JPS58190906A - Beam splitter - Google Patents

Abstract

PURPOSE:To control the polarization component ratio between the reflected light and the transmitted light for a beam splitter which is formed by using a multi- layer interference thin film layer formed, by laminating alternately a film layer of a low refractive index and a layer of a high refractive index. CONSTITUTION:A multi-layer interference thin film layer L is vapor-deposited to a prism block 11. A prism block 12 is joined to the block 11 via an adhesive 13. The layer L is generally formed with an N layer film. The 1st layer uses a film of a low refractive index (refractive index NL and film thickness lambda0/4); the 2nd layer uses a film of a high refractive index (refractive index NH and film thickness lambda0/4); and the highest N layer uses a film of a low refractive index respectively. The refractive index of a film layer of a low refractive index is set higher than the refractive index NS of a foundation substrate. With prescribed substrate refractive index NS and refractive index NL of a low refractive index film layer, both the refractive index NH of a high refractive index film layer and the number N of layers are varied to obtain the transmitting characteristics to desired Q and S polarization components.

Description

DETAILED DESCRIPTION OF THE INVENTION A beam splitter that uses a thin film to make the polarization components of reflected light and transmitted light equal to those of incident light, as well as to freely set the component ratio.
It is related to.

In general, is the degree to which light without an origin has an angle to the boundary of different media.
When incident, the reflected light and transmitted light at the interface contain P light modulation (modulated in four vibration directions parallel to the plane of incidence) and 81m light (polarized light with vibration direction perpendicular to the plane of incidence). The component ratio differs for each. This component ratio depends on the angle of incidence and the refractive index of both media, but normally the reflected light contains a large amount of the S@ original acid component, and the transmitted light contains many Plif components, and at the so-called Prewster angle, Sa+ components, Pli
It is also known that the light components are separated into reflected light and transmitted light, respectively. A polarizing prism that actively utilizes this phenomenon is known in Japanese Patent Publication No. 55-9683, etc., and this type of dimming f II system has been put into practical use, for example, in Philips' MCA-type disc playback optical system. has been done. However, the dimming delism used here is not essential as a basic element for signal reproduction, but is intended for stabilizing the output of a laser oscillator as a reproduction light source. In other words, in conventional laser oscillators used for optical disc playback, when there is a reverse incidence of signal light called puncture talk, the output of the oscillation output light varies depending on the phase relationship, which affects signal playback. This will result in negative effects. Therefore, in addition to the above-mentioned polarizing prism, a quarter wavelength plate has been used in a conventional original disk reproducing optical system to prevent pack talk. (
Note that the details of the functions of the single-light prism, the quarter-wave plate, and the reproduction optical system in this case are already known, and therefore will not be described. ) However, in recent years, various improvements have been made to laser oscillators, including ones that do not have the problem of pack talk mentioned above, and even some types of semiconductor lasers that utilize the self-coupling effect to eliminate reverse incident light. There have also been proposals for detecting signals using the same. Under these circumstances, not only the polarizing prism used in the conventional optical disk reproducing optical system but also the
The /4 wavelength plate is also unnecessary, and the reproduction optical system can be significantly simplified. Figure 1 shows an example of an optical disk reproducing optical system simplified in this way.The laser oscillator 1
It is assumed that a method is used that does not involve pack talk. The light from the laser oscillator 1 is converted into a parallel beam by the collimator lens 2 and sent to the beam splitter.
3. Beam splitter 3 has a half mirror
3' is formed, and for example, it is assumed that it has 5 degrees of light transmission and 50 degrees of reflection. The light beam reflected by the half mirror 3' is converged by the objective lens 4 onto the signal portion of the disk 5, and illuminates a concavo-convex signal portion called a pit provided as a signal portion as a spot. The reflected light from this signal section is phase modulated according to the bit shape and size, and is accompanied by a change in intensity due to optical interference, and this light enters the objective lens 4 again as signal light. The signal light, which has been made into a parallel light beam by the objective lens 4, also reaches the half mirror 3', and the light beam transmitted therethrough is detected by the photosensor 6. According to the above configuration, the light from the laser oscillator 1 is reflected once by the half mirror 3' and then transmitted, so if the transmittance (or reflectance) of the half mirror 3' is 501,
The amount of acid in the light reaching the photosensor 6 is 25%.
This place has the highest utilization rate of light ever.

However, in the optical system described above, the half mirror 3'
is used as a reflective surface and also as a transmitting surface1,
Therefore, if a conventionally commonly used half mirror is provided in this optical system, the light utilization efficiency will be further reduced. This is because, as already mentioned, in a normal half mirror, p
Since the reflection and transmission characteristics for t1 element and 81 polarized light are different, most of the P@ light is transmitted when it first acts as a reflecting surface, and most of the light of sm'lt is reflected on the disk 5.
directed towards. (However, it is assumed that the total amount of reflected light is 5 degrees.) Then, when the signal light mainly composed of AM light reflected from the disk 5 enters the half mirror 3' again, the general half mirror Due to the characteristics, most of this signal light is reflected again by the half mirror 3', and the light reaching the photosensor 6 becomes weak, increasing the load on the photosensor 6.

To solve this problem, use P@Hikari as a half mirror, sii
[: Both require properties that reflect (transmit) almost equally.

In addition, for example, in a photometric optical system of a camera, there are systems that perform brightness detection via a half mirror. In such an optical system, for example, one half of the half mirror is used for viewfinder observation, and the other is used for photometry, but most of the light that enters the half mirror is reflected light from the subject area. Therefore, this incident light is likely to contain a large amount of S@ original acid component light. %, if there is a reflector such as a water L glass window in the screen, the SII light component may be quite large depending on the angle. Then, considering that a normal half mirror reflects a lot of H81 light, the transmittance of the I-F mirror should be reduced to 50.
Even if it is unfortunate, the amount of light after being divided will be unbalanced, making it difficult to perform correct photometry. Such adverse effects are caused by the general characteristics of humira.

The present invention has been made based on the above technical background, and it is possible to solve problems that were not considered at all in conventional beam splitters, or that the combination of pH light and StS light as seen in conventional dimming beam splitters. In contrast, in the present invention, consideration is given only to the separation characteristics, whereas in the present invention, Pill light, 81
This makes it possible to obtain a beam splitter that not only can give equal reflectance and transmittance to all of the 111 light beams, but also can freely set the same reflectance and transmittance. Therefore, in the present invention, when constructing a beam splitter based on a multilayer interference thin film formed by alternately laminating low refractive index film layers and high refractive index film layers, the refractive index of the low refractive index film layer is set to the base substrate. This differs from conventional ones in that the refractive index is higher than that of the conventional one. Hereinafter, some embodiments of the present invention will be described in detail.

FIG. 2 is a conceptual diagram showing an example in which the present invention is applied to a prism-type beam sinter, and 11 and 12 are prism blocks. ! It is assumed that a multilayer interference thin film layer is deposited on the rhythm block 11 by vapor blue, and the prism block 12 is bonded thereon with an adhesive 13. Now, the characteristics of this beam splitter are PIl light,
When the reflectance and transmittance of the S@ light are set to be 50, respectively, the incident light I from the left side in the figure is divided into transmitted light T and reflected light R. At this time, the incident f and I are 2.8 for the P11 component (50 for each of the upper 8 for the illll light components)
If the total light amount including 4 pieces is 100, +t of the transmitted light T is 50 (TP: T8 recognition 25225), the light amount of the reflected light R is also 50 (RP: R8-25:25), and the transmitted light The component ratio of polarized light included in each of T and reflected light RVC matches that of the incident light. This means that no matter what the polarization component ratio (2) P/I8 of the incident light (2) is, this component ratio does not change between transmitted light and reflected light. Although this is just one example of the characteristics obtained with the beam splitter of the present invention, the specific film structure of the beam splitter of the present invention will be described below.

FIG. 3 is a conceptual diagram when the multilayer interference thin film/IL shown in FIG. 2 is composed of three layers. In FIG. 3, S is a base substrate, for example, a glass material such as BK7 (refractive index NS),
L1 is the first layer, which is a refractive XNL low refractive index film layer, L2 is the second layer, which is a refractive NHO high refractive index film layer, and L3 is the third layer, which is the first refractive index film layer.
This is the same low refractive index film layer as layer Ll. Further, O is an adhesive layer whose refractive index is N. It is. Note that the film thickness of each layer L 1 to L 3 is an optical film thickness of λ, /4 (λ is a reference design wavelength). For example, assuming an optical disk reproducing optical system using a near-infrared laser oscillator as an application, first, the reference design wavelength ~λ is determined. is set to 925nmK.

Then, the substrate refractive index, that is, the incident side refractive index N8, is set to 1.5.
2. Adhesive 7ill refractive index, that is, transmission side refractive index N.

is 156, the refractive index N of the low refractive index film layers L1 and L3 is fixed at 1.90 (>N, ), and the refractive index NH of the high refractive index film layer L2 is changed frequently, P, 8 When the spectral transmission characteristics at the incident angle 45 for both polarized light components are determined, a characteristic diagram as shown in FIG. 5 is obtained. Note that T in Figure 5
p1~? , 7 is the transmission characteristic for the P polarized light component, Tsl~
T87 shows transmission characteristics for the S-polarized light component, and the correspondence between these characteristics and the refractive index NH of the high refractive index film layer is shown in Table 1.

Table 1 (Fig. 5 - Three-layer structure) As is clear from Fig. 5, the film has a three-layer structure, and under the above conditions, the S
The transmittance T8 for polarized light components shows a maximum, especially for NH-
In the case of 350, TPl-Tsl-8 at around 800 nm
64, and the transmission coefficients for both the p and s polarization components are equal.

Therefore, for light of λ-750 to 820 nm, NL-
1,90 low refractive index film layers are used as the first and third layers, and NH
A three-layer film with a high refractive index film layer of -350 as the second layer, P,
It is possible to obtain a beam splitter with 86-reflective transmission that is completely unaffected by the ratio of the 8-polarized light components.

@Figure 4 is a conceptual diagram when the present invention is constructed with an N-layer film.
The layer is a low refractive film layer (refractive index NL1 thickness λ./4), the 21st
1 is a high refractive index film layer (refraction is used. (Therefore, the number of layers is the number.)
Regarding this Figure 4, the number of 'tJ is set to 5 layers, 7 layers, and 9 layers,
The same characteristics as in Figure 5 are obtained for tjI! , 6, 7, and 8. Note that the reference design wavelength, the refractive index NL1 of the low refractive index film layer, the refractive index NHO value of the high refractive index film layer, etc. in FIGS. 6 to 8 are as shown in Tables 2 to 4. (The refractive index Ns on the incident side, the refractive index N on the transmitted side, and the incident angle conditions are the same as in Fig. 5.) Table 2 (Fig. 6 - 5-layer structure) Table 4 (Fig. 8) -9 layer structure) As can be seen from these characteristics, under each condition λ =
Transmittance T for both P%S polarization components near 800 nm
and T8 can be made to match, and the values of the transmittances T1 and T8 can also be set within a certain range by selecting the number of layers. It goes without saying that it is also possible to set different transmittances without making TP%T8 the same.

By the way, considering that the beam splitter of the present invention is used in the optical disc reproduction optical system as described above, in terms of light utilization efficiency, it is necessary to use a beam splitter that transmits 50% of light, and moreover, transmits both P and S polarized light components. It is preferable that the ratios also match. To meet this requirement, the refractive index conditions are 3 to 9.
Table 5 shows the temperature values determined in degrees Celsius for each of the film configurations of the layers. Incidentally, the refractive index on the incident side is N8%, and the refraction on the transmission side is ``4''.
The Nos incident angle is the same as the previous condition, and an additional condition is to obtain the desired characteristics at λ-800 nm. FIG. 9 shows the spectral transmission characteristics T %T8 of both P and S polarized light components for each number of layers based on Table 5.

@Table 5 (Figure 9) Therefore, according to the characteristics shown in Figure 9, the refractive indexes NH and NL of the high and low refractive index film layers are determined according to the number of film structural layers. However, a beam splitter with 504 transmission (2% S for both polarization components) can be obtained.

However, considering the range in which the transmittances for both 2% S polarized light components can be considered to be almost the same, as the number of layers increases, the shape of the maximum transmittance T8 for the S polarized light component tends to become steeper. Considering this, it is advantageous to have fewer layers. However, as mentioned below, for example 3
When the layer structure is adopted, the tolerance range of the refractive index N7 required for the high refractive index film layer becomes particularly strict.

Figure 10 shows the high refractive index N required for the high refractive index film layer relative to the number of film constituent layers LN when obtaining equal transmittance for both P and S polarization components in the vicinity of λ-800±201 nm.
It shows the refractive wheel conditions of H and the low refractive index Nt required for the low refractive index film layer. Note that other conditions such as the incident side refractive index N8 and the incident angle remain the same as before. In addition, each broken line in the diagram @10 indicates P.
, s Equal transmittance T (TP ”Ts
) is a combination of conditions that give

As can be seen from Figure 10, by setting the refractive index conditions of NH%NL, the transmittances Tp and Ts of both P%S polarized light components are the same regardless of the number of film constituent layers, and the transmittance can be set to any desired value. can do. However, in general, the smaller the number of layers LN is, the more strict the low refractive index NL must be, and the larger the number of layers N is, the more strict the high refractive index NH is required to be.

Looking at the refractive index conditions for each number of layers, it is easy to control when manufacturing a five-layer structure.

In the above embodiments, a case has been described in which the incident side refractive index is 1.52 and the transmission one-law refractive index is 1.56, but the present invention is not necessarily limited to this. For example, if the laser oscillator used in the optical disk reproducing optical system is a near-infrared laser, the substrate may be made of a silicone or the like as long as it is transparent in the oscillation wavelength range. Figure 11 shows that in such a case, the refractive index on the incident side is 4.0, and the refractive index on the transmission side is also 4.0.
The figure shows some of the spectral transmission characteristics of five skin membrane structures in which the transmittance TP%T8 for both P%S polarized light components can be equal in the vicinity of λ-800 nm. Incidentally, the angle of incidence is 45' in both cases, and the refractive indexes NH and NL of each olfactory layer are as shown in Table 6.

Furthermore, according to the present invention, it is also possible to reverse the transmittance of both p and s polarized light components. In other words, with conventional beam splitters, much of the P-polarized light component is transmitted, and much of the 8-polarized light component is reflected, so is it transmitted? TP for T
>T8 is normal. However, as shown in FIG. 12, for example, depending on certain refractive index conditions, TP<
It is also possible to set it as Ts. Figure 12 shows Ns-1,5
2, No-1, 56, P%S double polarized light when the incident angle is 45, λ6m is 890 nm, the refractive index NL of the low refractive index film layer is fixed at 2.20, and the refractive index N of the high refractive index film layer is changed. It shows the transmittances Tp and Ts for the components. The film structure is a five-layer film (thickness of each layer λ./4), and the correspondence between each transmission characteristic TP%Ts and refractive index NI (correspondence is shown in Table 7).

Table 7 (Figure 12 - 5-layer configuration) It is impossible to obtain such characteristics with conventional beam splitters, but according to the present invention, such characteristics can be easily obtained. It is also possible to request new functions from various optical systems.

Fig. 13 shows another embodiment of the beam striper according to the present invention, which has a seven-layer structure, and also shows the characteristics when the incident angle is changed. The film thickness of the ratio film layer is set to 0.
It is made as thin as 55 (λo/4). Incidentally, the refractive index on the incident side is N-1, 52, and the refractive index on the transmission side is N. -1,56, N = 2.20, NH version 3.50, and the standard design wavelength λ. -1035 nm. The correspondence between the incident angle α and each characteristic is shown in Table 8.

Table 8 (Figure 13 - 7 layer configuration) In this way, in the present invention, the thickness of each layer is not necessarily all λ,
It doesn't have to be /4. It can also be seen that a change in the incident angle 1 results in an adjustable wavelength shift as seen in conventional thin film optical systems as a change in relative film thickness.

Above, we have described the film structure of the beam splinter of the present invention based on several examples, and clarified its adverse refraction conditions.
However, in carrying out the present invention, examples of vapor deposited substances that give the refractive index mentioned above include S11 for a high refractive index material and T10! for a low refractive index material. , ZnO□
8 n OH, Z n's', "C: molten to %" is suitable. It is advantageous because it can be changed over time. Note that a range of about 300° C. to 400° C. is usually used as the substrate temperature. Furthermore, in order to obtain a desired refractive index, an equivalent film may be used for each film layer.Using this equivalent film allows the equivalent film to have a However, it is possible to realize the actual m
This is a very effective method.

Further, the present invention can be applied not only to a prism type beam splitter, but also to a so-called ``fumiller'' beam splitter. In this case, the needle has a transmission side refractive index N. For example, I
It is sufficient to set K stages and find the refractive index conditions, etc.

Thus, according to the present invention, the transmission and reflection characteristics of a so-called beam splitter that separates incident light into transmitted light and reflected light can be made equal for both the P-polarized light component and the S-polarized light component, or the transmitted light and the reflected light can be made equal. The component ratio of the included light on both sides can be freely set, which makes it possible to achieve extremely versatile and practical effects. Moreover, the vapor deposition process does not require any new equipment or special vapor deposition substances,
! Since the vapor deposition material can be used as is, there are no restrictions during manufacturing, and the ta properties are sufficient.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of an example of an optical disc reproducing optical system when using the beam splitter of the present invention. Figure 2 is a conceptual diagram for explaining the characteristics of the beam splitter of the present invention. FIG. 3 is a conceptual diagram showing an embodiment of the three-layer film structure of the present invention. FIG. 4 is a conceptual diagram showing an embodiment of the N-layer film structure of the present invention. FIG. 5 is a spectral transmission characteristic diagram showing an example of the characteristics in the embodiment shown in FIG. 6, 7, and 8 are spectral transmission characteristic diagrams showing examples of characteristics when the number of layers is 5, 7, and 9 in the embodiment shown in FIG. 4, respectively. FIG. 9 is a spectral transmission characteristic diagram of an example in which the transmittances Tp%T8 are equal to each other by 50 degrees in the present invention. Figure 10 shows the present invention in TP with a 3- to 9-layer film structure.
-T8 is a diagram showing the relationship between the refractive index conditions NL and NH.5゜Figure 11 shows the spectral transmission of an embodiment of the present invention with a five-layer film configuration that can be used when the refractive index on the incident side and the transmission side is high. It is a characteristic diagram. FIG. 12 is a spectral transmission characteristic diagram of an embodiment of the present invention in which TP is T8. In FIG. 13, the film configuration is 711, and the film thicknesses of the second layer and the sixth layer are slightly λ. FIG. 4 is a spectral transmission characteristic diagram showing an example in which the thickness is thinner than /4. 1... Laser oscillator, 2... Collimator lens, 3... Beam splitter 14... Objective 7 lenses. 5... Tisfu, 6... Photo sensor, 11.12
... Prism block, L... Multilayer interference thin film layer, 1
3... Adhesive layer, ■... Incident light %T... Transmitted light,
R...Reflected light, TP...Transmitted light for P polarized light component, NL...Refractive index of low refractive index film layer, Nu''/refractive index of high refractive index film layer. x
i, Sc I\゛Ic Ii - Cleaning of the drawing (no change in content) Fig. 3 Fig. 4 Surplus four oaths and supplements. Womb 1 Call ÷ (To to do f g Amendment 1 μ to 8 of 1980. Commissioner of the Patent Office Kazuo Wakasugi 1. Indication of the case 1988 Patent Application No. 73 and No. 73 2, Title of the invention Beam splitter 3, relationship with the amended case Patent applicant address 700-4 Konaka-cho, Sano City, Tochigi Prefecture;
Date of amendment order: July 9, 1980 (Delivery date: July 27, 1980) 5゜ Subject of amendment Contents of amendment No. 66 on the specification and drawings I will submit an engraving of the specification and drawings as attached. (No change in content)

Claims (3)

[Claims] (1) On a transparent substrate with a refractive index N, a low refractive index film layer with a refractive index NL larger than N8 and a high refractive index film layer with an even larger refractive index NH are alternately applied to the bottom layer and Beam splitter 1 stacked so that the top layer is a low refractive index film layer (2) In the case where 1.3 < Ns < 4, 2,
5<NH<8.1.6<ML<5 Beam splitter-0 according to claim (1) (3) The optical thickness of each layer is λ. /4 Beam splitter-0 according to claim (1) or (2)