CN104914589B - A kind of monochromatic light proportion adjustable polarization-independent beam splitting device - Google Patents

Abstract

The invention discloses a polarization-independent beam splitter with an adjustable ratio of monochromatic light, which comprises: five beam shifters BD arranged in sequence, marked as BD1-BD5; wherein, after incident light enters BD1, it is divided into upper and lower Two beams; the upper and lower beams of light respectively pass through the half-wave plate and the glass compensation plate and then enter BD2. After the walk-off effect of BD2, the upper and lower beams of light are translated downward; the upper and lower beams of light respectively pass through the corresponding half-wave plate After entering BD3, the upper and lower beams of light are divided into two beams by BD3, and become four beams of light distributed from top to bottom; these four beams of light are injected into BD4 through a half-wave plate, and BD4 combines the two middle beams of light into one Beams become three beams of light distributed from top to bottom; these three beams of light respectively pass through the half-wave plate, glass compensation plate and half-wave plate and then enter BD5, and BD5 connects the middle beam with the upper and lower beams respectively Merge, merge into upper and lower two beams of light and then emit. The beam splitter disclosed by the invention can realize the adjustment of beam splitting at any ratio, and has high precision.

Description

A Polarization-Independent Beamsplitter with Adjustable Ratio of Monochromatic Light

technical field

The invention relates to the field of optical technology, in particular to a polarization-independent beam splitter with adjustable ratio of monochromatic light.

Background technique

The beam splitter is the basic device of various optical instruments and experiments. It can split a beam of light into two beams of light or combine two beams of light into one beam of light. Now the polarization-independent beam splitter of the mainstream of space light is the surface coating Type beam splitter (Beam Splitter BS for short), divided into two types: one is 45-degree type BS, but because the current coating process is difficult to coat the reflective and transmissive film well, the ratio cannot be well controlled, And often this kind of coating type BS can only achieve 50:50 for o light (ordinary light), or 50:50 for e light (extraordinary light), but cannot achieve both; the other kind of BS is 0-degree reflective BS , this kind of BS can achieve a very good splitting ratio, but it is inconvenient in practical application because of the 0-degree reflection; and these two kinds of BSs cannot adjust the splitting ratio, and cannot achieve arbitrary ratio adjustment.

In actual optical instruments or optical experiments, a more precise and adjustable splitting ratio is often required, such as the most common MZ interferometer in optics. If you need to observe a better interference visibility, you need a good polarization-independent BS. To achieve; therefore, a scale-adjustable, polarization-independent, high-precision beam splitter is needed to achieve some high-precision beam splitting.

Contents of the invention

The purpose of the present invention is to provide a monochromatic light adjustable ratio polarization-independent beam splitter, which can realize the adjustment of arbitrary ratio beam splitting and has higher precision.

The purpose of the present invention is achieved through the following technical solutions:

A polarization-independent beam splitter with adjustable ratio of monochromatic light, comprising: 5 beam shifters BD arranged in sequence, denoted as BD1-BD5; wherein, a half-wave plate and a glass compensation plate are arranged between BD1 and BD2 There are two half-wave plates between BD2 and BD3, one half-wave plate between BD3 and BD4, two half-wave plates and one glass compensation plate between BD4 and BD5;

After the incident light enters BD1, it is divided into upper and lower beams; the upper and lower beams respectively pass through the half-wave plate and the glass compensation plate and then enter BD2, and the upper and lower beams are translated downward through the walk-off effect of BD2; The upper and lower beams of light respectively pass through the corresponding half-wave plates and then enter BD3. BD3 divides the upper and lower beams of light into two beams, forming four beams of light distributed from top to bottom; these four beams of light are injected into the BD3 through the half-wave plate BD4, the middle two beams of light are combined into one beam by BD4, and become three beams of light distributed from top to bottom; these three beams of light respectively pass through the half-wave plate, the glass compensation plate and the half-wave plate and then enter BD5, and the light is transmitted by BD5 These three beams of light are combined into upper and lower beams and emitted.

Further, the BD1-BD5, and the half-wave plates and/or glass compensation plates between BD1-BD5 are arranged in parallel.

Further, BD1, BD2, and BD5 are all large-size BDs, and BD3 and BD4 are all small-size BDs; wherein, the length of the large-size BD is twice the length of the small-size BD.

Further, the BD is a natural birefringent crystal.

It can be seen from the technical solution provided by the present invention that, on the one hand, the separation of o-light and e-light is realized through the walk-off effect of natural birefringent crystals on o-light and e-light, which has a very high polarization beam splitting ratio, And the parallelism of the outgoing light can be maintained; on the other hand, the use of the wave plate to control the characteristics of the polarization realizes the adjustment of the beam at any ratio. The incident light has better coherence.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings on the premise of not paying creative efforts.

FIG. 1 is a schematic diagram of a monochromatic light adjustable ratio polarization-independent beam splitter provided by an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a BD provided by an embodiment of the present invention.

detailed description

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example

FIG. 1 is a schematic diagram of a polarization-independent beam splitter with an adjustable ratio of monochromatic light provided by an embodiment of the present invention. As shown in Figure 1, it mainly includes:

The five BDs (beam displacer, beam displacer) arranged in sequence are denoted as BD1~BD5; among them, there is a half-wave plate (HWP1 in Figure 1) and a glass compensation plate (HWP1 in Figure 1) between BD1 and BD2 Glass 1), two half-wave plates (HWP2~HWP3 in Figure 1) are set between BD2 and BD3, one half-wave plate (HWP4 in Figure 1) is set between BD3 and BD4, and between BD4 and BD5 There are two half-wave plates (HWP5~HWP6 in Figure 1) and one glass compensation plate (glass 2 in Figure 1).

In the embodiment of the present invention, the BD is a natural birefringent crystal. When a beam of light is incident on the birefringent crystal, two beams of refracted light will be generated. They propagate in different directions and become two beams of light when they leave the crystal. There is a special direction in the crystal. When light propagates along this special direction in the crystal, birefringence will not occur. This special direction is called the optical axis of the crystal.

Exemplarily, the embodiment of the present invention can use Iceland stone, as shown in Figure 2, cut along the place at an angle of 45 degrees to the optical axis, and then the o-light and e-light will be separated naturally, after propagating in the crystal In the air medium, it becomes two parallel beams of light. The distance between the two beams of light is related to the wavelength of the incident light and the length of the crystal, and can be set according to actual requirements.

In the above scheme of the embodiment of the present invention, the walk-off effect of natural birefringent crystals on o-light and e-light is used to realize the separation of o-light and e-light, because the distance of walk-off is different according to the wavelength, so The length of the required BD can be calculated according to the light of the corresponding wavelength. The size of the BD depends on the size of the beam distance to be separated. It must be greater than twice the distance of the BD to ensure that the beam can pass through the BD. In the embodiment of the present invention, BD1, BD2, and BD5 are large-size BDs, BD3 and BD4 are small-size BDs, and the length of the large-size BD is twice the length of the small-size BD.

In addition, 6 half-wave plates and 2 glass compensation plates are installed between BD1 and BD5. Through the characteristics of half-wave plates for polarization control, the adjustment of the beam in any proportion is realized. The purpose of setting glass compensation plates is to ensure that the The optical paths of the light beams are absolutely equal, so as to keep the outgoing light with good coherence.

Preferably, the above-mentioned BD1-BD5, and the half-wave plates and/or glass compensation plates between BD1-BD5 are all arranged in parallel, on the one hand, the optical paths of each light beam can be made as equal as possible; The incident light has better coherence.

The structure and principle of the monochromatic light adjustable ratio polarization-independent beam splitter provided by the present invention are described above, and the beam splitting process thereof will be described in detail below.

As shown in Figure 1, after the incident light enters BD1, it is divided into upper and lower beams; the separation distance depends on the wavelength of the incident light and the length of the crystal. ) are separated by 4 mm, and small size BDs (BD3 and BD4) are separated by 2 mm.

The upper and lower beams pass through the half-wave plate (HWP1) and the glass compensation plate (glass 1) respectively. Here, adjust the position of the half-wave plate (HWP1) to 45 degrees so that the upper beam of o light passes through the half-wave plate After (HWP1), it becomes e-light; for the beam below which is e-light, a glass compensation sheet (glass 1) is added for compensation. Its polarization direction remains unchanged; after that, it is injected into BD2, and the upper and lower beams are translated downward after the walk-off effect of BD2.

The upper and lower beams pass through the corresponding half-wave plates (HWP2~HWP3) respectively, and adjust the position of the half-wave plates (HWP2~HWP3) to 22.5 degrees. The function of these two wave plates is to convert a single horizontally polarized or vertically polarized light It becomes obliquely polarized light at any angle, so that the beam can be split at any ratio through the two half-wave plates.

Exemplarily, it can be realized by adjusting the rotation angle of the half-wave plate.

The Jones matrix for half-wave plate rotation is:

Among them, x is the rotation angle of the wave plate, that is to say, by rotating a certain angle, the polarization direction of the linearly polarized light can be changed. Assuming that the horizontally polarized light is H light and the vertically polarized light is V light, then one H light After half-wave plate rotation, it can become aH+bV, where a ² +b ² =1. In this way, a beam of H light or V light will be divided into any required ratio when passing through a half-wave plate, and then through BD3. As can be seen from the schematic diagram, the beam splitting ratio of the output light of BD3 directly determines the beam splitting of the final two output ports. Ratio, so HWP2 and HWP3 calculate the angle according to the ratio to achieve the required splitting ratio. It should be noted that the aforementioned o-light and e-light refer to the light whose polarization direction is always perpendicular to the optical axis and does not change with the change of the propagation direction relative to the crystal. The angle varies with the propagation direction; and the H light and V light here are relative to the laboratory coordinates, the H light refers to the light polarized along the horizontal direction, and the V light refers to the light polarized along the vertical direction. straight polarized light. After unifying the laboratory coordinates and the optical axis of the crystal, they can be converted to each other. Since the above problems are usually described in terms of laboratory coordinates, the H-light and V-light methods are also used here to describe.

After that, it is injected into BD3, and the upper and lower beams of light are divided into two beams by BD3 respectively, becoming four beams of light distributed from top to bottom.

These four beams of light pass through the half-wave plate, here, adjust the position of the half-wave plate (HWP4) to 45 degrees, so that all the light polarization directions are changed by 90 degrees; after that, enter BD4, and BD4 combines the middle two beams of light into one One beam becomes three beams of light distributed from top to bottom.

The three beams of light pass through the half-wave plate, the glass compensation plate and the half-wave plate respectively and then enter the BD5. The BD5 combines the three beams of light into upper and lower beams and then emits them.

The merging process is as follows: among the three beams, the first beam only includes e beam, the second beam includes both o beam and e beam, and the third beam only includes o beam; after entering BD5, the first beam will deflected downward, the o light in the second beam continues to propagate along the previous direction, and merges with the first beam into one beam, while the remaining e light is deflected downward and merged with the third beam, finally It emits light in two ways.

Compared with the prior art, the above solutions of the embodiments of the present invention mainly have the following advantages:

1) Using natural birefringent crystals, the beam splitting of o-light and e-light is natural, has a high polarization splitting ratio, and can maintain the parallelism of the outgoing light.

2) Use the half-wave plate to control the beam splitting ratio of the beam, so that any ratio of beam splitting can be adjusted.

3) Natural birefringent crystals are used, so it is convenient to adjust, as long as the crystals are kept parallel, the beam splitter can be constructed.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technical field can easily conceive of changes or changes within the technical scope disclosed in the present invention. Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (4)

1. A monochromatic light adjustable ratio polarization-independent beam splitter is characterized in that it comprises: 5 beam shifters BD arranged in sequence, denoted as BD1～BD5; wherein, a half-wave beam splitter is provided between BD1 and BD2 There are two half-wave plates between BD2 and BD3, one half-wave plate between BD3 and BD4, two half-wave plates and one glass compensation plate between BD4 and BD5; After the incident light enters BD1, it is divided into upper and lower beams; the upper and lower beams respectively pass through the half-wave plate and the glass compensation plate and then enter BD2, and the upper and lower beams are translated downward through the walk-off effect of BD2; The upper and lower beams of light respectively pass through the corresponding half-wave plates and then enter BD3. BD3 divides the upper and lower beams of light into two beams, forming four beams of light distributed from top to bottom; these four beams of light are injected into the BD3 through the half-wave plate BD4, the middle two beams of light are combined into one beam by BD4, and become three beams of light distributed from top to bottom; these three beams of light respectively pass through the half-wave plate, the glass compensation plate and the half-wave plate and then enter BD5, and the light is transmitted by BD5 These three beams of light are combined into upper and lower beams and emitted. 2. The beam splitter according to claim 1, characterized in that, the BD1-BD5, and the half-wave plates and/or glass compensation plates between BD1-BD5 are arranged in parallel. 3. The beam splitter according to claim 1, wherein BD1, BD2, and BD5 are all large-size BDs, and BD3 and BD4 are all small-size BDs; wherein, the length of the large-size BD is equal to the length of the small-size BD double. 4. The beam splitter according to claim 1, wherein the BD is a natural birefringent crystal.