JP2005181803A - Optical isolator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical isolator having a magnet, capable of solving the problem of reduction of a clear aperture resultant from misalignment of optical paths that occur between a light incidence plane and a light-emitting plane of each optical element disposed in a sloped manner, and the problem of misalignment of optical paths that occur between the incidence side and the emission side of the optical isolator, by only fitting and storing each optical element to it. <P>SOLUTION: The optical isolator has a through-hole in its magnet. A Faraday rotator is stored inside the magnet through the through-hole, in a way that it is exposed. Two light polarizers and the Faraday rotator are arranged in a flat shape. A concave part is formed for storing each of the light polarizers at both sides of the magnet on the light incidence side and the light emission side of the optical isolator, without their protruding from either side of the magnet. The two light polarizers are stored inside the concave, respectively, and one surface of the magnet is formed into a planar shape. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical isolator for removing return light generated when light emitted from a light source is incident on various optical elements or optical fibers.

  Conventionally, light emitted from a light source such as a laser light source is incident on various optical elements and optical fibers, but some of the incident light is reflected or scattered on the end surfaces and inside of the various optical elements and optical fibers. . A part of the reflected and scattered light tries to return to the light source as return light, and an optical isolator is used to prevent the return light. Such an optical isolator includes optical elements such as a polarizer, a Faraday rotator, and another polarizer (also referred to as an analyzer) between a light source and an optical fiber or between two optical fibers. In addition, a magnet for saturation magnetization of the Faraday rotator is disposed in the vicinity of the Faraday rotator.

For example, in the case of the “one-stage type”, a specific polarization-dependent optical isolator is disposed facing each other so that the polarization planes of the two polarizers are relatively different from each other by 45 ° around the optical axis. A single Faraday rotator with a thickness that rotates the polarization plane of incident light at a predetermined wavelength within a saturation magnetic field by 45 ° is placed between these polarizers, and they are held and fixed together. It is. As an example of such an optical isolator, the one shown in FIG. 13 has been devised (see Patent Document 1).
JP-A-62-118315 (page 2-3, Fig. 1)

  The principle of the optical isolator 100 shown in FIG. 13 will be described. When the light incident on the optical isolator 100 passes through the polarizer 1, only the polarization component having a certain plane of polarization with respect to the optical axis is transmitted and enters the Faraday rotator 2. Next, the polarization component is rotated by 45 ° in the direction of the polarization plane by the Faraday rotator 2 and emitted from the polarizer 3 to the outside. On the other hand, the return light reflected and scattered by the end face of the optical fiber and various optical elements is incident again on the optical isolator 100, and only the polarization component having a certain polarization plane is transmitted by the polarizer 3 as shown in FIG. However, since the plane of polarization is further rotated by 45 ° by the Faraday rotator 2, the plane of polarization of the light returning to the polarizer 1 is rotated 90 ° from the plane of polarization of the polarizer 3. 1 is absorbed and cannot pass. In this way, light in the light incident direction is allowed to pass, and return light from the opposite direction is removed.

  Further, the two polarizers 1 and 3 are mounted in cylindrical polarizer holders 5 and 6, respectively, and these polarizer holders 5 and 6 are joined to both end faces of the cylindrical magnet 4, respectively. Here, the mounting angle of the Faraday rotator 2 with respect to the cylindrical magnet 4, the mounting angle of the polarizers 1 and 3 and the polarizer holders 5 and 6, and the mounting angle of the cylindrical magnet 4 and both the polarizer holders 5 and 6 are devised. The Faraday rotator 2 and the polarizers 1 and 3 are arranged in an inclined state with respect to the light incident direction (arrow I direction). Thus, by tilting each optical element with respect to the light incident direction, the reflected light on the optical surface of each optical element is prevented from returning to the light source side.

  However, in the configuration of FIG. 13, the two polarizers 1 and 3 are attached to both end faces of the cylindrical magnet 4 via the cylindrical polarizer holders 5 and 6, respectively. was there. Further, since separate components such as the polarizer holders 5 and 6 are required, the number of components for forming the optical isolator 100 is increased, which increases the manufacturing cost.

  Further, since each optical element is disposed at an inclination, an optical path shift occurs between each light incident surface and each light exit surface, and an optical signal transmission area (hereinafter referred to as a clear aperture) on the light transmission surface of each optical element. There is also a problem in that the optical path shift occurs between the incident side and the exit side of the optical isolator, and positioning work at the time of optical coupling with an external optical component becomes difficult.

  The present invention has been made in view of the above problems, and its purpose is to reduce the size of the optical isolator in which the Faraday rotator and the polarizer are arranged in an inclined state with respect to the light transmission direction and to reduce the number of components. This is to reduce the manufacturing cost.

  Further, the clear aperture due to the optical path shift generated between each light incident surface and each light output surface of each optical element arranged in an inclined state is reduced, and the optical path shift generated between the incident side and the output side of the optical isolator. Is to realize an optical isolator having a magnet that can be eliminated simply by mounting and storing each optical element.

  The invention according to claim 1 of the present invention is an optical isolator in which a Faraday rotator is disposed between two polarizers, and a magnet for applying a magnetic field to the Faraday rotator is disposed. The Faraday rotator is housed inside the magnet so that its optical surface is exposed from the through hole when viewed from the light incident direction, and the two polarizers and the Faraday rotator are configured in a flat plate shape. At both ends of the magnet on the light entrance side and light exit side of the optical isolator, concave portions that can accommodate one polarizer without extending from both ends of the magnet are formed, and the two polarizers are respectively The present invention provides an optical isolator characterized in that it is housed in a recess and one surface of a magnet is formed in a flat shape.

に設定されることを特徴とする光アイソレータを提供するものである。 Further, according to the second aspect of the present invention, when viewed from the light incident direction, the refractive index of the polarizer which is the first optical element housed in the magnet is n1, the thickness is t1, and the height is h1, and the inclination angle of the light incident surface of the polarizer with respect to the direction perpendicular to the light incident direction is set to θ1, and when viewed from the light incident direction, it is the second inside the magnet. The Faraday rotator, which is an optical element housed in the optical element, has a refractive index of n2, a thickness of t2, a height of h2, and a light incident on the Faraday rotator when the direction perpendicular to the light incident direction is used as a reference. The inclination angle of the surface is set to θ2, and the two concave portions are formed at both ends of the magnet so that one surface of the inner surface is on the same line in the light incident direction, and the first polarization The child makes its ridge line abut against one surface of the inner surface, and light The refractive index of the polarizer, which is an optical element that is housed in the concave portion formed at the end of the magnet on the emitting side and is thirdly housed inside the magnet when viewed from the light incident direction, is n3, the thickness is t3, A concave portion for housing the third polarizer when the inclination angle of the light incident surface of the polarizer is set to θ3 when the height is h3 and the direction perpendicular to the light incident direction is set as a reference. Of the direction perpendicular to the light incident direction is

An optical isolator characterized by being set to be provided.

となるように構成されたことを特徴とする光アイソレータを提供するものである。 Further, according to the third aspect of the present invention, the refractive index of the polarizer, which is the first optical element housed in the magnet when viewed from the light incident direction, is set to n1 and the thickness is set to t1. When viewed from the light incident direction, the Faraday rotator, which is the second optical element housed inside the magnet when viewed from the light incident direction, has a refractive index n2 and a thickness t2. The refractive index of the polarizer, which is the third optical element housed inside the magnet, is set to n3, and the thickness is set to t3. Formed at both ends of the magnet so as to have inclination angles θ1 and θ3 with respect to a vertical direction, and the first and third polarizers abut the optical surface of the inner surface. Let the recesses formed at both ends of the magnet By being housed, the light incident surfaces of the first and third polarizers have inclination angles θ1 and θ3 with respect to a direction perpendicular to the light incident direction, and further, the Faraday rotator Is incident on the two polarizers and the Faraday rotator when the light incident surface is housed in the magnet so that the tilt angle θ2 is set when the direction perpendicular to the light incident direction is taken as a reference. The optical path shifts z1, z2, and z3 between the light and the outgoing light are as follows:

An optical isolator characterized by the above is provided.

  Furthermore, in the invention according to claim 4 of the present invention, the magnet surface opposite to the one surface of the magnet is removed, and a part of the inner peripheral surface of the through hole is opened with the optical elements interposed therebetween. An optical isolator characterized by the above is provided.

  Furthermore, in the invention according to claim 5 of the present invention, a groove parallel to the light incident direction is formed from the magnet surface opposite to the one surface of the magnet to the through hole with the optical elements interposed therebetween. An optical isolator characterized by the above is provided.

  Further, in the invention according to claim 6 of the present invention, a groove non-parallel to the light incident direction is formed from the magnet surface opposite to the one surface of the magnet to the through hole with the optical elements interposed therebetween. An optical isolator characterized by the above is provided.

  According to the optical isolator of the present invention, since one surface of the magnet is formed in a planar shape, an optical isolator that can be easily mounted on an external device can be provided. Furthermore, by limiting the shape and dimensions of the magnet, an optical path generated between each light incident surface and each light output surface of each optical element disposed in an inclined state by simply mounting and storing the optical element inside the magnet. The light transmitting portion of each optical element can be arranged at the optimum position corresponding to the deviation. Accordingly, it is possible to eliminate the decrease in the clear aperture of each optical element due to the optical path deviation.

  Further, by further changing the shape and dimensions of the magnet, it is possible to eliminate the optical path shift of incident light that occurs between the incident side and the emission side of the optical isolator only by housing the optical element inside the magnet.

  Furthermore, by forming these optical isolators by housing and fixing each optical element inside the magnet, it is possible to reduce the size of the entire optical isolator and reduce the manufacturing cost by removing other components such as a polarizer holder. I can do it.

<First Embodiment>
Hereinafter, a first embodiment of an optical isolator according to the present invention will be described in detail with reference to FIGS. 1 is a schematic perspective view showing the appearance of the optical isolator 7 of the present embodiment, FIG. 2 is a right side view of FIG. 1, and FIG. 3 is an enlarged view of one optical element extracted from FIGS. FIG. 4 is an optical element arrangement diagram in which only the optical element is taken out from the optical isolator 7 of FIG.

  As shown in FIG. 1 and FIG. 2, this optical isolator 7 arranges the polarizer 1, the Faraday rotator 2 and the polarizing element 3 in series in this order when viewed from the light incident direction (arrow I direction). It becomes. Accordingly, the Faraday rotator 2 is disposed between the two polarizers 1 and 3. Further, a magnet 4 is provided for housing the optical elements and applying a saturation magnetic field to the Faraday rotator.

  Hereinafter, each part which comprises the optical isolator 7 is demonstrated. The Faraday rotator 2 is made of a single crystal such as Bi-substituted rare earth iron garnet manufactured by the LPE method. When a saturation magnetic field is applied in the light incident direction, the polarization direction of the incident light is made around the optical axis. In order to rotate exactly 45 degrees, it is configured to have a predetermined thickness with respect to the light incident direction (arrow I direction). Its outer shape is configured as a square flat plate.

  The two polarizers 1 and 3 are both formed in a square flat plate shape and are formed of a flat glass substrate. The polarizers 1 and 3 include a type in which dielectric particles are encapsulated in a glass substrate, a type in which a dielectric is laminated on a glass substrate, and the like, for example, “trade name polar core” manufactured by Corning Inc. can be used. The polarization direction in the light transmitting portion of the polarizer 3 is formed to be the same as the rotation direction of the Faraday rotator 2 so as to be approximately 45 degrees different from the polarization direction of the polarizer 1.

  The magnet 4 is formed in a substantially block shape. Further, the magnet ends 4a and 4b on the light incident side and light emitting side of the optical isolator 7 are recessed portions 8 that can accommodate the polarizers 1 and 3 respectively. 9 is formed. One surface 4c of the magnet 4 is formed in a planar shape so as to be parallel to the light incident direction of the optical isolator. A through hole 10 for passing light is provided in the center of the magnet 4.

  The widths w of the recesses 8 and 9 are configured to be slightly larger than the widths of the polarizers 1 and 3, respectively, and the depths (dimensions in the direction of arrow I) are accommodated in the recesses 8 and 9, respectively. Sometimes, the polarizers 1 and 3 are formed so that they can be accommodated without extending from the both ends 4a and 4b in the direction of arrow I in the front-rear direction. The inner diameter of the through hole 10 is set larger than the square diagonal dimension of the Faraday rotator 2.

  Further, a groove 11 having a width slightly wider than the thickness of the Faraday rotator 2 is formed so as to cross the through hole 10. The groove 11 is formed so as to be non-parallel to the light incident direction from the magnet surface 4d on the side opposite to the one plane 4c of the magnet across the optical elements to the through hole 10. More specifically, it is formed obliquely so as to have a predetermined inclination angle θ2 with respect to the direction perpendicular to the light incident direction. The Faraday rotator 2 is accommodated so as to slide into the magnet 4 from the groove 11, and is accommodated in the through hole 10 so that the four apex angles come into contact with the inner peripheral surface of the through hole 10. Accordingly, when viewed from the light incident direction, the entire optical surface of the Faraday rotator 2 is exposed from the through hole 10.

  Furthermore, the bottom surfaces 8a and 9a, which are one of the inner surfaces of the recesses 8 and 9, are formed obliquely so as to have predetermined inclination angles θ1 and θ3 with respect to the direction perpendicular to the light incident direction. Accordingly, the polarizers 1 and 3 are brought into surface contact with the bottom surfaces 8a and 9a and accommodated in the recesses 8 and 9, so that the polarizers 1 and 3 are arranged obliquely at inclination angles θ1 and θ3 with respect to the light incident direction. Therefore, it is possible to prevent the optical signal reflected by the optical surfaces of the polarizers 1 and 3 from returning to the light source side.

  The polarizers 1 and 3 are fixed to the bottom surfaces 8a and 9a with an optical adhesive. When the polarizers 1 and 3 are housed in the recesses 8 and 9, one of the ridge lines of the polarizers 1 and 3 is fixed so as to contact the inner side surfaces 8b and 9c of the recesses. As shown in FIG. 2, when viewed from the light incident direction, the polarizer 1 which is the first optical element housed in the magnet 4 is such that one of its ridge lines contacts the lower inner surface 8b. The polarizer 3, which is fixed and is the third optical element housed inside the magnet 4 when viewed from the light incident direction, is fixed so that one of the ridge lines is in contact with the upper inner surface 9 c.

なる距離の光路ずれsが発生する。 When light is incident on the optical isolator 7 configured as described above, each light incident surface of each optical element is set to have inclination angles θ1, θ2, and θ3, and therefore, a direction perpendicular to the light incident direction. , The light incident on the light incident surface of the i-th optical element viewed from the light incident direction is light as shown in FIG. 3 where the inclination angle of the optical element is θ. It is incident at an incident angle θ with respect to the normal N of the incident surface, and is refracted at the light incident surface. Here, when the refractive index of the i-th optical element is set to ni and the thickness of the optical element is set to ti, according to Snell's law, between the incident light and the outgoing light,

An optical path deviation s of a distance occurs.

と表される。従って、３番目の偏光子３を１番目の偏光子１と同一高さに固定すると、前記光路ずれ量sc分だけ光入射面の中央からずれることとなる。よって、偏光子３の光入射面における光透過面積のうち、実際に光が透過するために使用される光通過使用可能面積（以後、クリアアパーチャと記す）が低減してしまう。 As shown in FIG. 4, since the Faraday rotator 2 and the two polarizers 1 and 3 are both tilted in the same direction and housed in the magnet 4, the light of the polarizer 1 that is the first optical element. When the light incident on the center (light transmission portion) of the incident surface reaches the light incident surface of the polarizer, which is the third optical element, the light path is shifted by the first polarizer 1 and viewed from the light incident direction. 4 is shifted upward in FIG. 4 by the amount of optical path deviation sc that includes the optical path deviation by the Faraday rotator 2 that is the optical element housed in the magnet 4 second. Here, the refractive index of the polarizer 1 is n1, the thickness is t1, the height is h1, the tilt angle is θ1, the refractive index of the Faraday rotator 2 is n2, the thickness is t2, the height is h2, and the tilt angle. Is set to θ2, the optical path shift amount sc is

It is expressed. Accordingly, when the third polarizer 3 is fixed at the same height as the first polarizer 1, the third polarizer 3 is displaced from the center of the light incident surface by the amount of the optical path deviation sc. Therefore, of the light transmission area on the light incident surface of the polarizer 3, the light passage usable area (hereinafter referred to as a clear aperture) used for actually transmitting light is reduced.

  Therefore, by setting the height dimension of the concave portion 9 that accommodates the polarizer 3, that is, the dimension in the direction perpendicular to the light incident direction, to a dimension that takes this optical path shift amount sc into consideration, the polarizer 3 has one of its ridge lines. It is possible to allow light to enter the center of the light transmitting portion of the third (light emitting side) polarizer 3 simply by bringing it into contact with the magnet 4.

と表される。ここで、偏光子１に対する偏光子３の光路ずれ量scを正確に導出するため、凹部８、９の内側面の一面が光入射方向において同一直線上に来るように、凹部８、９をマグネット４両端部4a、4bに形成するようにしなければならない。具体的には、側面8bと9bとを同一直線上に来るように凹部８、９を形成することが望ましい。何故なら、側面8bに偏光子１の稜線の一つが当接されて収納されており、当接された状態で偏光子１の光入射面の中央に光が入射されているためであり、側面8bと9bを基準面として、更に数６で表される光路ずれ量sc分だけ上方にシフトさせることにより、偏光子３の光入射面の中央に光を入射させることが可能になるためである。 The vertical dimension of the concave portion 9 is obtained as follows. First, when the thickness of the polarizer 3 is set to t3 and the height is set to h3, and the vertical dimension m3 required when the polarizer 3 is stored with the tilt angle θ3,

It is expressed. Here, in order to accurately derive the optical path shift amount sc of the polarizer 3 with respect to the polarizer 1, the recesses 8, 9 are magnetized so that one surface of the inner surface of the recesses 8, 9 is on the same straight line in the light incident direction. 4 must be formed at both ends 4a and 4b. Specifically, it is desirable to form the recesses 8 and 9 so that the side surfaces 8b and 9b are on the same straight line. This is because one of the ridge lines of the polarizer 1 is abutted and accommodated on the side surface 8b, and light is incident on the center of the light incident surface of the polarizer 1 in the abutted state. This is because light can be incident on the center of the light incident surface of the polarizer 3 by further shifting upward by the optical path deviation amount sc represented by Equation 6 using 8b and 9b as reference surfaces. .

なる寸法に設定されることが導き出される。凹部９の垂直方向の寸法hを数８に設定することにより、偏光子３を収納する際、その稜線の一つが側面9cに当接していれば、光入射面の中央に光を入射させられていることが分かり、当接していなければ前記中央に光を入射させられていないことが判明する。この様に、稜線の一つが当接しているかしていないかという明快な判定条件を以て、偏光子３をマグネット４に収納させるだけで光路ずれ量scに対応した最適位置に偏光子３を載置させることが可能となる。 From the above, the vertical dimension h of the concave portion 9 is the dimension obtained by adding the optical path deviation amount of Expression 6 to the dimension of Expression 7, that is,

It is derived that it is set to the dimension which becomes. By setting the vertical dimension h of the concave portion 9 to Equation 8, when one of the ridgelines is in contact with the side surface 9c when the polarizer 3 is accommodated, light can be incident on the center of the light incident surface. If it is not in contact, it is found that no light is incident on the center. In this way, the polarizer 3 is placed at the optimum position corresponding to the optical path shift amount sc by simply storing the polarizer 3 in the magnet 4 under the clear determination condition of whether one of the ridge lines is in contact. It becomes possible to make it.

  Furthermore, since one surface of the magnet 4 is formed to be a plane parallel to the light incident direction, the magnet 4 can be easily attached to a flat surface. Therefore, the optical isolator 7 can be easily attached to the inside of the communication device.

  The present embodiment can be variously changed based on the technical idea. For example, the groove retains the purpose of ensuring the ease of mounting the Faraday rotator as shown in FIGS. A groove 11 having a shape parallel to the light incident direction may be formed from the magnet surface 4d on the opposite side of the one plane 4c of the magnet 4 to the through hole 10 with each optical element interposed therebetween.

<Second Embodiment>
Hereinafter, a second embodiment of an optical isolator according to the present invention will be described in detail with reference to FIGS. 8 is a schematic perspective view showing the appearance of the optical isolator 12 of the present embodiment, FIG. 9 is a right side view of FIG. 8, and FIG. 10 is an optical element in which only the optical element is taken out from the optical isolator 12 of FIG. FIG. In addition, the same number is attached | subjected to the same location as the optical isolator 7 demonstrated in 1st Embodiment, and the overlapping description is abbreviate | omitted or simplified and described.

  A groove 11 having a width slightly wider than the thickness of the Faraday rotator 2 is formed in the magnet 4 so as to cross the through hole 10. The groove 11 is formed so as to be non-parallel to the light incident direction (direction of arrow I) from the magnet surface 4d on the opposite side to the one plane 4c of the magnet across the optical elements to the through hole 10. . More specifically, it is formed obliquely so as to have a predetermined inclination angle θ2 with respect to the direction perpendicular to the light incident direction. The Faraday rotator 2 is accommodated so as to slide into the magnet 4 from the groove 11, and is accommodated in the through hole 10 so that the four apex angles come into contact with the inner peripheral surface of the through hole 10. Therefore, when the Faraday rotator 2 is housed in the groove 11, it is housed in the magnet 4 so that its light incident surface has an inclination angle θ2 with respect to a direction perpendicular to the light incident direction. Is done.

  Concave portions 8 and 9 are formed at both ends 4a and 4b of the magnet on the light incident side and light emitting side of the optical isolator 12. Furthermore, the bottom surfaces 8a and 9a, which are one surface of the inner surfaces of the recesses 8 and 9, are formed obliquely so as to have predetermined inclination angles θ1 and θ3 when the direction perpendicular to the light incident direction is used as a reference. ing. Accordingly, the optical surfaces of the polarizers 1 and 3 (the light exit surface in the case of the polarizer 1 and the light incident surface in the case of the polarizer 3) are brought into contact with the bottom surfaces 8 a and 9 a so as to be stored in the recesses 8 and 9. By doing so, it becomes possible to arrange the polarizers 1 and 3 obliquely at inclination angles θ1 and θ3 with respect to the light incident direction.

  Note that the inclination angles of θ1, θ2, and θ3 are not 0 degrees. By doing so, as shown in FIGS. 9 and 10, the optical elements can be arranged obliquely at the respective inclination angles θ1, θ2, and θ3, so that the incident light reflected by the optical surface of each optical element can be obtained. Can be prevented from returning to the light source.

  As shown in FIG. 10, when light is incident on an optical isolator 12 having an optical element configuration in which the polarizer 1 and the polarizer 3 are tilted in the same direction and only the Faraday rotator 2 is tilted in another direction, the light enters the polarizer 1. When the transmitted light passes through the polarizer 1, its optical path is shifted upward by z 1, and when it passes through the Faraday rotator 2, its optical path is shifted downward by z 2. Next, when passing through the polarizer 3, the optical path is shifted upward by z3.

となるように前記傾き角θ1、θ2、θ3を定めれば良いのだが、次にその選定方法について説明する。 And in this embodiment, the total of this optical path deviation is

The inclination angles θ1, θ2, and θ3 may be determined so that

で与えられる。従って、前記偏光子１、３とファラデー回転子２の光路ずれの合計は各光学素子の数１０の合計により求められる。図１０の例では、偏光子１と偏光子３による上方向の光路ずれの和と、ファラデー回転子２による下方向の光路ずれとが等しくなるように傾き角θ1、θ2、θ3を設定すれば、光路ずれが解消されることになる。今、偏光子１の屈折率がn1、厚さがt1、ファラデー回転子２の屈折率がn2、厚さがt2、偏光子３の屈折率がn3、厚さがt3と設定されると、

となるように各傾き角θ1、θ2、θ3を求めれば、光学素子に入射する入射光と、出射光との光路ずれを解消することが出来る。光学素子の厚みtiと屈折率niは、寸法の選定や光学素子材料の選定等により予め設定することが可能なので、各光学素子の傾き角θ1、θ2、θ3も一義的に求められる。 From FIG. 3, the deviation s between the optical paths of the incident light and the outgoing light when the optical surface of the optical element is arranged to be inclined by an angle θ with respect to the direction perpendicular to the incident light is obtained. As shown in the figure, when the refractive index of the optical element is set to ni and the thickness is set to ti, the deviation s of the optical path of the outgoing light with respect to the optical path of the incident light is

Given in. Therefore, the sum of the optical path shifts of the polarizers 1 and 3 and the Faraday rotator 2 can be obtained by the sum of several tens of optical elements. In the example of FIG. 10, if the tilt angles θ1, θ2, and θ3 are set so that the sum of the optical path shifts in the upward direction by the polarizer 1 and the polarizer 3 and the optical path shift in the downward direction by the Faraday rotator 2 are equal. Therefore, the optical path deviation is eliminated. If the refractive index of the polarizer 1 is n1, the thickness is t1, the refractive index of the Faraday rotator 2 is n2, the thickness is t2, the refractive index of the polarizer 3 is n3, and the thickness is t3,

If the respective inclination angles θ1, θ2, and θ3 are obtained so that the optical path deviation between the incident light incident on the optical element and the outgoing light can be eliminated. Since the thickness ti and the refractive index ni of the optical element can be set in advance by selecting dimensions, selecting optical element materials, or the like, the inclination angles θ1, θ2, and θ3 of the optical elements are also uniquely determined.

のような結果となった。ファラデー回転子２の負号は逆方向を表す。表１に示された結果に基づき、マグネット４の各光学素子を収納する凹部底面8a、9a、及び溝11を、予め各傾き角θ1、θ2、θ3に形成すれば、各光学素子をマグネットに収納するだけで光路ずれを殆ど解消することが可能となる。これにより、この光アイソレータを外部機器内部に設置する際の光路調整を容易なものとすることが出来る。更に、マグネット４の一表面を、光入射方向に対し平行な平面となるように形成したので、マグネット４を平坦な表面に容易に取り付けることが可能となる。従って、通信機器内部への光アイソレータ７の取り付けを容易なものとすることが出来る。 In addition, in the optical isolator 12 shown in FIGS. 8 to 10, when the overall optical path deviation is 0, that is, when the inclination angles θ1, θ2, and θ3 that are expressed by Equation 11 are specifically obtained as an example, n1 = n3 = 1.5, n2 = 2.3, t1 = t3 = 0.2mm, t2 = 0.5mm (when θ1 = θ3)

The result was as follows. The negative sign of the Faraday rotator 2 represents the reverse direction. Based on the results shown in Table 1, if the concave bottom surfaces 8a and 9a and the grooves 11 for accommodating the optical elements of the magnet 4 are formed in advance at the inclination angles θ1, θ2, and θ3, the optical elements are used as magnets. It is possible to almost eliminate the optical path deviation simply by storing. Thereby, it is possible to easily adjust the optical path when the optical isolator is installed inside the external device. Furthermore, since one surface of the magnet 4 is formed to be a plane parallel to the light incident direction, the magnet 4 can be easily attached to a flat surface. Therefore, the optical isolator 7 can be easily attached to the inside of the communication device.

  The present embodiment can be variously changed based on the technical idea. For example, the magnet 4 holds the optical element sandwiched as shown in FIG. The magnet surface 4d opposite to the one flat surface 4c of the magnet 4 may be removed and a part of the inner peripheral surface of the through hole 10 may be opened.

  Further, while maintaining the purpose of ensuring the ease of mounting the Faraday rotator, the groove is sandwiched from the magnet surface 4d on the opposite side to the one plane 4c of the magnet 4 with the optical element interposed therebetween, as shown in FIG. A groove 11 having a shape parallel to the light incident direction may be formed over the through hole 10.

  By using the optical isolator of the present invention for passive optical devices such as optical communication modules, semiconductor laser modules, and optical amplifiers used in optical communication systems, it is possible to prevent reflected return light to the semiconductor laser light source, It is possible to prevent the occurrence of light resonance.

1 is a schematic perspective view showing an appearance of an optical isolator according to a first embodiment. The right view of FIG. The enlarged view which took out one optical element from FIG.1 and FIG.2. FIG. 3 is an optical element arrangement diagram in which only an optical element is taken out from the optical isolator of FIG. The schematic perspective view which shows the example of a change of the magnet of 1st Embodiment. The schematic perspective view which shows the external appearance of the optical isolator formed by accommodating each optical element in the magnet of FIG. The top view of FIG. The schematic perspective view which shows the external appearance of the optical isolator of 2nd Embodiment. The right view of FIG. FIG. 9 is an optical element arrangement diagram in which only the optical element is taken out from the optical isolator of FIG. The schematic perspective view of the optical isolator which shows the example of a change of the magnet of 2nd Embodiment. The schematic perspective view of the optical isolator which shows another modification of the magnet of 2nd Embodiment. The fragmentary sectional side view of the conventional optical isolator.

Explanation of symbols

1, 3 Polarizer 2 Faraday rotator 4 Magnet 5, 6 Polarizer holder 7, 12 Optical isolator 8, 9 Recess
10 Through hole
11 groove

Claims (6)

In an optical isolator in which a Faraday rotator is disposed between two polarizers and a magnet that applies a magnetic field to the Faraday rotator is disposed.
The magnet has a through hole, and when viewed from the light incident direction, the Faraday rotator is housed inside the magnet so that its optical surface is exposed from the through hole,
The two polarizers and the Faraday rotator are configured in a flat plate shape, and one polarizer is not extended from both ends of the magnet on the light incident side and the light exit side of the optical isolator. A recess that can be stored in the two polarizers is stored in the recess,
Further, the optical isolator is characterized in that one surface of the magnet is formed in a planar shape. 2. The optical isolator according to claim 1, wherein when viewed from the light incident direction, the polarizer, which is the first optical element housed in the magnet, has a refractive index of n1, a thickness of t1, a height of h1, and light. The tilt angle of the light incident surface of the polarizer when the direction perpendicular to the incident direction is set as a reference is set as θ1,
When viewed from the light incident direction, the Faraday rotator, which is the second optical element housed inside the magnet, has a refractive index of n2, thickness of t2, height of h2, and perpendicular to the light incident direction. The inclination angle of the light incident surface of the Faraday rotator with respect to the direction is set as θ2,
Further, the two recesses are formed at both end portions of the magnet so that one surface of the inner surface is on the same line in the light incident direction,
The first polarizer is housed in a recess formed at the end of the magnet on the light incident side, with the ridge line in contact with one surface of the inner surface.
When viewed from the light incident direction, the polarizer, which is the third optical element housed inside the magnet, has a refractive index of n3, a thickness of t3, a height of h3, and a direction perpendicular to the light incident direction. When the tilt angle of the light incident surface of the polarizer is set as θ3 with reference to
The dimension in the direction perpendicular to the light incident direction of the recess for housing the third polarizer is:

An optical isolator characterized by being set to 2. The optical isolator according to claim 1, wherein when viewed from the light incident direction, the refractive index of the polarizer, which is the first optical element housed in the magnet, is set to n1, and the thickness is set to t1.
When viewed from the light incident direction, the refractive index of the Faraday rotator, which is the second optical element housed inside the magnet, is set to n2, and the thickness is set to t2.
When viewed from the light incident direction, the refractive index of the polarizer, which is the third optical element housed inside the magnet, is set to n3, and the thickness is set to t3.
Furthermore, the two recesses are formed at both ends of the magnet so that one surface of the inner surface has inclination angles θ1 and θ3 when the direction perpendicular to the light incident direction is a reference.
The first and third polarizers are respectively housed in recesses formed at both ends of the magnet with their optical surfaces abutting against one surface of the inner surface, and thus the first and third polarizers. When the light incident surface of the light has a tilt angle θ1 and θ3 with respect to a direction perpendicular to the light incident direction,
Further, when the Faraday rotator is housed in the magnet so that the light incident surface has an inclination angle θ2 when the direction perpendicular to the light incident direction is a reference,
The optical path shifts z1, z2, and z3 between the incident light entering and exiting the two polarizers and the Faraday rotator are as follows:

An optical isolator characterized by being configured as follows.   4. The optical isolator according to claim 3, wherein a magnet surface opposite to one surface of the magnet is removed with each optical element interposed therebetween, and a part of an inner peripheral surface of the through hole is opened. .   4. The light according to claim 1, wherein a groove parallel to the light incident direction is formed from the surface of the magnet opposite to the one surface of the magnet to the through hole with the optical elements interposed therebetween. Isolator.   The groove | channel which is not parallel to the said light-incidence direction was formed from the magnet surface on the opposite side to the one surface of the said magnet to the said through-hole on both sides of each said optical element. Optical isolator.

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