JP5435044B2 - Fiber Bragg grating device - Google Patents

Description

  The present invention relates to a fiber Bragg grating device that can suppress fluctuations in the Bragg reflection wavelength of a fiber Bragg grating with respect to changes in ambient temperature.

  In recent years, communication demand has been rapidly increasing due to the spread of the Internet and the like. Correspondingly, high-speed and large-capacity networks using optical fibers and the like are being developed. As communication means for constructing such a network, Optical Time Division Multiplexing (OTDM), Wavelength Division Multiplexing (WDM), and Optical Code Division Multiplexing (OCDM). Is attracting attention.

  In transmission using these multiplexing techniques, optical pulse signals of a plurality of channels are generated in parallel. This optical pulse signal is modulated into an optical pulse train using an electrical signal including transmission data as information. On the transmission side, the optical pulse signal is modulated with a different code for each channel. This modulation on the transmission side is called encoding. On the receiving side, the original parallel optical pulse signal is restored by modulating with the same code used when encoding on the transmitting side. This modulation on the receiving side is called decoding.

  In transmission using OCDM, which is one of the multiplexing techniques, optical pulse signals of many channels can be transmitted simultaneously at the same wavelength.

  In addition, since OCDM is a transmission method that uses the same code as a key on the transmission side and the reception side, one of the features is high security in transmission.

  As a means for encoding the OCDM, a phase code method OCDM using the phase of light as a code is known. Then, as an encoder and a decoder, an FBG apparatus provided with a superstructured fiber Bragg grating (SSFBG: Superstructured Fiber Bragg Grating) configured by forming a fiber Bragg grating (FBG) in an optical fiber is used. Can do. Here, in order to set the same code to the encoder and the decoder using FBG, it is necessary that the FBGs of the encoder and the decoder have the same effective refractive index periodic structure and the same Bragg reflection wavelength. is there. The FBG device can be used for purposes other than the encoder and decoder, or can be applied to multiplexing techniques other than OCDM.

  The Bragg reflection wavelength of the FBG varies with, for example, changes in the ambient temperature of the encoder and decoder. When such a variation in the Bragg reflection wavelength occurs, the encoder and decoder do not match the codes, and crosstalk occurs between channels. Therefore, it is important to keep the Bragg reflection wavelength of the FBGs of the encoder and decoder the same.

  Therefore, there is a technique for suppressing fluctuations in the Bragg reflection wavelength of the FBG caused by changes in the ambient temperature (see, for example, Patent Document 1).

  The Bragg reflection wavelength of the FBG varies to the longer wavelength side as the ambient temperature increases. Therefore, in the FBG device disclosed in Patent Document 1, an optical fiber on which an FBG is formed is attached on the surface of a substrate having a negative thermal expansion coefficient (hereinafter also referred to as a negative expansion substrate). The optical fiber is fixed to the surface of the negative expansion substrate in at least two separated portions. In the FBG device according to Patent Document 1, fluctuations in the Bragg reflection wavelength of the FBG can be compensated for by the negative expansion substrate contracting as the ambient temperature increases. On the other hand, the Bragg reflection wavelength of the FBG varies to the short wavelength side as the ambient temperature decreases. When the ambient temperature is lowered, the negative expandable substrate expands to compensate for fluctuations in the Bragg reflection wavelength of the FBG.

Special Table 2000-503415

  FIG. 1A is a diagram showing the relationship between changes in ambient temperature and fluctuations in the Bragg reflection wavelength of the FBG. In FIG. 1A, the horizontal axis indicates the ambient temperature in units of ° C. Further, the vertical axis shows the fluctuation amount of the Bragg reflection wavelength of the FBG in units of pm. As shown in FIG. 1A, the fluctuation amount of the Bragg reflection wavelength of the FBG does not have a linear function relationship with the change in the ambient temperature.

  On the other hand, when the wavelength characteristic is compensated using the expansion or contraction of the negative expansion substrate, the compensation amount has a linear function relationship with the change in the ambient temperature.

  Due to the difference in dependence on the ambient temperature between the variation amount of the Bragg reflection wavelength and the compensation amount, the FBG device according to Patent Document 1 may be overcompensated or undercompensated depending on the ambient temperature.

  FIG. 1B shows the result of compensating for the fluctuation of the Bragg reflection wavelength of the FBG using the FBG device disclosed in Patent Document 1. In FIG. 1B, the horizontal axis indicates the ambient temperature in units of ° C. Further, the vertical axis shows the fluctuation amount of the Bragg reflection wavelength of the FBG in units of pm. A solid line is a result at the time of using the negative expansion | swelling board | substrate with which the thermal expansion coefficient which compensates the fluctuation | variation of the Bragg reflection wavelength in a high temperature range (temperature range in which the ambient temperature is approximately 20 to 80 ° C.) is set ( Reference numeral 101 is shown). Also, the broken line shows the result when a negatively expandable substrate is used in which a thermal expansion coefficient is set to compensate for fluctuations in the Bragg reflection wavelength in the intermediate temperature range (temperature range in which the ambient temperature is approximately in the range of −10 to 50 ° C.). (Denoted with reference numeral 103). In addition, the one-dot broken line shows a case where a negative expansion substrate is used in which a thermal expansion coefficient is set to compensate for a variation in Bragg reflection wavelength in a low temperature range (a temperature range in which the ambient temperature is approximately within a range of −40 to 20 ° C.). The result is shown (indicated by reference numeral 105).

  As shown in FIG. 1B, in the FBG apparatus disclosed in Patent Document 1, there is a temperature range in which excessive compensation or insufficient compensation occurs in each result. That is, when compensating for the fluctuation of the Bragg reflection wavelength in the high temperature region, excessive compensation occurs in the low temperature region. In addition, when compensating for the fluctuation of the Bragg reflection wavelength in the middle temperature range, excessive compensation occurs in the low temperature range and insufficient compensation occurs in the high temperature range. In addition, when compensating for the fluctuation of the Bragg reflection wavelength in the low temperature range, insufficient compensation occurs in the high temperature range. As described above, the FBG device according to Patent Document 1 cannot sufficiently compensate the wavelength characteristics corresponding to a wide range of ambient temperature changes.

  Accordingly, an object of the present invention is to provide an FBG device that can suppress fluctuations in the Bragg reflection wavelength of the FBG with respect to a wider range of temperature changes than in the prior art.

  In order to achieve the above object, the FBG device of the present invention includes an optical fiber, a mounting sleeve, a contact cushioning material, and a holder. FBG is built into the optical fiber. The mounting sleeve fixes the optical fiber and has a negative coefficient of thermal expansion. The holder sandwiches the mounting sleeve integrally from the direction along the extending direction of the optical fiber via the contact cushioning material, and has a positive thermal expansion coefficient.

  In the FBG device according to the present invention, as described above, the thermal expansion coefficient of the mounting sleeve is negative, and the thermal expansion coefficient of the holder is positive. Therefore, when the ambient temperature falls, the mounting sleeve expands and the holder contracts. Therefore, the expansion of the mounting sleeve is suppressed by the holder. As a result, when the ambient temperature is lowered, excessive compensation of the wavelength characteristics of the FBG by the mounting sleeve can be suppressed by the holder. For this reason, in the FBG device according to the present invention, the thermal expansion coefficient of the mounting sleeve is set so as to compensate for the wavelength characteristics in the high temperature range, so that the FBG Bragg can be applied to a wider range of temperature changes than in the past. It is possible to compensate for variations in the reflection wavelength.

(A) is a figure which shows the relationship between the change of ambient temperature, and the fluctuation | variation of the Bragg reflection wavelength of FBG. (B) is a figure which shows the relationship between the change of ambient temperature and the fluctuation | variation of the Bragg reflection wavelength of FBG in the conventional FBG apparatus. It is a perspective view of the FBG apparatus of this invention. (A) And (B) is an end elevation of the FBG device of this invention. It is a figure which shows the fluctuation | variation of the Bragg reflection wavelength of FBG in the optical fiber used with the FBG apparatus of this invention. It is a figure which shows the effect of the compensation of the wavelength characteristic by the FBG apparatus of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

  In this embodiment, for example, an FBG device that operates as an encoder or a decoder in the above-described OCDM will be described.

(Description of configuration)
2 and 3 are schematic views showing the FBG device according to this embodiment. FIG. 2 is a perspective view of the FBG device. FIG. 3A is an end view showing a cut surface of the FBG device taken along line II in FIG. FIG. 3B is an end view showing a cut surface obtained by cutting the FBG device along the line II-II in FIG. In FIG. 3B, hatching indicating a cut surface is omitted.

  The FBG device 11 includes an optical fiber 13, a mounting sleeve 15, a contact cushioning material 17, and a holder 19.

  As the optical fiber 13, the Bragg reflection wavelength of the FBG fluctuates with a positive correlation with changes in the ambient temperature (that is, the Bragg reflection wavelength of the FBG formed in the optical fiber 13 increases with increasing ambient temperature. Fiber). More specifically, as the optical fiber 13, for example, an ultraviolet photosensitive optical fiber PA1500 (hereinafter also referred to as optical fiber A) manufactured by FIBERCORE or an ultraviolet photosensitive optical fiber UVS652 (hereinafter also referred to as optical fiber B) manufactured by CorActive. ) Etc. can be used.

  With reference to FIG. 4, the fluctuation | variation of the Bragg reflection wavelength of FBG in the optical fiber A and the optical fiber B is demonstrated. FIG. 4 is a diagram showing the relationship between changes in ambient temperature and fluctuations in the Bragg reflection wavelength of the FBG in the optical fibers A and B. FIG. In FIG. 4, the horizontal axis indicates the ambient temperature in units of ° C. Further, the vertical axis shows the fluctuation amount of the Bragg reflection wavelength of the FBG in units of pm. From FIG. 4, it can be confirmed that the wavelength variation rate of the optical fiber A is 10 pm / ° C. and the wavelength variation rate of the optical fiber B is 9 pm / ° C. within an ambient temperature range of 20 to 80 ° C.

  Moreover, FBG is built in the optical fiber 13 (not shown). In this embodiment, the optical fiber 13 is fixed to the mounting sleeve 15 with the FBG contacting the mounting sleeve 15.

  The mounting sleeve 15 can have a rectangular parallelepiped shape, for example. The optical fiber 13 is fixed on the upper surface 15a side.

  In the configuration example shown in FIGS. 2 and 3, a groove portion 21 extending along the longitudinal direction of the mounting sleeve 15 is formed on the upper surface 15 a. Here, the cross section orthogonal to the extending direction of the groove portion 21 may be a rectangular shape having vertical and horizontal dimensions of 1 mm each, for example. The optical fiber 13 is accommodated in the groove portion 21 so that the extending direction thereof coincides with the groove portion 21. The FBG formed on the optical fiber 13 is in contact with the bottom surface 21 a of the groove 21.

  Further, the groove 21 is embedded with an adhesive 23 at both ends in the extending direction. The adhesive 23 is preferably an epoxy adhesive having a Young's modulus of 100 GPa or more and a glass transition temperature of 100 ° C. or more, for example. More specifically, an ultraviolet curable epoxy adhesive “PARQIT” manufactured by Otex Co., Ltd. can be used as the adhesive 23. Then, it is preferable to fix the optical fiber 13 in a state where a tensile tension of, for example, 100 g is applied at a temperature of 20 ° C. (a state where a wavelength variation of about 1 nm is applied).

  In this way, the optical fiber 13 is fixed in the groove portion 21 by the adhesive 23 in the vicinity of both ends in the extending direction.

The mounting sleeve 15 is made of a material having a negative thermal expansion coefficient. The thermal expansion coefficient of the mounting sleeve 15 is set to a value that compensates for fluctuations in the Bragg reflection wavelength of the optical fiber 13 in a range of 20 to 80 ° C. without excess or deficiency. For example, when the optical fiber A is used as the optical fiber 13, the thermal expansion coefficient of the mounting sleeve 15 is preferably −7.5 × 10 ⁻⁶ / ° C. For example, when the optical fiber B is used as the optical fiber 13, it is preferable that the thermal expansion coefficient of the mounting sleeve 15 is −6.5 × 10 ⁻⁶ / ° C. For example, CERSAT manufactured by Nippon Electric Glass Co., Ltd. can be used as the mounting sleeve 15.

  The contact cushioning material 17 includes a first contact cushioning material 17a provided between a compensation adjusting portion 19a of the holder 19 described later and the mounting sleeve 15, and a second contact cushioning material 17c provided between the fixing portion 19c and the mounting sleeve 15. The contact cushioning material 17b is included. The first contact cushioning material 17a and the second contact cushioning material 17b may be formed integrally or may be separated from each other. 2 and 3 show a configuration example in which the first contact cushioning material 17a and the second contact cushioning material 17b are formed apart from each other.

  The contact cushioning material 17 is preferably formed of a material that is softer than the mounting sleeve 15 and the holder 19 (for example, has a small Shore hardness or a small Young's modulus). The contact cushioning material 17 can be formed of, for example, a sponge material such as urethane, or polystyrene foam. As the contact buffer material 17, it can form with PE light A-8 by Neuac Corporation, for example.

  The holder 19 includes a pair of compensation adjustment portions 19a, a coupling portion 19b, and a fixing portion 19c.

  The pair of compensation adjusting portions 19 a sandwich the mounting sleeve 15 from the direction along the extending direction of the optical fiber 13. The compensation adjusting portion 19a is formed to face two surfaces (end surfaces 15b and 15c) of the mounting sleeve 15 that are orthogonal to the extending direction of the optical fiber 13. These compensation adjusting portions 19a sandwich the mounting sleeve 15 via the contact cushioning material 17 (first contact cushioning material 17a). Further, the pair of compensation adjustment units 19a are coupled by a coupling unit 19b and are integrally configured.

Further, the fixing portion 19 c wraps the mounting sleeve 15 from the direction orthogonal to the extending direction of the optical fiber 13. In the configuration example shown in FIGS. 2 and 3, the fixing portion 19 c includes the contact cushioning material 17 from the upper surface 15 a along the extending direction of the optical fiber 13 and the side surfaces 15 d and 15 e orthogonal to the upper surface 15 a. It is integrally wrapped through (second contact cushioning material 17b).

  In addition, the holder 19 should just be comprised including at least a pair of compensation adjustment part 19a and the coupling | bond part 19b, and can change the shape arbitrarily suitably according to design. Therefore, the holder 19 can be configured not to include the fixing portion 19c. In this case, for example, the frame is configured to include a pair of compensation adjusting portions 19a facing the end surfaces 15b and 15c of the mounting sleeve 15 and a pair of coupling portions 19b facing the side surfaces 15d and 15e. Alternatively, for example, the pair of compensation adjusting units 19a can be coupled by the coupling unit 19b facing the upper surface 15a or the lower surface 15f instead of the position facing the side surfaces 15d and 15e.

  On the other hand, when the fixing portion 19c is provided, the mounting sleeve 15 can be wrapped from the five surfaces of the upper surface 15a, the end surfaces 15b and 15c, and the side surfaces 15d and 15e by the fixing portion 19c. 15 can be fixed more reliably.

The holder 19 is made of a material having a positive thermal expansion coefficient. Here, the holder 19 is provided in the compensation adjustment unit 19a for the purpose of adjusting the expansion and contraction of the mounting sleeve 15 accompanying the change in the ambient temperature. Therefore, it is preferable that the thermal expansion coefficient of the holder 19 is, for example, at least 1.5 × 10 ⁻⁵ / ° C. or more. Further, the holder 19 can be formed of, for example, aluminum or copper.

  In addition, the shape and dimension of each component mentioned above can be suitably set according to each material.

(Description of action / effect)
In the FBG device 11 according to this embodiment, when the ambient temperature rises, the Bragg reflection wavelength of the FBG varies toward the long wavelength side. On the other hand, the mounting sleeve 15 fixing the optical fiber 13 contracts because the thermal expansion coefficient is negative. As described above, the thermal expansion coefficient of the mounting sleeve 15 is set based on the FBG wavelength fluctuation amount in a high temperature region (that is, for example, the ambient temperature is in the range of 20 to 80 ° C.). Therefore, the fluctuation of the Bragg reflection wavelength in the high temperature range is compensated by the shrinkage of the mounting sleeve 15. Note that the holder 19 having a positive thermal expansion coefficient expands when the ambient temperature rises. However, since the stress due to the shrinkage of the mounting sleeve 15 and the stress due to the expansion of the holder 19 are generated in directions away from each other, the effect of compensating the wavelength characteristic in the high temperature range is not affected.

  Here, as described above, when the thermal expansion coefficient of the mounting sleeve is set to a value that compensates for the wavelength characteristics of the FBG in a high temperature range without excess or deficiency, the compensation using only the mounting sleeve is as described in Patent Document 1 described above. Furthermore, excessive compensation occurs in a low temperature range (that is, a temperature range where the ambient temperature is lower than 20 ° C., for example).

  However, in the FBG device 11 according to this embodiment, when the ambient temperature falls, the mounting sleeve 15 expands and the holder 19 contracts. Therefore, in the low temperature range, the expansion of the mounting sleeve 15 is suppressed by the compensation adjustment unit 19a of the holder 19 (see FIG. 3B). As a result, excessive compensation of wavelength characteristics by the mounting sleeve 15 can be suppressed by the holder 19. Therefore, the FBG device 11 can compensate for fluctuations in the Bragg reflection wavelength of the FBG with respect to a wider range of temperature changes than in the past.

  Further, the FBG device 11 can compensate the wavelength characteristics by appropriately setting the thermal expansion coefficients of the mounting sleeve 15 and the holder 19. Therefore, it is possible to obtain the effect of compensating the wavelength characteristics in a wide temperature range without complicating the apparatus and without increasing the manufacturing cost. Furthermore, since it is not necessary to supply power to compensate the wavelength characteristic, it can be said that it is preferable from the viewpoint of energy saving.

Here, the inventor performed a simulation in order to confirm the effect of wavelength characteristic compensation by the FBG device 11. In this simulation, the effect of wavelength characteristic compensation was compared between the FBG device 11 (hereinafter also referred to as device A) and the FBG device (hereinafter also referred to as device B) configured without the holder 19. These FBG apparatuses have the same configuration except for the presence or absence of the holder 19. And the optical fiber B mentioned above was used as the optical fiber 13, and the thermal expansion coefficient of the mounting sleeve 15 was set to −6.5 × 10 ⁻⁶ / ° C.

  The result of this simulation is shown in FIG. In FIG. 5, the horizontal axis indicates the ambient temperature in units of ° C. Further, the vertical axis shows the fluctuation amount of the Bragg reflection wavelength of the FBG in units of pm. Further, the result relating to the device A is shown with reference numeral 51. In addition, the result relating to the apparatus B is shown by reference numeral 53.

  From FIG. 5, it can be seen that in the high temperature range where the ambient temperature is 20 to 80 ° C., both the devices A and B are compensated for the variation of the Bragg reflection wavelength.

  Further, in the low temperature range where the ambient temperature is lower than 20 ° C., the device B not provided with the holder 19 is overcompensated. On the other hand, it can be seen that the device A including the holder 19 suppresses overcompensation in the low temperature range and compensates for the variation in the Bragg reflection wavelength.

11: FBG device 13: optical fiber 15: mounting sleeve 17: contact cushioning material 19: holder 19a: compensation adjusting portion 19b: coupling portion 19c: fixing portion 21: groove portion 23: adhesive

Claims (4)

An optical fiber with a built-in fiber Bragg grating,
A mounting sleeve for fixing the optical fiber and having a negative coefficient of thermal expansion;
Contact cushioning material,
A fiber Bragg grating device comprising: a holder having a positive thermal expansion coefficient sandwiched integrally with the mounting sleeve from the direction along the extending direction of the optical fiber via the contact cushioning material. . 2. The fiber Bragg grating device according to claim 1, wherein the holder wraps the mounting sleeve through the contact cushioning material from a direction orthogonal to an extending direction of the optical fiber. 3. The fiber Bragg according to claim 1, wherein a thermal expansion coefficient of the mounting sleeve is determined based on a wavelength variation rate of the fiber Bragg grating at an ambient temperature within a range of 20 to 80 ° C. 4. Grating device. The fiber Bragg grating has a wavelength variation rate of 9 to 10 pm / ° C. at an ambient temperature within a range of 20 to 80 ° C., and the mounting sleeve is −6.5 × 10 ⁻⁶ to −7.5 × 10 ^−6. The fiber Bragg grating device according to claim 3, which has a coefficient of thermal expansion within a range of / ° C.

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