JPH0120404B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] This invention provides a multi-reflection type that uses a transparent medium and a polarization plane rotator that exhibit different transmittance and reflectance depending on the rotation angle of the polarization plane of light. Regarding optical delay devices.

[Conventional technology]

Conventionally, in order to obtain the delay time of light, it has been necessary to pass the light through a medium with a large refractive index, or to propagate the light over a long distance using a fiber or a reflecting mirror.

[Problem that the invention seeks to solve]

By using such means, it is possible to obtain a light delay time, but in order to obtain a large delay time, if a medium with a high refractive index is used, the loss of light will be large, so it is difficult to actually obtain a large delay time. In many cases, this is not practical, and when multiple reflections using fibers or reflectors are used, a long propagation path is required, and many parts and materials must be procured and installation locations must be secured. It was hot.

The present invention was made to solve the above-mentioned problems of conventional optical delay devices, and an object of the present invention is to provide a small-sized optical delay device that can obtain a desired light delay time with a simple configuration. The purpose is to

[Means and actions for solving problems]

In order to solve the above problems, the present invention arranges a transparent medium that transmits or reflects only light of a specific polarization plane between two reflecting mirrors, and a polarization plane rotator that rotates the polarization plane of the light. , the light with a specific polarization plane incident on the transparent medium is rotated each time it passes through the polarization plane rotator, and is passed through the reflecting mirrors at both ends of the optical path of the transparent medium and the polarization plane rotator. After repeating reflection a predetermined number of times, the polarization plane is set at a rotation angle that allows the light to pass through the transparent medium, and the light is emitted from the transparent medium, thereby obtaining a light delay time.

In the optical delay device configured in this way, when light with a certain plane of polarization is incident through the transparent medium, the plane of polarization of the light that has passed through the transparent medium is rotated by the plane of polarization rotator, and the plane of polarization is rotated at one end of the optical path. The light is reflected by one of the provided reflecting mirrors and passes through the polarization plane rotator again from the opposite direction, so that the plane of polarization is further rotated in the same direction. When it reaches the transparent medium, the plane of polarization will be different from the plane of polarization at the time of initial incidence, but with the plane of polarization at that rotation angle, most of the light re-entering the transparent medium will be reflected and not transmitted. If the other reflecting mirror is placed opposite the direction in which the light re-entering the transparent medium is reflected, the light will be reflected back to the transparent medium from this reflecting mirror. In this way, reflection is repeated several times in the reflection system consisting of the transparent medium, the polarization plane rotator, and both reflecting mirrors. After a predetermined number of reciprocations, when the rotation angle of the polarization plane of the light incident on the transparent medium satisfies the condition for transmitting through the transparent medium, the light confined in the reflection system passes through the transparent medium and is emitted. Thereby, it is possible to obtain an optical delay time corresponding to a predetermined number of reciprocations within the reflection system consisting of the transparent medium, polarization plane rotator, and reflection mirror.

〔Example〕

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to describing embodiments of the present invention, the basic configuration of the present invention will be described below. FIG. 1A is a basic configuration diagram of the present invention, in which the light propagation direction is the X-axis direction, the transparent medium 1 is placed in the direction perpendicular to the paper surface, that is, the Z-axis direction, and the transparent medium 1 is placed in the Z-axis direction. The normal N direction and the X axis are arranged so as to form an angle of θ ₁ . 2
is a polarization plane rotator, which is disposed between the reflective mirror 3 placed on the X-axis and the transparent medium 1. Reference numeral 4 denotes a reflecting mirror arranged perpendicularly to the direction of the reflected light from the transparent medium 1.

Now, if the light passes through the transparent medium 1 and heads towards the polarization plane rotator 2, the polarization plane for the electric field of the light will be as shown in Figure 1B when viewed from the rear where the light propagates. , ψ from the Z axis of the Y-Z plane perpendicular to the X axis
, and its amplitude is E ₀ , then there is a component E _H (component parallel to the plane of incidence) on the X-Y plane of the plane of polarization, and a component E _V (component parallel to the plane of incidence) on the X-Z plane of the plane of polarization. component perpendicular to the surface) is expressed by the following formula.

E _H = E ₀ sinψ ...(1) E _V = E ₀ cosψ ...(2) After the electric field with this polarization plane component passes through the polarization plane rotator 2, the polarization plane is rotated by Δψ without loss. ,
It is expressed by the following equation, where the polarization plane components of the electric field are E _H1 and _EV1 .

E _H1 = E ₀ sin (ψ + Δψ) ... (3) E _V1 = E ₀ cos (ψ + Δψ) ... (4) After passing through the polarization plane rotator 2, it is reflected by the reflector 3, and then the polarization plane rotator 2 , and its polarization plane is further rotated by Δψ in the same direction. If the polarization plane components of the output electric field are E _H2 and _EV2 , then the following equation holds true.

E _H2 = E ₀ sin (ψ+2Δψ) ...(5) E _V2 = E ₀ cos (ψ+2Δψ) ...(6) Next, the light transmitted through the polarization plane rotator 2 enters the transparent medium 1. Here, the refractive index of the transparent medium 1 is n ₂
If the refractive index of the medium other than the transparent medium is n ₁ , and if multiple reflections in the transparent medium 1 with refractive index n ₂ can be ignored, then the reflectance for the polarization plane components E _H and E _V is R _H , _RV and transmittance T _H , _TV are expressed by the following equations, respectively.

R _H = tan (θ ₁ - θ ₂ ) / tan (θ ₁ + θ ₂ ) ...(7) T _H = 2sinθ ₂ cosθ ₁ / sin (θ ₁ + θ ₂ ) cos (θ ₁ - θ ₂ )
……(8) R _V = sin(θ ₁ −θ ₂ )/sin(θ ₁ +θ ₂ )……(9) T _V =2cosθ ₁ sinθ ₂ /sin(θ ₁ +θ ₂ )……(10) However, θ ₁ is the angle of incidence, θ ₂ is the angle of refraction, and the refractive index
The following relationship exists between n ₁ , n ₂ , the incident angle θ ₁ , and the refraction angle θ ₂ .

n ₁ sin θ ₁ = n ₂ sin θ ₂ ...(11) Therefore, the component on the X-Y plane reflected by the transparent medium 1 of the light incident from the polarization plane rotator 2 and the
If the components on the −Z plane are E _HO2R and E _VO2R , (5),
It is expressed as follows using equations (6), (7), and (9).

E _HO2R = E _H2・R _H = E ₀ sin (ψ + 2Δψ) tan (θ ₁ − θ ₂ )
/tan (θ ₁ + θ ₂ ) ...(12) E _VO2R = E _V2・R _V = E ₀ cos (ψ + 2Δψ) sin (θ ₁ − θ ₂ )
/sin(θ ₁ +θ ₂ ) ...(13) Polarization plane component E _HO2R of light reflected by transparent medium 1,
E _VO2R is assumed to be reflected by the reflecting mirror 4 while preserving the polarization plane, and among the reflected light incident on the transparent medium 1, the transmitted component on the X-Y plane is E _H2PT and the reflected component is E _H2PR . , the transmitted component on the X-Z plane is E _V2PT ,
When the reflected components are expressed as E _V2PR , they are each expressed by the following equations.

E _H2PT = E _HO2R・T _H =E ₀ sin(ψ+2Δψ) ・tan(θ ₁ −θ ₂ )/tan(θ ₁ +θ ₂ )・2sinθ ₂ cosθ ₁
/sin (θ ₁ + θ ₂ ) cos (θ ₁ − θ ₂ ) ... (14) E _H2PR = E _HO2R・R _H = E ₀ sin (ψ + 2Δψ)・tan ² (θ ₁ − θ ₂ ) / tan ² ( θ ₁
+θ ₂ ) ……(15) E _V2PT = E _VO2R・T _V = E ₀ cos(ψ+2Δψ) sin(θ ₁ −θ ₂ )/sin ² (θ ₁ +θ ₂ )・2cosθ ₁ sinθ ₂ ……(16) E _V2PR = E _VO2R・R _V = E ₀ cos (ψ + 2Δψ) sin ² (θ ₁ − θ ₂ )/sin ² (θ ₁ +
θ ₂ ) ...(17) Therefore, from the transparent medium 1 to the polarization plane rotator 2,
The propagation of light that reaches the transparent medium 1 via the reflecting mirror 3, the polarization plane rotator 2, the transparent medium 1, and the reflecting mirror 4 is regarded as one round trip, and the light that reaches the transparent medium 1 from the reflecting mirror 4 after making m round trips is defined as one round trip. The component of the transmitted light on the X-Y plane is E _H2nT ,
Letting the component on the X-Z plane be E _V2nT and considering the loss on the propagation path, each is expressed by the following equations. However, m is 1, 2, 3, . . . A, B are loss coefficients smaller than 1.

E _H2nT =AE ₀ sin(ψ+2mΔψ)・{tan(θ ₁ −θ ₂ )/ta
n (θ ₁ + θ ₂ )} ^2m-1・2sinθ ₂ cosθ ₁ / sin (θ ₁ + θ ₂ ) cos (θ ₁ − θ ₂ ) ... (18) E _V2nT = BE ₀ cos (ψ + 2mΔψ) ・{sin ( θ ₁ −θ ₂ )/sin(θ ₁ +θ ₂ )} ^2m-1・2cosθ
₁ sin _{θ 2} /sin (θ ₁ + θ ₂ ) ... (19) As can be seen from equations (18) and (19) above, the incident angle of light into transparent medium 1 θ ₁ and the refractive index of transparent medium 1 n ₂ ,
The intensity of the transmitted light changes depending on the refractive index n ₁ of the light propagation path (air etc.) around the transparent medium 1 and the number m of round trips of the light propagation. In other words, the transmitted light polarization component
If the configuration is configured to detect only when the transmitted light of either E _H2nT or E _V2nT exceeds a predetermined intensity, the time required for the light to make one round trip is T, and the time at the detection point is If the number of round trips is m,
This means that a delay time of only mT can be obtained.

Next, specific examples of the present invention will be described.
FIG. 2 is a schematic diagram of an embodiment of an optical delay device according to the present invention. In the figure, 11 is a light source,
The light emitted from the light source 11 and passed through the transparent medium 12 is configured so that only light having a certain linear polarization is outputted by the polarizer 13 and guided to the polarization plane rotator 15 via the transparent medium 14. There is. The polarization plane rotator 15 rotates the polarization plane by Δψ every time the light passes through it once.
The light emitted from the polarization plane rotator 15 is reflected by a reflecting mirror 16 and passes through the polarization plane rotator 15 again. At this time as well, the plane of polarization is assumed to be rotated by Δψ in the same direction as the direction in which the light was rotated when it traveled from the transparent medium 14 toward the reflecting mirror 16. In other words, since the polarization plane of the light entering the polarization plane rotator 15 is configured so that it always rotates in the same direction no matter which direction it enters, the rotation angle of the polarization plane is added in either case. The light is reflected by the reflecting mirror 16, passes through the polarization plane rotator 15 again, has its polarization plane rotated by 2Δψ, and reaches the transparent medium 14. Part of this light passes through the transparent medium 14, and part of this light passes through the transparent medium 1.
It is reflected at 4. The light reflected by the transparent medium 14 is
Reflector 1 placed opposite transparent medium 14
7 and reaches the same position on the transparent medium 14 again. Therefore, part of it is transmitted through the transparent medium 14, and part of it is reflected in the direction of the polarization plane rotator 15 through the same propagation path that it passed before.

As described above, the light transmitted through the transparent medium 14 via the polarizer 13 is transmitted to the polarization plane rotator 15, the reflecting mirror 16,
polarization plane rotator 15, transparent medium 14, reflecting mirror 17,
This is defined as one round trip, and after m round trips, the light passes through the transparent medium 14 and passes through the analyzer 18 placed on the optical path of the transmitted light. The detector 19 is configured to detect only those having a level equal to or higher than a predetermined value. Note that the analyzer 18 includes a light source 11 and a transparent medium 1.
2. It is also used to remove reflected waves from the polarizer 13 and the transparent medium 14.

Next, the delay time of the optical delay device configured as described above will be explained. It is assumed that a delay time is defined for light emitted from the light source 11, reflected by the transparent medium 12, and detected by the detector 20. The optical propagation path length between the transparent medium 12 and the detector 20 is
L ₁ is the light propagation path length from the transparent medium 12 to the transparent medium 14 via the polarizer 13, L ₂ is the light propagation path length from the transparent medium 14 to the reflective mirror 16 via the polarization plane rotator ₁₅ , and is transparent. The light propagation path length between the medium 14 and the reflecting mirror 17 is L ₄ , the light propagation path length from the transparent medium 14 to the detector 19 via the analyzer 18 is L ₅ , and the light propagation from L ₁ to L ₅ The path is assumed to be equivalent to the propagation path of light in vacuum. Here, among the light emitted from the light source 11, what is detected by the detector 20 and after passing through the transparent medium 14 and reciprocating m times,
If the time difference from that detected by the detector 19 is Δt, it is expressed by the following equation.

Δt=1/C{ _L2 +2m( _L3 + _L4 )+ _L5 - _L1 }...(20) However, C is the speed of light.

Therefore, by appropriately setting the values of L ₁ , L ₂ , L ₃ , L ₄ , L ₅ and the value of m, a desired delay time can be obtained.

〔Effect of the invention〕

As described above based on the basic configuration and examples, the present invention combines a transparent medium whose transmittance and reflectance change depending on the rotation angle of the polarization plane, and a polarization plane rotator that rotates the polarization plane into two reflectors. The structure is such that the delay time is obtained by interposing the light incident on the transparent medium between the mirrors and emitting the light from the transparent medium after the light is reflected a predetermined number of times, so it is possible to easily obtain the desired delay time. It is possible to provide an optical delay device that is small in size and has a simple configuration.

[Brief explanation of drawings]

FIG. 1A is an explanatory diagram for explaining the basic configuration of the present invention, FIG. 1B is a diagram showing the polarization plane of light transmitted through a transparent medium, and FIG. 2 is an illustration of the optical delay device according to the present invention. It is a schematic diagram showing one example. In the figure, 1 is a transparent medium, 2 is a polarization plane rotator, 3 and 4 are reflecting mirrors, 11 is a light source, 12 is a transparent medium, 13 is a polarizer, 14 is a transparent medium, 15 is a polarization plane rotator, 16, 17 is a reflector, 18 is an analyzer,
19 and 20 indicate detectors.

Claims (1)

[Claims] 1 A transparent medium that transmits or reflects only light of a specific polarization plane between two reflecting mirrors and a polarization plane rotator that rotates the polarization plane of the light are arranged, and the polarization plane of the specific polarization plane incident on the transparent medium is arranged. The polarization plane of the light is rotated each time it passes through the polarization plane rotator, and the light is reflected a predetermined number of times through the transparent medium and the reflecting mirrors at both ends of the optical path of the polarization plane rotator. An optical delay device characterized in that the optical delay device is configured to emit light from a transparent medium with a polarization plane having a rotation angle that allows the light to pass through the medium, thereby obtaining a delay time of light.