A folded Mach-Zehnder electric field sensor and measurement system based on reflection

Abstract

This invention provides a reflection-based folded Mach-Zehnder electric field sensor and measurement system. The electric field sensor includes an end-face coupling structure and a thin-film lithium niobate platform. From bottom to top, the thin-film lithium niobate platform comprises a thin-film lithium niobate silicon substrate, a thin-film lithium niobate silicon dioxide substrate, a thin-film lithium niobate planar layer, a ridge waveguide layer, and a silicon dioxide cladding layer. The ridge waveguide layer includes a multimode 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 located 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 located at the end of the ridge waveguide layer and connected to the F-type electrode module. After folding the U-shaped waveguide structure, the end of the F-type electrode module is connected to the Bragg grating.

Description

Technical Field

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

[0002] Currently, most lithium niobate electric field sensors based on the electro-optic effect measure spatial electric fields by integrating modulation electrodes on bulk lithium niobate. The low refractive index contrast of bulk lithium niobate results in low integration density, with the entire device size on the centimeter scale. In existing technologies, patent documents CN108896838A, CN109975618A, and CN112858795A utilize proton exchange methods to fabricate integrated bulk lithium niobate, achieving a push-pull structure by designing the shape of the modulation electrodes. This is analogous to the two arms of a Mach-Zehnder interferometer sensing electric fields of the same magnitude but opposite directions, achieving high sensitivity. While patent document CN116520038A discloses the use of thin... Lithium niobate films and push-pull modulation of Mach-Zehnder electrode arms using LF structure electrodes have limitations, as they can only perform one modulation operation and have low modulation efficiency. The drawbacks of these technologies include: 1) Proton exchange methods result in excessively large device sizes, large waveguide widths, and low refractive index contrast of lithium niobate; 2) The asymmetric design of the waveguide to introduce the sensor's operating point increases losses and size; 3) Reflective films require large device sizes, while optical microstructures require smaller reflective gratings with higher degrees of freedom; 4) Bulk lithium niobate leads to excessively large electrode spacing, resulting in lower gain on the spatial electric field compared to thin-film lithium niobate; 5) Existing thin-film lithium niobate sensors can only perform one modulation operation, resulting in 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, which enables electric field sensors based on micro-rings or Mach-Zehnder interferometers to be at the millimeter or sub-millimeter level. Furthermore, by utilizing U-shaped waveguide structures, the thin-film lithium niobate platform can achieve higher integration, improve modulation efficiency, provide smaller electrode spacing, and achieve higher gain for spatial electric fields. Summary of the Invention

[0004] The present invention aims to overcome at least one of the defects (deficiencies) of the 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 and low modulation efficiency of traditional electric field sensors. It realizes the integration and miniaturization of the electric field sensor structure based on the thin film lithium niobate platform, and can increase the phase accumulation and the modulation region length by a factor of two without changing the size of the device.

[0005] The technical solution adopted in this invention is a reflection-based folded Mach-Zehnder electric field sensor. The electric field sensor includes an end-face coupling structure and a thin-film lithium niobate platform. From bottom to top, the thin-film lithium niobate platform comprises a thin-film lithium niobate substrate, a thin-film lithium niobate silica substrate, a thin-film lithium niobate planar layer, a ridge waveguide layer, and a silica cladding layer. The ridge waveguide layer includes 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 a multimode interferometer located 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 disposed 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 this invention, after the beam is coupled through the end-face coupling structure, the multimode interferometer splits the single-mode light into two beams that enter the modulation region. First, the beams on the two paths are modulated in both directions by an F-type electrode module. Then, the beams are modulated again in both directions after passing through a U-shaped waveguide structure. Finally, the beams at the end of the waveguide are modulated again after being reflected by a Bragg grating. Thus, by setting the U-shaped waveguide structure and the F-type push-pull electrode design, the overall modulation efficiency is improved by 8 times, i.e., 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 this invention has a smaller electrode spacing, higher integration, better gain, and higher modulation efficiency. It has the characteristics of large measurement bandwidth, high spatial resolution, and low invasiveness, and can be applied to a variety of sensing application scenarios.

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

[0009] In the U-shaped waveguide structure, the radii of the inner and outer semicircles are different, resulting in different arm lengths, which introduces the arm length difference. The arm length difference is set to 187μm, which is sufficient to provide the operating point required by the C-band electric field sensor while meeting the small length requirements of the device. At the same time, it can provide folding so that the waveguide can be modulated again, improving the sensitivity and modulation efficiency of the electric field sensor.

[0010] Preferably, the F-type electrode module consists of several F-type modulation electrode arrays and is combined with a U-shaped waveguide structure to form four straight waveguide modulation paths, which are used 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 traditional electric field sensors to provide a linear operating point, but the modulation length can also be doubled by folding while keeping the device length unchanged, thereby improving the modulation efficiency.

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

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

[0014]

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

[0016] The long electrode arm accumulates induced charges under the influence of the spatial electric field, collecting spatial electric field information. The charge accumulation at both ends of the waveguide forms a potential difference, thereby obtaining a corresponding phase change under the influence of the long electrode arm. This lays the foundation for simplifying the subsequent calculation of the output optical power, making the output optical power easier to calculate and improving computational efficiency.

[0017] Preferably, the multimode interferometer splits the input single-mode light into two beams while maintaining its original mode and polarization state. The beams are then fed into a straight waveguide modulation path and a U-shaped waveguide structure for push-pull modulation. After reflection through a Bragg grating, the beams are again subjected to push-pull modulation. Finally, the multimode interferometer combines the two reflected beams, causes interference, and outputs optical power.

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

[0019] Preferably, in the process of the multimode interferometer combining two reflected beams to interfere and output optical power, the method further includes: introducing a half-wave voltage E. π And combined with phase change To simplify the optical power calculation formula, and at the same time set the interference phase difference By positioning the electric field sensor at its operating wavelength and using the Taylor expansion formula to linearly represent the optical power calculation formula, the final output optical power P is obtained. out for:

[0020]

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

[0022] Therefore, in this invention, a half-wave voltage E is introduced. π And combined with phase change Furthermore, by setting the value of the interference phase difference to place the electric field sensor at the working wavelength point, the formula for calculating optical power is simplified, thereby ensuring that the system can not only guarantee high accuracy of output optical power, but also improve its output efficiency.

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

[0024] The mode converter is placed in the end-face coupling structure, which plays a key role in the optical fiber and optical waveguide system. By optimizing the mode matching of the optical signal, it can improve the optical fiber coupling efficiency, reduce the optical loss caused by mode mismatch, and thus improve the transmission efficiency and quality of the optical signal, 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 effectively balance loss and modulation efficiency, thereby effectively protecting the device from damage and reducing waveguide propagation loss with gold electrodes.

[0026] Preferably, the ridge angle of the hard mask in 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, improving the coupling efficiency of the optical signal, thereby reducing optical loss and mode mismatch. A suitable ridge angle can also reduce light scattering and reflection at the waveguide end face, reduce optical loss and improve the overall performance of the system, enabling the waveguide to better maintain the stability of the optical mode, reduce mode conversion interference, and improve the stability of optical signal transmission.

[0027] Secondly, the present invention also provides a measurement system, the system comprising: a tunable sensor, a single-mode optical fiber, a polarization controller, a ring isolator, the aforementioned reflection-based folded Mach-Zehnder electric field sensor, an erbium-doped fiber amplifier, an optical beam splitter, a spectrometer, an electro-optic detector, and an electronic spectrum analyzer.

[0028] The tunable sensor determines the operating wavelength of the electric field sensor through spectral analysis, adjusts it to the operating wavelength, and then transmits the light beam via single-mode fiber to a polarization controller for processing. This ensures that the input single-mode light is TE polarized, which can be achieved using the maximum electro-optic coefficient γ of x-cut lithium niobate. 33 Effective optical modulation is performed, and the beam is input into the reflection-based folded Mach-Zehnder electric field sensor according to any one of claims 1-9 for modulation through a ring isolator. Finally, the ring isolator transmits the received modulated and reflected beam to an erbium-doped fiber amplifier for optical power gain processing. After gain processing, the 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-optic detector and then connected to an electronic spectrum analyzer for linear characterization of the spatial electric field.

[0029] By introducing the aforementioned reflection-based folded Mach-Zehnder electric field sensor into this measurement system, the system achieves higher measurement efficiency, stronger anti-interference capability, higher integration and measurement sensitivity, and more accurate measurement results. It can realize wideband high-sensitivity electric field measurement under small-size devices and is applicable to various sensing application scenarios.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

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

[0032] (2) The U-shaped bend in the waveguide of the electric field sensor not only provides the arm length difference required by traditional electric field sensors to provide a linear operating point, but also achieves double the modulation length by folding while keeping the device length unchanged, which greatly improves the modulation efficiency.

[0033] (3) The final waveguide section of the electric field sensor uses a Bragg grating to reflect the beam, which enables the beam to be re-modulated while ensuring low loss. Compared with traditional reflective films, this optical microstructure has a higher degree of freedom and higher integration, further improving the modulation efficiency.

[0034] (4) In this electric field sensor, the reflection of the Bragg grating first doubles the modulation length of the phase change. The U-shaped waveguide structure provides the operating point and doubles the modulation length without increasing the device length. There are push-pull structures with positive and negative electric fields in the entire path modulation region. This technical solution makes the three work simultaneously, thus 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 with the traditional dipole electric field sensor. Attached Figure Description

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

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

[0037] Figure 3 This is a schematic diagram showing the cross-section of a portion of the sensor structure according to an embodiment of the present invention.

[0038] Figure 4 This is a top view of the multimode interferometer according to an embodiment of the present invention.

[0039] Figure 5 This is a top view and a partial magnified view of the Bragg grating according to an embodiment of the present invention.

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

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

[0042] Figure 8 The reflection spectrum of the Bragg grating in an embodiment of the present invention.

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

[0044] Figure descriptions: 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: Silica cladding layer; 6: F-type electrode module; 7: Multimode interferometer; 8: Bragg grating; 9: U-shaped waveguide structure; 10: Corresponding region of the modulation region cross section; 11: Tunable laser; 12: Single-mode fiber; 13: Polarization controller; 14: Circular isolator; 15: Reflection-based folded Mach-Zehnder electric field sensor; 16: Erbium-doped fiber amplifier; 17: Optical beam splitter; 18: Spectrometer; 19: Photodetector; 20: Electronic spectrum analyzer. DETAILED DESCRIPTION

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

[0046] Example 1

[0047] Figure 1 This is a perspective view of the overall structure of this embodiment. Figure 2 This is a top perspective view of the overall structure of this embodiment, as shown below. Figure 1 and Figure 2 As shown, the technical solution adopted in this embodiment is a reflection-based folded Mach-Zehnder electric field sensor. The electric field sensor includes an end-face coupling structure and a thin-film lithium niobate platform. The thin-film lithium niobate platform is provided with, from bottom to top, a thin-film lithium niobate silicon substrate 1, a thin-film lithium niobate silicon dioxide substrate 2, a thin-film lithium niobate flat plate layer 3, a ridge waveguide layer 4, and a silicon dioxide cladding layer 5. 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 located 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 located at the end of the ridge waveguide layer 4 and connected to the F-type electrode module 6; after being folded by the U-shaped waveguide structure 9, the end of the F-type electrode module 6 is connected to the Bragg grating 8.

[0049] from Figure 1 and Figure 2As can be seen from the diagram, in the electric field sensor described in this embodiment, after the light beam is coupled through the end-face coupling structure, the multimode interferometer 7 splits the single-mode light into two beams that enter the modulation region. First, the beams on two paths undergo a first positive and negative modulation via the F-type electrode module 6. Then, after passing through the U-shaped waveguide structure 9, the beams enter the other two paths of the F-type electrode module 6 for a second positive and negative modulation. Next, the beams at the waveguide end are reflected by the Bragg grating 8 for a third positive and negative modulation, and then pass through the U-shaped waveguide structure 9 again for a fourth positive and negative modulation, thus achieving the desired modulation effect. By setting a U-shaped waveguide junction 9, the modulation length is doubled without increasing the device length, resulting in a complete structure with positive and negative electric fields in the modulation region throughout the entire path. This ultimately improves the overall modulation efficiency by 8 times, introducing a gain of 9dB. Compared with traditional bulk lithium niobate crystal electric field sensors, the reflection-based folded Mach-Zehnder electric field sensor provided by this invention has a smaller electrode spacing, higher integration, better gain, and higher modulation efficiency. It also features a large measurement bandwidth, high spatial resolution, and low invasiveness, making it applicable to various sensing application scenarios.

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

[0051]

[0052]

[0053] Table 1

[0054] Preferably, such as Figures 1-3 As shown, in the U-shaped waveguide structure 9, the difference between the inner and outer semicircles of the U-shaped waveguide structure is 29.5 μm, as... Figure 7 As shown, the inner and outer semicircle difference c is obtained by adding the electrode width a and the electrode spacing b. Therefore, by converting the inner and outer semicircle difference, the arm length difference is calculated to be 187 μm. This arm length difference is used to generate the interference phase difference. Used to provide the required operating wavelength point for electric field sensors.

[0055] In the U-shaped waveguide structure 9, the radii of the inner and outer semicircles are different, which leads to the difference in the length of the two arms in the U-shaped waveguide structure. In this embodiment, the length difference is set to 187μm, which is sufficient to provide the operating point required by the C-band electric field sensor while meeting the small length requirements of the device. At the same time, it can provide folding 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 As can be clearly seen, the F-type electrode module 6 consists of several F-type modulation electrode arrays, and as... Figure 6 As shown, Figure 6 This is a schematic diagram of the cross-section of the modulation region provided in this embodiment. Combined with the U-shaped waveguide structure 9, six F-shaped modulation electrodes in the cross-sectional region of the modulation region form four straight waveguide modulation paths for electro-optic modulation, significantly increasing the modulation length of the light. Furthermore, the waveguide field modulation directions on its inner and outer diameters are as follows... Figure 7 The dashed arrows indicate the opposite direction, aiming to achieve high sensitivity while maintaining high integration. Furthermore, as shown in Table 1, this embodiment also provides specific parameter settings: the F-type modulation electrode spacing W3 is set to 4 μm, the waveguide width W4 is set to 0.8 μm, the F-type modulation electrode thickness H1 is set to 1 μm, the silicon dioxide cladding layer thickness H2 is set to 0.8 μm, the thin-film lithium niobate planar layer thickness H3 is set to 0.3 μm, the thin-film lithium niobate silicon dioxide substrate thickness H4 is set to 4.7 μm, and the waveguide thickness H5 is set to 0.3 μm.

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

[0058] Preferably, such as Figure 7 As shown, Figure 7 This is a top perspective view of a single F-type modulation electrode in this embodiment. The F-type modulation electrode also includes a long electrode arm, as shown in Table 1. In this embodiment, the length L3 of the long arm of the F-type modulation electrode is 3500 μm. The electric field E in the measured space is characterized by modulating the accumulation of induced charge on the long electrode arm. z ,like Figure 7 As shown, the F-type design allows the modulation electrodes to generate electric fields of equal magnitude but completely opposite directions on the waveguide to be modulated along two modulation paths. This embodiment utilizes an array modulation electrode structure to increase the modulation length, thereby improving the sensitivity of the electric field sensor. Furthermore, in this embodiment, the modulation length L4 of the F-type modulation electrode is set to 400 μm to obtain the measured spatial electric field E. z The relationship with the induced voltage V,

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

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

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

[0062]

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

[0064] The long electrode arm accumulates induced charges under the influence of the spatial electric field, collecting spatial electric field information. The charge accumulation at both ends of the waveguide forms a potential difference, which in turn generates a corresponding phase change under the influence of the long electrode arm. This lays the foundation for simplifying the subsequent calculation of the output optical power, making the output optical power easier to calculate and improving computational efficiency.

[0065] Preferably, such as Figure 4 As shown, Figure 4 This is a top view of the multimode interferometer provided in this embodiment. The multimode interferometer 7 splits the input single-mode light into two beams while maintaining their original modes and polarization states. The beams then enter the straight waveguide modulation path and the U-shaped waveguide structure 9 for push-pull modulation. After reflection by the Bragg grating 8, the beams undergo push-pull modulation again. Figure 5 As shown, Figure 5 This is a top view and a partial magnified view of the Bragg grating provided in this embodiment. The Bragg grating 8, as an integrated optical microstructure reflecting the target wavelength beam, has higher integration and freedom compared to traditional reflective coatings. The target wavelength can also be adjusted by changing the grating period length. Specifically, the center wavelength formula of the Bragg grating 8 is: 2n eff Λ=λ c , where n eff λ is the center average effective refractive index, Λ is the period length, and λ is the mean effective refractive index. c The center wavelength is given by the formula above. 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 for the 1550nm working band.

[0066] Furthermore, in this embodiment, the Bragg grating 8 has 50 periods, the Bragg grating period length W5 is 0.422 μm, the Bragg grating waveguide length W6 is 0.148 μm, and in conjunction with the attached... Figure 8 Due to the limitation of this embodiment, which uses 600nm lithium niobate etching at 300nm, the Bragg grating 8 reflects light with a bandwidth of 45nm around 1550nm, and from the attached... Figure 8 As can be seen, over 80% of the beam can be isolated and reflected back into the waveguide structure within a 45nm bandwidth, thus achieving high modulation sensitivity. Finally, the two reflected beams are combined and interfered through the multimode interferometer 7 to output optical power.

[0067] In this embodiment, the length L1 of the central region of the multimode interferometer 7 is set to 62 μm, the length L2 of the transition cone of the multimode interferometer 7 is set to 20 μm, the width W2 of the central region of the multimode interferometer 7 is set to 10 μm, and the spacing W3 of the F-type modulation electrodes in the modulation region is set to 4 μm. By using the multimode interferometer to shape the beam according to the above parameter settings, the input beam is converted into an output beam of different shapes and modes. This can effectively couple optical signals between different optical waveguides or optical fibers, improve the coupling efficiency of the optical system, reduce losses, and also extract electric field information from the output electrical signal of the optical receiver, converting phase modulation into intensity modulation.

[0068] Preferably, in the process of the multimode interferometer 7 combining two reflected beams to interfere and output optical power, the method further includes: introducing a half-wave voltage E. π And combined with phase change To simplify the optical power calculation formula, and at the same time set the interference phase difference The electric field sensor is positioned at the operating wavelength, 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 introduction of the half-wave voltage, the multimode interferometer 7 combines the two reflected beams, causes interference s, and outputs an optical power of:

[0070]

[0071] Among them, P out P represents the output optical power. in α is the input optical power, G is the total loss, and k is the photoelectric modulation gain. The amount of phase change, The interference phase difference;

[0072] To simplify the above optical power formula and improve modulation efficiency, a 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 electric field in the measured space and the optical mode field, and n e d is the effective refractive index of TE0 single-mode light, d is the electrode spacing, and L is the effective refractive index of TE0 single-mode light. clh is the modulation length in the electric field sensor. eff γ is the effective length of the electrode or antenna. 33 This is the maximum electro-optic effect coefficient.

[0075] Combining formulas (2), (3), and (4), the final optical power formula is obtained, which is:

[0076]

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

[0078]

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

[0080] Therefore, in this invention, a half-wave voltage E is introduced. π And combined with phase change Furthermore, by setting the value of the interference phase difference to place the electric field sensor at the working wavelength point, the optical power calculation formula is simplified. Through the introduction of electro-optic modulation gain, the electrode push-pull structure provides positive and negative modulation intensity, 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, introducing a total gain of 9dB. The modulation gain G introduced by this structure is 8 times higher than that of the traditional interference structure, thereby ensuring that the present invention can improve its output efficiency while ensuring high accuracy of output optical power.

[0081] Preferably, the end-face coupling structure includes a mode converter, which efficiently couples the beam from the input electric field sensor to the ridge waveguide layer for modulation.

[0082] The mode converter is placed in the end-face coupling structure, which plays a key role in the optical fiber and optical waveguide system. By optimizing the mode matching of the optical signal, it can improve the optical fiber coupling efficiency, reduce the optical loss caused by mode mismatch, and thus improve the transmission efficiency and quality of the optical signal, ensuring the efficient and stable operation of the system.

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

[0084] Preferably, the ridge angle of the hard mask in 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, improving the coupling efficiency of the optical signal, thereby reducing optical loss and mode mismatch. A suitable ridge angle can also reduce light scattering and reflection at the waveguide end face, reduce optical loss and improve the overall performance of the system, enabling the waveguide to better maintain the stability of the optical mode, reduce mode conversion interference, and improve the stability of optical signal transmission.

[0085] Example 2

[0086] like Figure 9 As shown, this embodiment provides a measurement system, which includes: a tunable sensor 11, a single-mode fiber 12, a polarization controller 13, a ring isolator 14, the aforementioned 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-optic detector 19, and an electronic spectrum analyzer 20.

[0087] The tunable sensor 11 first obtains the spectrum by scanning the wavelength, then determines the operating wavelength of the electric field sensor based on the spectrum, and adjusts it to the operating wavelength before transmitting the light beam via single-mode fiber 12 to the polarization controller 13 for processing. This ensures that the input single-mode light is TE polarized, which can be achieved using the maximum electro-optic coefficient γ of x-cut lithium niobate. 33 Effective optical modulation is performed, and the light beam is input into the reflection-based folded Mach-Zehnder electric field sensor 15 described in Example 1 for modulation via the ring isolator 14;

[0088] In the electric field sensor, the light beam first enters the end-face coupling structure and is efficiently coupled using a mode converter. Then, it enters the modulation region. First, the input single-mode light is split into two beams by a multimode interferometer 7. Then, the beam enters one of the two paths of the F-type electrode module 6 for the first positive and negative modulation. Then, the beam enters the other two paths of the F-type electrode module 6 after passing through the U-shaped waveguide structure 9 for the second positive and negative modulation. Next, the beam at the end of the waveguide is reflected by the Bragg grating 8 for the third positive and negative modulation. Then, it passes through the U-shaped waveguide structure again for the fourth positive and negative modulation. Finally, the two reflected beams are combined by the multimode interferometer 7 to interfere and are output to the ring isolator 14.

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

[0090]

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

[0092] By introducing the aforementioned reflection-based folded Mach-Zehnder electric field sensor into this measurement system, the measurement system achieves higher measurement efficiency, stronger anti-interference capability, higher integration and measurement sensitivity, and more accurate measurement results, making it applicable to various 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 of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A reflection-based folded Mach-Zehnder electric field sensor, characterized in that, The electric field sensor includes an end-face coupling structure and a thin-film lithium niobate platform. From bottom to top, the thin-film lithium niobate platform comprises a thin-film lithium niobate silicon substrate, a thin-film lithium niobate silicon dioxide substrate, a thin-film lithium niobate planar layer, a ridge waveguide layer, and a silicon dioxide cladding layer. The ridge waveguide layer includes a multimode interferometer, an F-type electrode module, a U-shaped waveguide structure, and a Bragg grating. The end-face coupling structure is connected to a multimode interferometer located 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 disposed 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. The reflection-based folded Mach-Zehnder electric field sensor according to claim 1, characterized in that, In the U-shaped waveguide structure, the two arms are set to different lengths to introduce an arm length difference, and an interference phase difference is generated through this arm length difference. The arm length difference is 187 μm, which is used to provide the required operating 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 consists of several F-type modulation electrode arrays, which are combined with a U-shaped waveguide structure to form four straight waveguide modulation paths, thereby multiplying the modulation length of the light.

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

5. A reflection-based folded Mach-Zehnder electric field sensor according to claim 4, characterized in that, The multimode interferometer splits the input single-mode light into two beams while maintaining their original modes and polarization states. The beams are then fed into a straight waveguide modulation path and a U-shaped waveguide structure for push-pull modulation. After reflection through a Bragg grating, the beams are again subjected to push-pull modulation. Finally, the multimode interferometer combines the two reflected beams, causing interference and outputting optical power.

6. A reflection-based folded Mach-Zehnder electric field sensor according to claim 5, characterized in that, The multimode interferometer, which combines two reflected beams to interfere and output optical power, also includes: introducing a half-wave voltage E. π And combined with phase change To simplify the optical power calculation formula, and at the same time set the interference phase difference By positioning the electric field sensor at its operating wavelength and using the Taylor expansion formula to linearly represent the optical power calculation formula, the final output optical power P is obtained. out for: Among them, P out P represents the output optical power. in α is the input optical power, α is the total loss, G is the photoelectric modulation gain, k is the extinction coefficient, and E is the input optical power. π For half-wave voltage, E z The electric field to be measured in space.

7. A reflection-based folded Mach-Zehnder electric field sensor according to claim 1, characterized in that, The end-face coupling structure includes a mode converter for efficiently coupling the light from the input electric field sensor and inputting it into the ridge waveguide layer for modulation.

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

9. A reflection-based folded Mach-Zehnder electric field sensor according to any one of claims 1-7, 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 includes: a tunable sensor, a single-mode fiber, a polarization controller, a ring isolator, a reflection-based folded Mach-Zehnder electric field sensor as described in any one of claims 1-9, an erbium-doped fiber amplifier, an optical beam splitter, a spectrometer, an electro-optic detector, and an electronic spectrum analyzer. The tunable sensor determines the operating wavelength of the electric field sensor through spectral analysis, adjusts it to the operating wavelength, and then transmits the light beam via single-mode fiber to a polarization controller for processing. This ensures that the input single-mode light is TE polarized, which can be achieved using the maximum electro-optic coefficient γ of x-cut lithium niobate. 33 Effective optical modulation is performed, and the beam is input into the reflection-based folded Mach-Zehnder electric field sensor according to any one of claims 1-9 for modulation through a ring isolator. Finally, the ring isolator transmits the received modulated and reflected beam to an erbium-doped fiber amplifier for optical power gain processing. After gain processing, the 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-optic detector and then connected to an electronic spectrum analyzer for linear characterization of the spatial electric field.

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