JP2000241762A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical isolator which can be easily produced and which can keep the characteristics of a conventional isolator. SOLUTION: This optical isolator consists of an absorptive polarizer 1, 45 deg. Faraday rotator 3 and reflective polarizer 2, each in a parallel plate form, arranged in this order as tilted from the optical axis of the incident light. The absorptive polarizer 1 and reflective polarizer 2 are disposed with the transmission polarizing directions making a 45 deg. angle from each other. A magnetic field H is applied along the propagation direction of incident light to the 45 deg. Faraday rotator 3. The absorptive polarizer 1 consists of a semiconductor multilayered film with a semiconductor interposed between dielectric layers. The reflective polarizer 2 consists of a photonic crystal. The 45 deg. Faraday rotator 3 consists of a hard magnetic garnet thick film showing a square hysteresis curve. Since the reflective polarizer 2 made of a photonic crystal does not require polishing, it can be easily produced at a low cost and it shows excellent characteristics for the environment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator which is used mainly in optical communication equipment and optical information processing equipment, and is an optical element which transmits incident light only in one direction and blocks the light in the opposite direction.

[0002]

2. Description of the Related Art In general, an optical isolator is constituted by combining, for example, two polarizers and a Faraday rotator to which a magnetic field is applied. In the case of an optical isolator that has been put into practical use, a birefringent single crystal prism, a glass polarizer containing metal particles, a composite multilayer film made of a dielectric and a metal, and the like are usually used as the polarizer material.

[0003]

In the case of the above-mentioned existing optical isolator, the material of the polarizer is expensive, and the manufacturing process of the polarizer requires processing steps such as cutting and polishing.
Due to these factors, it is difficult to reduce the manufacturing cost, and as a result, the price of the entire optical isolator becomes expensive (actually, the manufacturing cost of the polarizer is reduced by the manufacturing cost of the entire optical isolator. About 5
0% or more).

The present invention has been made to solve such problems, and a technical problem thereof is to provide an inexpensive optical isolator which can maintain existing isolator characteristics and is easy to manufacture. is there.

[0005]

According to the present invention, a first polarizer, a Faraday rotator, and a second polarizer, each of which is a parallel plate, are arranged and fixed in this order or in the reverse order. The first polarizer is a reflective polarizer, and the second polarizer is an absorptive polarizer.

In this optical isolator, the reflective polarizer is preferably made of a photonic crystal or a polymer multilayer film.

Further, according to the present invention, in any one of the above optical isolators, an optical isolator using a hard magnetic garnet having a square hysteresis curve as a Faraday rotator can be obtained.

Further, according to the present invention, in any one of the above optical isolators, an optical isolator provided with an optical fiber with a ferrule is obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical isolator according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a side view showing a basic configuration of an optical isolator according to Embodiment 1 of the present invention. This optical isolator is configured by arranging a parallel-plate absorption polarizer 1, a 45-degree Faraday rotator 3, and a reflection polarizer 2 in that order with respect to the optical axis of incident light. ,
The absorption-type polarizer 1 and the reflection-type polarizer 2 are set such that their transmission polarization directions form an angle of 45 degrees with each other.
A magnetic field H is applied to the 5-degree Faraday rotator 3 along the traveling direction of the incident light.

Among them, the absorption polarizer 1 is composed of a multilayer film having a structure in which a semiconductor is sandwiched between dielectrics, the reflection polarizer 2 is composed of a photonic crystal, and the 45-degree Faraday rotator 3 has a square hysteresis curve. consisting _{Eu 0.9 Ho 1.1 Fe 4.2 Ga 0.8} O 12 garnet thick film of hard magnetic garnet.

Here, the photonic crystal used for the reflective polarizer 2 is known as an object in which a photonic band gap is generated due to the periodic structure of the refractive index. If this photonic crystal is properly designed, the polarized component of the same wavelength in a certain direction cannot enter the photonic band gap and exist in the photonic crystal. Then, the polarization component in the direction perpendicular thereto is operated so as to pass through the photonic crystal without entering the photonic band gap.

In order to have a photonic band gap, the refractive index ratio of the two kinds of substances must be twice or more. Therefore, here, hydrogenated amorphous silicon (a-Si: H refractive index 3.4) which is a semiconductor is used. ) And SiO ₂ (refractive index: 1.44). When fabricating the reflective polarizer 2 using a photonic crystal, Si
A groove may be formed on an O ₂ substrate, and hydrogenated amorphous silicon and SiO ₂ may be alternately stacked by bias sputtering so that the shape of the groove is preserved on the SiO ₂ substrate.

The reflection type polarizer 2 made of the photonic crystal can be easily manufactured, can be configured in a large area, and can be manufactured at a low cost because polishing is not required. It is characterized by being excellent.

FIG. 2 is a side view of each optical element for explaining an optical path of transmitted light in the optical isolator. FIG. 2 (a) relates to forward incident light, and FIG. 2 (b). Is for light incident in the opposite direction. FIG.
2A and the two-way arrows shown near each optical element in FIG. 2B indicate the direction of polarization separation of incident light in each optical element.

First, referring to FIG. 2A, in the case of the forward incident light, after the incident light along the optical path indicated by the right-hand thick straight line arrow is incident on the absorption polarizer 1, the optical path is left as it is. Then, the light passes through the absorption polarizer 1, the 45-degree Faraday rotator 3, and the reflection polarizer 2 and then exits.

Next, referring to FIG. 2B, in the case of the incident light in the reverse direction, when the incident light along the optical path indicated by the thick arrow pointing left is incident on the reflective polarizer 2, a part of the light is The light is reflected along the optical path indicated by the slanted right arrow, and the other part is transmitted through the reflective polarizer 2 and the 45-degree Faraday rotator 3 along the optical path indicated by the left thin arrow and enters the absorption polarizer 1. I do. At this time, the polarization direction of the light incident on the absorption polarizer 1 is rotated by 90 degrees from the transmission direction of the absorption polarizer 1, and the light incident on the absorption polarizer 1 is absorbed.

Thus, in the case of this optical isolator,
Since the transmitted light in the reverse direction absorbs or reflects any polarization component, the basic function as an optical isolator is obtained while maintaining the same isolator characteristics (insertion loss and reverse loss) as the existing ones.

FIG. 3 is a side view showing a basic configuration of an optical isolator according to Embodiment 2 of the present invention. This optical isolator is configured by arranging a parallel-plate reflective polarizer 4, a 45-degree Faraday rotator 3, and an absorption polarizer 5 in that order with respect to the optical axis of incident light in this order. ,
The reflection type polarizer 4 and the absorption type polarizer 5 are set such that their transmission polarization directions form an angle of 45 degrees with each other.
A magnetic field H is applied to the 5-degree Faraday rotator 3 along the traveling direction of the incident light.

Among them, the reflective polarizer 4 is composed of a polymer multilayer film, the absorption polarizer 5 is composed of glass containing silver, and the 45-degree Faraday rotator 3 is Eu which is a hard magnetic garnet having a square hysteresis curve. _0.9 Ho _1.1 F
e _{4.2 A} Ga _0.8 O ₁₂ garnet thick film.

Here, the polymer multilayer film used for the reflective polarizer 4 is formed by laminating about 100 films having birefringence, and transmits a polarized light component in a specific direction and is perpendicular to the polarized light component. It operates so as to reflect a polarized light component in a different direction.

The reflective polarizer 4 made of this polymer multilayer film
Can be easily manufactured simply by laminating polymers,
In addition, it can be configured with a large area, and the manufacturing cost can be reduced because polishing is not required.

FIG. 4 is a side view of each optical element for explaining the optical path of the transmitted light in the optical isolator. FIG. 4 (a) relates to forward incident light, and FIG. 4 (b). Is for light incident in the opposite direction. The bidirectional arrows shown near each optical element in FIGS. 4A and 4B also indicate the direction of polarization separation of incident light in each optical element.

First, referring to FIG. 4A, in the case of the forward incident light, after the incident light along the optical path indicated by the right-handed straight bold arrow enters the reflective polarizer 4, the optical path remains unchanged. Then, the light passes through the reflective polarizer 4, the 45-degree Faraday rotator 3, and the absorption polarizer 5 and then exits.

Next, referring to FIG. 4B, in the case of the incident light in the opposite direction, when the incident light along the optical path indicated by the bold arrow pointing to the left enters the absorbing polarizer 5, a part of the incident light is lost. The light is absorbed, and the other part passes through the absorption polarizer 5 and the 45-degree Faraday rotator 3 along the optical path indicated by the thin arrow pointing left, and enters the reflection polarizer 4. At this time, the polarization direction of the light incident on the reflective polarizer 4 is rotated by 90 degrees from the transmission direction of the reflective polarizer 4, and the light incident on the reflective polarizer 4 is obliquely rightward by the reflective polarizer 4. The light is reflected along the optical path indicated by the thin arrow.

The light reflected by the reflective polarizer 4 passes through the 45-degree Faraday rotator 3 and enters the absorption polarizer 5. At this time, the polarization direction of the light incident on the absorption polarizer 5 is rotated by 90 degrees from the transmission direction of the absorption polarizer 5,
Light incident on the absorption polarizer 5 is absorbed.

As described above, in the case of this optical isolator, the transmitted light in the reverse direction absorbs any polarized light component, and therefore, has the same isolator characteristics (insertion loss and reverse loss) as existing ones. The basic function as an optical isolator is obtained.

FIG. 5 is a side view showing the basic structure of an optical system using the optical isolator of the first embodiment. The optical system includes a laser diode 11, a condenser lens 12,
The optical isolator 13 and the optical fiber 14 are arranged in this order. In this optical system device, when an optical isolator 13 is disposed at a position where a beam from a laser diode 11 is converged by a condenser lens 12, the optical isolator 1
Although it is possible to reduce the aperture diameter of No. 3, this makes it possible to reduce the size of the entire optical isolator including each optical element, thereby reducing the cost of the product. The position where the beam is most narrowed by the condenser lens 12 is the ferrule end face if the optical fiber 14 has a ferrule, and it is effective to dispose the optical isolator 13 immediately before this ferrule end face.

In the case of this optical system device, the inclination set for the entire optical element is 4 degrees, and the inclination of 4 degrees is effective for securing the return loss. In the case where the optical fiber 14 has a ferrule, if the end face of the ferrule is inclined at 6.5 degrees with respect to the capillary, it is similarly effective for securing the return loss. As a result, if these conditions are satisfied, a return loss of 55 dB or more can be realized. Incidentally, such a configuration of the optical system device can be similarly applied to the optical isolator shown in FIG.

FIG. 6 is a side sectional view showing a local configuration of an optical system device in which the optical isolator 13 is coupled to an optical fiber with a ferrule 18 by using a holder 15. In this optical system device, a magnet 16 is
The optical isolator 13 is adhesively fixed via a spacer 17 so that the optical isolator 13 is housed in the magnet 16 in a non-contact state, and a tapered ferrule as shown in FIG. End face 1
By joining and fixing the ferrule-equipped optical fiber 18 having the ferrule 9 by YAG welding, the ferrule-equipped optical fiber 18 and the optical isolator 13 are integrated. Incidentally, the local configuration of such an optical system device is shown in FIG.
The same can be applied to the optical isolator shown in FIG.

[0031]

As described above, according to the optical isolator of the present invention, the first polarizer, the Faraday rotator and the second polarizer, each of which is a parallel plate, are arranged and fixed in this order or in the reverse order. In the basic configuration, the first polarizer is a reflective polarizer and the second polarizer is an absorption polarizer, and one of the reflective polarizers can be easily manufactured and has a large area. The optical isolator is made of a photonic crystal or a polymer multi-layer film, which can be manufactured and the manufacturing cost can be reduced because polishing is not required. Therefore, the entire optical isolator has the existing isolator characteristics (insertion loss and reverse loss). By holding it, it becomes easier to manufacture, and it can be mass-produced more than before and provided at a lower price.

[Brief description of the drawings]

FIG. 1 is a side view showing a basic configuration of an optical isolator according to a first embodiment of the present invention.

FIG. 2 is a side view of each optical element shown for describing an optical path of transmitted light in the optical isolator shown in FIG. 1;
(A) relates to the forward incident light, and (b) relates to the backward incident light.

FIG. 3 is a side view showing a basic configuration of an optical isolator according to a second embodiment of the present invention.

4 is a side view of each optical element shown for explaining an optical path of transmitted light in the optical isolator shown in FIG. 3,
(A) relates to forward incident light, and (b) relates to reverse incident light.

FIG. 5 is a side view showing a basic configuration of an optical device using the optical isolator shown in FIG.

FIG. 6 is a side sectional view showing a local configuration of an optical device in which the optical isolator shown in FIG. 1 is coupled to an optical fiber with a ferrule using a holder.

[Explanation of symbols]

 Reference Signs List 1,5 Absorption polarizer 2,4 Reflection polarizer 3 45-degree Faraday rotator 11 Laser diode 12 Condensing lens 13 Optical isolator 14 Optical fiber 15 Holder 16 Magnet 17 Spacer 18 Optical fiber with ferrule 19 Ferrule end face H Magnetic field

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshiaki Masumoto 6-7-1, Koriyama, Taishiro-ku, Sendai City, Miyagi Prefecture Tokin Co., Ltd. (72) Haruhiko Tsuchiya 7-7-1, Koriyama, Tashiro-ku, Sendai City, Miyagi Prefecture. No. Tokinnai Co., Ltd. (72) Inventor Shojiro Kawakami 236 Toi, Wakabayashi-ku, Sendai-shi, Miyagi Atagobashi Mansion Pharaoh C-09 F-term (Reference) 2H099 AA01 BA02 CA11 CA17 DA05

Claims (5)

[Claims] A first polarizer, a Faraday rotator, and a second polarizer, each of which is a parallel plate, are arranged and fixed in this order or in the reverse order, and the first polarizer is a reflection type polarized light. An optical isolator, wherein the second polarizer is an absorption polarizer. 2. The optical isolator according to claim 1, wherein said reflective polarizer is made of a photonic crystal. 3. The optical isolator according to claim 1, wherein said reflective polarizer comprises a polymer multilayer film. 4. The optical isolator according to claim 1, wherein a hard magnetic garnet having a square hysteresis curve is used for the Faraday rotator. 5. The optical isolator according to claim 1, wherein an optical fiber with a ferrule is additionally provided.