Integrated Sagnac type sensor based on magneto-optical non-reciprocal phase shift waveguide

Abstract

The invention belongs to the technical field of optics, and particularly relates to an integrated Sagnac type sensor based on a magneto-optical nonreciprocal phase shift waveguide. According to the integrated Sagnac type sensor based on the magneto-optical non-reciprocal phase shift waveguide, the magneto-optical non-reciprocal phase shift waveguide is integrated in a traditional Sagnac sensor and used for replacing a traditional phase modulator, so that phase modulation in a Sagnac interference arm is carried out, and passive high-sensitivity magnetic field or inertial sensing is achieved. And a feasible path is provided for improving the sensitivity and engineering feasibility of the Sagnac type magnetic field / inertial sensor.

Description

Technical Field

[0001] This invention belongs to the field of optical technology, specifically an integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide. It replaces the traditional phase modulator with a magneto-optical non-reciprocal phase-shifting waveguide to achieve high-sensitivity magnetic field or inertial sensing. Background Technology

[0002] In inertial gyroscopes and magnetic field optical sensors based on Sagnac interferometer rings, the operating point of the loop is often placed at the steepest point of the phase response to obtain maximum sensitivity. Therefore, a phase modulator is traditionally introduced into the loop to achieve 90° orthogonal biasing of clockwise and counterclockwise propagating light. Common biasing methods include electro-optic, acousto-optic, or piezoelectric phase modulators. Although these schemes can dynamically adjust the operating point, they also bring significant problems: additional driving circuitry and power consumption are required, device size and system complexity increase, phase noise and perturbations introduced by modulation reduce the signal-to-noise ratio, and device insertion loss and long-term drift affect stability. At the same time, many modulation elements face process incompatibility, packaging and reliability challenges when integrated in a planar manner, and high-frequency driving limits the bandwidth and low power consumption requirements in certain application scenarios. For integrated optical sensors that pursue miniaturization, low power consumption and high stability, traditional active biasing devices show obvious limitations in practical engineering applications.

[0003] To overcome the aforementioned shortcomings, the industry has also attempted to achieve passive biasing through non-reciprocal elements or optical polarization methods. However, existing solutions mostly rely on external Faraday rotators, magneto-optical isolation elements, or high-loss magneto-optical thin films, often facing problems such as large size, high loss, poor coupling with waveguide platforms, and complex processes, making it difficult to achieve a balance between integration and performance. Therefore, how to provide a stable and near-90° non-reciprocal phase shift to replace traditional phase modulators while taking into account low loss, integrability, and the absence of dynamic driving has become a key unresolved issue for improving the overall performance and engineering feasibility of Sagnac-type sensors. Summary of the Invention

[0004] To address the aforementioned problems or shortcomings, this invention provides an integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide. It integrates a rare-earth iron garnet (RIG, where R represents a rare-earth element, including but not limited to Ce, Bi, Y, Tb, and Dy) thin film, a magneto-optical material with high Faraday swirl angle and low loss, onto the optical waveguide. By designing the magnetization direction and the length of the magneto-optical segment, a passive and non-volatile 90° non-reciprocal phase shift (NRPS) is achieved, demonstrating significant application value and technological prospects.

[0005] The technical solution of this invention is as follows:

[0006] The integrated Sagnac-type sensor based on magneto-optical non-reciprocal phase-shifting waveguide consists of a coupler, a non-reciprocal phase shifter, and a closed-loop optical waveguide. The incident light is split into two beams at the coupler and propagates in the loop in clockwise and counterclockwise directions, respectively. After passing through the optical waveguide once, the beams couple and interfere at the coupler.

[0007] The non-reciprocal phase shifter is a passively biased magneto-optical non-reciprocal phase shifter. It is formed by integrating rare earth iron garnet (RIG) thin films as magneto-optical materials onto an optical waveguide to create a non-reciprocal phase-shifting magneto-optical waveguide, thereby constituting a magneto-optical non-reciprocal phase shifter.

[0008] Rare-earth iron garnet (RIG) thin films are magnetic thin film materials with a significant Faraday effect. The doping of rare earth elements such as Ce and Bi significantly increases the Faraday effect, enabling large non-reciprocal deflection within a very short device length in the visible to near-infrared band. At the same time, high-quality RIG films maintain low optical absorption (low insertion loss) and act as insulators to avoid absorption of free carriers, thus balancing the requirements of large Faraday twist angle and low loss.

[0009] When the sensing waveguide does not undergo non-reciprocal phase shift due to rotation or magnetic field, the output light intensity of the transmitted waveguide is half of the incident light intensity. When the sensing waveguide undergoes non-reciprocal phase shift due to rotation or external magnetic field, the output intensity of the transmitted waveguide will undergo a measurable change, thereby realizing angular velocity or magnetic field sensing.

[0010] Furthermore, the rare earth element R in the rare earth iron garnet RIG film is Ce, Bi, Y, Tb or Dy.

[0011] Furthermore, the magneto-optical waveguide is designed to produce a non-reciprocal phase shift with a phase difference of 90°.

[0012] Furthermore, the design of the magneto-optical waveguide length is as follows:

[0013] The 90° non-reciprocal phase shift of the magneto-optical waveguide is achieved by the non-reciprocal phase shift effect of the magneto-optical material. The magneto-optical effect of the magneto-optical material is described by the off-diagonal elements of the material's dielectric tensor. Let the direction of light propagation be the z-direction, and the direction of the in-plane magnetic field perpendicular to the light propagation direction applied to the undamaged magneto-optical material be the x-direction. Then its dielectric tensor is expressed as:

[0014] ε =

[0015] Where j is the imaginary unit. = For the dielectric tensor off-diagonal elements, Let n be the vacuum wavenumber and n be the refractive index of the magneto-optical material. It is the Faraday rotation angle.

[0016] Consider using perturbation theory to calculate the non-reciprocal phase shift in a two-dimensional waveguide model. Assume the light is in TM mode and propagates along the z-direction. According to perturbation theory, the non-reciprocal phase shift is expressed as:

[0017] ( )=

[0018] Where N is the normalization constant of the waveguide mode.

[0019] As can be seen from the formula, the magnitude and sign of the non-reciprocal phase shift (NRPS) depend on the magnitude and sign of the Faraday rotation angle and the cross-sectional geometry of the waveguide.

[0020] The effective refractive index of the magneto-optical waveguide was obtained by setting off-diagonal elements of the dielectric tensor of the magneto-optical material using finite element simulation software. The propagation constant β is used to calculate the non-reciprocal phase shift per unit length. The interval length L for non-reciprocal phase shifts = .

[0021] Furthermore, the coupler is a 3 dB directional coupler or a multimode interferometer.

[0022] Furthermore, the normalized output strength of Sagnac is: ,in These are minute phase changes caused by variations in the magnetic field or rotational angular velocity.

[0023] In magnetic field sensors, = ,in The length of the magnetic field sensing segment. It is related to the magnitude and direction of the magnetic field.

[0024] In inertial sensors, for rotational angular velocity sensors, = ,in Let A be the number of turns of the waveguide and A be the area of ​​the ring. The wavelength of light The speed of light in a vacuum. ω is the rotational angular velocity.

[0025] At the bias point For small signals : And thus obtain I Therefore, the response slope at a bias of 90° is .

[0026] Compared to no bias or non-ideal bias, the equivalent input light intensity The output level change is greatest when the phase change is small, thus improving the signal-to-noise ratio (SNR).

[0027] Furthermore, the magneto-optical material integration method of the magneto-optical waveguide is direct chemical vapor deposition or wafer bonding.

[0028] In summary, this invention addresses the practical bottlenecks of traditional Sagnac rings that rely on active phase modulators to achieve quadrant bias (≈90°), which leads to challenges in energy consumption, size, phase noise, and packaging / integration. It proposes and demonstrates a passive RIG-based method... Feasible scheme for non-reciprocal phase shifters: By integrating a high Faraday rotation and low absorption RIG thin film on a silicon waveguide and saturating it under an applied magnetic field, the off-diagonal elements of the material's dielectric tensor are used as perturbation terms to correct the waveguide mode propagation constant, thereby generating controllable and near-reciprocal phase shifters within a finite length. The non-reciprocal phase shift enables static phase biasing of the Sagnac ring. Compared with existing active modulation schemes, the passive RIG scheme of this invention has significant advantages in reducing system complexity, eliminating driving noise, reducing insertion loss, and improving long-term stability. It also possesses process integrability with silicon photonics platforms and practical applicability in the 1550 nm band, thus providing a feasible new path for improving the sensitivity and engineering feasibility of Sagnac-type magnetic field / inertial sensors. Attached Figure Description

[0029] Figure 1 This is a schematic block diagram of the structure of the present invention;

[0030] Figure 2 This is a schematic diagram of the magnetic field sensor in the embodiment;

[0031] Figure 3 This is a schematic diagram of the inertial sensor structure in the embodiment;

[0032] Figure 4 This is a schematic diagram of the cross-sectional structure of a non-reciprocal phase-shifting magneto-optical waveguide in the embodiment.

[0033] Figure 5 The cross-section of the non-reciprocal phase-shifting magneto-optical waveguide in the embodiment is shown in 1550 nm TM mode. , Model field distribution diagram;

[0034] Figure 6 This is a flowchart illustrating the fabrication process of direct deposition of non-reciprocal phase-shifting magneto-optical waveguides in the embodiments;

[0035] Figure 7 This is a flowchart illustrating the fabrication process of direct bonding of non-reciprocal phase-shifting magneto-optical waveguides in the embodiments.

[0036] Figure 8 For the example, the magnetic field / inertial sensor is biased at (a) (a) Transmission spectral lines at time; (b) biased at The transmission spectral lines at that time. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0038] An integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide. Figure 1 This is a schematic diagram of an integrated Sagnac-type sensor system, including: a light source, a photodetector, a 3dB coupler, a magneto-optical non-reciprocal phase shifter, and a sensing area corresponding to a specific sensor. Light enters from the input port, is split into two beams by the 3dB coupler, passes through the sensing unit and the magneto-optical non-reciprocal phase shifter respectively, then returns to the 3dB coupler and exits from the output port. A photodetector is added at this port to detect changes in light intensity, thereby enabling the detection of the magnetic field and rotational angular velocity.

[0039] Figure 2 and Figure 3 These are two typical integrated Sagnac-type sensors based on magneto-optical non-reciprocal phase-shifting waveguides (magnetic field sensor and inertial sensor), respectively. Figure 2 and 3 The non-reciprocal phase shifter in the image is generated by a magnetic field provided by a permanent magnet above the magneto-optical material, which magnetizes the magneto-optical material (RIG) to produce a non-reciprocal phase shift effect. Non-reciprocal phase shift. For Figure 2 The magnetic field sensor in the image uses a straight waveguide with a deposited magneto-optical material (RIG) as the sensing unit; for Figure 3 The inertial sensor in the system consists of multiple segments of ring waveguide.

[0040] The cross-sectional structure of a magneto-optical non-reciprocal phase shifter is as follows: Figure 4 As shown, the optical field is mainly confined within the Si waveguide and propagates along the Z direction. A horizontal (X-direction) magnetic field is provided by a permanent magnet material, causing the magneto-optical material Ce:RIG / RIG to reach saturation magnetization, thereby obtaining the corresponding Faraday rotation angle. .like Figure 5 The diagram shows the mode field of the magneto-optical material cross-section. The device operates in TM mode at a wavelength of 1550 nm. The magneto-optical material is Ce:YIG / YIG, and the Faraday vortex angle is set at saturation magnetization. deg / cm, =4632.46 rad / m, further calculation of the length L of the non-reciprocal phase shift segment = ≈340 μm.

[0041] like Figure 6 The diagram shown is a process flow chart for fabricating magneto-optical non-reciprocal phase-shifting waveguides using direct deposition of magneto-optical materials.

[0042] Step 1: Photolithography and etching of a silicon oxide substrate containing a silicon nitride layer or a silicon layer to obtain an integrated optical waveguide, a planar waveguide structure, and a phase compensation structure.

[0043] Step 2: A cladding material (silicon oxide) is grown using methods such as chemical vapor deposition to cover the entire device. This cladding material also serves as a barrier layer for the deposited magneto-optical material.

[0044] Step 3: A window for depositing magneto-optical material is obtained on the upper surface of the designed magneto-optical waveguide through secondary photolithography etching. The window width is larger than the width of the optical waveguide. Under an external strong magnetic field perpendicular to the magneto-optical waveguide, the magneto-optical material can induce a non-reciprocal phase shift in the TM polarization mode within the waveguide.

[0045] Step 4: Deposit cerium-doped yttrium iron garnet at the window using physical vapor deposition.

[0046] Step 5: Photolithographically pattern the required gold wire pattern on the magneto-optical thin film, then deposit the gold thin film by thermal evaporation, and clean the remaining areas of the gold thin film by immersion in acetone solution. Then, continue to photolithographically pattern the periodic strip-shaped permanent magnet material thin film on the device, and finally deposit the permanent magnet material thin film by magnetron sputtering and wash away excess photoresist by the same stripping process.

[0047] like Figure 7 The diagram shown is a process flow chart for fabricating non-reciprocal phase-shifting waveguides using bonding technology:

[0048] Step 1: Prepare the wafers or chips to be bonded, such as silicon waveguide wafers and rare-earth iron garnet (RIG) chips. For silicon chips, similar to direct deposition, etching is used on the semiconductor (silicon, silicon nitride, silicon oxide) substrate to obtain the integrated optical waveguide structure. For RIG chips, high-quality cerium-doped yttrium iron garnet needs to be epitaxially grown on a single-crystal RIG substrate using physical vapor deposition. Both chip surfaces undergo pre-cleaning treatment.

[0049] Step 2: Activate the prepared chip surface by plasma irradiation to reduce surface roughness.

[0050] Step 3: In a vacuum environment, precisely align and bring the two surface-activated chips into close contact, apply constant pressure, and simultaneously perform heat annealing to enhance the bonding force at the bonding interface and form a strong bond connection.

[0051] like Figure 8(a) and (b) show the transmission spectrum (output light intensity versus magnetic field / rotational angular velocity) detected by the photodetector at the output port of the magnetic field / inertial sensor. Since the light intensity change caused by the detection signal is very small, the difference is greater when biased compared to the unbiased case (slope approaching 0). The absolute value of the response slope at time t is the maximum absolute value of the linear slope that can be obtained under any passive or active bias.

[0052] As can be seen from the above embodiments, the integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide provided by this invention achieves direction-dependent phase bias by integrating a magneto-optical thin film on the surface of a conventional optical waveguide and utilizing the non-reciprocal phase-shifting effect of the magneto-optical material under the action of a permanent magnet. This device can fix the interferometer's operating point at the point of maximum sensitivity without active phase driving, thereby simplifying the system structure, reducing power consumption, and eliminating the influence of driving noise on the measurement. Furthermore, the solution of this invention is compatible with standard silicon photonics processes, facilitating integrated packaging, and can improve the steady-state performance and signal-to-noise ratio of Sagnac-type / interferometric sensors. It provides a simple, feasible, and highly engineering-potential technical path for applications such as high-sensitivity magnetic field and rotation measurement.

Claims

1. An integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide, wherein the Sagnac interference structure consists of a coupler, a non-reciprocal phase shifter, and a closed-loop optical waveguide. Incident light is split into two beams at the coupler, propagating clockwise and counterclockwise in the loop respectively. After passing through one loop of the optical waveguide, interference occurs at the coupler. Its characteristics are: The non-reciprocal phase shifter is a passively biased magneto-optical non-reciprocal phase shifter. It is formed by integrating rare earth iron garnet (RIG) thin films on an optical waveguide to create a non-reciprocal phase-shifting magneto-optical waveguide. When the sensing waveguide does not undergo non-reciprocal phase shift due to rotation or magnetic field, the output light intensity of the transmitted waveguide is half of the incident light intensity. When the sensing waveguide undergoes non-reciprocal phase shift due to rotation or external magnetic field, the output intensity of the transmitted waveguide will undergo a measurable change, thereby realizing angular velocity or magnetic field sensing.

2. The integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide as described in claim 1, characterized in that: The rare earth element R in the rare earth iron garnet RIG film is Ce, Bi, Y, Tb or Dy.

3. The integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide as described in claim 1, characterized in that: The design of the magneto-optical waveguide length generates a non-reciprocal phase shift with a phase difference of 90°.

4. The integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide as described in claim 3, characterized in that, The design of the magneto-optical waveguide length is as follows: The 90° non-reciprocal phase shift of the magneto-optical waveguide is achieved by the non-reciprocal phase shift effect of the magneto-optical material. The magneto-optical effect of the magneto-optical material is described by the off-diagonal elements of the material's dielectric tensor. Let the direction of light propagation be the z-direction, and the direction of the in-plane magnetic field perpendicular to the light propagation direction applied to the undamaged magneto-optical material be the x-direction. Then its dielectric tensor is expressed as: ε = Where j is the imaginary unit. = For the dielectric tensor off-diagonal elements, Let n be the vacuum wavenumber and n be the refractive index of the magneto-optical material. It is the Faraday rotation angle; Consider using perturbation theory to calculate the non-reciprocal phase shift in a two-dimensional waveguide model. Assume the light is in TM mode and propagates along the z-direction. According to perturbation theory, the non-reciprocal phase shift is expressed as: ( )= Where N is the normalization constant of the waveguide mode; Therefore, the magnitude and sign of the non-reciprocal phase shift (NRPS) depend on the magnitude and sign of the Faraday rotation angle and the cross-sectional geometry of the waveguide; The effective refractive index of the magneto-optical waveguide was obtained by setting off-diagonal elements of the dielectric tensor of the magneto-optical material using finite element simulation software. The propagation constant β is used to calculate the non-reciprocal phase shift per unit length. The interval length L for non-reciprocal phase shifts = .

5. The integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide as described in claim 1, characterized in that: The coupler is a 3 dB directional coupler or a multimode interferometer.

6. The integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide as described in claim 1, characterized in that: Sagnac's normalized output strength is: ,in These are minute phase changes caused by variations in the magnetic field or rotational angular velocity. In magnetic field sensors, = ,in The length of the magnetic field sensing segment. It is related to the magnitude and direction of the magnetic field; In inertial sensors, for rotational angular velocity sensors, = ,in Let A be the number of turns of the waveguide and A be the area of ​​the ring. The wavelength of light The speed of light in a vacuum. It is the rotational angular velocity; At the bias point For small signals : And thus obtain I Therefore, the response slope at a bias of 90° is .

7. The integrated Sagnac-type sensor based on a magneto-optical non-reciprocal phase-shifting waveguide as described in claim 1, characterized in that: The magneto-optical waveguide is integrated using either chemical vapor deposition or wafer bonding.

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