A light trap for absorbing and suppressing laser stray light

Abstract

The present invention discloses a light trap for absorbing and suppressing laser stray light. The light trap comprises a reflector, on which a reflective cavity with a conical cross section is provided; the absorption rate of the reflective cavity to incident light is ε>95%; the taper of the reflective cavity is 2α; wherein 8°<α≤16.36°; the stray light suppression ratio of the reflector is: #imgabs0#n max The invention enables the stray light suppression ratio to reach above 1E-7, which meets the requirements of the current high-sensitivity system for stray light suppression capability.

Description

Technical Field

[0001] The present invention relates to an optical trap for absorbing and suppressing laser stray light. The optical trap can be used in active laser detection optical systems such as laser communication and laser radar to suppress and reduce the interference effect of emitted laser on detectors and improve the transmit-receive isolation of the active laser detection optical system. Background Art

[0002] The laser power emitted by active laser detection systems (such as laser communication systems, laser radar systems, etc.) is much higher than the laser power received. The ratio of the emitted laser power to the received laser power of some highly sensitive systems can even be as high as 10. 10 Such a high-power laser beam can easily cause stray light to overwhelm the received light power, making the system unable to work properly. Figure 1 The figure shows a common stray light path of the emitted laser beam. Part of the energy of the laser emitted by the emission channel hits the mechanical wall of the structure through the beam splitter, and part of the light is scattered by the mechanical wall and reaches the receiving channel through the beam splitter to form stray light. The usual way to reduce this stray light is to eliminate the stray light on the mechanical wall. Common stray light elimination methods include: 1) black anodizing; 2) spraying matte paint; 3) pasting black velvet, etc. The essence of these stray light elimination methods is to increase the absorption rate of the mechanical wall, but the stray light suppression ratio (ratio of the outgoing light energy to the incident light energy) of these methods is difficult to reach the order of 1E-4, which is difficult to meet the requirements of high-sensitivity systems for stray light suppression capabilities. Summary of the invention

[0003] In order to solve the problem that the stray light suppression ratio (ratio of outgoing light energy to incident light energy) of the existing stray light elimination processing methods in the background technology is difficult to reach the order of 1E-4, and it is difficult to meet the requirements of high-sensitivity systems for stray light suppression capability, the present invention proposes an optical trap that absorbs and suppresses laser stray light, and its stray light suppression ratio can be better than 1E-7, which can greatly reduce the stray light caused by the emitted laser.

[0004] The specific technical solution of the present invention is:

[0005] The present invention provides a light trap for absorbing and suppressing laser stray light, comprising a reflector, on which a reflective cavity with a conical cross section is provided;

[0006] The reflector's absorption rate of each reflection of incident light is ε>95%;

[0007] The taper of the reflection cavity is 2α; wherein 8°<α≤16.36°;

[0008] The stray light suppression ratio of the reflector is: n max It is the maximum number of reflections of light in the reflection cavity.

[0009] Furthermore, the above-mentioned reflective cavity has two forms:

[0010] First, the reflection cavity is a conical cavity.

[0011] Second, the reflection cavity is composed of two intersecting inclined planes with the same inclination angle, and the inclination angle of the inclined plane is α.

[0012] Furthermore, the maximum number of reflections of light by the above-mentioned reflection cavity is n max The specific calculation formula is: max =roundup(90 / α-0.5), where roundup() is the rounding up function.

[0013] Furthermore, the above light trap has two forms:

[0014] 1. The reflector is made of metal aluminum material. The surface of the reflective cavity of the reflector is polished into a mirror surface with a root mean square value of roughness less than 3nm. The surface of the reflective cavity is plated with an absorption film layer, which is a chromium plus dielectric anti-reflection film.

[0015] 2. The reflector is made of colored absorption glass, and the internal transmittance of the colored absorption glass per millimeter at the working wavelength is less than 0.01%; the reflective cavity surface of the reflector is polished into a mirror surface, and its root mean square value of roughness is less than 3nm; the surface of the reflective cavity is plated with an anti-reflection film.

[0016] Furthermore, the reflector is composed of two wedge-shaped pieces.

[0017] The beneficial effects of the present invention are:

[0018] 1. The light trap proposed in the present invention adopts a structure combining a reflection cavity and an absorption film layer. The incident laser is reflected multiple times in the reflection cavity, and the absorption rate is very high, so that the stray light suppression ratio can reach above 1E-7, which meets the requirements of the current high-sensitivity system for stray light suppression capability.

[0019] 2. The light trap proposed in the present invention consists of only a reflector with a reflection cavity inside and an absorption film layer, and has a simple structure, is easy to process and manufacture, and can be widely used.

[0020] 3. The light trap proposed in the present invention adopts a reflective cavity structure. No matter what the incident angle of the laser in the reflective cavity is, the angle of the emitted stray light is fixed, ensuring that the light trap can still ensure that the emitted stray light deviates from the receiving field of view even if there is an installation error. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a common stray light path of the emitted laser beam;

[0022] Figure 2It is a structural schematic diagram of a light trap in which the reflection cavity is a conical cavity in the present invention;

[0023] Figure 3 It is a schematic diagram of the structure of the reflection cavity of the present invention as two inclined light traps;

[0024] Figure 4 is the absorptivity curve of the absorption film of the present invention;

[0025] Figure 5 FIG. 4 is a diagram of the light path in the light trap of the present invention.

[0026] The reference numerals are as follows:

[0027] 1- reflector, 2- reflection cavity, 3- inclined surface, 4- wedge. DETAILED DESCRIPTION

[0028] In order to make the purpose, advantages and features of the present invention clearer, the light trap for absorbing and suppressing laser stray light proposed by the present invention is further described in detail below in combination with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that: the drawings are all in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention; secondly, the structure shown in the drawings is often part of the actual structure.

[0029] like Figure 2 and Figure 3 As shown, the light trap includes a reflector 1, on which a reflective cavity 2 with a conical cross section is provided; the taper of the reflective cavity 2 is 2α. Among them, 8°<α≤16.36°; the absorptivity ε of each reflection of the incident light by the reflector 1 is>95%; the reflective cavity 2 has two forms: 1. The reflective cavity is an integral conical cavity; 2. The reflective cavity is composed of two intersecting inclined planes 3 with the same inclination angle, and the inclination angle of the inclined plane 3 is α. Form 1 is more in line with the requirements of optical devices, and form 2 is easier to process and manufacture.

[0030] The light trap absorbs part of the light energy each time the light is incident. After multiple reflections, the light energy is absorbed multiple times in the reflection cavity of the light trap, and the final emitted light energy is much less than the incident light energy. (The reflector in the figure is composed of two wedge-shaped pieces 4, and a reflection cavity 2 is formed by splicing the two wedge-shaped pieces, see Figure 3 Alternatively, a reflective cavity 2 can be directly processed on a reflector, see Figure 2 )

[0031] There are two ways to implement reflectors:

[0032] The first type is that the reflector 1 is made of metal aluminum material, the surface of the reflective cavity 2 is polished into a mirror surface (the root mean square value of the roughness should be less than 3nm), and the surface of the reflective cavity 2 is plated with an absorption film layer for the laser wavelength (not shown in the figure), and the absorption rate of the absorption film layer at the working wavelength is greater than 90%. When the laser is incident on the surface of the reflective cavity, part of the laser energy is absorbed by the absorption film layer, and the absorption rate ε of this type of absorption film layer at a single wavelength can reach more than 95%. For example, the reflector is processed by polished aluminum material, and the absorption film layer of chrome plus dielectric anti-reflection film is plated on the inner surface of the reflective cavity. Its absorption rate is as follows Figure 3 shown.

[0033] The second type is that the reflector 1 is made of colored absorption glass, and the internal transmittance of the colored absorption glass per millimeter at the working wavelength is less than 0.01%. The surface of the reflection cavity 2 is polished into a mirror surface (the root mean square value of the roughness should be less than 3nm); the surface of the reflection cavity 2 is plated with a dielectric anti-reflection film for the working wavelength. The function of the anti-reflection film is to reduce the reflection on the surface of the reflection surface, so that more light enters the colored absorption glass, and is absorbed by the colored absorption glass. The transmittance of the anti-reflection film at the working wavelength should be greater than 99.5%. For example, for lasers in the 1550nm band, the reflector is made of Schott KG5 colored absorption glass material, and the surface of the KG5 colored absorption glass reflector is plated with an anti-reflection film. The reflectivity of the reflector surface in the 1550nm band is less than 0.5%, and the remaining 99.5% of the energy enters the KG5 glass. The internal transmittance of the 1550nm laser in the KG5 glass is only 4.25e-5 / mm, and almost all the light energy entering the glass is absorbed.

[0034] The two reflector schemes each have their own advantages. The first scheme uses metal aluminum material with strong processability; the second scheme has a higher absorption rate and stronger stray light suppression ability.

[0035] The light beam is reflected multiple times in the reflection cavity, and the incident angles for the 1st, 2nd, 3rd, ..., nth times are:

[0036] A 1 =90°-α (1)

[0037] A 2 =180°-(90°-A 1 )-2α-90°=90°-3α (2)

[0038] A 3 =180°-(90°-A 2 )-2α-90°=90°-5α (3)

[0039] ······

[0040] A n =180°-(90°-A n-1)-2α-90°=90°-(2n-1)α (4)

[0041] Among them, when A n >0, that is, n<(45 / α+0.5), the light beam propagates into the reflection cavity of the light trap; when A n <0, that is, when n>(45 / α+0.5), the light beam begins to propagate outside the reflection cavity of the light trap.

[0042] When 90°+A n When ≤2α, that is, (2n+1)α≥180°, the reflected light beam no longer intersects with the opposite reflection surface, and the light beam will be emitted from the light trap. Therefore, the maximum number of reflections can be calculated as:

[0043] n max =roundup(90 / α-0.5) (5)

[0044] Where roundup() is the rounding up function.

[0045] The exit angle is:

[0046] β=180°-2n max α (6)

[0047] The design of angle α should meet the following requirements: 1. As many reflection times as possible to absorb more light energy, generally the number of reflections should be greater than 6 times; 2. The angle of the outgoing light deviates from the receiving field of view θ of the receiving light path; 3. In order to meet a certain opening size of the reflection cavity, α cannot be too small, otherwise the length of the light trap will be too long, generally α should be greater than 8°. Therefore, the restriction conditions for α are:

[0048]

[0049] The receiving field of view of the receiving optical path is generally within 3°. From the above formula, the design constraint condition of angle α is:

[0050] 8°<α≤16.36° (8)

[0051] The stray light suppression ratio of the light trap is defined as the ratio of the light energy of the outgoing light trap to the light energy of the incident light trap. The stray light suppression ratio of the light trap is:

[0052]

[0053] Specific Examples

[0054] According to the range of angle α in formula (8), α=14°. The reflector is composed of two aluminum wedges. The surface of the reflective cavity is polished into a mirror surface (the roughness should be less than 3nm) by metal aluminum. An absorption film is plated on the surface of the reflective cavity. The absorption rate of the absorption film at 1550nm is 97.2%. When the laser is incident into the optical trap, the path of the laser is as follows: Figure 5 As shown. According to formula (7), the total number of reflections is calculated to be 6, which is consistent with the ray tracing result. Each time the light beam hits the absorption surface, 97.2% of the light energy is absorbed. After 6 absorptions, the energy of the exiting light trap is:

[0055]

[0056] Therefore, the stray light suppression ratio of this light trap is 4.8E-10.

[0057] Finally, it should be noted that the above description is only a description of the preferred embodiment of the present invention, and is not any limitation to the scope of the present invention. Any changes and modifications made by ordinary technicians in the field of the present invention based on the above disclosure are within the scope of protection of the claims.

Claims

1. An optical trap for absorbing and suppressing laser stray light, characterized in that: The reflector comprises a reflector, on which a reflective cavity with a conical cross section is provided; the reflector has an absorption rate ε>95% for each reflection of incident light; The taper of the reflection cavity is 2α; where 8°<α≤16.36°; The stray light suppression ratio of the reflector is: n max is the maximum number of reflections of light by the reflection cavity; The reflector is composed of two wedge-shaped pieces; The reflector is made of metal aluminum material, and the reflective cavity surface of the reflector is polished into a mirror surface with a root mean square value of roughness less than 3nm; the reflective cavity surface is plated with an absorption film layer, which is a chromium plus dielectric anti-reflection film.

2. The optical trap for absorbing and suppressing laser stray light according to claim 1, characterized in that: The reflection cavity is a conical cavity.

3. The optical trap for absorbing and suppressing laser stray light according to claim 1, characterized in that: The reflection cavity is composed of two intersecting inclined planes with the same inclination angle, and the inclination angle of the inclined plane is α.

4. The optical trap for absorbing and suppressing laser stray light according to claim 1, 2 or 3, characterized in that: The maximum number of reflections n of the light in the reflection cavity max The specific calculation formula is: max =roundup(90 / α-0.5), where roundup() is the rounding up function.

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