CN109633920B - Hermite-Gaussian mode beam splitter - Google Patents
Hermite-Gaussian mode beam splitter Download PDFInfo
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- CN109633920B CN109633920B CN201910040406.5A CN201910040406A CN109633920B CN 109633920 B CN109633920 B CN 109633920B CN 201910040406 A CN201910040406 A CN 201910040406A CN 109633920 B CN109633920 B CN 109633920B
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Abstract
A hermite-gaussian mode beam splitter comprising a phase converter and an interference device; the phase converter is added into an interference device, the interference device divides the light into a first light beam and a second light beam, the first light beam passes through the phase converter, the second light beam does not pass through the phase converter, and the two light beams are combined together at the outlet of the interference device. By changing the phase value and the arrangement mode of the phase value introduced by the phase converter, different phase differences can be correspondingly generated at the two outlets and are related to the horizontal parameter m or the vertical parameter n of the Hermite-Gaussian mode, and finally the input mode appears from different outlets, so that the splitting of the Hermite-Gaussian mode is realized. The method is based on two characteristic parameters of the Hermite-Gaussian mode in the horizontal and vertical directions, does not generate any mode conversion, and separates the mode under the condition of no damage to the mode; the whole process does not involve diffraction, and light is directly transmitted through the device or reflected, and can be regarded as a common transmission or reflection optical device.
Description
Technical Field
The invention belongs to the technical field of optics, and relates to a beam splitter of a high-order laser transverse mode, in particular to a Hermite-Gaussian mode beam splitter.
Background
The hermite-gaussian and laguerre-gaussian modes are two commonly used laser transverse modes. A beam splitter is a device used to separate the laser modes into different spatial locations. At present, the technology of the Laguerre-Gaussian mode beam splitter is mature, and the realization of the Hermite-Gaussian mode beam splitter is relatively difficult. The existing scheme of the Hermite-Gaussian mode beam splitter is that the mode is converted into Laguerre-Gaussian light, and then the existing Laguerre-Gaussian mode beam splitter is combined to realize beam splitting of the Hermite-Gaussian mode. The beam splitter is not directly suitable for a Hermite-Gaussian beam device, and therefore the structure is complicated. There is no known beam splitter of the hermitian-gaussian mode that does not undergo conversion.
The hermitian-gaussian mode has two characteristic parameters m and n, corresponding to two orthogonal directions (horizontal for m, vertical for n), respectively. In the intensity distribution, the number of the bright spots in each row in the horizontal direction is equal to m +1, and the number of the bright spots in each column in the vertical direction is equal to n + 1.
Disclosure of Invention
The invention aims to provide a mode-conversion-free Hermite-Gaussian mode beam splitter.
In order to achieve the purpose, the invention adopts the following technical scheme:
a hermite-gaussian mode beam splitter comprising a phase converter and an interference device; the phase converter consists of two cylindrical lenses, the planes of the two cylindrical lenses are opposite and coaxially arranged, and the two cylindrical lenses are divided into a horizontal arrangement mode and a vertical arrangement mode according to the states of curved surfaces of the two cylindrical lenses; adding a phase converter into an interference device, wherein the interference device firstly divides light into a first light beam and a second light beam, the first light beam passes through the phase converter, the second light beam does not pass through the phase converter, and the two light beams are combined together at an outlet of the interference device; by changing the phase value introduced by the phase converter and the arrangement mode of the two cylindrical lenses, different phase differences are correspondingly generated at the two outlets and are related to the horizontal parameter m or the vertical parameter n of the Hermite-Gaussian mode, namely, the input mode appears from different outlets, and the purpose of splitting the Hermite-Gaussian mode is achieved.
The invention is further improved in that the distance d between two cylindrical lenses in the phase converter satisfies d-2 sin (theta/2) f, where theta is a phase value introduced by the phase converter, and has a value range of [0, pi ], and f is the focal length of the cylindrical lens.
The invention further improves the technical scheme that a phase converter is arranged in a first optical path of the MZ interferometer in a horizontal arrangement mode, when Hermite-Gaussian modes with different values of a horizontal mode parameter m are input to pass through the phase converter, the introduced phase value is (m +1/2) theta, and therefore the phase difference related to the horizontal parameter m is introduced between the two optical paths of the MZ interferometer; when theta is equal to pi, adjusting the optical paths of the two optical paths, so that the total phase difference between the two optical paths is 2 pi for a Hermite-Gaussian mode with the horizontal parameter m being an even number, and then the light appears at the outlet of the MZ interferometer; for the mode with the odd horizontal parameter m, the phase difference introduced between the two arms is pi, and then light appears at the second outlet, so that the effect of splitting the Hermite-Gaussian modes with different horizontal parameter m values is achieved;
in the same way, the phase converter is vertically arranged in the first optical path of the MZ interferometer, so that input light with different vertical parameter n values appears at different outlets of the interferometer, and accordingly hermitian-Gaussian mode beam splitting with different vertical parameter n values is achieved.
The invention has the further improvement that the phase converter is arranged in a first light path of the Sagnac interferometer in a horizontal arrangement mode, and the effect of splitting the Hermite-Gaussian modes with different horizontal parameter m values is correspondingly realized; and the phase converter is placed in a first light path of the Sagnac interferometer in a vertical arrangement mode, and beam splitting in a Hermite-Gaussian mode is realized according to the value of a vertical parameter n.
The invention has the further improvement that the beam splitters with different phase values and placing modes introduced by the phase converter are sequentially connected into the multistage beam splitter, so that the separation of Hermite-Gaussian modes is realized.
A Hermite-Gaussian mode beam splitter loads a phase converter on a spatial light modulator in the form of a Fresnel phase plate, sets incident light to be polarized at 45 degrees, and utilizes the characteristic that a reflective phase type spatial light modulator modulates single polarization, so that a horizontal polarization component in the incident light passes through the phase converter, a vertical polarization component does not pass through, and a phase difference related to mode parameters is introduced between the two polarization components; when gratings representing a horizontal arrangement mode and a vertical arrangement mode of the phase converter are loaded on the spatial light modulator respectively, beam splitting of Hermite-Gaussian modes with different m values and n values is achieved respectively.
Compared with the prior art, the invention has the following beneficial effects:
1. compared with other Hermite-Gaussian mode beam splitters, the invention is based on two characteristic parameters of Hermite-Gaussian mode in horizontal and vertical directions, does not generate any mode conversion, and separates the Hermite-Gaussian mode beam splitters under the condition of no damage to the Hermite-Gaussian mode beam splitters;
2. compared with the existing Hermite-Gaussian mode beam splitter, the invention does not involve diffraction in the whole process, and the light is directly transmitted through the device or reflected, so that the device can be regarded as a common transmission or reflection optical device.
3. The function realized by the cylindrical lens can be simulated and replaced by a computer program, and the focal length and the micro displacement of the cylindrical lens are digitalized and adjustable, so that the whole device has good stability and high precision, and gets rid of the limitation that the attribute (such as the focal length) of an optical device is fixed and unchanged.
Further, there are many types of interference devices available, and in principle, the light is split into two beams and then the two beams are combined together, which satisfy the design of the present invention, such as a Mach-zehnder (mz) interferometer, a Sagnac interferometer, and the like.
Furthermore, the multi-stage beam splitter is reasonably cascaded, and beam splitting of any Hermite-Gaussian mode can be realized.
Drawings
FIG. 1 is a schematic view of example 1 of the present invention.
Fig. 2 is a schematic view of embodiment 2 of the present invention.
Fig. 3 is a schematic diagram of embodiment 3 of the present invention.
Fig. 4 is a schematic diagram of the horizontal arrangement of the phase converter according to the present invention.
Fig. 5 is a schematic diagram of the vertical arrangement of the phase converter according to the present invention.
Fig. 6 is a grating pattern with a corresponding horizontal arrangement of phase shifters loaded on the spatial light modulator in embodiment 3 of the present invention.
Fig. 7 is a grating pattern with a corresponding phase converter vertically disposed on a spatial light modulator in embodiment 3 of the present invention.
Fig. 8 is an exemplary diagram of the cascading principle of the present invention.
In the figure, 1 is a light source, 2 is a beam splitter, 3 is a mirror, 4 is a cylindrical lens, 5 is a polarizing beam splitter, 6 is a half-wave plate, and 7 is a spatial light modulator.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
The Hermite-Gaussian mode beam splitter of the invention is composed of two parts, namely a phase converter and an interference device.
The phase converter is composed of two cylindrical lenses, the planes of the two cylindrical lenses are opposite and coaxially arranged, the two cylindrical lenses are arranged in a horizontal and vertical arrangement mode according to the state of the curved surface (as shown in figures 4 and 5), and when the phase converter is used, the two cylindrical lenses respectively correspond to a parameter m of a Hermite-Gaussian mode in the horizontal direction and a parameter n of a Hermite-Gaussian mode in the vertical direction, namely, the two cylindrical lenses are used for introducing pi, pi/2, pi/4 and other discrete phases for the Hermite-Gaussian mode of which the mode parameter is m or n. For two cylindrical lenses, the distance d between them is a set of specially designed discrete values, and d is 2sin (theta/2) f, where theta is the phase introduced by the phase converter, and takes a value range [0, pi ], and f is the focal length of the cylindrical lens.
The phase converter is incorporated into a suitable interferometric device (as described in the specific embodiments) to form a complete beam splitter. The interference device is suitable in many specific forms, but the principle of the whole beam splitter can be summarized as that the interference device firstly splits the light into two beams, namely a first beam and a second beam, the first beam passes through the phase converter, the second beam does not pass through the phase converter, then the two beams are combined together, different phase differences can be generated at two outlets of the interference device by adjusting the introduced phase value and the arrangement mode of the phase converter, the phase differences are related to m or n, finally, different incident modes appear from different outlets, and therefore the beam splitting of the hermite-gaussian mode is realized.
The present invention will design a beam splitter based on the m and n parameters of the Hermite-Gaussian modes. The principle of the design is based on two characteristic parameters of the Hermite-Gaussian mode, so that the beam splitter does not generate extra conversion, and theoretically, the lossless mode distinguishing can be realized.
According to the principle of the invention, a phase converter is added in an interference device to realize Hermite-Gaussian mode differentiation, and three preferred embodiments are designed. Hereinafter, the structures and operations of the three exemplary embodiments will be described in detail with reference to the accompanying drawings.
In the 3 embodiments shown in fig. 1, 2 and 3, the light source 1, the beam splitter 2, the mirror 3, the cylindrical lens 4, the polarization beam splitter 5, the half-wave plate 6 and the spatial light modulator 7 are included.
Example 1
As shown in fig. 1, the phase converter is placed in a horizontal arrangement in the first beam path of a Mach-zehnder (mz) interferometer. The optical paths of the MZ interferometer caused by the two optical routing paths are equal, and different phase differences can be caused by different reflection times of two emergent beams of light at different outlets. At the first outlet, the phase difference of the two beams is 0, so that interference and phase lengthening occur; at the second exit, the two beams have a phase difference of pi, so that interference cancellation occurs. When different hermite-gaussian modes of mode parameter m pass through the phase converter, a phase (m +1/2) θ is introduced, thereby introducing a phase difference between the two optical paths of the interferometer that is related to mode parameter m. When theta is equal to pi, the lengths of the two light paths are properly adjusted, so that for the Hermite-Gaussian mode with the mode parameter m being an even number, the total phase difference between the light paths is 2 pi, and the light still appears at the outlet I; for the mode with the odd mode parameter m, the phase difference introduced between the two optical paths is pi, and light appears at exit two. According to the principle, the effect of splitting Hermite-Gaussian modes with different m values is achieved. Similarly, if the phase converter is placed in the first optical path of the MZ interferometer in a vertical arrangement, the modes appear in different outlets of the interferometer according to the parity of the value of the vertical parameter n, thereby realizing the beam splitting of the hermitian-gaussian modes with different values of the vertical parameter n.
Example 2
As shown in fig. 2, the phase converter is placed in the first optical path of the Sagnac interferometer in a horizontal arrangement mode, the principle is the same as that of the M-Z interferometer, and the effect of splitting hermitian-gaussian modes with different M values can be achieved. In a similar way, the phase converter is vertically arranged in the Sagnac interferometer, and beam splitting in the hermitian-gaussian mode can be realized according to the value of n.
Example 3
As shown in fig. 3, the present embodiment uses orthogonal polarization states to realize interference, two orthogonal polarization states (usually horizontal and vertical polarization) are used to replace two optical paths of the interference device, and the phase converter shown in fig. 4 and 5 is loaded on the spatial light modulator in the form of a fresnel phase plate, corresponding to fig. 6 and 7. Setting incident light to 45°Polarization, which utilizes the property of a reflective phase-type spatial light modulator to modulate only a single polarization (e.g., Holoeye Pluto-VIS-016 modulates only horizontal polarization), so that the horizontal polarization component of the incident light passes through the phase converter while the vertical polarization component is equivalent to not passing, thereby introducing a phase difference between the two polarization components that is related to the mode parameter. When the grating is used to replace the horizontal arrangement mode of the phase converterThe space light modulator is loaded on the space light modulator, and accordingly the effect of splitting Hermite-Gaussian modes with different m values can be realized; similarly, when the grating replacing the vertical arrangement mode of the phase converter is loaded on the spatial light modulator, the Hermite-Gaussian mode beam splitting with different n values is correspondingly realized.
Cascading of beam splitters: the aim of splitting any Hermite-Gaussian mode can be achieved by changing the cascade structure of the beam splitter, including changing the arrangement mode and the theta value of the phase converter. The principle and examples are as follows:
1. when a phase converter theta in the beam splitter is pi and horizontally arranged, only Hermite-Gaussian modes with different m parity can be separated;
2. if m and n are different hermitian-gaussian modes to be separated simultaneously, a beam splitter with a horizontally arranged phase converter and a beam splitter with a vertically arranged phase converter need to be cascaded, for example: the phase converter theta in the first-stage beam splitter is pi and horizontally arranged, and Hermite-Gaussian modes with different m parity respectively appear at different outlets. The secondary beam splitter is arranged behind the outlet of the primary beam splitter, and the phase converter theta is phi and vertically arranged, so that the aim of simultaneously separating Hermite-Gaussian modes with different m and n parities is fulfilled;
3. to more finely separate the different hermite-gaussian modes of m or n, it is necessary to cascade a plurality of stages of beam splitters having different θ -value phase converters, for example: and the phase converter theta in the primary beam splitter is equal to pi and horizontally arranged, the mode with the even number m is at the first outlet, and the mode with the odd number m is at the second outlet. A beam splitter with a phase converter θ ═ pi/2 and horizontally disposed is placed after the exit one of the primary beam splitter, so that hermitian-gaussian modes with integer multiples of 4 and even m values other than integer multiples of 4 are split at the exit of the secondary beam splitter.
The cascade process is specifically described below by taking two-stage cascade as an example: as shown in FIG. 8, to HG00、HG01、HG10、HG11(the first number in the lower corner represents parameter m, the second number represents parameter n) four modes are divided intoExample, in the figure
Indicating that the phase converter is oriented horizontally and theta is pi,
denotes that the phase converter is oriented vertically and θ ═ pi. First stage
The beam splitter of (1) enables the HG00、HG01Emerging from the upper channel, HG10、HG11And exits the lower channel (where the channel corresponds to the exit of the above-mentioned several interference devices). The second stage consists of two
The two groups of modes obtained from the first stage are further split, and finally the HG is enabled00、HG01、HG10、HG11Exiting from four different channels.
The interference device required in the present invention is not limited to the above-mentioned ones, as long as the interference device satisfies the form of first dividing the incident light into two beams, the first beam and the second beam, and then combining the two beams together through the same optical path.
The above description is only exemplary of the preferred embodiments of the present invention, and is not intended to limit the present invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (1)
1. A Hermite-Gaussian mode beam splitter is characterized in that a phase converter is loaded on a spatial light modulator in a Fresnel phase plate mode, incident light is set to be 45-degree polarized, and the characteristic that a reflective phase type spatial light modulator modulates single polarization is utilized, so that a horizontal polarization component in the incident light passes through the phase converter, a vertical polarization component does not pass through, and a phase difference related to a mode parameter is introduced between the two polarization components; when gratings representing a horizontal arrangement mode and a vertical arrangement mode of the phase converter are loaded on the spatial light modulator respectively, beam splitting of Hermite-Gaussian modes with different m values and n values is achieved respectively.
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| CN112505935A (en) * | 2020-11-12 | 2021-03-16 | 西安交通大学 | Hermite-Gaussian mode beam splitter based on single polarization modulation device |
| CN112304445A (en) * | 2020-11-20 | 2021-02-02 | 中国科学技术大学 | Expandable multi-mode light quantum interference device and construction method thereof |
| CN113448105B (en) * | 2021-04-29 | 2022-08-16 | 西安交通大学 | Linear constrained laser transverse high-order mode beam splitting unit and system |
Citations (3)
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| JP4506329B2 (en) * | 2004-07-26 | 2010-07-21 | ソニー株式会社 | Hologram recording apparatus, information processing apparatus, and hologram recording method |
| CN105258808A (en) * | 2015-11-10 | 2016-01-20 | 中国计量学院 | A method for determining the direction of a partially-coherent laguerre-gaussian light beam vortex |
| CN206133049U (en) * | 2016-09-13 | 2017-04-26 | 西安交通大学 | Column mode conversion lens and because gauss's light mode conversion ware of these lens |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4506329B2 (en) * | 2004-07-26 | 2010-07-21 | ソニー株式会社 | Hologram recording apparatus, information processing apparatus, and hologram recording method |
| CN105258808A (en) * | 2015-11-10 | 2016-01-20 | 中国计量学院 | A method for determining the direction of a partially-coherent laguerre-gaussian light beam vortex |
| CN206133049U (en) * | 2016-09-13 | 2017-04-26 | 西安交通大学 | Column mode conversion lens and because gauss's light mode conversion ware of these lens |
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