JPH11160543A - Chirp variable reflection type optical fiber grating filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chirp variable reflection type optical fiber grating filter in a simple structure wherein the center wavelength of reflected light does not depend upon the variation of a chirp. SOLUTION: On end of a supporting body 2 which supports a reflection type optical fiber grating filter 1 in one body is fixed to a pedestal 3 through a clamp 4 and the other end of the supporting body 2 is fitted to the pedestal 3 through a stage 7 constituted by combining a clamp 6 and two sliders 7a and 7b which are movable in only one direction so that their moving directions cross each other at right angles; the displacement of the stage 7 is provided by a micrometer head 5 and the clamp 6 is moved as it is in parallel with the clamp 4 to impart a strain distribution including linear compression as well as linear elongation to the grating 1a of the reflection type optical fiber grating filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type optical fiber grating filter whose chirp can be changed.

[0002]

2. Description of the Related Art A conventional reflection type optical fiber grating filter is disclosed in JP-A-8-101310 or K.K.
O.Hill "Fiber Grating Fiber Device"
OPTRONICS, 1995, pp 135-141. D. Garthe eta is a reflective optical fiber grating filter with a variable chirp.
l., “Ajustable dispersion equlizer for 10 and 20 G
bit / s over distance up 160km ”Electron Letters, V
ol.30, No.25, 1994, pp2159-2160, or S. Huang et a
l., “Fiber optic intra-grating distributed strain
sensor ”Proc.SPIE, Vol.2294, 1994, or Takeyuki Imai et al.“ Control of dispersion characteristics of chirped fiber gratings ”described in IEICE Electronics Society Conference Proceedings, C-3-40, 1997, pp. 149 There is something.

FIG. 1 shows an example of a conventional chirp variable reflection type optical fiber grating filter.
1 is a reflection type optical fiber grating filter, 2 is a support, 3 is a pedestal, 4 is a clamp, and 5 is a micrometer head.

The reflection type optical fiber grating filter 1 is formed by irradiating the core of an optical fiber with ultraviolet rays to form a grating 1a, and a part of the light incident from one end 1b is reflected by the grating 1a to be reflected by the grating 1a. 1b
From the other end, and the rest is radiated to the outside from the other end 1c which has been subjected to the non-reflection termination processing. The support 2 is made of a flexible material, and integrally supports the reflection type optical fiber grating filter 1 with an adhesive or the like (not shown). The pedestal 3 holds and fixes the clamp 4 and the micrometer head 5 on one surface 3a. The clamp 4 grips one end of the support 2 in a fixed manner, and the micrometer head 5 applies a displacement to the other end of the support 2 in a plane parallel to the one surface 3a.

In the above configuration, when the other end of the support 2 is displaced and bent, an extension strain is applied to a portion of the reflection type optical fiber grating filter 1 outside the bend. Here, the length from the point (fixed point) of the support 2 fixed by the clamp 4 to the contact point with the micrometer head 5 is l, the elongation of the support 2 outside the bend by bending is Δl, Assuming that the thickness of the body 2 is d and the displacement given by the micrometer head 5 is z, the strain ε at a position x in the longitudinal direction on the support 2 starting from the fixed point
(x) is expressed as ε (x) = Δl / l ／ (d / 2) (3z / l ³ ) (l−x) (1)

The maximum value of the distortion is obtained at a fixed point and its magnitude is 3zd / 2l ² . That is, the magnitude of the strain can be changed by the displacement z. Also, the distortion decreases linearly with increasing x, and as can be seen from equation (1), x
= L takes the minimum value 0.

Here, if the reflection type optical fiber grating filter 1 is arranged outside the bend of the support 2, a similar extension strain distribution is given to the reflection type optical fiber grating filter 1. If the reflection type optical fiber grating filter 1 is arranged inside the bend of the support 2, the reflection type optical fiber grating filter 1 is given a compressive strain distribution.

At this time, the distortion ε given to the reflection type optical fiber grating filter 1 having the reflection light wavelength λ and the distortion ε
Is proportional to Δλ / λ = 0.78ε (2), a linear chirp is given to the reflection spectrum of the reflection type optical fiber grating filter 1. Can be

Therefore, the light reflected by the reflection type optical fiber grating filter 1 can be chirped. The size of the chirp can be changed by the displacement z.

[0010]

However, in the above-described conventional chirp variable reflection type optical fiber grating filter, since the expansion strain or the compression strain is uniformly applied over the entire length of the reflection type optical fiber grating filter, There has been a problem that the reflected light wavelength transitions to a longer wavelength side or a shorter wavelength side according to the given chirp.

An object of the present invention is to provide a chirp variable reflection type optical fiber grating filter having a simple structure in which the center wavelength of reflected light does not depend on a change in chirp.

[0012]

In order to achieve the above object, according to the first aspect of the present invention, a grating is formed by irradiating an ultraviolet ray to a core of an optical fiber, and a part of light incident from one end thereof is formed. Is reflected from the grating and emitted from the one end, and the rest is added to the reflection type optical fiber grating filter that emits the outside from the other end by applying a strain distribution to a chirp variable reflection type optical fiber grating filter capable of changing the chirp. A strain applying means for applying a strain distribution including linear expansion and linear compression in the longitudinal direction of the grating is provided.

According to the first aspect of the present invention, since a strain distribution including linear compression and linear compression can be given to the grating, the chirp can be changed without causing transition of the center wavelength of the reflected light. An optical fiber grating filter can be realized.

According to a third aspect of the present invention, a grating is formed by irradiating the core of the optical fiber with ultraviolet rays, and a part of light incident from one end thereof is reflected by the grating and emitted from the one end. By adding a strain distribution to a reflection type optical fiber grating filter that emits the rest to the outside from the other end, a chirp variable reflection type optical fiber grating filter capable of changing the chirp,
It is characterized by comprising a strain applying means for applying a strain distribution including a linear elongation and a linear compression in the longitudinal direction of the grating, and a strain control means for controlling a ratio between the elongation and the compression.

According to the third aspect of the present invention, a strain distribution including linear compression and linear compression can be given to the grating and the ratio thereof can be controlled, so that the chirp is variable and the center of the reflected light is variable. A reflection type optical fiber grating filter whose wavelength can be arbitrarily changed can be realized.

Here, specifically, as the strain applying means, specifically, a support made of a flexible material and integrally supporting a reflection type optical fiber grating filter according to claim 2 or 4 of the present invention. And a pair of clamps that respectively hold one end and the other end of the support, and a unit that moves one clamp while keeping it relatively parallel to the other clamp.

In this case, the support is given an S-shaped or inverted S-shaped bend. However, since the reflection type optical fiber grating filter is integrally supported by the support, the grating itself is provided. Is provided with this S-shaped or inverted S-shaped bend, whereby claim 1 or 2
According to the invention, the chirp can be controlled without causing the transition of the center wavelength of the reflected light.
According to the fourth aspect of the invention, the ratio between the expansion and the compression can be controlled by another strain control means, specifically, a means for rotating one clamp relative to the other clamp by an arbitrary angle. The center wavelength of light can be set arbitrarily.

Japanese Patent Laid-Open No. 9-5 describes a technique for giving an S-shaped bend to a reflection type optical fiber grating filter.
As described in Japanese Patent No. 4216, in this application, an S-shaped bend is given to a portion other than the grating to attenuate the light passing through the grating and further control the attenuation. Is completely different.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 2 shows a first embodiment of a chirp variable reflection type optical fiber grating filter according to the present invention.
In the drawings, the same components as those of the conventional example are denoted by the same reference numerals. That is, 1 is an optical fiber grating, 2 is a support, 3 is a pedestal, 4 and 6 are clamps, 5 is a micrometer head, and 7 is a stage.

The clamp 6 fixedly holds the other end of the support 2. The stage 7 is formed by combining two sliders 7a and 7b that can move in only one direction so that their moving directions are orthogonal to each other. A lower half member (hereinafter, referred to as a fixed portion) constituting the slider 7a is a pedestal. 3 face 3
The micrometer head 5 abuts on an upper half member (hereinafter, referred to as a moving portion), and the fixed portion of the slider 7b is fixed and held on the moving portion of the slider 7a. A clamp 6 is provided on the moving part of the slider 7b.
Are attached so as to be parallel to the clamp 4.

Here, the moving direction of the slider 7a is set in a direction orthogonal to the clamps 4 and 6, and when the micrometer head 5 displaces the slider 7a of the stage 7, the clamp 6 moves the slider 7b. The mirror 3 moves (displaces) without rotating in a plane parallel to the surface 3 a of the pedestal 3, thereby bending the reflective optical fiber grating filter 1 via the support 2.

How the strain distribution is applied to the reflection type optical fiber grating filter by this bending will be described with reference to FIG.

When the slider 7a of the stage 7 is pushed in,
The clamp 6 moves in the horizontal direction while keeping the clamp 6 parallel to the clamp 4. For this reason, the support 2 is made of S as shown in FIG.
It bends into a letter shape. At this time, if the reflection type optical fiber grating filter 1 is disposed on the side surface of the support 2 as shown in FIG. Is subjected to elongational strain, and compressive strain is applied to the portion inside the bend. That is, a strain distribution including linear compression and linear compression in the longitudinal direction is applied.

The magnitude of this distortion is given by: ε (x) = Δl / l ≒ (d / 2) (6z / l) where x is a longitudinal position from the fixing point of the support 2 by the clamp 4 as a starting point. ³ ) (l-2x) ... (3) Here, the sign of z is positive in the upward direction in the drawing.

In the formula (3), x = 1/2, that is, the support 2
Is zero at the center of, and the maximum and minimum values of the distortion are obtained at x = 0 and x = 1, respectively, and the magnitude is +6.
zd / a 2l ² and -6zd / 2l ^2. The strain distribution is linear with respect to x.

As described above, since the magnitude of the distortion is proportional to the transition of the reflected light wavelength, the reflection spectrum is shifted to the longer wavelength side and the shorter wavelength side with respect to the portion where the transition does not occur because the distortion is not applied. The transition is symmetrical, and the chirp can be changed without changing the center wavelength of the reflected light.

FIG. 4 is a graph showing a change in chirp according to the present embodiment. Here, the vertical axis indicates the delay amount, and the horizontal axis indicates the optical wavelength, and the slope of the graph becomes chirp.
Here, a strain distribution was applied to a reflective optical fiber grating filter having a length of 10 cm, a chirp of 791 ps / nm, and a reflection band of 1.04 nm, and the change in the amount of chirp was measured.

At this time, an iron rod having a diameter of 1.5 mm was used as a support, a hot-melt plastic was used as an adhesive for fixing the reflective optical fiber grating filter to the support, and a reflective optical fiber was connected with a heat-shrinkable tube. The fiber grating filter and the support were assembled. The distance 1 between the clamps 4 and 6 was 16.5 cm.

When a displacement of z = 5 mm is given to the clamp 6, the chirp inherent in the reflection type optical fiber grating filter is canceled, and z = 10 m
When a displacement of m was given, a linear chirp with a sign of +932 ps / nm inverted was obtained. FIG. 5 shows the change in the reflection spectrum at this time.
It is suppressed to 09 nm.

Next, in FIG. 4, when a displacement of z = 5 mm is given, a point where the measurement result around 600 to 800 ps disappears and measurement data such that a plurality of lines are drawn around 200 ps delay are obtained. The following describes the points that have been performed.

The above-described experimental system has a structure in which a chirp in the opposite direction is given to a reflection type optical fiber grating filter having a linear chirp. z
In the case of = 5 mm, both the linear chirp and the reverse chirp are essentially canceled out and there is no chirp.

Regarding the relationship between wavelength (frequency) and delay (Time Delay) of a chirpless fiber grating, see A. Carballar et al., J. of lightwave technol.
ogy, Vol.15, No.8, 1997, pp.1314-1322.

The center of this graph, frequency 1.9288-
It is U-shaped at 1.9293 × 10 ¹⁴ Hz. Left and right of the U-shaped, and the near i.e. ^{1.9287 × 10 14 Hz, 1.9294 ×} 10 14 Hz vicinity, the delay value drops is a feature of this graph.

Therefore, since the peak of the U-shape is steep, in the graph of FIG. 4 showing the measurement data of the first embodiment, the vicinity of a delay of 600 to 800 ps at z = 5 mm can be observed as a measurement point. And z =
A plurality of measurement lines near a delay of 200 ps at 5 mm reflect the sharp drop.

(Second Embodiment) FIG. 6 shows a second embodiment of a chirp variable reflection type optical fiber grating filter according to the present invention.
Here, an example is shown in which the angle between the clamps 4 and 6 can be arbitrarily set independently of the movement by the stage 7 in the first embodiment.

That is, in the drawing, reference numeral 8 denotes a rotary stage, which is composed of two members rotatable about a predetermined axis. One of the members (hereinafter, referred to as the axis) is orthogonal to the surface 3a of the pedestal 3. , Base portion) is a slider 7 of the stage 7.
b, and a clamp 6 is mounted on the other member (hereinafter, referred to as a rotating part). Also,
Reference numeral 9 denotes a micrometer head, which is fixed to the base of the rotary stage 8 and applies a rotational displacement to the rotary unit.

How the strain distribution is applied to the reflection type optical fiber grating filter at this time will be described with reference to FIG.

When a displacement z is given by moving the stage 7 and an angle i is given between the clamps 4 and 6 by rotating the stage 8, the strain distribution ε (x) in the longitudinal direction becomes ε (x) = Δl / l {(d / 2)} (6z / l ³ ) (l−2x) + (3x / l−1) (2i / l)} (4) Here, the sign of i is positive in the clockwise direction in FIG. 7 and negative in the counterclockwise direction.

From equation (4), it can be seen that a linear strain distribution is obtained with respect to x, and the position where the strain becomes 0 is given as a function of the angle i. If i is positive, the position where the distortion becomes 0 moves to the clamp 4 side from the center of the support 2, and if i is negative, it moves to the clamp 6 side. That is, by adjusting the angle i, it is possible to control the ratio between linear elongation and linear compression in the longitudinal direction. Thereby, the center wavelength of the chirp and the center wavelength of the reflected light can be respectively changed.

[0041]

As described above, according to the first aspect of the present invention,
According to the method, it is possible to provide the grating with a strain distribution including linear expansion and linear compression, and to realize a reflection type optical fiber grating filter whose chirp is variable without causing transition of the center wavelength of reflected light. In long-distance, large-capacity communication using optical fibers, a chirp tunable filter that does not cause a transition in the reflection wavelength has been desired for cases such as adjusting the dispersion characteristics of an optical communication line.
According to the present invention, an optical filter capable of easily controlling chirp can be realized.

Further, according to the third aspect of the present invention, it is possible to give a strain distribution including linear expansion and linear compression to the grating, further control the ratio thereof, to have a variable chirp and to obtain a reflected light. A reflection type optical fiber grating filter whose center wavelength is arbitrarily variable can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a conventional chirp variable reflection type optical fiber grating filter.

FIG. 2 is a configuration diagram illustrating a chirp variable reflection type optical fiber grating filter according to a first embodiment of the present invention;

FIG. 3 is a diagram showing how a strain distribution is applied in the first embodiment.

FIG. 4 is a graph showing a change in chirp in the first embodiment.

FIG. 5 is a graph showing a change in a reflection spectrum according to the first embodiment;

FIG. 6 is a configuration diagram showing a chirp variable reflection type optical fiber grating filter according to a second embodiment of the present invention;

FIG. 7 is a diagram showing how a strain distribution is applied in a second embodiment.

[Explanation of symbols]

1: reflection type optical fiber grating filter, 1a:
Grating 2: Support, 3: Pedestal, 4, 6: Clamp, 5, 9: Micrometer head, 7: Stage,
8: Rotary stage.

Claims (4)

[Claims] 1. A grating is formed by irradiating an ultraviolet ray to a core of an optical fiber, and a part of light incident from one end thereof is reflected by the grating and emitted from the one end,
By applying strain distribution to a reflection type optical fiber grating filter that emits the rest from the other end to the outside, a chirp variable chirp variable reflection type optical fiber grating filter that can change the chirp is linear with elongation in the longitudinal direction of the grating. A chirp variable reflection type optical fiber grating filter, comprising: strain applying means for applying a strain distribution including compression. 2. A strain applying means comprising a support made of a flexible material and integrally supporting a reflection type optical fiber grating filter, and a pair of clamps respectively holding one end and the other end of the support. 2. A chirp variable reflection type optical fiber grating filter according to claim 1, further comprising means for moving one of the clamps while keeping the other clamp relatively parallel to the other clamp. 3. A grating is formed by irradiating the core of the optical fiber with ultraviolet light, and a part of light incident from one end thereof is reflected by the grating and emitted from the one end,
By applying strain distribution to a reflection type optical fiber grating filter that emits the rest from the other end to the outside, a chirp variable chirp variable reflection type optical fiber grating filter that can change the chirp is linear with elongation in the longitudinal direction of the grating. A chirp tunable reflection type optical fiber grating filter comprising: strain applying means for applying a strain distribution including various compression; and strain controlling means for controlling a ratio between the elongation and the compression. 4. A strain applying means comprising a support made of a flexible material and integrally supporting a reflection type optical fiber grating filter, and a pair of clamps respectively holding one end and the other end of the support. Means for moving one clamp while keeping it relatively parallel to the other clamp, wherein the distortion control means is means for rotating one clamp by an arbitrary angle relative to the other clamp. 4. The chirp variable reflection type optical fiber grating filter according to claim 3, wherein the filter comprises: