of acoustic loss is due to intrinsic acoustic losses. By cooling the device to below 30 K, the quality factor Q shows a T−4 dependence characteristic of intrinsic acoustic losses. Below 4–10 K a plateau region is reached. High Q values in the range of 1.5×105 have been obtained at 4.2 K for 416-MHz devices, yielding a Q×f product of 7.5×1013 almost as good as for cooled bulk devices. Another set of measurements on a lithium niobate (LiNbO3) resonator at 847 MHz does not give a significant increase of quality factor Q at low temperature. This is due to the presence of other loss mechanisms not related to intrinsic acoustic losses because the LiNbO3 resonator operates in a leaky mode rather than a Rayleigh mode. The applications of the method to the characterization of new kinds of SAW resonators will be helpful for optimizing high-Q surface wave resonators at high frequencies, based on new modes or new materials.

Automated measurement and CAD analysis technique for accurate determination of UHF acoustic resonator equivalent circuit parameters

Many measurement techniques have been reported for accurate determination of equivalent electrical circuit parameters of HF and VHF acoustic resonators. Recent technological advances in the fabrication and processing of conventional bulk- and surface-wave resonators, and in the development of monolithic sputtered film resonators, have extended device operating frequencies into the UHF range. At UHF, resonator package and bond-wire parasitic reactances are nonnegligible and can significantly mask the impedance characteristics of the resonator itself and result in inaccurate determination of device equivalent circuit. This paper describes an automated resonator measurement and data analysis technique that has been developed for accurate determination of UHF acoustic resonator equivalent circuit parameters. The procedure consists of computer-controlled measurement of resonator input reflection coefficient using an HP4191 RF impedance analyzer. Subsequent automatic data transfer, in the form of a circuit analysis file, is used in conjunction with the Super Compact1 RF analysis/optimization software for determination and “removal” of effects of packaged resonator parasitic reactances from the measured data, based on device out-of-band impedance characteristics. The residual resonator motional arm impedance characteristic is calculated from which equivalent circuit element values are readily determined. The HP4191 RF analyzer control software enables determination and identification of individual resonator desired and spurious (anharmonic) resonances in specified search bands. This is extremely helpful when the resonator exact operating frequency is unknown as is often the case for sputtered, thin-film, monolithic devices. Examples will be given showing the results of measurement of UHF resonators including conventional surface acoustic wave (SAW), bulk-wave quartz and lithium niobate resonators, and monolithic sputtered aluminum nitride and zinc oxide and ZnO film resonators.

Low temperature coefficient lithium niobate resonators by use of temperature sensitive capacitances

To obtain the zero resonant-temperature coefficient of piezoelectric resonators, a method is presented in which a series capacitance alters both the effective value and the temperature behavior of the electromechanical coupling factor. This method is applied to a lithium niobate resonator and avails to obtain the zero temperature coefficient of the frequency.