Modulation transfer function based integrated spectral unit

Abstract

The application belongs to the technical field of laser frequency stabilization, and specifically discloses an integrated spectrum unit based on modulation transfer spectrum, wherein a first light source assembly is used to provide pump light, and a second light source assembly is used to provide probe light; in use, the first light source assembly, the 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, a non-saturated iodine cell, a photoelectric differential detector, a first photoelectric low-noise detector and a second photoelectric low-noise detector are cooperated to ensure the directivity and stability of system light beams; meanwhile, the reflection assembly is used to realize multiple coincident interactions of light beams in the non-saturated iodine cell, so that the length of interaction is increased under the condition that the size is small, the system structure is simpler, more miniaturized and lower in cost, the system light beams have better directivity, strong thermal stability and robustness, and the overall temperature control and packaging of the spectrum unit are facilitated.

Description

TECHNICAL FIELD

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

[0002] Establishing a laser frequency standard requires locking the frequency of a laser to a stable frequency reference source, and there are many laser frequency stabilization methods using gas atoms or molecules as a reference source. The three commonly used methods are saturated absorption spectroscopy (SAS) frequency stabilization method, frequency modulation spectroscopy (FMS) frequency stabilization method and modulation transfer spectroscopy (MTS) frequency stabilization method. The SAS frequency stabilization method has a Doppler broadening effect, and the system stability of this method is limited. The modulation frequency of the FMS frequency stabilization method can be arbitrary, and the signal is easily disturbed by the external environment. The modulation frequency of the MTS frequency stabilization method is related to the molecular or atomic line width and is small, and it is a high-sensitivity heterodyne spectroscopy technology. It uses the third-order nonlinear four-wave mixing effect to effectively suppress various technical noises in the detection system, and its detection sensitivity can reach the shot noise limit. Therefore, we use the MTS frequency stabilization method to lock the laser frequency.

[0003] The laser frequency stabilization system mainly includes two parts, namely an optical path part and an electrical circuit part. The optical path part needs to interact the laser output by the oscillator with the medium gas of the frequency reference source, so that the output laser carries the frequency information of the medium gas. The electrical circuit part is a signal processing system. When the frequency of the laser output by the oscillator is higher or lower than the resonance frequency of the medium gas, the amplitude and phase of the oscillator frequency signal passing through the medium gas will change accordingly to produce an error signal. The error signal is transmitted to the servo system in the electrical circuit to actively control the frequency of the oscillator.

[0004] The part where the medium gas interacts with the laser is the spectrum unit in the optical path. Two beams of light with different intensities are incident in opposite directions, and overlap in the medium gas to produce an error signal. Under certain conditions, the longer the effective optical path of the laser in the medium gas, the larger the signal degree, but the higher the required requirements.

[0005] At present, most optical path integrated systems, such as the system developed by the German Aerospace Center, are not integrated with spectrum units. Figure 2The system shown integrates optical elements into a Zerodur base with a size of 55cm*25cm*5cm, the optical elements are all made of fused quartz, a commercial fiber collimator is used to input pump light and probe light into the iodine spectral unit, an optical wedge is used to adjust the angle of the light path, the length of the gas chamber is 30cm, the light beam goes back and forth for 3 times to form an effective optical path. The iodine cell is a saturated iodine cell, the cold finger control temperature point is-13°C, the MTS error signal is detected by a low noise detector (Noise Canceling, NC), and then a servo control system is used to lock the laser frequency to the R(56)32-0:a1 absorption line.

[0006] However, due to the complex structure of the device, the directivity and stability of the laser beam are poor. SUMMARY

[0007] The purpose of the present application is to provide an integrated spectral unit based on modulation transfer spectrum, which can increase the effective optical path of the laser beam in the medium gas, make the system structure simpler and more miniaturized, and has strong thermal stability and robustness, which ensures the directivity and stability of the laser beam, has good practicability, and is worth promoting.

[0008] To achieve the above purpose, the specific technical solutions provided by the present application are as follows:

[0009] An integrated spectral unit based on modulation transfer spectrum, comprising a photoelectric differential detector, a first photoelectric low noise detector, a non-saturated iodine cell and a second photoelectric low noise detector, further comprising: a first light source assembly, a first polarization beam splitter, a first beam splitter and a second mirror arranged in sequence and located on a first light path; a second light source assembly, a second polarization beam splitter, a second beam splitter and a first mirror arranged in sequence and located on a second light path; a reflection assembly distributed on one side of the non-saturated iodine cell;

[0010] The first light source assembly is used to provide pump light, the second light source assembly is used to provide probe light, the pump light is transmitted to the first beam splitter through the first polarization beam splitter to divide reflected light and transmitted light, the reflected light enters the first photoelectric low noise detector to stabilize the power, and the transmitted light is emitted after being incident to the reflection assembly through the second mirror; the probe light is divided into reflected light and transmitted light through the second polarization beam splitter, the reflected light is incident to the photoelectric differential detector as reference light, the transmitted light is divided into reflected light and transmitted light through the second beam splitter, the reflected light is incident to the second photoelectric low noise detector to stabilize the power, and the transmitted light is incident to the reflection assembly through the first mirror, and the transmitted light is emitted to the second mirror after entering the non-saturated iodine cell for multiple times of reciprocation through the action of the reflection assembly; the transmitted light through the first beam splitter is reflected to the photoelectric differential detector through the first polarization beam splitter, and then an error signal is output after comparison with the reference light.

[0011] Further, a third half-wave plate is arranged on the second light path, and the third half-wave plate is located between the second polarization beam splitter and the second beam splitter, and is used for changing the polarization state of the transmitted light.

[0012] Further, the reflection assembly comprises a third mirror, a fifth mirror, a fourth mirror and a hollow ridge mirror, the hollow ridge mirror is located on one side of the non-saturated iodine cell and is used for achieving 180° turning of the light, and the third mirror, the fifth mirror and the fourth mirror are located on the other side of the non-saturated iodine cell and are used for cooperating with the hollow ridge mirror to achieve multiple passing of the light in the non-saturated iodine cell and multiple superposition of the light paths.

[0013] Further, the first mirror, the second mirror, the third mirror, the fifth mirror and the fourth mirror are plane mirrors.

[0014] Further, the first light source assembly comprises a first collimating head, a first polarizer and a first half-wave plate which are arranged in sequence and located on the first light path, and after the first collimating head emits the pump light, the pump light sequentially passes through the first polarizer and the first half-wave plate, so as to change the polarization state of the pump light.

[0015] Further, the second light source assembly comprises a second collimating head, a second polarizer and a second half-wave plate which are arranged in sequence and located on the second light path, and after the second collimating head emits the probe light, the probe light sequentially passes through the second polarizer and the second half-wave plate, so as to change the polarization state of the probe light.

[0016] Further, 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 mirror, the second mirror, 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 the base.

[0017] Further, the first mirror, the second mirror, the third mirror and the fourth mirror are located on the same horizontal plane, and the distance values from the first mirror, the second mirror, the third mirror and the fourth mirror to the base are greater than the distance value from the fifth mirror to the base.

[0018] Further, the base is connected with the first collimating head, the second collimating 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 the mounting frames respectively.

[0019] Further, an adhesive layer is arranged between the mounting frames and the base.

[0020] Compared with the prior art, the integrated spectrum unit based on modulation transfer spectrum of the application utilizes the cooperation of the first light source assembly, the second light source assembly, the reflection assembly, the first polarization beam splitter, 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 to ensure the directivity and stability of the system light beam, and due to the utilization of the reflection assembly, the multiple coincident interactions of the laser beam in the non-saturated iodine cell are realized, the effective optical path of the laser beam in the medium gas is increased in the case of ensuring the small size of the system, the system structure is more simple and miniaturized, meanwhile, the system has strong thermal stability and robustness, the directivity and stability of the laser beam are ensured, the overall temperature control and packaging of the spectrum unit are facilitated, the practicability is strong, and the application is worth promoting. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The overall structure schematic diagram provided by the application is shown.

[0022] Figure 2 The structure schematic diagram of the related prior art provided by the application is shown.

[0023] Reference signs:

[0024] 1, first collimating head; 2, second collimating head; 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 mirror; 13, second mirror; 14, third mirror; 15, fifth mirror; 16, fourth mirror; 19, non-saturated iodine cell; 20, hollow ridge mirror; 21, photoelectric differential detector; 22, first photoelectric low-noise detector; 23, second photoelectric low-noise detector; 24, base. DETAILED DESCRIPTION

[0025] In order to enable the technical personnel in the art to better understand the technical solutions of the application and to implement them, the following will be combined with the accompanying drawings to clearly and exhaustively describe the technical solutions in the application. Figure 1 The technical solutions in the application are clearly and exhaustively described.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] Furthermore, it should be further explained that in the description of the embodiments of the present invention, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of the present invention, "multiple" means two or more.

[0028] The terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Thus, a feature defined as "first," "second," "third," or "fourth" may explicitly or implicitly include one or more of that feature, and in the description of this invention, unless otherwise stated, "multiple" means two or more.

[0029] Example 1

[0030] This invention provides an integrated spectral unit based on modulation transfer spectrum, such as... Figure 1 As shown, the system includes a substrate 24 and a first collimator 1, a second collimator 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 polarizing beam splitter 8, a second polarizing beam splitter 10, a first beam splitter 9, a second beam splitter 11, an unsaturated iodine cell 19, a first reflector 12, a second reflector 13, a third reflector 14, a fifth reflector 15, a fourth reflector 16, a hollow roof reflector 20, a photoelectric differential detector 21, a first photoelectric low-noise detector 22 and a second photoelectric low-noise detector 23, wherein the first light source assembly, the first polarizing beam splitter 8, the first beam splitter 9 and the second reflector 13 are arranged sequentially and located on the first optical path, and the second light source assembly, the second polarizing beam splitter 10, the second beam splitter 11 and the first reflector 12 are arranged sequentially and located on the second optical path, and the second optical path is parallel to the first optical path.

[0031] Preferably, the dimensions of the substrate 24 are 330mm*110mm*30mm.

[0032] The first collimating head 1, the first polarizer 3 and the first half-wave plate 5 arranged in sequence and located in the same light path serve as a first light source assembly, and the second collimating head 2, the second polarizer 4 and the second half-wave plate 6 arranged in sequence and located in the same light path serve as a second light source assembly. The first collimating head 1 is used to provide pump light with relatively strong light power, and the second collimating head 2 is used to provide probe light with relatively weak light power in a certain spectral range, and the power and frequency components of the pump light and the probe light are inconsistent. After the pump light is emitted by the first collimating head 1, it successively passes through the first polarizer 3 and the first half-wave plate 5 to change the polarization state of the pump light, and after the probe light is emitted by the second collimating head 2, it successively passes through the second polarizer 4 and the second half-wave plate 6 to change the polarization state of the probe light.

[0033] The third mirror 14, the fifth mirror 15, the fourth mirror 16 and the hollow ridge mirror 20 jointly form a reflection assembly, the length direction of the unsaturated iodine cell 19 is parallel to the first light path and the second light path, the hollow ridge mirror 20 is located on one side of the length direction of the unsaturated iodine cell 19, and the first mirror 12, the second mirror 13, the third mirror 14, the fifth mirror 15 and the fourth mirror 16 are located on the other side of the length direction of the unsaturated iodine cell 19.

[0034] The pump light passes through the first polarizer 3 and the first half-wave plate 5, is completely transmitted by the first polarization beam splitter 8, is split into reflected light and transmitted light by the first beam splitter 9, the reflected light enters the first photoelectric low-noise detector 22 to stabilize the power, the transmitted light enters the unsaturated iodine cell 19 through the second mirror 13 and the fourth mirror 16, is turned by 180° by the hollow ridge mirror 20 again, is reflected by the fourth mirror 16 and the fifth mirror 15 to enter the unsaturated iodine cell 19 again, and finally is turned by 180° by the hollow ridge mirror 20 to be emitted.

[0035] The probe light passes through the second polarizer 4, the second half-wave plate 6, passes through the second polarization beam splitter 10, and is divided into reflected light and transmitted light. The reflected light is incident to the photoelectric differential detector 21 as reference light, and the transmitted light changes the polarization state through the third half-wave plate 7, and then passes through the second beam splitter 11 to divide the reflected light and the transmitted light. The reflected light is incident to the second photoelectric low-noise detector 23 for power stabilization, and the transmitted light is sequentially incident to the non-saturated iodine cell 19 through the first mirror 12 and the third mirror 14, and then is turned by 180° through the hollow ridge mirror 20, is reflected by the fifth mirror 15 and the fourth mirror 16, and is incident to the non-saturated iodine cell 19 again. The transmitted light is transmitted through the non-saturated iodine cell 19 by 180° through the hollow ridge mirror 20, is incident to the fourth mirror 16, and is finally reflected through the second mirror 13. The transmitted light passing through the first beam splitter 9 is completely reflected to the photoelectric differential detector 21 through the first polarization beam splitter 8. After comparison with the reference light in the photoelectric differential detector 21, an error signal is output, which is transmitted to the feedback control system in the signal processing system. After signal processing by the feedback control system, a control signal for actively controlling the laser frequency of the oscillator output is generated.

[0036] As a further refinement of the above embodiment, the first mirror 12, the second mirror 13, the third mirror 14 and the fourth mirror 16 are plane mirrors, and the first mirror 12, the second mirror 13, the third mirror 14 and the fourth mirror 16 are located on the same horizontal plane. The distance from the first mirror 12, the second mirror 13, the third mirror 14 and the fourth mirror 16 to the base 24 is greater than the distance from the fifth mirror 15 to the base 24. This device can greatly reduce the space size. By using the first mirror 12, the second mirror 13, the third mirror 14, the fourth mirror 16 and the fifth mirror 15 with different heights and the hollow ridge mirror 20 for 180° turning, the laser beam passes through the non-saturated iodine cell 19 four times along the length direction of the non-saturated iodine cell 19, realizes a longer effective optical path, has a good recombination effect, and ensures a large signal degree. In addition, the use of the non-saturated iodine cell 19 eliminates the need for separate temperature control of the iodine cell, which ensures that the subsequent optical spectrum unit can be controlled and packaged as a whole, thereby reducing costs.

[0037] Further, the base 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 and the third half-wave plate 7, the non-saturated iodine cell 19, the photoelectric differential detector 21, the first photoelectric low-noise detector 22 and the second photoelectric low-noise detector 23 through mounting frames, 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 mirror 12, the second mirror 13, the third mirror 14, the fifth mirror 15, the fourth mirror 16 and the hollow ridge mirror 20 are directly bonded to the base 24.

[0038] As a further refinement of the above embodiment, the mounting frame is made of invar material, and an adhesive layer is arranged between the mounting frame and the base 24, the adhesive layer being an epoxy resin adhesive layer, various lenses and the non-saturated iodine cell 19 are fixed by the mounting frame, and the various elements are bonded by the epoxy resin method to improve the thermal stability of the system.

[0039] 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.

[0040] The first beam splitter 9 and the second beam splitter 11 simply split the light in proportion.

[0041] The first collimating head 1 and the second collimating head 2 are optical fiber devices, which are light beam input units.

[0042] 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.

[0043] 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.

[0044] Overall, the present application has the following beneficial effects:

[0045] The application utilizes the cooperation of the first light source assembly, the second light source assembly, the reflection 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 non-saturated iodine cell 19, the photoelectric differential detector 21, the first photoelectric low-noise detector 22 and the second photoelectric low-noise detector 23, ensures the directivity and stability of the system light beam, and simultaneously, due to the reflection assembly realizing the multiple coincidence interaction of the light beam in the non-saturated iodine cell 19, the length of the interaction is increased in the case of ensuring the small size of the system, the system structure is simpler, the system light beam directivity is better, meanwhile, the system has strong thermal stability and robustness, and the overall temperature control and packaging of the spectrum unit are facilitated. In addition, the overall size of the product obtained by using the scheme provided by the application is 330mm*110mm*80mm, the volume is 30% of the smallest product in the prior art, the volume of the product is greatly reduced, and the product is more miniaturized.

[0046] It can be understood that the application is described through some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to the features and embodiments without departing from the spirit and scope of the application.

[0047] In addition, under the guidance of the application, the features and embodiments can be modified to adapt to specific conditions and materials without departing from the spirit and scope of the application. Therefore, the application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the application belong to the scope of protection of the application.

Claims

1. An integrated spectral unit based on modulation transfer spectrum, characterized in that, The device includes a photoelectric differential detector (21), a first photoelectric low-noise detector (22), an unsaturated iodine cell (19), and a second photoelectric low-noise detector (23). It also includes: a first light source assembly, a first polarization beam splitter (8), a first beam splitter (9), and a second reflector (13) arranged sequentially on the 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 sequentially on the second optical path; and a reflection assembly distributed on one opposite side of the unsaturated iodine cell (19). The first light source component provides pump light, and the second light source component provides probe light. The pump light is transmitted through the first polarization beam splitter (8) to the first beam splitter (9) to split into reflected light and transmitted light. The reflected light enters the first photoelectric low noise detector (22) for power stabilization, and the transmitted light is incident on the reflective component through the second reflector (13) and then exits. The probe light is split 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, and the transmitted light is split 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, and the transmitted light is incident on the reflective component through the first reflector (12). After being repeatedly entered into the unsaturated iodine cell (19) by the action of the reflective component, it exits on the second reflector (13). The transmitted light through the first beam splitter (9) is reflected by the first polarization beam splitter (8) to the photoelectric differential detector (21), and after being compared with the reference light, an error signal is output. A third half-wave plate (7) is provided in 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. The reflective assembly includes a third reflector (14), a fifth reflector (15), a fourth reflector (16), and a hollow roof reflector (20). The hollow roof reflector (20) is located on one side of the unsaturated iodine pool (19) to achieve a 180° turn of light. The third reflector (14), the fifth reflector (15), and the fourth reflector (16) are located on the other side of the unsaturated iodine pool (19) and are used in conjunction with the hollow roof reflector (20) to enable light to pass through the unsaturated iodine pool (19) multiple times and for the light path to overlap multiple times. The first light source assembly includes a first collimator (1), a first polarizer (3), and a first half-wave plate (5) arranged sequentially on the first optical path. After the light exits 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. The second light source assembly includes a second collimator (2), a second polarizer (4), and a second half-wave plate (6) arranged sequentially on the second optical path. After the light exits 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 probe light. The first light source assembly, the second light source assembly, the reflector 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 unsaturated iodine cell (19), the photoelectric differential detector (21), the first photoelectric low-noise detector (22), and the second photoelectric low-noise detector (23) are disposed on the substrate (24); 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 distance from the first reflector (12), the second reflector (13), the third reflector (14) and the fourth reflector (16) to the substrate (24) is greater than the distance from the fifth reflector (15) to the substrate (24).

2. The integrated spectral unit based on modulation transfer spectrum according to claim 1, 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.

3. The integrated spectral unit based on modulation transfer spectrum according to claim 1, characterized in that, The substrate (24) is connected to the first collimator (1), the second collimator (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 unsaturated iodine cell (19), the photoelectric differential detector (21), the first photoelectric low-noise detector (22), and the second photoelectric low-noise detector (23) respectively via the mounting bracket.

4. The integrated spectral unit based on modulation transfer spectrum according to claim 3, characterized in that, An adhesive layer is provided between the mounting bracket and the base (24).

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