JPH07140421A - Method and device for assembling optical isolator - Google Patents

Abstract

PURPOSE:To provide a method and device for assembling an optical isolator suitable for an optical fiber communication, specially, an optical isolator which does not depend on the polarization direction of incident light. CONSTITUTION:This device is provided with an optical fiber type coupler 2 connected to the input side of the optical isolator 1 and having a 50% coupling ratio, a 1mu2 switch 3 connected to the output side of the optical isolator 1, and a measuring instrument constituted by connecting a light source 4 and a power meter 5 to two input sides of the optical fiber type coupler 2 and a resistive terminal 6 to the output side and also connecting a power meter 7 and a completely reflective terminal 8 to two output sides of the 1mu2 switch 3; while the forward loss, reflection attenuation quantity, or isolation is measured by this measuring instrument, the angle between the normal on the surface of an optical element and the optical axis of a collimator, the relative position the optical element perpendicular to the optical axis of the collimator, and the azimuth angle of the optical element in a direction perpendicular to the optical axis of the collimator are adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator suitable for optical fiber communication, and more particularly to a method and apparatus for assembling an optical isolator which does not depend on the polarization direction of incident light.

[0002]

2. Description of the Related Art Conventionally, an optical isolator of this type is shown in FIG. In the figure, 20 is an incident light beam, 1
Reference numeral 1 is a birefringent crystal plate. When a light beam 20 is incident on this crystal plate, it is divided into two light beams having oscillating planes perpendicular to each other, one of which goes straight (ordinary ray) and the other of which goes diagonally. (Anomalous rays) After passing through the crystal plate, these rays propagate as two parallel rays. Reference numeral 12 has a crystal axis that is tilted by 67.5 degrees from the direction in which the crystal optical axes of the birefringent crystal plates 11 and 14 are projected on the surface. A half-wave plate rotated by 45 degrees, 13 is a Faraday element composed of a magneto-optical crystal plate, 14 is a birefringent crystal plate in which crystal axes are arranged in the same direction as the birefringent crystal plate 11, and 15 is elements 11-14. Is a substrate for holding the Faraday element 13, and 16 is a magnet for magnetizing the Faraday element 13. These elements constitute the optical isolator main body 10.

Next, the operation of this optical isolator body will be described. The unpolarized light 20 incident from the left side is split into light beams having mutually perpendicular polarization in the crystal of the birefringent crystal plate 11. The polarization of each light is rotated by 45 degrees in the half-wave plate 12, and is further rotated by 45 degrees clockwise by the Faraday element 13. The birefringent crystal plate 14 is the birefringent crystal plate 11.
Since the directions of the crystal axes are the same, the two lights polarized by 90 degrees from the initial state are recombined.

Next, let us consider the light incident from the right side.
The incident light ray 20 'is separated by the birefringent crystal plate 14 into an ordinary ray that travels straight with polarizations perpendicular to each other and an extraordinary ray that travels obliquely. Due to the non-reciprocity of the Faraday element 13, the polarization direction of each light is counterclockwise with respect to the traveling direction.
Rotate 5 degrees. When the light further passes through the half-wave plate 12, each light returns to the state when passing through the birefringent crystal plate 14 which rotates 45 degrees clockwise because of the polarization direction. Therefore, the respective lights that have reached the birefringent crystal plate 11 are not combined and further promoted the separation, and are emitted to a position different from the incident position of the light beam 20. Therefore, it is possible to completely separate unpolarized light that enters from the left side and unpolarized light that enters from the right side.

Such an optical isolator has a forward loss, a return loss, and a reverse loss (isolation).
Since the characteristics must be satisfied at the same time, it is necessary to confirm the characteristics at an intermediate stage of assembling this. By the way, isolation is expressed by the ratio of the power level transmitted through the optical isolator to the power level transmitted in the opposite direction, so checking at the stage of assembling the main body of the optical isolator requires replacing the input / output fiber wiring. This is a time-consuming operation, and the optical isolator main body 10 is fixed in the housing 19 as shown in FIG. 2, and the collimator lenses 17 are attached to both sides of the housing, so that the measurement cannot be easily performed. .

FIG. 8 is a schematic diagram showing the structure of another optical isolator. Compared to the case of FIG. 3, it is characterized by not using a half-wave plate, but as in the case of FIG. 3, unpolarized light entering from the left side and unpolarized light entering from the right side are included. It can be completely separated from light.

[0007]

In such an optical isolator, the relative positions of the constituent elements and the adjustment of the optical axes of the optical element and the collimator are delicate, and the forward loss, the return loss, and the isolation. Since it has to be satisfied at the same time, it takes a long time to assemble it, and it is difficult to satisfy the optimum conditions. Therefore, an object of the present invention is to provide a method of assembling an optical isolator and a device therefor which solve the above problems.

[0008]

In the method of assembling an optical isolator according to the present invention, two birefringent crystal plates and an optical element including at least a Faraday element and a ½ wavelength plate are provided between them on a substrate. When assembling the optical isolator by introducing the optical isolator main body formed by inserting the substrate into a cylindrical magnet into a housing having collimators on both end faces, measurement of forward loss, return loss, and isolation While measuring forward loss, return loss or isolation using a device capable of forming an angle between the normal line of the optical element and the optical axis of the collimator, the relative position of the optical element perpendicular to the optical axis of the collimator or The azimuth angle of the optical element in the direction perpendicular to the optical axis of the collimator is adjusted.

In the above-mentioned assembly method, the wavelength characteristic of the isolation is measured in advance for one optical isolator using the azimuth angle θ as a parameter, and λ _n when the isolation becomes maximum corresponding to each θ _n , Deviation Δλ _n from the reference wavelength λ ₀ and deviation Δθ _n from the reference azimuth θ ₀
The relational expression Δλ _n / Δθ _n is obtained in advance, and then the wavelength characteristic of the isolation is measured for one azimuth angle θ ₁ for the unadjusted optical isolator, and the wavelength λ ₁ at which the isolation is maximum is obtained. the calculated, then, corresponds to a deviation wavelength [Delta] [lambda] ₁ from the lambda ₀ for lambda _1, the theta ₁ obtains the deviation azimuth [Delta] [theta] ₁ from theta ₀ from the relationship, and thereafter, the deviation from the reference azimuth angle The azimuth angle of the optical isolator is adjusted based on Δθ ₁ .

In the method of assembling the optical isolator according to the present invention, an optical element including two birefringent crystal plates and at least a Faraday element between them and not including a ½ wavelength plate is provided on the substrate. At the time of assembling the optical isolator by introducing the optical isolator main body formed by inserting into a cylindrical magnet into the housing provided with collimators on both end surfaces,
The angle between the normal line of the optical element and the optical axis of the collimator or the collimator while measuring the forward loss, return loss or isolation using a device capable of measuring the forward loss, return loss and isolation. The relative position of the optical element in the direction perpendicular to the optical axis of is adjusted.

An optical isolator assembling apparatus according to the present invention is provided with two birefringent crystal plates on a substrate and an optical element including at least a Faraday element and a half-wave plate between them, and the substrate is a cylindrical magnet. A device for assembling an optical isolator used when fixing an optical isolator body formed by inserting the optical isolator body into a housing provided with collimators on both end surfaces, wherein the coupling ratio connected to the input side of the optical isolator is A 50% optical fiber type coupler and a 1 × 2 switch connected to the output side of the optical isolator are provided, and a light source and a power meter are respectively provided on two input sides of the optical fiber type coupler.
A non-reflective end is connected to the output side of the 1 × 2 switch, and a power meter and a perfect reflective end are connected to the two output sides of the 1 × 2 switch, respectively. , The angle between the normal of the optical element surface and the optical axis of the collimator while measuring return loss or isolation, the relative position of the optical element in the direction perpendicular to the optical axis of the collimator, or the optics in the direction perpendicular to the optical axis of the collimator. The feature is that the azimuth angle of the element can be adjusted.

Further, the optical isolator assembling apparatus according to the present invention is provided with two birefringent crystal plates on the substrate and an optical element including at least a Faraday element between them and not including a ½ wavelength plate. A device for assembling an optical isolator, which is used when an optical isolator main body formed by inserting a substrate into a cylindrical magnet is introduced and fixed in a casing having collimators at both end surfaces, and is connected to an input side of the optical isolator. The optical fiber type coupler having a coupling ratio of 50% and a 1 × 2 switch connected to the output side of the optical isolator are provided, and a light source and a power meter are provided at the two input sides of the optical fiber type coupler, and their outputs. The non-reflective end is connected to the side,
Further, each of the two output sides of the 1 × 2 switch is provided with a measuring device in which a power meter and a perfect reflection end are connected,
The angle between the optical axis of the collimator and the normal line of the optical element surface or the relative position of the optical element perpendicular to the optical axis of the collimator is adjusted while measuring the forward loss, return loss, or isolation by the measuring device. It is characterized by being able to do it.

[0013]

The method of assembling the optical isolator according to the present invention is as follows.
Since the optical isolator main body and the housing are independently assembled, it is possible to make fine adjustments and assembly. Since the range of azimuth angles for adjustment is investigated in advance and adjustment is performed based on this data, the repetition of adjustment is reduced and the assembling efficiency is improved. Since the optical isolator assembling apparatus according to the present invention can measure forward loss, return loss, and isolation during assembly, it can be assembled and adjusted in a short time.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. (Embodiment 1) FIG. 1 is a schematic view showing the entire structure relating to an assembling method, and FIG. 2 is a view showing an optical isolator applied to this embodiment. In the figure, the optical isolator body 1
0 is introduced into the housing 19, and a collimator including a collimator lens 17 and an optical fiber 18 is attached to both sides of the housing 19 to form the optical isolator 1. here,
Details of the configuration of the optical isolator body 10 are shown in FIG.

The optical isolator 1 to be adjusted and assembled has an optical fiber coupler 2 connected to the input side thereof with a coupling ratio of 50%, and 1 × connected to the output side of the optical isolator 1.
2 of the optical fiber type coupler 2
A light source 4 and a power meter 5 are respectively connected to one input side, a non-reflecting end 6 made of, for example, matching oil is connected to an output side, and a power meter 7 and a multi-layer, for example, a multilayer are respectively provided to two output sides of the 1 × 2 switch 3. It is an optical isolator assembling apparatus including a measurement system to which the reflection end 8 of the film is connected. The optical isolator main body 10 while measuring the forward loss, return loss or isolation by means of a stage that rotates and moves this measuring system and an optical isolator (not shown).
And the angle between the normal line of the optical element surface of the housing 19 and the optical axis of the collimator, the relative position of the optical element in the direction orthogonal to the optical axis of the collimator, or the azimuth angle of the optical element in the direction orthogonal to the optical axis of the collimator. can do.

Next, the adjusting method of the present invention will be described.
The output side of the 1 × 2 switch 3 is switched to the power meter 7. The light from the light source 4 propagates through the coupler 2, the optical isolator 1, and the switch 3 and is received by the power meter 7 to measure the power level P ₁ . Here, the insertion losses of the coupler 2 and the switch 3 are P ₂ and P ₃ , respectively, and the output level of the light source 4 is P _0.
Then, the loss in the forward direction of the optical isolator = (P ₀ −3) −P ₁ −P ₂ −P ₃ (dB) ... Here, since the adjustment of the optical isolator main body 10 itself has been completed, the relative position of the optical element mainly in the direction perpendicular to the optical axis of the collimator is adjusted so that the equation becomes the minimum. An example of measurement after adjustment is shown in FIG.

In the above measurement state, the power meter 5
Measure the power level P ₄ of. Since the reflection of the coupler 2 itself is sufficiently small, it is represented by the return loss of the optical isolator = − (P ₀ −3) + (P ₄ +3) (dB). This return loss also applies to the collimator and the optical isolator main body 10
Since it is determined by the relative positional relationship between and, the expression must be minimized, and at the same time, the angle between the normal line of the optical element surface and the optical axis of the collimator must be adjusted so that the absolute value of the expression is maximized. In FIG. 2, the angle formed by the normal line of the optical isolator main body and the optical axis of the collimator is set to be slightly inclined so that the whole is not returned when reflection occurs.

Next, the switch 3 is switched to the side of the reflecting end 8. The light from the light source 4 propagates through the coupler 2, the optical isolator 1, and the switch 3, and once reaches the reflection end 8. The light reflected here travels in the opposite direction and measures the power level P ₅ of the power meter 5. Isolation of optical isolator = (P ₀ −3) − (P ₅ +3) (dB) Since this value mainly depends on the angle between the normal line of the optical element surface and the optical axis of the collimator, it is adjusted so that the absolute value of the formula becomes maximum.

When the optical isolator has a half-wave plate as shown in FIG. 3, the isolation of the equation is also influenced by the azimuth angle θ of the optical element in the direction perpendicular to the optical axis of the collimator. This point will be described below and the adjustment method will be described. For one optical isolator having the configuration shown in FIG. 3, the wavelength characteristic of the isolation was measured using the azimuth angle θ as a parameter (the result is shown in FIG. 4), and the maximum isolation was found for each θ _n. In this case, the relational expression Δλ _n / Δθ _n between the deviation Δλ _n from the reference wavelength λ ₀ and the deviation Δθ _n from the reference azimuth θ ₀ is obtained, and then one azimuth angle θ by measuring the wavelength characteristics of isolation for _one obtains the wavelength lambda ₁ that isolation is maximum (the results are shown in FIG. 5 (b)), then, corresponds to the deviation [Delta] [lambda] ₁ from lambda ₀ theta ₀ previously determined deviation [Delta] [theta] ₁ from the relationship from, thereafter, to have not a group to shift [Delta] [theta] ₁ from the reference azimuth is a method of adjusting the azimuth angle of the optical isolator.

When measuring the isolation using the above-mentioned measuring device, the power level P _{5 of the} power meter 5 is measured.
When measuring, the collimator is fixed and the azimuth angle θ of the optical element is changed. At this time, it is difficult to adjust the maximum value of isolation to the desired wavelength and it takes a long time, so the value including the magnitude of the azimuth angle θ and the positive or negative direction should be obtained in advance. The adjustment can be completed in a short time. Incidentally FIG. 7 is a diagram showing the configuration of two optical isolator using half-wave plate, but can be easily adjusted by the same procedure as in FIG 3, the [Delta] [lambda] _n and [Delta] [theta] _n The relationship is shown in FIG. As described above,
The forward loss, return loss, and isolation of the optical isolator can be checked while measuring the formula, and this can be repeated to adjust to the optimum state.

The ten optical isolators shown in FIG. 2 were prepared, and the angle between the normal line of the optical element surface and the optical axis of the collimator, and the direction perpendicular to the optical axis of the collimator were formed by using the apparatus shown in FIG. The relative position of the optical element and the azimuth angle θ of the optical element in the direction perpendicular to the optical axis of the collimator were adjusted for assembly. As a result, the time required for adjustment / assembly is shortened to 2/3 of that of the conventional method, and 40% of the conventional methods cannot be adjusted. Was 0.8 dB or less, the return loss was 50 dB or less, and the isolation was 35 dB or more.

(Embodiment 2) The optical isolator shown in FIG. 8 does not have a ½ wavelength plate as shown in FIG. 3 or 7. Therefore, the isolation is hardly influenced by the azimuth angle θ of the optical element in the direction perpendicular to the optical axis of the collimator. Therefore, in this case, it is sufficient to adjust the absolute value of the direct expression to the maximum without performing the preliminary investigation shown in FIG. 4 or FIG.

[0023]

As described above, in the method of assembling the optical isolator according to the present invention, the optical isolator main body and the housing are independently assembled, so that delicate adjustment and assembly can be performed. Since the range of azimuth angles for adjustment is investigated in advance and adjustment is performed based on this data, the repetition of adjustment is reduced and the assembling efficiency is improved. Since the optical isolator assembling apparatus according to the present invention can measure forward loss, return loss, and isolation during assembly, it can be assembled and adjusted in a short time.

[Brief description of drawings]

FIG. 1 is an overall view showing a configuration of an embodiment relating to an assembling apparatus of the present invention.

FIG. 2 is a diagram showing a configuration of an optical isolator used in this embodiment.

FIG. 3 is a cross-sectional view showing a configuration of an optical isolator main body used in this embodiment.

FIG. 4 is a diagram showing measured values of isolation with respect to wavelength of the optical isolator according to the present embodiment.

FIG. 5 is a diagram showing a relationship between an azimuth angle and a wavelength when the optical isolator according to the present embodiment is adjusted.

FIG. 6 is a diagram showing measured values of forward loss with respect to wavelength of the optical isolator according to the present embodiment.

FIG. 7 is a cross-sectional view showing the configuration of another optical isolator used in this embodiment.

FIG. 8 is a sectional view showing the configuration of another optical isolator used in this embodiment.

[Explanation of symbols]

 1: Optical isolator 2: Optical fiber type coupler 3: Switch 4: Light source 5, 7: Power meter 6: Non-reflective end 8: Reflective end 9, 18: Optical fiber 10: Optical isolator main body 11, 14: Birefringent crystal plate 12: 1/2 wavelength plate 13: Faraday element 15: Substrate 16: Magnet 17: Collimator lens 19: Housing 20, 20 ': Light beam

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuhiro Kawanami, 1st Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor: Shigeru Semura 1st, Taya-cho, Sakae-ku, Yokohama, Kanagawa Denki Kogyo Co., Ltd. Yokohama Works (72) Inventor Dai Yui 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Denki Kogyo Co., Ltd. Yokohama Works

Claims (5)

[Claims] 1. An optical isolator main body formed by inserting two birefringent crystal plates and an optical element including at least a Faraday element and a half-wave plate between them on a substrate, and inserting the substrate into a cylindrical magnet. When assembling the optical isolator by introducing into the housing with collimators on both end faces, use a device that can measure the forward loss, return loss, and isolation. The angle between the normal line of the optical element and the optical axis of the collimator, the relative position of the optical element in the direction perpendicular to the optical axis of the collimator, or the azimuth angle of the optical element in the direction perpendicular to the optical axis of the collimator A method of assembling an optical isolator, comprising: 2. One optical isolator in advance,
The wavelength characteristics of the isolation are measured using the azimuth angle θ as a parameter, and the deviation Δ from the reference wavelength λ ₀ for λ _n when the isolation is maximum corresponding to each θ _n.
Relational expression of λ _n and deviation Δθ _n from the reference azimuth θ ₀ Δλ _n /
Δθ _n is obtained in advance, and then the wavelength characteristics of the isolation are measured for one azimuth angle θ ₁ for the unadjusted optical isolator, and the wavelength λ ₁ at which the isolation is maximized is obtained. corresponding to deviation wavelength [Delta] [lambda] ₁ from the lambda ₀ for ₁ obtains the deviation azimuth [Delta] [theta] ₁ from theta ₀ for theta ₁ from the relationship, after which it had not a group to shift [Delta] [theta] ₁ from the reference azimuth angle The method for assembling the optical isolator according to claim 1, wherein the azimuth angle of the optical isolator is adjusted. 3. A substrate is provided with two birefringent crystal plates and an optical element which includes at least a Faraday element and does not include a half-wave plate between them, and is formed by inserting the substrate into a cylindrical magnet. When assembling the optical isolator by introducing the main body of the optical isolator into the housing with collimators on both end faces, use a device that can measure the forward loss, return loss, and isolation. A method for assembling an optical isolator characterized by adjusting an angle formed between a normal line of an optical element surface and an optical axis of a collimator or a relative position of the optical element in a direction perpendicular to the optical axis of the collimator while measuring the amount or isolation. . 4. An optical isolator main body formed by inserting two birefringent crystal plates and an optical element including at least a Faraday element and a half-wave plate between them on a substrate, and inserting the substrate into a cylindrical magnet. Is an apparatus for assembling an optical isolator used when it is introduced and fixed in a housing having collimators on both end faces, and the coupling ratio connected to the input side of the optical isolator is 50.
% Optical fiber type coupler and a 1 × 2 switch connected to the output side of the optical isolator, the two input sides of the optical fiber type coupler each have a light source and a power meter, and the output side thereof has a non-reflective end. And a measuring device having a power meter and a perfect reflection end connected to the two output sides of the 1 × 2 switch, respectively, to measure forward loss, return loss or isolation by the measuring device. While measuring, you can adjust the angle between the normal of the optical element surface and the optical axis of the collimator, the relative position of the optical element in the direction orthogonal to the optical axis of the collimator, or the azimuth angle of the optical element in the direction orthogonal to the optical axis of the collimator. A device for assembling a characteristic optical isolator. 5. A substrate is provided with two birefringent crystal plates and an optical element which includes at least a Faraday element and does not include a half-wave plate between them and is formed by inserting the substrate into a cylindrical magnet. A device for assembling an optical isolator used when the optical isolator main body is introduced and fixed in a casing having collimators at both end faces, wherein a coupling ratio connected to an input side of the optical isolator is 50.
% Optical fiber type coupler and a 1 × 2 switch connected to the output side of the optical isolator, the two input sides of the optical fiber type coupler each have a light source and a power meter, and the output side thereof has a non-reflective end. And a measuring device having a power meter and a perfect reflection end connected to the two output sides of the 1 × 2 switch, respectively, to measure forward loss, return loss or isolation by the measuring device. An apparatus for assembling an optical isolator, wherein an angle between a normal line of an optical element surface and an optical axis of a collimator or a relative position of an optical element in a direction perpendicular to the optical axis of a collimator can be adjusted while measuring.