JP2006078649A - Property variable fiber grating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a property variable fiber grating that is small in size, easy to manufacture, and capable of efficiently varying a dispersion quantity, and that also makes the dispersion quantity variable without causing the operating central wavelength to change by temperature. <P>SOLUTION: The property variable fiber grating is equipped with an optical fiber Bragg grating 1 and a fibrous member 2 arranged around the optical fiber Bragg grating 1. The fibrous member 2 has a negative coefficient of thermal expansion, shrinking by rise in temperature to actuate a compressive force in the longitudinal direction of the optical fiber Bragg grating 1, and possessing a shrinkage actuating quantity longitudinally different in the grating part 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a variable-characteristic fiber grating that can change a grating characteristic used as an external resonator, a dispersion compensator, or the like in optical communication.

  An optical fiber Bragg grating (FBG) is an optical element product having a characteristic of reflecting light of a specific wavelength by producing a portion having a periodic refractive index change in the length direction of the optical fiber. Conventionally, such an optical fiber Bragg grating has been used as an external resonator for stabilizing the wavelength of a laser diode light source, an optical multiplexer / demultiplexer (OADM), an optical switch, an optical filter, a dispersion compensator, etc. It is one of the indispensable optical elements.

  Such an optical fiber Bragg grating is manufactured by irradiating a quartz part of an optical fiber made of quartz doped with germanium (Ge) with ultraviolet rays to increase the refractive index of the irradiated part. That is, the optical fiber Bragg grating is manufactured by removing the coating resin of the optical fiber to expose the quartz portion, and irradiating ultraviolet light having a periodic intensity distribution from the side surface of the quartz portion.

  In the optical fiber Bragg grating manufactured as described above, the portion where the refractive index is changed is periodically formed in the longitudinal direction of the optical fiber. In such an optical fiber in which the portion where the refractive index is changed is periodically formed, the light having a specific wavelength of the incident light is reflected or the light having a specific wavelength of the incident light is emitted. The characteristic of radiating out of the fiber is obtained. Therefore, the optical fiber Bragg grating having such characteristics can be used as a wavelength selection filter or the like.

In addition, as an ultraviolet light source used for producing such an optical fiber Bragg grating, a wavelength of 260 nm or less such as a second harmonic of a krypton fluoride (KrF) excimer laser or an argon ion (Ar ²⁺ ) laser is used. Ultraviolet laser is used. In order to give this ultraviolet light a periodic intensity distribution, the ultraviolet light is transmitted through a quartz substrate called a phase mask in which periodic grooves are formed.

Here, the reflection wavelength λ _B in the optical fiber Bragg grating can be expressed as (Equation 1) below using the grating period Λ and the effective refractive index neff.

λ _B = 2neffΛ (1)
This optical fiber Bragg grating usually has a characteristic that the center reflection wavelength fluctuates to the long wave side due to temperature rise. This is because the optical fiber having positive linear expansion expands due to the temperature rise, and the period Λ in (Equation 1) increases, and as a result, the reflection wavelength λ _B increases. Furthermore, the change in effective refractive index due to temperature rise also affects the center wavelength characteristics. For example, when the optical fiber material is quartz, the temperature dependency of the refractive index is about 1 × 10 ⁻⁵ [1 / ° C.], and the reflection wavelength λ _B increases as the temperature rises. As a result of the action of these two characteristics, the temperature characteristic of the optical fiber grating is determined.

  Conventionally, a temperature-compensated fiber Bragg grating that compensates for variations in reflected wavelength due to temperature changes has been proposed. For example, as described in Patent Document 1 and Patent Document 2, a fiber Bragg grating in which a material having a negative expansion coefficient is arranged around an optical fiber Bragg grating has been proposed. In this fiber Bragg grating, the fluctuation of the reflected wavelength in the optical fiber Bragg grating is suppressed by balancing the expansion of the optical fiber due to the temperature rise and the shrinkage of the material disposed around the optical fiber Bragg grating due to the temperature rise. Temperature compensation can be achieved.

  Further, as described in Patent Document 3, a fiber Bragg grating is proposed in which a liquid crystal polymer (LCP) having negative expansion characteristics is arranged around an optical fiber Bragg grating. Yes. In this fiber Bragg grating, the expansion of the optical fiber due to the temperature rise is suppressed by the contraction of the liquid crystal polymer polymer, and temperature compensation is achieved.

  By the way, as one of the optical fiber Bragg gratings, there is a chirped fiber grating (CFG) in which the period of the portion where the refractive index is changed changes in the longitudinal direction of the optical fiber. Chirped fiber gratings are widely used for broadband filters and the like, and in particular, attention is focused on application to dispersion-compensating fiber gratings (DCFG) that compensate for chromatic dispersion accumulated in an optical fiber transmission line.

  FIG. 11 is a side view showing the operation principle of the dispersion compensating fiber grating.

  As shown in FIG. 11, the light that has entered the dispersion compensating fiber grating (DCFG) 102 via the circulator 101 is reflected by the grating unit 103. In the dispersion compensating fiber grating 102, since the period of the portion where the refractive index is changed in the grating portion 103 changes in the longitudinal direction of the optical fiber, the reflection position differs depending on the wavelength. Therefore, the reflected light from the dispersion compensating fiber grating 102 is emitted from the dispersion compensating fiber grating 102 through an optical path length that varies depending on the wavelength. When this reflected light is taken out by the circulator 101, a time difference occurs for each wavelength in the reflected light. Such a time difference due to wavelength is called chromatic dispersion, and is usually expressed in units of [ps / nm].

  A single mode fiber used for general optical communication has a wavelength dispersion of about 17 ps / nm per 1 km of optical fiber length at a wavelength of 1550 nm. When such chromatic dispersion increases, the shape of the optical pulse transmitted through the optical fiber deteriorates, and there is a possibility that information cannot be transmitted.

  Therefore, by using the dispersion compensating fiber grating 102 having a chromatic dispersion that is just opposite to the chromatic dispersion generated by the optical fiber in the transmission line, it becomes possible to compensate the chromatic dispersion accumulated in the transmission line, and the characteristics of the optical communication system. Can be greatly improved.

  By the way, the chromatic dispersion of the transmission line changes due to environmental changes such as temperature. For this reason, the amount of compensation required differs depending on the time zone and season such as daytime and nighttime. Therefore, conventionally, the dispersion compensating fiber grating has a problem that the chromatic dispersion cannot be completely compensated under all circumstances for the temperature change of the transmission line.

  In view of this, a dispersion compensating fiber grating having a variable structure in which the dispersion characteristics can be changed as necessary has been proposed. In order to change the dispersion characteristic in the dispersion compensating fiber grating, it is necessary to control the longitudinal dependence of the wavelength of the reflected light. As a configuration for controlling the dependence of the wavelength of reflected light on the longitudinal direction, so-called “heat distribution method” and “strain distribution method” have been proposed.

  In the “heat distribution method”, the reflection wavelength is changed by providing a heat distribution in the longitudinal direction of the grating portion. In this “heat distribution method”, it is required to generate an accurate temperature distribution along the longitudinal direction of the optical fiber. Depending on the point heat source, it is difficult to make the temperature distribution in a desired state, so it is necessary to use a distributed heat source. As this dispersion compensation fiber grating of the “heat distribution system”, a dispersion compensation fiber grating in which a gold thin film is deposited to adjust the temperature of the entire dispersion compensation fiber grating has been proposed.

On the other hand, in the “strain distribution method”, the reflection wavelength is changed by generating different strains along the longitudinal direction of the grating portion.
Japanese Patent Laid-Open No. 11-160554 JP 2000-32442 A International Publication No. 097/14983 Pamphlet

  As described above, the conventional fiber Bragg grating used as the dispersion compensating fiber grating has several problems to be solved as described below.

  That is, the chromatic dispersion caused by the transmission path varies depending on the type and length of the optical fiber used. Therefore, in order to perform complete compensation of chromatic dispersion, it is necessary to individually design a dispersion compensating fiber grating for each transmission line.

  Usually, the dispersion compensating fiber grating is manufactured using a phase mask, but in order to manufacture a dispersion compensating fiber grating having different specifications, a different phase mask is required. Since this phase mask is difficult and expensive to manufacture, the need to prepare a different phase mask for each dispersion-compensating fiber grating specification is one of the reasons for increasing the price of dispersion-compensating fiber gratings. there were.

  In addition, in the “thermal distribution type” dispersion compensating fiber grating in which the dispersion characteristics are changed as necessary, there is a problem that an apparatus for depositing a metal film is expensive and the manufacturing cost is high. Further, in this type of dispersion compensating fiber grating, it is necessary to accurately change the vapor deposition film thickness in the longitudinal direction of the grating portion, so that complicated control is required in the vapor deposition process, and it is difficult to manufacture. Furthermore, this type of dispersion compensating fiber grating has a complicated structure, such as the need to attach electrodes to the deposited metal film, and requires precise work in the manufacturing process. Therefore, this dispersion compensating fiber grating has a low yield in the manufacturing process, and as a result, becomes extremely expensive.

  In addition, in the “thermal distribution type” dispersion compensating fiber grating, the center wavelength of the dispersion compensating fiber grating itself is shifted to the long wavelength side by applying heat to the grating portion. That is, in this dispersion compensating fiber grating, it is difficult to change the dispersion characteristics in a state where the operating wavelength is fixed to a specific wavelength as required in “wavelength multiplexing communication”.

  In the “distortion distribution type” dispersion compensating fiber grating, it is difficult to continuously change the strain in the longitudinal direction, and it is difficult to obtain a large amount of dispersion change.

  The present invention has been made in view of the above, and as its purpose, it is small in size, easy to manufacture, can efficiently change the amount of dispersion, and preferably has an operation center wavelength. An object of the present invention is to provide a variable characteristic fiber grating in which the amount of dispersion can be varied without changing with temperature.

  According to the first aspect of the present invention, there is provided an optical fiber Bragg grating composed of an optical fiber in which a grating structure having a periodically changing refractive index is formed, and a fibrous member disposed around the optical fiber Bragg grating. The fibrous member has a negative linear expansion characteristic that contracts in the longitudinal direction of the fiber when the temperature rises and expands in the longitudinal direction of the fiber when the temperature decreases, and contracts the fiber when the temperature rises, and expands the fiber when the temperature decreases Thus, the optical fiber Bragg grating has a structure in which a compressive force or an extension force in the longitudinal direction of the optical fiber Bragg grating is applied, and the compression force or the extension force applied to the optical fiber by the expansion or contraction of the fiber member is The amount of action is in the grating part of this optical fiber Bragg grating. It is characterized in different for the longitudinal direction.

  According to a second aspect of the present invention, in the first aspect of the present invention, the number of fibers constituting the fibrous member is different in the longitudinal direction of the grating portion of the optical fiber Bragg grating.

According to a third aspect of the present invention, in the invention according to any one of the first to second aspects, the fiber constituting the fibrous member has a linear expansion coefficient in the fiber longitudinal direction of −6.0 × 10 ^−6. Thru | or -15.0 * 10 < ^-6 > [1 / degreeC], It is characterized by the above-mentioned.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the fibrous member is made of high molecular weight polyethylene.

  The present invention according to claim 5 is the invention according to any one of claims 1 to 3, wherein the fibrous member is a polyparaphenylene benzobisoxazole fiber. .

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the gaps between the fibers forming the fibrous member and between the fibers and the optical fiber Bragg grating are resin. It is characterized by being filled with a material.

  The present invention according to claim 7 is the invention according to claim 6, wherein the resin material is a material having a Young's modulus of 500 MPa or less in the operating temperature range.

  The present invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the change directions of the reflected wavelengths at both ends of the fiber Bragg grating are opposite to each other with respect to the temperature change within the operating temperature range. It is characterized by a direction.

  The present invention according to claim 9 is the invention according to any one of claims 1 to 8, further comprising a temperature adjusting mechanism for adjusting the temperature of the fiber Bragg grating.

  According to the first aspect of the present invention, the fibrous member contracts due to an increase in temperature, so that the compressive force in the longitudinal direction of the optical fiber Bragg grating acts on the optical fiber Bragg grating, and the optical fiber. Since the amount of contraction acting on the optical fiber in the longitudinal direction of the grating portion of the Bragg grating is different, the amount of dispersion can be changed efficiently. At the same time, the fibrous member expands due to a decrease in temperature, thereby exerting an extension force in the longitudinal direction of the optical fiber Bragg grating on the optical fiber Bragg grating, and in the longitudinal direction of the grating portion of the optical fiber Bragg grating. Since the amount of stretching action is different with respect to the optical fiber, the amount of dispersion can be changed efficiently. The variable characteristic fiber grating is easy to manufacture and can be manufactured at low cost.

  According to the second aspect of the present invention, since the number of fibers constituting the fibrous member differs in the longitudinal direction of the grating portion of the optical fiber Bragg grating, the amount of contraction and extension of the fibrous member with respect to the optical fiber is reduced. The longitudinal direction of the grating portion is different.

According to the third aspect of the present invention, the optical fiber member is quartz, and the linear expansion coefficient in the longitudinal direction of the fibrous member is −6.0 × 10 ^{−6 to} −15.0 × 10 ⁻⁶ [1 / [C], it is possible to exert a sufficiently large compression / contraction action in the longitudinal direction of the optical fiber, so that the amount of dispersion can be changed efficiently.

  According to the fourth aspect of the present invention, since the fibrous member is made of high molecular weight polyethylene, the amount of dispersion can be changed efficiently.

  According to the present invention described in claim 5, since the fibrous member is a polyparaphenylene benzobisoxazole fiber, the amount of dispersion can be changed efficiently.

  According to the sixth aspect of the present invention, since the gaps between the fibers forming the fibrous member and between the fibers and the optical fiber Bragg grating are filled with the resin material, the fibrous member is the optical fiber Bragg grating. On the other hand, it is possible to reliably apply a compressive force or an extension force, and to change the amount of dispersion efficiently.

  According to the seventh aspect of the present invention, since the resin material is a material having a Young's modulus of 500 MPa or less in the operating temperature range, the distortion of the resin material does not cause stress in the optical fiber, and the optical fiber Bragg grating This will not cause deterioration of the characteristics.

  According to the eighth aspect of the present invention, the change in the reflected wavelength at both ends of the fiber Bragg grating is opposite to the change in temperature within the operating temperature range, so that the change in the operating center wavelength due to the temperature is suppressed. The amount of dispersion can be varied.

  According to the ninth aspect of the present invention, since the temperature adjusting mechanism for adjusting the temperature of the fiber Bragg grating is provided, the amount of dispersion can be changed efficiently.

  That is, the present invention is small in size, easy to manufacture, can efficiently change the amount of dispersion, and can further vary the amount of dispersion while suppressing changes in the operating center wavelength due to temperature. A variable fiber grating can be provided.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  The present invention provides a variable characteristic fiber that can be used as a dispersion compensating fiber grating (DCFG) having a variable dispersion amount by disposing a fibrous member having a negative thermal expansion coefficient in the longitudinal direction around an optical fiber having a grating structure. It constitutes a grating.

  FIG. 1 is a longitudinal sectional view and a transverse sectional view showing a configuration of a variable characteristic fiber grating according to the present invention.

  As shown in FIG. 1, this variable-characteristic fiber grating is a fibrous member having negative thermal expansion characteristics around an optical fiber manufactured as an optical fiber Bragg grating (FBG) 1 which is a chirped fiber grating (CFG). 2 is arranged. As described above, the chirped fiber grating is an optical fiber Bragg grating in which the period of the portion where the refractive index has changed is changed in the longitudinal direction of the optical fiber.

  The optical fiber Bragg grating 1 irradiates a quartz portion of an optical fiber made of quartz to which germanium (Ge) is added with ultraviolet light having a periodic intensity distribution, so that a predetermined position periodically in the longitudinal direction of the optical fiber is obtained. Is produced by increasing the refractive index. That is, the optical fiber Bragg grating 1 is manufactured by irradiating ultraviolet light having a periodic intensity distribution from the side surface of the quartz portion in a state where the coating resin of the optical fiber is removed and the quartz portion is exposed. Has been. The optical fiber Bragg grating 1 has characteristics of reflecting light having a specific wavelength of incident light or emitting light having a specific wavelength of incident light to the outside of the optical fiber.

  The fibrous member 2 has a negative thermal expansion characteristic that contracts in the longitudinal direction of the fiber forming the fibrous member 2 due to a temperature rise. As shown in FIG. 1, the fibrous member 2 is disposed at least around the grating portion 3 where the refractive index is increased in the optical fiber Bragg grating 1.

  Here, the operation principle of the dispersion compensating fiber grating (DCFG) is shown below.

The optical fiber Bragg grating usually has a characteristic that the reflection center wavelength fluctuates to the long wave side due to a temperature rise. This is because the optical fiber having a positive thermal expansion coefficient expands due to the temperature rise, and the effect of increasing the period Λ in the above-described (Equation 1) (λ _B = 2neffΛ) and the effective refractive index neff increase due to the temperature rise. As a result, the reflection wavelength λ _B increases. Even in a chirped fiber grating in which the grating period gradually changes in the longitudinal direction of the optical fiber, the reflection center wavelength shifts due to temperature rise.

  FIG. 2 is a graph showing how the reflection center wavelength changes due to temperature rise in the chirped fiber grating.

  In FIG. 2, the solid line shows the characteristics before the temperature rise, the dotted line shows the characteristics after the temperature rise, (a) shows the reflection characteristics, and (b) shows the group delay time characteristics in the reflection band.

  When the chirped fiber grating is used as a dispersion compensator, the wavelength dependence of the group delay time shown in (b) of FIG. 2 is used. That is, the slope of the characteristic shown in (b) in FIG. 2 is the chromatic dispersion amount that can be compensated by the dispersion compensator. As can be seen from FIG. 2, in the normal chirped fiber grating, the entire reflection center wavelength is shifted to the long wavelength side due to the temperature rise. As a result, the dispersion amount does not change, and the variable dispersion compensator is obtained. It is not possible.

  FIG. 3 is a graph showing the change of the reflection center wavelength when the temperature dependence of the change of the reflection center wavelength in the chirped fiber grating changes in the longitudinal direction.

  On the other hand, when the temperature dependence of the fluctuation of the reflection center wavelength in the chirped fiber grating changes in the longitudinal direction of the chirped fiber grating, as shown in (a) and (c) of FIG. As shown in FIGS. 3 (b) and 3 (d), the wavelength dependence of the group delay time (inclination of the graph), that is, the chromatic dispersion changes. It can be used as a dispersion compensator.

(C) and (d) show the case where the short wave side of the CFG reflection wavelength varies in the opposite direction to the short wave side and the long wave side varies in the opposite direction to the long wave side.

  3A and 3B show a case where both the short wavelength side and the long wavelength side of the reflected wavelength in the chirped fiber grating change to the long wavelength side due to temperature rise, but the amount of change is different. . (C) and (d) in FIG. 3 show the case where the short wavelength side of the reflected wavelength in the chirped fiber grating changes to the short wavelength side due to temperature rise, and the long wavelength side changes to the long wavelength side due to temperature rise. Yes. In any of these cases, the amount of dispersion changes due to temperature changes. However, when the short wavelength side of the reflected wavelength is changed to the short wavelength side due to the temperature rise and the long wavelength side is changed to the long wavelength side due to the temperature rise, the fluctuation of the reflection center wavelength due to the temperature change can be suppressed. It is more preferable than the case where both the short wavelength side and the long wavelength side change to the long wavelength side due to temperature rise.

  In consideration of the characteristics required when operating such a chirped fiber grating as a dispersion compensator with variable dispersion, a dispersion compensator with variable dispersion comprising a fibrous member having a negative thermal expansion coefficient will be described below. .

As described above, the reflection center wavelength λ _B of the grating portion changes to the longer wavelength side due to the temperature rise. In order to change the temperature dependence of the fluctuation of the reflection center wavelength in the optical fiber Bragg grating, the linear expansion coefficient of the optical fiber may be changed along the longitudinal direction of the optical fiber.

  In the variable characteristic fiber grating according to the present invention, as shown in FIG. 1, the expansion and the expansion of the fibrous member 2 having a negative thermal expansion coefficient in the longitudinal direction disposed around the optical fiber Bragg grating 1 having a grating structure. According to the contraction, the optical fiber Bragg grating 1 is expanded and contracted.

  In this variable characteristic fiber grating, the contraction of the fibrous member 2 due to a temperature rise acts as a compressive stress on the optical fiber Bragg grating 1 and suppresses the thermal expansion of the optical fiber Bragg grating 1 having a positive thermal expansion coefficient. In this way, by suppressing the thermal expansion of the optical fiber Bragg grating 1, the temperature characteristics of the optical fiber Bragg grating 1 can be changed.

  In this variable characteristic fiber grating, the expansion and contraction rate of the optical fiber Bragg grating 1 changes along the longitudinal direction of the grating portion 3. This is due to the fact that the compressive stress applied to the optical fiber Bragg grating 1 by the fibrous member 2 changes along the longitudinal direction of the grating portion 3, and this characteristic variable fiber grating is used as a variable dispersion compensator. be able to.

  Here, as shown in FIG. 1, a fibrous member 2 having a negative thermal expansion coefficient is disposed around the optical fiber Bragg grating 1, and all the compressive stress due to the contraction of the fibrous member 2 is the optical fiber Bragg grating 1. It is assumed that the structure is transmitted to When the cross-sectional area of the optical fiber Bragg grating 1 is defined as Sf, the Young's modulus is defined as Ef, the total of the cross-sectional areas of the fibers forming the fibrous member 2 is defined as Sn, and the Young's modulus is defined as En, Is established.

SfEfuf + SnEun = 0 (Equation 2)
In (Equation 2), uf and un are displacement amounts from the equilibrium point of the optical fiber Bragg grating 1 and the fibrous member 2, respectively. That is, by designing the displacement amount uf of the optical fiber Bragg grating 1 to change along the longitudinal direction of the optical fiber Bragg grating 1 in the grating portion 3, a dispersion compensation fiber grating with a variable dispersion amount is configured. . Here, since it is difficult to change the Young's moduli Ef and En of the material along the longitudinal direction of the optical fiber Bragg grating 1, the cross-sectional area Sf of the optical fiber Bragg grating 1 or the total Sn of the fiber cross-sectional areas Sn. By changing the length along the longitudinal direction of the optical fiber Bragg grating 1, desired characteristics can be realized.

Further, as shown in (c) and (d) in FIG. 3, since the short wavelength side of the reflected wavelength fluctuates to the short wavelength side due to the temperature rise, the negative thermal expansion coefficient necessary for the fibrous member 2 is Depending on the material of the optical fiber Bragg grating 1 to be used, when using a silica-based optical fiber widely used for communication, −6.0 to −15.0 × 10 ⁻⁶ [1 / ° C] grade. That is, the thermal expansion coefficient of the fibrous member 2 is desirably in the range of −6.0 to −15.0 × 10 ⁻⁶ [1 / ° C].

  In this variable characteristic fiber grating, since the fibrous member 2 is arranged directly around the optical fiber Bragg grating 1 and the contraction of the fibrous member 2 is utilized, the outer diameter including the fibrous member 2 is 1 mm or less, and downsizing is possible.

  FIG. 4 is a longitudinal sectional view and a transverse sectional view showing a configuration in which the number of fibers constituting the fibrous member 2 is changed along the longitudinal direction of the grating portion 3.

  As shown in FIG. 4, the variable-characteristic fiber grating according to the present invention has a number of fibers (total sum of cross-sectional areas) constituting the fibrous member 2 having a negative thermal expansion coefficient arranged around the optical fiber Bragg grating 1. It is desirable to change along the longitudinal direction of the grating part 3.

  In this variable characteristic fiber grating, the cross-sectional area of the fibrous member 2 around the grating portion 3 can be easily changed along the longitudinal direction of the optical fiber Bragg grating 1, and the amount of dispersion can be varied by changing the temperature. The dispersion compensating fiber grating can be easily manufactured.

  That is, if the fibrous member 2 is cut into a conical shape so as to have desired characteristics, it is arranged around the optical fiber Bragg grating 1 as being composed of hundreds to thousands of fibers. The total cross-sectional area of the fibers can be continuously changed along the longitudinal direction of the optical fiber Bragg grating 1.

  Such cutting of the fibrous member 2 is easier than continuously changing the cross-sectional area of the optical fiber Bragg grating 1 and can be performed with good reproducibility, thus reducing the manufacturing cost. In addition, the characteristics can be stabilized and the defect rate can be reduced.

And as a material which makes the fibrous member 2, ultra high molecular weight polyethylene with a crystallinity degree of 85% or more is preferable. This ultra high molecular weight polyethylene has a large negative thermal expansion coefficient among the fibrous members having negative thermal expansion characteristics. High molecular weight polyethylene can increase the negative expansion characteristic by increasing the crystallinity, and by increasing the crystallinity of the high molecular weight polyethylene to 85% or more, the expansion coefficient in the fiber direction is about −10 × 10 ⁻⁶ [1 / ° C] and a particularly large negative expansion characteristic. Thus, the high molecular weight polyethylene has sufficient characteristics to perform temperature compensation for the optical fiber Bragg grating 1 made of a silica-based optical fiber.

  When the fibrous member 2 is made of such a high molecular weight polyethylene, since the negative thermal expansion coefficient is large, it becomes possible to perform sufficient temperature compensation with a small amount of fiber, and the characteristics including the fibrous member 2 can be varied. The outer diameter of the fiber grating can be 1 mm or less. Further, since the high molecular weight polyethylene is excellent in impact resistance, light resistance, and chemical resistance, the fibrous member 2 can also play a role of protecting the optical fiber Bragg grating 1, and is suitable for optical element use. A variable fiber grating can be constructed.

  Here, as the high molecular weight polyethylene, for example, “Dyneema” (trade name) manufactured by Toyobo Co., Ltd. can be used.

Furthermore, it is desirable to use polyparaphenylene benzobisoxazole fiber as the material forming the fibrous member 2. This polyparaphenylene benzobisoxazole fiber also has a large negative thermal expansion coefficient of about −6.0 × 10 ⁻⁶ [1 / ° C], and has characteristics sufficient for temperature compensation of the optical fiber Bragg grating 1. have.

  Since this polyparaphenylene benzobisoxazole fiber has a decomposition temperature as high as about 650 ° C., it is particularly suitable for use in a variable characteristic fiber grating used under high temperature.

  As the polyparaphenylene benzobisoxazole fiber, “Zylon” (trade name) manufactured by Toyobo Co., Ltd. can be used.

  FIG. 5 is a longitudinal sectional view showing a variable property fiber grating according to the present invention, in which the fibers constituting the fibrous member 2 and the gap between these fibers and the optical fiber Bragg grating 1 are filled with the resin material 5. FIG.

  In this variable characteristic fiber grating, as shown in FIGS. 5A and 5B, the fibers 4 constituting the fibrous member 2 having negative thermal expansion characteristics and the fibers 4 and the optical fiber Bragg grating are provided. 1 is filled with the resin material 5.

  In this way, by filling the gaps between the fibers 4 and between the fibers 4 and the optical fiber Bragg grating 1 with the resin material 5, the contraction of the fibrous member 2 when the temperature rises is applied to the optical fiber Bragg grating 1. On the other hand, it can be reliably transmitted as a compressive stress.

  That is, in the case where there is no filling with the resin material 5, when the fibrous member 2 contracts due to a temperature rise, the static frictional force between the fibrous member 2 and the optical fiber Bragg grating 1 causes a force against the optical fiber Bragg grating 1. Stress is generated. Here, when the static frictional force between the fibrous member 2 and the optical fiber Bragg grating 1 is not sufficient, even if the fibrous member 2 contracts, between the fibrous member 2 and the optical fiber Bragg grating 1. In some cases, slippage occurs at the interface, and sufficient compressive stress on the optical fiber Bragg grating 1 cannot be obtained. When the gaps between the fibers 4 and between the fibers 4 and the optical fiber Bragg grating 1 are filled with the resin material 5, between the resin material 5 and the fibers 4 and between the resin material 5 and the optical fiber Bragg grating 1. Thus, the compressive stress is reliably transmitted to the optical fiber Bragg grating 1.

  Therefore, by selecting a material having high adhesion between the fiber 4 and the optical fiber Bragg grating 1 as the resin material 5, the fibrous member 2 and the optical fiber Bragg grating are contracted or expanded by the contraction or expansion of the fibrous member 2. It is possible to reliably generate a compressive stress or an extension stress on the optical fiber Bragg grating 1 without causing slippage between the optical fibers.

  5A shows a case where the resin material 5 is used only in a region where the number of fibers constituting the fibrous member 2 continuously changes, and FIG. 5B shows the fibrous member 2. The case where the resin material 5 is uniformly arranged around the optical fiber Bragg grating 1 is shown regardless of the amount of the fibers forming. In either case, since the stress generated in the optical fiber Bragg grating 1 at the time of temperature change continuously changes, it can be used as a dispersion compensating fiber grating with a variable dispersion amount.

  As this resin material 5, most resin materials, such as a thermosetting resin material, an ultraviolet curable resin material, and a humidity curable resin material, can be used. As the resin material 5, a material having a small curing shrinkage rate is desirable because it does not cause excessive stress to the optical fiber Bragg grating 1 during curing. The curing shrinkage rate of the resin material 5 is preferably 5% or less, for example.

  And as this resin material 5, the material whose Young's modulus in the use temperature range (for example, -20 degreeC thru | or 80 degreeC) in the ground, the seabed, the air etc. is 500 Mpa or less is desirable. When the Young's modulus of the resin material 5 is 500 MPa or less, the strain stress caused by the shrinkage of the fibrous member 2 and the expansion of the resin material 5 when the temperature rises can be reduced, and the characteristics of the optical fiber Bragg grating 1 can be reduced. It can be stabilized.

  That is, in this characteristic variable fiber grating, when the optical fiber Bragg grating 1, the fibrous member 2 and the resin material 5 are displaced due to temperature changes and stress is generated, the cross-sectional area of the optical fiber Bragg grating 1 is Sf, Young When the rate is defined as Ef, the total cross-sectional area of the fibers constituting the fibrous member 2 is defined as Sn, the Young's modulus is defined as En, the total cross-sectional area of the resin material 5 is defined as Sr, and the Young's modulus is defined as Er. Equation 3) holds.

SfEfuf + SnEun + SrErur = 0 (Equation 3)
In (Expression 3), uf, un, and ur are displacement amounts from the equilibrium point of the optical fiber Bragg grating 1, the fibrous member 2, and the resin material 5, respectively. That is, the temperature compensation structure is realized by designing Sf, Ef, Sn, En, Sr, Er so that the displacement amount uf of the optical fiber Bragg grating 1 cancels the displacement due to the thermal expansion of the optical fiber Bragg grating 1. Is done.

Here, the structural parameters Sf and Ef of the optical fiber Bragg grating 1 are uniquely determined by the optical fiber to be used. For example, when an optical fiber made of quartz glass having a diameter of 125 μm is used, Sf = 1.23 × 10 ⁻² [mm ² ] and Ef = 73 [GPa].

  The constants Sn and En for the fibrous member 2 can also be accurately determined by the material of the fibrous member 2 to be used and the number of fibers disposed around the optical fiber Bragg grating 1. For example, the Young's modulus of “Dyneema” (trade name) is about En≈100 [GPa] depending on the grade, and the area Sn is also unique by determining the number of fibers, for example, 2000. Therefore, there is almost no manufacturing variation.

  On the other hand, since the cross-sectional area Sr of the resin material 5 changes depending on the amount of the resin material filled around the optical fiber Bragg grating 1, it is difficult to accurately control in the manufacturing process. For this reason, it is necessary to minimize the influence of the variation in the cross-sectional area Sr of the resin material 5 in the manufacturing process on the temperature compensation characteristics. Here, from (Equation 3), since the cross-sectional area Sr and Young's modulus Er of the resin material 5 are multiplied by each other, in order to reduce the influence of the variation of the cross-sectional area Sr on the displacement amount ur, the resin material The Young's modulus Er of 5 may be reduced.

  That is, by using a material having a Young's modulus Er as small as possible as the resin material 5, variations in the manufacturing process can be suppressed. The level of the Young's modulus Er at which the influence on the temperature compensation characteristic due to the variation in the cross-sectional area Sr of the resin material 5 becomes almost negligible is at most 1% of the Young's modulus of the fibrous member 2 and the optical fiber Bragg grating 1. It is desirable to keep it.

  Here, since the Young's modulus of quartz glass which is the main material of the optical fiber is 73 [GPa], 1% thereof is 730 [MPa]. Accordingly, the resin material 5 is a material having a Young's modulus of about 500 [MPa] or less in a normally used temperature range (for example, −20 ° C. to 80 ° C.) (for example, 500 [MPa at −20 ° C.). Stable characteristics can be obtained by using 10 [MPa] at 80 ° C.

  Furthermore, by using a material having a Young's modulus of 500 [MPa] or less as the resin material 5, it is possible to reduce the influence of strain upon curing of the resin material on the optical fiber Bragg grating 1. In this case, since the buffer layer required in the conventional variable characteristic fiber grating using liquid crystal polymer is not required, it is possible to construct a variable characteristic fiber grating that has a simple structure and can be manufactured at low cost. it can.

  Further, by setting the Young's modulus of the resin material 5 to 500 [MPa] or less, the optical fiber Bragg grating 1 is bent after the resin material 5 is disposed around the fibrous member 2 and the optical fiber Bragg grating 1. This is advantageous when it is incorporated into a module, and the module can be downsized. That is, since the resin material 5 is made of a soft material, even if the entire characteristic variable fiber grating is bent, a large stress is not applied to the optical fiber Bragg grating 1, and the characteristic is not deteriorated.

  In the variable characteristic fiber grating according to the present invention, when the temperature changes within the operating temperature range, the reflected wavelength changing directions at both ends of the optical fiber Bragg grating 1 are opposite to each other. desirable.

  When the direction of change in the reflected wavelength at both ends of the optical fiber Bragg grating 1 is opposite to each other, when the temperature change is applied to the variable characteristic fiber grating and the amount of dispersion is changed, (c) in FIG. As shown in (d), the behavior is such that the short wavelength side of the reflected wavelength changes to the short wavelength side due to the temperature rise, and the long wavelength side changes to the long wavelength side due to the temperature rise, thereby suppressing the fluctuation of the reflection center wavelength. It becomes possible.

  In addition, by suppressing fluctuations in the reflection center wavelength, it is possible to suppress the influence on the adjacent communication wavelength when used in a wavelength division multiplexing communication system, etc., and to realize desirable characteristics as a dispersion compensation fiber grating with variable dispersion amount Can do.

In order to realize such characteristics, the fibrous member 2 needs to have a large negative thermal expansion coefficient. For example, when quartz is used as the optical fiber, the fibrous member 2 is in the longitudinal direction. It must have a negative thermal expansion coefficient of about −8.0 × 10 ⁻⁶ [1 / ° C]. Examples of such a fibrous member 2 include high molecular weight polyethylene (for example, “Dyneema” (trade name) manufactured by Toyobo Co., Ltd.) as described above.

[Example 1]
In Example 1, a change in the temperature dependence of the reflection center wavelength of the optical fiber Bragg grating 1 when the number of fibers constituting the fibrous member 2 arranged around the grating portion 3 was changed was confirmed.

  As the optical fiber Bragg grating 1, a quartz optical fiber having a diameter of 125 μm, which is widely used in general optical communications, in which the grating portion 3 is produced by the phase mask method is used.

  Further, as the fibrous member 2 having a negative thermal expansion coefficient in the longitudinal direction, polyethylene (“Dyneema” (trade name) manufactured by Toyobo Co., Ltd.) was used. The polyethylene fiber used is 1.2 dtex per filament.

  After disposing the fibrous member 2 around the optical fiber Bragg grating 1, an ultraviolet curable resin is infiltrated into the fibrous member 2 as the resin material 5, and between the fibers forming the fibrous member 2 and between these fibers and the optical fiber. The space between the Bragg grating 1 was filled with an ultraviolet curable resin, and the ultraviolet curable resin was further cured by irradiation with ultraviolet rays. The ultraviolet curable resin used had a Young's modulus at room temperature of 50 [MPa].

  Thereafter, the temperature of the optical fiber Bragg grating 1 was changed from 0 ° C. to 60 ° C., and the wavelength variation per 1 ° C. was obtained by linearly approximating the fluctuation characteristics of the center reflection wavelength.

  FIG. 6 is a graph showing changes in temperature characteristics with the horizontal axis as the number of fibers in Example 1.

  As shown in FIG. 6, the temperature characteristics of the optical fiber Bragg grating 1 changed as the number of fibers constituting the fibrous member 2 increased, and it was found that the temperature characteristic can be made almost independent of about 2000, that is, 2400 dtex. . That is, it has been confirmed that the temperature dependence of the optical fiber Bragg grating 1 can be changed in the longitudinal direction by utilizing such a change in temperature characteristics.

[Example 2]
In Example 2, a chirped fiber grating having a length of 90 mm and a chirp rate of 0.07 nm / cm was prepared using a phase mask method, and a fiber-like fiber having a negative thermal expansion coefficient around the chirped fiber grating. The member 2 was arranged by continuously changing the number of constituent fibers as shown in FIG.

  As the fibrous member 2, polyethylene (“Dyneema” (trade name) manufactured by Toyobo Co., Ltd.) was used.

  On one end side of the grating part 3, the number of fibers was 2300, that is, 2760 dtex, and gradually decreased toward the other end side so that the number finally became zero. In this example, the side with 2300 fibers was defined as the short wavelength side of the chirp period. The change in the number of fibers was designed based on the result of Example 1 so that the temperature characteristic change was linear in the longitudinal direction of the fiber Bragg grating 1.

  Then, an ultraviolet curable resin is infiltrated into the fibrous member 2 as the resin material 5, and the gaps between the fibers forming the fibrous member 2 and between the fibers and the optical fiber Bragg grating 1 are filled with the ultraviolet curable resin. Further, the ultraviolet curable resin was cured by irradiating ultraviolet rays. The ultraviolet curable resin used had a Young's modulus at room temperature of 50 [MPa].

  Thereafter, the temperature of the optical fiber Bragg grating 1 was changed from 0 ° C. to 60 ° C., and the reflection intensity spectrum and group delay characteristics in the grating portion 3 were measured.

  FIG. 7 is a graph showing changes in the reflection intensity spectrum and the group delay characteristic with the horizontal axis as the reflection wavelength in Example 2.

  As can be seen from the reflection spectrum shown in (a) in FIG. 7 and the group delay characteristic shown in (b) in FIG. 7, on the short wavelength side where the number of fibers around the grating portion 3 is 2300, the temperature is Although there is almost no wavelength fluctuation even if it changes, on the long wavelength side where the number of fibers is 0, the wavelength changes to the long wave side due to temperature rise, and as a result, the slope of the reflection band and the group delay time, that is, The chromatic dispersion is changing.

  According to this example, it was confirmed that the chromatic dispersion changes in the range of 600 nm / ps to 1000 nm / ps, and a change amount of 400 nm / ps is obtained, and a practically sufficient variable range of chromatic dispersion is obtained.

  In this embodiment, since there is almost no change in the reflection wavelength on the short wavelength side, the change in the reflection center wavelength is suppressed to a small value. For example, in this embodiment, it is possible to use in the entire temperature range by setting the use wavelength to 1550.4 nm.

  Here, the grounds for setting the used wavelength to 1550.4 nm are as follows. That is, as shown in FIGS. 7A and 7B, when the temperature is changed from 0 ° C. to 60 ° C., the band of the optical fiber Bragg grating 1 is changed to 0 ° In C, the band becomes the narrowest. Here, if the wavelength used is 1551 nm, it falls within the band of the optical fiber Bragg grating 1 at 60 ° C. and 30 ° C., but becomes out of band at 0 ° C. When light having a wavelength of 1550.4 nm is incident on the optical fiber Bragg grating 1, all light falls within the band of the optical fiber Bragg grating 1 in the temperature range of 0 ° C to 60 ° C. Therefore, in this embodiment, it is desirable to set the operating wavelength to 1550.4 nm. However, if the characteristics of the optical fiber Bragg grating 1 are different, the wavelength used is also different.

Example 3
In Example 3, a chirped fiber grating having a length of 90 mm and a chirp rate of 0.07 nm / cm was prepared by using a phase mask method, and a fibrous fiber having a negative thermal expansion coefficient around the chirped fiber grating. The member 2 was arranged by continuously changing the number of constituent fibers as shown in FIG.

  As the fibrous member 2, polyethylene (“Dyneema” (trade name) manufactured by Toyobo Co., Ltd.) was used.

  On one end side of the grating part 3, the number of fibers was 2300, that is, 2760 dtex, and gradually decreased toward the other end side so that the number finally became zero. In this example, the side with 2300 fibers was defined as the long wavelength side of the chirp period. The change in the number of fibers was designed based on the result of Example 1 so that the temperature characteristic change was linear in the longitudinal direction of the fiber Bragg grating 1.

  Then, an ultraviolet curable resin is infiltrated into the fibrous member 2 as the resin material 5, and the gaps between the fibers forming the fibrous member 2 and between the fibers and the optical fiber Bragg grating 1 are filled with the ultraviolet curable resin. Further, the ultraviolet curable resin was cured by irradiating ultraviolet rays. The Young's modulus at room temperature of the used ultraviolet curable resin was 800 [MPa].

  Thereafter, the temperature of the optical fiber Bragg grating 1 was changed from 0 ° C. to 60 ° C., and the reflection intensity spectrum and group delay characteristics in the grating portion 3 were measured.

  FIG. 8 is a graph showing changes in reflection intensity spectrum and group delay characteristics with the horizontal axis as the reflection wavelength in Example 3.

  As can be seen from the reflection spectrum shown in FIG. 8 (a) and the group delay characteristic shown in FIG. 8 (b), on the long wavelength side where the number of fibers around the grating portion 3 is 2300, the temperature is Although there is almost no wavelength fluctuation even if it changes, on the short wavelength side where the number of fibers is zero, the wavelength changes to the long wave side due to temperature rise, and as a result, the slope of the reflection band and group delay time, that is, The chromatic dispersion is changing.

  In this embodiment, the disturbance of the reflection spectrum is larger than that in the second embodiment. This is because the used ultraviolet curable resin has a Young's modulus of 800 [MPa], and the distortion generated in the ultraviolet curable resin when the ultraviolet curable resin is cured and when the temperature changes is applied to the optical fiber Bragg grating 1. This is thought to be due to the stress.

  According to this example, it was confirmed that a sufficient amount of change in chromatic dispersion was obtained, and a practically sufficient variable range of chromatic dispersion was obtained. However, since the distortion increases when the Young's modulus of the ultraviolet curable resin is high, it has been confirmed that the Young's modulus of the ultraviolet curable resin should be 800 [MPa] or less, preferably 500 [MPa] or less.

[Configuration with temperature adjustment mechanism]
The variable characteristic fiber grating according to the present invention may be used in combination with a temperature adjustment mechanism for adjusting the temperature.

  When used in combination with the temperature adjustment mechanism, the dispersion amount in the dispersion compensation fiber grating with variable dispersion amount can be changed to a desired value and can be fixed at the desired value.

  The temperature adjustment mechanism has a function of measuring the temperature of the dispersion compensating fiber grating with a variable dispersion amount, and has a function of giving feedback so as to reduce the difference between the measured temperature and the set temperature, or an optimum dispersion amount. It has a function to measure the deviation from the above, and a function to apply feedback so as to reduce the deviation.

  FIG. 9 is a side view showing a first configuration of the variable characteristic fiber grating combined with the temperature adjusting mechanism.

  In this embodiment, the signal light in which the chromatic dispersion is accumulated in the transmission path is incident on the optical fiber Bragg grating 1 which becomes a dispersion compensating fiber grating installed in the temperature adjusting unit 7 through the circulator 6. The light reflected by the optical fiber Bragg grating 1 is separated by the circulator 6, received by the light receiving unit 8, and converted into an electrical signal.

  The output from the light receiving unit 8 is sent to the dispersion amount analyzing unit 9, and the residual dispersion amount is analyzed. The dispersion amount analysis unit 9 sends a signal to the temperature control unit 10 based on the analyzed value of the residual dispersion amount. The temperature control unit 10 adjusts the dispersion amount by changing the temperature of the optical fiber Bragg grating 1 by the temperature adjustment unit 7 so that the residual dispersion amount becomes small.

  In this embodiment, the light receiving unit 8 and the dispersion amount analyzing unit 9 also function as an optical signal receiving unit.

  FIG. 10 is a side view showing a second configuration of the variable characteristic fiber grating combined with the temperature adjustment mechanism.

  In this embodiment, the signal light in which the chromatic dispersion is accumulated in the transmission path is incident on the optical fiber Bragg grating 1 which becomes a dispersion compensating fiber grating installed in the temperature adjusting unit 7 through the circulator 6. The light reflected by the optical fiber Bragg grating 1 is separated by the circulator 6, further branched by the optical coupler 11, received by the light receiving unit 8, and converted into an electric signal.

  The output from the light receiving unit 8 is sent to the dispersion amount analyzing unit 9, and the residual dispersion amount is analyzed. The dispersion amount analysis unit 9 sends a signal to the temperature control unit 10 based on the analyzed value of the residual dispersion amount. The temperature control unit 10 adjusts the dispersion amount by changing the temperature of the optical fiber Bragg grating 1 by the temperature adjustment unit 7 so that the residual dispersion amount becomes small.

  In this embodiment, the light receiving unit 8 and the dispersion amount analyzing unit 9 do not function as an optical signal receiving unit, and the optical signal receiving unit (not shown) receives an optical component that is not branched by the optical coupler 11. Then, an optical signal is received.

It is the longitudinal cross-sectional view and cross-sectional view which show the structure of the variable characteristic fiber grating which concerns on this invention. It is a graph which shows a mode that a reflection center wavelength changes with a temperature rise in a chirped fiber grating. It is a graph which shows the change of the reflection center wavelength when the temperature dependence of the fluctuation | variation of the reflection center wavelength in a chirped fiber grating is changing about the longitudinal direction. In the characteristic variable fiber grating, there are a longitudinal sectional view and a transverse sectional view showing a configuration in which the number of fibers constituting the fibrous member is changed along the longitudinal direction of the grating portion. In the characteristic variable fiber grating, it is a longitudinal sectional view showing a configuration in which fibers forming a fibrous member and gaps between the fibers and the optical fiber Bragg grating are filled with a resin material. In Example 1, it is a graph which shows a temperature characteristic change by making a horizontal axis into a fiber number. In Example 2, it is a graph which shows the change of a reflection intensity spectrum and a group delay characteristic by making a horizontal axis into a reflective wavelength. In Example 3, it is a graph which shows the change of a reflection intensity spectrum and a group delay characteristic by making a horizontal axis into a reflective wavelength. It is a side view showing the 1st composition of a characteristic variable fiber grating combined with a temperature control mechanism. It is a side view showing the 2nd composition of a characteristic variable fiber grating combined with a temperature control mechanism. It is a side view which shows the principle of operation of a dispersion compensation fiber grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber Bragg grating 2 Fibrous member 3 Grating part 4 Fiber 5 Resin material

Claims (9)

An optical fiber Bragg grating composed of an optical fiber in which a grating structure with a periodically changing refractive index is formed;
A fibrous member disposed around the optical fiber Bragg grating,
The fibrous member has a negative linear expansion characteristic that contracts in the fiber longitudinal direction when the temperature rises and expands in the fiber longitudinal direction when the temperature falls. The optical fiber Bragg grating has a structure in which a compressive force or an extension force in the longitudinal direction of the optical fiber Bragg grating is applied, and the fiber member expands or contracts in the grating portion of the optical fiber Bragg grating. A variable-characteristic fiber grating characterized in that the amount of compressive force or tensile force applied differs in the longitudinal direction of the optical fiber.   2. The variable characteristic fiber grating according to claim 1, wherein the number of fibers constituting the fibrous member is different in the longitudinal direction of the grating portion of the optical fiber Bragg grating. The optical fiber member in which the optical fiber Bragg grating is formed is quartz, and the linear expansion coefficient in the fiber longitudinal direction of the fibrous member is −6.0 × 10 ^{−6 to} −15.0 × 10 ⁻⁶ [1 / ° C.] The variable characteristic fiber grating according to claim 1 or 2, wherein   The variable fiber grating according to any one of claims 1 to 3, wherein the fibrous member is made of high molecular weight polyethylene.   The variable fiber grating according to any one of claims 1 to 3, wherein the fibrous member is a polyparaphenylene benzobisoxazole fiber.   6. The gap between the fibers forming the fibrous member and between the fibers and the optical fiber Bragg grating is filled with a resin material. 6. Characteristic variable fiber grating.   The variable-characteristic fiber grating according to claim 6, wherein the resin material is a material having a Young's modulus of 500 MPa or less in an operating temperature range.   The variable characteristic fiber according to any one of claims 1 to 7, wherein a change direction of a reflection wavelength at both ends of the fiber Bragg grating is opposite to each other with respect to a temperature change within a use temperature range. Grating.   The characteristic variable fiber grating according to any one of claims 1 to 8, further comprising a temperature adjusting mechanism that adjusts a temperature of the fiber Bragg grating.

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