JPH02165105A - Polarizer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding polarizers used in various optical technology fields such as optical signal processing, optical applied measurement, and optical communication, we have developed a polarizer that can be miniaturized and can withstand high temperature and high humidity. For the purpose of The optical path length of the birefringent material is set so that the transmittance of the birefringent material is close to zero and the transmittance of the birefringent material is close to one.

[Industrial application field]

The present invention relates to a polarizer used in various optical technical fields such as optical signal processing, optical applied measurement, and optical communication.

[Traditional techniques]

As conventional polarizers, there are known polarizers made of prisms, polarization separation films, wedge-shaped birefringent materials, and the like.

[Problem to be solved by the invention]

However, among the above-mentioned conventional polarizers, those made of prisms and those made of wedge-shaped birefringent materials are both large in shape (for example, in the case of prisms, the minimum is about 2 Peng angles). There was a problem. Also,
The problem with devices made of polarization separation films is that they are sensitive to high-temperature, high-humidity environments.

An object of the present invention is to provide a polarizer that can be miniaturized and can withstand high temperature and high humidity.

[Means to solve the problem]

The polarizer of the present invention comprises an etalon type filter made of a birefringent material. At that time5. The optical axis of the birefringent material is set within the filter plane. Furthermore, by adjusting the optical path length of the birefringent material, the transmittance for one of the extraordinary light and the ordinary light is close to zero, while the transmittance for the other is 1.
so that it is close to

[For production]

In general, when an etalon type filter is configured, the dependence of its transmittance on the optical path length is as shown in Figure 1, for example. In other words, as the optical path length is changed, the transmittance peaks periodically. It will be done.

If an etalon type filter having such characteristics is constructed using a birefringent material, the optical path length will be different for extraordinary light and ordinary light. Therefore, as mentioned above, by adjusting the optical path lengths of the four extraordinary rays and ordinary rays, the transmittance for one of the extraordinary rays and ordinary rays is close to zero, and the transmittance for the other is close to 1. If this is done, it will function as a polarizer. For example, as shown in Figure 1, the optical path length of the ordinary light (Noda) is set at the position where the transmittance peaks, and the optical path length of the extraordinary light (N, *d) is set at the position midway between the peaks. In this way, a polarizer that transmits only ordinary light and reflects extraordinary light can be obtained.

In the polarizer of the present invention, the optical path length can be adjusted to be long or short, so if the optical path length is adjusted as short as possible, it is possible to set the thickness to 1 mm or less, for example. Therefore, miniaturization can be realized.Furthermore, since there is no need to use a material that is sensitive to high temperature and high humidity, such as a polarization separation film, a polarizer that is resistant to high temperature and high humidity environments can be realized.

(Examples) Examples of the present invention will be described below with reference to the drawings.

FIG. 2 is a perspective view showing a polarizer according to an embodiment of the present invention.

The polarizer shown in the figure consists of an etalon-type filter using a birefringent material such as TiO2 crystal, and an Aff
It is coated with a reflective film 2 made of a metal film such as i or Au or a dielectric multilayer film.

The optical axis 1a of the birefringent material it is set within the filter plane, and the thickness d of the birefringent material 1 is set so as to substantially satisfy the following two equations.

Nll * a= (2Ml) *λ/2
・--(1)N, *d= (2M2 +1)*
λ/2 ・ ・ ・ (2) Here, λ is the wavelength used, N
o is the refractive index of ordinary light, N6 is the refractive index of extraordinary light, and M+ and Mz are arbitrary natural numbers.

That is, the above formula (1) indicates that the optical path length (Noda) of ordinary light is set so that the transmittance for ordinary light is 1, and the above formula (2) indicates that the transmittance for extraordinary light is zero. This shows that the optical path length (N6*d) of the extraordinary light is set so that As shown in Fig. 2, in a polarizer configured with such a G setting, only the polarized component of the incident light L+ of wavelength λ, which corresponds to ordinary light, is obtained as transmitted light Lt, and corresponds to extraordinary light. The polarized component becomes reflected light Lm.

Here, a thickness d that substantially satisfies the above equations (1) and (2) will be determined. The method is to substitute natural numbers within an appropriate range into a round-robin formula for equation (1), and then search for one that satisfies equation (2) among the thicknesses d determined by M+. .

Specifically, according to equation (1), d "" (M+ / No) *λ
・ ・ ・(3) is obtained. This second (3) is expressed as formula (2)
By substituting and rearranging with 7, we get the following.

2 (N, /No) Ml = 2M2
+1 ·− · (4) Then, M, which almost satisfies equation (4), is found. For this purpose, a very compact polarizer is obtained.

The extinction ratio T of this polarizer is determined by the equation of the etalon transmittance in the absence of absorption ("Fundamentals of Optoelectronics" A, Yar.
X= + 2 (N, /N0)M.

-1nt (2(N,/No)Ml)・・
・(5) Then, it is sufficient to find Ml such that X in equation (5) is sufficiently small. Note that int (x) is an integer function that truncates the fraction below the decimal point.

As a specific example, a case will be described in which the wavelength λ used is 1.31 μm and TiO2 is used as the birefringent material.

In this case, No”'2,462, N, =2.72
It is 0. Therefore, Ml that minimizes X in equation (5) is
When calculated in the range of 50≦M1≦3000, Ml = 12
31 (at this time, x = I Xl0-' or less).

Then, the thickness d at this time is 655,0 μm,
1 ■ or less (1-R) ” ・ ・ ・ (6) Here, x = I Xl0-', R = 0.9
5 (R is the reflectance of one side of the etalon), by substituting these into equation (6) above, Tζ1521″#
31.8 dB is achieved.

According to this embodiment, as described above, by appropriately selecting Ml and Mz, the thickness d can be set to 1 mm or less, and therefore, significant miniaturization can be achieved. Moreover, since there is no need to use a material that is sensitive to high temperature and humidity, such as a polarization separation film, a polarizer with excellent temperature resistance and moisture resistance can be realized.

In addition, in the above-mentioned formulas (1) and (2), No,
N- may be interchanged. That is, contrary to the above embodiment, the optical path length may be adjusted so that the transmittance for ordinary light is close to zero and the transmittance for extraordinary light is close to 1.

Furthermore, the conditions of the above equations (1) and (2) may be substantially satisfied by tilting the filter made of the above-mentioned birefringent material 1.

Furthermore, it goes without saying that the present invention includes both birefringent material 1 coated with reflective film 2 on both sides and those not coated with reflective film 2.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a polarizer that can be downsized and is resistant to high temperature and humidity environments.

FIG. 2 is a perspective view showing a polarizer according to an embodiment of the present invention.

1...birefringent substance, la...optical axis, 2... Reflective film.

Claims (1)

[Claims] An etalon type filter is constructed using a birefringent substance (1), the optical axis (1a) of the birefringent substance is set within the filter plane, and the transmittance for one of extraordinary light and ordinary light is zero. A polarizer, characterized in that the optical path length of the birefringent material is set so that the transmittance of the birefringent substance is close to 1 and the transmittance of the birefringent substance is close to 1.