Output optical power proportionally adjustable fiber coupling system for atomic physics research

Abstract

The application discloses an output light power proportion adjustable fiber coupling system for atomic physics research, comprising a first fiber collimator, and further comprising a second fiber collimator, a first reflector, a second reflector, a liquid crystal variable retarder, a polarization beam splitter prism, a first half-wave plate and a second half-wave plate; the application can work in two modes of proportion adjustable beam splitting and beam combining according to specific requirements; the proportion of laser entering the first fiber collimator and the second fiber collimator can be quickly adjusted; the utilization efficiency of laser in a set of experimental system and the stability of the experimental system are improved; the space occupied by the experimental system is reduced, and a large amount of experimental resources is saved.

Description

Technical Field

[0001] This invention relates to fiber optic coupling systems for laser applications, and more particularly to fiber optic coupling systems with adjustable output optical power ratios for atomic physics research. Background Technology

[0002] In the field of laser research, it is often necessary to couple space-transmitted laser light into optical fibers and then guide it to other locations in the experimental system for flexible use. Taking the experiment of laser cooling atoms as an example, various optical devices on an optical platform can be used to appropriately shift, split, and combine the seed laser light transmitted in space to obtain the required laser frequency, intensity, and polarization. Then, the corresponding laser light is guided to the physical system through optical fibers, thereby realizing various manipulations of atoms in the vacuum cavity. (See reference: Measurements of local gravity via a cold atominterferometer. L. Zhou et al., Chin. Phys. Lett. 28. 013701 (2011)). With the development of atomic and molecular optical physics research, the functional requirements of lasers are becoming increasingly complex. In cold atom interferometer research, it is often necessary to use single-mode polarization-maintaining fibers to couple two or more beams of lasers with different applications, such as cooling light, pump-back light, push-carry light, Raman light, probe light, and quenching light, into the same fiber. These beams are then guided from the optical platform to the beam expander of the interferometer system. Specific intensity ratios between the cooling and Raman laser beams are required, as detailed in the reference (Test of Equivalence Principle at 10E-8 Level by a Dual-Species Double-Diffraction Raman Atom Interferometer. L. Zhou, et al. Phys. Rev. Lett. 115, 013004 (2015)). Achieving this involves splitting and combining laser beams of various frequencies, controlling optical power, and coupling spatial light into the fiber. Existing laser coupling technologies meet the requirements in terms of coupling efficiency, but the coupling system occupies a large space, which affects the long-term stability of the optical system, necessitating frequent calibration of the laser power coupled into the fiber. Furthermore, existing coupling methods lack control over the relative power changes of the two laser beams after splitting, making it functionally insufficient to meet current technological needs. To address these requirements, a fiber optic coupling system capable of coupling or outputting two lasers with an adjustable output power ratio is needed. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of existing technologies in terms of stability, integration and laser utilization efficiency of laser coupling systems, and to provide an optical fiber coupling system with adjustable output optical power ratio for atomic physics research.

[0004] The above-mentioned objectives of the present invention are achieved through the following technical means:

[0005] An optical fiber coupling system with adjustable output optical power ratio for atomic physics research includes a first optical fiber collimator, a second optical fiber collimator, a first mirror, a second mirror, a liquid crystal variable delay unit, a polarizing beam splitter, a first half-wave plate, and a second half-wave plate.

[0006] After being reflected by the first reflecting mirror, the laser beam is incident on a polarizing beam splitter with an adjustable rotation angle via a liquid crystal variable retarder.

[0007] At the first rotation angle, the polarizing beam splitter splits the emitted laser from the liquid crystal variable delay device into a first transmitted polarized laser and a first reflected polarized laser. The first reflected polarized laser is incident on the first fiber collimator via the first half-wave plate, and the first transmitted polarized laser is reflected by the second mirror and then incident on the second fiber collimator via the second half-wave plate.

[0008] At the second rotation angle, the laser emitted from the liquid crystal variable delay device is transmitted through the polarization beam splitter to form a second transmitted polarized laser. Another laser beam passes through the first fiber collimator and the first half-wave plate, and is then reflected by the polarization beam splitter to form a second reflected polarized laser. The second transmitted polarized laser and the second reflected polarized laser are combined to form a combined beam. The combined beam is reflected by the second mirror and then passes through the second half-wave plate and enters the second fiber collimator.

[0009] As described above, the first fiber collimator, the second fiber collimator, the first reflector, the liquid crystal variable delay device, the first half-wave plate, and the second half-wave plate are all fixed on the coupling frame base, and the polarizing beam splitter is mounted on the coupling frame base via a rotating bracket.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] 1. It can operate in two modes: adjustable beam splitting and beam combining, depending on specific needs;

[0012] 2. The ratio of laser light entering the first fiber collimator and the second fiber collimator can be quickly adjusted according to the different voltages applied to the liquid crystal variable delay device;

[0013] 3. The ratio of transmitted polarized laser to reflected polarized laser varies from 1 to 1000;

[0014] 4. The laser can be switched between two single-mode polarization-maintaining fibers in a time-division manner, which greatly improves the utilization efficiency of the laser.

[0015] 5. The coupled system exhibits minimal long-term drift and high overall stability;

[0016] In summary, this invention enables the same laser beam to be quickly and conveniently coupled into different optical fibers in a time-division manner, improving the utilization efficiency and stability of the laser in an experimental system, reducing the space occupied by the experimental system, and saving a lot of experimental resources. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the working principle of the polarizing beam splitter of the present invention at the first rotation angle.

[0018] Figure 2 The working principle diagram of the polarizing beam splitter of the present invention at the second rotation angle.

[0019] Wherein: 0 - Free space laser; 1-1, First reflecting mirror; 1-2, Second reflecting mirror; 2, Liquid crystal variable delay device; 3, Polarizing beam splitter; 4-1, First half-wave plate; 4-2, Second half-wave plate; 5, First fiber collimator; 6, Second fiber collimator; 7, Coupler base. Detailed Implementation

[0020] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] I: Overall

[0022] By controlling the amplitude of the voltage applied to the liquid crystal variable delay device 2, the polarization of the laser entering the polarization beam splitter 3 is changed, thereby achieving time-division and beam-splitting coupling of the same laser beam.

[0023] like Figure 1 An optical fiber coupling system with adjustable output optical power ratio for atomic physics research includes a first optical fiber collimator 5, a second optical fiber collimator 6, a first reflector 1-1, a second reflector 1-2, a liquid crystal variable delay unit 2, a polarizing beam splitter 3, a first half-wave plate 4-1, and a second half-wave plate 4-2.

[0024] After being reflected by the first reflecting mirror 1-1, the laser light passes through the liquid crystal variable retarder 2 and is then incident on the adjustable rotation angle polarizing beam splitter 3.

[0025] At the first rotation angle, the polarizing beam splitter 3 splits the emitted laser from the liquid crystal variable delay unit 2 into a first transmitted polarized laser and a first reflected polarized laser. The first reflected polarized laser is incident on the first fiber collimator 5 via the first half-wave plate 4-1, and the first transmitted polarized laser is reflected by the second mirror 1-2 and then incident on the second fiber collimator 6 via the second half-wave plate 4-2.

[0026] At the second rotation angle, the laser emitted from the liquid crystal variable delay device 2 is transmitted through the polarization beam splitter 3 to form a second transmitted polarized laser. The other laser beam passes through the first fiber collimator 5 and the first half-wave plate 4-1, and is then reflected by the polarization beam splitter 3 to form a second reflected polarized laser. The second transmitted polarized laser and the second reflected polarized laser are combined to form a combined beam. The combined beam is reflected by the second mirror 1-2 and then enters the second fiber collimator 6 through the second half-wave plate 4-2.

[0027] The first fiber collimator 5, the second fiber collimator 6, the first reflector 1-1, the liquid crystal variable delay device 2, the first half-wave plate 4-1 and the second half-wave plate 4-2 are all fixed on the coupling frame base 7, and the polarizing beam splitter 3 is mounted on the coupling frame base 7 via a rotating bracket.

[0028] The first rotation angle and the second rotation angle differ by 90 degrees.

[0029] In this embodiment, the free-space laser is incident on the first reflecting mirror 1-1 at a 45-degree angle in the horizontal direction, and after reflection, the laser passes vertically downward through the liquid crystal variable delay unit 2.

[0030] The radio frequency drive source is connected to the liquid crystal variable delay unit 2 to realize the polarization axis control of the liquid crystal variable delay unit 2;

[0031] Depending on the direction of laser polarization, the polarization beam splitter 3 can be used to select either transmitted polarized laser or reflected polarized laser.

[0032] The first reflected polarized laser passes sequentially through the first half-wave plate 4-1 and the first fiber collimator 5. The first half-wave plate 4-1 is used to adjust the laser polarization axis so that it coincides with the fiber polarization axis. The first fiber collimator 5 is connected to a single-mode polarization-maintaining fiber to achieve the coupled output of the first reflected polarized laser.

[0033] The first transmitted polarized laser passes sequentially through the second reflector 1-2, the second half-wave plate 4-2, and the second fiber collimator 6. The second half-wave plate 4-2 is used to adjust the laser polarization axis so that it coincides with the fiber polarization axis. The second fiber collimator 6 is connected to a single-mode polarization-maintaining fiber to achieve the coupled output of the first transmitted polarized laser.

[0034] II: Functional Components

[0035] Coupler base 7: The coupler base is used to fix optical components and is machined after the design is completed.

[0036] First reflector 1-1 and second reflector 1-2: First reflector 1-1 and second reflector 1-2 are devices used to reflect polarized lasers and change their propagation direction.

[0037] Liquid crystal variable delay 2: Liquid crystal variable delay 2 is a device used to control the polarization direction of the laser by applying voltage.

[0038] Polarizing beam splitter 3: Polarizing beam splitter 3 is a device used to split or combine linearly polarized laser beams.

[0039] The first half-wave plate 4-1 and the second half-wave plate 4-2 are devices used to adjust the direction of laser polarization.

[0040] First fiber collimator 5 and second fiber collimator 6: First fiber collimator 5 and second fiber collimator 6 are devices that couple laser into an optical fiber or collimate laser emitted from an optical fiber into a parallel beam of a certain diameter, and consist of a flange for fixing the optical fiber and a focusing lens.

[0041] Single-mode polarization-maintaining fiber: Single-mode polarization-maintaining fiber is a type of fiber used to transmit linearly polarized lasers.

[0042] Radio frequency driver: The radio frequency driver can output a square wave signal with a certain power and can perform frequency modulation (including frequency modulation, i.e., FM and frequency shift keying, i.e., FSK) and amplitude modulation (AM) on the signal, which drives the liquid crystal variable delay unit 2 to realize the control of laser polarization.

[0043] III. Working Principle

[0044] The working principle of this invention will be explained in detail below.

[0045] The working principle of this invention is based on a liquid crystal variable delay device (Thorlabs LCC1411-B).

[0046] The overall structure of the liquid crystal variable retarder 2 includes a fused quartz substrate, an organic polyimide film, an insulating layer, and filamentary liquid crystal material. Transparent conductive films are deposited on two parallel surfaces of its transparent cell wall, allowing voltage to be applied to the liquid crystal cell. Due to the electro-optic birefringence of the liquid crystal material, the laser phase delay introduced by the liquid crystal variable retarder is proportional to the optical path difference and inversely proportional to the laser wavelength. Its slow axis is marked on the mechanical housing and is parallel to the surface of the liquid crystal variable retarder. Without voltage applied, the orientation of the liquid crystal molecules is determined by the alignment direction of the molecules in the alignment film during manufacturing. When an AC voltage is applied, the liquid crystal molecules change their alignment direction according to the applied voltage. Therefore, changing the applied voltage allows for active control of the delay of the liquid crystal variable retarder, thereby altering the beam splitting ratio of the first transmitted polarized laser and the first reflected polarized laser after the laser passes through the polarization beam splitter.

[0047] Free-space laser 0 is incident horizontally at a 45-degree angle onto the first reflecting mirror 1-1. After reflection, the laser beam descends vertically, passing sequentially through the liquid crystal variable delay unit 2 and the polarization beam splitter 3. The first reflected polarized laser beam passes through the first half-wave plate 4-1, and then is coupled into the optical fiber using the first fiber collimator 5. The first half-wave plate 4-1 is used to adjust the laser polarization axis to align it with the optical fiber polarization axis; the first fiber collimator 5 is connected to a single-mode polarization-maintaining fiber to achieve the coupled output of the first reflected polarized laser beam.

[0048] The first transmitted polarized laser beam from the polarization beam splitter prism 3 passes sequentially through the second reflecting mirror 1-2 and the second half-wave plate 4-2, and then the spatial light is coupled into the optical fiber using the second fiber collimator 6. The second half-wave plate 4-2 is used to adjust the laser polarization axis to coincide with the optical fiber polarization axis; the second fiber collimator is connected to a single-mode polarization-maintaining fiber to achieve the coupled output of the first transmitted polarized laser beam.

[0049] By changing the voltage applied to the liquid crystal variable delay device 2, the laser intensity ratio in the single-mode polarization-maintaining fiber connected to the back end of the first fiber collimator 5 and the second fiber collimator 6 can be quickly adjusted to achieve the final ratio.

[0050] Furthermore, this invention can be easily modified to operate in beam-combining mode. Compared to beam-splitting mode, operating in beam-combining mode only requires rotating the polarizing beam splitter 3 counterclockwise by 90 degrees. After modification, one free-space laser beam is incident horizontally at a 45-degree angle onto the first reflecting mirror 1-1. After reflection, the laser propagates vertically downwards and passes through the liquid crystal variable delay unit 2. Adjusting the voltage applied to the liquid crystal variable delay unit 2 ensures that the laser polarization direction is consistent with the transmission polarization direction of the polarizing beam splitter 3. The other laser beam is incident from the first fiber collimator 5, propagating horizontally and passing through the first half-wave plate 4-1. Adjusting the polarization axis of the first half-wave plate 4-1 ensures that the laser polarization direction is consistent with the reflection polarization direction of the polarizing beam splitter 3. At this point, the two laser beams can be combined through the polarizing beam splitter 3. The combined laser beam then passes sequentially through the second reflecting mirror 1-2, the second half-wave plate 4-2, and then couples into the second fiber collimator 6.

[0051] In summary, this invention overcomes the shortcomings of existing laser coupling systems, such as poor stability and large space occupation, and can work conveniently and stably in proportionally adjustable beam splitting and beam combining modes, greatly improving the optical path utilization efficiency and saving experimental resources.

[0052] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. An optical fiber coupling system with adjustable output optical power ratio for atomic physics research, comprising a first optical fiber collimator (5), characterized in that, It also includes a second fiber collimator (6), a first reflector (1-1), a second reflector (1-2), a liquid crystal variable delay unit (2), a polarizing beam splitter (3), a first half-wave plate (4-1), and a second half-wave plate (4-2). After being reflected by the first reflecting mirror (1-1), the laser light passes through the liquid crystal variable retarder (2) and is incident on the polarizing beam splitter (3) with an adjustable rotation angle. At the first rotation angle, the polarizing beam splitter (3) splits the emitted laser from the liquid crystal variable delay unit (2) into a first transmitted polarized laser and a first reflected polarized laser. The first reflected polarized laser is incident on the first fiber collimator (5) through the first half-wave plate (4-1), and the first transmitted polarized laser is reflected by the second mirror (1-2) and then incident on the second fiber collimator (6) through the second half-wave plate (4-2). At the second rotation angle, the laser emitted from the liquid crystal variable delay device (2) is transmitted through the polarization beam splitter (3) to form a second transmitted polarized laser. The other laser beam passes through the first fiber collimator (5) and the first half-wave plate (4-1), and is then reflected by the polarization beam splitter (3) to form a second reflected polarized laser. The second transmitted polarized laser and the second reflected polarized laser are combined to form a combined beam. The combined beam is reflected by the second mirror (1-2) and then enters the second fiber collimator (6) through the second half-wave plate (4-2).

2. The fiber optic coupling system with adjustable output optical power ratio for atomic physics research according to claim 1, characterized in that, The first fiber collimator (5), the second fiber collimator (6), the first reflector (1-1), the liquid crystal variable delay device (2), the first half-wave plate (4-1) and the second half-wave plate (4-2) are all fixed on the coupling frame base (7), and the polarizing beam splitter (3) is set on the coupling frame base (7) by a rotating bracket.

Images