Optical comb frequency interval multiplication device and implementation method thereof

Abstract

The invention discloses an optical comb frequency interval multiplication device and an implementation method thereof. The device comprises an optical frequency comb, an optical splitter, a vacuum chamber and a plurality of interval multiplication branches. Each interval multiplication branch comprises a first polarization beam splitter, an FP cavity, a broadband Faraday rotator, a half-wave plate, a second polarization beam splitter, a broadband Faraday isolator, a first reflector and a second reflector. The broadband Faraday rotator is ingeniously matched with the half-wave plate, the spectrum which passes through the FP cavity for the first time and is multiplied in frequency is guided into the same FP cavity again, the side mode rejection ratio is multiplied, and meanwhile interstage oscillation and collinear interference are avoided; long-term stable frequency interval multiplication can be realized; the generated calibration spectral line can be used for planet mass measurement, dark substance discovery, precise distance measurement, low-noise microwave generation, high-speed analog-to-digital conversion and the like; the whole system is simple in structure, and the adjusting method is simple.

Description

Technical Field

[0001] The present invention relates to an optical frequency comb technology, and in particular to an optical comb frequency interval multiplication device and an implementation method thereof. Background Art

[0002] As the requirements for calibration technology in high-resolution spectroscopy increase, femtosecond laser frequency combs are considered to be a new generation of calibration light sources due to their equal frequency spacing (comb tooth spacing) and uniformly distributed spectral lines. However, the frequency spacing of conventional mode-locked lasers used to generate laser frequency combs is difficult to exceed 1 GHz.

[0003] Lasers with frequency intervals above 1 GHz have problems with wide pulses, low pulse energy, and difficulty in direct spectrum expansion, requiring complex amplification, compression, and even pulse shaping. The so-called microcavity optical comb, although the frequency interval can reach tens of GHz or even hundreds of GHz, the wavelength is concentrated in the spectral range centered at 1.5 microns, which cannot be used in the visible light band. It also has problems such as the need for a complex startup process, low power, wide pulses, large differences in spectral intensity distribution, and poor thermal stability, making it difficult to use for astronomical spectrum calibration.

[0004] The femtosecond optical frequency comb commercialized in astronomical spectrometers has a single frequency interval and a wavelength range of more than 500nm, which is not suitable for the resolution of the short wavelength part of the spectrometer. It has a small coverage range, a large volume, a high price, and a complex system with high operation difficulty. Therefore, there is an urgent need for a simple and reliable calibration device for high-resolution spectrometers suitable for harsh environments.

[0005] The calibration light source used for astronomical spectrum calibration is composed of a series of resolvable optical frequency standards. Above the spectrum, a series of resolvable light spots can be seen. The size of these light spots is fitted by the diffraction spots. If this optical frequency standard is filtered by a dense optical frequency standard, the size and symmetry of the filtered side mode determines the accuracy of the calibration. According to the error formula of these filtered optical frequency standards for the radial velocity (RV), astronomical spectrum calibration requires a very high side mode suppression ratio and symmetry. The formula is:

[0006]

[0007] Among them, f R is the comb tooth spacing of the laser frequency comb; f A is the optical frequency of the calibrated comb teeth after multiplication, c is the speed of light in vacuum, I +1 and I -1 They are respectively the main mode I under the FP cavity envelope 0 Two adjacent side modes. Formula (1) shows that (I +1 -I -1 ) / I 0 is the main mode I under the FP cavity envelope 0The ratio of, and especially the difference between, the error in the radial velocity plays a crucial role. +1 -I -1 ≠0, (I +1 -I -1 ) / I 0 It should be as small as possible, that is, the side mode suppression ratio should be as high as possible.

[0008] Therefore, spectral filtering must first be symmetrical, that is, the resonant frequency (or extinction spectrum interval) of the FP cavity used for filtering is an integer multiple of the optical frequency comb. The frequency is multiplied by the FP cavity. The calculation formula of the side mode suppression ratio S (the ratio of the main mode to the side mode under the transmission line width) is expressed in dB as follows:

[0009]

[0010] Where F is the fineness of the FP cavity, and M is the frequency multiplication factor. If the reflectivity of the FP cavity's reflector is 99%, and the frequency multiplication factor is M = 30, then F = 312, and the side mode suppression ratio S is only 26dB, which does not meet the requirement of greater than 30dB. Therefore, it is necessary to pass through the FP cavity twice or more.

[0011] Although the cascaded FP cavity can solve the problem of side mode suppression, when two or more FP cavities are cascaded, the light output from the first FP cavity will oscillate between the two FP cavities, resulting in the first-stage multiplied spectrum not being able to completely pass through the second FP cavity, or the spectrum being severely modulated.

[0012] At the same time, the frequency interval of the two FP cavities required for cascading must be exactly the same. If it is an actively stabilized FP cavity (driven by PZT), there is no problem with cascading. However, the actively stabilized FP cavity needs to be optically locked with continuous light, then frequency-shifted as a reference light, and then the reference light and the reflection spectrum differential locking method (PDH) are used to lock the FP cavity. The system is complex and has poor long-term stability.

[0013] The passively stabilized FP cavity uses ultra-low expansion (ULE) glass as a spacer and has no moving parts. As long as the temperature is stable, the FP cavity can be kept stable for a long period of time. For the passively stabilized FP cavity, it is difficult to make two identical FP cavities in reality. The best way is to pass the light that passed through the FP cavity for the first time through the same FP cavity again. Doing so will have the following problems:

[0014] If the light passing through the first FP cavity is returned to the first FP cavity through a Faraday rotator and a half-wavelength plate, although the reflection and oscillation on the surfaces of the two FP cavities can be isolated, the reflected light will be mixed into the final output light, causing the second filtering failure. Summary of the invention

[0015] In order to solve the problem that the side mode suppression ratio of a single-pass FP cavity is insufficient and thus leads to inaccurate spectrum calibration, the present invention proposes an optical comb frequency interval multiplication device and an implementation method thereof.

[0016] An object of the present invention is to provide an optical comb frequency interval multiplication device.

[0017] The optical comb frequency interval multiplication device of the present invention comprises: an optical frequency comb, a beam splitter, a vacuum chamber and a multi-path interval multiplication branch;

[0018] A plurality of light entrance windows are provided on one side of the vacuum chamber, corresponding to each of the light entrance windows, and a plurality of light exit windows are provided on the other side opposite to the vacuum chamber; a plurality of spaced multiplication branches are located in the vacuum chamber, and each spaced multiplication branch corresponds to a pair of corresponding light entrance windows and light exit windows; each spaced multiplication branch comprises: a first polarization beam splitter, a Fabry-Perot (FP) cavity, a broadband Faraday rotator, a half-wave plate, a second polarization beam splitter, a broadband Faraday isolator, and first and second reflectors, and the optical axes of the first polarization beam splitter, the FP cavity, the broadband Faraday rotator, the half-wave plate, and the second polarization beam splitter, which are sequentially arranged along a horizontal line, are coaxial with the corresponding light entrance window and light exit window;

[0019] The optical frequency comb emits a broadband optical comb spectrum, and the polarization state of the optical comb spectrum is adjusted to horizontal polarization; the broadband optical comb spectrum is divided into multiple paths according to wavelength by a beam splitter, and one wavelength band corresponds to an interval multiplication branch; the horizontally polarized light enters the vacuum chamber through the corresponding vacuum chamber light entrance window, and is incident on the first polarization beam splitter; the horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity of the corresponding wavelength band; the frequency interval is set by adjusting the cavity length of the FP cavity to perform frequency multiplication, and the required frequency, i.e., the comb teeth, is selected, and the light after frequency multiplication The comb spectrum is first transmitted to the broadband Faraday rotator and the half-wave plate; the polarization state is converted from horizontal polarization to vertical polarization by the broadband Faraday rotator and the half-wave plate, and then transmitted to the second polarization beam splitter; the vertically polarized light returned from the incident surface of the FP cavity is reflected to the second reflector by the first polarization beam splitter; the vertically polarized light transmitted from the exit surface of the FP cavity is reflected by the second polarization beam splitter, and then reflected to the broadband Faraday isolator by the first reflector, and the vertically polarized light returned from the incident surface of the FP cavity is transmitted to the second reflector by the broadband Faraday isolator. The vertical polarized light reflected from the incident surface of the FP cavity is isolated to prevent the vertical polarized light reflected from the incident surface of the FP cavity from returning to the exit surface of the FP cavity, thereby avoiding the reflection light of the incident surface of the FP cavity from mixing with the signal light transmitted for the second time; the vertical polarized light transmitted from the exit surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter; the vertical polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, and is filtered for the second time through the same FP cavity, thereby realizing multiple filtering using one FP cavity to increase the side mode suppression ratio; the vertically polarized light comb spectrum passing through the FP cavity for the second time is restored to horizontally polarized light through the broadband Faraday rotator and the half-wave plate, thereby making the polarization states of the light comb spectrum passing through the FP cavity for the first time and the light comb spectrum passing through the FP cavity for the second time perpendicular to each other through the broadband Faraday rotator and the half-wave plate, thereby distinguishing the light comb spectrum passing through the FP cavity for the first time from the light comb spectrum passing through the FP cavity for the second time, and the parallel polarized light comb spectrum passing through the FP cavity for the second time is transmitted from the second polarization beam splitter as the calibration light output.

[0020] The FP cavity includes two cavity mirrors and a gasket. The first cavity mirror is a plano-concave reflector with one side flat and the other side concave, and the concave side faces inward; the second cavity mirror is a flat reflector with both sides flat, and there is a certain angle between the two planes, generally 30 minutes, to prevent the sub-cavity effect. The inner surfaces of the two plane reflectors are coated with a high reflection film of the wavelength band, and the other plane reflector is coated with an anti-reflection film of the wavelength band; a gasket is arranged between the two cavity mirrors, and a vent is opened on the side of the gasket. The gasket interval defines the distance between the two cavity mirrors, that is, the cavity length of the FP cavity. The two cavity mirrors and a gasket are made of ultra-low expansion rate (ULE) glass. The frequency interval is set by adjusting the spacing between the two cavity mirrors of the FP cavity, that is, the frequency multiplication factor is set, and the required frequency is selected.

[0021] The vacuum chamber is made of stainless steel. The light entrance window and light exit window of the vacuum chamber are made of quartz glass. Both sides of the light entrance window and the light exit window are coated with broadband anti-reflection film. The light entrance window and the light exit window are fixed and sealed with the vacuum chamber by standard flanges. The vacuum chamber has an exhaust pipe, through which the vacuum chamber is evacuated to a vacuum better than 10 -5 Pa, after evacuation, the vacuum chamber will be maintained by an ion pump.

[0022] Broadband Faraday rotator and broadband Faraday isolator use magneto-optical material cerium trifluoride (CeF 3 ), has a broad transparent band in visible light.

[0023] Another object of the present invention is to provide a method for realizing an optical comb frequency interval multiplication device.

[0024] The method for implementing the optical comb frequency interval multiplication device of the present invention comprises the following steps:

[0025] 1) The optical frequency comb emits a broadband optical comb spectrum, and the polarization state of the optical comb spectrum is adjusted to horizontal polarization;

[0026] 2) The broadband optical comb spectrum is divided into multiple paths according to wavelength by an optical splitter, and one wavelength band corresponds to one interval multiplication branch;

[0027] 3) Entering the vacuum chamber through the light entrance window of the corresponding vacuum chamber, the horizontally polarized light is incident on the first polarization beam splitter;

[0028] The horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity of the corresponding wavelength band;

[0029] 4) Frequency multiplication is performed by adjusting the cavity length of the FP cavity to set the frequency interval, and the required frequency, i.e., the comb teeth, is selected. The frequency-multiplied optical comb spectrum is first transmitted to the broadband Faraday rotator and the half-wave plate;

[0030] 5) The polarization state is converted from horizontal polarization to vertical polarization through a broadband Faraday rotator and a half-wave plate, and transmitted to the second polarization beam splitter; the vertically polarized light returned from the incident surface of the FP cavity is reflected to the second reflector through the first polarization beam splitter;

[0031] 6) The vertical polarized light transmitted from the exit surface of the FP cavity is reflected by the second polarization beam splitter, and then reflected by the first reflector to the broadband Faraday isolator. The broadband Faraday isolator isolates the vertical polarized light returned from the incident surface of the FP cavity, preventing the vertical polarized light reflected from the incident surface of the FP cavity from returning to the exit surface of the FP cavity, thereby preventing the reflected light from the incident surface of the FP cavity from mixing with the signal light transmitted for the second time;

[0032] 7) The vertically polarized light transmitted from the output surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter;

[0033] 8) The vertically polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, and is filtered for the second time by the same FP cavity, thereby realizing multiple filtering using one FP cavity to increase the side mode suppression ratio;

[0034] 9) The vertically polarized light comb spectrum that passes through the FP cavity for the second time passes through a broadband Faraday rotator and a half-wave plate and is restored to horizontally polarized light, so that the polarization states of the light comb spectrum that passes through the FP cavity for the first time and the light comb spectrum that passes through the FP cavity for the second time are perpendicular to each other through the broadband Faraday rotator and the half-wave plate, thereby distinguishing the light comb spectrum that passes through the FP cavity for the first time from the light comb spectrum that passes through the FP cavity for the second time, and the parallel polarized light comb spectrum that passes through the FP cavity for the second time passes through the second polarization beam splitter and is output as calibration light.

[0035] In step 3), the vacuum chamber is evacuated to a temperature better than 10 -5 Pa.

[0036] In step 4), the FP cavity includes two cavity mirrors and a gasket, and the distance between the two cavity mirrors, that is, the cavity length of the FP cavity, is defined by the gasket, and the frequency interval is set, that is, the frequency multiplication multiple is set.

[0037] Advantages of the present invention:

[0038] The present invention ingeniously uses the cooperation of a broadband Faraday rotator and a half-wave plate to re-introduce the frequency-doubled spectrum that passes through the FP cavity for the first time into the same FP cavity, thereby doubling the side mode suppression ratio and avoiding inter-stage oscillation and collinear interference; it can achieve long-term stable frequency interval doubling; the generated calibration spectrum lines can be used for planetary mass measurement, dark matter discovery, precise ranging, low-noise microwave generation, high-speed analog-to-digital conversion, etc.; the entire system structure of the present invention is concise and the adjustment method is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of an interval multiplication branch of an embodiment of the optical comb frequency interval multiplication device of the present invention;

[0040] Figure 2 The figure is a schematic diagram of two interval multiplication branches of an embodiment of the optical comb frequency interval multiplication device of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0042] like Figure 1As shown, the optical comb frequency interval multiplication device of this embodiment includes: an optical frequency comb, a beam splitter, a vacuum chamber and two interval multiplication branches;

[0043] A plurality of light entrance windows are provided on one side of the vacuum chamber, corresponding to each of the light entrance windows, and a plurality of light exit windows are provided on the other side opposite to the vacuum chamber, corresponding to the outputs of the frequency multiplication branches of each wavelength; two spaced multiplication branches are located in the vacuum chamber, and each spaced multiplication branch corresponds to a pair of corresponding light entrance windows and light exit windows; each spaced multiplication branch comprises: a first polarization beam splitter, a Fabry-Perot (FP) cavity, a broadband Faraday rotator, a half-wave plate, a second polarization beam splitter, a broadband Faraday isolator, and a first and a second reflector, all of which are located in the vacuum chamber, and the optical axes of the first polarization beam splitter, the FP cavity, the half-wave plate, and the second polarization beam splitter, which are sequentially placed along a horizontal line, are coaxial with the corresponding light entrance window and light exit window.

[0044] The optical frequency comb emits a broadband optical comb spectrum with a frequency interval of 1 GHz, and the polarization state of the optical comb spectrum is horizontal polarization; the broadband optical comb spectrum is divided into two paths according to the wavelength by a beam splitter, a wavelength of 560 to 900 nm optical comb spectrum and a wavelength of 400 to 550 nm optical comb spectrum, and the two wavelength bands correspond to one interval multiplication branch respectively; the horizontally polarized light enters the vacuum chamber through the corresponding light entrance window of the vacuum chamber, and is incident on the first polarization beam splitter; the horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity; the frequency interval is set by adjusting the cavity length of the FP cavity, that is, the frequency multiplication is set. The frequency is multiplied by multiples of , and the required frequency is selected. One channel is multiplied by 30 times to become 30GHz, and the other channel is multiplied by 45 times to become 45GHz. The optical comb spectrum after frequency multiplication is first transmitted to the broadband Faraday rotator and the half-wave plate; the polarization state is converted from horizontal polarization to vertical polarization through the broadband Faraday rotator and the half-wave plate, and then transmitted to the second polarization beam splitter; the vertically polarized light returned from the incident surface of the FP cavity is reflected by the first polarization beam splitter to the second reflector; the vertically polarized light transmitted from the exit surface of the FP cavity is reflected by the second polarization beam splitter, and then transmitted to the first reflector. The vertical polarized light reflected from the incident surface of the FP cavity is reflected by the second reflector to the broadband Faraday isolator, and the broadband Faraday isolator is used to isolate the vertical polarized light returned from the incident surface of the FP cavity, so as to prevent the vertical polarized light reflected from the incident surface of the FP cavity from returning to the exit surface of the FP cavity, thereby avoiding the reflection light of the incident surface of the FP cavity from mixing with the signal light transmitted for the second time; the vertical polarized light transmitted from the exit surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter; the vertical polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, and is filtered for the second time through the same FP cavity , realizing multiple filtering with one FP cavity to increase the side mode suppression ratio; the vertically polarized light comb spectrum that passes through the FP cavity for the second time passes through a broadband Faraday rotator and a half-wave plate to be restored to horizontally polarized light, so that the polarization states of the light comb spectrum that passes through the FP cavity for the first time and the light comb spectrum that passes through the FP cavity for the second time are perpendicular to each other through the broadband Faraday rotator and the half-wave plate, thereby distinguishing the light comb spectrum that passes through the FP cavity for the first time from the light comb spectrum that passes through the FP cavity for the second time, and the parallel polarized light comb spectrum that passes through the FP cavity for the second time passes through the second polarization beam splitter to be output as calibration light.

[0045] The FP cavity includes two cavity mirrors and a gasket. The first cavity mirror is a plano-concave reflector with one side flat and the other side concave, and the concave side faces inward. The second cavity mirror is a plane reflector with both sides flat. There is a certain angle between the two planes (usually 30 minutes). The inner surfaces of the two plane reflectors are coated with a high reflection film of the wavelength band, and the other surfaces are coated with an anti-reflection film of the wavelength band. The plane reflection of the first cavity mirror serves as the incident surface of the FP cavity, and the outer plane reflector of the second cavity mirror serves as the exit surface of the FP cavity. A gasket is arranged between the two cavity mirrors, and a vent is opened on the side of the gasket. The gasket interval defines the distance between the two cavity mirrors, that is, the cavity length of the FP cavity. The two cavity mirrors and a gasket are made of ultra-low expansion rate (ULE) glass. The frequency interval is set by adjusting the spacing between the two cavity mirrors of the FP cavity, and the required frequency is selected.

[0046] The vacuum chamber is made of stainless steel. The light entrance window and light exit window of the vacuum chamber are made of quartz glass. Both sides of each window are coated with broadband anti-reflection film. The light entrance window and light exit window are fixed and sealed with the vacuum chamber by standard flanges. The vacuum chamber has an exhaust pipe, through which the vacuum chamber is evacuated to a vacuum better than 10 -5 Pa, after evacuation, the vacuum chamber will be maintained by an ion pump.

[0047] Broadband Faraday rotator and broadband Faraday isolator using magneto-optical material CeF 3 , has a wide transparent band in visible light.

[0048] The beam splitter uses a two-color filter.

[0049] Finally, it should be noted that the purpose of publishing the embodiments is to help further understand the present invention, but those skilled in the art can understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments, and the scope of protection claimed by the present invention shall be subject to the scope defined in the claims.

Claims

1. A light comb frequency interval multiplication device, characterized in that: The optical comb frequency interval multiplication device comprises: an optical frequency comb, a beam splitter, a vacuum chamber and multiple interval multiplication branches; A plurality of light entrance windows are provided on one side of the vacuum chamber, corresponding to each of the light entrance windows, and a plurality of light exit windows are provided on the other side opposite to the vacuum chamber; a plurality of spaced multiplication branches are located in the vacuum chamber, and each spaced multiplication branch corresponds to a pair of corresponding light entrance windows and light exit windows; each spaced multiplication branch comprises: a first polarization beam splitter, a Fabry-Perot FP cavity, a broadband Faraday rotator, a half-wave plate, a second polarization beam splitter, a broadband Faraday isolator, and first and second reflectors, and the optical axes of the first polarization beam splitter, the FP cavity, the broadband Faraday rotator, the half-wave plate, and the second polarization beam splitter, which are sequentially arranged along a horizontal line, are coaxial with the corresponding light entrance window and light exit window; The optical frequency comb emits a broadband optical comb spectrum, and the polarization state of the optical comb spectrum is adjusted to horizontal polarization; the broadband optical comb spectrum is divided into multiple paths according to wavelength by a beam splitter, and one wavelength band corresponds to an interval multiplication branch; the horizontally polarized light enters the vacuum chamber through the corresponding vacuum chamber light entrance window, and is incident on the first polarization beam splitter; the horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity of the corresponding wavelength band; the frequency interval is set by adjusting the cavity length of the FP cavity to perform frequency multiplication, and the required frequency, i.e., the comb teeth, is selected, and the light after frequency multiplication The comb spectrum is first transmitted to the broadband Faraday rotator and the half-wave plate; the polarization state is converted from horizontal polarization to vertical polarization by the broadband Faraday rotator and the half-wave plate, and then transmitted to the second polarization beam splitter; the vertically polarized light returned from the incident surface of the FP cavity is reflected to the second reflector by the first polarization beam splitter; the vertically polarized light transmitted from the exit surface of the FP cavity is reflected by the second polarization beam splitter, and then reflected to the broadband Faraday isolator by the first reflector, and the vertically polarized light returned from the incident surface of the FP cavity is transmitted to the second reflector by the broadband Faraday isolator. The vertical polarized light reflected from the incident surface of the FP cavity is isolated to prevent the vertical polarized light reflected from the incident surface of the FP cavity from returning to the exit surface of the FP cavity, thereby avoiding the reflection light of the incident surface of the FP cavity from mixing with the signal light transmitted for the second time; the vertical polarized light transmitted from the exit surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter; the vertical polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, and is filtered for the second time through the same FP cavity, thereby realizing multiple filtering using one FP cavity to increase the side mode suppression ratio; the vertically polarized light comb spectrum passing through the FP cavity for the second time is restored to horizontally polarized light through the broadband Faraday rotator and the half-wave plate, thereby making the polarization states of the light comb spectrum passing through the FP cavity for the first time and the light comb spectrum passing through the FP cavity for the second time perpendicular to each other through the broadband Faraday rotator and the half-wave plate, thereby distinguishing the light comb spectrum passing through the FP cavity for the first time from the light comb spectrum passing through the FP cavity for the second time, and the parallel polarized light comb spectrum passing through the FP cavity for the second time is transmitted from the second polarization beam splitter as the calibration light output.

2. The optical comb frequency interval multiplication device according to claim 1, characterized in that: The FP cavity includes two cavity mirrors and a gasket. The first cavity mirror is a plano-concave reflector with one side flat and the other side concave, and the concave side faces inward; the second cavity mirror is a plane reflector with both sides flat, and there is a certain angle between the two planes, generally 30 minutes, to prevent the sub-cavity effect. The inner surfaces of the two plane reflectors are coated with a high-reflection film of the wavelength band, and the other plane reflector is coated with an anti-reflection film of the wavelength band; a gasket is arranged between the two cavity mirrors, and a vent hole is opened on the side of the gasket.

3. The optical comb frequency interval multiplication device according to claim 1, characterized in that: The vacuum chamber adopts a stainless steel structure, and the light entrance window and the light exit window of the vacuum chamber adopt quartz glass. Both sides of the light entrance window and the light exit window are plated with broadband anti-reflection films.

4. The optical comb frequency interval multiplication device according to claim 1, characterized in that: The light entrance window and the light exit window are fixed and sealed to the vacuum chamber by using standard flanges.

5. The optical comb frequency interval multiplication device according to claim 1, characterized in that: The vacuum chamber is provided with an exhaust pipe, through which the vacuum chamber is evacuated to a vacuum better than 10 -5 Pa.

6. The optical comb frequency interval multiplication device according to claim 1, characterized in that: The broadband Faraday rotator and the broadband Faraday isolator are made of magneto-optical materials.

7. A method for implementing the optical comb frequency interval multiplication device as claimed in claim 1, characterized in that: The implementation method comprises the following steps: 1) The optical frequency comb emits a broadband optical comb spectrum, and the polarization state of the optical comb spectrum is adjusted to horizontal polarization; 2) The broadband optical comb spectrum is divided into multiple paths according to wavelength by an optical splitter, and one wavelength band corresponds to one interval multiplication branch; 3) Entering the vacuum chamber through the light entrance window of the corresponding vacuum chamber, the horizontally polarized light is incident on the first polarization beam splitter; The horizontally polarized light passes through the first polarization beam splitter and is transmitted to the FP cavity of the corresponding wavelength band; 4) Frequency multiplication is performed by adjusting the cavity length of the FP cavity to set the frequency interval, and the required frequency, i.e., the comb teeth, is selected. The frequency-multiplied optical comb spectrum is first transmitted to the broadband Faraday rotator and the half-wave plate; 5) The polarization state is converted from horizontal polarization to vertical polarization through a broadband Faraday rotator and a half-wave plate, and transmitted to the second polarization beam splitter; the vertically polarized light returned from the incident surface of the FP cavity is reflected to the second reflector through the first polarization beam splitter; 6) The vertical polarized light transmitted from the exit surface of the FP cavity is reflected by the second polarization beam splitter, and then reflected by the first reflector to the broadband Faraday isolator. The broadband Faraday isolator isolates the vertical polarized light returned from the incident surface of the FP cavity, preventing the vertical polarized light reflected from the incident surface of the FP cavity from returning to the exit surface of the FP cavity surface. This prevents the reflected light from the incident surface of the FP cavity from mixing with the signal light that is transmitted for the second time; 7) The vertically polarized light transmitted from the output surface of the FP cavity is reflected by the second reflector through the broadband Faraday isolator and transmitted to the first polarization beam splitter; 8) The vertically polarized light is reflected by the first polarization beam splitter and transmitted to the same FP cavity again, and is filtered for the second time by the same FP cavity, thereby realizing multiple filtering using one FP cavity to increase the side mode suppression ratio; 9) The vertically polarized light comb spectrum that passes through the FP cavity for the second time passes through a broadband Faraday rotator and a half-wave plate and is restored to horizontally polarized light, so that the polarization states of the light comb spectrum that passes through the FP cavity for the first time and the light comb spectrum that passes through the FP cavity for the second time are perpendicular to each other through the broadband Faraday rotator and the half-wave plate, thereby distinguishing the light comb spectrum that passes through the FP cavity for the first time from the light comb spectrum that passes through the FP cavity for the second time, and the parallel polarized light comb spectrum that passes through the FP cavity for the second time passes through the second polarization beam splitter and is output as calibration light.

8. The implementation method according to claim 7, characterized in that: In step 3), the vacuum chamber is evacuated to a temperature better than 10 -5 Pa.

9. The implementation method according to claim 7, characterized in that: In step 4), the FP cavity includes two cavity mirrors and a gasket, and the distance between the two cavity mirrors, that is, the cavity length of the FP cavity, is defined by the gasket to set the frequency multiplication multiple.

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