JP2007058161A - Optical isolator and optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical isolator designed such that an isolation characteristic change caused by a sudden temperature change is restrained and cost performance is excellent; and to provide an optical module having the optical isolator. <P>SOLUTION: The optical isolator X1 comprises a composite element 20 including a Faraday rotator 21 and polarizers 22 and 23; and a support substrate 10 for supporting the composite element 20. The support substrate 10 is composed of a composite substrate that includes: a first substrate 11 disposed at the side of the composite element 20 and containing metal; and a second substrate 12 having heat conductivity lower than that of the first substrate 11 and containing a nonmetal composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical isolator used in optical communication technology and an optical module having the optical isolator.

  Optical isolators are used in optical amplifiers, semiconductor laser devices, and the like. The optical isolator has a function of transmitting light incident from the forward direction and blocking light incident from the reverse direction. For example, the relative angle of two polarizers is set to about 45 °, A Faraday rotator with a Faraday rotation angle set to about 45 ° is inserted between them and fixed to each other.

  In recent years, there has been a strong demand for miniaturization, mass production, and cost reduction for optical isolators, and an optical isolator 80 configured as shown in FIG. 8 has been developed as a countermeasure. The optical isolator 80 includes a flat alignment substrate 81, an optical isolator element 85 including a Faraday rotator 82 and two polarizers 83 and 84, and two rectangular parallelepiped magnets 86. 86 is bonded and fixed on the alignment substrate 81 with alloy solder. An optical isolator 80 having such a configuration is disclosed in Patent Document 1, for example.

FIG. 9 is a schematic sectional view showing an LD (laser diode) module 90 including the optical isolator 80. The LD module 90 includes a submount 92 for mounting the LD chip 91, a thermoelectric cooling device TEC (Thermoelectric Cooler) 93 for controlling the temperature of the LD chip 91, and a receptacle for receiving light oscillated from the LD chip 91. Lenses 95 and 96 for transmitting to the lens 94, a lens holder 97 for holding the lens 96, a sleeve 98 for optically aligning the receptacle 94 in the optical axis direction, an optical isolator 80, an LD chip 91, and the like. And a package 99 for storage. The optical isolator 80 is directly mounted on the TEC 93.
JP-A-10-227996

  Since the above-described optical isolator 80 is directly mounted on the TEC 93, it is susceptible to a temperature change of the TEC 93. Further, as shown in FIG. 10, the optical isolator 80 has a temperature dependency in the isolation characteristic that blocks light in the reverse direction. Therefore, in order to stabilize the light output and wavelength from the LD chip 91, it is necessary to control the temperature fairly accurately by the TEC 93.

  In addition, it is necessary to increase the transmission capacity due to the development of today's communication industry. In order to cope with this increase in transmission capacity, a plurality of types of LD modules having an oscillation wavelength of 20 nm intervals in a certain wavelength range are provided. Multiplex communication is taking place. Therefore, it is necessary to mount an optical isolator corresponding to each wavelength in each LD module having a different wavelength, and it is necessary to prepare a polarizer and a Faraday rotator according to each wavelength. Accordingly, there is a problem that the cost is high as a result, since the product management is complicated and the parts cannot be shared.

  Therefore, it is conceivable to use an optical isolator common to a plurality of wavelengths. However, when an optical isolator used at an oscillation wavelength of 1550 nm is used at 1530 nm and 1570 nm, the isolation lower limit standard is set at 25 ° C. as shown in FIG. The above-mentioned optical isolator mounted directly on the TEC can be configured to be satisfactory, but when the temperature rises rapidly to + 5 ° C. or more due to overshoot as shown in FIG. If the optical isolator used at the wavelength of 1570 nm falls below the lower limit of the standard and falls sharply to -5 ° C or higher, the optical isolator used at the oscillation wavelength of 1530 nm falls below the lower limit of the standard. Unreflected reflected return light passes through the optical isolator to the LD chip. Ri, causes the light output variations, transmission characteristics caused deteriorates.

  Accordingly, an object of the present invention is to provide an optical isolator excellent in cost performance and an optical module including the optical isolator while suppressing variations in isolation characteristics due to a rapid temperature change.

  As a result of intensive studies in view of the above-described problems, the present inventors have found that, when an optical isolator element is placed on a TEC via a support substrate, the temperature change due to the TEC can be mitigated from the support substrate. The TEC overshoot suppresses the optical isolator from falling below the lower limit of the standard, and the reflected return light passing through the optical isolator in the reverse direction is reduced, whereby the optical output can be maintained constant. The invention has been completed.

  The present invention includes a composite element including a Faraday rotator and a polarizer, and a support substrate for supporting the composite element. The support substrate is located on the composite element side and includes a metal. An optical isolator is a composite substrate having a first substrate and a second substrate having a lower thermal conductivity than the first substrate and including a non-metallic composition.

  Further, the present invention is characterized in that the first substrate has a plurality of convex portions on at least one of the surface on the composite element side and the surface on the second substrate side.

  The present invention also provides an optical isolator characterized in that a low thermal conductivity material having a lower thermal conductivity than the first substrate is disposed between the convex portions of the first substrate.

  The present invention also provides an optical isolator, wherein the support substrate has irregularities on at least a part of a side surface of the support substrate.

  Further, the present invention is characterized in that the Faraday rotator includes a Bi-substituted garnet.

  The optical module of the present invention includes a stub optically connected to a plug inserted from the outside, a sleeve for obtaining alignment between the plug and the stub, and light toward the stub. And an optical element for receiving light via the stub, and the optical isolator optically coaxial with the stub and the optical element.

  An optical isolator according to the present invention includes a first substrate having a support substrate positioned on the composite element side and including a metal, and a second substrate having a lower thermal conductivity than the first substrate and including a non-metallic composition. For example, when the support substrate is arranged so as to be in contact with the thermoelectric cooling device with a rapid temperature change, when the heat transfer cooling device has a sudden temperature change due to overshoot However, since the heat transfer to the optical isolator is delayed, fluctuations in the isolation characteristics of the optical isolator can be suppressed. Further, since the optical isolator mounted on the LD module having a plurality of wavelengths can be shared, a low-cost optical isolator can be obtained.

  In the support substrate, it is preferable that the first substrate has a plurality of convex portions on at least one of the surface on the composite element side and the surface on the second substrate side. By adopting such a configuration, the contact area between the first substrate 11 and the composite element 20 or the first substrate 11 and the second substrate is reduced, so that a sudden temperature change occurs due to overshoot of the thermoelectric cooling device. The heat transmitted to the composite element 20 through the first substrate can also be suppressed.

  In addition, it is preferable that the support substrate is provided with a low thermal conductivity material having a lower thermal conductivity than the first substrate between the convex portions of the first substrate. With such a configuration, the composite element 20 or the second substrate can be supported on the surface of the low thermal conductive material 11b with the above-described effect of suppressing excessive heat transfer. Alternatively, the second substrate can be fixed with high accuracy.

  Moreover, it is preferable that the said support substrate has an unevenness | corrugation in the side surface of the 1st board | substrate with a large thermal conductivity at least. By providing unevenness on the side surface of the substrate having high thermal conductivity to increase the surface area, it is possible to promote heat dissipation from the substrate, delay thermal conduction to the optical isolator, and suppress variation in isolation characteristics.

  In the optical isolator according to the present invention, the Faraday rotator described above may include Bi-substituted garnet or YIG garnet, and the first substrate may include metal and / or ceramics. It is preferable to use a Bi-substituted garnet for the Faraday rotator because the thickness of the Faraday rotator can be reduced and the optical isolator can be reduced in size.

  The present invention also provides the above-described optical isolator, a stub optically connected to the plug, a sleeve for obtaining alignment between the plug and the stub, and emitting light toward the stub. Or an optical element for receiving light derived through the stub. By mounting the above-described optical isolator, it is possible to provide a low-cost LD module having excellent transmission characteristics.

  FIG. 1 is a schematic perspective view showing an optical isolator X1 according to this embodiment. The optical isolator X1 includes a support substrate 10, a composite element 20, and two magnets 30.

  The support substrate 10 is a member for mounting and integrating the composite element 20 and the magnet 30 and has a substantially rectangular shape. The support substrate 10 in the present embodiment includes a first substrate 11 and a second substrate 12, and has a configuration in which the first substrate 11 and the second substrate 12 are bonded.

  The first substrate 11 constitutes a portion of the support substrate 10 that is located on the side where the composite element 20 and the magnet 30 are mounted. The material constituting the first substrate 11 is preferably a material whose thermal expansion coefficient approximates the thermal expansion coefficient of the Faraday rotator 21 of the composite element 20 described later, for example, 50 Ni—Fe (thermal conductivity: 16. 74 W / m · K), SUS430 (thermal conductivity: 27.21 W / m · K), SUS303 (thermal conductivity: 16.33 W / m · K), SF20T (thermal conductivity: 26.1 W / m · K) ) And the like. The optical isolator X1 made of such a material is suitable for stabilizing its optical characteristics. As a manufacturing method of the first substrate 11 in the case where a metal is adopted as a material constituting the first substrate 11, for example, precision processing such as cutting and end mill, MIM molding, and the like can be given.

  The 2nd board | substrate 12 comprises the site | part located in the side directly joined with respect to the thermoelectric cooling apparatus in the support substrate 10, for example. As a material constituting the second substrate 12, it is possible to mitigate the influence caused by a rapid temperature change on the mounting target side such as a thermoelectric cooling device on the composite element 20 mounted on the first substrate 11 side. Those having as low a thermal conductivity as possible are preferable. For example, quartz glass (thermal conductivity: 1.9 W / m · K) and zirconia ceramics (thermal conductivity: 3.77 W / m · K) are desirable.

  The bonding surface of the first substrate 11 with the second substrate 12 and the bonding surface of the second substrate 12 with the first substrate 11 are bonded to increase the bonding strength between the first substrate 11 and the second substrate 12. Roughening treatment, shot blasting treatment, and satin treatment for the purpose of increasing the area and obtaining the anchor effect are preferably performed. In addition, as a joining material for joining the 1st board | substrate 11 and the 2nd board | substrate 12, various resin, such as an epoxy resin, metal solder, low melting glass, etc. are mentioned.

  The composite element 20 is a member including a Faraday rotator 21 and two polarizers 22 and 23, and is a support substrate via a bonding material (various resins such as epoxy resin, metal solder, low-melting glass, etc.). It is mounted on ten first substrates 11. Specifically, the polarizers 22 and 23 are bonded and integrated with the Faraday rotator 21 by a transparent adhesive (for example, trade name: 353-ND, manufactured by Epotec). The Faraday rotator 21 is a member having a function of rotating a polarization direction of incident light by a predetermined angle by applying a predetermined magnetic field. For example, a Bi-substituted garnet added with any of Tb, Gd, and Ho And YIG garnet. The thickness of the Faraday rotator 21 is set so that, for example, the polarization direction of incident light rotates 45 °. The polarizers 22 and 23 are members for selectively transmitting light having a predetermined angle of polarization direction. In the composite element 20, the light transmission polarization direction of the polarizer 22 and the light transmission polarization of the polarizer 23 are used. The direction is shifted by a predetermined angle (for example, 45 °). Examples of the polarizers 22 and 23 include a glass substrate containing dielectric particles and a laminate formed by laminating dielectric layers.

  The two magnets 30 are members for applying a predetermined magnetic field to the Faraday rotator 21 of the composite element 20, and support substrates via bonding materials (various resins such as epoxy resin, metal solder, low-melting glass, etc.) It is mounted on ten first substrates 11. The material constituting the magnet 30 is preferably a material having excellent heat resistance of the magnetic field strength so as to apply a sufficient saturation magnetic field strength to the Faraday rotator 21, such as an Sm—Co magnet or an Nd—Fe—B magnet. Is mentioned. Note that the surface of the magnet 30 may be plated with Ni or the like. In the magnet 30 that has been subjected to such plating treatment, it is possible to prevent powder from adhering to the surface of the main body during the production of the main body, which is a sintered body, and block the optical path of the optical isolator X1 as a foreign substance, It is possible to prevent the magnet 30 itself from being damaged due to the above.

  In the optical isolator X1 according to the present embodiment, for example, the thermal conductivity of the second substrate 12 that is in direct contact with the thermoelectric cooling device is small. Therefore, in the isolator X1, even when the thermoelectric cooling device overshoots and a sudden temperature change occurs, the influence of the temperature change on the Faraday rotator 21 via the support substrate 10 can be reduced. Therefore, the optical isolator X1 can suppress fluctuations in its isolation characteristics. In addition, the optical isolator X1 is suitable for reducing the manufacturing cost of an optical module including the optical isolator X1 because the single optical isolator X1 can handle light sources having a plurality of wavelengths.

  In the optical isolator X1, by adopting a material whose thermal expansion coefficient approximates that of the Faraday rotator 21 as the constituent material of the first substrate 11, the Faraday rotator 21 and the first substrate at the time of temperature change are adopted. The generation of stress due to the difference in thermal expansion coefficient with the number 11 can be reduced. That is, in the optical isolator X1, the influence of the stress that the Faraday rotator 21 receives can be reduced. Therefore, the optical isolator X1 can suppress fluctuations in its isolation characteristics.

  FIG. 2 is a side view showing an optical isolator X2 according to the second embodiment of the present invention. The optical isolator X2 is provided with a plurality of protrusions on the surface of the first substrate 11 on the side of the composite element 20 (FIG. 2A) or on the surface of the first substrate 11 on the second substrate side. The point (FIG. 2B) is different from the optical isolator X1. Other configurations of the optical isolator X2 are the same as those described above regarding the optical isolator X1. According to such a configuration, since the contact area between the first substrate 11 and the composite element 20 or the first substrate 11 and the second substrate is reduced, even when a sudden temperature change occurs due to overshoot of the thermoelectric cooling device. The heat transmitted to the composite element 20 through the first substrate can be suppressed. Therefore, the optical isolator X2 is suitable for mitigating the influence of temperature change on the Faraday rotator 21 via the support substrate 10. When a metal is employed as the material constituting the first substrate 11, a method for producing the convex portion on the surface of the first substrate 11 includes, for example, cutting.

  FIG. 3 is a side view showing an optical isolator X3 according to the third embodiment of the present invention. The optical isolator X3 is filled with a low thermal conductivity material having a lower thermal conductivity than the first substrate 11 between a plurality of convex portions 11a provided on the surface of the first substrate 11 on the composite element 20 side (FIG. 3A). ) Or a point where a plurality of convex portions 11a provided on the surface of the first substrate 11 on the second substrate side is filled with a low thermal conductivity material 11b having a lower thermal conductivity than the first substrate 11 (FIG. 3B). , Different from the optical isolator X2. Other configurations of the optical isolator X3 are the same as those described above regarding the optical isolator X2. According to such a configuration, since the contact area between the first substrate 11 and the composite element 20 or the first substrate 11 and the second substrate is reduced, even when a sudden temperature change occurs due to overshoot of the thermoelectric cooling device. The composite element 20 or the second substrate can be supported on the surface of the low thermal conductive material 11b, together with the point that heat transmitted to the composite element 20 through the first substrate is suppressed. This is also preferable in that the element 20 or the second substrate is fixed with high accuracy. In the low thermal conductive material 11b, the first substrate 11 has, for example, 50Ni—Fe (thermal conductivity: 16.74 W / m · K), SUS430 (thermal conductivity: 27.21 W / m · K), SUS303 (thermal conductivity). : 16.33 W / m · K), SF20T (thermal conductivity: 26.1 W / m · K), epoxy resin (thermal conductivity: 0.19 W / m · K), etc. Or low melting point glass such as lead glass (thermal conductivity: 0.97 W / m · K). Furthermore, when filling the low thermal conductive material 11b whose thermal conductivity is smaller than the 1st board | substrate 11 between the convex parts 11a provided in the surface by the side of the 1st board | substrate 11 at the composite element 20, the 1st board | substrate 11 and a composite element are filled. If the joining material for joining 20 is made of the same material as the low thermal conductive material 11b, the composite material 20 is firmly joined to the first substrate 11 by the joining material entering between the convex portions 11a. can do.

  FIG. 4 is a schematic perspective view showing an optical isolator X4 according to the fourth embodiment of the present invention. The optical isolator X4 is different from the optical isolator X1 in that the side surface of the first substrate 11 has an uneven shape. Other configurations of the optical isolator X2 are the same as those described above regarding the optical isolator X1. According to such a configuration, since the surface area of the support substrate 1 increases, the heat transmitted to the first substrate 11 through the second substrate 12 can be more efficiently dissipated. Therefore, the optical isolator X4 is suitable for mitigating the influence of temperature change on the Faraday rotator 21 via the support substrate 10.

  FIG. 5 is a plan view showing an optical isolator X5 according to the fifth embodiment of the present invention. The optical isolator X5 is different from the optical isolator X1 in that the side surface 20a of the composite element 20 is arranged on the support substrate 10 so as to be inclined by 4 to 10 ° with respect to the side surface 10a of the support substrate 10. Other configurations of the optical isolator X5 are the same as those described above regarding the optical isolator X1. The optical isolator X5 having such a configuration prevents light incident on the side surface 20a of the composite element 20 from a light source (not shown) perpendicular to the side surface 10a of the support substrate 10 from returning to the light source and returning as light. It is suitable.

  FIG. 6 is a plan view showing an optical isolator X6 according to the sixth embodiment of the present invention. The optical isolator X4 differs from the optical isolator X5 in that the composite element 20 employs a parallelogram shape in plan view. Other configurations of the optical isolator X5 are the same as those described above regarding the optical isolator X5. The optical isolator X6 having such a configuration is suitable for reducing the width W of the optical isolator X6.

  FIG. 7 is a schematic sectional view showing an optical module Y including the optical isolator X1 according to the present invention. The optical module Y includes an optical isolator X1, a semiconductor element (LED, LD, etc.) 40 for outputting light, a submount 41 for mounting the semiconductor element 40, and a temperature for controlling the semiconductor element 40. Control means (for example, TEC) 42, lenses 43 and 44 for collecting and transmitting light output from the semiconductor element 40, optical isolator X1, semiconductor element, submount 41, control means 42 and lens 43 A package 45 for housing the optical fiber, a holder 46 for coupling the package 45 and holding the lens 44, an optical receptacle 47 for connecting to a light guide member (for example, an optical fiber) (not shown), and an optical receptacle And a sleeve 48 for optically aligning 47 with respect to the optical axis. The optical isolator X1 is directly mounted on the control means 42. According to such a configuration, an optical module Y having excellent transmission characteristics and low cost can be obtained.

  Although specific embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  For example, in the optical isolators X1 to X6, when the Faraday rotator 21 having a self-holding force is adopted, the two magnets 30 may not be provided. Such a configuration is suitable for reducing the size of the optical isolators X1 to X6.

  Next, examples of the present invention will be described.

  An optical isolator having the same configuration as the optical isolator X1 shown in FIG. 1 was produced. In the manufactured optical isolator, the size of the support substrate 10 is 3 mm wide × 2 mm deep × 0.4 mm high, the first substrate 11 is made of 50Ni—Fe, and the size is 3 mm wide × 2 mm deep × height 0. The second substrate 12 of 4 mm and made of zirconia ceramic was cured and fixed with a bonding material. On the other hand, the composite element 20 was formed by cutting into a rectangular solid of □ 0.9 mm × thickness 0.8 mm in order to include the beam diameter of the emitted light from the light source in accordance with φ0.8 mm. A bonding material was dropped onto the bonding surface 10a with a dispenser, and the bonding material was placed on the bonding surface 10a so as to coincide with the substantially central portion of the composite element 20. The bonding material was cured and fixed by heating. At this time, the transmission polarization plane of the polarizer 22 is installed so as to be parallel to the bonding surface 10 a of the support substrate 10. A rectangular parallelepiped magnet 30 (width 0.8 mm × depth 1.8 mm × height 1.2 mm) for applying a magnetic field to the Faraday rotator 21 is made of Sm—Co, and the surface thereof is plated with Ni. .

Similarly, a bonding material was dropped on the bonding surface 10a, a magnet 304 was placed thereon, and the bonding material was cured and fixed by heating. Although a thermosetting bonding material is used this time, an ultraviolet curable bonding material or a visible curable bonding material that can ensure bonding strength may be used.

  An optical isolator having the same configuration as that of the optical isolator 80 shown in FIG. 8 was produced. In the manufactured optical isolator, the material of the support substrate 10 'is 50Ni-Fe, and the other manufacturing methods are the same as those in the examples of the present invention. The optical isolator of the present invention shown in FIG. 1 and the conventional optical isolator shown in FIG. 8 correspond to wavelengths of 1550 nm, and each optical isolator is an optical module having oscillation wavelengths of 1530 nm and 1570 nm as shown in FIG. Mounted on. After measuring the output light of the LD chip as the light source and using it as a reference, magnetization was performed so that the magnetization direction NS of the magnet 30 of each optical isolator was reversed, so that the insertion loss was isolated. A temperature change by temperature control of the TEC 42 for suppressing the output fluctuation of the LD chip was loaded on the optical isolator, and the optical output from the optical isolator at that time was measured to perform isolation characteristics. The comparison result is shown in FIG.

  The optical isolator of the conventional example has an abrupt temperature change due to overshoot due to temperature control of the TEC 42, that is, an isolation with an oscillation wavelength of 1570 nm for a change of + 5 ° C. or more, and an isolation with an oscillation wavelength of 1530 nm for a change of −5 ° C. or more. However, the optical isolator of the present invention was able to satisfy the isolation standard lower limit with respect to the temperature change due to the temperature control of the TEC 42, and showed stable isolation characteristics against the temperature change.

  As described above, in the conventional example and the present embodiment, the thermal conductivity of the second substrate 12 of the optical isolator in contact with the TEC 42 is reduced with respect to the temperature change of the TEC 42 for controlling the optical output and the oscillation wavelength of the LD chip. As a result, it is possible to delay the rapid change of the temperature due to the overshoot of the TEC 42 from being transmitted to the optical isolator, and thus it is possible to provide an optical isolator that suppresses variations in isolation characteristics.

1 is a schematic perspective view of an optical isolator according to a first embodiment of the present invention. It is a side view of the optical isolator which concerns on the 2nd Embodiment of this invention. It is a side view of the optical isolator which concerns on the 3rd Embodiment of this invention. It is a schematic perspective view of the optical isolator which concerns on the 4th Embodiment of this invention. It is a top view of the optical isolator which concerns on the 5th Embodiment of this invention. It is a top view of the optical isolator which concerns on the 6th Embodiment of this invention. It is sectional drawing of an optical module provided with the optical isolator shown in FIG. It is a schematic perspective view of the conventional optical isolator. It is sectional drawing of the conventional optical module. It is a figure showing the temperature dependence of the isolation characteristic of an optical isolator. It is a figure showing the isolation fluctuation | variation of the optical isolator of this invention accompanying an optical output fluctuation | variation. It is a figure showing the isolation fluctuation | variation of the conventional optical isolator accompanying the optical output fluctuation | variation.

Explanation of symbols

X1 to X6 Optical isolator Y Optical module 10 Support substrate 20 Composite element 21 Faraday rotator 22, 23 Polarizer

Claims (6)

A composite element including a Faraday rotator and a polarizer, and a support substrate for supporting the composite element;
The support substrate is located on the composite element side, and includes a first substrate that includes a metal, and a second substrate that has a lower thermal conductivity than the first substrate and includes a non-metallic composition. An optical isolator characterized by being:   The optical isolator according to claim 1, wherein the first substrate has a plurality of convex portions on at least one of the surface on the composite element side and the surface on the second substrate side.   The optical isolator according to claim 2, wherein a low thermal conductive material having a lower thermal conductivity than that of the first substrate is disposed between the convex portions of the first substrate.   The optical isolator according to claim 1, wherein the support substrate has irregularities on at least a part of a side surface of the support substrate.   The optical isolator according to claim 1, wherein the Faraday rotator includes a Bi-substituted garnet.   A stub optically connected to a plug inserted from the outside, a sleeve for obtaining alignment between the plug and the stub, and for emitting light toward the stub, or An optical module comprising: an optical element for receiving light via a stub; and the optical isolator according to any one of claims 1 to 5, which is optically coaxial with the stub and the optical element. .

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