A high-speed, high-threshold acousto-optic modulator based on lithium niobate

Abstract

The present invention relates to a high-speed, high-threshold acousto-optic modulator based on lithium niobate, belonging to the field of optoelectronics; the acousto-optic modulator comprises an acousto-optic medium, a bonding layer, a transducer and a surface electrode; the sound-transmitting surface of the acousto-optic medium is equipped with a transducer through the bonding layer, and the surface electrode is plated on the surface of the transducer; the acousto-optic medium is a lithium niobate crystal, the [100] axis of the lithium niobate crystal is perpendicular to the sound-transmitting surface of the acousto-optic medium, the [010] axis of the lithium niobate crystal is located within the sound-transmitting surface of the acousto-optic medium, and the angle between the [010] axis of the lithium niobate crystal and the incident light is 0.5°±0.3°. The present invention adopts lithium niobate crystal as the acousto-optic medium, improves the acousto-optic figure of merit of the lithium niobate crystal, and also improves the ability of the acousto-optic device to withstand high-power lasers; at the same time, the present invention also plates an anti-reflection film on the light-transmitting surface of the acousto-optic medium to improve the utilization rate of light energy by the acousto-optic device. Overall, the present invention can better meet the modulation requirements of high speed and high threshold.

Description

Technical Field

[0001] The invention relates to a high-speed high-threshold acousto-optic modulator based on lithium niobate, and belongs to the field of optoelectronics. Background Art

[0002] An acousto-optic modulator (AOM) is an acousto-optic device that controls laser intensity variations. It primarily consists of a surface electrode, a transducer, a bonding layer, an acousto-optic medium, a matching network, and a high-frequency socket. The high-frequency socket is connected to the matching network via leads, while the surface electrode is located on the transducer surface. The acousto-optic medium and transducer are connected via a bonding layer. The RF signal is transmitted to the transducer's surface electrode via the high-frequency socket, matching network, and gold wire (or silicon-aluminum wire). The transducer converts the RF signal into ultrasonic waves and transmits them to the acousto-optic medium, where a refractive index grating forms. The incident light interacts with the refractive index grating through an acousto-optic interaction, producing diffracted light.

[0003] Tellurium oxide crystals have a high acousto-optic figure of merit and stable performance, making them a commonly used acousto-optic medium material for making acousto-optic modulators. However, the defects of tellurium oxide crystals, such as low acoustic wave velocity and low laser damage threshold, can no longer meet the needs of rapid development. Summary of the Invention

[0004] To address the above technical issues, the present invention provides a high-speed, high-threshold acousto-optic modulator based on lithium niobate. The technical solution adopted is as follows:

[0005] The device comprises an acousto-optic medium, a bonding layer, a transducer and a surface electrode; the sound-transmitting surface of the acousto-optic medium is provided with a transducer through the bonding layer, and the surface of the transducer is plated with a surface electrode; the acousto-optic medium is a lithium niobate crystal, the

[100] axis of the lithium niobate crystal is perpendicular to the sound-transmitting surface of the acousto-optic medium, the

[010] axis of the lithium niobate crystal is located within the sound-transmitting surface of the acousto-optic medium, and the angle between the

[010] axis of the lithium niobate crystal and the incident light is 0.5°±0.3°

[0006] The present invention uses lithium niobate crystals instead of traditional tellurium oxide crystals as the acousto-optic medium material. Although the acousto-optic figure of merit of lithium niobate crystals is relatively low, only one-fifth of that of tellurium oxide crystals, lithium niobate crystals have a fast sound velocity and a high laser damage threshold, which can better meet the high-speed and high-threshold modulation requirements.

[0007] Furthermore, the lithium niobate crystal may include a normal lithium niobate crystal, a near-stoichiometric lithium niobate crystal, or a doped lithium niobate crystal.

[0008] Furthermore, the doped lithium niobate crystal includes doped magnesium oxide (MgO) with a concentration of 2 mol% to 5 mol%; or doped zinc oxide (ZnO) with a concentration of 3 mol% to 6.5 mol%; or doped indium oxide (In2O3) with a concentration of 1 mol% to 1.5 mol%; or doped scandium oxide (Sc2O3) with a concentration of 1 mol% to 1.5 mol%; or doped iron oxide (Fe2O3) with a concentration of 2 mol% to 4 mol%.

[0009] Furthermore, the present invention also coats an anti-reflection film on the light-transmitting surface of the acousto-optic medium according to the wavelength of light.

[0010] Optionally, when the wavelength of light is in the visible and near-infrared bands, the antireflection film is made of hafnium oxide (H f O2) and silicon dioxide (SiO2).

[0011] Optionally, when the wavelength of light is in the short to medium wavelength band, the antireflection film is made of hafnium oxide (H f O2) and yttrium fluoride (YbF).

[0012] Furthermore, before coating the anti-reflection film, an aluminum oxide (A12O3) transition layer is coated on the light-transmitting surface of the acousto-optic medium, thereby improving the adhesion of the anti-reflection film and ensuring the laser damage threshold of the lithium niobate crystal.

[0013] Beneficial effects of the present invention:

[0014] (1) Improved optical pulse rise time. When ultrasonic longitudinal waves propagate along the direction of lithium niobate crystal

[100] , their acoustic wave velocity is as high as 6570 m / s, which is 1.6 times the longitudinal wave velocity of tellurium oxide (4200 m / s). The acoustic wave velocity is inversely proportional to the optical pulse rise time of the acousto-optic device. Therefore, under the same conditions, the optical pulse rise time of the lithium niobate acousto-optic device is only 1 / 1.6 of that of the tellurium oxide acousto-optic device. That is, the lithium niobate acousto-optic device improves the optical pulse rise time by nearly 40%.

[0015] (2) Improved the ability of acousto-optic devices to withstand high-power lasers. Taking 1064nm continuous laser as an example, tellurium oxide crystals can only withstand less than 10W / mm 2 Laser, ordinary lithium niobate crystal can withstand about 40W / mm 2 The laser, and the acousto-optic device made of doped lithium niobate crystal can withstand 200W / mm 2 It is obvious that the acousto-optic devices based on lithium niobate crystals have greatly improved their ability to withstand high-power lasers.

[0016] (3) The acoustic-optical figure of merit of lithium niobate crystal is improved. The present invention changes the angle between the light transmission direction and the

[010] axis of lithium niobate crystal, so that the acoustic-optical interaction between the incident o light and the acoustic wave transmitted along the

[100] axis of lithium niobate crystal is optimized. At this time, the acoustic-optical figure of merit of the incident o light is 7.3×10 -15 S 3 / kg, which is 5% higher than the acousto-optic figure of merit of conventional lithium niobate crystals. The acousto-optic figure of merit is proportional to the diffraction efficiency of the acousto-optic device. Therefore, under the same conditions, acousto-optic devices based on the new-cut lithium niobate crystal can achieve higher diffraction efficiency. The higher the diffraction efficiency, the greater the utilization of the incident light energy, and the better the performance of the acousto-optic device.

[0017] (4) Improved the adhesion of the anti-reflection film. According to the anti-reflection film theory, hafnium oxide (HfO2) is used on the light-transmitting surface of lithium niobate. f O2), silicon dioxide (SiO2) coating visible light and near infrared band (400nm-2000nm) antireflection film, or hafnium oxide (H f The short- and medium-wave (2000nm-5000nm) anti-reflection coatings coated with aluminum oxide (Al2O3) and yttrium fluoride (YbF) can improve the utilization rate of light energy in acousto-optic devices. Furthermore, the present invention first coats a transition layer of aluminum oxide (Al2O3) on the light-transmitting surface of the lithium niobate crystal, and then coats the anti-reflection coating according to the wavelength of light. This improves the adhesion of the anti-reflection coating and ensures the stability of the anti-reflection coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of the high-speed, high-threshold acousto-optic modulator based on lithium niobate of the present invention;

[0019] In the figure, 1, acousto-optic medium, 2, incident light, 3, sound-transmitting surface, 4, bonding layer, 5, transducer, 6, surface electrode, 7, diffracted light, 8, 0th-order light, 9, light-transmitting surface. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, a high-speed, high-threshold acousto-optic modulator based on lithium niobate includes an acousto-optic medium 1, a bonding layer 4, a transducer 5 and a surface electrode 6; the sound-transmitting surface 3 of the acousto-optic medium 1 is mounted with the transducer 5 through the bonding layer 4, and the surface of the transducer 5 is plated with a surface electrode 6. The acousto-optic medium 1 is a lithium niobate crystal.

[0022] In an embodiment of the present invention, the material of the traditional acousto-optic medium is replaced by lithium niobate crystal from tellurium oxide crystal. Although the acousto-optic figure of merit of lithium niobate crystal is relatively low, only one-fifth of that of tellurium oxide crystal, lithium niobate crystal has a fast sound velocity and a high laser damage threshold, which can better meet the high-speed and high-threshold modulation requirements.

[0023] In an embodiment of the present invention, the lithium niobate crystal can be a doped lithium niobate crystal or an undoped lithium niobate crystal, wherein the undoped lithium niobate crystal can be divided into ordinary lithium niobate crystal and stoichiometric lithium niobate crystal. The ordinary lithium niobate crystal here is a conventional lithium niobate crystal, that is, a lithium niobate crystal that has not been subjected to doping treatment, stoichiometric treatment or other treatment.

[0024] Compared with conventional lithium niobate crystals of the same composition, the electro-optic coefficient, nonlinear optical coefficient, periodic polarization reversal voltage, applied photorefractive index and other performance of stoichiometric lithium niobate crystals have been greatly improved.

[0025] Compared with conventional lithium niobate crystals and stoichiometric lithium niobate crystals, doped lithium niobate crystals have a higher laser damage threshold than non-doped lithium niobate crystals (ordinary lithium niobate crystals, stoichiometric lithium niobate crystals) and can meet higher power laser modulation requirements.

[0026] In an embodiment of the present invention, the lithium niobate crystals in the acousto-optic medium 1 are doped in a variety of different ways, including magnesium oxide (MgO) doping at a concentration of 2 mol% to 5 mol%, zinc oxide (ZnO) doping at a concentration of 3 mol% to 6.5 mol%, indium oxide (In2O3) doping at a concentration of 1 mol% to 1.5 mol%, scandium oxide (Sc2O3) doping at a concentration of 1 mol% to 1.5 mol%, or iron oxide (Fe2O3) doping at a concentration of 2 mol% to 4 mol%. The above doping methods can generally increase the laser damage threshold of the doped lithium niobate crystals by more than five times compared to ordinary lithium niobate crystals.

[0027] In a preferred embodiment of the present invention, a new crystal tangent is used for lithium niobate crystals to improve the acousto-optic figure of merit of lithium niobate crystals. When lithium niobate crystals are used to make acousto-optic devices, the commonly used crystal tangent is: the angle between the light transmission direction and the

[010] axis of the lithium niobate crystal is 35°. At this time, the acousto-optic interaction effect between the incident e-light and the acoustic wave transmitted along the

[100] axis is the best, and the acousto-optic figure of merit of the incident e-light is 6.95×10 -15 S 3 / kg. In the present invention, a new lithium niobate crystal tangent is designed by changing the angle between the light transmission direction and the

[010] axis of the lithium niobate crystal: the

[100] axis of the lithium niobate crystal is perpendicular to the sound-transmitting surface 3 of the acousto-optic medium, the

[010] axis of the lithium niobate crystal is located within the sound-transmitting surface 3 of the acousto-optic medium, the angle θ between the incident light 2 and the

[010] axis of the lithium niobate crystal is 0.5°±0.3°, the radio frequency signal (RF) is transmitted to the transducer 5 via the surface electrode, the transducer 5 absorbs the radio frequency signal and converts it into ultrasonic vibration, which is then transmitted to the acousto-optic medium 1 via the bonding layer 4, forming an ultrasonic longitudinal wave in the acousto-optic medium 1, and the ultrasonic longitudinal wave propagates along the

[100] axis of the lithium niobate crystal. The incident light 2 and the ultrasonic longitudinal wave interact with each other to generate diffracted light 7, and the remaining light in the incident light 2 except the diffracted light 7 is zero-order light 8. At this time, the acoustic-optical interaction between the incident o light and the acoustic wave transmitted along the

[100] axis of the lithium niobate crystal (sound velocity 6570 m / s) is the best, and the acoustic-optical figure of merit of the incident o light is 7.3×10 -15 S 3 / kg; ultrasonic longitudinal waves propagate along the

[100] axis of the crystal.

[0028] In the preferred embodiment of the present invention, considering that the refractive index of lithium niobate crystal is as high as 2.2, the single-side residual reflection reaches 14% without coating, which greatly affects the utilization rate of light. Therefore, it is necessary to coat the light-transmitting surface 9 of the lithium niobate crystal with an anti-reflection film to improve the utilization rate of light energy by the acousto-optic device. In order to improve the adhesion of the anti-reflection film and ensure the laser damage threshold of the lithium niobate crystal, the present invention first coats a layer of aluminum oxide (A12O3) transition layer on the light-transmitting surface 9 of the lithium niobate crystal, and then coats the anti-reflection film according to the wavelength of light. For the visible light and near-infrared bands (400nm-2000nm), the anti-reflection film on the light-transmitting surface 9 of the lithium niobate crystal is made of hafnium oxide (HfO3). f O2) and silicon dioxide (SiO2); for short and medium wavelengths (2000nm-5000nm), the antireflection film on the light-transmitting surface 9 of the lithium niobate crystal is made of hafnium oxide (H f O2) and yttrium fluoride (YbF).

[0029] In one specific embodiment of the present invention, a high-speed, high-threshold acousto-optic modulator (AOM) was fabricated using a lithium niobate crystal doped with 5 mol% MgO. The ultrasonic longitudinal wave propagated along the crystal's

[100] axis at a speed of 6570 m / s. For a beam with a diameter of 1 mm, the optical pulse rise time reached 96 ns. Under the same conditions, an AOM fabricated from a tellurium oxide crystal, with a speed of only 4200 m / s, required a pulse rise time of 154 ns. Clearly, the new AOM improved the optical pulse rise time by nearly 40%.

[0030] This high-speed, high-threshold acousto-optic modulator can also withstand 200W / mm 21064nm laser, while conventional tellurium oxide acousto-optic modulators can only withstand less than 10W / mm 2 The 1064nm laser shows that the acousto-optic device based on lithium niobate crystal has greatly improved its ability to withstand high-power lasers.

[0031] The above embodiments of the present invention are merely examples for illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations and modifications can be made based on the above description. It is not possible to enumerate all embodiments here. Any obvious variations or modifications arising from the technical solution of the present invention remain within the scope of protection of the present invention.

[0032] In the description of the present invention, it should be understood that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inside", "outside", "front", "center", "both ends", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0033] In the present invention, unless otherwise clearly stipulated and limited, the terms "installation", "setting", "connection", "fixation", "rotation" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0034] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A high-speed, high-threshold acousto-optic modulator based on lithium niobate, comprising an acousto-optic medium, a bonding layer, a transducer, and a surface electrode; the transducer is mounted on the sound-transmitting surface of the acousto-optic medium through the bonding layer, and the surface electrode is plated on the surface of the transducer, characterized in that: The acousto-optic medium is a lithium niobate crystal, the [100] axis of the lithium niobate crystal is perpendicular to the sound-transmitting surface of the acousto-optic medium, the [010] axis of the lithium niobate crystal is located within the sound-transmitting surface of the acousto-optic medium, and the angle between the [010] axis of the lithium niobate crystal and the incident light is 0.5°±0.3°.

2. The high-speed, high-threshold acousto-optic modulator based on lithium niobate according to claim 1, characterized in that: The lithium niobate crystal includes a near-stoichiometric lithium niobate crystal or a doped lithium niobate crystal.

3. The high-speed, high-threshold acousto-optic modulator based on lithium niobate according to claim 2, characterized in that: The doped lithium niobate crystal includes doped magnesium oxide (MgO) with a concentration of 2 mol% to 5 mol%; or doped zinc oxide (ZnO) with a concentration of 3 mol% to 6.5 mol%; or doped indium oxide (In2O3) with a concentration of 1 mol% to 1.5 mol%; or doped scandium oxide (Sc2O3) with a concentration of 1 mol% to 1.5 mol%; or doped iron oxide (Fe2O3) with a concentration of 2 mol% to 4 mol%.

4. The high-speed, high-threshold acousto-optic modulator based on lithium niobate according to claim 1, characterized in that: On the light-transmitting surface of the acousto-optic medium, an anti-reflection film is deposited according to the wavelength of light.

5. The high-speed, high-threshold acousto-optic modulator based on lithium niobate according to claim 4, characterized in that: When the wavelength of light is in the visible and near-infrared bands, the antireflection film is made of hafnium oxide (H f O2) and silicon dioxide (SiO2).

6. The high-speed, high-threshold acousto-optic modulator based on lithium niobate according to claim 4, characterized in that: When the wavelength of light is in the short and medium wavelength band, the antireflection film is made of hafnium oxide (H f O2) and yttrium fluoride (YbF).

7. A high-speed, high-threshold acousto-optic modulator based on lithium niobate according to claim 4, 5 or 6, characterized in that: Before coating the antireflection film, an aluminum oxide (A12O3) transition layer is also coated on the light-transmitting surface of the acousto-optic medium.

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