Self-interference optical microcavity and method for regulating the same

Abstract

The present application relates to a kind of self-interference optical micro resonator and its regulation method, wherein, self-interference optical micro resonator includes, microcavity structure, by the waveguide of head-to-tail connection is constituted;Bus waveguide, with the microcavity structure is coupled 2n+1 times and is constituted 2n+1 couplers, and the optical path of adjacent two couplers on the waveguide of the microcavity structure is different from the optical path of adjacent two couplers on the bus waveguide.The present application can regulate the resonant transmittance of optical micro resonator without changing the absolute resonant frequency of optical micro resonator.

Description

Technical Field

[0001] This invention relates to the field of integrated optics technology, and in particular to a self-interference optical micro-resonator and its control method. Background Technology

[0002] Integrated optics is an important branch of modern information technology, and optical microcavities are a crucial fundamental optical component. The most representative basic structure of an optical microcavity consists of a microcavity coupled with a straight optical waveguide and a ring waveguide. This optical element satisfies resonance conditions at specific optical frequencies, forming multiple nearly equidistant resonance peaks in the transmission spectrum. These resonance characteristics have led to the widespread application of optical microcavities in optical communication, optical sensing, and nonlinear optics. Transmittance at microcavity resonance is a key parameter; modulating it would greatly enrich the functionality of optical microcavities. However, once fabricated, the structural parameters of such integrated optical microcavities cannot be altered, meaning that the key parameter affecting transmittance is difficult to adjust, limiting their functional applications. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a self-interference optical micro-resonator and its control method, which can control the resonant transmittance of the optical micro-resonator without changing the absolute resonant frequency of the optical micro-resonator.

[0004] The technical solution adopted by this invention to solve its technical problem is: to provide a self-interference optical micro-resonator, comprising:

[0005] The microcavity structure is composed of waveguides connected end to end;

[0006] The bus waveguide is coupled to the microcavity structure 2n+1 times to form 2n+1 couplers. The optical path length of two adjacent couplers on the waveguide where the microcavity structure is located is different from that of two adjacent couplers on the bus waveguide.

[0007] The optical path length between any two adjacent couplers on the waveguide where the microcavity structure is located is equal; the optical path length between any two adjacent couplers on the bus waveguide is equal, that is, the optical path difference between any two adjacent couplers on the waveguide where the microcavity structure is located and on the bus waveguide is equal.

[0008] The ratio of the intrinsic linewidth of the microcavity structure to the coupling linewidth of a single coupler enables some of the resonance peaks of the self-interference optical micro-resonator to reach a critical coupling state.

[0009] The microcavity structure includes, but is not limited to: ring structure, racetrack-shaped structure, or interdigitated structure.

[0010] The waveguides and bus waveguides are made of materials including, but not limited to: silicon, silicon nitride, lithium niobate, aluminum nitride, aluminum gallium arsenide, or silicon carbide.

[0011] The technical solution adopted by the present invention to solve its technical problem is: a self-interference optical micro-resonator modulation method is also provided, which is applied to the above-mentioned self-interference optical micro-resonator, and the optical path difference between two adjacent couplers on the waveguide and bus waveguide where the micro-cavity structure is located is controlled by applying and controlling the physical field.

[0012] The physical principles underlying the methods of modulating physical fields include, but are not limited to: electro-optic effect, thermo-optic effect, or stress-refractive index effect.

[0013] When the optical path length of the bus waveguide between two adjacent couplers is controlled by changing the physical field, the number of waveguides between the two adjacent couplers is divided into a first part of the waveguide and a second part of the waveguide. A physical field in a first direction is applied to the first part of the waveguide, and a physical field in a second direction is applied to the second part of the waveguide. The physical field in the first direction and the physical field in the second direction refer to additional optical path length changes in opposite directions. This control method can change the transmittance of the microcavity resonant peak without changing the absolute resonant frequency of the microcavity resonant peak.

[0014] Beneficial effects

[0015] By employing the above-mentioned technical solution, this invention has the following advantages and positive effects compared with the prior art: The coupling number between the bus waveguide and the microcavity structure in the optical microresonator of this invention is 2n+1 times. The transmittance of a specific resonance peak in this optical microresonator can be adjusted by the refractive index of the waveguide constituting the microcavity structure and the difference in waveguide length, thereby controlling the resonant transmittance of the optical microresonator without changing its absolute resonant frequency. Furthermore, this invention can use a multi-physics field modulation method to achieve this modulation, making the transmission spectrum of the optical microresonator more regular when modulated. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the self-interference optical micro-resonator of Example 1;

[0017] Figure 2 This is a graph showing the relationship between the transmittance of the resonant peak and the resonant peak frequency of the self-interference optical micro-resonant cavity in Example 1.

[0018] Figure 3 This is a graph showing the transmittance versus frequency under different values ​​after tuning the self-interference optical micro-resonator in Example 1.

[0019] Figure 4 This is a schematic diagram of the self-interference optical micro-resonator of Example 2;

[0020] Figure 5 This is a graph showing the relationship between the transmittance of the resonant peak and the resonant peak frequency of the self-interference optical micro-resonant cavity in Example 2. Detailed Implementation

[0021] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0022] The present invention relates to a self-interference optical micro-resonator, comprising: a microcavity structure consisting of waveguides closed at both ends; and a bus waveguide coupled to the microcavity structure 2n+1 times to form 2n+1 couplers, wherein the distance between two adjacent couplers on the loop of the microcavity structure is different from the distance between two adjacent couplers on the bus waveguide.

[0023] In this embodiment, the microcavity structure includes, but is not limited to, a ring structure, a racetrack-shaped structure, or an interdigitated structure. The materials used to fabricate the waveguide and bus waveguide include, but are not limited to, silicon, silicon nitride, lithium niobate, aluminum nitride, aluminum gallium arsenide, or silicon carbide.

[0024] Based on the above structure, this embodiment can adjust the optical path difference between two adjacent couplers on the waveguide and bus waveguide where the microcavity structure is located by applying and controlling a physical field. The physical principles on which the method of controlling the physical field is based include, but are not limited to, the electro-optic effect, the thermo-optic effect, and the stress-refractive index effect.

[0025] The following four specific examples further illustrate this implementation method.

[0026] Example 1:

[0027] like Figure 1As shown, the self-interference optical microresonator in this embodiment is fabricated based on an x-cut lithium niobate platform on an insulator. From top to bottom, the top lithium niobate layer is the device layer, containing the optical microresonator described in this embodiment; the middle layer is a silicon oxide layer; and the bottom layer is a silicon support substrate. The microcavity structure of the optical microresonator is a racetrack-shaped structure. The straight waveguide region of this racetrack-shaped microcavity structure is along the crystallographic y-direction of lithium niobate, facilitating subsequent electro-optical modulation of the refractive index of the straight waveguide. The cross-section of the lithium niobate waveguide is ridge-shaped, with a planar layer height of 300 nm, a ridge height of 300 nm, a ridge width of 1000 nm, and a sidewall tilt angle of approximately 60°. The effective refractive index of the TE fundamental mode supported in the communication band (around 1550 nm) is approximately 1.95. The radius of the annular region of the lithium niobate racetrack-shaped microcavity is 200 μm, and the straight waveguide region is along the y-direction of the lithium niobate crystal. The coupling between the microcavity structure and the bus waveguide uses a directional coupler, with a coupling frequency of 3 times. The distances between coupler 1 and coupler 2, and between coupler 2 and coupler 3 in the straight waveguide region of the microcavity (i.e., the distance on the ring) are all 1000um. The distances between coupler 1 and coupler 2, and between coupler 2 and coupler 3 in the bus waveguide are 1.2 times the distance on the ring (approximately 1200um).

[0028] Assuming the coupling linewidth of the directional coupler does not change or changes very little with the frequency of the light wave, then for the self-interference optical microresonator in this embodiment, the transmittance of the resonance peaks at different frequencies depends on the optical path difference generated between adjacent couplers on the microcavity waveguide and the bus waveguide. Specifically, the amplitude transmittance of each resonance peak will be modulated, such as... Figure 2 As shown, the specific modulation function is as follows:

[0029]

[0030] Where E3 is the amplitude at the output of the bus waveguide, and E1 is the amplitude at the input of the bus waveguide, therefore |E3 / E1| 2 Let κ0 be the transmittance of the resonant peak at a certain frequency, and κ0 be the linewidth of the coupling of a single coupler. i Let Δφ1 represent the intrinsic linewidth of the microcavity structure, Δφ2 represent the phase difference between the bus waveguide and the microcavity waveguide between coupler 1 and coupler 2, and Δφ2 represent the phase difference between the bus waveguide and the microcavity waveguide between coupler 2 and coupler 3. i This represents the amplitude change generated by the waveguide between coupler 1 and coupler 2. It is generally assumed that this value tends to 1, therefore it can be treated as equal to 1 without affecting the derivation of the principle in this application. φ i This refers to the phase change generated on the microcavity waveguide between coupler 1 and coupler 2.

[0031] As shown in the above formula, the transmittance in this embodiment only changes with Δφ1 and Δφ2. Without adjustment, φ1 represents the phase change between coupler 1 and coupler 2 on the bus waveguide, φ2 represents the phase change between coupler 2 and coupler 3 on the bus waveguide, ΔL1 represents the difference in waveguide length between coupler 1 and coupler 2, ΔL2 represents the difference in waveguide length between coupler 2 and coupler 3, n eff This represents the effective refractive index of the waveguide that constitutes the microcavity structure. It can be seen that the transmittance of a specific resonance peak can be adjusted simply by adjusting the length difference between the two waveguides between the couplers and the effective refractive index of the waveguide.

[0032] In this embodiment, the length difference between the two waveguides between coupler 1 and coupler 2 is equal to the length difference between the two waveguides between coupler 2 and coupler 3. If the effective refractive index of the two additional waveguides is modulated by changing the physical field, and the phase change direction of the modulation is reversed, then the following can be achieved:

[0033] Δφ1+Δφ2=const

[0034]

[0035] Where const indicates that the sum of Δφ1 and Δφ2 is a constant.

[0036] Take Δφ1-Δφ2 respectively π The transmittance versus frequency curve at 2π is shown below. Figure 3 As shown. (Through) Figure 3 It can be seen that the transmittance curve changes with different values ​​of Δφ1-Δφ2, and the transmittance of the resonant peak at a specific frequency changes, while the overall curve pattern does not drift in the high-frequency or low-frequency direction.

[0037] In addition, through reasonable design The value of can achieve a large variation in transmittance, making it suitable for implementing modulator and sensor functions. In this embodiment... Values It is approximately equal to 7.828.

[0038] Example 2:

[0039] like Figure 4As shown, the self-interference optical microresonator in this embodiment is fabricated on 4H-silicon carbide on an insulator. The 4H-silicon carbide is approximately 400 nm thick and serves as the device layer, forming the waveguide and optical microresonator. The surface of the device layer is a deposited silicon dioxide layer with a thickness of approximately 2 μm. Below the 4H-silicon carbide layer are a silicon dioxide layer with a thickness of approximately 3 μm and a silicon support substrate with a thickness of approximately 500 μm. The 4H-silicon carbide waveguide has a rectangular cross-section, with a height of 400 nm and a width of 1000 nm. The effective refractive index of the TE fundamental mode supported in the communication band (around 1550 nm) is approximately 2.15. The radius of the 4H-silicon carbide annular microcavity is 200 μm. The microcavity structure is coupled to the bus waveguide three times using point coupling. The distances between couplers 1 and 2, and between couplers 2 and 3 on the ring are each one-quarter of the ring circumference (approximately 314 μm). The distances between couplers 1 and 2, and between couplers 2 and 3 on the bus waveguide are 1.2 times the distances on the ring (approximately 376.8 μm). The ratio of the intrinsic linewidth of the microcavity to the coupling linewidth of a single coupler is [value missing]. The curves showing the relationship between the resonant peak transmittance and the resonant peak frequency of the aforementioned self-interference optical micro-resonator are as follows: Figure 5 As shown.

[0040] Example 3:

[0041] This embodiment, based on Embodiment 1, illustrates a multiphysics modulation method. On a fabricated lithium niobate optical chip, gold electrodes are grown on both sides of the bus waveguide between coupler 1 and coupler 2, and between coupler 2 and coupler 3, using a lift-off process. The length of the gold electrodes is approximately equal to the length of the bus waveguide (1200 μm), the thickness of the gold electrodes is between 200 and 1000 nm, the width of the gold electrodes is between 2 and 10 μm, and the distance between the metal electrodes and the waveguide is 2 to 5 μm. When a voltage is applied to the gold electrodes on both sides of the bus waveguide between coupler 1 and coupler 2, and between coupler 2 and coupler 3, opposite voltages are applied, with a voltage magnitude between -100 and 100 V. Therefore, the resulting additional phase has opposite directions. In this case, the absolute frequency of the microcavity's resonant peak does not change; only the transmittance is modulated by the applied voltage value.

[0042] Example 4:

[0043] This embodiment, based on Embodiment 2, illustrates another method for multiphysics field manipulation. On the fabricated 4H-silicon carbide optical chip, a bottom electrode layer Mo with a thickness of 50-200 nm, an aluminum nitride layer with a thickness of 100-1000 nm, and a top electrode layer Al with a thickness of approximately 50-200 nm are grown sequentially using a lift-off process. The aforementioned aluminum nitride stress actuators are positioned directly above the bus waveguides between the couplers. When a voltage is applied between the top electrode Al and the bottom electrode Mo, an electric field is generated in the aluminum nitride layer. Due to the piezoelectric effect of aluminum nitride, stress is generated, which is transmitted to the silicon carbide layer. Due to the presence of stress, the refractive index of silicon carbide undergoes a slight change, thereby affecting the phase change (optical path) on the bus waveguides. There is an aluminum nitride stress actuator between coupler 1 and coupler 2, and between coupler 2 and coupler 3. When a voltage is applied, the two actuators apply opposite voltages, with the voltage magnitude between -200 and 200 V. Therefore, the resulting additional phase has opposite directions. In this case, the absolute frequency of the microcavity's resonant peak does not change; only the transmittance is modulated by the applied voltage value.

[0044] It is easy to see that the coupling number between the bus waveguide and the microcavity structure in the optical microresonator of this invention is 2n+1 times. The transmittance of a specific resonance peak in this optical microresonator can be adjusted by the refractive index of the waveguide constituting the microcavity structure and the difference in waveguide length, thereby controlling the resonant transmittance of the optical microresonator without changing its absolute resonant frequency. During modulation, this invention can use a multi-physics field modulation method, making the transmission spectrum of the optical microresonator more regular when modulated.

Claims

1. A self-interference optical micro-resonator modulation method, characterized in that, It is applied to a self-interference optical micro-resonator, the self-interference optical micro-resonator comprising: The microcavity structure is composed of waveguides connected end to end; The bus waveguide is coupled to the microcavity structure 2n+1 times to form 2n+1 couplers. The optical path length of two adjacent couplers on the waveguide where the microcavity structure is located is different from the optical path length of two adjacent couplers on the bus waveguide. The optical path difference between two adjacent couplers on the waveguide and bus waveguide of the microcavity structure is controlled by applying and regulating physical fields. Specifically, the waveguide between two adjacent couplers is divided into a first part waveguide and a second part waveguide. A physical field in a first direction is applied to the first part waveguide, and a physical field in a second direction is applied to the second part waveguide. The physical fields in the first and second directions refer to additional optical path changes in opposite directions.

2. The self-interference optical micro-resonator modulation method according to claim 1, characterized in that, The physical principles underlying the methods of modulating physical fields include, but are not limited to: electro-optic effect, thermo-optic effect, and stress-refractive index effect.

3. The self-interference optical micro-resonator modulation method according to claim 1, characterized in that, The optical path length between any two adjacent couplers on the waveguide containing the microcavity structure is equal; the optical path length between any two adjacent couplers on the bus waveguide is equal.

4. The self-interference optical micro-resonator modulation method according to claim 1, characterized in that, The ratio of the intrinsic linewidth of the microcavity structure to the coupling linewidth of a single coupler enables some of the resonance peaks of the self-interference optical micro-resonator to reach a critical coupling state.

5. The self-interference optical micro-resonator modulation method according to claim 1, characterized in that, The microcavity structure includes, but is not limited to: ring structure, racetrack-shaped structure, or interdigitated structure.

6. The self-interference optical micro-resonator modulation method according to claim 1, characterized in that, The waveguides and bus waveguides are made of materials including, but not limited to: silicon, silicon nitride, lithium niobate, aluminum nitride, aluminum gallium arsenide, or silicon carbide.

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