Integrated spectrum unit based on modulation transfer spectrum

Abstract

The invention belongs to the technical field of laser frequency stabilization, and particularly discloses an integrated spectrum unit based on a modulation transfer spectrum, a first light source assembly is used for providing pump light, and a second light source assembly is used for providing probe light. A first light source assembly, a second light source assembly, a reflection assembly, a third half-wave plate, a first polarization beam splitter, a second polarization beam splitter, a first beam splitter, a second beam splitter, an unsaturated iodine pool, a photoelectric differential detector, a first photoelectric low-noise detector and a second photoelectric low-noise detector are matched, so that the directivity and stability of light beams of the system are ensured; meanwhile, multiple times of coincidence interaction of the light beams is realized in the unsaturated iodine pool by utilizing the reflection assembly, and the interaction length is increased under the condition that the size is relatively small, so that the system is relatively simple in structure, relatively small in size and relatively low in cost, and has high thermal stability and robustness while the light beam directivity of the system is relatively good; and subsequent overall temperature control and packaging of the spectrum unit are also facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of laser frequency stabilization and relates to an integrated spectrum unit based on modulation transfer spectrum. Background Art

[0002] Establishing a laser frequency standard requires locking the laser frequency to a stable frequency reference source. Numerous laser frequency stabilization methods utilize the transition lines of gas atoms or molecules as reference sources. Three commonly used methods are saturated absorption spectroscopy (SAS), frequency modulation spectroscopy (FMS), and modulation transfer spectroscopy (MTS). SAS frequency stabilization suffers from Doppler broadening, limiting system stability. FMS frequency stabilization allows for arbitrary modulation frequencies, making the signal susceptible to environmental interference. MTS frequency stabilization, however, relies on molecular or atomic linewidths for a relatively low modulation frequency. This highly sensitive optical heterodyne spectroscopy technique utilizes third-order nonlinear four-wave mixing (FWM) to effectively suppress various technical noise in the detection system, achieving shot-noise-limited detection sensitivity. Therefore, we use the MTS frequency stabilization method to lock the laser frequency.

[0003] The laser frequency stabilization system consists of two main components: the optical path and the circuit. The optical path requires the interaction between the laser output from the oscillator and the dielectric gas of the frequency reference source, so that the output laser carries the frequency information of the dielectric gas. The circuit is a signal processing system. When the laser frequency output by the oscillator is higher or lower than the resonant frequency of the dielectric gas, the amplitude and phase of the oscillator frequency signal passing through the dielectric gas will change accordingly, generating an error signal. This error signal is transmitted to the servo system in the circuit to actively control the oscillator frequency.

[0004] The part where the dielectric gas and the laser interact is the spectral unit in the optical path. Two beams of light with different intensities are incident in opposite directions and overlap in the dielectric gas to generate an error signal. Under certain conditions, the longer the effective optical path of the laser in the dielectric gas, the greater the signal intensity, but the requirements are also higher.

[0005] At present, most optical path integrated systems, such as those developed by the German Space Agency, Figure 2The system shown integrates optical components onto a 55cm*25cm*5cm Zerodur substrate. These optical components are made of fused silica. A commercial pigtail collimator is used to input the pump and probe beams into the iodine spectroscopy unit. An optical wedge is used to adjust the optical path angle. The gas cell length is 30cm, and the beam makes three round trips to form an effective optical path. The iodine cell uses a saturated iodine cell with a cold-point temperature of -13°C. The MTS error signal is detected by a low-noise detector (NC). The laser frequency is then locked to the R(56)32-0:a1 absorption line using a servo control system.

[0006] However, due to the complex structure of the device, the directionality and stability of the laser beam are poor. Summary of the Invention

[0007] The purpose of the present invention is to provide an integrated spectral unit based on modulation transfer spectroscopy, which can increase the effective optical path of the laser beam in the dielectric gas, make the system structure simpler and more miniaturized, and at the same time have strong thermal stability and robustness, ensuring the directionality and stability of the laser beam, good practicality, and worthy of promotion.

[0008] To achieve the above objectives, the specific technical solutions provided by the present invention are as follows: An integrated spectral unit based on modulation transfer spectroscopy includes a photoelectric differential detector, a first photoelectric low-noise detector, a non-saturated iodine cell, and a second photoelectric low-noise detector. The unit also includes: a first light source assembly, a first polarization beam splitter, a first beam splitter, and a second reflector, which are sequentially arranged and located on a first optical path; a second light source assembly, a second polarization beam splitter, a second beam splitter, and a first reflector, which are sequentially arranged and located on a second optical path; and a reflective assembly, which is distributed on one opposite side of the non-saturated iodine cell. Among them, the first light source assembly is used to provide pump light, and the second light source assembly is used to provide detection light. The pump light is transmitted to the first beam splitter through the first polarization beam splitter to separate the reflected light and the transmitted light. The reflected light enters the first photoelectric low-noise detector for power stabilization, and the transmitted light is incident on the reflection assembly through the second reflector and then emitted; the detection light is separated into reflected light and transmitted light through the second polarization beam splitter, and the reflected light is incident on the photoelectric differential detector as reference light. The transmitted light is separated into reflected light and transmitted light through the second beam splitter, and the reflected light is incident on the second photoelectric low-noise detector for power stabilization. The transmitted light is incident on the reflection assembly through the first reflector, and enters the non-saturated iodine pool after multiple reciprocating cycles under the action of the reflection assembly and then emitted to the second reflector. The transmitted light through the first beam splitter is reflected by the first polarization beam splitter to the photoelectric differential detector, which is compared with the reference light and then outputs an error signal.

[0009] Furthermore, a third half-wave plate is provided on the second optical path, and the third half-wave plate is located between the second polarization beam splitter and the second beam splitter, and is used to change the polarization state of the transmitted light.

[0010] Furthermore, the reflective assembly includes a third reflector, a fifth reflector, a fourth reflector and a hollow ridge reflector. The hollow ridge reflector is located on one side of the unsaturated iodine pool and is used to achieve 180° deflection of light. The third reflector, the fifth reflector and the fourth reflector are located on the other side of the unsaturated iodine pool and are used to cooperate with the hollow ridge reflector to achieve multiple passages of light in the unsaturated iodine pool and multiple overlaps of the light path.

[0011] Further, the first reflector, the second reflector, the third reflector, the fifth reflector and the fourth reflector are plane mirrors.

[0012] Furthermore, the first light source assembly includes a first collimator, a first polarizer, and a first half-wave plate, which are arranged in sequence and located on a first optical path. After the first collimator emits the pump light, it passes through the first polarizer and the first half-wave plate in sequence to achieve a change in the polarization state of the pump light.

[0013] Furthermore, the second light source assembly includes a second collimator, a second polarizer, and a second half-wave plate, which are arranged in sequence and located on the second optical path. After the second collimator emits the detection light, it passes through the second polarizer and the second half-wave plate in sequence to achieve a change in the polarization state of the detection light.

[0014] Furthermore, the first light source assembly, the second light source assembly, the reflection assembly, the third half-wave plate, the first polarization beam splitter, the first reflector, the second reflector, the second polarization beam splitter, the first beam splitter, the second beam splitter, the non-saturated iodine cell, the photoelectric differential detector, the first photoelectric low-noise detector and the second photoelectric low-noise detector are arranged on a substrate.

[0015] Furthermore, the first reflector, the second reflector, the third reflector and the fourth reflector are located on the same horizontal plane, and the distances from the first reflector, the second reflector, the third reflector and the fourth reflector to the substrate are greater than the distance from the fifth reflector to the substrate.

[0016] Furthermore, the base is respectively connected to the first collimation head, the second collimation head, the first polarizer, the second polarizer, the first half-wave plate, the second half-wave plate and the third half-wave plate, the non-saturated iodine cell, the photoelectric differential detector, the first photoelectric low-noise detector and the second photoelectric low-noise detector through a mounting frame.

[0017] Furthermore, an adhesive layer is provided between the mounting frame and the base.

[0018] Compared with the prior art, the integrated spectral unit based on modulation transfer spectrum of the present invention utilizes a first light source component, a second light source component, a reflection component, a first polarization beam splitter, a second polarization beam splitter, a first beam splitter, a second beam splitter, a non-saturated iodine pool, a photoelectric differential detector, a first photoelectric low-noise detector and a second photoelectric low-noise detector to cooperate, thereby ensuring the directionality and stability of the system light beam. At the same time, due to the use of the reflection component, the laser beam realizes multiple overlapping interactions in the non-saturated iodine pool, and the effective optical path of the laser beam in the dielectric gas is increased while ensuring the small size of the system, making the system structure simpler and more miniaturized. At the same time, it has strong thermal stability and robustness, ensuring the directionality and stability of the laser beam, and facilitating the subsequent overall temperature control and packaging of the spectral unit. It is highly practical and worthy of promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the overall structure provided by the present invention.

[0020] Figure 2 This is a schematic diagram of the structure of the related prior art provided by the present invention.

[0021] Reference numerals: 1. First collimator; 2. Second collimator; 3. First polarizer; 4. Second polarizer; 5. First half-wave plate; 6. Second half-wave plate; 7. Third half-wave plate; 8. First polarization beam splitter; 9. First beam splitter; 10. Second polarization beam splitter; 11. Second beam splitter; 12. First reflector; 13. Second reflector; 14. Third reflector; 15. Fifth reflector; 16. Fourth reflector; 19. Unsaturated iodine cell; 20. Hollow roof reflector; 21. Photoelectric differential detector; 22. First photoelectric low-noise detector; 23. Second photoelectric low-noise detector; 24. Substrate. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solution of the present invention and to implement it, the following Figure 1 , clearly and comprehensively describe the technical solutions in the present invention.

[0023] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0024] Further, it needs to be further pointed out that, in the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B: "and / or" in the text only describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can mean that A exists alone, A and B exist together, and B exists alone, and in addition, in the description of the embodiments of the present application, "multiple" means two or more than two.

[0025] The following terms "first", "second", "third", "fourth" are only for description purpose, and cannot be understood as implying or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second", "third", "fourth" can explicitly or implicitly include one or more of the features, and in the description of the present application, unless otherwise specified, the meaning of "multiple" is two or more than two.

[0026] Embodiment 1 The present application provides an integrated optical spectrum unit based on modulation transfer spectrum, as shown in Figure 1 As shown, it comprises a substrate 24 and a first collimating head 1, a second collimating head 2, a first polarizer 3, a second polarizer 4, a first half-wave plate 5, a second half-wave plate 6 and a third half-wave plate 7, a first polarization beam splitter 8, a second polarization beam splitter 10, a first beam splitter 9, a second beam splitter 11, a non-saturated iodine cell 19, a first mirror 12, a second mirror 13, a third mirror 14, a fifth mirror 15, a fourth mirror 16, a hollow ridge mirror 20, a photoelectric differential detector 21, a first photoelectric low noise detector 22 and a second photoelectric low noise detector 23 arranged on the substrate 24, wherein the first light source assembly, the first polarization beam splitter 8, the first beam splitter 9 and the second mirror 13 are arranged in sequence and located on the first light path, the second light source assembly, the second polarization beam splitter 10, the second beam splitter 11 and the first mirror 12 are arranged in sequence and located on the second light path, and the second light path is parallel to the first light path.

[0027] Preferably, the size of the substrate 24 is 330mm*110mm*30mm.

[0028] Among them, the first collimator head 1, the first polarizer 3, and the first half-wave plate 5, which are arranged in sequence and located on the same optical path, serve as the first light source component, and the second collimator head 2, the second polarizer 4, and the second half-wave plate 6, which are arranged in sequence and located on the same optical path, serve as the second light source component. The first collimator head 1 is used to provide pump light with relatively high optical power, and the second collimator head 2 is used to provide probe light with relatively low optical power within a certain spectral range. The power and frequency components of the pump light and the probe light are inconsistent. After the first collimator head 1 emits the pump light, it passes through the first polarizer 3 and the first half-wave plate 5 in sequence to change the polarization state of the pump light. After the second collimator head 2 emits the probe light, it passes through the second polarizer 4 and the second half-wave plate 6 in sequence to change the polarization state of the probe light.

[0029] Among them, the third reflector 14, the fifth reflector 15, the fourth reflector 16 and the hollow roof reflector 20 work together to form a reflective component. The length direction of the unsaturated iodine pool 19 is parallel to the first light path and the second light path. The hollow roof reflector 20 is located on one side of the length direction of the unsaturated iodine pool 19, and the first reflector 12, the second reflector 13, the third reflector 14, the fifth reflector 15 and the fourth reflector 16 are located on the other side of the length direction of the unsaturated iodine pool 19.

[0030] The pump light passes through the first polarizer 3 and the first half-wave plate 5, completely transmits the first polarization beam splitter 8, and is separated into reflected light and transmitted light by the first beam splitter 9. The reflected light enters the first photoelectric low-noise detector 22 for power stabilization, and the transmitted light enters the unsaturated iodine pool 19 through the second reflector 13 and the fourth reflector 16, and then passes through the hollow roof reflector 20 to turn 180°, and then is reflected by the fourth reflector 16 and the fifth reflector 15 to enter the unsaturated iodine pool 19 again, and finally passes through the hollow roof reflector 20 to turn 180° to be emitted.

[0031] The detection light passes through the second polarizer 4, the second half-wave plate 6, and the second polarization beam splitter 10 to separate the reflected light and the transmitted light. The reflected light is incident on the photoelectric differential detector 21 as the reference light. The transmitted light changes its polarization state through the third half-wave plate 7 and then passes through the second beam splitter 11 to separate the reflected light and the transmitted light. The reflected light is incident on the second photoelectric low-noise detector 23 for power stabilization. The transmitted light passes through the first reflector 12 and the third reflector 14 in sequence and is incident on the non-saturated iodine pool 19. It then passes through the hollow roof reflector 20 and turns 180° to be reflected by the fifth reflector 15 and the fourth reflector. 16 is reflected, and is incident on the non-saturated iodine pool 19 again, and then passes through the non-saturated iodine pool 19 in the opposite direction of 180° through the hollow roof reflector 20 to enter the fourth reflector 16, and is finally reflected by the second reflector 13. The transmitted light passes through the first beam splitter 9 and is completely reflected by the first polarization beam splitter 8 to the photoelectric differential detector 21. After comparison with the reference light in the photoelectric differential detector 21, an error signal is output and transmitted to the feedback control system in the signal processing system. After signal processing by the feedback control system, a control signal is generated to actively control the laser frequency output by the oscillator.

[0032] As a further refinement of the above embodiment, the first reflector 12, the second reflector 13, the third reflector 14, and the fourth reflector 16 are plane mirrors, and the first reflector 12, the second reflector 13, the third reflector 14, and the fourth reflector 16 are located on the same horizontal plane. The distances from the first reflector 12, the second reflector 13, the third reflector 14, and the fourth reflector 16 to the substrate 24 are greater than the distances from the fifth reflector 15 to the substrate 24. This device can greatly reduce the spatial dimensions. By using the first reflector 12, the second reflector 13, the third reflector 14, the fourth reflector 16, and the fifth reflector 15 of different heights and the hollow roof reflector 20 that realizes 180° steering, the laser beam passes through the length direction of the unsaturated iodine pool 19 four times, achieving a longer effective optical path, and having a good overlap, thereby ensuring a large signal level. In addition, the unsaturated iodine pool 19 is adopted so that the iodine pool does not need to be temperature-controlled separately, ensuring that the spectrum unit can be subjected to overall temperature control and packaging in the future, thereby reducing costs.

[0033] Furthermore, the base 24 is respectively connected to the first collimating head 1, the second collimating head 2, the first polarizer 3, the second polarizer 4, the first half-wave plate 5, the second half-wave plate 6 and the third half-wave plate 7, the unsaturated iodine cell 19, the photoelectric differential detector 21, the first photoelectric low-noise detector 22 and the second photoelectric low-noise detector 23 through the mounting frame, and the first polarization beam splitter 8, the second polarization beam splitter 10, the first beam splitter 9, the second beam splitter 11, the first reflector 12, the second reflector 13, the third reflector 14, the fifth reflector 15, the fourth reflector 16 and the hollow roof reflector 20 are directly bonded to the base 24.

[0034] As a further refinement of the above embodiment, the mounting frame is made of invar material, and an adhesive layer made of epoxy resin is arranged between the mounting frame and the base 24, and the mounting frame is used to fix various lenses and the non-saturated iodine cell 19, and the epoxy resin is used to bond various components to improve the thermal stability of the system.

[0035] It should be noted that in the present application, the light is divided into reflected light and transmitted light by the individual action of the first polarization beam splitter 8 and the second polarization beam splitter 10, wherein the reflected light is in S polarization state, and the transmitted light is in P polarization state.

[0036] The first beam splitter 9 and the second beam splitter 11 simply split the light in proportion.

[0037] The first collimating head 1 and the second collimating head 2 are optical fiber devices, which are light beam input units.

[0038] The first polarizer 3 and the second polarizer 4 can ensure the polarization state of the light beam, the first half-wave plate 5 adjusts the polarization state of the pump light so that it is completely transmitted through the first polarization beam splitter 8, and the second half-wave plate 6 adjusts the polarization state of the probe light so that when it passes through the polarization beam splitter, part of it is reflected into the photoelectric differential detector 21 as reference light, and the remaining transmitted light passes through the third half-wave plate 7, its polarization state changes, and then passes through the second beam splitter 11, the reflected light enters the second photoelectric low-noise detector 23 for power stabilization. The transmitted light is reflected by the first mirror 12, the third mirror 14, the hollow ridge mirror 20, the fifth mirror 15, the fourth mirror 16, the hollow ridge mirror 20, the fourth mirror 16, the second mirror 13 in turn, and then passes through the first beam splitter 9, the transmitted light is completely reflected by the first polarization beam splitter 8, and the reason for this complete reflection is that the transmitted light after the probe light passes through the second polarization beam splitter 10 is in P polarization state, and after passing through the third half-wave plate 7, the polarization state changes to S polarization state, and the light in S polarization state can be completely reflected by the first polarization beam splitter 8.

[0039] In addition, it should be noted that the reflected light of the probe light passing through the first beam splitter 9 is not shown in the figure, because it is not needed, and for the probe light, we only need the transmitted light after passing through the first beam splitter 9.

[0040] Overall, the present application has the following beneficial effects: The present invention utilizes the first light source assembly, the second light source assembly, the reflecting assembly, the third half-wave plate 7, the first polarization beam splitter 8, the second polarization beam splitter 10, the first beam splitter 9, the second beam splitter 11, the unsaturated iodine pool 19, the photoelectric differential detector 21, the first photoelectric low-noise detector 22 and the second photoelectric low-noise detector 23 to cooperate, ensure that the directivity and stability of the system beam, simultaneously because the reflecting assembly realizes the multiple overlap interactions of light beams in the unsaturated iodine pool 19, when ensuring that the system size is small, the length of interaction is also increased, the system structure is made simpler, while making the system beam directivity better, there is strong thermal stability, robustness, also facilitates the follow-up overall temperature control and packaging of the spectral unit. In addition, the product obtained by the scheme provided by the present invention, its overall size is 330mm*110mm*80mm, and volume is 30% of the product of the existing minimum model, greatly reduces the volume of product, makes the product more miniaturized.

[0041] It will be understood that the present invention is described through some embodiments, and those skilled in the art will appreciate that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention.

[0042] Furthermore, these features and embodiments may be modified to suit specific circumstances and materials under the teachings of the present invention without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present invention are intended to be protected by the present invention.

Claims

1. An integrated spectral unit based on modulation transfer spectroscopy, characterized in that: The invention comprises a photoelectric differential detector (21), a first photoelectric low-noise detector (22), a non-saturated iodine pool (19) and a second photoelectric low-noise detector (23), and further comprises: a first light source assembly, a first polarization beam splitter (8), a first beam splitter (9) and a second reflector (13) arranged in sequence and located on a first optical path; a second light source assembly, a second polarization beam splitter (10), a second beam splitter (11) and a first reflector (12) arranged in sequence and located on a second optical path; and a reflector assembly distributed on one opposite side of the non-saturated iodine pool (19); The first light source assembly provides pump light, and the second light source assembly provides detection light. The pump light is transmitted through the first polarization beam splitter (8) to the first beam splitter (9) to separate the reflected light and the transmitted light. The reflected light enters the first photoelectric low-noise detector (22) for power stabilization. The transmitted light is incident on the reflection assembly through the second reflector (13) and then emitted. The detection light is separated into reflected light and transmitted light through the second polarization beam splitter (10). The reflected light is incident on the photoelectric differential detector (21) as reference light. The transmitted light is separated into reflected light and transmitted light through the second beam splitter (11). The reflected light is incident on the second photoelectric low-noise detector (23) for power stabilization. The transmitted light is incident on the reflection assembly through the first reflector (12). After being repeatedly reciprocated by the reflection assembly, it enters the non-saturated iodine pool (19) and then is emitted to the second reflector (13). The transmitted light passing through the first beam splitter (9) is reflected by the first polarization beam splitter (8) to the photoelectric differential detector (21) and outputs an error signal after being compared with the reference light.

2. The integrated spectral unit based on modulation transfer spectroscopy according to claim 1, characterized in that: A third half-wave plate (7) is provided on the second optical path. The third half-wave plate (7) is located between the second polarization beam splitter (10) and the second beam splitter (11) and is used to change the polarization state of the transmitted light.

3. The integrated spectral unit based on modulation transfer spectroscopy according to claim 2, characterized in that: The reflective assembly comprises a third reflector (14), a fifth reflector (15), a fourth reflector (16) and a hollow ridge reflector (20), wherein the hollow ridge reflector (20) is located on one side of the non-saturated iodine pool (19) and is used to realize 180-degree deflection of light, and the third reflector (14), the fifth reflector (15) and the fourth reflector (16) are located on the other side of the non-saturated iodine pool (19) and are used to cooperate with the hollow ridge reflector (20) to realize multiple passages of light in the non-saturated iodine pool (19) and multiple overlaps of light paths.

4. The integrated spectral unit based on modulation transfer spectroscopy according to claim 3, characterized in that: The first reflector (12), the second reflector (13), the third reflector (14), the fifth reflector (15) and the fourth reflector (16) are plane mirrors.

5. The integrated spectral unit based on modulation transfer spectroscopy according to claim 3, characterized in that: The first light source assembly comprises a first collimator (1), a first polarizer (3), and a first half-wave plate (5) which are sequentially arranged and located on a first optical path; after the light is emitted through the first collimator (1), it passes through the first polarizer (3) and the first half-wave plate (5) in sequence, thereby changing the polarization state of the pump light.

6. The integrated spectral unit based on modulation transfer spectroscopy according to claim 5, characterized in that: The second light source assembly comprises a second collimator (2), a second polarizer (4), and a second half-wave plate (6) which are sequentially arranged and located on a second optical path. After the light is emitted through the second collimator (2), it passes through the second polarizer (4) and the second half-wave plate (6) in sequence, thereby changing the polarization state of the detection light.

7. The integrated spectral unit based on modulation transfer spectroscopy according to claim 6, characterized in that: The first light source assembly, the second light source assembly, the reflective assembly, the third half-wave plate (7), the first polarization beam splitter (8), the first reflector (12), the second reflector (13), the second polarization beam splitter (10), the first beam splitter (9), the second beam splitter (11), the non-saturated iodine pool (19), the photoelectric differential detector (21), the first photoelectric low-noise detector (22), and the second photoelectric low-noise detector (23) are arranged on a substrate (24).

8. The integrated spectral unit based on modulation transfer spectroscopy according to claim 7, characterized in that: The first reflector (12), the second reflector (13), the third reflector (14) and the fourth reflector (16) are located on the same horizontal plane, and the distances from the first reflector (12), the second reflector (13), the third reflector (14) and the fourth reflector (16) to the substrate (24) are greater than the distance from the fifth reflector (15) to the substrate (24).

9. The integrated spectral unit based on modulation transfer spectroscopy according to claim 8, characterized in that: The substrate (24) is connected to the first collimating head (1), the second collimating head (2), the first polarizer (3), the second polarizer (4), the first half-wave plate (5), the second half-wave plate (6), the third half-wave plate (7), the non-saturated iodine pool (19), the photoelectric differential detector (21), the first photoelectric low-noise detector (22), and the second photoelectric low-noise detector (23) respectively through a mounting frame.

10. The integrated spectral unit based on modulation transfer spectroscopy according to claim 9, characterized in that: An adhesive layer is provided between the mounting frame and the base (24).

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