JPH07120704A - Optical isolator and its production - Google Patents

Abstract

PURPOSE:To improve mass production by arranging a Faraday rotor, an optically rotatory element (or quarter-wave plate) having reciprocity to rotate the plane of polarization 45 deg. and an analyzer (or polarizer) in this order in such a manner that the planes of transmission polarization of the polarizer and the analyzer are aligned to each other. CONSTITUTION:The absorption type polarizer 1, the Faraday rotor 2 of a YIG crystal, the quartz crystal quarter-wave length plate 3, the absorption type polarizer 4 and a magnet 5 of a cylindrical shape are arranged in prescribed positions and are assembled in an inert gas 6 using gaseous argon or gaseous nitrogen for heat insulation. This magnet 5 impresses saturation magnetization to the Faraday rotor 2. As a result, the Faraday rotor 2 rotates the plane of the transmission polarization 45 deg.. The quartz crystal quarter-wave length plate 3 is so arranged that the light (forward direction) from the Faraday rotor 2 rotates the plane of transmission polarization 45 deg. in a direction opposite from the Faraday rotation. The planes of the transmission polarization of the absorption type polarizer 1 and the Faraday rotor 4 are aligned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element used for constructing optical isolators and optical circulators for optical fiber communication and optical heads for optical disks, and light sources for optical fiber communication and optical heads for optical disks. The present invention relates to an optical isolator used to prevent light returning to a semiconductor laser.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional optical isolator includes a polarizer 11, a Faraday rotator 12 made of YIG (yttrium-iron-garnet) crystal, and an analyzer 1.
4 and a magnet 15, and a polarizer made of the same material as the polarizer 11 is used as the analyzer 14. Polarizer 11
The analyzer 14 and the analyzer 14 are arranged such that the transmission polarization directions thereof are inclined by 45 degrees. Faraday rotator 12 placed between them
Has a thickness such that a Faraday rotation angle of 45 degrees can be obtained by saturation magnetization. A permanent magnet 15 having a sufficient magnetic field is arranged outside in order to apply this saturation magnetization.

[0003]

However, the conventional optical isolator must be adjusted in position so that the transmission polarization planes of the polarizer and the analyzer are inclined by 45 degrees with each other, which makes mass production difficult. Further, the characteristics of individual parts are easily affected by temperature, which has been an obstacle in manufacturing. Moreover, the performance of the completed optical isolator is directly affected by the temperature under the usage environment.

An object of the present invention is to provide an optical isolator excellent in mass productivity in order to solve the above problems.

[0005]

The optical isolator of the present invention has a non-reciprocal property such as a first polarizer and a YIG (yttrium-iron-garnet) crystal capable of obtaining a Faraday rotation angle of 45 ° due to saturation magnetization. A Faraday rotator,
A reciprocal optical rotator (or a quarter-wave plate) that rotates the polarization plane by 45 ° and an analyzer (or a second polarizer) are arranged in this order, and the transmission polarization planes of the polarizer and the analyzer. Are optical isolators arranged so as to coincide with each other.

Further, according to the method of manufacturing an optical isolator of the present invention, the first polarizer and a non-reciprocal Faraday such as YIG (yttrium-iron-garnet) crystal, which can obtain a Faraday rotation angle of 45 ° due to saturation magnetization, are used. A rotor,
A reciprocal optical rotator (or a quarter-wave plate) that rotates the plane of polarization by 45 ° and an analyzer (or a second polarizer) are arranged in this order in a heat-insulating inert gas to produce the polarized light. It is arranged so that the transmitted polarization directions of the probe and the analyzer coincide with each other.

[0007]

The linearly polarized light, which is the forward light incident on the first polarizer, passes through the first polarizer, and the polarization plane is rotated by 45 degrees by the Faraday rotator. ), The plane of polarization is rotated in the opposite direction by 45 degrees. Therefore, the transmission polarization plane of this light coincides with the transmission polarization plane of the analyzer (second polarizer), passes through the analyzer (second polarizer), and is emitted as transmitted light.

On the other hand, when the return light in the direction opposite to the forward direction is incident on the analyzer (second polarizer), only the component matching the transmission polarization plane of the analyzer (second polarizer) is detected. (Second
After passing through the polarizer (1), the polarization plane is rotated by 45 degrees by the optical rotator (quarter wave plate), and the Faraday rotator further rotates the polarization direction by 45 degrees in the same direction as this rotation. Since the Faraday rotator has non-reciprocity, this rotation direction is constant regardless of the light traveling direction (forward direction and reverse direction). Therefore, the return light that has undergone Faraday rotation has a polarization plane orthogonal to the transmission polarization plane of the first polarizer.
Cannot pass through the polarizer.

Since this optical isolator is assembled in a heat insulating inert gas, it is not affected by the external environmental temperature and mass productivity is improved.

Further, by sealing the heat insulating inert gas in the optical isolator as it is at the time of manufacturing, the temperature dependency becomes small even after the manufacturing.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of the optical isolator during assembly. In the optical isolator, an absorption polarizer 1, a Faraday rotator 2 of YIG crystal, a crystal quarter wavelength plate 3, an absorption polarizer 4, and a cylindrical magnet 5 are arranged as shown in FIG. It is assembled in an inert gas 6 using argon gas or nitrogen gas. Magnet 5 is Faraday rotator 2
Apply saturation magnetization to. As a result, the Faraday rotator 2 rotates the transmitted polarization plane by 45 °. The crystal quarter-wave plate 3 is arranged so that the light (forward light) from the Faraday rotator 2 rotates the transmitted polarization plane by 45 ° in the direction opposite to the Faraday rotation. The transmission polarization planes of the absorption polarizer 1 and the absorption polarizer 4 are matched. This optical isolator is assembled in an inert gas 6, and the inert gas 6 is sealed in the isolator as it is. The seal is
The Faraday rotator 2 and the crystal quarter-wave plate 3 are sealed together with the inert gas 6 in the magnet 5 with the absorption polarizers 1 and 4 as lids.

The operation of the optical isolator shown in FIG. 1 will be described with reference to FIG. FIG. 2A is a change state diagram of the polarization plane of the forward direction light as seen from the absorption polarizer 1 side, and FIG.
Is before the incidence of the absorptive polarizer 1, (b) is after the emission from the absorptive polarizer 1, (c) is after the emission from the Faraday rotator 2, and (d) is from the quartz quarter-wave plate 3. After the emission of
(E) shows the state after emission from the absorptive polarizer 4.

As for the forward light having the orthogonal polarization components in (a), only the component matching the transmission polarization plane of the absorption polarizer 1 can pass through the absorption polarizer 1 as shown in (b). The Faraday rotator 2 rotates this light by 45 ° as shown in (c). The crystal quarter-wave plate 3 rotates the Faraday-rotated light by 45 ° in the opposite direction as shown in (d) and returns it to the state of (b). Since the absorptive polarizer 1 and the absorptive polarizer 4 have the same polarization plane, the light in (d) can be transmitted through the absorptive polarizer 4 as it is as in (e).

On the other hand, FIG. 2 (B) is a change state diagram of the polarization plane of the returning light as seen from the absorption polarizer 1 side.
(A) is after emission from the absorption type polarizer 1, (b) is after emission from the Faraday rotator 2, (c) is after emission from the quartz quarter-wave plate 3, and (d) is absorption type. After being emitted from the polarizer 4, (e) shows the state before the absorption-type polarizer 4 is incident. Since the return light is light in the reverse direction that is incident on the absorption type polarizer 4 side into the optical isolator, it will be described from (e).
Of the return light propagating in the opposite direction due to reflection or the like shown in (e), the component that coincides with the transmission polarization plane of the absorption polarizer 4 passes through the absorption polarizer 4 as shown in (d). As shown in (c), this light has a polarization plane of 4 with a quarter-wave plate 3 of quartz crystal.
It is rotated 5 °. This rotation direction is reverse rotation, unlike the case of forward light shown in (d) of FIG. 2A above, because the quarter-wave plate 3 of crystal has reciprocity. On the other hand, the Faraday rotator 2 has non-reciprocity, and the Faraday rotation direction always rotates the polarization plane in the same direction regardless of the traveling direction of light. Therefore, the crystal quarter-wave plate 3
In the Faraday rotator 2, the light whose polarization plane is rotated by 45 ° is further rotated in the same direction by the polarization plane as shown in (b).
It will be rotated 5 °. Therefore, the polarization plane of the return light emitted from the Faraday rotator 2 is orthogonal to the transmission polarization plane of the absorptive polarizer 1, so that the absorptive polarizer 1 cannot be transmitted as in (a).

[0015]

The optical isolator of the present invention does not require the position adjustment for inclining the transmission polarization planes of the polarizer and the analyzer with each other by 45 degrees as in the conventional optical isolator, and has good mass productivity. Further, since the incoming and outgoing transmission polarization planes are the same, when configuring a multi-stage optical isolator in which a plurality of optical isolators are stacked,
It is possible to easily match the transmission polarization planes of the optical isolators.

Further, according to the method of manufacturing the optical isolator of the present invention, the optical isolator is assembled in the heat insulating inert gas, so that it is not affected by the external environmental temperature during manufacturing.
Mass productivity is dramatically improved. Moreover, by sealing the heat insulating inert gas as it is, it becomes easy to manufacture a high-performance optical isolator that is always stable in operation regardless of the external environment temperature during use.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical isolator of the present invention during manufacturing.

FIG. 2 is a change state diagram of a polarization plane of the optical isolator of the present invention, (A) is a change state diagram when forward light is emitted, and (B) is a change state diagram when return light is emitted.

FIG. 3 is a structural diagram of a conventional optical isolator.

[Explanation of symbols]

1, 4: Absorption type polarizer 2: Faraday rotator 3: Quartz quarter wave plate 5: Magnet 6: Inert gas

Claims (2)

[Claims] 1. A first polarizer, a non-reciprocal Faraday rotator capable of obtaining a Faraday rotation angle of 45 degrees with saturation magnetization, and a reciprocal rotator having a reciprocal polarization plane rotated by 45 degrees. The quarter-wave plate and the analyzer or the second polarizer are arranged in this order so that the transmission polarization planes of the first polarizer and the analyzer or the first polarizer and the second polarizer are aligned with each other. An optical isolator characterized by being arranged. 2. A first polarizer, a non-reciprocal Faraday rotator capable of obtaining a Faraday rotation angle of 45 degrees by saturation magnetization, and an optical rotator having a reciprocity in which a transmission polarization plane is rotated by 45 degrees. The 1/4 wavelength plate and the analyzer or the second polarizer are arranged in this order in the heat insulating inert gas to form the first
2. A method for manufacturing an optical isolator, wherein the polarizer and the analyzer or the first polarizer and the second polarizer are arranged so that their transmission polarization planes are aligned with each other.