JPS6028603A - Prism type beam splitter - Google Patents

Abstract

PURPOSE:To reduce the effect of polarization by forming a light semitransmitting film composed of three layers of the first dielectric layer, a silver metal layer, and the second dielectric layer between prisms. CONSTITUTION:A light semitransmitting film HM is formed between the junction faces of two right triangular prisms 2, 4 of n0 refractive index. This film HM is composed of the three layers of the first dielectric layer M having a refractive index of n1 and an optical thickness of n1d1, a silver metal layer, and the second dielectric layer having n2 and n2d2. C in the figure is an adhesive layer. The following relationships are satisfied: n0<n1, 1.55<=n1<=1.75, 1.85<=n2<=2.45, n1d1=n2d2=0.25lambda0, where lambda0 is a designed wavelength selected within the range of 400-700nm, and the algebraic thickness of the silver layer is selected within the range of 10-50nm in accordance with a desired reflectance to transmittance ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a prism type beam splitter used in still cameras, cine cameras, etc. that perform exposure control and focus detection using TTL photometry.

Prior art: Japanese Patent Application Laid-open No. 56-43, which was first filed and published by the applicant.
Publication No. 601 discloses that in a prism type beam splitter, a first dielectric layer made of a dielectric material having a lower refractive index than that of the glass, and Ag A metal layer 5 consisting of a metal layer 5 and a second dielectric layer consisting of a dielectric with a higher refractive index than the glass are laminated, and the optical thicknesses of the first and second dielectric layers are both λO/ 4 (λ0: design wavelength) is disclosed. However, in such a configuration, as shown in the table of Publication M, there is a difference of 20% or more in transmittance and reflectance between the P component and the S component for light at an incident angle of 45°. Therefore, when the angle of incidence on the light semi-transmissive film of a beam splitter, such as the above-mentioned still camera or cine camera, is around 45°, the influence of polarization is large.

Purpose The present invention has been made in view of the points mentioned above.
The purpose is to provide a prism type beam splitter that is easy to manufacture and has little influence of polarization on light with an incident angle of 45°.

SUMMARY OF THE INVENTION In the groove of the present invention, the refractive index of the eleventh dielectric layer is made higher than that of glass, and when a material having a refractive index of 1.55 to 1.75 is used, the influence of polarized light can be reduced. The present invention has been made based on the discovery that the object can be achieved. Therefore, in the present invention, the first glass is made of glasses having substantially the same refractive index. In a prismatic beam splitter in which a light semi-transparent film is formed between the second prisms, the light semi-transparent film is
It has a three-layer structure consisting of, in order from the Sl prism side to the second prism side, a first dielectric layer made of a dielectric, a metal layer made of Ag, and a second dielectric layer made of a dielectric. The refractive index is no, the refractive index of the first dielectric layer is old, the optical thickness is nrdt, and the refractive index of the second dielectric layer is 12. [11n
o<nt +21 1.55'old≦1.75 +31 1.85<nz G 2.45 (41n+
It is characterized by satisfying the following conditions: dt = nzdz = Q, 25λ0.

To explain each condition (4), the condition (2) defines the magnitude relationship of the refractive index between the first dielectric layer and the glass and the refractive index range of the first dielectric layer. , if condition (11) is exceeded, the influence on polarization becomes greater.Furthermore, if the lower limit of condition (+21) is exceeded, the refractive index of the prism must be lowered even further to satisfy condition (1), which becomes difficult to achieve. , when the upper limit of condition (2) is exceeded, the refractive index difference with the second dielectric layer becomes small and the influence on polarization increases.Condition (3) defines the refractive index range of the second dielectric layer. If the upper limit is exceeded, the applicable substance does not exist and it becomes impossible to realize, and if the lower limit is exceeded, the difference in refractive index with the first dielectric layer becomes small and the influence on polarization becomes small.Condition (41 !1 defines the optical film thickness of the 'i42 dielectric layer, and if it deviates from this, monitoring the film thickness during vacuum deposition of each layer becomes complicated, and it takes time and effort to manufacture.

Example Examples of the present invention will be described in detail below.

FIG. 1 is a diagram showing a prismatic beam splitter according to an embodiment of the present invention. In the same figure, +2141 is a first and second prism made of right-angled isosceles triangular prisms of the same shape and made of the same glass, respectively; Both prisms +2
1 +4], a semi-light-transmitting film (HM) is formed on the bonding surface. The light semi-transparent film (HM) is applied to the prisms t21t4 in order from the first prism +21 side to the second prism (4) side.
A three-layer structure: a first dielectric layer (Ml) made of a dielectric with a medium refractive index higher than the refractive index of 1, a metal layer (Ag) made of Ag, and a second dielectric layer made of a dielectric with a high refractive index. The optical thickness of the first and second dielectric layers fly114 is
The design wavelength is 0.25λO, respectively. (C1 is an adhesive layer. The geometric thickness of the metal layer (Ag) is selected within the range of 10 to 5 Q nm depending on the desired reflectance and transmittance.

The beam splitter constructed as described above has a medium refractive index dielectric material, Ag, on the cemented surface of the first prism (2).

A high refractive index dielectric material is vacuum-deposited in order until each film has a predetermined thickness, and an adhesive is applied on top of it. @' Just connect the J2 prism (4). In addition, the adhesive layer tel
may be provided between the first prism (2) and the first dielectric layer +Ml.

In the beam splitter, light enters from the first prism (2) side, and this incident light +II is split into two into reflected light (R1 and transmitted light fTl).On the contrary, the second prism (4) side Although it may be used so that the light is incident from the beam splitter, the absorption of light by the beam splitter becomes slightly large, resulting in a slightly large optical loss.

The specific configuration of each example is shown in the table below.

Example 1 SO=55Qnm The spectral characteristics of this example are shown in FIG. In Figure 2,
Rs is the reflectance of the S wave component, Rp is the reflectance of the P wave component,
Ts indicates the transmittance of the S-wave component, and Tp indicates the transmittance of the P-wave component, respectively. As is clear from FIG. 2, according to this example, the reflectance and transmittance are relatively flat over the entire 1-IJ visible wavelength range, and Rs, Rp, and TS
Since the difference between Tp and Tp is as small as several percent or less, the influence of polarization is small, and light loss due to absorption is also small. Furthermore, according to this embodiment, since the optical thicknesses of both dielectric layers are equal to each other and are at the design wavelength of V4, vacuum deposition is particularly difficult to monitor.
Vapor deposition is stopped when the reflectance power ≦ the extreme value; L
c Good quality < -IIK Thickness control is simple and manufacturing is easy.

Example 2 λo = 48Qnn1 The spectral characteristics of this example are shown in FIG. 3 in the same manner as in FIG. 2. As is clear from FIG. 3, also in this example, the spectral characteristics are flat over the entire visible wavelength range, with little optical loss, and little influence of polarization. Furthermore, both dielectric layers)
Since the optical film thickness of both films is λ0/4, film thickness control is simple and manufacturing is easy.

FIG. 4 shows a prismatic beam splitter (
BS) is used in a cine camera.The light that passes through the photographic lens (TL) is split into two by the beam splitter (BS), the transmitted light is guided to the film surface, and the reflected light is sent to the finder system (FS). Be guided by.

In addition, in the present invention, the second dielectric layer (the river is as in the embodiment)
Not limited to Zr0z and TiO2, Ce
Any dielectric material with a refractive index of 1.85 to 2.45 such as O2 or ZnS may be used, and the first dielectric layer also has a refractive index of 1.
．． It suffices if it is made of a dielectric material having a diameter of 55 to 1.75.

[Effect] As shown in item 2, the present invention is characterized by satisfying the conditions such as ``two series,'' and thereby, +j
It has spectral characteristics with flat reflectance and transmittance over the entire J-visual wavelength range, has little influence of polarization, and has little optical loss.
Second, since the optical thicknesses of both dielectric layers are both λO/4, it is possible to obtain a prism type beam splitter having a three-layer structure that is easy to manufacture.

[Brief explanation of drawings]

FIG. 1 shows a prism type beam splitter according to an embodiment of the present invention, and FIGS. 2 and 3 show the angle of incidence 4 of embodiments 1 and 2.
FIG. 4 is a graph showing the spectral characteristics for 5° light, and is a diagram showing an example in which the beam splitter according to the present invention is used in a cine camera. (21; first prism, [4); second prism,
(HM). Light semi-transparent film, [M+ + first dielectric layer + (Ag);
metal layer. Shout: Second dielectric layer. Applicant: Minolta Camera Co., Ltd.

Claims (1)

[Claims] α, first and second glass made of glass having substantially the same refractive index;
In a prismatic beam splitter in which a light semi-transparent film is formed between prisms, the light semi-transparent film is formed of a first dielectric film consisting of 11 dielectric bodies in order from the first prism side to the second prism side.
a dielectric layer, a metal layer made of Ag, and a second layer made of dielectric.
A prism type beam splitter having a three-layer structure of dielectric layers and satisfying the following conditions: 110<old 1.55'G old≦1.75], 35% n2≦2 .45n+d+ =
r+zd2=Q, 25λ0 However, here, 110; refractive index of the first prism. 111; refractive index of the first dielectric layer 2 n2; refractive index of the second dielectric layer. Htdt; optical thickness of the first dielectric layer. r+zd2: optical thickness of the second dielectric layer. λO; Design wavelength selected within the range of 4QQnm to 700nm. It is.