Stepping phase interferometer with double nonlinear phase generators

Abstract

The invention discloses a stepping phase interferometer with double nonlinear phase generators, which comprises a beam splitter, a first phase generator and a second phase generator, and is characterized in that the right side of the beam splitter is correspondingly provided with the first phase generator, and the upper part of the beam splitter is correspondingly provided with the second phase generator; the first phase generator sequentially comprises a first reflecting surface and a second reflecting surface from the beam splitter to the outside, and the first reflecting surface and the second reflecting surface form a first resonant cavity; the second phase generator sequentially comprises a third reflecting surface and a fourth reflecting surface from the beam splitter to the outside, and the third reflecting surface and the fourth reflecting surface form a second resonant cavity; the first resonant cavity and the second resonant cavity have the same optical path length, and the difference between the optical path length from the first reflecting surface to the beam splitter and the optical path length from the third reflecting surface to the beam splitter is half of the optical path length of the first resonant cavity.

Description

Technical Field

[0001] The invention belongs to the technical field of optical communication, and in particular relates to a dual nonlinear phase generator stepping phase interferometer. Background Art

[0002] Interleaver is one of the most important passive components in the field of optical communication. Its function is to interleave the incident signal light and then split it to two output ports. In other words, it splits the odd channels (channels 1, 3, 5, ...) and even channels (channels 2, 4, 6, ...) to two ports.

[0003] As one of the interleaving splitters, the phase stepping interferometer can achieve the purpose of interleaving splitting, dividing the optical signal into odd signal channels and even signal channels. The traditional phase stepping interferometer design uses a single GT-resonance cavity to generate a nonlinear phase beam, which then interferes with another linear phase beam generated by a reflector to form the required spectrum.

[0004] This design is widely accepted in many communication systems. However, as channel spacing becomes denser and modulation bandwidth becomes wider, an optical component that can provide better isolation is needed to meet the above requirements. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a dual nonlinear phase generator stepping phase interferometer to solve the problems existing in the above prior art.

[0006] To achieve the above object, the present invention provides a dual nonlinear phase generator stepping phase interferometer, comprising: a beam splitter, a first phase generator and a second phase generator, wherein the first phase generator is correspondingly arranged on the right side of the beam splitter, and the second phase generator is correspondingly arranged above the beam splitter;

[0007] The first phase generator includes a first reflection surface and a second reflection surface in sequence from the beam splitter to the outside; the first reflection surface and the second reflection surface form a first resonance cavity; the second phase generator includes a third reflection surface and a fourth reflection surface in sequence from the beam splitter to the outside, the third reflection surface and the fourth reflection surface form a second resonance cavity; the first resonance cavity and the second resonance cavity have the same optical path length, and the difference between the optical path length from the first reflection surface to the beam splitter and the optical path length from the third reflection surface to the beam splitter is half of the optical path length of the first resonance cavity.

[0008] Optionally, a first carrier and a second carrier are arranged in sequence between the beam splitter and the first reflecting surface, and the medium between the first carrier and the second carrier is air, wherein an anti-reflection film is arranged on a side of the first carrier away from the beam splitter and a side of the second carrier close to the beam splitter, and the first reflecting surface is arranged on a side of the second carrier away from the beam splitter.

[0009] Optionally, a third carrier and a fourth carrier are arranged in sequence between the beam splitter and the third reflecting surface, and the medium between the third carrier and the fourth carrier is air, wherein an anti-reflection film is arranged on the side of the third carrier away from the beam splitter and the side of the fourth carrier close to the beam splitter, and the third reflecting surface is arranged on the side of the fourth carrier away from the beam splitter.

[0010] Optionally, the first phase generator and the second phase generator adopt a GT resonant cavity or an asymmetric Fabry-Perot resonant cavity.

[0011] Optionally, when both the first phase generator and the second phase generator adopt an asymmetric Fabry-Perot resonant cavity, the reflected light phases of the first phase generator and the second phase generator are:

[0012]

[0013] Among them, R1 and R2 are respectively the reflection surfaces away from the beam splitter, v represents the light frequency, and v 0 represents the FSR of the resonant cavity.

[0014] Optionally, when the first phase generator and the second phase generator both adopt an asymmetric Fabry-Perot resonant cavity, the reflectivities of the first reflection surface, the second reflection surface, the third reflection surface and the fourth reflection surface are set to 85%, 75%, 11% and 96% respectively.

[0015] Optionally, when both the first phase generator and the second phase generator adopt an inhomogeneous Fabry-Perot resonant cavity, the reflectivities of the first reflection surface, the second reflection surface, the third reflection surface and the fourth reflection surface are set to 50%, 90%, 5% and 96% respectively.

[0016] Optionally, in special cases, the distance between the third reflecting surface and the beam splitter is 0, and the optical path length from the first reflecting surface to the beam splitter is half of the optical path length of the first resonant cavity.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects:

[0018] Based on the above structure, the present invention can use a dual GT-resonance cavity or a dual UFP resonance cavity to manufacture an interleaving splitter, so that its passband and stopband are improved at the same time. If a UFP resonant cavity is used to manufacture an optical interleaving splitter, the FWHM can be reduced to achieve better channel isolation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0020] Figure 1 It is a conventional phase stepping interferometer; the reference numerals are: 1, first phase generator; 2, second phase generator; 3, beam splitter; 41, first output light; 42, second output light;

[0021] Figure 2 It is a standard GT-resonance cavity; the reference numerals are: 51, front reflective surface; 52, rear reflective surface, the rear reflective surface 52 is a mirror coating with a reflectivity close to 100%, and the front reflective surface 51 is a partial reflective coating with a reflectivity of 0 to 100%;

[0022] Figure 3 It is a standard single GT-resonance cavity interleaved splitter; the reference numerals are: 3, beam splitter; 211, first reflection surface; 212, second reflection surface; 222, third reflection surface; 223, anti-reflection film;

[0023] Figure 4 It is a schematic diagram of the phase difference between the reflected light beams of the first phase generator and the second phase generator at the second output light 42 of the standard single GT-resonance cavity interleaved splitter;

[0024] Figure 5 for Figure 4 Schematic diagram of the corresponding power loss spectrum;

[0025] Figure 6 Schematic diagram of the difference loss spectrum of the first output light 41 and the second output light 42 of the standard single GT interleaved splitter; wherein the abscissa is the frequency and the ordinate is the loss (IL) in dB;

[0026] Figure 7 The spectrum intersection diagram of the first output light 41 and the second output light 42 of the standard single GT50 / 100G interleaved splitter; wherein the spectrum of the first output light 41 and the second output light 42 intersects at + / -25GHz from the center of the passband; at the intersection point, the insertion loss is 3dB, the horizontal axis is the frequency, and the vertical axis is the IL in dB;

[0027] Figure 8Schematic diagram of the structure of a dual NLPG interleaver according to an embodiment of the present invention; the reference numerals are: 3, beam splitter; 11, first reflection surface; 12, second reflection surface; 21, third reflection surface; 22, fourth reflection surface; 131, first anti-reflection film; 132, second anti-reflection film; 231, third anti-reflection film; 232, fourth anti-reflection film;

[0028] Fig. 9 The relationship between the phase difference and the frequency of the embodiment of the present invention; the dotted line corresponds to the single GT interleaver, PR = 14%, the solid line corresponds to the double GT interleaver, and its design parameters are (R11, R12, R21, R22) = (43%, 100%, 3.3%, 100%);

[0029] Fig.10 yes Fig. 9 The power difference loss spectrum corresponding to the phase difference; the dotted line corresponds to the phase difference function of the single GT interleaver, and the solid line corresponds to the phase difference function of the double GT interleaver;

[0030] Fig.11 : It is the reflection power spectrum of the two resonant cavities UFP-1 (solid line) and UFP-2 (dashed line) of the dual UFP cavity interleaver of the embodiment of the present invention; its corresponding reflectivity is (85%, 75%) and (11%, 96%), wherein the horizontal axis is the frequency and the vertical axis is the reflectivity on a linear scale;

[0031] Fig.12 for Fig.11 Phase difference diagram of two interfering lights at output -T, where the horizontal axis is frequency and the vertical axis is phase difference;

[0032] Fig.13 for Fig.12 The difference loss spectrum corresponding to the phase difference is the power spectrum of the dual UFP-resonance cavity interleaving splitter of the embodiment of the present invention; the dotted line in the figure is the difference loss spectrum of the standard PR-14%, single GT cavity interleaver;

[0033] Fig.14 The phase difference loss spectrum of the dual UFP cavity interleaver according to the embodiment of the present invention is shown in FIG. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0036] In the present invention, two methods are proposed to enhance the performance of the interleaver: 1) using a dual GT-resonant cavity design to widen the passband and stopband, and 2) replacing the GT-cavity with an asymmetric Fabry-Perot resonant cavity (UFP) to remove the constraint that the 3dB bandwidth must be equal to the channel spacing.

[0037] 1. Introduction to existing single GT-resonance cavity stepping phase interferometer:

[0038] Figure 1 The schematic diagram of the step phase interferometer of a single GT-resonance cavity is shown. It consists of a 50 / 50 non-polarized beam splitter 3 and two phase generators (first phase generator 1 and second phase generator 2). The beam splitter 3 splits the incident light beam into two paths at point P, where point P is the splitting point of the incident light beam in the beam splitter 3. The two beams are reflected back to the beam splitter 3 from the upper and right phase generators, namely the second phase generator 2 and the first phase generator 1, respectively, and after meeting at point Q, two output light beams are formed on the left and lower sides of the beam splitter 3, namely the first output light 41 and the second output light 42, where point Q is the meeting point of the reflected light in the beam splitter 3. The output of the first output light 41 is located on the left side of the beam splitter 3, and the output of the second output light 42 is located at the bottom of the beam splitter 3. In an optical system without energy loss, the sum of the power of the first output light 41 and the second output light 42 is equal to the power of the input light entering the system from the left side of the beam splitter 3. Since the power spectra of the first output light 41 and the second output light 42 are complementary, the following discussion only needs to focus on the second output light 42. In addition, in the present invention, all phases are referenced to point P. For this type of interferometer, what is really important is the phase change from point P to point Q, including the direct influence of the actual optical path length and the phase caused by Fresnel transmission or reflection on the beam splitter.

[0039] The intensity of the first output light 41 and the second output light 42 depends on the phase difference between the two light beams reflected from the first phase generator 1 and the second phase generator 2 reaching the left and bottom sides of the beam splitter 3. In the present invention, this phase difference is called the phase response of the interleaved splitter. If they are in phase, the intensity of the output light reaches a maximum (passband). On the contrary, if they are out of phase, the output light reaches a minimum (stopband). In a traditional interleaved splitter, the first phase generator 1 is a GT resonant cavity and the second phase generator 2 is a reflector. Figure 2The structure of the GT resonant cavity is shown, which consists of two parallel reflective surfaces. The rear reflective surface 52 is a mirror coating with a reflectivity equal to or approximately equal to 100%, and the front reflective surface 51 is a partial reflective coating with a reflectivity between 0 and 100% (called partial reflection, PR).

[0040] Since the rear reflective surface 52 of the GT resonant cavity is 100% reflective, all the light entering the GT resonant cavity is reflected regardless of the reflectivity of the front reflective surface 51, but the phase is modulated. The amount of phase modulation is determined by the reflectivity of the front reflective surface 51. For the special case of zero reflection of the front reflective surface 51, the phase of the reflected light beam is linearly related to the optical frequency. Figure 2 As shown, if the power reflectivity of the front reflection surface 51 of the GT resonant cavity is R, the phase φ of the reflected light GT The relationship with the light frequency ν is as follows:

[0041]

[0042] Where α is the reflection coefficient, ν 0 represents the FSR of the GT resonant cavity, C represents the speed of light, and L represents the length of the GT resonant cavity.

[0043] In the present invention, although a 50G / 100G interleaved splitter is used as an example, the principle can still be applied to any channel spacing.

[0044] Figure 3 The standard single GT-resonance cavity interleaved splitter is shown, which includes a beam splitter 3, a first reflection surface 211 and a second reflection surface 212 arranged on the right side of the beam splitter 3, an anti-reflection film 223 and a third reflection surface 222 arranged on the top of the beam splitter 3, the first reflection surface 211 and the second reflection surface 212 constitute a GT-resonance cavity, the third reflection surface 222 is a reflection film of nearly 100%, and the first reflection surface 211, the second reflection surface 212, the third reflection surface 222 and the beam splitter 3 are connected by a transparent material (or a non-transparent material). The first reflective surface 211 and the second reflective surface 212 are fixed in position by a light-transmitting material (or a non-light-transmitting material). The optical path length between the first reflective surface 211 and the beam splitter 3 is S11, the optical path length between the first reflective surface 211 and the second reflective surface 212 is S12, the optical path length between the beam splitter 3 and the anti-reflection film 223 is S21, and the optical path length between the anti-reflection film 223 and the third reflective surface 222 is S22, wherein S11=S21, S12=2·S22. Figure 1 The first phase generator 1 is a GT resonant cavity with a first reflection surface 211 having a 14% coating and a FSR=50GHz, and the third reflection surface 222 in the second phase generator 2 is a mirror coated with a mirror. Figure 4The phase difference between the second output light 42 reflected from the first phase generator 1 and the second phase generator 2 is shown. It is highly nonlinear and increases by π (GT-FSR of the resonant cavity) for every 50 GHz. Figure 5 is the corresponding power spectrum of the second output light 42. Figure 4 For any integer m, in the region where the phase difference is close to 2mπ, it is the passband of the interleaved splitter (constructive interference); on the contrary, for the region where the phase difference is close to (2m+1)π, it is the stopband (destructive interference). Figure 6 and Figure 7 The first output light 41 (dashed line) and the second output light 42 (solid line) are shown, and at the intersection, the insertion loss is 3 dB. The vertical axis is in dB. At the intersection, the second output light 42 and the first output light 41 have the same optical power and are both equal to 1 / 2 of the total power, indicating that the FWHM of the interleaved splitter is 50 GHz. Regardless of the reflectivity of the first reflective surface 211 in the GT resonant cavity, this is true for any interleaved splitter using a GT resonant cavity and a reflector.

[0045] The following is a description of the relevant contents provided by the present invention:

[0046] 2. Dual Nonlinear Phase Generator (NLPG) Interleaved Divider

[0047] like Figure 8 As shown, the present invention shows the structure of a dual nonlinear phase interleaver.

[0048] It includes a beam splitter 3 and a first reflection surface 11 and a second reflection surface 12 arranged outwardly in sequence on the right side of the beam splitter 3; the first reflection surface 11 and the second reflection surface 12 form a first resonance cavity; a third reflection surface 21 and a fourth reflection surface 22 are arranged outwardly in sequence on the top of the beam splitter 3, and the third reflection surface 21 and the fourth reflection surface 22 form a second resonance cavity; the first resonance cavity and the second resonance cavity have the same optical path length, and the difference between the optical path length from the first reflection surface to the beam splitter and the optical path length from the third reflection surface to the beam splitter is half of the optical path length of the first resonance cavity.

[0049] A first carrier is bonded to the right side of the beam splitter 3, a first anti-reflection film 131 is arranged on the side of the first carrier away from the beam splitter 3, a second carrier is arranged at a certain interval on the right side of the first carrier, a second anti-reflection film 132 is arranged on the side of the second carrier close to the beam splitter 3, a first reflecting surface 11 is arranged on the side of the second carrier away from the beam splitter 3, the first carrier and the second carrier are made of light-transmitting materials such as glass, and the medium between them is air, and fixing materials are arranged at both ends of the first carrier and the second carrier to set them in parallel and fix them so as to set the first anti-reflection film 131, the second anti-reflection film 132 and the first reflecting surface 11 at a fixed distance and in parallel, a reflector for carrying the second reflecting surface 12 is arranged on the right side of the second carrier, and fixing materials are also arranged between the reflector and the second carrier to set them in parallel and fix them so as to set the second reflecting surface 12 and the first reflecting surface 11 at a fixed distance and in parallel.

[0050] A third carrier is bonded to the top of the beam splitter 3, and a third anti-reflection film 231 is arranged on the side of the third carrier away from the beam splitter 3. A fourth carrier is arranged at a certain interval on the top of the third carrier, and a fourth anti-reflection film 232 is arranged on the side of the fourth carrier close to the beam splitter 3, and a third reflecting surface 21 is arranged on the side of the fourth carrier away from the beam splitter 3. The third carrier and the fourth carrier are made of light-transmitting materials such as glass, and the medium between them is air. Fixing materials are arranged at both ends of the third carrier and the fourth carrier to set them in parallel and fix them so as to set the third anti-reflection film 231, the fourth anti-reflection film 232 and the third reflecting surface 21 at a fixed distance and in parallel. A reflector for carrying the fourth reflecting surface 22 is arranged on the top of the fourth carrier, and fixing materials are also arranged between the reflector and the fourth carrier to set them in parallel and fix them so as to set the fourth reflecting surface 22 and the third reflecting surface 21 at a fixed distance and in parallel.

[0051] In this structure, Figure 8 The first phase generator 1 and the second phase generator 2 in the embodiment are both nonlinear phase generators. The nonlinear phase generators can be made of a GT resonant cavity or an asymmetric Fabry-Perot resonant cavity (UFP).

[0052] refer to Figure 8 , in the first resonance cavity on the right, the reflectivities of the first reflection surface 11 and the second reflection surface 12 are set to be R11 and R12 respectively, the optical path length between the first reflection surface 11 and the beam splitter 3 is L11, and the cavity length of the first resonance cavity, i.e., the optical path length between the first reflection surface 11 and the second reflection surface 12 is L12; in the second resonance cavity at the top, the reflectivities of the third reflection surface 21 and the fourth reflection surface 22 are set to be R21 and R22 respectively, the optical path length between the third reflection surface 21 and the beam splitter 3 is L21, and the cavity length of the second resonance cavity, i.e., the optical path length between the third reflection surface 21 and the fourth reflection surface 22 is L22;

[0053] In the dual nonlinear phase generator setting, the optical path lengths of L12 and L22 are the same, i.e., L12 = L22, and the optical path length difference between L11 and L21 is half of the optical path length of L12, i.e. In special cases, in order to simplify the structure and reduce costs, L21 can be set to 0. In this case, the optical path length of L11 is half of L12, that is,

[0054] 3.Dual GT-resonance cavity interleaver;

[0055] refer to Figure 4 In order to increase the width of the passband (phase difference = 2mπ) and the stopband (phase difference = (2m+1)π), it is necessary to Figure 4 The platform part of the function should be as wide as possible. In other words, the rising part of the function must be as steep as possible. For the dual GT resonant cavity design, R12 and R22 are fixed to 100%, and the spectrum performance can only be optimized by adjusting R11 and R21.

[0056] exist Fig. 9 In the figure, the solid line spectrum is the functional relationship between the phase difference and frequency of the two beams of light participating in the interference in the second output light 42. The reflectivity at this time is (R11, R12, R21, R22) = (42%, 100%, 3.3%, 100%). Compared with the design of a single GT-resonance cavity (dashed line spectrum), the platform part of the function is wider. At the edge of the channel (i.e., the frequency is f k =25+50k, k is an integer) the phase response is steeper. Fig.10 In the figure, the solid curve is the corresponding power response function of the dual GT-resonance cavity. Compared with the dashed spectrum, the solid spectrum has a wider passband and stopband. In this example, compared with the single GT-resonance cavity, the 0.5dB passband and 25dB stopband of the dual GT-resonance cavity are 12% and 40% wider, respectively. It is particularly important to emphasize that the 40% stopband widening plays a key role in blocking the interference of the adjacent channel signal in the communication system. Designers can choose various combinations of (R11, R21) to achieve specific goals.

[0057] 4. Dual UFP-Resonant Cavity Interleaver

[0058] As mentioned above, all GT-resonant cavity-based interleavers have a fixed 3-dB bandwidth that is always equal to the channel spacing. For example, for a 50G / 100G interleaver, the other FWHM of the GT-resonant cavity-based interleavers is 50 GHz, regardless of (PR, R11, R21). In some applications, a smaller FWHM is required to block optical signals from two adjacent channels, so a different design must be used.

[0059] To reduce the 3-dB bandwidth, the interleaver must be designed near the channel edge (i.e., frequency f k =25GHz+50k) to drop some power so that the sum of the power of the odd and even channels here is less than the power entering the interleaver. To achieve this goal, it is recommended to replace the GT resonant cavity with an asymmetric Fabry-Perot (UFP) resonant cavity. The UFP resonant cavity consists of two parallel surfaces, both of which are partially reflective surfaces with reflectivities R1 and R2. When the reflectivity R2 of the second surface is 100%, it becomes a GT-resonant cavity.

[0060] Phase φ of reflected light from an asymmetric Fabry-Perot cavity UFP It can be expressed by the following equation:

[0061]

[0062] Where R1 and R2 are the reflectivity of the reflection surfaces in the asymmetric Fabry-Perot resonant cavity that are away from the beam splitter, v represents the optical frequency, and v 0 represents the FSR of the resonant cavity.

[0063] Based on this change in the reflectivity R1 and R2 of the two surfaces, the phase of the reflected light can be optimized.

[0064] Fig.11 is the reflected power spectrum of the 50G-FSR UFP resonant cavity. In the figure, the FSR of both resonant cavities is 50GHz. The ordinate is the reflectivity of the resonant cavity, using a linear scale. The solid line is the UFP resonant cavity with a coating of (85%, 75%); the dotted line is the UFP resonant cavity with a coating of (11%, 96%). In brackets, the first and second numbers are the reflectivities R1 and R2 of the front and back surfaces, respectively. For the (85%, 75%) UFP cavity, the transmittance is less than 10% at + / -25GHz, which will play a major role in narrowing the 3db bandwidth of the UFP resonant cavity interleaving splitter.

[0065] Based on the structure of the dual nonlinear phase interleaver, when the above two UFP resonant cavities are used to construct the interleaving splitter, (R11, R12, R21, R22) = (85%, 75%, 11%, 96%), the phase response and power spectrum are as follows Fig.12 and 13 The horizontal axis is in GHz, and the vertical axis is the phase difference in π.

[0066] Fig.13 The dashed line in is the power spectrum of a single GT-resonant cavity interleaved shunt. As expected, the UFP interleaved shunt has a narrower and steeper power response spectrum in the range from 0 to -10 dB.

[0067] There are many combinations of (R11, R12, R21, R22) that can be used to construct UFP interleaved splitters. Depending on the target performance, by changing these parameters, the passband and stopband width, dispersion and other performance can be optimized as needed. Fig.14 The power spectrum shown is another example, corresponding to (R11, R12, R21, R22) = (50%, 90%, 5%, 96%). In this example, the stopband ratio Fig.13 The design shown is wider. The trade-off is higher dispersion.

[0068] The present invention can use a double GT-resonance cavity to manufacture an interleaved splitter, so that the passband and stopband of the interleaved splitter can be improved simultaneously.

[0069] The present invention can use an asymmetric Fabry-Perot (UFP) resonant cavity to manufacture an optical interleaving splitter to reduce FWHM and achieve better channel isolation.

[0070] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. Dual nonlinear phase generator stepping phase interferometer, characterized in that: include: A beam splitter, a first phase generator and a second phase generator, wherein the first phase generator is correspondingly arranged on the right side of the beam splitter, and the second phase generator is correspondingly arranged on the top of the beam splitter; The first phase generator includes a first reflection surface and a second reflection surface in sequence from the beam splitter to the outside; the first reflection surface and the second reflection surface form a first resonance cavity; the second phase generator includes a third reflection surface and a fourth reflection surface in sequence from the beam splitter to the outside, the third reflection surface and the fourth reflection surface form a second resonance cavity; the first resonance cavity and the second resonance cavity have the same optical path length, and the difference between the optical path length from the first reflection surface to the beam splitter and the optical path length from the third reflection surface to the beam splitter is half of the optical path length of the first resonance cavity.

2. The dual nonlinear phase generator stepping phase interferometer according to claim 1, characterized in that: A first carrier and a second carrier are arranged in sequence between the beam splitter and the first reflecting surface, the medium between the first carrier and the second carrier is air, an anti-reflection film is arranged on a side of the first carrier away from the beam splitter and a side of the second carrier close to the beam splitter, and the first reflecting surface is arranged on a side of the second carrier away from the beam splitter.

3. The dual nonlinear phase generator stepping phase interferometer according to claim 1, characterized in that: A third carrier and a fourth carrier are arranged in sequence between the beam splitter and the third reflecting surface, the medium between the third carrier and the fourth carrier is air, wherein an anti-reflection film is arranged on a side of the third carrier away from the beam splitter and a side of the fourth carrier close to the beam splitter, and the third reflecting surface is arranged on a side of the fourth carrier away from the beam splitter.

4. The dual nonlinear phase generator stepping phase interferometer according to claim 1, characterized in that: The first phase generator and the second phase generator use a GT resonant cavity or an asymmetric Fabry-Perot resonant cavity.

5. The dual nonlinear phase generator stepping phase interferometer according to claim 1, characterized in that: When both the first phase generator and the second phase generator adopt an asymmetric Fabry-Perot resonant cavity, the reflected light phases of the first phase generator and the second phase generator are: Wherein, R1 and R2 are reflection surfaces which are respectively away from the beam splitter, v represents the light frequency, and v0 represents the FSR of the resonant cavity.

6. The dual nonlinear phase generator stepping phase interferometer according to claim 1, characterized in that: When the first phase generator and the second phase generator both adopt asymmetric Fabry-Perot resonant cavity, the reflectivities of the first reflection surface, the second reflection surface, the third reflection surface and the fourth reflection surface are set to 85%, 75%, 11% and 96% respectively.

7. The dual nonlinear phase generator stepping phase interferometer according to claim 1, characterized in that: When both the first phase generator and the second phase generator adopt an inhomogeneous Fabry-Perot resonant cavity, the reflectivities of the first reflection surface, the second reflection surface, the third reflection surface and the fourth reflection surface are set to 50%, 90%, 5% and 96% respectively.

8. The dual nonlinear phase generator stepping phase interferometer according to claim 1, characterized in that: In special cases, the distance between the third reflection surface and the beam splitter is 0, and the optical path length from the first reflection surface to the beam splitter is half of the optical path length of the first resonance cavity.

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