JPH1164790A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical isolator of a low production cost by forming a non-reflection coating only on the one end face of an optical collimator and optical isolator optical element facing each other and packing an optical adhesive having the refractive index equal to the refractive index of the end face on the side not subjected to the non-reflection coating between the end faces. SOLUTION: The optical adhesive 3 has the refractive index equal to the refractive index distribution type lens 2a of the optical collimator 2. The non- reflection coating 4 formed on the end face of the optical isolator optical element 1 matches the refractive index of the end face of the optical element 1 and the refractive index of the adhesive 3. The adhesive 3 consists of a UV curing resin, etc., having the assigned refractive index, is more inexpensive than multilayered dielectric films constituting the non-reflection coating and facilitates packing work. As a result, the end faces to be subjected to the non- reflection coating are decreased from four points to two points and the production cost of the points associated with the non-reflection coating is reduced to about 70%. In addition, the occurrence of the reflection by the difference in the refractive index is averted and the inexpensive production of the good optical isolator is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator used for an optical measurement system, an optical communication system, or the like.

[0002]

2. Description of the Related Art A typical non-polarization type optical isolator is
An optical isolator optical element composed of a birefringent substance (calcite, rutile crystal), a Faraday rotator and a magnet for applying a magnetic field to the Faraday rotator, and an input / output optical collimator arranged at both ends of the optical isolator (References:
JP-B-58-28561, O plus E
May 1996).

FIG. 3 shows an example of the optical system, in which 31 is an optical isolator optical element in which a birefringent substance and a Faraday rotator are laminated and bonded, 32 is a magnet for applying a magnetic field to the Faraday rotator, and 33 is an optical element. An optical collimator disposed at both ends of the isolator, which is accommodated in a case 34, adjusted in relative position, and fixed by welding, bonding, or the like. The optical collimator is a single mode fiber 33.
b and a fiber-shaped refractive index distribution type lens 33a are fusion-spliced and housed in a glass tube 33c, and are arranged such that the axes are shifted on the input side and the output side by the displacement of the optical path axis by the optical isolator optical element. I have.

[0004] Since the two optical collimators are arranged at a mutual position such that the coupling efficiency is maximized and the optical isolator optics are arranged therebetween, there is usually a slight distance between the optical collimator and the optical isolator optics. Space is created.
Since reflection at the end face of the optical collimator or optical isolator optical element is expected due to a difference in refractive index from air, each end face is provided with an anti-reflection coating to minimize reflection against air. . This non-reflective coating is formed by coating a dielectric multilayer film on the end surface of the birefringent substance of the optical isolator optical element or the end surface of the refractive index distribution type lens of the optical collimator so as to match the respective refractive indexes. I have. This dielectric multilayer film is formed by adjusting the refractive index by repeating a layer of titanium oxide and a layer of silicon oxide, and this has led to an increase in the number of steps for manufacturing an optical isolator and an increase in manufacturing cost.

[0005]

In the optical isolator according to the prior art described above, it is necessary to form a non-reflection coating on each of the four end faces of the optical collimator and the optical isolator optical element. It is an object of the present invention to provide an optical isolator having a low manufacturing cost by minimizing an increase in manufacturing steps and manufacturing costs due to the formation of a reflection coating.

[0006]

According to the present invention, a non-reflective coating is formed only on one end face of an optical collimator and an optical isolator optical element facing each other, and the refraction of an end face on which no non-reflective coating is applied is provided between the end faces. An optical adhesive having a refractive index equal to the refractive index is filled.

That is, when the non-reflective coating is formed on the end face of the refractive index distribution type lens of the optical collimator, the refractive index (refractive index of the birefringent material) is equal to the refractive index of the birefringent material of the optical isolator optical element. When the refractive index is No for ordinary light and Ne for extraordinary light, the equivalent refractive index is an average value thereof, that is, (No + Ne) / 2 is an equivalent refractive index). However, when the non-reflective coating is formed on the end surface of the birefringent material of the optical isolator optical element, the refractive index is equal to the refractive index of the gradient index lens of the optical collimator (the center of the gradient index lens). An optical adhesive having the same refractive index as the refractive index) may be filled.

The non-reflective coating is formed by selecting a material and a film thickness of the dielectric multilayer film so as to match the refractive index of the end face forming the same and the refractive index of the optical adhesive to be filled. In this case, the dielectric multilayer film is also formed by coating the titanium oxide layer and the silicon oxide layer repeatedly while adjusting the thickness in substantially the same manner as in the prior art.

[0009]

1 and 2 are diagrams schematically showing the present invention. 1 and 2, reference numeral 1 denotes an optical isolator optical element, and reference numeral 2 denotes an optical collimator. Reference numeral 3 denotes an optical adhesive having a refractive index equivalent to that of the gradient index lens 2a of the optical collimator 2. Reference numeral 4 denotes a non-reflection coating formed on the end face of the optical isolator optical element 1 for matching the refractive index of the end face of the optical isolator optical element 1 with the refractive index of the optical adhesive 3. Reference numeral 5 denotes an optical adhesive having a refractive index equivalent to the refractive index of the end face material of the optical isolator 1. Reference numeral 6 denotes an anti-reflection coating formed on the end surface of the gradient index lens 2a of the optical collimator 2, which matches the refractive index of the gradient index lens 2a with the optical adhesive 5. In addition, it is also effective to diagonally polish the end surface of the refractive index distribution type lens of the optical collimator to guide the reflected light out of the optical path and to prevent performance deterioration due to surface reflection.

The optical adhesive is made of an ultraviolet-curable resin having a specified refractive index, an epoxy resin, or the like, and is much less expensive than a dielectric multilayer film having a non-reflective coating.
The filling operation is also easy. The optical isolator optical element and the optical collimator are fixed to a protective case (not shown) together with a magnet by an adhesive or welding.
Or, 5 does not necessarily need to have the function of fixing the optical isolator optical element and the optical collimator. The optical adhesive only needs to have a function as a filler that matches the optical refractive index. Also, it is needless to say that the relative positions of the optical collimators on both sides are aligned so that the coupling efficiency is maximized.

Also, polishing the end face of the refractive index distribution type lens 2a of the optical collimator 2 at an angle of several degrees is effective in guiding the reflected light out of the optical path and reducing the deterioration in performance due to surface reflection. In addition, as the optical adhesive 3 or 5, -40 to 8
If a change in refractive index due to temperature in a range of 5 ° C. is 1/1000 or less, for example, Optodyne UV-3000 is selected and used, the change in return loss due to temperature change is 70d.
It can be suppressed to about B, and can sufficiently withstand changes in the ambient temperature.

1 and 2, a gradient index lens 2a is provided on a single mode fiber 2b as an optical collimator.
Although the optical collimator used in the present invention is not limited to such a form, the one in which a single mode fiber and a selfoc lens, a ball lens and the like are separated and fixed is also applied. Is possible.

[0013]

EXAMPLE As Example 1, the one shown in FIG. Since the refractive index of the central axis of the refractive index distribution type lens of the optical collimator is 1.461, a transparent epoxy resin in the infrared long wavelength band having a refractive index of 1.461 is selected and filled as an optical adhesive, and the optical isolator is filled. On the end face of the optical element, a dielectric multilayer coating of titanium oxide and silicon oxide was formed so as to be non-reflective at a wavelength of 1.55 μm and a refractive index of 1.461. When the relative positions of the optical collimator and the optical isolator optical element were adjusted and fixed, and the characteristics were measured, it was confirmed that a good optical isolator could be obtained with an insertion loss of 0.5 dB, an isolation of 50 dB, and a return loss of 55 dB.

FIG. 2 shows a second embodiment of the present invention. Since the intermediate value of the ordinary and extraordinary refractive index of the birefringent substance on the end face of the optical isolator optical element is 2.58, a transparent epoxy resin in the infrared long wavelength band with a refractive index of 2.58 is selected as the optical adhesive. After filling, an end face of the optical collimator was coated with a dielectric multilayer film of titanium oxide and silicon oxide which was non-reflective at a wavelength of 1.55 μm and a refractive index of 2.58. When the relative position of the optical collimator and optical isolator optical element was adjusted and fixed, and the characteristics were measured,
It was confirmed that a good optical isolator can be obtained with an insertion loss of 0.8 dB, an isolation of 50 dB, and a return loss of 56 dB.

[0015]

According to the optical isolator of the present invention, a non-reflective coating is formed only on one end face of the opposing optical collimator and the optical isolator optical element, and a non-reflective coating is formed between the optical collimator and the end face of the optical isolator optical element. Since the optical adhesive having the same refractive index as the end face on which the non-reflection coating is applied is filled, the number of the end faces to be subjected to the anti-reflection coating is reduced from four places to two places. The manufacturing cost at the place where the operation is performed is reduced to about 70%. In addition, even the end face not coated with non-reflective coating is filled with an optical adhesive having the same refractive index, so that there is no reflection due to the difference in refractive index, and a good optical isolator can be manufactured at low cost. It is.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an optical isolator of the present invention.

FIG. 2 is a diagram showing another embodiment of the optical isolator of the present invention.

FIG. 3 is a diagram showing an optical isolator according to the related art.

[Explanation of symbols]

 1: optical isolator optical element 2: optical collimator 2a: gradient index lens 2b: single mode fiber 3, 5: optical adhesive 4, 6: non-reflective coating

Claims (4)

[Claims] 1. An optical isolator having an optical isolator optical element and input / output optical collimators at both ends of the optical isolator, wherein one of an end face of the optical isolator optical element and an end face of the optical collimator opposed thereto is non-reflective. An optical isolator characterized in that a gap between an end face of an optical isolator optical element and an end face of an optical collimator facing the optical isolator is coated with an optical adhesive having a refractive index equal to that of the other end face after being coated. 2. The optical isolator according to claim 1, wherein the optical collimator is formed by fusing a fiber-shaped gradient index lens to the tip of a single mode fiber. 3. The optical adhesive according to claim 1, wherein the refractive index of the optical adhesive is equal to the refractive index of the end face of the optical collimator, and the end face of the optical isolator optical element facing the optical adhesive has an anti-reflection coating matched with the optical adhesive. Claim 1 or Claim 2
An optical isolator according to claim 1. 4. The optical adhesive according to claim 1, wherein a refractive index of the optical adhesive is equal to a refractive index of an end face of the optical isolator optical element, and an end face of the optical collimator opposed thereto is coated with an anti-reflection coating matched with the optical adhesive. Claim 1 or Claim 2
An optical isolator according to claim 1.