Solid-state optical cavity with thin-film lithium niobate layers for resonance tuning.

Abstract

The solid-state optical cavity may include a first mirror and a second mirror that provide reflective surfaces for reflecting light back and forth within the cavity to create a standing wave at a resonant frequency. A thin-film lithium niobate layer may be deposited between the first mirror and the second mirror. The thin-film lithium niobate layer may be configured to be electrically tunable to optically select the resonant frequency.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 425,730, filed November 16, 2022, which is incorporated by reference in its entirety into this application.

[0002] FIELD OF THE DISCLOSURE This disclosure relates to optical cavities, and more particularly to solid-state optical cavities with thin film niobate layers for resonance tuning. [Background technology]

[0003] Optical cavities (also known as optical resonators or resonant cavities) use reflective surfaces to generate standing waves of light. Optical cavities are highly frequency selective based on their geometry - the dimensions of the optical cavity cause the selection of certain frequencies to generate standing waves through constructive interference, while other frequencies are canceled out through destructive interference. The selected frequencies are known as resonant frequencies.

[0004] For various practical applications, it may be desirable to have a variable optical cavity whose corresponding resonant frequency can be changed. For example, the same cavity may be desired to generate radiation of different frequencies at different times. The conventional process for creating a variable optical cavity involves mechanical motion: a piezoelectric actuator is used to move one of the two reflective surfaces to vary the distance between them.

[0005] However, frequency variation based on mechanical motion is cumbersome due to size limitations. Piezoelectric actuators necessarily have a minimum size, for example, on the order of millimeters and centimeters. While this minimum size imposes constraints on miniaturization, and other properties of the optical cavity can be utilized to make it smaller, accommodating the relatively bulky piezoelectric actuator means that the optical cavity must remain above a certain size. Mechanical motion also brings its own tuning issues, where achieving the desired precision motion can be technically challenging. Moving parts also mean that the optical cavity is prone to mechanical malfunction and failure. Summary of the Invention

[0006] In some embodiments, a solid-state optical cavity may be provided. The solid-state optical cavity may include a first mirror and a second mirror that provide reflective surfaces so that light reflects back and forth within the cavity to create a standing wave at a resonant frequency. A thin-film lithium niobate layer may be located between the first mirror and the second mirror. The thin-film lithium niobate layer may be configured to be electrically tunable to optically select the resonant frequency.

[0007] In some embodiments, an optical encoder for wavelength division multiplexing may be provided. The optical encoder may include multiple solid-state optical cavities for corresponding resonant wavelengths. Each of the multiple solid-state cavities may include a first mirror and a second mirror providing reflective surfaces for reflecting light back and forth within the solid-state optical cavity to create a standing wave for the corresponding resonant wavelength, and a thin-film lithium niobate layer between the first mirror and the second mirror. The thin-film lithium niobate layer may be configured to be electrically tunable to optically select the corresponding resonant wavelength. To perform wavelength division multiplexing, different signals may be encoded at the corresponding different wavelengths.

[0008] In some embodiments, an optical decoder for decoding signals using wavelength division multiplexing may be provided. The optical decoder may include multiple solid-state optical cavities for corresponding resonant wavelengths. Each of the multiple solid-state cavities may include a first mirror and a second mirror providing reflective surfaces for reflecting light back and forth within the solid-state optical cavity to create a standing wave for the corresponding resonant wavelength, and a thin-film lithium niobate layer between the first mirror and the second mirror. The thin-film lithium niobate layer may be configured to be electrically tunable to optically select the corresponding resonant wavelength. The wavelength division multiplexed signals may be decoded at various corresponding wavelengths.

[0009] In some embodiments, a spectrometer may be provided. The spectrometer may include a plurality of solid-state optical cavities for corresponding resonant wavelengths. Each of the plurality of solid-state optical cavities may include a first mirror and a second mirror providing reflective surfaces for reflecting light back and forth within the solid-state optical cavity to create a standing wave for the corresponding resonant wavelength, and a thin-film lithium niobate layer between the first mirror and the second mirror. The thin-film lithium niobate layer may be configured to be electrically tunable to optically select the corresponding resonant wavelength. The corresponding resonant wavelength may be configured to be used in a wavelength sweep to measure the spectral characteristics of the radiation source. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 illustrates an exemplary optical cavity according to an exemplary embodiment of the present disclosure. [Figure 2] FIG. 10 shows a graph illustrating the tunability of an optical cavity, according to an exemplary embodiment of the present disclosure. [Figure 3] FIG. 1 illustrates an optical encoding and decoding system using an optical cavity, according to an exemplary embodiment of the present disclosure. [Figure 4]FIG. 1 illustrates an exemplary high-resolution spectrometer, according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] It should be understood that the figures are for the purpose of illustrating example embodiments, but the disclosure is not limited to the arrangements and instrumentality shown in the drawings, in which like reference numerals identify at least generally similar elements.

[0012] The embodiments described herein can solve the technical problems of the prior art and provide other solutions as well. In the disclosed examples, frequency selection in an optical cavity can be achieved by changing the optical properties of a material between reflective surfaces (e.g., mirrors) of the optical cavity. For example, a thin-film lithium niobate may be deposited on one of the reflective surfaces. Electrical terminals may be provided on the thin-film niobate through which an electrical signal can be provided to precisely control the optical properties of the lithium niobate. The electrical signal can affect the orientation of covalent bonds in the lithium niobate to produce desired optical properties. Thus, optical cavities with controllable resonant frequencies without mechanical motion may be provided in a solid state with a smaller form factor. Exemplary applications of these solid-state, non-mechanical, and miniaturized optical cavities include encoders and decoders for dense wavelength division multiplexing optical communications and high-resolution spectroscopy.

[0013] Due to the lack of bulky piezoelectric actuators and moving parts, optical cavities according to exemplary embodiments can be miniaturized with fewer constraints than those with moving parts. For example, multiple optical cavities can be formed within a single die, where the multiple cavities can function as encoders and / or decoders in optical communications. As another example, the multiple cavities can function as high-resolution spectrometers with large yet fairly fine wavelength / frequency sweeps. Due to their miniaturized size, chips including multiple optical cavities can fully replace other conventional bulky encoders / decoders and / or spectrometers.

[0014] 1 illustrates an exemplary optical cavity 100 in accordance with an exemplary embodiment of the present disclosure. As shown, the optical cavity 100 may include, among other components, a first mirror 102 (also referred to as a top distributed Bragg reflector, DBR), a second mirror 104 (also referred to as a bottom DBR), and a thin-film lithium niobate 106 layer on the second mirror 104. However, it should be understood that the components of the optical cavity 100 illustrated in FIG. 1 and described herein are merely examples, and that optical cavities having additional, alternative, and fewer components should be considered within the scope of the present disclosure.

[0015] One of the more first mirrors 102 and second mirrors 104 may be made of any reflective material and / or may be a layer of reflective material. As shown, each of the first mirror 102 and second mirror 104 may be a DBR.

[0016] The thin-film lithium niobate 106 may be deposited on at least one of the first mirror 102 and the second mirror 104. In some embodiments, the thin-film lithium niobate 106, such as that shown in FIG. 1, is deposited on the second mirror 104. In some embodiments, the thin-film lithium niobate may be deposited between the mirrors 102 and 104 (e.g., within the dielectric 112) or on both mirrors 102, 104. Generally, the thin-film lithium niobate 106 may be deposited / positioned anywhere within the optical cavity 100 to produce the desired optical properties through the application of an electrical signal. The dielectric 112 may be formed of a transparent material that may allow light 114 to pass through without a change in optical properties. For example, the dielectric may be formed of silicon dioxide.

[0017] A signal electrode 108 and a ground electrode 110 may be used to provide an electrical signal to the thin-film lithium niobate 106. The signal may be supplied as an electrical potential through the electrodes 108, 110. Based on these signals, the electrical properties of the thin-film lithium niobate may change, for example, the orientation of covalent bonds may change, and the change in electrical properties may cause a change in optical properties. The changed optical properties may then create a frequency resonance for light 114 (or any other form of electromagnetic radiation) passing through the optical cavity 100.

[0018] In operation, resonance is based on a change in wavelength and also a change in velocity of the light 114. The light 114 may have multiple wavelengths and frequencies. Each wavelength of the light 114 may be attenuated as the light 114 passes through the thin-film lithium niobate 106. The amount of this attenuation may be controlled by varying signals at the electrodes 108, 110. Such attenuation may cause constructive interference of the light 114 at some wavelengths, while other wavelengths may interfere destructively and cancel each other out as the light 114 travels back and forth between the mirrors 102 and 104. Therefore, only specific wavelengths of the light 114 are selected within the optical cavity (e.g., only corresponding frequencies may resonate).

[0019] In some embodiments, the thin-film lithium niobate 106 can be made to act as a lens by altering its electrical properties. The lensing action can be based on an electric field generated by an electrical signal passing through the electrodes 108, 110, but the electrical signal is not uniformly applied across the entire thin-film lithium niobate. Thus, in addition to high wavelength (and frequency) selectivity, the thin-film lithium niobate 106 can change the direction of light 114 (note that the change in direction can also have high wavelength / frequency selectivity). The lens-like properties can be used when light 114 is not perpendicularly (i.e., normal to) the mirrors 102, 104. Such non-perpendicular incidence can cause light 114 to escape the optical cavity 100 after several back-and-forth reflections, but the thin-film lithium niobate 106 can circumvent that problem by bending the light 114 as desired.

[0020] Thus, optical cavities can be realized using the embodiments disclosed herein in a solid state without the use of moving parts. Furthermore, significant miniaturization can be achieved compared to conventional systems. Without bulky moving parts, changes in resonant frequency can be achieved by simply varying an electrical signal (in the form of an electrical potential) applied across the thin-film lithium niobate 106. Furthermore, because there is multiple back and forth motion of the light 114 within the cavity, large lithium niobate crystals may not be required. Thin films with thinner crystals (as shown) can produce gradual changes in the light 114, which can compound over time to achieve the desired resonance.

[0021] The optical cavity 100 is also relatively easy to manufacture. The mirrors 102, 104, the dielectric 112, and the thin-film lithium niobate 106 can be deposited in layers. Portions of the thin-film lithium niobate 106 can then be evaporated and used to deposit / attach the electrodes 108, 110.

[0022] FIG. 2 shows a graph 200 illustrating the tunability of an optical cavity according to an exemplary embodiment of the present disclosure. The specific tuning shown in graph 200 is merely an example and should not be considered limiting. In graph 200 showing an electrically tunable transmission spectrum, curve 204 shows the resonant wavelength (with a corresponding resonant frequency) when a 0 volt signal is applied to the electrodes in the thin-film lithium niobate. As shown, curve 204 is narrow, thereby illustrating the precision of the tuning of the optical cavity. Curve 202 shows the resonant wavelength when a 50 V / micrometer signal is applied to the optical cavity. Curve 202 is also narrow and precise, and the shift between the resonant wavelengths is precise and achieved without the use of any moving parts.

[0023] Optical cavities according to embodiments herein may have several different applications, some non-limiting example applications are described below.

[0024] 3 illustrates an optical cavity-based optical coding system 300 according to an exemplary embodiment of the present disclosure. It should be understood that the components of system 300 illustrated in FIG. 3 are merely examples, and that systems having additional, alternative, and fewer components should be considered within the scope of the present disclosure.

[0025] Within the system 300, the encoder 306 may include multiple optical cavities. Each optical cavity may have a resonant wavelength 310 (having a resonant frequency). Each resonant wavelength 310 may be individually tuned using a corresponding electrical signal within the electrodes within the thin-film lithium niobate. In other words, each cavity may be modulated at its resonant wavelength / frequency, and the transmitted signal may be encoded at that frequency. After modulation, each output 312 may be fed to a lens coupler 314. The lens coupler 314 may combine all outputs 312 to generate a combined output 316 that passes through a single-mode optical fiber 318. This combined output 316 may achieve strict wavelength division multiplexing in a relatively smaller footprint. This is because the encoder 306 can be made smaller, at least because the optical cavities have no moving parts.

[0026] The decoder 308 may be similar to the encoder 306 (e.g., a mirror image of the encoder 306). An input 320 from the optical fiber 318 may be separated by another lens coupler 322 as a separate input 324 and fed to the decoder 308. The input 324 may resonate within a corresponding optical cavity to form a resonant input 326. Information may be extracted from the resonant input 326 through a detector 328, thereby decoding the signal encoded by the encoder 306.

[0027] 4 illustrates an exemplary high-resolution spectrometer 400 in accordance with an exemplary embodiment of the present disclosure. It should be understood that the components of spectrometer 400 are merely exemplary, and that spectrometers having additional, alternative, or fewer components should also be considered within the scope of the present disclosure. As shown, spectrometer 400 may be used to detect the spectral signature of a radiation source 402.

[0028] The radiation source 402 can be any material (e.g., a chemical compound, a biological organism, etc.) that can emit a signature spectral pattern that can be used to identify the material. For example, the signature spectral pattern may include a wavelength / frequency combination. A spectrometer 400 including multiple individual tunable optical cavities may be used to generate a broad sweep. Furthermore, because the optical cavities can be closely spaced (because no moving parts are involved), the resolution of the sweep can be significantly increased; that is, both the range of the sweep and the step of the sweep can be increased.

[0029] For example, exemplary portion 404 of the spectral pattern can be detected by resonant light 406, which can be generated as output 408 to detector 410. Detector 410 can then measure the spectral intensity of exemplary portion 404.

[0030] Due to its smaller footprint, spectrometer 400 can be slid into existing detection systems. In particular, existing bulky spectrometers that include bulky mechanical components can be completely replaced with spectrometer 400.

[0031] Further examples of the presently described method and device embodiments are suggested in accordance with the structures and techniques described herein. Other non-limiting examples may be configured to work separately or may be combined in any permutation or combination with any one or more of the other examples provided above or throughout this disclosure.

[0032] It will be understood by those skilled in the art that the present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the present disclosure is indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and scope of the claims and equivalents thereof are intended to be embraced therein.

[0033] It should be noted that the terms "comprises" and "comprising" should be interpreted to mean "including, but not limited to." Unless already expressly recited in a claim, the term "a" should be interpreted as "at least one," and terms such as "the," "said," etc. should be interpreted as "at least one of," "said at least one," etc. Furthermore, it is Applicant's intent that only claims containing the phrases "means for" or "step for" be interpreted under 35 U.S.C. 112(f). Claims that do not expressly contain the phrases "means for" or "step for" should not be interpreted under 35 U.S.C. 112(f).

Claims

1. 1. A solid-state optical cavity comprising: a first mirror and a second mirror that provide reflective surfaces so that light reflects back and forth within the cavity to create a standing wave at a resonant frequency; a thin-film lithium niobate layer deposited between the first mirror and the second mirror, the thin-film lithium niobate layer configured to be electrically tunable to optically select the resonant frequency.

2. 10. The solid-state optical cavity of claim 1, further comprising a first electrode and a second electrode in the thin-film lithium niobate layer configured to receive an electrical tuning signal to select the resonant frequency.

3. 3. The solid-state optical cavity of claim 2, wherein the first electrode and the second electrode are disposed on evaporated portions of the thin-film lithium niobate layer.

4. The solid-state optical cavity of claim 1 , wherein at least one of the first mirror and the second mirror comprises a distributed Bragg reflector.

5. The solid-state optical cavity of claim 1 further comprising a dielectric material.

6. The solid-state optical cavity of claim 5 , wherein the dielectric material comprises silicon dioxide.

7. 10. The solid-state optical cavity of claim 1, wherein the thin-film lithium niobate layer is further configured to be electrically tunable to act as a lens to change the path of light.

8. 8. The solid-state optical cavity of claim 7, wherein the change in path is for light that is non-normally incident on the cavity.

9. The solid-state optical cavity of claim 1 , wherein the standing wave is generated by constructive interference of waves at the resonant frequency.

10. The solid-state optical cavity of claim 1 , wherein non-resonant frequencies are canceled through destructive interference.

11. 1. An optical encoder for wavelength division multiplexing, comprising: a plurality of solid-state optical cavities for corresponding resonant wavelengths, each of the plurality of solid-state optical cavities comprising: a first mirror and a second mirror providing reflective surfaces for reflecting light back and forth within the solid-state optical cavity to create a standing wave for a corresponding resonant wavelength; a thin-film lithium niobate layer deposited between the first mirror and the second mirror, the thin-film lithium niobate layer configured to be electrically tunable to optically select the corresponding resonant wavelength; Different signals are encoded on corresponding different wavelengths to achieve wavelength division multiplexing; Optical encoder.

12. The optical encoder of claim 11 , further comprising a lens coupler configured to combine the different signals encoded at the different corresponding wavelengths and provide the combined signal to an optical fiber.

13. Each of the plurality of solid-state optical cavities comprises: The optical encoder of claim 11 , further comprising first and second electrodes in the thin-film lithium niobate layer configured to receive an electrical tuning signal to select the corresponding resonant wavelength.

14. 14. The optical encoder of claim 13, wherein the first electrode and the second electrode are disposed on evaporated portions of the thin-film lithium niobate layer.

15. The optical encoder of claim 11 , wherein at least one of the first mirror and the second mirror comprises a distributed Bragg reflector.

16. The optical encoder of claim 11 , wherein each of the plurality of solid-state optical cavities further comprises a dielectric material.

17. 1. An optical decoder for decoding signals using wavelength division multiplexing, comprising: a plurality of solid-state optical cavities for corresponding resonant wavelengths, each of the plurality of solid-state optical cavities comprising: a first mirror and a second mirror providing reflective surfaces for reflecting light back and forth within the solid-state optical cavity to create a standing wave for a corresponding resonant wavelength; a thin-film lithium niobate layer deposited between the first mirror and the second mirror, the thin-film lithium niobate layer configured to be electrically tunable to optically select the corresponding resonant wavelength; the wavelength division multiplexed signals are decoded at corresponding different wavelengths; Optical decoder.

18. 18. The optical decoder of claim 17, further comprising a lens coupler configured to receive a combined signal from an optical fiber and separate the combined signal into the signals encoded at the different corresponding wavelengths.

19. Each of the plurality of solid-state optical cavities comprises:

18. The optical decoder of claim 17, further comprising first and second electrodes in the thin-film lithium niobate layer configured to receive an electrical tuning signal to select the corresponding resonant wavelength.

20. a plurality of solid-state optical cavities for corresponding resonant wavelengths, each of the plurality of solid-state optical cavities comprising: a first mirror and a second mirror providing reflective surfaces for reflecting light back and forth within the solid-state optical cavity to create a standing wave for a corresponding resonant wavelength; a thin-film lithium niobate layer deposited between the first mirror and the second mirror, the thin-film lithium niobate layer configured to be electrically tunable to optically select the corresponding resonant wavelength; The corresponding resonant wavelength is configured to be used in a wavelength sweep to measure the spectral characteristics of the radiation source. Spectrometer.

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