Reflection-based folded Mach-Zehnder electric field sensor and measurement system

Abstract

The invention provides a reflection-based folding Mach-Zehnder electric field sensor and a measurement system, and the electric field sensor comprises an end face coupling structure and a thin-film lithium niobate platform. A thin film lithium niobate silicon substrate, a thin film lithium niobate silicon dioxide substrate, a thin film lithium niobate flat plate layer, a ridge waveguide layer and a silicon dioxide coating layer are sequentially arranged in the thin film lithium niobate platform from bottom to top; wherein the ridge-shaped waveguide layer comprises a multi-mode interferometer, an F-like electrode module, a U-shaped waveguide structure and a Bragg grating; the end face coupling structure is connected with a multi-mode interferometer located at the front end of the ridge-shaped waveguide layer; the multimode interferometer is connected to the front end of the F-like electrode module; the U-shaped waveguide structure is arranged at the tail end of the ridge-shaped waveguide layer and is connected with the F-like electrode module; after the U-shaped waveguide structure is folded, the tail end of the F-like electrode module is connected with the Bragg grating.

Description

Technical Field

[0001] The present invention relates to the field of sensors, and more specifically, to a reflection-based folded Mach-Zehnder electric field sensor and a measurement system. Background Art

[0002] At present, most of the lithium niobate electric field sensors based on the electro-optical effect integrate modulation electrodes on block lithium niobate to measure the spatial electric field. The low refractive index contrast of block lithium niobate makes the electric field sensor less integrated, and the size of the entire device is in the order of centimeters. In the prior art, patent documents CN108896838A, CN109975618A, and CN112858795A all use the proton exchange method to make integrated block lithium niobate, and the push-pull structure is realized by designing the shape of the modulation electrode, that is, the two arms of the Mach-Zehnder interferometer sense the electric field of the same size and opposite direction to achieve high sensitivity; and although patent document CN116520038A discloses the use of thin Thin-film lithium niobate and LF structure electrodes are used to realize push-pull modulation of Mach-Zehnder electrode arms, but they can only perform one modulation and have low modulation efficiency; the disadvantages of the above technologies are: 1) the proton exchange method leads to a large device size, a large waveguide width, and a low refractive index contrast of lithium niobate; 2) the asymmetric structural design of the waveguide introduced to the sensor working point increases the loss and increases the size; 3) the reflective film requires a large device size, and the reflective grating size of the optical microstructure is smaller and has a higher degree of freedom; 4) the block lithium niobate leads to a large electrode spacing, and the gain of the spatial electric field is smaller than that of thin-film lithium niobate; 5) the existing thin-film lithium niobate sensors can only perform one modulation and have low modulation efficiency.

[0003] Therefore, in order to solve the above problems, this technical solution proposes an on-chip integrated electric field sensor based on thin-film lithium niobate, so that the electric field sensor based on microring or Mach-Zehnder interferometer can reach the millimeter or submillimeter level, and use U-shaped structure waveguide to make the thin-film lithium niobate platform have a higher degree of integration, improve the modulation efficiency, and provide a smaller electrode spacing and a higher gain for the spatial electric field. Summary of the invention

[0004] The present invention aims to overcome at least one defect (shortcoming) of the above-mentioned prior art and provide a reflection-based folded Mach-Zehnder electric field sensor and measurement system to solve the problems of large size, low integration, small electric field gain, low sensitivity, low modulation efficiency, etc. of traditional electric field sensors, and realizes the integrated miniaturization of the electric field sensor structure based on a thin film lithium niobate platform, and can multiply the phase accumulation and multiply the modulation zone length without changing the size of the device.

[0005] The technical solution adopted by the present invention is a folded Mach-Zehnder electric field sensor based on reflection, wherein the electric field sensor comprises an end face coupling structure and a thin film lithium niobate platform, wherein a thin film lithium niobate substrate, a thin film lithium niobate silicon dioxide substrate, a thin film lithium niobate flat layer, a ridge waveguide layer and a silicon dioxide cladding layer are sequentially arranged from bottom to top in the thin film lithium niobate platform; wherein the ridge waveguide layer comprises a multimode interferometer, an F-type electrode module, a U-shaped waveguide structure and a Bragg grating;

[0006] The end face coupling structure is connected to the multimode interferometer at the front end of the ridge waveguide layer; the multimode interferometer is connected to the front end of the F-type electrode module; the U-shaped waveguide structure is arranged at the end of the ridge waveguide layer and connected to the F-type electrode module; after the U-shaped waveguide structure is folded, the end of the F-type electrode module is connected to the Bragg grating.

[0007] In the present invention, after the light beam is coupled by the end face coupling structure, the multimode interferometer evenly splits the single-mode light into two beams and enters the modulation area. First, the light beams on two paths are positively and negatively modulated by the F-type electrode module, and then the light beams are positively and negatively modulated again after passing through the U-shaped waveguide structure. Finally, the light beam at the end of the waveguide is modulated again after being reflected by the Bragg grating. Therefore, in the present invention, the overall modulation efficiency is improved by 8 times by setting the U-shaped waveguide structure and the F-type push-pull electrode design, that is, a gain of 9dB is introduced. Compared with the traditional block lithium niobate crystal electric field sensor, the reflection-based folded Mach-Zehnder electric field sensor provided by the present invention has a smaller electrode spacing, higher integration, better gain effect, and higher modulation efficiency. It has the characteristics of large measurement bandwidth, high spatial resolution, low invasiveness, etc., and can be applied to a variety of sensing application scenarios.

[0008] Preferably, in the U-shaped waveguide structure, the lengths of the two arms are set to be different to introduce an arm length difference, and the interference phase difference is generated by the arm length difference. The arm length difference is 187 μm, which is used to provide the required working wavelength point for the electric field sensor.

[0009] In the U-shaped waveguide structure, the radii of the inner and outer semicircles are different, so that the lengths of the two arms are different to introduce an arm length difference, and the arm length difference is set to 187μm, so that when the device meets the small length size, this length can be sufficient to provide the working point required by the C-band electric field sensor. At the same time, folding can be provided so that the waveguide can be modulated again, thereby improving the sensitivity and modulation efficiency of the electric field sensor.

[0010] Preferably, the F-type electrode module is composed of a plurality of F-type modulation electrode arrays, and is combined with a U-shaped waveguide structure to form 4 straight waveguide modulation paths, so as to multiply the modulation length of light.

[0011] By setting up a U-shaped waveguide structure, not only is the required arm length difference provided for the traditional electric field sensor to provide a linear working point, but the modulation length can also be doubled by folding while ensuring that the device length remains unchanged, thereby improving the modulation efficiency.

[0012] Preferably, the F-type modulation electrode further includes an electrode long arm, and the electric field E to be measured is characterized by modulating the accumulation of induced charges on the electrode long arm. z , and obtain the electric field E of the space to be measured z Relationship with induced voltage V: V = h eff E z , where h eff is the effective length of the electrode or antenna;

[0013] Combined with the above formula, under the action of the electrode long arm, the phase change obtained is for:

[0014]

[0015] Where λ is the wavelength of the input light, Γ is the overlap factor between the measured spatial electric field and the optical mode field, and n e is the effective refractive index of TE0 single-mode light, d is the electrode spacing, L cl is the modulation length in the electric field sensor, γ 33 is the maximum electro-optical effect coefficient.

[0016] The long electrode arms accumulate induced charges under the action of the spatial electric field and collect spatial electric field information. The charges accumulate at both ends of the waveguide to form a potential difference, thereby obtaining a corresponding phase change under the action of the long electrode arms. This lays the foundation for the subsequent simplification of the calculation of the output optical power, making the output optical power easier to calculate and improving the calculation efficiency.

[0017] Preferably, the multimode interferometer divides the input single-mode light into two beams and maintains its original mode and polarization state to enter the straight waveguide modulation path and the U-shaped waveguide structure for push-pull structure modulation, and then reflects through the Bragg grating and performs push-pull structure modulation again. Finally, the multimode interferometer combines the two reflected light beams to interfere and output optical power.

[0018] By using a multimode interferometer to shape the light beam, converting the input light beam into an output light beam of different shapes and modes while keeping its original mode, the modulation efficiency can be greatly improved. It can also effectively couple the optical signals between different optical waveguides or optical fibers, improve the coupling efficiency of the optical system, reduce losses, and extract the electric field information from the output electrical signal of the optical receiver, converting phase modulation into intensity modulation.

[0019] Preferably, the multimode interferometer combines the two reflected light beams to interfere and output optical power, further comprising: introducing a half-wave voltage E π Combined with the phase change To simplify the optical power calculation formula, and set the interference phase difference The electric field sensor is placed at the working wavelength point, and the optical power calculation formula is linearly expressed using the Taylor expansion formula to obtain the final output optical power. The optical power calculation formula P out for:

[0020]

[0021] Among them, P out is the output optical power, P in is the input optical power, α is the total loss, G is the photoelectric modulation gain, k is the extinction coefficient, E π is the half-wave voltage, E z is the electric field to be measured in space;

[0022] Therefore, in the present invention, by introducing the half-wave voltage E π Combined with the phase change And by setting the value of the interference phase difference so that the electric field sensor is at the working wavelength point, the optical power calculation formula is simplified, thereby ensuring that the system can ensure the high accuracy of the output optical power while improving its output efficiency.

[0023] Preferably, the end face coupling structure comprises a spot converter for efficiently coupling the light input to the electric field sensor and inputting it into the ridge waveguide layer for modulation.

[0024] The mode spot converter is set in the end coupling structure so that it can play a key role in the optical fiber and optical waveguide system. It can improve the transmission efficiency and quality of the optical signal by optimizing the mode matching of the optical signal, improving the optical fiber coupling efficiency, and reducing the light loss caused by the mode mismatch, thereby ensuring the efficient and stable operation of the system.

[0025] Preferably, the thickness of the silicon dioxide coating layer is 800 nm. By setting the thickness of the silicon dioxide coating layer to 800 nm on the thin-film lithium niobate platform, this thickness can well balance the loss and modulation efficiency, thereby effectively protecting the device from damage and reducing the waveguide propagation loss with gold electrodes.

[0026] Preferably, the ridge angle of the hard mask of the ridge waveguide layer is in the range of 70° to 80°. By setting the ridge angle of the hard mask, the mode fields of the optical fiber and the waveguide can be effectively matched, the coupling efficiency of the optical signal can be improved, and thus the optical loss and mode mismatch can be reduced. The appropriate ridge angle can also reduce the scattering and reflection of light at the end face of the waveguide, reduce optical loss and improve the overall performance of the system, so that the waveguide can better maintain the stability of the optical mode, reduce the interference of mode conversion, and improve the stability of optical signal transmission.

[0027] In a second aspect, the present invention further provides a measurement system, the system comprising: a tunable sensor, a single-mode optical fiber, a polarization controller, a ring isolator, the above-mentioned reflection-based folded Mach-Zehnder electric field sensor, an erbium-doped fiber amplifier, an optical beam splitter, a spectrum analyzer, an electro-optical detector, and an electronic spectrum analyzer;

[0028] The tunable sensor determines the working point wavelength of the electric field sensor through the spectrum, and after adjusting it to the working point wavelength, transmits the light beam using a single-mode optical fiber, and transmits it to the polarization controller for processing to ensure that the input single-mode light is TE polarization. The TE polarization can utilize the maximum electro-optical effect coefficient γ of x-cut lithium niobate. 33 Effective light modulation is performed, and the light beam is input into the reflection-based folded Mach-Zehnder electric field sensor described in any one of claims 1-9 through an annular isolator for modulation. Finally, the annular isolator transmits the received modulated and reflected light beam to an erbium-doped fiber amplifier for optical power gain processing. After gain processing, the light beam is split by an optical beam splitter. One part enters a spectrum analyzer to observe the spectral response, and the other part is converted into an electrical signal by an electro-optical detector and connected to an electronic spectrum analyzer for linear characterization of the spatial electric field.

[0029] By introducing the above-mentioned reflection-based folded Mach-Zehnder electric field sensor into the measurement system, the measurement efficiency of the measurement system is higher, the anti-interference ability is stronger, the integration and measurement sensitivity are also higher, the measurement results are more accurate, and broadband and high-sensitivity electric field measurements can be achieved in small-size devices, which can be applied to various different sensing application scenarios.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The structure of the electric field sensor is different from that of the traditional bulk lithium niobate crystal. The present invention is based on a thin-film lithium niobate platform, with low waveguide transmission loss, high integration, and small size, so that the spacing between the array modulation electrodes can be smaller, the spatial electric field gain is increased, and the anti-interference ability is strong, which can be applied to a variety of sensing application scenarios;

[0032] (2) The U-shaped bending part of the waveguide in the electric field sensor not only provides the arm length difference required by the traditional electric field sensor to provide a linear working point, but also folds to double the modulation length without changing the device length, greatly improving the modulation efficiency;

[0033] (3) The Bragg grating is used at the end of the waveguide part of the electric field sensor to reflect the light beam, so that the light beam can be re-modulated while ensuring low loss. Compared with the traditional reflective film, the optical microstructure has a higher degree of freedom and a higher degree of integration, further improving the modulation efficiency;

[0034] (4) In the electric field sensor, first, the reflection of the Bragg grating doubles the modulation length of the phase change. The U-shaped waveguide structure provides a working point and doubles the modulation length without increasing the length of the device. The full-path modulation area has a push-pull structure of positive and negative electric fields. This technical solution enables the three to work simultaneously, thereby achieving a three-fold increase in modulation efficiency, thereby increasing the modulation efficiency by 8 times. After superposition, it can have a gain of 9dB compared to the traditional dipole electric field sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a perspective view of the overall structure of an embodiment of the present invention.

[0036] Figure 2 It is an overall top perspective view of an embodiment of the present invention.

[0037] Figure 3 It is a schematic diagram of the identification of a partial cross section of the sensor structure according to an embodiment of the present invention.

[0038] Figure 4 FIG. 4 is a top view of a multi-mode interferometer according to an embodiment of the present invention.

[0039] Figure 5 1 is a top view and a partially enlarged view of a Bragg grating according to an embodiment of the present invention.

[0040] Figure 6 4 is a cross-sectional view of a modulation region according to an embodiment of the present invention.

[0041] Figure 7 FIG. 4 is a top perspective view of a single F-type modulation electrode according to an embodiment of the present invention.

[0042] Figure 8 The reflection spectrum of the Bragg grating of the embodiment of the present invention is

[0043] Fig. 9 2 is a diagram of an electric field sensing test system according to an embodiment of the present invention.

[0044] Description of the drawings: 1: thin film lithium niobate silicon substrate; 2: thin film lithium niobate silicon dioxide substrate; 3: thin film lithium niobate planar layer; 4: ridge waveguide layer; 5: silicon dioxide cladding layer; 6: F-type electrode module; 7: multimode interferometer; 8: Bragg grating; 9: U-shaped waveguide structure; 10: corresponding area of ​​the cross section of the modulation area; 11: tunable laser; 12: single-mode optical fiber; 13: polarization controller; 14: ring isolator; 15: reflection-based folded Mach-Zehnder electric field sensor; 16: erbium-doped fiber amplifier; 17: optical beam splitter; 18: optical spectrum analyzer; 19: photodetector; 20: electronic spectrum analyzer. DETAILED DESCRIPTION

[0045] The drawings of the present invention are only for illustrative purposes and should not be construed as limiting the present invention. In order to better illustrate the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0046] Example 1

[0047] Figure 1 is a perspective view of the overall structure of this embodiment, Figure 2 FIG. 1 is a top perspective view of the overall structure of this embodiment. Figure 1 and Figure 2 As shown, the technical solution adopted in this embodiment is a folded Mach-Zehnder electric field sensor based on reflection, and the electric field sensor includes an end face coupling structure and a thin film lithium niobate platform, in which a thin film lithium niobate silicon substrate 1, a thin film lithium niobate silicon dioxide substrate 2, a thin film lithium niobate flat layer 3, a ridge waveguide layer 4 and a silicon dioxide cladding layer 5 are sequentially arranged from bottom to top; wherein the ridge waveguide layer 4 includes a multimode interferometer 7, an F-type electrode module 6, a Bragg grating 8 and a U-shaped waveguide structure 9;

[0048] The end face coupling structure is connected to the multimode interferometer 7 at the front end of the ridge waveguide layer 4; the multimode interferometer 7 is connected to the front end of the F-type electrode module 6; the U-shaped waveguide structure 9 is arranged at the end of the ridge waveguide layer 4 and connected to the F-type electrode module 6; after the U-shaped waveguide structure 9 is folded, the end of the F-type electrode module 6 is connected to the Bragg grating 8.

[0049] from Figure 1 and Figure 2It can be seen that in the electric field sensor described in this embodiment, after the light beam is coupled by the end face coupling structure, the multimode interferometer 7 evenly splits the single-mode light into two beams and enters the modulation area. First, the light beams on two of the paths are subjected to the first positive and negative modulation through the F-type electrode module 6. Then, the light beams pass through the U-shaped waveguide structure 9 and enter the other two paths of the F-type electrode module 6 for the second positive and negative modulation. Then, the light beam at the end of the waveguide is reflected by the Bragg grating 8 and subjected to the third positive and negative modulation. Then, the light beam passes through the U-shaped waveguide structure 9 again and subjected to the fourth positive and negative modulation. By setting a U-shaped waveguide junction 9, the modulation length is doubled without increasing the device length, so that there is a push-through structure of positive and negative electric fields in the entire path modulation area, and finally the overall modulation efficiency is increased by 8 times, that is, a gain of 9dB is introduced. Compared with the traditional bulk lithium niobate crystal electric field sensor, the reflection-based folded Mach-Zehnder electric field sensor provided by the present invention has a smaller electrode spacing, higher integration, better gain effect, and higher modulation efficiency. It has the characteristics of large measurement bandwidth, high spatial resolution, low invasiveness, etc., and can be applied to a variety of sensing application scenarios.

[0050] Preferably, in this embodiment, specific parameters of each microstructure of the entire electric field sensor device are also provided, and the parameters are shown in Table 1. The parameters given in Table 1 are only for exemplary description and are not limited to the parameters in the setting table. The specific values ​​can be set by those skilled in the art according to actual needs.

[0051]

[0052]

[0053] Table 1

[0054] Preferably, if Figure 1-Figure 3 As shown, in the U-shaped waveguide structure 9, the inner and outer semicircular difference of the U-shaped waveguide structure is 29.5 μm. Figure 7 As shown, the inner and outer semicircular difference c is obtained by adding the electrode width a and the electrode spacing b, so that the arm length difference is 187 μm by converting the inner and outer semicircular difference. The interference phase difference is generated by the arm length difference Used to provide the required working wavelength points for the electric field sensor.

[0055] In the U-shaped waveguide structure 9, since the radii of the inner and outer semicircles are different, the lengths of the two arms in the U-shaped waveguide structure are different to introduce an arm length difference. In the present embodiment, the arm length difference is set to 187 μm, so that when the device meets the small length dimension, this length can be sufficient to provide the required working point of the C-band electric field sensor. At the same time, folding can be provided so that the waveguide can be modulated again, thereby improving the sensitivity and modulation efficiency of the electric field sensor.

[0056] Preferably, from Figure 2 It can be clearly seen that the F-type electrode module 6 is composed of a plurality of F-type modulation electrode arrays, and as shown in FIG. Figure 6 As shown, Figure 6 The schematic diagram of the cross section of the modulation area provided in this embodiment, combined with the U-shaped waveguide structure 9, 6 segments of F-shaped modulation electrodes in the cross section of the modulation area form 4 straight waveguide modulation paths for electro-optical modulation, which increases the modulation length of light exponentially, and the waveguide electric field modulation direction on the inner diameter and outer diameter is as follows: Figure 7 The dotted arrows in the middle indicate the opposite direction, aiming to achieve high sensitivity while achieving high integration. In addition, as shown in Table 1, specific parameter settings are also provided in this embodiment, and the modulation area F-type modulation electrode spacing W3 is set to 4μm, the waveguide width W4 is set to 0.8μm, the F-type modulation electrode thickness H1 is set to 1μm, the silicon dioxide coating layer thickness H2 is set to 0.8μm, the thin film lithium niobate plate layer thickness H3 is set to 0.3μm, the thin film lithium niobate silicon dioxide substrate thickness H4 is set to 4.7μm, and the waveguide thickness H5 is set to 0.3μm.

[0057] Therefore, in this embodiment, by setting the U-shaped waveguide structure 9, not only the required arm length difference is provided for the traditional electric field sensor to provide a linear working point, but also the modulation length is doubled by folding while ensuring that the device length remains unchanged, thereby improving the modulation efficiency.

[0058] Preferably, if Figure 7 As shown, Figure 7 : is a top perspective view of a single F-type modulation electrode of this embodiment. The F-type modulation electrode also includes an electrode long arm. As shown in Table 1, in this embodiment, the length L3 of the F-type modulation electrode long arm is 3500 μm. The electric field E to be measured is characterized by modulating the accumulation of induced charges on the electrode long arm. z ,like Figure 7 As shown, the F-type design enables the modulation electrode to generate electric fields of the same magnitude and completely opposite directions on two modulation paths to act on the waveguide to be modulated. This embodiment uses an array modulation electrode structure to increase the modulation action length, thereby improving the sensitivity of the electric field sensor. In this embodiment, the modulation length L4 of the F-type modulation electrode is set to 400 μm to obtain the spatial electric field E to be measured. z The relationship between the induced voltage V and

[0059] The relationship is: V = h eff E z (1)

[0060] Among them, h eff is the effective length of the electrode or antenna;

[0061] Secondly, combined with the above formula (1), under the action of the long electrode arm, the phase change obtained is for:

[0062]

[0063] Where λ is the wavelength of the input light, Γ is the overlap factor between the measured spatial electric field and the optical mode field, and n e is the effective refractive index of TE0 single-mode light, d is the electrode spacing, L cl is the modulation length in the electric field sensor, γ 33 is the maximum electro-optical effect coefficient.

[0064] The long electrode arms accumulate induced charges under the action of the spatial electric field and collect spatial electric field information. The charges accumulate at both ends of the waveguide to form a potential difference, thereby obtaining a corresponding phase change under the action of the long electrode arms. This lays the foundation for the subsequent simplification of the calculation of the output optical power, making the output optical power easier to calculate and improving the calculation efficiency.

[0065] Preferably, if Figure 4 As shown, Figure 4 FIG. 1 is a top view of a multimode interferometer provided in this embodiment. The multimode interferometer 7 divides the input single-mode light into two beams and maintains its original mode and polarization state to enter the straight waveguide modulation path and the U-shaped waveguide structure 9 for push-pull structure modulation, and then reflects through the Bragg grating 8 and performs push-pull structure modulation again, as shown in FIG. Figure 5 As shown, Figure 5 The top view and partial magnified view of the Bragg grating provided in this embodiment. The Bragg grating 8, as an integrated optical microstructure, reflects the light beam of the target band. Compared with the traditional reflective film, it has higher integration and freedom. The target band can also be adjusted by changing the grating period length. Specifically, the central wavelength formula of the Bragg grating 8 is: 2n eff Λ=λ c , where n eff is the center average effective refractive index, Λ is the period length, λ c is the center wavelength. From the above formula, it can be easily seen that the center wavelength can be easily changed by adjusting the period length. The technical solution described in this embodiment is aimed at the 1550nm working band.

[0066] In addition, in this embodiment, the number of periods of the Bragg grating 8 is 50, the Bragg grating period length W5 is 0.422 μm, the Bragg grating waveguide length W6 is 0.148 μm, and Figure 8 In this embodiment, the parameters of etching 300nm with 600nm lithium niobate are used, so that the Bragg grating 8 reflects the light with a bandwidth of 45nm near 1550nm, and Figure 8 It can be seen that more than 80% of the light beams can be isolated and reflected back to the waveguide structure in a 45nm bandwidth, thereby achieving high modulation sensitivity. Finally, the two reflected light beams are combined by the multimode interferometer 7 to interfere and output optical power.

[0067] In this embodiment, the length L1 of the center area of ​​the multimode interferometer 7 is set to 62μm, the transition cone length L2 of the multimode interferometer 7 is set to 20μm, the width W2 of the center area of ​​the multimode interferometer 7 is set to 10μm, and the F-type modulation electrode spacing W3 in the modulation area is set to 4μm. According to the setting of the above parameters, the multimode interferometer is used to shape the light beam and convert the input light beam into an output light beam of different shapes and modes, which can effectively couple the optical signals between different optical waveguides or optical fibers, improve the coupling efficiency of the optical system, reduce the loss, and extract the electric field information from the output electrical signal of the optical receiver, and convert the phase modulation into intensity modulation.

[0068] Preferably, the multimode interferometer 7 further includes: introducing a half-wave voltage E π Combined with the phase change To simplify the optical power calculation formula, and set the interference phase difference The electric field sensor is placed at the working wavelength point, and the optical power calculation formula is linearly expressed using the Taylor expansion formula to obtain the final output optical power.

[0069] First, before the half-wave voltage is introduced, the multi-mode interferometer 7 combines the two reflected light beams to interfere with each other and outputs an optical power of:

[0070]

[0071] Among them, P out is the output optical power, P in is the input optical power, α is the total loss, G is the photoelectric modulation gain, k is the extinction coefficient, is the phase change, is the interference phase difference;

[0072] In order to simplify the above optical power formula and improve the modulation efficiency, the half-wave voltage E is introduced. π , the half-wave voltage formula is:

[0073]

[0074] Where λ is the wavelength of the input light, Γ is the overlap factor between the measured spatial electric field and the optical mode field, and n e is the effective refractive index of TE0 single-mode light, d is the electrode spacing, L clis the modulation length in the electric field sensor, h eff is the effective length of the electrode or antenna, γ 33 is the maximum electro-optical effect coefficient.

[0075] Combining formula (2), (3), and (4) we get the final optical power formula:

[0076]

[0077] When the U-shaped waveguide structure introduces the interference phase difference caused by the arm length difference When the electric field sensor is at the working wavelength point, the formula (5) is expanded to the first-order term using Taylor. At this time, the output optical power P out Linear expression, thus obtaining the optical power calculation formula P out for:

[0078]

[0079] Among them, P out is the output optical power, P in is the input optical power, α is the total loss, G is the photoelectric modulation gain, k is the extinction coefficient, E π is the half-wave voltage, E z is the electric field to be measured in space;

[0080] Therefore, in the present invention, by introducing the half-wave voltage E π Combined with the phase change And by setting the value of the interference phase difference so that the electric field sensor is at the working wavelength point, the optical power calculation formula is simplified. By introducing the electro-optical modulation gain, the electrode push-pull structure provides positive and negative modulation intensities, the U-shaped waveguide structure increases the modulation electrode length by two times, and the Bragg reflection grating increases the modulation electrode length by two times, a total gain of 9 dB is introduced. The modulation gain G introduced by this structure is increased by 8 times compared with the traditional interference structure, thereby ensuring that the present invention can improve its output efficiency while ensuring the high accuracy of the output optical power.

[0081] Preferably, the end face coupling structure includes a pattern spot converter, which utilizes the pattern spot converter to efficiently couple the light beam input to the electric field sensor and input it into the ridge waveguide layer for modulation.

[0082] The mode spot converter is set in the end coupling structure so that it can play a key role in the optical fiber and optical waveguide system. It can improve the transmission efficiency and quality of the optical signal by optimizing the mode matching of the optical signal, improving the optical fiber coupling efficiency, and reducing the light loss caused by the mode mismatch, thereby ensuring the efficient and stable operation of the system.

[0083] Preferably, in the embodiment, the thickness of the silicon dioxide coating layer 5 is set to 800 nm. This thickness can well balance the loss and modulation efficiency, thereby effectively protecting the device from damage and reducing the waveguide propagation loss with gold electrodes.

[0084] Preferably, the ridge angle of the hard mask of the ridge waveguide layer 4 is in the range of 70° to 80°. By setting the ridge angle of the hard mask, the mode fields of the optical fiber and the waveguide can be effectively matched, the coupling efficiency of the optical signal can be improved, and thus the optical loss and mode mismatch can be reduced. A suitable ridge angle can also reduce the scattering and reflection of light at the end face of the waveguide, reduce optical loss and improve the overall performance of the system, so that the waveguide can better maintain the stability of the optical mode, reduce the interference of mode conversion, and improve the stability of optical signal transmission.

[0085] Example 2

[0086] like Fig. 9 As shown, this embodiment provides a measurement system, which includes: a tunable sensor 11, a single-mode optical fiber 12, a polarization controller 13, a ring isolator 14, the above-mentioned reflection-based folded Mach-Zehnder electric field sensor 15, an erbium-doped fiber amplifier 16, an optical beam splitter 17, a spectrum analyzer 18, an electro-optical detector 19 and an electronic spectrum analyzer 20;

[0087] The tunable sensor 11 first obtains a spectrum by scanning the wavelength, and then determines the working point wavelength of the electric field sensor through the spectrum, and after adjusting it to the working point wavelength, transmits the light beam using the single-mode optical fiber 12, and transmits it to the polarization controller 13 for processing to ensure that the input single-mode light is TE polarization. The TE polarization can utilize the maximum electro-optical effect coefficient γ of x-cut lithium niobate. 33 Effectively perform optical modulation, and input the light beam into the reflection-based folded Mach-Zehnder electric field sensor 15 described in Example 1 through the annular isolator 14 for modulation;

[0088] In the electric field sensor, the light beam first enters the end face coupling structure and uses the mode spot converter for efficient coupling, and then enters the modulation area, firstly, the input single-mode light is evenly divided into two beams by the multimode interferometer 7, and then enters two of the paths of the F-type electrode module 6 to perform the first positive and negative modulation on the light beam, and then the light beam passes through the U-shaped waveguide structure 9 and enters the other two paths of the F-type electrode module 6 to perform the second positive and negative modulation, and then the light beam at the end of the waveguide is reflected by the Bragg grating 8 and then performs the third positive and negative modulation, and then passes through the U-shaped waveguide structure again and performs the fourth positive and negative modulation, and finally the two reflected light beams are interfered by the multimode interferometer 7 and output to the annular isolator 14;

[0089] The annular isolator 14 transmits the received light beam reflected after modulation to the erbium-doped fiber amplifier 16 for optical power gain processing, and then performs optical splitting processing through the optical beam splitter 19 after gain processing. In this embodiment, the optical beam splitter 19 is a 1:9 optical beam splitter, which can split the light beam according to a specific ratio. The specific division ratio can be selected according to actual needs, such as a 1:1 optical beam splitter, etc., and then the split light beam is divided into two paths and input into different detection instruments for analysis, thereby increasing the flexibility of the system, enabling the system to perform multi-dimensional optical analysis at the same time, and improving the richness of data and the accuracy of the experiment. In this embodiment, a part of the light beam enters the spectrometer to observe the spectral response, and the other part of the light beam is converted into an electrical signal by an electro-optical detector and then connected to an electronic spectrum analyzer to perform linear characterization processing on the spatial electric field. After the wavelength is controlled at the working wavelength point, the output optical power of the linear characterization processing is:

[0090]

[0091] Among them, P out is the output optical power, P in is the input optical power, α is the total loss, G is the photoelectric modulation gain, k is the extinction coefficient, E π is the half-wave voltage, E z is the electric field to be measured in space.

[0092] Therefore, by introducing the above-mentioned reflection-based folded Mach-Zehnder electric field sensor into the measurement system, the measurement efficiency of the measurement system is higher, the anti-interference ability is stronger, the integration and measurement sensitivity are also higher, the measurement results obtained are more accurate, and it can be applied to various different sensing application scenarios.

[0093] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation methods of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the claims of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A folded Mach-Zehnder electric field sensor based on reflection, characterized in that: The electric field sensor includes an end face coupling structure and a thin film lithium niobate platform, in which a thin film lithium niobate silicon substrate, a thin film lithium niobate silicon dioxide substrate, a thin film lithium niobate flat layer, a ridge waveguide layer and a silicon dioxide cladding layer are arranged in order from bottom to top; wherein the ridge waveguide layer includes a multi-mode interferometer, an F-type electrode module, a U-shaped waveguide structure and a Bragg grating; The end face coupling structure is connected to the multimode interferometer at the front end of the ridge waveguide layer; the multimode interferometer is connected to the front end of the F-type electrode module; the U-shaped waveguide structure is arranged at the end of the ridge waveguide layer and connected to the F-type electrode module; after the U-shaped waveguide structure is folded, the end of the F-type electrode module is connected to the Bragg grating.

2. A reflection-based folded Mach-Zehnder electric field sensor according to claim 1, characterized in that: In the U-shaped waveguide structure, the lengths of the two arms are set to be different to introduce an arm length difference, and the interference phase difference is generated by the arm length difference. The arm length difference is 187 μm, which is used to provide the required working wavelength point for the electric field sensor.

3. A reflection-based folded Mach-Zehnder electric field sensor according to claim 2, characterized in that: The F-type electrode module is composed of a plurality of F-type modulation electrode arrays and is combined with a U-shaped waveguide structure to form 4 straight waveguide modulation paths for multiplying the modulation length of light.

4. A reflection-based folded Mach-Zehnder electric field sensor according to claim 3, characterized in that: The F-type modulation electrode also includes an electrode long arm, and the induced charge accumulation on the electrode long arm is modulated to characterize the electric field E to be measured. z , and obtain the electric field E of the space to be measured z Relationship with induced voltage V: V = h eff E z , where h eff is the effective length of the electrode or antenna; Combined with the above formula, under the action of the electrode long arm, the phase change obtained is for: Where λ is the wavelength of the input light, Γ is the overlap factor between the measured spatial electric field and the optical mode field, and n e is the effective refractive index of TE0 single-mode light, d is the electrode spacing, L cl is the modulation length in the electric field sensor, γ 33 is the maximum electro-optical effect coefficient.

5. The reflection-based folded Mach-Zehnder electric field sensor according to claim 4, characterized in that: The multimode interferometer divides the input single-mode light into two beams and maintains its original mode and polarization state to enter the straight waveguide modulation path and the U-shaped waveguide structure for push-pull structure modulation, and then reflects through the Bragg grating and performs push-pull structure modulation again. Finally, the multimode interferometer combines the two reflected light beams to interfere and output optical power.

6. A reflection-based folded Mach-Zehnder electric field sensor according to claim 5, characterized in that: In the multimode interferometer combining two reflected light beams to interfere and output optical power, the following steps are also included: introducing a half-wave voltage E π Combined with the phase change To simplify the optical power calculation formula, and set the interference phase difference The electric field sensor is placed at the working wavelength point, and the optical power calculation formula is linearly expressed using the Taylor expansion formula to obtain the final output optical power. The optical power calculation formula P out for: Among them, P out is the output optical power, P in is the input optical power, α is the total loss, G is the photoelectric modulation gain, k is the extinction coefficient, E π is the half-wave voltage, E z is the electric field to be measured in space.

7. The reflection-based folded Mach-Zehnder electric field sensor according to claim 1, characterized in that: The end face coupling structure includes a spot converter, which is used to efficiently couple the light input to the electric field sensor and input it into the ridge waveguide layer for modulation.

8. A reflection-based folded Mach-Zehnder electric field sensor according to any one of claims 1 to 7, characterized in that: The thickness of the silicon dioxide coating layer is 800 nm.

9. A reflection-based folded Mach-Zehnder electric field sensor according to any one of claims 1 to 7, characterized in that: The ridge angle of the hard mask of the ridge waveguide layer is in the range of 70° to 80°.

10. A measurement system, characterized in that: The system comprises: a tunable sensor, a single-mode optical fiber, a polarization controller, a ring isolator, a reflection-based folded Mach-Zehnder electric field sensor according to any one of claims 1 to 9, an erbium-doped fiber amplifier, an optical beam splitter, a spectrum analyzer, an electro-optical detector, and an electronic spectrum analyzer; The tunable sensor determines the working point wavelength of the electric field sensor through the spectrum, and after adjusting it to the working point wavelength, transmits the light beam using a single-mode optical fiber, and transmits it to the polarization controller for processing to ensure that the input single-mode light is TE polarization. The TE polarization can utilize the maximum electro-optical effect coefficient γ of x-cut lithium niobate. 33 Effective light modulation is performed, and the light beam is input into the reflection-based folded Mach-Zehnder electric field sensor described in any one of claims 1-9 through an annular isolator for modulation. Finally, the annular isolator transmits the received modulated and reflected light beam to an erbium-doped fiber amplifier for optical power gain processing. After gain processing, the light beam is split by an optical beam splitter. One part enters a spectrum analyzer to observe the spectral response, and the other part is converted into an electrical signal by an electro-optical detector and connected to an electronic spectrum analyzer for linear characterization of the spatial electric field.

Images