Miniaturized quantum sensor detection optical module based on wire grid polaroid

Abstract

The invention relates to a wire grid polarizer-based miniaturized quantum sensor detection optical module, and belongs to the field of optical system miniaturization. The module comprises a polarizer, a reflector with a through hole, a 1 / 4 wave plate, a wire grid polaroid, a collimating lens, an alkali metal gas chamber, a polarization beam splitter and a balance detector. On the basis of an existing quantum sensor detection light system, light beam polarization is controlled through the wire grid polaroid, the reflector with the through hole and the 1 / 4 wave plate, light paths are reflected twice, light path folding is achieved, and therefore the system is ultra-thin, meanwhile, the polarization degree of detection light is improved through the wire grid polaroid, and the detection accuracy is improved. A polarization beam splitter and a balance detector are combined to realize optical rotation angle detection. And the miniaturization propulsion of the atomic inertial sensor and the improvement of the detection stability are facilitated.

Description

Technical Field

[0001] The present invention relates to a miniaturized quantum sensor detection optical module based on a wire grid polarizer, belonging to the field of miniaturization of optical systems. Background Art

[0002] Quantum sensors are an important direction in the current development of sensors, and theoretically have the advantages of high precision and small size at the same time. The linearly polarized light detection system is an indispensable part of the quantum precision measurement system, and is also an important part that cannot be ignored in the process of miniaturizing quantum sensors. With the increasing technical requirements of chip-based inertial measurement, magnetic field measurement, etc., higher requirements are put forward for the miniaturization and integration of the linearly polarized light detection module.

[0003] The main structure of the existing linearly polarized light detection system includes a collimation and beam expansion part, a linearly polarized light regulation part, an alkali metal gas cell, and an optical rotation angle measurement part. The alkali metal gas cell has requirements for both the spot size and the degree of linear polarization of the detection light. Therefore, it is necessary to expand, collimate, and polarize the divergent light emitted by the laser, which requires a large physical space. In traditional optical solutions, generally, the laser light emitted by the laser passes through a commercial collimator to obtain a collimated spot matching the size of the gas cell, and then passes through traditional polarization devices such as a linear polarizer or a polarization beam splitter for polarization. Although the optical path is clear and simple, limited by the spot size requirements, commercial collimators generally have a large volume, and the polarization device is located outside the collimation and beam expansion part, further inevitably occupying the volume of the quantum sensor. In the current quantum sensing system, the detection optical system occupies a large proportion of the physical volume of the quantum sensor. Therefore, in order to promote the miniaturization process of quantum sensors, a more integrated and miniaturized detection optical module is needed. Summary of the Invention

[0004] In order to solve at least one of the above-mentioned defects existing in the prior art, the present invention proposes a miniaturized quantum sensor detection optical module based on a wire grid polarizer. The method has a simple optical path, a compact structure, integrated functions, and can improve the stability of the linearly polarized light detection module at the same time. By building a folded optical path with a wire grid polarizer and a mirror, it is possible to reduce the physical length required for the optical path and integrate the function of improving the degree of linear polarization of the detection light, effectively promoting the miniaturization process of quantum sensors while improving the system stability.

[0005] To achieve the above solution, the present application is realized through the following technical solutions:

[0006] A miniaturized quantum sensor detection optical module and method based on a wire grid polarizer. The module includes a polarizer, a through-hole mirror, a quarter-wave plate, a wire grid polarizer, a collimating lens, an alkali metal gas cell, a polarization beam splitter, and a balanced detector. The polarizer is connected to a laser, the through-hole mirror is connected to the polarizer, the wire grid polarizer and the through-hole mirror are separated by a fixed distance L to form a folded optical path reflection cavity, the quarter-wave plate is located between the through-hole mirror and the wire grid polarizer, and the collimating lens is connected to the wire grid polarizer. The divergent light generated by the laser reaches the required spot size after traveling back and forth three times in the reflection cavity formed by the through-hole mirror and the wire grid polarizer, achieving the effect of optical path folding, thereby reducing the volume required for the beam expansion optical path while enhancing the linear polarization of the outgoing light using the wire grid polarizer. The large-spot, high-linear-polarization-degree collimated light generated after passing through the collimating lens carries the optical rotation angle information through the gas cell, and the balanced photodetector receives the detection light passing through the polarization beam splitter. Through the subsequent signal acquisition and processing unit, the optical rotation angle information carried by the detection light is extracted therefrom.

[0007] The wire grid polarizer is a nanostructure-based reflective polarizer. A series of parallel sub-wavelength metal wires form a periodic array on a transparent substrate, which can be used to generate and separate polarized light. When light irradiates the wire grid polarizer, the light with the electric vector perpendicular to the metal wires can pass through the wire grid, and the light with the electric vector parallel to the metal wire direction will be reflected. Let the direction of the electric vector during transmission be the transmission axis direction of the wire grid polarizer.

[0008] The polarizer is generally a true zero-order quarter-wave plate, which converts the light generated by the laser into circularly polarized light.

[0009] The through-hole mirror is a metal film mirror with a very small circular through-hole in the center for light transmission. When the light beam reaches the mirror for the first time, it all passes through the through-hole for transmission. When it reaches the mirror for the second time, the spot is much larger than the through-hole, and it is approximately completely reflected.

[0010] The quarter-wave plate realizes the polarization state conversion between circularly polarized light and linearly polarized light in the reflection cavity. The fast axis direction of the quarter-wave plate is the same as the fast axis direction of the polarizer, and both are at 45° to the transmission axis direction of the wire grid polarizer.

[0011] The parameters of the collimating lens are selected according to the required size of the outgoing light spot and the divergence angle of the incident laser, and are adjusted according to the requirements of the size of the alkali metal gas cell for the detection light spot size. The shape of the lens can be, but is not limited to, plano-convex lens, biconvex lens, etc., and the material can be, but is not limited to, optical glass or optical plastic.

[0012] After passing through the alkali metal gas cell, the detection light contains the optical rotation angle information. Let the optical rotation angle of the linearly polarized light be θ and the total light intensity of the linearly polarized light be I 0, after passing through the polarization beam splitter, it is divided into two orthogonal polarization components, S and P. Let the light intensity of the P polarization component be I P , and the light intensity of the S polarization component be I S , then:

[0013] I P = I 0 cos 2 θ,

[0014] I S = I 0 sin 2 θ.

[0015] If the optical rotation angle is θ, then: In summary, the present application includes at least the following beneficial effects:

[0016] Based on the traditional detection optical module, the present invention uses a wire grid polarizer to build a folded optical path to further shorten the physical space required for the optical path, reducing the beam expander and collimator function module that originally occupied a large amount of space to 1 / 3 of the physical space occupied by the traditional solution. At the same time, the function of generating linearly polarized light is integrated into the beam expansion and collimation process, omitting the physical space occupied by the polarization regulation function. It promotes the miniaturization development of quantum inertial sensors.

[0017] The present invention is a miniaturized quantum sensor detection optical module based on a wire grid polarizer, which improves the linear polarization degree of the linearly polarized light entering the alkali metal gas cell and reduces the circular polarization component therein, which is beneficial to improving the measurement stability of the quantum inertial sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic structural diagram of a miniaturized quantum sensor detection optical module based on a wire grid polarizer of the present invention.

[0019] Figure 2 is a schematic diagram of the optical path polarization of the folded optical path part of the present invention.

[0020] Figure 3 is the optical path diagram of the folded optical path part of the present invention.

[0021] Description of the reference numerals: 1, polarizer; 2, mirror with through hole; 3, quarter-wave plate; 4, wire grid polarizer; 5, collimating lens; 6, alkali metal gas cell; 7, polarization beam splitter; 8, balanced detector. DETAILED DESCRIPTION OF THE INVENTION

[0022] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] To further miniaturize the detection optical system of the quantum inertial sensor and reduce the actual physical space occupied by the detection optical path optical system, starting from shortening the actual physical space length occupied by the optical path, the present invention proposes a miniaturized quantum sensor detection optical module based on a wire grid polarizer. By adopting the idea of a folded optical path, a reflection cavity is built using a mirror and a wire grid polarizer, and the polarization of the light beam is controlled by a quarter-wave plate to regulate the number of reflections, realizing the function of keeping the optical path length unchanged while shortening the actual physical length, thereby achieving the integration of collimation, beam expansion, ultra-thinness, and polarization control functions, improving the polarization degree of the detection light, and further enhancing the measurement stability.

[0024] Figure 1 Figure 4 is a schematic structural diagram of a miniaturized quantum sensor detection optical module based on a wire grid polarizer of the present invention. Refer to Figure 1 As shown, a miniaturized quantum sensor detection optical module based on a wire grid polarizer includes a polarizer 1, a through-hole mirror 2, a quarter-wave plate 3, a wire grid polarizer 4, a collimating lens 5, which are arranged in sequence, as well as an alkali metal gas cell 6, a polarization beam splitter 7, and a balanced detector 8. The fast axis direction of the quarter-wave plate forms a 45-degree angle with the transmission axis direction of the wire grid polarizer. The divergent light generated by the laser is converted into circularly polarized light by the polarizer. Between the through-hole mirror 2 and the wire grid polarizer 4, it is reflected twice, and beam expansion is achieved to the required spot size using 1 / 3 of the physical distance. Finally, the light emerging from the wire grid polarizer 4 is a linearly polarized detection beam with a very high degree of linear polarization, which is collimated after passing through the collimating lens 5. The detection light carries the optical rotation angle information after passing through the alkali metal gas cell 6, and the intensity of the detection light is I 0 . The polarization beam splitter 7 decomposes the detection light into two orthogonal direction components, namely the light intensity I P of the P polarization component and the light intensity I S of the S polarization component. The balanced detector 8 receives and collects the light intensity information of the two components, and calculates the optical rotation angle through the subsequent signal processing module. If the optical rotation angle is θ, then:

[0025]

[0026] The core idea of realizing miniaturization in the present invention is to use polarization control based on a wire grid polarizer to achieve a folded optical path and improve space utilization. The linearly polarized light emitted by the laser is converted into left-handed circularly polarized light by the polarizer 1. The through-hole mirror 2 and the wire grid polarizer 4 form a reflection cavity, and the divergent light is reflected and expanded into a spot size that meets the detection light requirements of the alkali metal gas cell 7 at the same time. The quarter-wave plate 2 controls the change in the polarization state of the light beam in the reflection cavity.

[0027] Figure 2 Figure 5 shows the polarization change of the light beam in the folded optical path part. The Stokes vector of the light beam after passing through the polarizer is S 1 :

[0028] S 1 =(100 - 1) T 。

[0029] When the light beam propagates to the right in Figure 2 , the Mueller matrix of the quarter-wave plate 3 is:

[0030]

[0031] The Stokes vector of the light beam passing through the quarter-wave plate 3 for the first time is S 2 , then:

[0032] S 2 = M R_1 / 4 ·S 1 =(1 1 0 0) T 。

[0033] Set the direction of the transmission axis of the wire grid polarizer 4 to be orthogonal to the direction of S 2 . The light beam is reflected. After passing through the wire grid polarizer 4, the propagation direction of the reflected light beam is opposite. The Stokes vector of the light beam is S 3 = S 2 . When the light beam propagates to the left in Figure 2 , the Mueller matrix of the quarter-wave plate 3 is:

[0034]

[0035] The Stokes vector S 4 of the light beam passing through the quarter-wave plate 3 for the second time, then:

[0036] S 4 = M L_1 / 4 ·S 3 =(1 0 0 - 1) T 。

[0037] After being reflected by the mirror 2, the circular polarization direction of the circularly polarized light is reversed. The Stokes vector of the light beam is S 5 =(1 0 0 1) T 。

[0038] The Stokes vector of the light beam passing through the quarter-wave plate for the third time is S 6 , then:

[0039] S 6 = M R_1 / 4 ·S 5 =(1 - 1 0 0) T 。

[0040] S 6 represents linearly polarized light with a polarization direction parallel to the transmission axis of the wire grid polarizer. The Stokes vector of the light beam finally transmitted through the wire grid polarizer is S6 .

[0041] The light generated by the laser is converted into left-handed circularly polarized light after passing through the polarizer and becomes S-polarized light after passing through the quarter-wave plate 3. At this time, the polarization direction of the light is perpendicular to the transmission axis direction of the wire grid polarizer and is reflected. The horizontally polarized reflected light becomes left-handed circularly polarized light again after passing through the quarter-wave plate 3 for the second time. The polarization direction of the reflected light after being reflected by the mirror 3 becomes right-handed circularly polarized light. The light beam becomes P-polarized light after passing through the quarter-wave plate 3 for the third time. The polarization direction is consistent with the transmission axis direction of the wire grid polarizer, and the light beam is transmitted. Then, after passing through the collimating lens 5, the light beam is collimated. Attached Figure 3 shows the optical path diagram of the folded optical path part, and it can be seen that the light spot becomes larger during the two reflections. The folded optical path reflection cavity formed by the combination of the wire grid polarizer and the quarter-wave plate effectively reduces the actual physical space required for the optical path.

[0042] The linearly polarized light vector of the detected light after passing through the polarizer 1, the through-hole mirror 2, the quarter-wave plate 3, the wire grid polarizer 4, and the collimating lens 5 is written as E 0 = A(0 1) T , where A is the amplitude of the linearly polarized light.

[0043] After passing through the alkali metal gas cell 6, the rotation angle of the linearly polarized light is θ, and the Jones matrix J of the alkali metal gas cell C is:

[0044]

[0045] Then the light vector propagating to the polarization beam splitter 7 is E 1 = J C ·E 0 = A(sinθ cosθ) T .

[0046] The polarization beam splitter separates the polarization components in two orthogonal directions and are respectively received by the two channels of the balanced detector 8 and the optical intensity signals are collected. The optical intensity signals of the two channels are respectively:[[]]

[0047] I P = I 0 cos 2 θ,

[0048] I S = I 0 sin 2 θ.

[0049] Furthermore, the light rotation angle θ can be obtained:[[]]

[0050]

[0051] The detection of the optical rotation angle of a quantum sensor can be achieved by the above-mentioned miniaturized quantum sensor based on a wire grid polarizer for detecting an optical module, and the present invention improves the space utilization rate and is conducive to promoting the research on the miniaturization of quantum sensors.

[0052] The polarizer 1 is close to the light source and functions as a polarizer to convert the linearly polarized light emitted by the light source (usually an optical fiber) into circularly polarized light, and has no effect on the divergence angle of the light beam. The light beam passing through the polarizer 1 maintains its original divergence angle.

[0053] The through-hole mirror 2 is tightly assembled with the polarizer 1 to increase the proportion of the reflection cavity in the total volume as much as possible. The circular through-hole on the mirror is located at the center of the mirror and has the same size as the light spot when the detection light first reaches the through-hole mirror 2.

[0054] The quarter-wave plate 3 is located between the through-hole mirror and the wire grid polarizer 4 and can be placed closely to the wire grid polarizer. The quarter-wave plate 3 controls that only two reflections occur in the reflection cavity, making the optical path length controllable.

[0055] The polarization state performance of the transmitted light of the wire grid polarizer 4 directly affects the polarization performance of the collimated light emitted by the system and is the core component of the present invention. The wire grid polarizer has excellent polarization selectivity, and the proportion of the circularly polarized component in the finally transmitted light is lower than that in the traditional scheme, which is conducive to improving the measurement stability of the detection light. The distance between the wire grid polarizer and the through-hole mirror determines the length of the reflection cavity and is the key to reducing the length of the collimation and beam expansion part to 1 / 3 of the original. Finally, it determines the actual space occupied by the collimation and beam expansion function. Therefore, in the design, the proportion of the distance L between the wire grid polarizer and the through-hole mirror in the total length of the module should be increased as much as possible.

[0056] The collimating lens 5 is generally a plano-convex lens and is tightly installed with the wire grid polarizer. Its focal length parameter is jointly determined by the target light spot size and the divergence angle of the laser light source. The calculation optical path diagram is as attached Figure 3 。

[0057] The cross-section of the polarization beam splitter 7 is as shown in Figure 1 and functions to separate the linearly polarized light S and P polarization components carrying the optical rotation angle information and cooperate with the subsequent balanced detector to detect the optical rotation angle information.

[0058] The present invention can be applied to the optical systems of quantum sensors such as atomic inertial sensors and atomic magnetometers.

[0059] The present invention greatly reduces the physical volume occupied by the detection optical system, improves the functional integration degree, and can be matched with any subsequent optical rotation angle detection method.

[0060] It should be noted that although the embodiments described above of the present invention are illustrative, they are not a limitation of the present invention. Therefore, the present invention is not limited to the above specific embodiments. Without departing from the principle of the present invention, any other embodiments obtained by those skilled in the art under the inspiration of the present invention are regarded as being within the protection scope of the present invention.

Claims

1. A miniaturized quantum sensor detection optical module based on a wire grid polarizer, characterized in that: The invention comprises a polarizer, a reflector with a through hole, a quarter wave plate, a wire grid polarizer, a collimating lens, an alkali metal gas chamber, a polarization beam splitter and a balanced detector which are arranged in sequence. The polarizer converts the light generated by the laser into left-handed circularly polarized light; the through hole on the through-hole reflector transmits the left-handed circularly polarized divergent light for the first time; the 1 / 4 wave plate converts the left-handed circularly polarized light into S-polarized light for the first time; the wire grid polarizer reflects the S-polarized light for the first time; the 1 / 4 wave plate converts the S-polarized light into left-handed circularly polarized light for the second time; the through-hole reflector reflects the left-handed circularly polarized light and converts the reflected light into right-handed circularly polarized light; the 1 / 4 wave plate converts the right-handed circularly polarized light into P-polarized light for the third time; the wire grid polarizer transmits P-polarized light; the collimating lens collimates the divergent light; the highly linearly polarized P-polarized collimated light carries the optical rotation angle information through the alkali metal gas chamber; the polarization beam splitter divides the detection light into two orthogonal components; the two receiving ends of the balanced detector respectively receive the light intensity information of the two orthogonal components, and complete the detection by calculating the optical rotation angle through the light intensity information.

2. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 1, characterized in that: The wire grid polarizer and the reflector with through holes form a reflection cavity. The 1 / 4 wave plate controls the number of light beam reflections by changing the polarization state. The light beam is reflected twice in the reflection cavity, and the physical length is one third of the light path length, thereby realizing light path folding.

3. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 2, characterized in that: The center of the reflector with through hole has a small circular light-transmitting through hole with a radius matching the spot radius, so that the light emitted by the laser can be transmitted when it reaches the reflector with through hole for the first time.

4. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 2, characterized in that: The fast axis direction of the 1 / 4 wave plate forms an angle of 45 degrees with the transmission axis direction of the wire grid polarizer.

5. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 2, characterized in that: The wire grid polarizer is a reflective polarizer based on a subwavelength structure, which transmits linear polarized light whose polarization direction is consistent with the transmission axis direction, and reflects linear polarized light whose polarization direction is perpendicular to the transmission axis direction.

6. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 5, characterized in that: The wire grid polarizer has high polarization selectivity, and the circular polarization content of the transmitted light is lower than that of the transmitted light of the traditional linear polarizer.

7. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 1, characterized in that: The focal length of the collimating lens is calculated according to the divergence angle of the incident light and the required spot size.

8. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 1, characterized in that: The polarization beam splitter divides the detection light carrying the light rotation angle information into two components in orthogonal directions, S and P. The two channels of the balanced detector detect the light intensity of the two components respectively.

9. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 7, characterized in that: The light rotation angle is θ, the total light intensity of the detection light is I0, and the light intensity of the S direction component is I S =I0sin 2 θ, the light intensity of the P direction component is I P =I0cos 2 I.

10. The miniaturized quantum sensor detection optical module based on wire grid polarizer according to claim 7, characterized in that: The optical rotation angle

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