JP4858208B2 - Fiber Bragg grating device - Google Patents

Description

  The present invention relates to a fiber Bragg grating device for heating or cooling an optical fiber device having a fiber Bragg grating (FBG) structure by a thermo module controlled by a temperature controller.

  A superstructure FBG (SSSFBG) having a multipoint phase shift structure can be used as an encoder or a decoder in phase code system OCDM (optical code division multiplexing). In the SSFBG, a plurality of unit FBG structures having the same length and the same period of the refractive index change region (that is, having the same reflection wavelength) are arranged on the optical fiber at intervals according to the symbols (including the interval 0). And it is the optical fiber device formed by providing the number according to the code | symbol to comprise. In the OCDM encoder and the OCDM decoder that form a pair, even if the wavelength difference between the two is only a few pm, the OCDM decoder cannot perform decoding. Therefore, the wavelengths of the OCDM encoder and the OCDM decoder that form a pair need to be matched with high accuracy.

  However, the FBG is a device in which a refractive index change region (grating) is formed in a lattice shape in the core of the optical fiber, and the refractive index of the FBG has temperature dependence. Therefore, the reflection wavelength of the FBG largely fluctuates with changes in the environmental temperature.

  In Japanese translation of PCT publication No. 2000-503415 (Patent Document 1), FBG is fixed on a plate-shaped glass ceramic substrate having a negative thermal expansion coefficient, thereby changing the reflection wavelength of FBG caused by changes in environmental temperature. Suppression techniques have been proposed. However, with this technique, it is difficult to precisely control the amount of wavelength variation required for the OCDM encoder and the OCDM decoder.

  Japanese Patent Laying-Open No. 2005-173246 (Patent Document 2) proposes a technique for suppressing fluctuations in reflection wavelength caused by changes in environmental temperature by heating or cooling SSFBG.

Special Table 2000-503415 JP 2005-173246 A

  If the code length is increased in order to provide higher communication security in the phase code method OCDM, the number of unit FBGs constituting the SSFBG increases, so that the total length of the SSFBG becomes longer. Since the SSFBG is composed of the unit FBGs having the same length and the same refractive index change region period, a predetermined encoding or decoding operation cannot be performed unless the individual unit FBGs exhibit the same reflection characteristics. That is, in order for the unit FBGs constituting the SSFBG to exhibit the same reflection characteristics, the temperature needs to be uniform throughout the SSFBG formation region.

  In order to make the temperature of the entire SSFBG formation region uniform, the temperature of the member on which the SSFBG is mounted and fixed needs to be uniform. For this purpose, it is sufficient that the thermal conductivity of the member is high. However, for example, a material having high thermal conductivity such as copper or aluminum also has a high coefficient of thermal expansion. Therefore, when SSFBG is mounted and fixed on such a material, wavelength variation due to thermal expansion and contraction of the member is caused by wavelength variation due to temperature control. In addition, there is a problem that the wavelength adjustment resolution deteriorates.

  In the encoder or decoder proposed in Patent Document 2, the SSFBG is mounted and fixed on a mounting plate formed of a material having a low thermal expansion coefficient, and the mounting plate is installed on a base plate formed of a high thermal conductive material. The heat is uniformly conducted to the SSFBG without transmitting thermal expansion and contraction accompanying heating or cooling. However, in this case, there is a problem that the number of parts constituting the encoder or decoder increases, and the time and cost required for the processing and assembly increase.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and the object thereof is a fiber resulting from thermal expansion or contraction of a support member to which the fiber Bragg grating is fixed with a small number of parts. An object of the present invention is to provide a fiber Bragg grating device that can suppress changes in characteristics of the Bragg grating and can control the reflection wavelength only by the temperature of the fiber Bragg grating.

The fiber Bragg grating device of the present invention includes an optical fiber device including a fiber Bragg grating, a support member to which the optical fiber device is fixed, a housing for housing the optical fiber device and the support member, A thermo module that is sandwiched between an inner surface and the support member and performs at least one of heating and cooling of the optical fiber device in the housing, and a first temperature for detecting the temperature of the optical fiber device in the housing A temperature controller that controls heating or cooling by the thermo-module so that a temperature detected by the first temperature sensor is close to a set temperature, and a temperature controller that holds a set temperature and that is detected by the first temperature sensor; Has a coefficient of thermal expansion of 1.7 × 10 ⁻⁶ / K or less and a thermal conductivity. Is made of a material having a power of 190 W / (m · K) or more, and the support member and the casing are a composite material of silicon carbide ceramic and silicon .

  According to the fiber Bragg grating device of the present invention, the characteristic change of the fiber Bragg grating due to the thermal expansion or contraction of the support member to which the fiber Bragg grating is fixed can be suppressed with a small number of parts, and the fiber Bragg grating can be suppressed. Since the reflection wavelength can be controlled only by the temperature, it is possible to simplify the configuration of the apparatus and improve the adjustment resolution of the reflection wavelength.

<1. Description of configuration>
FIG. 1 is a schematic configuration diagram of a fiber Bragg grating (FBG) device according to an embodiment of the present invention, and shows a cross-sectional structure of an FBG package 1. 2 is a cross-sectional view taken along line S ₂ -S ₂ of the FBG package 1 shown in FIG. The FBG device according to the embodiment of the present invention is, for example, an OCDM encoder module or an OCDM decoder module.

  As shown in FIG. 1, the FBG device according to the embodiment of the present invention includes an FBG package (that is, an OCDM encoder module package or an OCDM decoder module package) 1 and a temperature electrically connected to the FBG package 1. And a controller 2.

The FBG package 1 includes an optical fiber device 3 including an FBG, a mounting plate 4 that is a support member to which the optical fiber device 3 is fixed, a housing 5 that houses the optical fiber device 3 and the mounting plate 4, and a housing 5. The thermo-module 7 is interposed between the inner surface of the optical fiber device and the mounting plate 4 and performs at least one of heating and cooling of the optical fiber device 3. The mounting plate 4 is fixed to the inner surface of the housing 5 via the thermo module 7. For example, an adhesive may be used for fixing the mounting plate 4 and the thermo module 7 and fixing the thermo module 7 and the inner surface of the housing 5. The FBG package 1 also includes a first temperature sensor 10 that detects the temperature of the optical fiber device 3 and a second temperature sensor 11 that detects the environmental temperature of the place where the FBG device is installed. The temperature controller 2 determines the set temperature T _set based on the temperature (environment temperature) T ₂ detected by the second temperature sensor 11 and the reference data 2 a held in advance, and is detected by the first temperature sensor 10. Heating or cooling by the thermo module 7 is controlled so that the temperature T ₁ to be _set approaches the set temperature T _set .

  The optical fiber device 3 is a device in which SSFBG is formed on the fiber core. SSFBG is manufactured by irradiating periodically changing ultraviolet light to a single-mode optical fiber with enhanced ultraviolet sensitivity by adding germanium or the like to the fiber core to form a multipoint phase shift structure. can do.

The mounting plate 4 is made of a material having a thermal expansion coefficient of 1.7 × 10 ⁻⁶ / K or less and a thermal conductivity of 190 W / (m · K) or more. The mounting plate 4 has a prismatic shape (or a round bar shape) in which a groove 4 a for fixing the optical fiber device 3 is formed. The mounting plate 4 is a composite material of SiC (silicon carbide: silicon carbide) ceramic and Si (silicon: silicon) characterized by high thermal conductivity and low thermal expansion. However, it is not limited to this. The thermal conductivity of this material is 190 w / (m · K), which is almost the same as that of aluminum. Moreover, the thermal expansion coefficient of this material is 1.7 × 10 ⁻⁶ / K, which is equivalent to Invar.

  The thermo module 7 is a heating and / or cooling module using a Peltier element. The thermo module 7 is installed on the bottom surface inside the housing 5 so as to be sandwiched between the mounting plate 4 and the inner surface of the housing 5. When the thermo module 7 heats the mounting plate 4, the surface 7 a on the mounting plate 4 side of the thermo module 7 becomes the temperature control surface (heat dissipating surface) of the thermo module 7, and the opposite surface (that is, the housing). The surface 7 b facing the inner surface of the body 5 is the heat absorbing surface of the thermo module 7. Further, when the thermo module 7 cools the mounting plate 4, the surface 7 a on the mounting plate 4 side of the thermo module 7 becomes the temperature control surface (heat absorption surface) of the thermo module 7, and the opposite surface (that is, the surface) The surface 7 b facing the inner surface of the housing 5 is the heat radiating surface of the thermo module 7. The thermo module 7 preferably has a size opposite to the SSFBG formation region of the optical fiber device 3 and is not smaller than the SSFBG formation region. In the following description, the surface 7a where the thermo module 7 contacts the mounting plate 4 is the temperature control surface of the thermo module 7, and the opposite surface (ie, the surface which contacts the housing 5 of the FBG package) 7b is the thermo module 7. The heat dissipation surface.

  Moreover, the 1st temperature sensor 10 and the 2nd temperature sensor 11 which are shown by FIG. 1 are comprised from the thermistor, for example. However, the 1st temperature sensor 10 and the 2nd temperature sensor 11 are not limited to a thermistor, For example, you may use other temperature sensors, such as a thermocouple and a platinum thermal resistor.

  The first temperature sensor 10 is installed on the mounting plate 4, for example, but may be installed at other positions such as being embedded in the mounting plate 4. A plurality of first temperature sensors 10 may be provided such as both ends of the optical fiber device 3.

  The second temperature sensor 11 is preferably installed on the outer surface of the housing 5, for example. However, the second temperature sensor 11 may be installed at another position such as on a substrate (not shown) on which the housing 5 is installed. A plurality of second temperature sensors 11 may be provided. Further, the installation position of the second temperature sensor 11 is not limited to the illustrated example.

  The temperature controller 2 records reference data 2a based on characteristics of the FBG device (for example, characteristics as a phase encoder / decoder). The temperature controller 2 is connected to the first temperature sensor 10, the second temperature sensor 11, and the thermo module 7, and according to the detected temperatures of the first temperature sensor 10 and the second temperature sensor 11, Controls the operation of module 7.

The temperature controller 2 refers to the reference data 2a according to the detected temperature T2 of the _second temperature sensor 11, and also detects the temperature of the optical fiber device 3 (that is, the temperature detected by the first temperature sensor 10). A set temperature T _set which is a target value is determined. Further, the temperature controller 2 controls heating or cooling by the thermo module 7 so that the temperature T ₁ detected by the first temperature sensor 10 approaches the set temperature T _set .

  FIG. 3 is an explanatory diagram showing an example of the SSFBG structure formed in the optical fiber device 3 shown in FIG. 1, and shows an SSFBG when a 15-bit M-sequence is used as a code string. In FIG. 3, each of the unit FBGs indicated by the symbols ‘A’ to ‘O’ has the same length and the same refractive index modulation region period. Here, between the units FBG'C 'and' D ', between the units FBG'G' and 'H', between the units FBG'H 'and' I ', and between the units FBG'I' and 'J'. , Between the units FBG 'J' and 'K', between the units FBG 'L' and 'M', and between the units FBG 'N' and 'O', when the wavelength of the optical carrier is λ An interval corresponding to / 4 is provided, and the unit FBGs are arranged with an interval of 0 (zero) between the other unit FBGs, that is, adjacent unit FBGs are arranged in close contact with each other. means. Since the interval corresponding to λ / 4 is the interval corresponding to the phase π / 2 of the optical carrier wave, for example, when an optical pulse is incident from the left side (unit FBG′A ′ side) of FIG. 3, the unit FBG′A The reflected pulses in units FBG'D ',' E ',' F ', and' G 'are π-shifted in phase with respect to the reflected pulses at', 'B', and 'C'. Become.

  The optical fiber device 3 is, for example, bonded and fixed at both ends of the mounting plate 4 and in close contact with the mounting plate 4 in a state where no stress such as tensile tension or compressive force is generated. The SSFBG is included between the adhesive fixing points to the mounting plate 4. The adhesive fixing to the mounting plate 4 of the optical fiber device in the present embodiment uses an ultraviolet curable acrylic adhesive (manufactured by Summers Optical, product number: VTC-2), but is not limited thereto. In addition, an epoxy-based adhesive can also be used.

The housing 5 is made of a material having a thermal expansion coefficient of 1.7 × 10 ⁻⁶ / K or less and a thermal conductivity of 190 W / (m · K) or more. The housing 5 is preferably composed of the same silicon carbide ceramic and silicon composite material as the mounting plate 4. It is desirable that the mounting plate 4 and the housing 5 have the same thermal expansion coefficient and the same thermal conductivity. The mounting plate 4 and the housing 5 have the same thermal expansion coefficient and the same thermal conductivity so that even if the environmental temperature changes and the mounting plate 4 and the housing 5 expand or contract, Alternatively, the amount of shrinkage is approximately the same, and no stress is generated inside the thermo module 7 even if the environmental temperature changes. In addition, the case 5 can also be comprised from the aluminum which gave the gold plating to the surface, for example. The housing 5 has a box shape, and has a power supply terminal to the thermo module 7 included in the SSFBG mounting portion and an output terminal from the first temperature sensor 10 on its side surface. These terminals are connected to the temperature controller 2 to control heating or cooling of the thermo module 7. Moreover, the optical fiber which comprises the optical fiber device 3 has penetrated the wall surface of the housing | casing 5, and the penetration location is sealed by the gel-like flexible sealing member, for example.

<2. Explanation of operation>
Depending on the difference between the set temperature T _set of the temperature controller 2 and the measured temperature T ₁ by the first temperature sensor 10, the temperature controller 2 determines that the measured temperature T _{1 of} the first temperature sensor 10 is equal to the set temperature T _set . Thus, the heating or cooling of the thermo module 7 is controlled. By controlling the thermo module 7 by the temperature controller 2, the mounting plate 4 is maintained at a constant temperature. Here, although the mounting plate 4 is heated or cooled by heating or cooling of the thermo module 7, the temperature distribution in the longitudinal direction (lateral direction in FIG. 1) of the mounting plate 4 is high because the thermal conductivity of the mounting plate 4 is high. The temperature difference is suppressed to a low value (small temperature gradient).

  Further, since the thermal expansion coefficient of the mounting plate 4 is small, the mounting plate 4 itself hardly expands or contracts. The SSFBG included in the optical fiber device 3 is fixed to the mounting plate 4, but the expansion and contraction of the mounting plate 4 itself hardly occurs. Therefore, the SSFBG hardly expands and contracts due to the temperature change. There is no change in the internal stress of the SSFBG due to expansion / contraction, and therefore no change in the reflection wavelength due to expansion / contraction of the mounting plate 4 itself. Therefore, in the embodiment of the present invention, only the temperature of the SSFBG changes with the temperature change of the mounting plate 4 (the internal stress of the SSFBG does not change), and the reflection wavelength of the SSFBG is controlled only by the temperature. Can do.

  FIG. 4 is a diagram showing a result of actually measuring the relationship between the set temperature and the amount of change in the reflected wavelength in the temperature controller 2 and a straight line based on the measured value. In FIG. 4, the horizontal axis indicates the set temperature (° C.) of the temperature controller, the vertical axis indicates the amount of fluctuation (pm) in the reflected wavelength of the OCDM encoder module, and three measured values (square points) are shown. Yes. As shown in FIG. 4, when linearly approximating the temperature controller setting temperature (° C.) as the x axis and the reflected wavelength variation (pm) as the y axis, the wavelength variation per 1 ° C. of the temperature controller 2 is 10 .3pm.

When the predetermined wavelength is set in the temperature controller 2, the set temperature T _{set of the} thermo module 7 from the reference data 2 a recorded in the temperature controller 2 based on the temperature outside the housing 5 detected by the second temperature sensor 11. The temperature controller 2 controls heating or cooling of the thermo module 7 so that the temperature of the mounting plate 4 detected by the first temperature sensor 10 becomes equal to the set temperature T _set .

Here, when the temperature of the housing 5 (substantially equal to the environmental temperature) detected by the second temperature sensor 11 changes, the thermo module 7 in the temperature controller 2 is calculated from the temperature change amount of the housing 5 and the reference data 2a. The set temperature T _set for control is calculated again. Then, the temperature of the mounting plate 4 is readjusted so as to obtain a predetermined reflection wavelength for fine adjustment of the temperature. In this way, the _set wavelength is set by repeating readjustment of the set temperature T _set for controlling the thermo module 7 as appropriate according to the change in the ambient temperature T ₂ on the outer periphery of the housing 5 detected by the second temperature sensor 11. It can be maintained automatically and stably.

  The reference data 2a in the embodiment of the present invention includes wavelength adjustment characteristics (a relationship between a thermomodule set temperature and a wavelength, see FIG. 4) at a constant environmental temperature (for example, 25 ° C.) of an encoder to be controlled. , And is defined from the relationship of the wavelength variation characteristic depending on the relative environmental temperature with respect to the thermo module set temperature.

FIG. 5 is a flowchart showing the contents of control by the temperature controller 2 of the FBG device according to the embodiment of the present invention. As shown in FIG. 5, first, by the user, the used wavelength is input (step ST1), a second temperature sensor 11 detects the environmental temperature T ₂ (step ST2), the detected temperature T2 Based on the reference data 2a (step ST3), a set temperature T _set for controlling the thermo module 7 is calculated and set (step ST4). Next, it controls the operation of the thermo module 7 (step ST5), the first temperature sensor 10 detects the temperature _{T 1} of the SSFBG (step ST6), whether or not the temperature _{T 1} is equal to the set temperature _{T set} Judgment is made (step ST7). If the temperature _{T 1} is not equal to the set temperature _{T set,} the determination in step ST7 is made NO, and to approximate the temperature _{T 1} of the set temperature _{T set,} and controls the operation of the thermo module 7 (step ST5). Then, perform the first detection of the temperature _{T 1} of the SSFBG by temperature sensor 10 (step ST6) and the temperature _{T 1} is determined whether equal to the set temperature _{T The set} (step ST7), the temperature _{T 1} is the set temperature equal to T _{the set,} determination in step ST7 becomes YES, the process proceeds to step ST2.

  Next, the FBG device has a wavelength of 1550.000 nm, a wavelength adjustment characteristic of 10 pm / ° C., and a wavelength fluctuation characteristic of 0.5 pm / ° C. depending on the relative environment temperature, for example, when the thermo module at 25 ° C. is set at 25 ° C. The case of an OCDM encoder module will be described. In this case, first, the wavelength 1550.100 nm is input by the user (step ST1).

The second temperature sensor 11 detects the temperature (environmental temperature) _{T 2} (step ST2), for the 1550.100nm wavelengths in environmental temperature 25 ° C., to perform the control by the temperature controller 2. For this purpose, the temperature controller 2 refers to the reference data 2a (step ST3), and calculates and sets a set temperature T _set for controlling the thermo module 7 from the following equation (1) (step ST4). From the following equation (1), the set temperature T _set when the ambient temperature is 25 ° C. is 35 ° C.

In this case, when the relative environmental temperature is −10 ° C. (= environment temperature−set temperature = 25 ° C.−35 ° C.), the adjustment wavelength by the thermo module set temperature is −5 pm (= −10 ° C. × 0.5 pm / ° C) It is assumed that the wavelength fluctuates, and the thermomodule set temperature T _set is increased by 0.5 ° C to 35.5 ° C (= 35 ° C + 0.5 ° C). At this time, the relative environment temperature also changes by 0.5 ° C., but the wavelength variation due to the change in the relative environment temperature is minute and can be ignored.

Further, in step ST4 in FIG. 5, when the detected temperature (environment temperature) T2 of the _second temperature sensor 11 becomes 27 ° C., the relative environment temperature becomes −8.5 ° C. (= environment temperature−set temperature = 27 ° C.−). 35.5 ° C), +1 pm (= (27 ° C-25 ° C) x 0.5 pm / ° C) with respect to the wavelength adjusted by the thermo-module setting temperature is assumed to change. Is reduced by 0.1 ° C. to 35.4 ° C. At this time, the relative environment temperature also changes by 0.1 ° C., but the wavelength fluctuation due to the change in the relative environment temperature is also minute and can be ignored.

<3. Explanation of effects>
As described above, by adopting the configuration of the embodiment of the present invention, the optical fiber device 3 for conducting heat uniformly with another member different from the mounting plate 4, for example, a material that suppresses thermal expansion. It is not necessary to provide the fixing member, the number of parts can be reduced, and the manufacturing cost and the manufacturing time can be reduced.

  In addition, according to the embodiment of the present invention, an FBG device capable of adjusting the reflection wavelength with a high wavelength adjustment resolution can be realized at a low cost with a simple configuration, and a manufacturing error of the SSFBG included in the encoder module can be realized. The wavelength can be adjusted with high accuracy without being affected by the above.

Furthermore, by automatically repeating readjustment of the set temperature T _set of the thermo module 7 by the temperature controller 2, even when the environmental temperature T ₂ changes, a predetermined reflection wavelength can be stably maintained.

<4. Modification>
In the above description, the case where the FBG device is an OCDM encoder module or an OCDM decoder module has been described. However, the FBG device of the present invention is not limited to these. The FBG device of the present invention can also be applied to, for example, an encoder or decoder in wavelength hopping OCDM, a filter device in a WDM system, etc., and obtains the same effect as when the FBG device is an OCDM encoder module. Can do.

  Further, the drawings used in the above description show one configuration example of the apparatus to which the present invention is applied, and only schematically show the cross-sectional shape and arrangement relationship of each component to the extent that the invention can be understood. The invention is not limited to the illustrated example.

  Furthermore, in the above description, specific materials, conditions, dimensions, etc. are illustrated, but these materials, conditions, dimensions, etc. show one of preferred examples, and the present invention is not limited to these. It is not something.

It is a schematic block diagram of the FBG apparatus which concerns on embodiment of this invention. FIG. ₂ is a cross-sectional view of the FBG package shown in FIG. 1 taken along line S ₂ -S ₂ . It is explanatory drawing which shows an example of the SSFBG structure formed in the optical fiber device shown by FIG. It is a figure which shows the straight line based on the result of having actually measured the relationship between the setting temperature in a temperature controller, and the variation | change_quantity of reflected wavelength, and a measured value. It is a flowchart which shows the control content by the temperature controller of the FBG apparatus which concerns on embodiment of this invention.

Explanation of symbols

  1 FBG package, 2 temperature controller, 2a reference data, 2b set temperature, 3 optical fiber device, 4 mounting plate, 4a groove, 5 housing, 7 thermo module, 7a surface of thermo module mounting plate side, 7b of thermo module A housing-side surface, 10 a first temperature sensor, and 11 a second temperature sensor.

Claims (7)

An optical fiber device including a fiber Bragg grating;
A support member to which the optical fiber device is fixed;
A housing for housing the optical fiber device and the support member;
A thermo module that is sandwiched between an inner surface of the housing and the support member, and performs at least one of heating and cooling of the optical fiber device in the housing;
A first temperature sensor for detecting a temperature of the optical fiber device in the housing;
A temperature controller that holds a set temperature and controls heating or cooling by the thermo module so that the temperature detected by the first temperature sensor approaches the set temperature;
The support member is made of a material having a thermal expansion coefficient of 1.7 × 10 ⁻⁶ / K or less and a thermal conductivity of 190 W / (m · K) or more ,
The fiber Bragg grating device, wherein the support member and the casing are a composite material of silicon carbide ceramic and silicon . The housing is made of a material having a thermal expansion coefficient of 1.7 × 10 ⁻⁶ / K or less and a thermal conductivity of 190 W / (m · K) or more. Item 2. The fiber Bragg grating device according to Item 1.   The fiber Bragg grating device according to claim 1, wherein the support member and the housing have the same thermal expansion coefficient and the same thermal conductivity. A second temperature sensor for detecting an environmental temperature at a place where the fiber Bragg grating device is installed;
The temperature controller holds reference data,
The temperature controller is a fiber Bragg according to any one of claims 1 to 3, characterized in that to change the set temperature based on the temperature and the reference data detected by said second temperature sensor Grating device. The fiber Bragg grating device according to claim 4 , wherein the second temperature sensor is disposed on an outer peripheral surface of the housing. Said fiber Bragg grating, a fiber Bragg grating device according to any one of claims 1 to 5, characterized in that a superstructure fiber Bragg grating having a plurality of unitary fiber Bragg grating structure. The optical fiber device is an OCDM encoder or an OCDM decoder;
The fiber Bragg grating device according to claim 6 , wherein the fiber Bragg grating device constitutes an OCDM encoder module or an OCDM decoder module.

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