On-chip acousto-optic modulator with high side mode suppression ratio

Abstract

The application discloses a high-side mode rejection ratio on-chip acousto-optic modulator, comprising: an insulating substrate and a lithium niobate substrate arranged on the insulating substrate, a chalcogenide optical waveguide is heterogeneously integrated on the lithium niobate substrate, and an interdigital transducer is arranged on the chalcogenide optical waveguide, the interdigital transducer comprises a plurality of even pairs of interdigital electrodes. The chalcogenide optical waveguide is a multimode RT runway type optical waveguide. The application combines the acousto-optic characteristics of the chalcogenide glass material and the piezoelectric effect of the lithium niobate thin film, utilizes the multimode waveguide structure of the micro-ring resonator, fully confines the surface acoustic wave and the optical wave energy excited by the interdigital transducer in the waveguide structure, and realizes the amplification of a single sideband and the suppression of other side modes under the phase matching condition of the sideband signal generated through the acousto-optic interaction in the micro-ring structure, thereby realizing the high-efficiency and high-suppression-ratio acousto-optic modulation. The high-side mode rejection ratio on-chip acousto-optic modulator has the characteristics of high modulation efficiency, low cost and easy realization of on-chip large-scale integration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronics, in particular to a high side mode rejection on-chip acousto-optic modulator. BACKGROUND

[0002] Acousto-optic modulation device is a multi-physical field coupling element related to the interaction of sound wave and light wave, and has a special position in the diversified optoelectronic information processing technology field. By using the interaction of light and sound wave, the related acousto-optic devices such as deflector, tunable filter, frequency shifter and Q switch can be realized. These acousto-optic functional devices are essentially realized by the refractive index perturbation of the light medium caused by the photoelastic effect in the medium. In the medium, the sound wave and the light wave can be transmitted independently, combined with the electro-acoustic transducer and the piezoelectric crystal material, the sound wave can be used to regulate the related parameters of the incident light wave signal in multiple dimensions. With the rapid development of piezoelectric transduction technology and integrated optics technology, thin film acousto-optic modulator has attracted widespread attention. This thin film acousto-optic modulator is driven by surface acoustic wave, and has the advantages of small driving power, small size, high modulation efficiency, easy integration and the like, and has broad application and development prospects in the fields of quantum conduction, optical communication, laser processing technology, laser ranging technology, optical radar technology and laser medical technology. However, acousto-optic modulation devices still face great challenges in the light wave application frequency band, sound wave modulation rate, sound wave to light wave conversion efficiency and electrical power consumption. Therefore, how to enhance the interaction intensity of sound wave and light wave under the micro / nano scale photonic / phononic structure, while improving the modulation rate and the efficient utilization of sideband is the inevitable trend of future development.

[0003] With the emergence of various new acousto-optic materials, acousto-optic modulation devices of different structures have also appeared in the public eye, such as acousto-optic modulators based on MZI interferometer, photonic crystal resonator, superconducting structure and optical mechanical resonant cavity. In particular, micro-ring resonators have attracted great attention in the study of acousto-optic modulators due to their low cost, compact structure, high integration, low insertion loss and low crosstalk. Acousto-optic devices based on micro-ring resonators can help improve the acousto-optic coupling efficiency, and have great practical significance for the research of high-speed, high-modulation-efficiency and high-side-mode-rejection acousto-optic modulators. SUMMARY

[0004] The purpose of the present application is to provide a high side mode rejection on-chip acousto-optic modulator, which combines the excellent acousto-optic properties of chalcogenide glass material, the piezoelectric effect of lithium niobate substrate, uses multimode optical waveguide, fully utilizes the intermodal scattering and phase matching principle, realizes the amplification of single sideband, suppresses other optical sidebands, and has the characteristics of high side mode rejection, high modulation efficiency, low cost, non-reciprocity and easy realization of large-scale on-chip integration.

[0005] To achieve the above purpose, the present application provides the following scheme:

[0006] An on-chip high side mode rejection ratio acousto-optic modulator comprises: an insulating substrate and a lithium niobate substrate disposed on the insulating substrate, a chalcogenide optical waveguide is integrated on the lithium niobate substrate, and an interdigital transducer is disposed on the lithium niobate substrate, the interdigital transducer comprises a plurality of even pairs of interdigital electrodes.

[0007] Further, the lithium niobate substrate comprises a silicon dioxide layer and a lithium niobate thin film on the silicon dioxide layer.

[0008] Further, the thickness of the lithium niobate thin film is 100 nm to 1500 nm.

[0009] Further, the chalcogenide optical waveguide is a multimode RT racetrack optical waveguide.

[0010] Further, the chalcogenide optical waveguide has a width of 300 nm to 30 μm, a height of 150 nm to 2500 nm, and a working wavelength of 600 nm to 20000 nm.

[0011] Further, the multimode RT racetrack optical waveguide is composed of a single-mode directional coupler or a pulley coupler and a high-Q multimode micro-ring resonant cavity.

[0012] Further, the waveguide width of the single-mode directional coupler or the pulley coupler is 200 nm to 2 μm.

[0013] Further, the interdigital transducer is a bidirectional electrode structure for exciting a specific frequency acoustic wave, the interdigital transducer is disposed between the two arms of the multimode RT racetrack optical waveguide at a set tilt angle, and the center of the interdigital transducer is the same distance from the two arms of the multimode RT racetrack optical waveguide.

[0014] Further, the specific frequency acoustic wave is a Rayleigh surface acoustic wave with a frequency of 0.1 GHz to 10 GHz, and the set tilt angle is 2° to 30°.

[0015] Further, the insulating substrate is a silicon substrate.

[0016] According to the specific embodiments of the present application, the following technical effects are disclosed: the on-chip acousto-optic modulator with high side mode suppression ratio provided by the present application has the following advantages: first, thanks to the excellent piezoelectric effect and photoelastic effect of lithium niobate and chalcogenide material, the acoustic surface wave excited by the interdigital transducer has greater disturbance to the bound optical wave mode, which increases the overlap factor of the optical wave and the acoustic wave mode, and improves the acousto-optic modulation efficiency; second, the chalcogenide waveguide can adopt the waveguide structure design of the multimode RT micro-ring resonator, which can stabilize the transmission of the fundamental mode and the first-order mode and other high-order modes, breaking the principle of traditional acousto-optic modulators based on fundamental mode modulation; third, the design of the multimode micro-ring waveguide makes the first-order sideband signal generated by the acousto-optic interaction be significantly amplified due to the resonance characteristics under the condition of satisfying the frequency and phase matching conditions, while other order modes are effectively suppressed, in addition, the micro-ring waveguide capable of stabilizing the transmission of the fundamental mode, the first-order mode, the second-order mode and the third-order mode can be designed according to the requirements, and the amplification of the first-order, second-order and third-order sideband signals is realized in turn, solving the problem of low sideband utilization rate of traditional acousto-optic modulators and realizing efficient and high side mode suppression ratio acousto-optic modulation; fourth, the interdigital transducer is placed at a certain inclination angle, and combined with the scattering principle between the modes in the waveguide, non-reciprocal optical wave modulation can be realized under the condition of satisfying the phase matching condition, which is helpful to realize the on-chip electrically driven high-performance optical isolator. Compared with the prior art, the present application provides a new idea for the research and application of the acousto-optic modulator with high side mode suppression ratio. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative labor.

[0018] Figure 1 It is a top view structural schematic diagram of the on-chip acousto-optic modulator with high side mode suppression ratio of the present application embodiment.

[0019] Figure 2 It is an end face structural schematic diagram of the on-chip acousto-optic modulator with high side mode suppression ratio of the present application embodiment.

[0020] Figure 3 It is a phase matching schematic diagram of the on-chip acousto-optic modulator with high side mode suppression ratio of the present application embodiment.

[0021] Figure 4 It is a phase matching schematic diagram of the on-chip acousto-optic modulator with high side mode suppression ratio of the present application embodiment.

[0022] Figure 5 It is a test system schematic diagram of the on-chip acousto-optic modulator with high side mode suppression ratio of the present application embodiment.

[0023] Figure 6 The non-reciprocal schematic diagram of the on-chip acousto-optic modulator with high side mode suppression ratio in the third embodiment of the present application;

[0024] Figure 7 The test system schematic diagram of the on-chip acousto-optic modulator with high side mode suppression ratio in the third embodiment of the present application.

[0025] The label explanation: 1, Si (silicon); 2, SiO2 (silicon dioxide); 3, LiNbO3 (lithium niobate); 4, ChG (chalcogenide glass); 5, Au (gold). DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] The purpose of the present application is to provide an on-chip acousto-optic modulator with high side mode suppression ratio, which comprehensively utilizes the excellent acousto-optic characteristics of chalcogenide glass material and the outstanding piezoelectric effect of lithium niobate film, and combines the matching design of micro-ring resonator and coupling waveguide geometry, on the one hand, to realize the amplification of specific optical sidebands and improve the energy utilization rate of sidebands; on the other hand, to achieve double modulation effect, significantly reduce the electrical driving power of the device, and be conducive to realizing non-reciprocal optical wave modulation.

[0028] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0029] As shown in Figure 1 and Figure 2 The on-chip acousto-optic modulator with high side mode suppression ratio provided by the present application comprises: an insulating substrate and a lithium niobate substrate arranged on the insulating substrate, a chalcogenide optical waveguide is heterogeneously integrated on the lithium niobate substrate, and an interdigital transducer is arranged on the chalcogenide optical waveguide, the interdigital transducer comprises a plurality of even pairs of interdigital electrodes. The lithium niobate substrate comprises a silicon dioxide layer and a lithium niobate film on the silicon dioxide layer. The insulating substrate can be a silicon substrate, the silicon substrate is formed by using silicon 1, the silicon dioxide layer is formed on the silicon substrate by using silicon dioxide 2, the lithium niobate film is formed on the silicon dioxide layer by arranging lithium niobate 3, and the interdigital electrodes are made of gold 5; the chalcogenide optical waveguide is made of chalcogenide glass 4.

[0030] The sulfur-based optical waveguide is a multimode RT runway-type optical waveguide. The multimode RT runway-type optical waveguide is composed of a single-mode directional coupler or a pulley coupler and a high-Q multimode micro-ring resonant cavity, which can support the conversion and transmission of the fundamental mode, the first-order mode, the second-order mode and other high-order modes, while other modes are suppressed; the input and output of the runway-type waveguide are matched with the pulley coupler. The interdigital transducer is a bidirectional electrode structure for exciting acoustic waves of a specific frequency, the interdigital transducer is placed between the two arms of the multimode RT runway-type optical waveguide at a set tilt angle θ, and the center of the interdigital transducer is the same distance from the two arms of the multimode RT runway-type optical waveguide. The interdigital transducer can excite a Rayleigh surface acoustic wave of 0.1 GHz to 10 GHz; the angle of the interdigital transducer is 2° to 30°.

[0031] For example, the thickness of the lithium niobate thin film is 100 nm to 1500 nm. The width of the sulfur-based optical waveguide is 300 nm to 30 μm, the height is 150 nm to 2500 nm, and the working wavelength is 600 nm to 20000 nm.

[0032] The waveguide width of the single-mode directional coupler or the pulley coupler is 200 nm to 2 μm.

[0033] Due to the inverse piezoelectric coupling effect of the lithium niobate thin film, the input microwave signal is converted into a surface acoustic wave signal of the lithium niobate thin film through the interdigital transducer, so that a mechanical strain field distribution appears in the lithium niobate thin film, and the mechanical acoustic wave generated on the surface of the lithium niobate thin film propagates at an angle of θ relative to the optical waveguide. Due to the photoelastic disturbance of the driving acoustic wave to the medium, intermodal scattering occurs between optical modes under the condition of satisfying the phase matching condition, and further phase modulation is realized. The angle and finger width of the interdigital transducer are carefully selected to generate a two-dimensional acoustic wave with appropriate momentum in the propagation direction and the transverse direction, and the interdigital transducer is placed in the middle of the waveguide, which greatly enhances the light-mechanical coupling strength and helps to realize a high-efficiency, high-side-mode-suppression-ratio, non-reciprocal on-chip acousto-optic modulator.

[0034] Case 1

[0035] As Figure 1As shown, the on-chip acousto-optic modulator with high side mode suppression ratio provided by the embodiment of the present application adopts a bidirectional interdigital transducer, an even number of interdigital electrodes are arranged on the lithium niobate thin film, a multimode RT racetrack-shaped optical waveguide is heterogeneously integrated on the lithium niobate thin film, the width of the multimode RT racetrack-shaped optical waveguide is 1.8-2.1 μm, which is equal to the wavelength of the acoustic wave, on the one hand, the stable transmission of the fundamental mode and the first-order mode is realized, and on the other hand, the overlap integral of the acoustic field and the optical field is maximized. The waveguide width of the input end pulley coupler is 0.8-1.5 μm, which realizes single-mode low-loss coupling into the micro-ring resonant cavity. The multimode RT racetrack-shaped optical waveguide works in the communication waveband near 1550 nm, and the interdigital transducer excites a 2 GHz surface acoustic wave. The interdigital transducer is placed at an angle of 6.15° with the two arms of the multimode RT racetrack-shaped optical waveguide, which can generate a two-dimensional surface acoustic wave, so that the momentum conservation is satisfied in the propagation direction. As shown in the figure, Figure 3 As shown, under the condition of perfect phase matching, the micro-ring resonator is in a critical coupling state, the pump light is placed at the first-order mode, and the first-order sideband generated after modulation will be amplified at the fundamental mode, so that the sideband conversion efficiency is maximum, and other order sidebands will be suppressed.

[0036] Figure 5 As shown, the corresponding test system of the present application mainly includes: a tunable quantum laser, a doped fiber amplifier, a high-speed photodetector, a vector network analyzer, and a spectrometer.

[0037] When the device is tested, a microwave signal of a certain frequency is loaded on the interdigital transducer, at this time, two-dimensional surface acoustic waves propagating to both sides will be excited under the action of the inverse piezoelectric effect of the lithium niobate thin film, and the microwave-to-optical conversion is completed on the chalcogenide optical waveguide under the action of the acoustic wave. Under the action of the acoustic wave, intermodal scattering is realized in the chalcogenide optical waveguide, the equivalent refractive index changes, further changes the phase of the optical signal, and finally realizes intensity modulation. The output optical signal is converted into an electrical signal by the photodetector, and the S 21 parameters of the modulated signal can be obtained after the network analyzer. 21 Through the analysis of the S 21 parameters, the voltage required to change π phase can be calculated, and the half-wave voltage length product can be obtained by multiplying the calculated voltage and the length of the modulation region, so as to evaluate the conversion efficiency and modulation performance of the acousto-optic modulator. The output signal is passed through the spectrometer to observe the first-order sideband signal after modulation, and the maximum conversion efficiency of the sideband can be calculated.

[0038] Embodiment two

[0039] As shown in the figure, Figure 1As shown, the on-chip acousto-optic modulator with high side-mode suppression ratio provided in this embodiment of the invention employs a bidirectional interdigital transducer. An even number of interdigital electrodes are disposed on a lithium niobate thin film. A multimode RT racetrack-shaped optical waveguide is heterogeneously integrated on the lithium niobate thin film. The width of the multimode RT racetrack-shaped optical waveguide is 2.5–3 μm, which should be equal to the acoustic wavelength. This ensures stable transmission of the fundamental mode, first-order mode, and second-order mode, and maximizes the overlap integral of the acoustic and optical fields. The input pulley coupler waveguide has a width of 1–1.8 μm, enabling low-loss coupling of single-mode signals into and out of the microring resonator. The waveguide operates in the communication band near 1550 nm, and the interdigital transducer excites 5 GHz surface acoustic waves. The interdigital transducer is placed at an angle of 7.21°, enabling the generation of two-dimensional surface acoustic waves with conserved momentum in the propagation direction. Figure 4 As shown, under perfect phase matching conditions, the microring resonator is in a critical coupling state. When the pump light is placed at the second-order mode, the second-order sideband generated after modulation will be amplified at the fundamental mode, so that the sideband conversion efficiency is maximized, while other order sidebands will be suppressed.

[0040] The testing system and testing steps corresponding to this second embodiment are the same as those in the first embodiment.

[0041] Implementation Case 3

[0042] like Figure 1 As shown, the on-chip acousto-optic modulator with high side-mode suppression ratio provided in this embodiment of the invention employs a bidirectional interdigital transducer. An even number of interdigital electrodes are disposed on a lithium niobate thin film. A multimode RT racetrack-shaped optical waveguide is heterogeneously integrated on the lithium niobate thin film. The width of the multimode RT racetrack-shaped optical waveguide is 2–2.5 μm, which should be equal to the acoustic wavelength, to achieve stable transmission of the fundamental mode and first-order mode within the waveguide. The waveguide width of the input pulley coupler is 0.8–1.5 μm, enabling low-loss coupling of the fundamental mode into and out of the micro-ring resonant cavity. The interdigital transducer excites a 3 GHz surface acoustic wave and is positioned at a certain angle in the middle of the multimode RT racetrack-shaped optical waveguide, achieving forward and backward phase matching, thereby realizing a highly efficient, non-reciprocal acousto-optic modulator.

[0043] like Figure 5 As shown, TE 00 The optical resonant frequency of the mode is higher than that of TE. 10 In optical modes, the resonant frequency is low, satisfying the forward-matching condition, allowing light to propagate only forward. The modulated sideband signal can then be observed at the output. Conversely, if light propagates backward, the phase matching condition is not met, and the modulated signal cannot be detected at the output. Similarly, TE... 00 The optical resonant frequency of the mode is higher than that of TE. 10The resonant frequency of the optical mode is high, the backward phase matching condition is met, and only the backward transmitted light can be observed at the output end to obtain the modulated sideband signal.

[0044] Figure 6 A corresponding test system of the application is shown in the figure, and the test system mainly comprises a tunable quantum laser, a doped fiber amplifier, an optical switch, a high-speed photodetector, an acousto-optic frequency shifter, a vector network analyzer and a spectrum analyzer.

[0045] During device testing, the light is first divided into two paths in a 50:50 ratio, one of which is used for detecting the device, and the other of which is used as a reference. The light in the reference path is provided with a predetermined offset through the acousto-optic frequency shifter. An optical switch is used to change the direction of the 1550nm light. The IDT generates a surface acoustic wave under the drive of a microwave signal, and under the action of the acoustic wave, the mode scattering in the optical waveguide is realized, the equivalent refractive index is changed, and the acousto-optic modulation is realized. The modulated signal and the signal of the reference path are frequency-mixed through a high-speed photodetector, and the intensity of the corresponding signal is observed through a spectrum analyzer. By observing the signal of the spectrum analyzer, the non-reciprocal characteristics of the device can be verified, and the conversion efficiency of the sideband signal can be further calculated.

[0046] In summary, the application provides an on-chip acousto-optic modulator with high side mode suppression ratio, which comprises a lithium niobate substrate on an insulating substrate and a chalcogenide optical waveguide and an interdigital transducer arranged on the lithium niobate substrate. The chalcogenide optical waveguide is composed of a single-mode directional coupler or a pulley coupler and a high-Q multimode micro-ring resonator, which can support the conversion and transmission of fundamental mode, first-order mode, second-order mode and other high-order modes. The interdigital transducer is placed on the lithium niobate film at a certain θ angle and is placed in the middle of the micro-ring. The application fully combines the acousto-optic characteristics of chalcogenide glass material and the piezoelectric effect of lithium niobate film, and utilizes the multimode waveguide structure of the micro-ring resonator to fully confine the surface acoustic wave excited by the interdigital transducer and the optical wave energy in the waveguide structure. The sideband signal generated through acousto-optic interaction can be amplified in a single sideband under the phase matching condition in the micro-ring structure, and other side modes are suppressed, thereby realizing efficient and high-suppression-ratio acousto-optic modulation. The on-chip acousto-optic modulator with high side mode suppression ratio provided by the application has the characteristics of high modulation efficiency, low cost and easy realization of on-chip large-scale integration.

[0047] The principles and implementation modes of the application are described herein by using specific examples, and the above examples are only used to help understand the method of the application and its core idea; meanwhile, for those skilled in the art, the specific implementation modes and application ranges can be changed according to the idea of the application. In summary, the content of the specification should not be understood as a limitation of the application.

Claims

1. An on-chip acousto-optic modulator with high side-mode suppression ratio, characterized in that, include: An insulating substrate and a lithium niobate substrate disposed on the insulating substrate, wherein a chalcogenide optical waveguide is heterogeneously integrated on the lithium niobate substrate and an interdigital transducer is disposed thereon, wherein the interdigital transducer includes a plurality of even-number pairs of interdigital electrodes. The chalcogenide optical waveguide is a multimode RT racetrack-type optical waveguide; the multimode RT racetrack-type optical waveguide is composed of a single-mode directional coupler or a pulley coupler and a high-Q multimode micro-ring resonator; the waveguide width of the single-mode directional coupler or the pulley coupler is 200nm to 2μm. The interdigital transducer has a bidirectional electrode structure and is used to excite acoustic waves of a specific frequency. The interdigital transducer is placed between the two arms of the multimode RT racetrack-shaped optical waveguide at a set tilt angle, and the center of the interdigital transducer is the same distance from the two arms of the multimode RT racetrack-shaped optical waveguide. The acoustic wave of the specific frequency is a Rayleigh surface acoustic wave of 0.1 GHz to 10 GHz. The set tilt angle is 2° to 30°.

2. The on-chip acousto-optic modulator with high side-mode suppression ratio according to claim 1, characterized in that, The lithium niobate substrate includes a silicon dioxide layer and a lithium niobate film on the silicon dioxide layer.

3. The on-chip acousto-optic modulator with high side-mode suppression ratio according to claim 2, characterized in that, The thickness of the lithium niobate film is 100nm to 1500nm.

4. The on-chip acousto-optic modulator with high side-mode suppression ratio according to claim 1, characterized in that, The chalcogenide optical waveguide has a width of 300nm to 30μm, a height of 150nm to 2500nm, and an operating wavelength of 600nm to 20000nm.

5. The on-chip acousto-optic modulator with high side-mode suppression ratio according to claim 1, characterized in that, The insulating substrate is a silicon substrate.

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