JPH0723925B2 - Variable optical attenuator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a variable optical attenuator used for continuous attenuation adjustment of the amount of transmitted light in an optical fiber communication circuit or the like, and more specifically, it is particularly harmful. The present invention relates to a high-performance variable optical attenuator that minimizes reflected return light loss.

(Problems to be Solved by Conventional Techniques and Inventions) As a variable optical attenuator used for adjusting the attenuation of the light quantity of an optical fiber communication circuit, various types have been proposed and put into practical use.

FIG. 6 is a schematic diagram for explaining the operation of a conventional variable optical attenuator using a glass plate whose transmittance changes continuously.

A glass plate 3 on which a metal thin film is vapor-deposited is arranged between the two rod lenses 1 and 2 arranged in the transmission optical path 4 so that the concentration continuously changes.

This glass plate 3 is moved in a direction (shown by an arrow) at right angles to the optical axis by an adjusting device (not shown) so that an arbitrary portion of the glass plate 3 is made to correspond to the optical axis to adjust the light amount of the optical path 4.

Reflection occurs at the end surfaces (air interface) of the rod lenses 1 and 2 and the air interface of the vapor deposition glass plate 3.

The so-called reflected return light loss increases and this is returned to the light source and affects the light source.

Further, in this device, the transmittance of the glass plate 3 changes with time,
Attenuation becomes unstable.

It is known that, unlike the method described above, the amount of light attenuation can be changed by adjusting the distance between the connection end faces of the optical connectors facing each other.

FIG. 7 is a cross-sectional view for explaining an attenuator that adjusts the distance between the end faces of the ferrule member to continuously change the attenuation amount.

The connector structure for adjusting the distance between the connection end faces of the illustrated optical connector is based on the proposal by the present inventor.

The alignment adapter member 5 is a cylindrical member made of metal and has a through hole 20 for receiving the ferrule members 14 and 15 in the center.
Is provided.

An adjusting screw nut is provided on the inner circumference of one end of the alignment adapter member 5.
A threaded portion 22 that engages with 21 is provided.

Optical connector plugs on both ends of the outer diameter portion of the alignment adapter member 5.
Threaded portions 12 and 13 that engage with the threaded portions 10 and 11 of the coupling nuts 8 and 9 of 6 and 7 are provided.

Further, the screw portions 12 and 13 are provided with rotation stopper keys 16 and 16 provided on the outer diameter portions of the ferrule members 14 and 15 of the optical connector plugs 6 and 7, respectively.
Keyways 18, 19 into which the 17 is fitted are provided.

The biasing compression spring 22 is inserted between the coupling nut 8 and the ferrule member 14, and the other compression spring 23 is inserted into the coupling nut 9 and the ferrule member 15 to move the ferrule members 14 and 15 toward the center of the alignment adapter member 5, respectively. I am biased.

Retaining rings 24 and 25 are in groove 2 of ferrule members 14 and 15, respectively.
It is fitted in 6,27.

One end of the adjusting screw nut 21 has a suitable groove for turning.
28 is provided.

The adjustment of the attenuation amount of this variable optical attenuator will be briefly described.

First, the optical connector plugs 6 and 7 and the adjusting screw nut 21 are attached to the adapter member 5 as shown.

An optical fiber 29 is connected to a light source (not shown), and an optical fiber 30 is similarly connected to an optical power meter (not shown) to read the attenuation value of the light quantity.

The operation of adjusting the amount of screwing of the adjusting screw nut 21 (adjusting the interval S) is repeated many times until the optical connector plug 7 is detached and attached until the required attenuation value is obtained.

As described above, this device is extremely complicated to adjust.

Further, similarly to the above-mentioned device, the loss of reflected return light at the air interface is as large as about 10 to 12 dB. Therefore, this attenuator cannot be used for long-distance large-capacity communication or video communication.

A main object of the present invention is to provide a novel variable optical attenuator which has a small loss of reflected return light and can easily set an arbitrary attenuation amount and can be easily coupled.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the variable optical attenuator according to the present invention is configured such that the end faces of a pair of ferrules in which an optical fiber is attached to a central hole are provided with respect to a plane perpendicular to the optical axis. Use the ones that are slantly polished to have an inclination angle of 7 to 20 degrees, urge each ferrule end surface to press against each other, fix one of the ferrules, and rotate the other in the range of 0 to 180 degrees. Then, the distance between the optical fibers is adjusted.

Thus, the amount of light transmitted from one optical fiber to another optical fiber can be attenuated by an arbitrary amount without attaching or detaching each ferrule from the adapter member.

That is, the variable optical attenuator according to the present invention is a variable optical attenuator that attenuates light incident from one optical fiber to the other optical fiber coupled to the optical fiber by an arbitrary amount and transmits the attenuated optical fiber. An alignment adapter member, a first ferrule member in which a transmission terminal surface exposing an optical fiber end and the optical fiber end surface have a certain inclination with respect to an optical axis, and the first ferrule member in the alignment adapter member. The first fixing means for restricting and supporting the rotation and the transmission terminal surface for exposing the optical fiber end have the same inclination with the optical fiber end surface as the first ferrule member with respect to the optical axis. The ferrule member and the alignment adapter member are combined to constantly bias the second ferrule member toward the first ferrule member, And a predetermined angle and rotatably supported above and the optical fiber connector member secured to the alignment adapter member at an arbitrary angle position within the range concentric to seal member.

The alignment adapter member has an alignment sleeve hole that precisely fits the outer diameter portions of the first and second ferrule members, and at least allows the second ferrule member to be rotatably supported.

The pair of ferrule end faces can be formed by oblique polishing so that they have the same inclination angle of 7 degrees or more and 20 degrees or less with respect to a plane perpendicular to the optical axis of the optical fiber.

The optical fiber connector member limits the movement of the second ferrule member in the axial direction and rotatably supports the second ferrule member, and a holder member that is linearly guided in the optical axis direction with respect to the alignment adapter member, and a penetrating bottom portion. A coupling nut that receives and supports the holder member in the hole and is screwed to the alignment adapter member at the opening, and the second ferrule member inserted between the coupling nut and the holder member via the holder member. The first ferrule member may be composed of spring means that constantly biases the ferrule member.

An optical fiber connector member having the same structure as the optical fiber connector member can be used as the first fixing means for supporting the first ferrule member on the alignment adapter member while limiting the rotation.

When the second ferrule member is rotated within 180 degrees with respect to the alignment adapter member, the slope of each ferrule is changed from the minimum attenuation state in which the end faces of which the distances between the optical fibers are the smallest to be in close contact to each other to the maximum angle of the slope. The maximum attenuation position can be continuously varied.

The second ferrule member is rotated to a position at which necessary attenuation is obtained with respect to the first ferrule member, and the rotational positions of the holder member and the ferrule member are fixed to obtain a certain amount of attenuation. be able to.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a partially cutaway view of an embodiment of a variable optical attenuator according to the present invention, showing a state in which the amount of attenuation is adjusted to a minimum.

FIG. 2 is a partially cutaway view of an embodiment of the variable optical attenuator according to the present invention in a state where the attenuation amount is adjusted to the maximum.

FIG. 3 is a transverse cross-sectional view of an embodiment of the variable optical attenuator according to the present invention, taken along the line XX in FIG.

FIG. 4 is a graph showing operating characteristics of the variable optical attenuator according to the present invention.

FIG. 5 is a histogram showing the results of actually measuring the reflection return loss of many variable optical attenuators according to the present invention.

The variable optical attenuator according to this embodiment is provided with one optical fiber.
It is a variable optical attenuator capable of transmitting the light incident from 33 to the other optical fiber 34 coupled to the optical fiber by attenuating it by an arbitrary amount and vice versa.

This variable optical attenuator is basically composed of a first optical connector plug 31 shown on the left side in FIG. 1, an alignment adapter member 59 and a second optical connector plug 32 shown on the right side. It is configured.

The alignment adapter member 59 has a through hole 64 at the center and threaded portions 60, 61 at both ends.

Keyways 62, 63 are provided in the screw portions 60, 61.

The first ferrule member 41 is composed of a small diameter portion 41a fitted into the alignment adapter member 59, a larger diameter portion 41b fitted into the holder member 51, and a knob portion 41c.
A groove 41d is provided on the outer circumference of the b portion.

Similarly, the second ferrule member 42 is also composed of a small diameter portion 42a, a larger diameter portion 42b and a knob portion 42c, and a groove 42d is provided on the outer circumference of the 42b portion.

The first holder member 51 includes the first ferrule member 41.
A through hole 47 that rotatably receives the 41b portion is provided. A groove 49 is provided on the inner periphery of the through hole at a position corresponding to the groove 41d of the first ferrule member 41, and the retaining ring 37 is inserted between these grooves.

As a result, the first ferrule member 41 becomes the first holder member.
It is rotatably supported, although its axial movement is restricted by 51.

A flange 43 is provided on the outer periphery of the right end of the holder member 51, and a detent key 45 is provided on the flange 43, and the key 45 is engaged with the key groove 62 of the alignment adapter member.

The second holder member 52 includes the second ferrule member 42.
A through hole 48 that rotatably receives the 42b portion is provided. A groove 50 is provided on the inner periphery of the through hole 48 at a position corresponding to the groove 42d of the second ferrule member 42, and the stop ring 38 is inserted between these grooves.

Further, a flange 44 is provided on the outer periphery of the left end of the holder member 52, and a rotation stop key 46 is provided on the flange 44, and the key 46 is engaged with the key groove 63 of the alignment adapter member.

The first caprig nut 57 is in the shape of a cap nut, and the holder member 51 is loosely received in the through hole at the bottom, and the screw 55 is provided on the inner circumference of the opening side, and is coupled to the screw portion 60 of the alignment adapter member 59. Has been made.

A coil spring 53 is inserted between the flange portion 43 of the first holder member 51 and the first coupling nut 57,
The spring 53 constantly urges the first ferrule member 41 toward the alignment adapter member 59 via the first holder member 51.

The second coupling nut 58 also loosely receives the holder member 52 in the through hole at the bottom thereof, and is connected to the threaded portion 61 of the alignment adapter member 59 with a screw 56.

The coil spring 54 is also inserted between the flange portion 44 of the second holder member 52 and the second coupling nut 58 in the same manner as described above, and the second ferrule member 42 is always attached in the direction of the alignment adapter member 59. I am energetic.

Next, the adjustment for obtaining an arbitrary amount of attenuation will be briefly described.

Each component is assembled as shown in FIG. 1, one optical fiber 33 is connected to a light source (not shown), and the optical fiber 34 is connected to an optical power meter (not shown).

Since the optical connector plug 31 on the fixed side does not require adjustment, the ferrule member 41 and the holder member 51 are bonded and fixed from the beginning.

While holding the outer end 42c of one ferrule member 42 and reading the attenuation value, the ferrule member 42 is rotated within a range of 180 degrees.

The fast-curing adhesive is injected into the gap between the ferrule member 42 and the holder member 52 and fixed at the rotation angle position where the attenuation value reaches the required numerical value.

After this fixing, the second coupling nut 58 is loosened, the optical connector plug 31 on the adjusting side is removed, and even if the attachment and detachment is repeated, the relative angle of the second ferrule member 42 with respect to the first ferrule member 41 and the distance between the fibers. Since the distance is accurately restored, the set attenuation amount does not change.

FIG. 4 is a graph showing operating characteristics of the variable optical attenuator according to the present invention.

This graph shows the amount of optical attenuation when the distance S between the optical fibers is changed by a pair of ferrules in which the angle θ of the end face of the ferrule member with respect to the plane perpendicular to the optical axis is 12 degrees in the variable optical attenuator. It is a graph.

In the structure described above, the distance between the optical fibers can be continuously changed by rotating one ferrule member.

FIG. 2 shows that the second ferrule member 42 is rotated 180 degrees with respect to the first ferrule member 41, and the distance S between the optical fibers is increased.
Shows a state in which is maximized.

For reference, the attenuation characteristics are also shown for the case where θ is 0 degree. It should be understood that this was measured with the structure as shown in FIG.

As can be seen from this graph, the amount of attenuation increases as θ and S increase.

Using this graph, the angle θ of oblique polishing can be determined from the required attenuation range.

FIG. 5 is a histogram showing the results of actually measuring the reflection return loss of many variable optical attenuators according to the present invention.

As the optical fiber, SM-10 / 125 (a single mode optical fiber having a core diameter of 10 μm and a cladding diameter of 125 μm) was used. The result of actually measuring the reflected return light loss is shown by preparing 150 variable optical attenuators having the above structure using a member of the ferrule with an inclination angle θ = 12 °. A wavelength (λ = 13
μm) laser diode was used.

The average loss of reflected return light is -67.9 dB. Standard deviation is
At 1.6 dB, good results with very little variation are obtained. The reflected return light loss does not change depending on the rotation angle of the ferrule.

(Effect of the Invention) As described above, the variable optical attenuator according to the present invention is
The structure of the optical connector can be used almost as it is.

Polish the tip of the ferrule diagonally in the range of 7 to 20 degrees according to the required optical attenuation, insert one of the optical connector plugs into the alignment adapter and fix it, and set the ferrule part of the other optical connector plug to 0 Since the light attenuation can be changed by a simple operation of turning it in the range of 180 degrees, it is not necessary to adjust the attenuation by repeating attachment and detachment as in the past, and the adjustment is easy.

Furthermore, the reflection return loss can be significantly reduced by obliquely polishing the ferrule tip surface to 7 to 8 degrees.

It is known that this can reduce the return due to surface reflection, but in the present invention as well, the optical attenuator is constructed by using a ferrule that is tanned and polished in the range of 7 to 20 degrees, so that the distance between the end faces of the optical fiber is almost the same. No matter the fifth
It is possible to mass-produce a variable optical attenuator having excellent reflected light loss characteristics as shown in the histogram of reflected return light loss in the figure.

As described above, since the variable optical attenuator according to the present invention has a simple structure principle, easy adjustment, and excellent reflected return light loss characteristics, it is low-priced and variable in various conventional types. There is no restriction on the application like the optical attenuator,
The effect that can be used for all purposes is great.

[Brief description of drawings]

FIG. 1 is a partially cutaway view of an embodiment of a variable optical attenuator according to the present invention, showing a state in which the amount of attenuation is adjusted to a minimum. FIG. 2 is a partially cutaway view of an embodiment of the variable optical attenuator according to the present invention in a state where the attenuation amount is adjusted to the maximum. FIG. 3 is a transverse cross-sectional view of an embodiment of the variable optical attenuator according to the present invention, taken along the line XX in FIG. FIG. 4 is a graph showing operating characteristics of the variable optical attenuator according to the present invention. FIG. 5 is a histogram showing the results of actually measuring the reflection return loss of many variable optical attenuators according to the present invention. FIG. 6 is a schematic diagram for explaining the operation of a conventional variable optical attenuator using a glass plate whose transmittance changes continuously. FIG. 7 is a cross-sectional view for explaining an attenuator that adjusts the distance between the end faces of the ferrule member to continuously change the attenuation amount. 31,32 …… Optical connector plug 51,52 …… Holder member 53,54 …… Compression spring for biasing ferrule 55,56 …… Coupling nut thread 57,58 …… Coupling nut 43,44 …… Flange 45 , 46 …… Rotating key 47,48 …… Through hole 49,50 …… Groove 59 …… Alignment adapter member 60,61 …… Screw part 62,63 …… Key groove 64 …… Through hole

Claims (7)

[Claims] 1. A variable type optical attenuator for transmitting light incident from one optical fiber to the other optical fiber coupled to the optical fiber after attenuating the optical fiber by an arbitrary amount, and an alignment adapter member and an optical fiber. A transmission terminal surface exposing an end of the fiber and the end surface of the optical fiber having a constant inclination with respect to the optical axis;
Ferrule member, first fixing means for supporting the first ferrule member on the alignment adapter member while limiting rotation, and a transmission terminal surface exposing an optical fiber end together with the optical fiber end surface with respect to the optical axis. And a second ferrule member having substantially the same inclination as the first ferrule member, and the alignment adapter member, and constantly biasing the second ferrule member toward the first ferrule member, A variable optical attenuator comprising an optical fiber connector member which is concentrically supported by the first ferrule member so as to be rotatable by a predetermined angle or more and is fixed to the alignment adapter member at an arbitrary angular position within the range. 2. The aligning adapter member has an aligning sleeve hole that precisely fits the outer diameter portions of the first and second ferrule members, and can rotatably support at least the second ferrule member. The variable optical attenuator according to claim 1. 3. The pair of ferrule end faces are obliquely polished so that they have the same inclination angle of 7 degrees or more and 20 degrees or less with respect to a plane perpendicular to the optical axis of the optical fiber. Variable optical attenuator. 4. A holder member, wherein the optical fiber connector member rotatably supports the second ferrule member while limiting the axial movement thereof, and is linearly guided with respect to the alignment adapter member in the optical axis direction. A coupling nut that receives and supports the holder member in a through hole at the bottom and is screwed to the alignment adapter member at an opening; and a second ferrule member that is inserted between the coupling nut and the holder member 2. The variable optical attenuator according to claim 1, wherein the variable optical attenuator is constituted by spring means which constantly urges the first ferrule member through a member. 5. The first fixing means for supporting the first ferrule member on the alignment adapter member while restricting rotation thereof is an optical fiber connector member having the same structure as the optical fiber connector member. Variable optical attenuator. 6. The second ferrule member is rotated within 180 degrees with respect to the alignment adapter member, so that the slope of each ferrule changes from a state of minimum attenuation in which the end faces having the minimum distance between the optical fibers are in close contact with each other to a slope. The variable optical attenuator according to claim 1, wherein the variable optical attenuator is capable of being continuously varied to a position where the maximum attenuation is obtained. 7. The second ferrule member is rotated to a position where a necessary attenuation is obtained with respect to the first ferrule member, and the rotational positions of the holder member and the ferrule member are fixed to provide a constant attenuation amount. The variable optical attenuator according to claim 4, which is configured to obtain.