JP2006337955A - Wavelength adjuster - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an undesirable variation in the reflection wavelength of a fiber Bragg grating with a high degree of precision. <P>SOLUTION: An wavelength adjuster for adjusting the reflection wavelength of a fiber Bragg grating comprises an optical fiber 102 in which a fiber Bragg grating 106 is formed, a temperature control device for controlling the temperature of the fiber Bragg grating 106, a base member 104 to which the optical fiber 102 is fixed, and a support means for supporting the base member 104, and has an expansion and contraction absorbing material intervening between the support means and the base member 104. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wavelength adjuster that adjusts the reflection wavelength of a fiber Bragg grating.

  In recent years, communication demand has increased rapidly due to the spread of the Internet, and high-speed and large-capacity networks using optical fibers are being developed. In such a high-speed, large-capacity optical network, wavelength division multiplexing (hereinafter also referred to as WDM) transmission technology is indispensable, and in particular, the optical carrier is made dense on the wavelength axis by narrowing the wavelength interval. A so-called high density WDM (Dense WDM, hereinafter also referred to as DWDM) system is attracting attention.

  In addition, optical code division multiplexing (hereinafter also referred to as OCDM) transmission system, which has high demultiplexing degree and communication security, and is expected to increase the wavelength utilization efficiency when used in combination with the WDM or DWDM system. Is also attracting attention. The OCDM system is a system for performing demultiplexing by modulating with a different code for each channel on the transmitting side and decoding with the same code as the transmitting side on the receiving side. The arrangement order of a plurality of wavelengths and each wavelength on the time axis is determined. There are known a wavelength hop / time spreading combination method (hereinafter also referred to as a wavelength hop method) used as a code, a phase code method using a relative phase difference of a diffused optical pulse train as a code, and the like.

  As an optical filter device in a WDM or DWDM system or an encoder / decoder in an OCDM system, one using a fiber Bragg grating (hereinafter also referred to as FBG) is known. The FBG is a device in which a refractive index change region, a so-called grating, is formed in a lattice shape in the core of an optical fiber, and has a characteristic of reflecting light of a specific wavelength. However, the reflection wavelength of the FBG varies greatly due to a change in temperature around the FBG (hereinafter also referred to as environmental temperature) due to the temperature dependence of the refractive index and the expansion and contraction of the optical fiber depending on the temperature. It has been known.

  As a method for suppressing the fluctuation of the reflection wavelength of the FBG due to the environmental temperature, for example, the method disclosed in Patent Document 1 can be cited. According to the method described in this document, an optical fiber having an FBG formed on a plate-like glass ceramic substrate having a negative thermal expansion coefficient is fixed. And the fluctuation | variation of the reflection wavelength of FBG by the change of environmental temperature is compensated with the fluctuation | variation amount of the reflection wavelength of FBG resulting from an optical fiber expanding / contracting according to expansion / contraction of a sheet glass ceramic substrate.

Special Table 2000-503415

  However, in particular, when FBG is used in the above encoder / decoder, transmission quality deteriorates if there is a deviation in the reflection wavelength of the FBG between the pair of encoder and decoder. Must match. The above method still causes wavelength fluctuations that can cause a wavelength difference between the encoder and the decoder that exceeds a wavelength difference that does not degrade the transmission quality.

  Therefore, the present invention has been made in view of such a problem, and an object of the present invention is to provide a wavelength adjuster capable of preventing undesired fluctuations in the reflection wavelength of the FBG with high accuracy. It is in.

  In order to solve the above problems, according to one aspect of the present invention, there is provided a wavelength adjuster for adjusting a reflection wavelength of a fiber Bragg grating, an optical fiber on which the fiber Bragg grating is formed; and a temperature of the fiber Bragg grating; A wavelength control device comprising: a temperature control device to be controlled; a base member to which an optical fiber is fixed; and a support means for supporting the base member; and a stretchable absorbing material interposed between the support means and the base member Is provided.

  According to the above invention, since the temperature of the FBG is controlled by the temperature control device, expansion and contraction of the optical fiber due to temperature change can be prevented by controlling the temperature of the FBG so as to be kept at a predetermined temperature. Further, even when the support means for supporting the base member to which the optical fiber is fixed expands and contracts, the expansion / contraction absorber interposed between the support means and the base member absorbs the expansion and contraction of the support means. Therefore, the expansion and contraction of the support means is not transmitted to the optical fiber fixed to the base member, so that the expansion and contraction of the optical fiber accompanying the expansion and contraction of the support means can be prevented. As a result, undesired fluctuations in the reflected wavelength of the FBG can be prevented with high accuracy. Further, if the temperature of the FBG is controlled to a desired temperature by the temperature control device, the reflected wavelength of the FBG can be set to a desired wavelength. In this case, since the reflected wavelength of the FBG changes only by temperature control by the temperature control device without being affected by the expansion and contraction of the support means, it can be guided to a desired wavelength with high accuracy. That is, the reflected wavelength of the FBG can be adjusted with high accuracy by temperature control by the temperature control device. For this reason, for example, even with respect to fluctuations in the wavelength of the light source, the wavelength can be matched by performing temperature control. The expansion and contraction of the support means can occur, for example, by expanding / contracting according to changes in environmental temperature and by applying stress.

  The stretchable absorbent material absorbs expansion / contraction of the support means accompanying a change in temperature. With this configuration, it is possible to prevent the expansion / contraction of the support means from being transmitted to the base member.

  The base member may be made of a low thermal expansion material. According to such a configuration, it is possible to suppress the expansion / contraction of the base member accompanying the change in the environmental temperature or the like. Therefore, the optical fiber fixed to the base member can be prevented from expanding and contracting due to the expansion / contraction of the base member.

  The base member may be configured to surround at least the outer periphery of the portion where the FBG of the optical fiber is formed. The expansion and contraction of the support means is absorbed by the expansion and contraction absorbent material, but there is a possibility that not all can be absorbed. Even in such a case, according to such a configuration, since the base member surrounds the optical fiber, transmission of expansion and contraction of the support means to the optical fiber is blocked by the base member.

  The support means may be one or both of a casing of the wavelength adjuster and a holder that supports the base member inside the casing.

  The holder supports the base member via the stretchable absorbent material.

  The temperature control device includes: a temperature sensor that detects the temperature of the base member; a thermo module that is in contact with the holder; a controller that controls the thermo module so that the temperature detected by the temperature sensor is maintained at a predetermined temperature; The thermo module may be configured to heat / cool the base member via the holder.

  According to the above configuration, the temperature of the optical fiber fixed to the base member can be controlled by controlling the temperature of the base member with the temperature sensor, the thermo module, and the controller. At this time, a holder may be interposed between the thermo module and the base member, and the base member may be heated / cooled via the holder. In this case, if the holder and the base member are in close contact with each other via the stretchable absorbent material, heat transfer between the holder and the base member is efficiently performed.

  The holder may be made of a highly heat conductive material. According to such a configuration, since heating / cooling by the thermo module is easily transmitted from the holder to the base member, the temperature of the base member can be adjusted without delay according to the control of the controller.

  The base member and the holder may be engaged at one place. According to such a configuration, the base member can be prevented from moving in the extending direction of the optical fiber. Further, by engaging at one place, the base member is prevented from being affected by the expansion / contraction of the holder at the engagement portion.

  The one place may be a central portion of the holder in the extending direction of the optical fiber. According to such a configuration, the engaging portion is provided in the central portion where the positional deviation is unlikely to occur even when the holder is expanded / contracted. Therefore, it is possible to prevent the base member from being affected by the expansion / contraction of the holder at the engaging portion. The engaging part may be constituted by a protruding part and a groove part. In that case, it is desirable that there is a gap between the protrusion and the groove in the engaged state.

  The wavelength adjuster may further include a heat conduction preventing member made of a low thermal conductivity material, and the base member may be configured to be surrounded by the holder and the heat conduction preventing member. As described above, the holder is interposed between the thermo module and the base member, and the heat conduction preventing member is preferably disposed away from the thermo module so as not to hinder the transfer of heat from the thermo module to the base member. . Note that the holder and the heat conduction preventing member may be integrally formed. According to such a configuration, since the heat conduction preventing member suppresses the change in environmental temperature from being transmitted to the base member, it is possible to prevent the temperature distribution from occurring in the base member.

  On the other hand, as described above, the support means may be a casing.

  Through holes for inserting the optical fiber are formed at both ends of the casing in the extending direction of the optical fiber. Both ends of the base member are respectively inserted into through holes formed at both ends of the casing. The base member may be supported via the stretchable absorbent material at the location. According to such a configuration, the base member is supported by inserting both ends of the base member into the through hole of the casing. And in the part of the through-hole of a casing, the expansion-contraction absorber is interposed between the casing and the base member inserted therethrough. Therefore, the expansion / contraction of the casing is not transmitted to the base member, and therefore the expansion / contraction of the casing is not transmitted to the optical fiber fixed to the base member.

  A gap between the through hole of the casing and the base member may be sealed with a stretchable absorbent material. According to such a configuration, since the through-hole of the casing is sealed, it is possible to prevent dust and moisture from entering the inside of the casing and prevent them from affecting the contained FBG.

  Both ends of the base member may protrude outward from the through hole of the casing. According to such a configuration, the expansion / contraction of the casing can be more reliably prevented from being transmitted to the optical fiber.

  As described above, according to the present invention, it is possible to provide a wavelength adjuster that can prevent undesired fluctuations in the reflected wavelength of the FBG with high accuracy.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
In the following description, the wavelength adjuster according to the present invention is applied to the wavelength adjuster 100 that can be used as an encoder / decoder in the phase code system OCDM. In an encoder / decoder in the phase code system OCDM, a superstructure FBG (Superstructure FBG, hereinafter also referred to as SSFBG) having a multipoint phase shift structure may be used. The SSFBG is a unit FBG that is arbitrarily set according to a code constituting a plurality of FBGs (hereinafter referred to as unit FBGs) having the same length and the same period of the refractive index change region (that is, the same reflection wavelength). An interval (including 0) is provided between them. In this case, even if the wavelength difference between the encoder and decoder in a pair is only a few pm (picometers), decoding cannot be performed accurately, so the wavelengths of the encoder and decoder must be matched with high accuracy. is there.

  The wavelength adjuster 100 according to the present embodiment can prevent undesired fluctuations in the reflection wavelength of the FBG. Therefore, if the wavelength adjuster 100 is applied to an encoder / decoder, the reflection wavelength of the unit FBG provided in each of the encoder and the decoder fluctuates, so that the wavelength shifts between the encoder and the decoder. Can be prevented.

  Further, the wavelength adjuster 100 according to the present embodiment can adjust the reflection wavelength of the FBG to a desired wavelength. Therefore, if the wavelength adjuster 100 is applied to an encoder / decoder, the wavelength of the encoder / decoder can be adjusted to a desired wavelength to cope with fluctuations in the light source.

  There are two factors that cause the FBG reflection wavelength to fluctuate: temperature and stress. The temperature is the temperature of the FBG, and the reflection wavelength varies with changes in the temperature of the FBG. Therefore, when the temperature around the FBG (environmental temperature) changes, the temperature change is transmitted to the FBG, and the reflection wavelength of the FBG changes. The stress is a stress applied to the optical fiber on which the FBG or the FBG is formed, and the reflection wavelength varies with the change of the stress. The stress includes stress in the radial direction of the optical fiber and stress in the extension direction of the optical fiber. According to the wavelength adjuster 100 according to the present embodiment, fluctuations in the reflected wavelength of the FBG due to stress transmission to the optical fiber accompanying expansion and contraction of the casing 110 can be suppressed. Further, it is possible to suppress undesired fluctuations in the reflected wavelength of the FBG due to temperature changes. Further, by controlling the temperature of the FBG while suppressing the reflection wavelength of the FBG due to a change in stress, the reflection wavelength of the FBG can be led to a desired wavelength. Hereinafter, the wavelength adjuster 100 will be described in detail.

  FIG. 1 is a perspective view schematically showing the external appearance of the wavelength adjuster 100. As shown in FIG. 1, the wavelength adjuster 100 includes a casing 110, a base member 104, and an optical fiber 102. The optical fiber 102 is surrounded by the base member 104. The base member 104 protrudes from both ends of the casing 110. Between the base member 104 and the casing 110, a first stretchable absorbent material 101 that absorbs expansion / contraction of the casing 110 is interposed.

  The configuration of the wavelength adjuster 100 will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view of the wavelength adjuster 100. The wavelength adjuster 100 includes an optical fiber 102 on which an SSFBG 106 is formed, a base member 104, a holder 108, a casing 110, a temperature sensor 112, a thermo module 116, a heat insulating material 118, and a temperature controller (not shown). Is mainly provided.

<Description of the relationship between each component>
First, the relationship between each component which comprises the wavelength tuner 100 is demonstrated.

  The optical fiber 102 on which the SSFBG 106 is formed is bonded to the base member 104 at two bonding portions 114 and fixed to the base member in a state where no stress such as tensile force or compressive force is applied. The adhesive portion 114 will be described later with reference to FIG. The optical fiber 102 may be in close contact with the base member with a material having high thermal conductivity such as silicone grease.

  The base member 104 is supported by the holder 108. At this time, the base member 104 and the holder 108 are arranged so that the SSFBG 106 formed on the optical fiber 102 fixed to the base member is positioned in the center of the holder 108 in the extending direction of the optical fiber 102. Is desirable. However, the SSFBG 106 may be arranged so as to be positioned in the holder 108 even if it is not in the central portion. A second stretchable absorbent material 103 is interposed between the base member 104 and the holder 108. The configuration of the portion where the holder 108 supports the base member 104 will be described in detail later with reference to FIG. Further, the base member 104 is engaged with the holder 108 at the engaging portion 124. The configuration of the engaging portion will be described in detail later with reference to FIG. Hereinafter, the extending direction of the optical fiber 102 in the holder 108 is also referred to as the longitudinal direction of the holder 108. Similarly, the extending direction of the optical fiber 102 in the casing 110 is also referred to as the longitudinal direction of the casing 110, and the extending direction of the optical fiber 102 in the base member 104 is also referred to as the longitudinal direction of the base member 104.

  The base member 104 is also supported by the casing 110. More specifically, through holes for inserting the optical fiber 102 are formed at both ends of the casing 110. In the wavelength adjuster 100, the optical fiber 102 is inserted into the through hole of the casing 110 while being fixed to the base member. That is, both ends of the base member 108 are also inserted through through holes formed at both ends of the casing 110, respectively. The base member 104 is supported by the casing 110 via the first stretchable absorbent material 101 at the positions of the through holes at both ends of the casing 110. The configuration of the portion where the casing 110 supports the base member 104 will be described in detail later with reference to FIG.

  A temperature sensor 112 is provided at the center of the base member 104. In addition, even if it is not a center part, if it is the vicinity of SSFBG106, it does not matter. The temperature sensor 112 detects the temperature of the base member 104. In FIG. 2, the temperature sensor 112 is disposed in the engaging portion 124, but may not be the engaging portion 124 as long as it is in the vicinity of the SSFBG 106 as described above.

  The holder 108 is in contact with the thermo module 116 and the heat insulating material 118. The holder 108 is fixed to the casing 110 with a screw 120 made of a low thermal conductivity material.

  The thermo module 116 is fixed to a part of the inner surface of the casing 110. The thermo module contacts the holder 108 and heats / cools the holder 108. A heat insulating material 118 is disposed on both sides of the thermo module 110, and the heat insulating material 118 is also fixed to the inner surface of the casing 110. The thermo module 116 and the temperature sensor 112 are connected to a temperature controller outside the casing 110.

  Next, the bonding portion 114 will be described with reference to FIG. At the bonding portion 114, the optical fiber 102 is bonded to the base member 104 with an adhesive 150. Fig.8 (a) shows the structure of the adhesion part 114 in case a base member is a cross-sectional concave shape. FIG. 8B and FIG. 8C show the configuration of the bonding portion 114 when the base member is cylindrical. When the base member has a concave cross-sectional shape, the optical fiber 102 is bonded to the base member 104 by the adhesive 150 while being placed in the concave portion of the base member 104 as shown in FIG. When the base member is cylindrical, as shown in FIG. 8C, the optical fiber 102 may be bonded with an adhesive 150 so as to be in contact with a part of the inside of the base member. As shown in FIG. 8B, the adhesive 150 may be interposed between the base member and the base member without direct contact. As the adhesive, an ultraviolet curable acrylic adhesive or an epoxy adhesive can be used.

  Next, referring to FIG. 4, the configuration and function of the portion where the holder 108 supports the base member 104 will be described. FIG. 4 is a cross-sectional view showing the AA section of FIG.

  As shown in FIG. 4, a second stretchable absorbent material 103 is interposed between the holder 108 and the base member 104. That is, the holder 108 supports the base member 104 via the second stretchable absorbent material 103. In other words, even if the base member 104 is in contact or in close contact, only the part to which the force is applied moves, and is mechanically fixed by welding, soldering, fixing with screws, bolts and pins, adhesion, or the like. No. The second stretchable absorbent material 103 absorbs the expansion / contraction of the holder 108 accompanying the temperature change. Therefore, the expansion / contraction of the holder 108 is not transmitted to the base member. An example of the second stretchable absorbent material 103 is silicone grease. If the base member 104 and the holder 108 are brought into close contact with each other through the silicone grease, not only the expansion / contraction of the holder 108 is absorbed by improving the lubricity therebetween, but also the heat conduction between the base member 104 and the holder 108. Efficiency can be increased. The second stretchable absorbent material 103 is not limited to silicone grease, and can absorb the expansion / shrinkage of the holder 108 and can bring the base member 104 and the holder 108 into close contact with each other. It may be a gel-like substance or a viscous substance. Furthermore, it is more preferable if it is a substance with high thermal conductivity.

  Next, with reference to FIG. 6, the configuration and function of the portion where the casing 110 supports the base member 104 will be described. FIG. 6 is a cross-sectional view showing the BB cut surface of FIG.

  As shown in FIG. 6, the base member 104 is inserted into the through hole formed in the casing 110, and the first stretchable absorbent 101 is interposed between the through hole and the base member. That is, the casing 110 supports the base member 104 via the first stretchable absorbent material 101 and is not mechanically fixed to the base member 104. And the 1st expansion-contraction absorber 101 absorbs expansion / contraction of the casing 110 accompanying a temperature change. Therefore, the expansion / contraction of the casing 110 is not transmitted to the base member.

  Further, a gap between the through hole of the casing 110 and the base member 104 inserted through the through hole is sealed with the first stretchable absorbent 101. By sealing the gap, foreign matter such as dust and moisture can be prevented from entering the casing 110. Examples of the first stretchable absorbent material 101 include silicone rubber. Since the silicone rubber is flexible even after being cured, the base member 104 and the casing 110 are not firmly fixed and the expansion / contraction of the casing 110 can be absorbed. The first stretchable absorbent material 101 is not limited to silicone rubber, has flexibility even after curing, can absorb expansion / contraction of the casing 110, and has a through hole and a base member. As long as it is a substance that can seal the gap between the two, a gel-like substance or a viscous substance may be used.

  Next, the configuration and function of the engaging portion between the base member 104 and the holder 108 will be described with reference to FIG.

  The engaging portion 124 includes a protruding portion 142 formed on the base member 104 and a groove portion 140 formed on the holder 108. As described above, the base member 104 is supported by the holder 104 and the casing 110, but is not mechanically fixed to any of them. Therefore, when the optical fiber 102 is pulled, the base member 104 may move in the extending direction of the optical fiber 102 and come out of the casing 110. Accordingly, the base member 104 is prevented from moving in the extending direction of the optical fiber 102 by inserting and engaging the protruding portion 142 of the base member 104 with the groove portion 140 of the holder 108.

  At that time, the holder 108 and the base member 104 must be engaged at one place. This is because the base member 104 is easily affected by the expansion / contraction of the holder 108 when engaged at a plurality of locations. For example, the base member 104 has two projections, the holder 108 has two grooves at intervals corresponding to the projections, and the projections are inserted into the respective grooves so that the base member 104 and the holder 108 are two. In the case of engaging at a place, if the position of each groove changes due to expansion / contraction of the holder 108 and the distance between the two grooves changes, the distance between the two protrusions of the base member 104 also changes accordingly. Instead, the base member 104 expands and contracts as a result. If there is only one engaging portion, the above problem does not occur, and the expansion / contraction of the holder 108 is caused by the second stretchable absorbent material 103 interposed between the base member 104 and the holder 108 also in the engaging portion 124. And is not transmitted to the base member.

  Further, in order to prevent the engagement portion 124 from transmitting the expansion / contraction of the holder 108 to the base member 104 more reliably, there is a gap of at least 0.5 mm between the projection portion 142 and the groove portion 140. Is desirable. This gap is also filled with the second expansion / contraction prevention material 103 as described above.

  Further, the engaging portion 124 may be disposed at the center portion of the holder 108 in the longitudinal direction. That is, the distances A and B from each end portion of the holder 108 in the longitudinal direction to the engaging portion 124 may be substantially the same. This is because when the holder 108 is heated / cooled uniformly, the holder 108 expands / contracts around the central portion in the longitudinal direction, and the central portion is not easily displaced even by expansion / contraction.

  Note that the configuration of the engaging portion 124 is not limited to the above. For example, the protruding portion may be formed on the holder 108 and the groove portion may be formed on the base member 104. Further, the number of grooves may be two or more.

<Description of each component>
In the above, the relationship between each component which comprises the wavelength regulator 100 was demonstrated. Next, each component will be described in detail.

  The casing 110 is made of copper whose surface is gold-plated, but is not limited to this. For example, an inexpensive and easily processable material such as aluminum can be used. The casing 110 in the present embodiment is box-shaped, and has a terminal portion including a pair of power supply terminals to the thermo module 11 ″ 6 and a pair of input terminals from the temperature sensor 112 on any side surface in the longitudinal direction. A temperature controller is connected through this terminal portion.

  The heat insulating material 118 is made of a glass epoxy material, but is not limited to this. For example, a low heat conductive material such as a peak material or mica can be used. It is also possible to remove the heat insulating material 118 and bridge and fix the holder 108 with a screw made of a low heat conductive material to achieve air heat insulation or vacuum heat insulation.

  The thermo module 116 includes a heating / cooling module using a Peltier element. In the present embodiment, the thermo module 116 is described as one, but a plurality of thermo modules 116 may be arranged in accordance with the shape and dimensions of the holder 108.

The base member 104 is made of a low thermal expansion material. Examples of the low thermal expansion material include invar and glass ceramic. The base member 104 is preferably made of a material having a thermal expansion coefficient of 1.2 × 10 ⁻⁶ / K or less. The shape of the base member 104 is desirably a shape surrounding the optical fiber 102 to be fixed. Although the expansion / contraction of the holder 108 and the casing 110 is absorbed by the expansion / contraction absorber, there is a possibility that not all of the expansion / contraction can be absorbed depending on the degree of expansion / contraction. Even in such a case, if the shape of the base member 104 surrounds the optical fiber 102, the rigidity of the base member is greater than the stress transmitted by the stretchable absorbent material. Transmission to the optical fiber 102 is interrupted. The base member 104 in this embodiment has a prismatic shape in which a groove for fixing the optical fiber 102 is formed and the cross section is concave. The shape of the base member 104 is not limited to a prismatic shape, and may be a cylindrical shape with a circular cross section as shown in FIG. As shown in c), the cross section may be V-shaped or U-shaped, or any other shape as long as it surrounds the optical fiber. The length of the base member 104 in the extending direction of the optical fiber 102 is equal to or longer than the length of the casing 102 in the extending direction of the optical fiber 102.

  The holder 108 is made of a highly heat conductive material. Examples of the highly heat conductive material include copper and aluminum. The holder 108 is preferably made of a material having a thermal conductivity of 398 W / (m · K) or more.

  The temperature sensor 112 is a thermistor, but is not limited to this, and for example, a thermocouple or a platinum thermal resistor can be used.

  The optical fiber 102 is obtained by forming an SSFBG 106 having a multi-point phase shift structure on a single mode optical fiber whose ultraviolet sensitivity is enhanced by adding germanium or the like to a core. FIG. 3 shows a schematic configuration of the SSFBG 61 when a 15-bit M sequence is used as a code string. In FIG. 3, the unit FBGs indicated by “A” to “P” are all equal in length and have the same refractive index modulation region period. Here, “λ / 4” shown in the units FBG “C” and “D” or between “G” and “H” is λ / 4 when the wavelength of the optical carrier wave is λ. The unit FBG is arranged with a corresponding interval, and “0” means that the adjacent unit FBGs are arranged in close contact with each other (that is, the interval is 0). Since the interval corresponding to λ / 4 is an 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 “ In contrast to the reflected pulses at “A”, “B” and “C”, the reflected pulses at the units FBG “D”, “E”, “F” and “G” are shifted in phase by π. .

<Description of operation and action>
In the above, each component which comprises the wavelength regulator 100 was demonstrated in detail. Next, the operation and action of the wavelength adjuster 100 will be described.

  The wavelength adjustment of the wavelength adjuster 100 is performed by changing the temperature of the optical fiber 102 including the SSFBG 106. More specifically, the wavelength adjuster 100 controls the temperature of each unit FBG included in the SSFBG 106, thereby adjusting the reflection wavelength of the FBG and adjusting the wavelength of the entire SSFBG 106.

  When the set temperature is set to a predetermined value in the temperature controller, the temperature controller determines that the temperature detected by the temperature sensor 112 is equal to the set value according to the difference between the set value and the temperature detected by the temperature sensor 112. Control heating / cooling of Heat from the thermo module 116 is transmitted to the base member 104 through the holder 108. That is, the thermo module 116 heats / cools the base member 104 via the holder 108. Therefore, the base member 104 is kept constant at a predetermined temperature by the control of the thermo module 116 by the temperature controller.

  Here, since the high thermal conductivity holder 108 that transmits the heat of the thermo module 116 to the base member 104 covers the base member 108, the occurrence of temperature distribution in the longitudinal direction of the base member 104 can be suppressed.

  Further, the base member 104 is not mechanically fixed to the holder 108 and is only supported via the second stretchable absorbent material 103. Therefore, the heating / cooling by the thermo module 116 and the expansion / contraction of the holder 108 caused by the change in environmental temperature are not transmitted to the base member 104. Further, the base member 104 is not mechanically fixed to the casing 110 but is only supported via the first stretchable absorbent material 101. Therefore, the expansion / contraction of the casing 110 generated by the change in the environmental temperature is not transmitted to the base member 104. Further, since the base member 104 is made of a low thermal expansion material, the base member 104 itself does not expand / contract. Since the SSFBG 106 included in the optical fiber 102 is fixed to the base member 104, the expansion / contraction of the holder 108 and the casing 110 is not transmitted to the SSFBG 106. That is, the stress applied to the SSFBG 106 does not change depending on the expansion / contraction of the holder 108 or the casing 110. Therefore, even if the holder 108 or the casing 110 expands / contracts, the reflection wavelength of each unit FBG of the SSFBG 106 does not change. The wavelength does not fluctuate.

  Therefore, the wavelength of the SSFBG 106 varies only with a change in temperature. The temperature of the SSFBG 106 is controlled to be maintained at a predetermined temperature by a temperature control device including a temperature sensor 112, a thermo module 116, and a temperature controller. Therefore, the wavelength of the SSFBG 106 can be kept at a predetermined wavelength by temperature control by the temperature control device. Further, the wavelength of the SSFBG 106 can be guided to a desired wavelength by changing the temperature of the SSFBG 106 with the temperature control device.

When the temperature of the SSFBG 106 changes, the effective refractive index n _eff of each grating and the grating pitch Λ in the unit FBG constituting the SSFBG 106 change according to the temperature change.

The fluctuation amount Δλ _{B_Temp} of the center wavelength due to the temperature change is obtained by the following formula 1 (for example, refer to Andrea Othonos and Kyriacos Kalli: Fiber Bragg Gratings).

・・・（数式１）

... (Formula 1)

In Equation 1, ΔT represents the temperature change width, and dΛ / dT represents the thermal expansion coefficient of the optical fiber.
The reflection center wavelength fluctuation amount Δλ _{B_Temp} obtained by Equation 1 is the fluctuation amount toward the long wavelength side when the temperature of the base member 104 is increased by the temperature controller, and the short wavelength side when the temperature of the base member 104 is decreased. The amount of change to

  FIG. 9 shows wavelength adjustment characteristics according to the set temperature of the temperature controller in the wavelength adjuster 100 according to the present embodiment. The horizontal axis in FIG. 9 is the set temperature of the temperature controller, and the vertical axis indicates the change amount Δλ of the reflected wavelength of the SSFBG 106. In FIG. 9, points indicated by black triangles are measurement points, and values obtained by smoothing these measurement points are indicated by straight lines 160. As can be seen from FIG. 9, the wavelength of the wavelength adjuster 100 can be adjusted by 300 pm or more at a set temperature of 15 ° C. to 45 ° C. For this reason, for example, wavelength adjustment according to fluctuations in the light source wavelength is sufficiently possible.

  FIG. 10 shows the ambient temperature dependence of the reflected wavelength when the temperature controller set temperature is 45 ° C. in the wavelength adjuster 100 according to the present embodiment. The horizontal axis of FIG. 10 indicates the environmental temperature, and the vertical axis indicates the change amount Δλ of the reflection wavelength of the SSFBG 106. In FIG. 10, points indicated by black triangles are measurement points, and values obtained by smoothing those measurement points are indicated by straight lines 170. As can be seen from FIG. 10, the maximum wavelength fluctuation amount in the range from 0 ° C. to + 55 ° C. is 5 pm, and the wavelength fluctuation rate is 0.01 pm per 1 ° C. environmental temperature fluctuation.

  As can be seen from FIGS. 9 and 10, if the temperature controller can set the temperature in units of 0.1 ° C., not only the reflection center wavelength of the wavelength adjuster 100 can be adjusted with the wavelength adjustment resolution of 1 pm, but also the environmental temperature can be adjusted. Even if it fluctuates, the reflection wavelength can be stably maintained without readjusting the set temperature by the temperature controller.

  As described above, according to the wavelength adjuster 100 according to the present embodiment, the wavelength adjustment width is 300 pm or more, and adjustment to an arbitrary wavelength can be performed with a wavelength adjustment resolution of 1 pm or less. Due to the wavelength adjustment capability of the wavelength adjuster 100, readjustment of minute wavelength fluctuations caused by changes in the environmental temperature and arbitrary wavelength adjustment according to fluctuations in the light source wavelength can be performed. Further, when the wavelength adjuster 100 is used as a phase encoder and a phase decoder, the wavelength of the phase encoder and the phase decoder forming a pair is highly accurate without being affected by the manufacturing error of the SSFBG 106 included in the wavelength adjuster 100. Can match.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the second embodiment, the wavelength adjuster according to the present invention will be described by applying it to a wavelength adjuster 200 that can be used as an encoder / decoder in the phase code system OCDM. The wavelength adjuster 200 according to the second embodiment has almost the same configuration and function as the wavelength adjuster 100 according to the first embodiment, but the base member is made of a material with high thermal conductivity and a material with low thermal conductivity. A portion surrounded by a cover made of is different from the wavelength adjuster 100. In the following description, components having substantially the same configuration and function as those of the wavelength adjuster 100 are denoted by the same reference numerals in the drawing, description thereof is omitted, and portions different from the wavelength adjuster 100 are described.

<Description of configuration>
In the wavelength adjuster 200, the base member 104 is supported by the holder 208 via the second stretchable absorbent material 103. In the first embodiment, the holder 108 has a shape surrounding the entire outer periphery of the base member. In the present embodiment, the holder 208 has a box shape with an opening at the top, and a base member is placed on the bottom. The holder 208 has a shape surrounding a part of the outer periphery of the base member. The opened upper portion of the holder 208 is closed by a cover 210 which is an example of a heat conduction preventing member. The holder 208 is made of a material having high thermal conductivity, like the holder 108 of the first embodiment. The cover 210 is made of a low thermal conductivity material. Examples of the low thermal conductivity material include a glass epoxy material and a peak material. The cover 210 is preferably made of a material having a thermal conductivity of 0.8 W / (m · K) or less.

  12A is a cross-sectional view taken along the line CC of FIG. As shown in FIG. 12A, the holder 208 has a concave cross section and surrounds the outer periphery other than the upper portion of the base member 104. The second stretchable absorbent material 103 is interposed between the holder 208 and the base member 104 as in the first embodiment, and the holder 208 supports the base member 104 via the second stretchable absorbent material 103. In addition, heat from the thermo module 116 is transmitted to the base member 104.

  The upper portion of the holder 208 and the base member 104, that is, the opposite side of the contact portion (bottom surface) of the holder 208 with the thermo module 116 is covered with a cover 210. The second stretchable absorbent material 103 is also interposed between the cover 210 and the base member 104 and the holder 208, and the cover 210 and the base member 104, and the cover 210 and the holder 208 are placed via the second stretchable absorbent material 103. Are in close contact. Accordingly, the base member 104 is surrounded by the holder 208 and the cover 210 via the second stretchable absorbent material 103. According to such a configuration, it is possible for the thermo module 116 to heat / cool the base member 104 via the holder 208, and to prevent the cover 210 from transmitting a change in environmental temperature to the base member 104. it can. Therefore, compared with the first embodiment, the occurrence of the temperature distribution in the longitudinal direction of the base member 104 can be more reliably suppressed.

  In the above description, the heat conduction preventing member is configured as the cover 210 separately from the holder 208, but the holder 208 and the heat conduction preventing member may be integrally formed. For example, as shown in FIG. 12B, the portion from the contact portion with the thermo module 116 to the bottom surface of the base member 104 (region indicated by reference numeral 208a) is made of a material having high thermal conductivity so as to correspond to the holder. The portion surrounding the side surface and the upper portion of the base member 104 (region indicated by reference numeral 210a) may be made of a low heat conductive material so as to correspond to the heat conduction preventing member. The ratio of the portion made of the high thermal conductivity material and the portion made of the low thermal conductivity material can be set as appropriate, but at least heat from the thermo module 116 is efficiently transmitted to the base member 104. The region from the portion in contact with the thermo module 116 to the portion reaching the part of the base member 104 is preferably made of a material having high thermal conductivity.

<Description of operation and action>
FIG. 13 shows wavelength adjustment characteristics depending on the set temperature of the temperature controller in the wavelength adjuster 200 according to this embodiment. In FIG. 13, the horizontal axis indicates the set temperature of the temperature controller, and the vertical axis indicates the change amount Δλ of the reflected wavelength of the SSFBG 106. In FIG. 13, points indicated by black triangles are measurement points, and values obtained by smoothing these measurement points are indicated by straight lines 260. As can be seen from FIG. 13, the reflection wavelength of the wavelength adjuster 200 can be adjusted by 300 pm or more when the set temperature is 15 ° C. to 45 ° C. For this reason, for example, wavelength adjustment according to fluctuations in the light source wavelength is sufficiently possible.

  FIG. 14 shows the ambient temperature dependence of the reflected wavelength when the set temperature of the temperature controller in the wavelength adjuster 200 according to this embodiment is 45 ° C. The horizontal axis of FIG. 14 indicates the environmental temperature, and the vertical axis indicates the change amount Δλ of the reflection wavelength of the SSFBG 106. In FIG. 14, points indicated by black triangles are measurement points, and values obtained by smoothing these measurement points are indicated by a straight line 270. As can be seen from FIG. 14, the maximum wavelength fluctuation amount in the range of the environmental temperature from −10 ° C. to + 55 ° C. is 7 pm, and the wavelength fluctuation rate is 0.05 pm per 1 ° C. of the environmental temperature fluctuation.

  As can be seen from FIGS. 13 and 14, if the temperature controller in this embodiment can set the temperature in units of 0.1 ° C., the reflection center wavelength of the wavelength adjuster 200 can be adjusted with the wavelength adjustment resolution of 1 pm. Even when the environmental temperature fluctuates, the reflection wavelength can be stably maintained without readjusting the set temperature by the temperature controller.

  In the wavelength adjuster 200 according to the present embodiment, the base member 104 is uniformly heated / cooled by heat conduction from the holder 208, and the cover 210 suppresses temperature changes due to heat radiation through the casing 110. Generation of temperature distribution in the longitudinal direction of the member 104 is suppressed. As described above, the SSFBG 106 included in the wavelength adjuster 200 of the present embodiment is composed of a plurality of unit FBGs. The temperature distribution in the longitudinal direction of the base member 104 means that the temperature of each unit FBG is different. In this case, the encoding wavelength (phase decoder, such as the reflection wavelength of each unit FBG is different, the reflection wavelength of the wavelength adjuster 200 is changed, or the relative phase difference of the optical pulse train to be changed is changed. In this case, the decoding characteristics) are different.

  Here, in the wavelength adjuster 200 according to the present embodiment, when the temperature distribution on the surface of the base member 104 is examined when the set temperature of the temperature controller is 25 ° C., 35 ° C., and 45 ° C. at the environmental temperature of 25 ° C., FIG. As shown in FIG. In the figure, the measured value in the case of the base member 104 alone is shown as a comparison target. The horizontal axis of FIG. 15 shows the set temperature of the temperature controller, and the vertical axis shows the maximum temperature difference of the base member 104 (the measured temperature of the hottest portion and the measured temperature of the coldest portion of the surface of the base member 104). Difference value). In FIG. 15, measurement points of the temperature difference of the surface temperature of the base member 104 in the wavelength adjuster 200 are indicated by black squares, and values obtained by smoothing these measurement points are indicated by straight lines 282. Further, the measurement points of the temperature difference in the case of the base member 104 alone are indicated by black triangles, and the values obtained by smoothing these measurement points are indicated by the straight line 280. As can be seen from FIG. 15, the base member 104 alone has a maximum temperature difference when the set temperature is 45 ° C., and the temperature difference is about 9 ° C. On the other hand, the temperature difference between the base member 104 in the wavelength adjuster 200 of the present embodiment, that is, the base member 104 surrounded by the holder 208 and the cover 210 is 0.1 ° C. at the maximum. This result agrees with the fact that the reflection wavelength is stable against environmental temperature fluctuations as shown in FIG.

  Consider the influence of the temperature distribution state of the base member 104 on the encoding / decoding operation when the wavelength adjuster 200 is used as a phase encoder / phase decoder. The temperature distribution is not set in the base member 104 on the phase encoder side, and the temperature distribution is given to the base member 104 on the phase decoder side, and the ratio of the autocorrelation peak to the sub-peak in the decoded waveform (hereinafter referred to as P / W and 16 is obtained from calculation (the light source wavelength and the reflection wavelength of the phase encoder and the phase decoder match), as shown in FIG. In FIG. 16, the horizontal axis represents the maximum temperature difference of the base member 104, and the vertical axis represents the ratio of the autocorrelation peak to the sub peak. In FIG. 16, the points indicated by black triangles are calculated values. As can be seen from FIG. 16, P / W decreases as the temperature distribution of the base member 104 increases, and P / W <1 when the temperature distribution is between 3 ° C. and 4 ° C. Since P / W is the ratio of the autocorrelation peak to the sub-peak as described above, it is desirable that P / W is large in order to reliably perform the decoding operation.

  As can be seen from FIG. 15, according to the wavelength adjuster 200 of the present embodiment, no temperature distribution occurs in the base member 104 even when the environmental temperature changes. In particular, even when there is a difference between the set temperature of the temperature controller and the environmental temperature, the temperature in the longitudinal direction of the base member 104 can be kept uniform, that is, the temperature of each unit FBG constituting the SSFBG 106 is kept uniform. be able to. Therefore, as can be seen from FIG. 16, when the wavelength adjuster 200 is used as an encoder / decoder, the encoding characteristic / decoding characteristic has an effect depending on the change of the environmental temperature or the difference between the set temperature and the environmental temperature. Not.

  As described above, in the wavelength adjuster 200 of this embodiment, for example, even when the environmental temperature becomes lower than the set temperature of the temperature controller, the temperature of the SSFBG 106 is kept uniform, and the wavelength is adjusted to an arbitrary wavelength without affecting the encoding characteristics. Adjustment and stable maintenance of the wavelength.

  As described above, according to the wavelength adjuster 200 according to the present embodiment, the wavelength adjustment width is 300 pm or more, and adjustment to an arbitrary wavelength can be performed with a wavelength adjustment resolution of 1 pm or less. Further, even if the set temperature of the temperature controller is changed in order to adjust the wavelength, the temperature of the SSFBG 106 can be kept uniform, so that the encoding characteristics / decoding characteristics are not affected. Due to the wavelength adjustment capability of the wavelength adjuster 100, readjustment of minute wavelength fluctuations caused by changes in the environmental temperature and arbitrary wavelength adjustment according to fluctuations in the light source wavelength can be performed. Furthermore, the wavelength of the phase encoder and the phase decoder forming a pair can be matched with high accuracy without being affected by the manufacturing error of the SSFBG 106 included in the wavelength adjuster 100.

  As described above, the wavelength adjuster 100 and the wavelength adjuster 200 according to the present embodiment fix the optical fiber on which the FBG is formed to the base member, and extend the base member to the holder and the casing, which are support means. By supporting it through an absorber so that it is not mechanically fixed to either the holder or the casing, the expansion / contraction of the holder and the casing is prevented from being transmitted to the optical fiber. Therefore, the stress applied to the optical fiber does not fluctuate with the expansion / contraction of the holder or the casing, and the FBG does not fluctuate the reflection wavelength due to the change of the stress. In addition, since the temperature of the FBG is controlled by the temperature control device, by keeping the temperature of the FBG constant, the FBG does not change in the reflection wavelength due to the temperature change. Therefore, according to the wavelength adjuster 100 and the wavelength adjuster 200 according to the present embodiment, it is possible to prevent undesired fluctuations in the reflected wavelength of the FBG.

  Further, the wavelength adjuster 100 and the wavelength adjuster 200 according to the present embodiment can adjust the reflected wavelength of the FBG to a desired wavelength by changing the temperature of the FBG to a desired temperature by the temperature control device.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are of course within the technical scope of the present invention. Understood.

  For example, in the said embodiment, although the base member is supported by both the holder and the casing, it is not limited to this example. The base member may be supported by either the holder or the casing. In other words, the base member may be supported by the holder and the casing may be omitted, or the base member may be supported by the casing and the holder may be absent.

  In the above embodiment, the casing and the holder have a prismatic shape with a square cross section. However, the present invention is not limited to the above example, and the casing and the holder may have a circular shape with a circular cross section. The shape may be a polygon such as a triangle or a pentagon.

  Moreover, in the said embodiment, although the both ends of a base member have each protruded from each through-hole formed in the both ends of a casing, it is not limited to the said example. Even if it does not protrude, it is only necessary that the positions of both ends of the base member reach the same position as the outer surface of the casing in each through hole of the casing. Accordingly, the length of the base member in the extending direction of the optical fiber may be equal to or longer than the length between the through holes at both ends of the casing.

  In the above embodiment, it has been described that the wavelength adjuster according to the present invention can be used as a phase encoder / phase decoder in a phase code system OCDM. However, the present invention is not limited to this. For example, an encoder in a wavelength hop system OCDM is used. The wavelength adjuster of the present invention can be used as a decoder device, a filter device in a WDM system, and the like.

It is a perspective view which shows the external appearance of the wavelength adjuster concerning 1st, 2nd embodiment of this invention. It is sectional drawing of the wavelength adjuster concerning 1st Embodiment. It is explanatory drawing which shows the structure of SSFBG in the embodiment. It is sectional drawing of the AA cut surface of FIG. It is explanatory drawing which shows the modification of the shape of the base member in the embodiment. It is sectional drawing of the BB cut surface of FIG. It is explanatory drawing which shows the base member and the engaging part of a holder in the embodiment. It is explanatory drawing which shows the adhesion part of the base member and optical fiber in the embodiment. It is a graph which shows the wavelength variation | change_quantity of the wavelength regulator accompanying the change of setting temperature in the same embodiment. It is a graph which shows the wavelength variation | change_quantity of the wavelength regulator accompanying the change of environmental temperature in the same embodiment. It is sectional drawing of the wavelength adjuster concerning 2nd Embodiment. It is sectional drawing of the CC cut surface of FIG. It is a graph which shows the wavelength variation | change_quantity of the wavelength regulator accompanying the change of setting temperature in the same embodiment. It is a graph which shows the wavelength variation | change_quantity of the wavelength regulator accompanying the change of setting temperature in the same embodiment. It is a graph which shows the maximum temperature difference of the base member with the change of preset temperature in the same embodiment. It is a graph which shows the relative P / W value accompanying the maximum temperature difference of a base member in the same embodiment.

Explanation of symbols

100, 200 Wavelength Tuner 101 First Stretch Absorber 102 Optical Fiber 103 Second Stretch Absorber 104 Base Member 106 SSFBG
108, 208 Holder 110 Casing 112 Temperature sensor 116 Thermo module 124 Engagement part 210 Cover

Claims (15)

A wavelength adjuster for adjusting the reflection wavelength of the fiber Bragg grating;
An optical fiber on which the fiber Bragg grating is formed;
A temperature control device for controlling the temperature of the fiber Bragg grating;
A base member to which the optical fiber is fixed;
Support means for supporting the base member;
And a stretchable absorber is interposed between the support means and the base member.   The wavelength adjuster according to claim 1, wherein the stretchable absorber absorbs expansion / contraction of the support means accompanying a change in temperature.   The wavelength adjuster according to claim 1, wherein the base member is made of a low thermal expansion material.   The wavelength adjuster according to claim 1, wherein the base member surrounds at least an outer periphery of a portion of the optical fiber where the fiber Bragg grating is formed.   5. The method according to claim 1, wherein the support means is one or both of a casing for the wavelength adjuster and a holder for supporting the base member inside the casing. Wavelength adjuster as described.   6. The wavelength adjuster according to claim 5, wherein the support means is a holder that supports the base member via the stretchable absorber. The temperature control device is:
A temperature sensor for detecting the temperature of the base member;
A thermo module in contact with the holder;
A controller for controlling the thermo module so that the temperature detected by the temperature sensor is maintained at a predetermined temperature;
The wavelength adjuster according to claim 6, wherein the thermo module heats / cools the base member via the holder.   The wavelength adjuster according to claim 7, wherein the holder is made of a material having high thermal conductivity.   The wavelength adjuster according to claim 7 or 8, wherein the base member and the holder are engaged at one place.   The wavelength adjuster according to claim 9, wherein the one place is a central portion of the holder in the extending direction of the optical fiber. A heat conduction prevention member made of a low thermal conductivity material;
The wavelength adjuster according to claim 7, wherein the base member is surrounded by the holder and the heat conduction preventing member.   6. The wavelength adjuster according to claim 5, wherein the supporting means is the casing. At both ends of the casing in the extending direction of the optical fiber, through holes for inserting the optical fiber are formed,
Both ends of the base member are respectively inserted into the through holes at both ends of the casing,
The wavelength adjuster according to claim 12, wherein the casing supports the base member via the stretchable absorbent material at the location of the through hole.   The wavelength adjuster according to claim 13, wherein a gap between the through hole of the casing and the base member is sealed by the stretchable absorber. The wavelength adjuster according to claim 13 or 14, wherein both ends of the base member protrude outward from the through hole of the casing.

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