JP2008310068A - In-line optical isolator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the two-step in-line optical isolator of the conventional reflection type causes characteristic deterioration since a polarized wave isolating direction in an optical isolator core approaches a border plane between an incidence side and an emission side, deteriorates by the input of light of 980 nm wavelength and has structure holding no high reliability and to fully make the best use of features of a reflection type optical isolator of small size and low price constitution. <P>SOLUTION: The polarized wave isolating direction is made to be in parallel with the border plane between the incidence side and the emission side. The optical isolator core 3 is assembled by using an inorganic adhesive without using a general optical adhesive or a space is set between optical elements and fixed. After a core block 15 is assembled, the optical isolator core 3 is cut out with an angle conformed to the end face angle of an optical fiber array 2 and is fixed to the vicinity of the end faces of input/output fibers 6, 7 by using a main holder 9 with a slit 9a so as to have minimum size. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention prevents light transmitted in the reverse direction such as reflected light of a transmitted optical signal in an optical signal path of an optical communication system, an optical sensor system, etc., from being input to a signal processing unit of the optical transmission device, etc. The present invention relates to a polarization-independent optical isolator that is not dependent on the polarization direction of light, and particularly relates to an in-line optical isolator having an optical fiber as an input / output terminal.

  An in-line optical isolator is an optical component that has a function of blocking the light in the forward direction while passing the optical signal in the forward direction, and is connected to the optical transmission line alone or as an optical module, optical device, etc. Used in. In general, since the polarization state of an optical signal in an optical transmission line is not constant, a polarization-independent inline optical isolator whose optical characteristics do not depend on the polarization state of the optical signal is used as the inline optical isolator. . This polarization-independent in-line optical isolator is an essential component for preventing deterioration of amplification characteristics in an optical amplifier that amplifies an optical signal as it is without converting it into an electrical signal.

  In recent years, among the polarization-independent in-line optical isolators, as disclosed in the following Patent Documents 1 to 4, the reflective in-line has excellent characteristics, is small, and can greatly reduce the optical fiber handling range. Several optical isolators have been proposed.

  A conventional polarization-independent in-line optical isolator is, for example, a reflection type optical isolator disclosed in Patent Document 1 by using a reflector as shown in FIG. A single wave separation element (birefringent plate) is formed. However, in a non-reflective optical isolator in which an input / output optical fiber protrudes from both ends, two birefringent plates are required.

  In addition, the reflection type optical isolators disclosed in Patent Documents 1 to 4 have a single optical fiber collimator instead of the conventional two, compared with the conventional inline optical isolator in which the input / output optical fibers are exposed from both ends. That's it. This is because the conventional inline optical isolator uses two optical fiber collimators, whereas the reflective optical isolator uses one reflective optical collimator.

  Here, the input / output end of the optical fiber used for the reflection type optical fiber collimator is referred to as “optical fiber array” here, but “(multi-core) ferrule”, “(multi-core) capillary”, “optical fiber block” And so on.

  Furthermore, as for the assembly process, the number of operations for precise alignment of the optical axis, which is the center of the assembly process, is two times when each optical collimator is assembled and one time when the entire optical collimator is assembled in a non-reflection type optical isolator. Although it was necessary three times, in the case of a reflection type optical isolator, only one time is required for assembly. Thereby, the occupation time of the precision alignment apparatus is greatly reduced, and the productivity per precision alignment apparatus is greatly improved.

  Due to these features, the reflective in-line optical isolator has a feature that the product price can be greatly reduced as compared with a conventional product that is not a reflective type.

  Further, conventional polarization-independent in-line optical isolators include a one-stage optical isolator having one optical isolator core and a two-stage optical isolator having two optical isolator cores in series. In general, the two-stage optical isolator has an advantage that the application range is wide, such as a broadband optical amplifier, because the optical isolation value is large and the bandwidth is remarkably wide as compared with the single-stage optical isolator. However, there are disadvantages that the number of constituent elements increases, the structure becomes complicated and the size increases, and the product price becomes expensive, resulting in poor economic efficiency.

  As means for solving this, as disclosed in Patent Document 5, a two-stage optical isolator constituted by a reflection type has been proposed. According to this configuration, as shown in FIGS. 13a and 13b of the same document, since the optical elements constituting the optical isolator core are shared in two stages, the reflection type optical isolator is configured in a small size and at a low price. Features that can be used.

Further, as a method for manufacturing an optical isolator core at a low cost, Patent Document 6 discloses a method in which large optical elements are laminated with an optical adhesive, and then the optical isolator core is cut out and used.
Japanese Patent No. 2710451 JP-A-5-313094 JP 2005-17904 A Japanese Patent Laid-Open No. 2005-241992 US Patent US 6,480,331 B1 US Patent US 5,808,793 A

  In the structure of the conventional reflection type two-stage optical isolator as disclosed in Patent Document 5 with reference to FIGS. 13a and 13b, an optical signal is transmitted by the aligned surface of the input / output optical fiber and the polarization separation element. The plane including each direction branched by polarization separation substantially coincides.

  In addition, the interval between optical fibers in a commercially available optical fiber array is 0.125 mm or 0.25 mm.

  The polarization separation width of the optical signal obtained by the polarization separation element needs to be about 0.03 mm in order to prevent recombination of the light propagating in the reverse direction to the input optical fiber after the polarization separation. The thickness of the optical fiber of the polarization separation element for obtaining the polarization separation width in the optical axis direction is 0.3 mm. The optical thickness of this polarization separation element is about 0.12 mm. The optical thickness of a commercially available reciprocal polarization plane rotating element is about 0.06 mm. From these values, the optical distance between the end face of the optical fiber and the end face on the opposite side of the reciprocal polarization plane rotating element is 0.22 (= 0 if the total thickness of the adhesive layer is about 0.04 mm. .12 + 0.06 + 0.04) mm. Therefore, the spread of the single mode light having a wavelength of 1.55 μm emitted from the optical fiber at this distance is about 0.11 mm as the outer diameter. At this position, two reciprocal polarization plane rotating elements must be fixed to the input optical fiber side and the output optical fiber side, respectively, within a range that covers the entire spread of light.

  Further, the boundary position accuracy between the two reciprocal polarization plane rotation elements is 0.05 mm, the roughness of the side surface of one reciprocal polarization plane rotation element is about 0.03 mm, and the distance between the combined reciprocal polarization plane rotation elements is 0. Assuming 03 mm, the sum of these values is 0.14 (= 0.05 + 0.03 × 2 + 0.03) mm. That is, it is necessary to consider that the width of the boundary region between the two reciprocal polarization plane rotating elements is about 0.14 mm.

  Adding this value and the light spread value of 0.11 mm gives 0.25 (= 0.14 + 0.11) mm. This is because even if an optical fiber array with an optical fiber spacing of 0.25 mm is used, there is almost no room for these reciprocal polarization plane rotating elements to cover all the light, and these processing and assembly accuracy are essential. Means that

  However, when the direction of polarization separation by the polarization separation element coincides with the width direction of the reciprocal polarization plane rotation element perpendicular to the boundary surface between the reciprocal polarization plane rotation elements, this polarization separation width is about 0.03 mm. Therefore, with such processing accuracy and assembly accuracy, the reciprocal polarization plane rotation element cannot cover all the spread of the optical signal. In actual manufacturing, the yield is greatly reduced.

  In order to solve this, the structure of the conventional reflection type two-stage optical isolator requires a special optical fiber array in which the distance between the optical fibers is wider than 0.25 mm as an optical fiber array. Therefore, there is a drawback that the merit of the reflective structure cannot be fully utilized. Increasing the distance between the optical fibers more than necessary is related to the effective diameter of the lens used, and may cause a reduction in coupling efficiency. In addition, improving the accuracy of the fixed position of the reciprocal polarization plane rotating element and the processing accuracy of the constituent materials also lead to an increase in the manufacturing cost, which is not an appropriate method.

  Under these circumstances, as a method that does not use special optical fiber arrays, does not change the processing accuracy and assembly accuracy, and does not reduce the product yield, the polarization separation direction by the polarization separation element is the reciprocal polarization plane rotation element. There is a demand for an optical isolator core structure in which the spread of light does not increase in a direction parallel to the interface between them.

  Patent Document 6 discloses a method of using an adhesive as a method of laminating an optical isolator core, and also discloses a method of using an adhesive in an optical path even in the reflective two-stage optical isolator of Patent Document 5. Yes.

  In general, a nonreciprocal polarization plane rotation element has an absorption band of light on the short wavelength side. For example, when excitation light of an optical amplifier having a strong wavelength near 980 nm is inserted, the temperature of the nonreciprocal polarization plane rotation element is It may rise to 100 degrees or more. In this case, if an optical adhesive is present between the optical elements in the optical path, the optical adhesive is generally an organic system that is weak at high temperatures, so that the adhesive deteriorates, which causes a significant increase in loss. However, the optical isolator is likely to fail. Therefore, a method for assembling an optical isolator core in a compact manner without using a general optical adhesive in the optical path is desired.

  Furthermore, in patent document 6, the laminated | stacked optical isolator core material was cut out in the direction perpendicular | vertical to an end surface. However, when the optical isolator core is installed in the vicinity of the input / output optical fiber terminal for the purpose of miniaturizing the optical isolator core and reducing the price, the optical isolator core is effectively used to suppress the influence of reflected light. Since the axis of the isolator core is fixed perpendicularly to the oblique end face of the optical fiber array, with this state, the axial direction of the optical isolator core is mounted obliquely with respect to the optical axis of the optical signal. In this case, since the optical isolator core needs to cover the entire spread of light, the cross section of the optical isolator core needs to be sized in consideration of the optical axis deviation. Therefore, when the optical isolator core is cut out from a laminated optical isolator core material of a certain size, the number of optical isolator cores cut out is reduced compared to the case where the optical isolator core is simply cut into a cross-sectional size covering the spread of light. Have the drawbacks to be. Therefore, a method for cutting out the optical isolator core for minimizing the cross section of the optical isolator core is desired.

  As an assembly structure of the reflection type two-stage optical isolator, for example, a structure in which respective constituent materials are stacked as in the one-stage optical isolator shown in FIG. Although this method can simplify the structure and simplify the assembling work, the lens to be applied is limited to a refractive index distribution type rod lens whose end face can be easily formed obliquely, and has excellent coupling efficiency. There is a drawback that it cannot be applied to an aspherical lens whose end face is difficult to form at an angle. Furthermore, when an optical fiber array and a lens are laminated as in Patent Document 3, it is necessary to design in consideration of variations in the length and focal length of the lens, and as a result, an adhesive layer of about 30 μm or more is provided between the lenses. There was a need. However, this relatively thick adhesive layer may cause a change in characteristics due to temperature or a decrease in long-term reliability. Therefore, the reflection type two-stage optical isolator is applicable to an aspheric lens, and an assembly structure for keeping the adhesive layer thickness to a minimum is desired.

The present invention has been made to solve such problems,
An optical fiber array including a first optical fiber arranged on the incident side and a second optical fiber arranged on the emission side, and optical axes of the first optical fiber and the second optical fiber being parallel to each other When,
The forward optical signal and the reverse light are introduced on both the incident side and the outgoing side, and the forward optical signal incident from the first optical fiber is emitted from the second optical fiber. An optical isolator core that realizes an optical isolator function that does not emit light in the reverse direction incident from the first optical fiber;
Condensing means for converting the condensing state of the light signal in the forward direction and the light in the reverse direction on both the incident side and the exit side;
Reflecting and introducing the forward light signal introduced from the incident side of the light collecting means to the outgoing side, reflecting the reverse light introduced from the outgoing side of the light collecting means to the incident side, Each of these is a polarization-independent in-line optical isolator, in which the reflecting means to be introduced again into the light collecting means are aligned and fixed in this order, and the optical isolator core includes:
One light input / output surface is disposed near the end face of the optical fiber array in the vicinity of the end face of the optical fiber array including the end face of the first optical fiber and the end face of the second optical fiber,
The incident side portion and the emission side portion each function as an independent optical isolator core,
As the optical element constituting the optical isolator core, the first polarization separation element and the nonreciprocal polarization plane rotation element or the reciprocal polarization plane rotation element and the second polarization separation element,
These optical elements are held in a state arranged in this order and shared between the incident side portion and the emission side portion,
When the non-reciprocal polarization plane rotation element is provided, the first reciprocal polarization plane rotation element and the optical isolator are disposed on the incident side of the optical isolator core between the first polarization separation element and the non-reciprocal polarization plane rotation element. On the output side of the core, there is a second reciprocal polarization plane rotation element,
When the reciprocal polarization plane rotation element is provided, the first non-reciprocal polarization plane rotation element and the optical isolator core are disposed on the incident side of the optical isolator core between the first polarization separation element and the reciprocal polarization plane rotation element. A second non-reciprocal polarization plane rotation element on the emission side of
The directions of polarization separation by the first polarization separation element and the second polarization separation element are perpendicular to the plane including the optical axis of the first optical fiber and the optical axis of the second optical fiber, and the respective lights It exists in the surface containing the optical axis of a fiber, It is characterized by the above-mentioned.

  According to this configuration, the optical isolator core is inserted between the optical fiber array and the condensing means, and one of the light input / output surfaces is disposed in the vicinity of the end face of the optical fiber array. Since one optical input / output surface of the optical isolator core is inserted in a place where the outer diameter of the spread of the emitted optical signal is the smallest, the cross-sectional size of the optical isolator core can be minimized. .

  In addition, according to this configuration, the aligned surfaces of the first and second optical fibers and the surface including each direction in which the optical signal is polarized and separated by the polarization separation element are positioned substantially perpendicularly. Therefore, the spread of light by polarization separation is increased in the direction perpendicular to the boundary surface between the first and second reciprocal polarization plane rotation elements or the boundary surface between the first and second non-reciprocal polarization plane rotation elements. Therefore, the yield of products can be significantly improved compared to the conventional one without using a special optical fiber array and without changing the processing accuracy and the assembly accuracy.

The present invention also provides:
Anti-reflective coating for air is applied to all surfaces through which optical signals of a plurality of optical elements constituting the optical isolator core pass,
These optical elements are characterized in that these opposing surfaces are fixed to each other with a space maintained between the respective surfaces.

  According to this configuration, since it is possible to assemble the optical isolator core without using a general optical adhesive in the optical path, even when pumping light or the like of the optical amplifier is inserted without changing the assembly structure The optical isolator is not deteriorated.

The present invention also provides:
Of the surfaces through which optical signals of the plurality of optical elements constituting the optical isolator core pass, at least a pair of mutually facing surfaces are fixed to each other by an inorganic optical adhesive, and at least one of these two surfaces An antireflective coating is applied to the inorganic optical adhesive.

  According to this configuration, since an inorganic adhesive that can withstand high temperatures is used in the optical path instead of a general optical adhesive, the optical isolator does not deteriorate even when excitation light or the like of the optical amplifier is inserted. .

The present invention also provides:
A plurality of optical elements constituting an optical isolator core, at least a pair of adjacent elements that are rectangular optical elements are fixed to each other to form a block-shaped core block, and then the core block has a desired size. A plurality of the above-mentioned combined devices of the respective elements are formed, and
The cutting angle of the core block is adjusted to the inclination angle of the end face of the optical fiber array facing the optical isolator core including the end face of the first optical fiber and the end face of the second optical fiber. .

  According to this configuration, at least a part of the optical isolator core is composed of each element having a light input / output end face that is inclined in the same manner as the end face of the optical fiber array, and a plurality of pieces are manufactured collectively from one core block, When the optical input / output end face is cut obliquely, the axial direction of the core block substantially coincides with the optical axis direction. This makes it possible to minimize the number of optical isolator core materials cut out from the same-sized core block with a small volume, so that many optical isolator cores can be obtained with a small amount of material. In addition, the cross-sectional area of the optical isolator can be minimized.

  Further, according to the present invention, the end surface opposite to the end surface facing the optical fiber array of the condensing means is located in the vicinity of the focal position of the condensing means and is disposed substantially perpendicular to the optical axis of the condensing means. Thus, the reflection means is formed.

  According to this configuration, the end face opposite to the end face facing the optical fiber array of the condensing means functions as the reflecting means as it is. For this reason, it is not necessary to provide a separate reflecting means adjacent to the light collecting means, the number of parts is reduced and a part of the assembly process is simplified, so that the optical isolator can be made inexpensive, It becomes possible to make it compact.

  In the present invention, the inner surface of the main holder is fixed to one side surface of the optical fiber array or the light collecting means to which the reflecting means is fixed, and the end surface of the main holder is fixed to the other end surface. It is characterized by.

  According to this configuration, the optical fiber array and the light collecting means to which the reflecting means are fixed are integrated by fixing the other end face to the end face of the main holder fixed to one of the side faces. Is done. At this time, the optical fiber array and the reflecting means are moved by moving the main holder along the side surface of either the optical fiber array or the light collecting means in the axial direction of the main holder, that is, in the optical axis direction of each optical fiber. The relative position in the optical axis direction of each optical fiber with the light collecting means to which is fixed is adjusted. Further, the optical axis of each optical fiber between the optical fiber array and the light collecting means to which the reflecting means is fixed is moved by moving the position where the end face of the main holder and the other end face are aligned in the radial direction of the main holder. The relative position in the direction orthogonal to is precisely adjusted.

  For this reason, it is possible to adjust a slight misalignment between the optical fiber array and the light collecting means to which the reflecting means is fixed due to variations in the focal point of the light collecting means to an optimum position in the three-dimensional direction. become. Therefore, in the conventional optical isolator, the relative position in the optical axis direction of each optical fiber was adjusted by the thickness of the adhesive that fixes the components, but in the optical isolator of this configuration, as described above, By moving the main holder along the side surface of either the optical fiber array or the light collecting means, the relative position in the optical axis direction of each optical fiber is adjusted, so that the end surface of the main holder and the other end surface are The adhesive thickness required to fix can always be kept to a minimum. As a result, the positional deviation caused by the curing of the adhesive can be minimized, the deterioration of the optical characteristics caused by the positional deviation can be suppressed, and the long-term reliability is also improved.

Further, in the present invention, one or more splits are formed in the length direction on a portion fixed to at least one side surface of the optical fiber array or the light collecting means of the main holder, and
It is characterized in that at least a part of one side surface of either the optical fiber array or the condensing means is in close contact with a part of the inner surface of the main holder.

  According to this configuration, since at least a part of one of the side surfaces of the optical fiber array or the condensing unit is in close contact with a part of the inner surface of the main holder, the outer diameter accuracy of the optical fiber array or the condensing unit In consideration of the inner diameter accuracy of the main holder, it is not necessary to make a large space between the two so that the two fit together, and the two can be brought into close contact with each other.

  If no split is formed on the main holder, in order to fit both, the space between the two will greatly exceed 10 μm in consideration of manufacturing errors. It becomes necessary to fill with solder. Accordingly, the relative position between the optical fiber array and the light condensing means is slightly shifted due to a change in temperature or the like, resulting in a significant increase in optical signal insertion loss, resulting in unstable optical characteristics.

  According to this configuration, it is possible to closely fix and fix both without changing the processing accuracy of both, so that the optical characteristics such as optical signal insertion loss are stable even if the temperature and humidity change, Long-term reliability is improved.

According to the inline optical isolator of the present invention, as described above, the direction perpendicular to the boundary surface of the first and second reciprocal polarization plane rotating elements or the boundary surface of the first and second non-reciprocal polarization plane rotating elements. Because there is no increase in the spread of light due to polarization separation, it is possible to dramatically improve the product yield compared to the conventional one without using special optical fiber array, changing the processing accuracy and assembly accuracy. Become.

  Furthermore, since the size of the optical isolator core can be minimized and the productivity is improved, it is possible to provide a reflection type two-stage optical isolator that is small and inexpensive.

  Next, the best mode for carrying out the inline optical isolator according to the present invention will be described.

  FIG. 1A is a plan view of the inline optical isolator 1 according to the present embodiment, and FIG. 1B is a side view thereof.

  The inline optical isolator 1 includes an optical fiber array 2, an optical isolator core 3, an aspherical lens 4, and a total reflection mirror 5 arranged in this order.

  In the optical fiber array 2, an input optical fiber 6 that constitutes a first optical fiber and an output optical fiber 7 that constitutes a second optical fiber are arranged in parallel and fixed. The optical isolator core 3 is positioned and fixed to the end face 2b of the optical fiber array 2 via the core spacer 8, and the total reflection mirror 5 is fixed to the aspherical lens 4 via the mirror holder 10. ing. The relative distance between the aspherical lens 4 and the total reflection mirror 5 is controlled by the length shape of the mirror holder 10, and the mirror surface 5 a of the total reflection mirror 5 is positioned substantially at the focal point of the aspherical lens 4. It is perpendicular to the optical axis.

  Here, the end face 2 b of the optical fiber array 2 is formed obliquely with respect to the vertical plane of the optical axes of the input / output optical fibers 6 and 7. Further, the end faces of the respective elements of the optical isolator core 3 are all formed obliquely in the same manner. Therefore, in the inline optical isolator 1, the surfaces substantially perpendicular to the optical axes of the input / output optical fibers 6 and 7 are only the flat surface 4 d of the aspheric lens 4 and the mirror surface 5 a of the total reflection mirror 5. These surfaces 4d and 5a are not exactly parallel, and the flat surface 4d of the aspherical lens 4 is not located near the focal point of the aspherical lens 4, so that the shapes of the light on the surfaces 4d and 5a match. In addition, the multiple reflection due to the formation of a cavity between the surfaces 4d and 5a does not have an adverse effect. All the other end faces are sufficiently angled with respect to the optical axes of the input / output optical fibers 6 and 7 while minimizing reflection by refractive index matching and anti-reflection (AR) coating. Therefore, the incident light signal is not combined with the reflected light. From these facts, the present embodiment has a configuration in which internal reflection is effectively suppressed, no ripple is generated by reflection, and a sufficiently practical value of the return loss is obtained.

  The optical fiber array 2 to which the optical isolator core 3 is fixed and the aspherical lens 4 to which the total reflection mirror 5 is fixed are fixed via a main holder 9. Here, a part of the optical fiber array 2 is inserted inside the main holder 9 so that the optical isolator core 3 is included in the main holder 9, and a part of the outer diameter of the optical fiber array 2 and the main holder A part of the inner diameter of 9 is fixed in close contact with each other. On the other hand, the end surface on the aspheric lens 4 side of the main holder 9 and the side surface on the optical fiber array side of the lens barrel 4b of the aspheric lens 4 are fixed in close contact with each other. The in-line optical isolator 1 manufactured by these steps is packaged with a package (not shown) to ensure reliability and be commercialized.

  The optical fiber array 2 is a commercially available product that is a quartz glass cylinder having an outer diameter of 1.8 [mm], and an input optical fiber 6 and an output optical fiber 7 whose optical axes are parallel to each other at the center. Are arranged in parallel at an interval of 250 [μm] and integrated. The input optical fiber 6 and the output optical fiber 7 are used by being connected to an external optical transmission line made of an optical fiber (not shown) on the end face 2a side of the optical fiber array 2, and the optical signal incident from the input optical fiber 6 is the other. The output optical fiber 7 is configured to emit light. Further, the end surfaces of the input optical fiber 6 and the output optical fiber 7 on the side of each optical component are arranged on the same plane as the end surface 2 b on the optical component side of the optical fiber array 2.

  The end face 2b facing the optical isolator core 3 has each optical axis of the input optical fiber 6 and the output optical fiber 7 as the rotation axis with the axis of intersection with the surface including the optical axes of the input optical fiber 6 and the output optical fiber 7. It is formed at an angle of 8 ° with respect to a plane perpendicular to the surface, optically polished and anti-reflective (AR) coating for air. A core spacer 8 is bonded and fixed to the end face 2b.

The core spacer 8 has a rectangular shape with an outer shape of 0.7 [mm] and a width of 1.0 [mm], a cross-sectional area of 0.7 × 1.0 [mm ² ], and a thickness of 150 [mm]. It is made of a hard plastic plate of μm], and a hole 8a having a cross-sectional area of 0.15 × 0.4 [mm ² ], which is 0.15 mm in length and 0.4 mm in width, is in the center. The input / output optical signal passes through the hole 8a. When fixing the core spacer 8 to the end face 2b of the optical fiber array 2, the core hole 8 is aligned and fixed so that the centers of the center hole 8a and the contours of the input and output optical fibers 6 and 7 coincide with each other. Is done.

The core spacer 8 has a cross-sectional area of 0.6 × 0.85 [rectangular shape of 0.6 mm in length and 0.85 mm in width in the center of the end face on the side of the optical isolator core 3. A flat hollow of mm ² ] and depth of 0.1 [mm] is formed, and the optical isolator core 3 is inserted and fixed in this hollow.

The optical isolator core 3 has an oblique end face of 0.5 [mm] in length and 0.8 [mm] in width, and a thickness of 1.2 [mm] in a direction perpendicular to the oblique end face. The rectangular parallelepiped has a cross-sectional area of 0.5 × 0.8 [mm ² ] and a volume of 0.5 × 0.8 × 1.2 [mm ³ ]. However, the thickness direction has an inclination of 8 degrees from the core axis direction perpendicular to the cross section, and the core spacer 8 and the optical axis directions of the input / output optical fibers 6 and 7 substantially coincide with each other. Fixed in the indentation.

  The core used in the conventional optical isolator has a height of 1.2 [mm] and a width of 1.2 [mm] or more in the case of a normal straight type optical isolator that is not a reflection type. Compared to this, the cross-sectional area is about 1/3 or less, and material costs can be greatly reduced.

  The optical isolator core 3 includes a first rutile 11a constituting the first polarization separation element, a first half-wave plate 12a constituting the first reciprocal polarization plane rotation element, and a second reciprocal polarization plane rotation element. It comprises a second half-wave plate 12b that constitutes, a garnet 13 that constitutes a non-reciprocal polarization plane rotation element, and a second rutile 11b that constitutes a second polarization separation element.

  The optical isolator core 3 is manufactured by a process described later. The optical input / output end faces of these elements are arranged substantially parallel to the end face 2b of the optical fiber array 2, and both end faces 3a of the optical isolator core 3 are arranged. 3b is anti-reflective (AR) coating for air.

  The first rutile 11a, the garnet 13 and the second rutile 11b are composed of an incident side portion located on the optical axis of the input optical fiber 6 and an emission side portion located on the optical axis of the output optical fiber 7. Become. The first half-wave plate 12 a is located on the optical axis of the input optical fiber 6, and the second half-wave plate 12 b is located on the optical axis of the output optical fiber 7. The optical isolator core 3 is formed of a common material on the incident side and the outgoing side except for the first half-wave plate 12a and the second half-wave plate 12b, and two independent optical isolator cores on the incident side and the outgoing side. Has an integrated structure. Here, the first rutile 11a and the second rutile 11b have the same thickness perpendicular to the light input / output end face and the same optical axis direction. Further, the optical axis direction of the first rutile 11a, the second rutile 11b, the first half-wave plate 12a and the second half-wave plate 12b and the magnetization direction of the garnet 13 are described below. Determined by implementation method.

  In this case, the garnet 13 uses a self-magnetization retention type garnet and does not require an external magnetic field for operating the non-reciprocal polarization plane rotation action by the magneto-optical effect, so no permanent magnet is used.

  As described above, the first half-wave plate 12a is positioned on the incident side and needs to include all the light distribution on the incident side, and the second half-wave plate 12b is positioned on the output side and has the light distribution on the output side. All must be included. Therefore, the boundary surface between the first half-wave plate 12a and the second half-wave plate 12b needs to coincide with the central boundary surface between the light distribution on the incident side and the light distribution on the output side.

  The optical isolator core 3 is fixed to the recess of the core spacer 8, whereby the optical isolator core 3 is fixed at a substantially constant position with respect to the input / output optical fibers 6 and 7, and the first half-wave plate 12 a The position of the boundary surface with the second half-wave plate 12b includes the center line of the two optical axes of the optical signal emitted from the input / output optical fibers 6 and 7, and with respect to the plane including these two optical axes. It almost coincides with the position of the vertical surface. Further, by fixing the optical isolator core 3 in the recess of the core spacer 8, one of the optical input / output end faces 3a is disposed in the vicinity of the end face 2b of the optical fiber array 2 so as to face the end face 2b. A light distribution emitted from the fiber 6 and spreading on the end face opposite to the input optical fiber 6 in the first half-wave plate 12 a and a second half of the light signal emitted from the output optical fiber 7 and spread. The light distribution on the end face opposite to the output optical fiber 7 in the wave plate 12b is set so as not to overlap each other on the boundary face. That is, the design is such that the amount of light that is blocked by the boundary surface between the two lights incident on the optical isolator core 3 from the two optical fibers 6 and 7 is minimized.

  Here, conventionally, the polarization separation direction by rutile is the direction perpendicular to this boundary surface as in Patent Document 5, etc., and either one of the input and output is separated in the direction approaching this boundary surface. It had been. Therefore, in this case, there is a high possibility that this boundary surface blocks the end of the distribution of light that is approached, which causes deterioration of optical characteristics.

  In the present embodiment, the direction of polarization separation by the rutiles 11a and 11b is parallel to this boundary surface, and therefore, the light separated by polarization separation does not approach this boundary surface unlike the conventional configuration. , Do not block the end of the light distribution. Further, if positioning is performed with processing accuracy and assembly accuracy as in this embodiment, the positional accuracy of the optical isolator core 3 is ensured, and the yield does not decrease.

  The aspherical lens 4 is a commercially available product, and a lens portion 4a having an outer diameter of 2 [mm] is formed of optical glass to constitute a light collecting means, and is made of stainless steel having an outer diameter of 3 [mm]. It is inserted into the lens barrel 4b. Similarly to the optical isolator core 3, the lens portion 4 a also includes an incident side portion located on the optical axis of the input optical fiber 6 and an emission side portion located on the optical axis of the output optical fiber 7. And the output side. Anti-reflective (AR) coating for air is applied to the lens surface 4c of the aspherical lens 4 and the opposite end surface 4d. The end face 4d is a plane that is nearly perpendicular to the lens optical axis, and faces the optical fiber array 2 and the optical isolator core 3.

  The total reflection mirror 5 is formed of a square glass substrate having an outer shape of 1.2 [mm] and a width of 1.2 [mm], and the reflection surface of this glass substrate has a total reflection of a wavelength of 1.55 [μm]. A dielectric multilayer filter is deposited as a mirror to form a mirror surface 5a.

  The mirror holder 10 is also made of glass and has a hollow cylindrical shape with an inner diameter of 1.2 [mm], an outer diameter of 3 [mm], and a thickness of 1.57 [mm]. The total reflection mirror 5 is fixed to the lens barrel 4 b of the aspherical lens 4 through the mirror holder 10. In this case, the position of the mirror surface 5 a of the total reflection mirror 5 is substantially equal to one focal position of the aspherical lens 4.

A front view, a side view, and a rear view of the main holder 9 are shown in FIGS. 2 (a), 2 (b), and 2 (c), respectively, an outer diameter 3 [mm], an inner diameter 1.79 [mm], and a length 2 [mm] stainless steel cylinder. This main holder 9 is equally spaced at three points in the circumferential direction, length 1 [mm] in the length direction, width 0.2 [mm]
The split 9a is formed.

  The alignment between the optical fiber array 2 to which the optical isolator core 3 is fixed and the aspherical lens 4 to which the total reflection mirror 5 is fixed using the main holder 9 minimizes optical signal insertion loss and the like. In order to optimize the overall characteristics, a precision alignment device (not shown) was used.

  First, the component side of the optical fiber array 2 to which the optical isolator core 3 was fixed was inserted into the side of the end face 9b to which the split 9a of the main holder 9 was applied. In this case, the outer diameter of the optical fiber array 2 is slightly larger than the inner diameter of the main holder 9 even if both dimensional errors are taken into account. However, since the main holder 9 has a split 9a and the material of the main holder 9 has a spring property, it can be inserted with a small pressing force, and the parallelism between the two is ensured, and the relative position Is stable.

  In this state, the aspherical lens 4 to which the optical fiber array 2 and the total reflection mirror 5 are fixed is mounted on the precision alignment device, and the light intensity of the monitor light inserted from the input optical fiber 6 is changed from the output optical fiber 7. As a condition for detecting and maximizing the value, the relative positions of each other were precisely adjusted.

  In this case, before adjustment of the relative position, the relative angle between the end surface 9c of the main holder 9 and the lens barrel end surface 4e of the aspherical lens 4 which are opposed to each other is set to be parallel on the precision alignment device. After that, the relative position in the three-axis direction was adjusted.

  In this state, by adjusting the position of the main holder 9, the distance between the end surface 9 c where the split 9 a of the main holder 9 is not provided and the lens barrel end surface 4 e of the aspherical lens 4 is minimized. After adjusting the relative position with respect to the main holder 9 and confirming again that the relative position between the optical fiber array 2 and the aspherical lens 4 is not deviated from the optimum position, the optical fiber array 2, the main holder 9, and the main holder 9 And the aspherical lens 4 were fixed with an adhesive. At this time, the optical fiber array 2 and the main holder 9 are already in close contact with each other. However, since the pressing force is small, it is necessary to fix them using an adhesive so as not to cause displacement in the length direction. is there.

  In this state, the optical axis of the aspheric lens 4 is arranged substantially parallel to the optical axes of the optical fibers 6 and 7, and the position of the optical axis on the end surface 2 b of the optical fiber array 2 is the aspheric lens 4. The position of the mirror surface 5a of the total reflection mirror 5 is substantially equal to the other focus position of the aspherical lens 4, and the mirror surface 5a of the total reflection mirror 5 is on the optical axis of the aspherical lens 4. It is arranged substantially perpendicular to it. For this reason, at the end face 2 b of the optical fiber array 2, the mode field diameter of the optical signal emitted from the input optical fiber 6 and the mode field diameter of the optical signal propagated to the output optical fiber 7 substantially coincide with each other from the input optical fiber 6. Since the emission angle of the emitted optical signal and the incident angle of the optical signal to the output optical fiber 7 substantially coincide with each other, the propagation efficiency of the optical signal propagating from the input optical fiber 6 to the output optical fiber 7 becomes the best.

  Further, although the thickness of the adhesive layer between the main holder 9 and the aspherical lens 4 is not strictly measured, it is considered to be 10 μm or less from microscopic observation. When such a flexible structure is not adopted, the thickness of the adhesive layer may be about 30 μm or more in consideration of variations in the focal position of the aspheric lens 4 and variations in the length of the core spacer 8. There is a need to consider.

  By these steps, the three-dimensional position between the optical fiber array 2 to which the optical isolator core 3 is fixed and the aspheric lens 4 to which the total reflection mirror 5 is fixed due to variations in the focus of the aspheric lens 4 and the like. A subtle shift can be optimally adjusted at the fixed position of the main holder 9 and the aspherical lens 4. Therefore, the thickness of the adhesive layer that fixes the main holder 9 and the aspherical lens 4 can be kept to a minimum, so that the positional deviation due to the curing of the adhesive is minimized, and the deterioration of the characteristics due to this is reduced. In addition to being able to suppress, it also contributes to the improvement of long-term reliability.

  In the above configuration, an operation when an optical signal having a wavelength of 1.55 [μm] propagates in the forward direction through the inline optical isolator 1 will be described. FIG. 1 described above shows an optical signal path when an optical signal is incident in the forward direction from the input optical fiber 6.

  The optical signal incident in the forward direction from the input optical fiber 6 is first incident on the incident side of the optical isolator core 3. The optical isolator core 3 is operated as an optical isolator, but since it is in the forward direction, it is basically emitted from the incident side of the optical isolator core 3 and then incident on the aspheric lens 4. To do. The optical signal incident on the aspheric lens 4 is converted into collimated light inside the aspheric lens 4, reaches the total reflection mirror 5, and is reflected as collimated light. When the optical signal is reflected and emitted from the aspherical lens 4, the optical signal is converted into condensed light and is incident on the emission side of the optical isolator core 3. Then, after receiving the operation as the optical isolator again in the optical isolator core 3, it is emitted from the emission side of the optical isolator core 3, finally enters the output optical fiber 7, and is sent out to the external optical transmission line.

  FIG. 3 shows the configuration of the optical isolator core 3 and the polarization state at each position of the optical signal propagating in the forward direction from the input optical fiber 6 through the optical isolator core 3.

  The optical signal incident in the forward direction from the input optical fiber 6 is first incident on the optical isolator core 3 on the incident side, and the first single polarized light 14a and the second single polarized light are first transmitted by the first rutile 11a. The polarized light is separated into two single polarized lights 14b. The first single-polarized light 14a is not subject to spatial displacement by the first rutile 11a as ordinary light, but the second single-polarized light 14b is subject to spatial displacement by the first rutile 11a as extraordinary light. Will be separated.

  The polarization separation direction is the same as the inclination direction of the end face 2b of the optical fiber array 2, and is downward when considered in FIG. According to this configuration, the forward optical signal incident from the first optical fiber 6 is subjected to spatial displacement by the first polarization separation element 11a and the second polarization separation element 11b, and two single polarization signals are obtained. Axis deviation that occurs when the optical axes of the wave lights 14a and 14b coincide can be minimized.

  Conventionally, since the direction of polarization separation is the left-right direction when considered in FIG. 1A, considering the position passing through the next first half-wave plate 12a, the boundary with the second half-wave plate 12b is considered. Polarization separation was performed in the direction approaching the surface. In this embodiment, since the polarization separation directions are all in the vertical direction in FIG. 1B, the polarized light does not approach this boundary surface.

  When these two single-polarized light beams 14a and 14b pass through the next first half-wave plate 12a, the plane of polarization rotates 45 degrees counterclockwise. Next, when passing through the garnet 13, the planes of polarization of these two single polarized lights 14a and 14b are further rotated 45 degrees counterclockwise. Through these two processes, the polarization planes of these two single-polarized light beams 14a and 14b are rotated by 90 degrees in total counterclockwise, and the polarization directions are switched. Here, the first rutile 11a and the second rutile 11b have the same optical axis direction and the same thickness. Therefore, for the second rutile 11b, the first single-polarized light 14a becomes abnormal light, and the second single-polarized light 14b becomes ordinary light. Therefore, when these lights pass through the second rutile 11b, only the first single-polarized light 14a is the same as the spatial displacement direction received by the first rutile 11a by the second single-polarized light 14b. It is subject to spatial displacement in the direction of. As a result, the first single-polarized light 14a and the second single-polarized light 14b that have passed through the second rutile 11b have the same optical axis and follow the same locus.

  Accordingly, these lights are emitted from the incident side of the optical isolator core 3 as a single light.

  The optical signal emitted from the incident side of the optical isolator core 3 enters the aspherical lens 4, is converted into collimated light, and is reflected by the total reflection mirror 5. The single light reflected by the total reflection mirror 5 is emitted as the condensed light from the end face 4 d of the aspherical lens 4 and enters the emission side of the optical isolator core 3.

  The optical signal is subjected to the same action on the exit side of the optical isolator core 3 as on the entrance side. In other words, the forward optical signal incident on the output side of the optical isolator core 3 is first transmitted by the second rutile 11b into two single light beams of the first single polarized light 14a and the second single polarized light 14b. Polarized light is separated into single polarized light. At this time, the second single-polarized light 14b is not subject to spatial displacement by the second rutile 11b as ordinary light, but the first single-polarized light 14a is subject to spatial displacement by the second rutile 11b as extraordinary light. Next, when passing through the garnet 13, the planes of polarization of these two single polarized lights 14a and 14b rotate 45 degrees counterclockwise. Next, when passing through the second half-wave plate 12b, the polarization planes of these two single-polarized light beams 14a and 14b are further rotated 45 degrees counterclockwise. Through these two processes, the polarization planes of these two single polarized lights 14a and 14b are rotated by 90 degrees in total counterclockwise, and the polarization directions are switched. Accordingly, for the first rutile 11a, the second single-polarized light 14b becomes abnormal light, and the first single-polarized light 14a becomes ordinary light. Therefore, when these lights pass through the first rutile 11a, only the second single-polarized light 14b has the same spatial displacement direction as that received by the second rutile 11b. Subject to spatial displacement in the direction. As a result, the first single-polarized light 14a and the second single-polarized light 14b that have passed through the first rutile 11a have the same optical axis and become a single light, and follow the same locus. This single light enters the output optical fiber 7 and is transmitted to an external optical transmission line.

  As described above, in this configuration, the optical signal input from the input optical fiber 6 is separated and integrated into the two single-polarized light beams 14a and 14b by the two polarization separation elements 11a and 11b. The output side is repeated once each, but since the optical path lengths of the two single-polarized light beams 14a and 14b are substantially equal, the occurrence of polarization mode dispersion can be substantially eliminated. Therefore, the difference in time required for propagation of ordinary light and extraordinary light from the first optical fiber 6 to the second optical fiber 7 is almost eliminated, so that it can be applied to a high-speed optical transmission line or the like. Will spread significantly.

  Next, an operation when light having a wavelength of 1.55 [μm] propagates in the reverse direction through the inline optical isolator 1 will be described with reference to FIG.

  FIG. 4 shows the configuration of the optical isolator core 3 and the polarization state at each position of light propagating in the opposite direction from the output optical fiber 7 in the optical isolator core 3.

  The reverse optical signal incident from the output optical fiber 7 is first output by the first rutile 11a on the output side in the optical isolator core 3, and then the first single polarized light 14a and the second single polarized light 14b. Are separated into two single polarization lights. At this time, the first single-polarized light 14a is not subject to spatial displacement by the first rutile 11a as ordinary light, but the second single-polarized light 14b is subject to spatial displacement by the first rutile 11a as extraordinary light. Next, when passing through the second half-wave plate 12b, the polarization planes of these two single-polarized light beams 14a and 14b rotate 45 degrees clockwise. However, next, when passing through the garnet 13, the planes of polarization of these two single polarized lights 14a and 14b rotate 45 degrees counterclockwise. Through these two processes, the polarization planes of these two single-polarized light beams 14a and 14b cancel each other and the total rotation angle becomes 0 degrees, and the direction of the polarization plane does not change after all. Accordingly, for the second rutile 11b, similarly, the first single-polarized light 14a becomes ordinary light, and the second single-polarized light 14b becomes abnormal light. Therefore, when these optical signals pass through the second rutile 11b, only the second single-polarized light 14b is further subjected to spatial displacement as abnormal light. As a result, the first single-polarized light 14a and the second single-polarized light 14b enter the aspheric lens 4 from the output side of the optical isolator core 3 as two lights separated from each other.

  However, the 45-degree rotation action of the second half-wave plate 12b and the garnet 13 is affected by the extinction ratio of each element, and further causes a slight deviation due to changes in wavelength and temperature. Therefore, in general, the first single-polarized light 14a and the second single-polarized light 14b are subjected to a spatial displacement similar to that in the forward direction and have a slight component (= higher order component) 14c whose optical axes coincide with each other. 14d remains as indicated by the dotted line in FIG. The presence of high-order components caused by this slight deviation becomes a hindrance to isolation in the conventional one-stage in-line optical isolator, and further causes the isolation to vary greatly depending on the wavelength. Was the cause of the decline.

  These three lights follow different trajectories, are reflected by the total reflection mirror 5 via the aspherical lens 4, and then enter the incident side of the optical isolator core 3. As shown in FIG. 4, the polarization-separated first single-polarized light 14 a and second single-polarized light 14 b are further polarized and separated on the incident side of the optical isolator core 3. Therefore, light that travels in the opposite direction does not enter the input optical fiber 6, and no light is emitted from the input optical fiber 6 to the external optical transmission line.

  Similarly, the higher-order components 14c and 14d indicated by the dotted lines are also polarized and separated as two single-polarized lights 14c and 14d corresponding to ordinary light and extraordinary light on the incident side of the optical isolator core 3, and the optical isolator core. 3 is emitted from the incident side. For this reason, these two single-polarized lights 14c and 14d are not incident on the input optical fiber 6 and are not emitted from the input optical fiber 6 to the external optical transmission line, which is higher than the conventional one-stage inline optical isolator. Isolation in the opposite direction is realized and functions as a two-stage inline optical isolator.

  FIG. 5 is a perspective view showing an assembly structure of the core block 15 for cutting out the optical isolator core 3.

As the optical isolator core material, strip-shaped materials are used as shown in FIG. The material of the first and second half-wave plates 12a and 12b has a width of 0.4 [mm], a length of 6 [mm], and a longitudinal sectional area of 0.4 × 6 [mm ² ]. The size of the material that becomes the first and second rutiles 11a and 11b and the garnet 13 is a width of 0.8 [mm], a length of 6 [mm], and a longitudinal sectional area of 0.8 × 6 [mm ² ]. It is. The thickness of each material is 0.3 [mm] for the material of the first and second rutiles 11a and 11b, and 0.1 [mm] for the material of the first and second half-wave plates 12a and 12b, respectively. The material of the garnet 13 is 0.5 [mm].

  Each material is adhered to each other using lead-free low melting point (optical) glass as shown in FIG. Adhesion is performed by reflowing at 350 ° C. for 5 minutes so that air bubbles are not mixed, and the material of the garnet 13 and the materials of the first and second half-wave plates 12a and 12b, the material of the garnet 13 and the second rutile 11b. The material, the material of the first and second half-wave plates 12a and 12b, and the material of the first rutile 11a were sequentially used. At this time, in each bonding step, the positional relationship of each element was maintained using a jig so that the bonding surface in the previous step was not shifted. After this, the garnet 13 was magnetized. In addition, although it is possible to bond the materials together, in this case, it is important to prevent air bubbles from being mixed.

  In addition, the antireflective (AR) coating for low melting glass was previously given to both surfaces of the material of the garnet 13. Regarding the materials of the first and second rutiles 11a and 11b, the adhesive surface was subjected to an AR coating for low-melting glass, and the opposite surface was subjected to an AR coating for air. In the present embodiment, both surfaces of the materials of the first and second half-wave plates 12a and 12b are not subjected to the AR coating for low-melting glass. However, in order to further suppress reflection on these surfaces, these surfaces are used. In some cases, AR coating may be required.

  FIG. 6 is a side view for explaining a method of cutting out the core block 15 assembled as shown in FIG.

  The cutting angle of the core block 15 shown in FIG. 5A is matched with the angle of the end face 2b of the optical fiber array 2, and cut by cutting at an angle inclined by 8 degrees from the vertical, as shown in FIG. Ten optical isolator cores 3 were produced from one core block 15. Since the plurality of optical isolator cores 3 are manufactured in a lump in this way, alignment of crystal axes is facilitated, which contributes to an improvement in the yield of the optical isolator 1. Further, since a large material is used, there is an advantage that the material cost is greatly reduced. Although some residue is generated at both ends of the core block 15 by cutting, this is not a problem.

  In the above embodiment, even if the iron component of the crystal of the garnet 13 absorbs light having a wavelength of 0.98 [μm] and generates heat, there is no organic adhesive having low heat resistance on the optical path of the optical signal. Therefore, the adhesive does not deteriorate due to the temperature rise of the heat generation, and the characteristic change does not occur as in the conventional case. When light of 100 [mW] was actually irradiated for 24 hours at a wavelength of 0.98 [μm], it was confirmed that there was no change in characteristics before and after irradiation.

  In the above-described embodiment, the aspheric lens 4 and the total reflection mirror 5 are prepared separately. However, as shown in FIG. 7, the aspheric lens 16 and the total reflection mirror 17 can be integrated. . In this case, the aspherical lens 16 is configured by inserting the lens portion 16a into the lens barrel 6b, and the end surface 16d opposite to the lens surface 16c of the lens portion 16a is positioned in the vicinity of the focal position of the aspherical lens 16, In addition, the total reflection mirror 17 is formed so as to be substantially perpendicular to the optical axis of the aspherical lens 16.

  That is, since the total reflection mirror 17 is formed by vapor deposition on the end surface 16d opposite to the lens surface 16c of the aspherical lens 16, the end surface 16d opposite to the lens surface 16c of the aspherical lens 16 is totally reflected as it is. It functions as a mirror 17. Further, the lens surface 16c of the aspherical lens 16 faces the optical fiber array 2, and the influence of this surface on the optical characteristics of the reflected light is further reduced. In this case, the inline optical isolator 1 can be further downsized.

  Further, in the above embodiment, the non-spherical lens 4 is provided with the total reflection mirror 5 which is provided with the AR coating of air on the end surfaces 4c and 4d of the aspheric lens 4 and vapor-deposited separately on the glass substrate. The spherical lens 16 realizes a reduction in processing steps and a reduction in material, and is inexpensive. However, the above-described configuration of the aspherical lens 16 requires a special specification lens as the aspherical lens 16, so that it is difficult to obtain such a special specification aspherical lens 16 or is expensive even if it is available. In some cases, this structure may not be appropriate.

  Further, in the optical isolator core 3 of the above embodiment, the half-wave plate which is a reciprocal polarization plane rotating element is separated on the incident side and the emission side, and the first rutile 11a, the first half-wave plate 12a and the second The case where the half-wave plate 12b, the garnet 13, and the second rutile 11b are arranged in this order has been described. However, the half-wave plate is not separated and is common to the incident side and the emission side, and the garnet, which is a non-reciprocal polarization plane rotating element, is separated on the incident side and the emission side to obtain the first rutile 11a and the first garnet. The second garnet, the half-wave plate, and the second rutile 11b may be arranged in this order.

  The main holder 9 is made of stainless steel, but may be made of a material such as phosphor bronze or hard plastic.

  In the above embodiment, the main holder 9 is cylindrical. However, the shape of the main holder 9 is somewhat complicated and simple due to the shapes of the optical fiber array 2, the optical isolator core 3, the aspherical lens 4, and the like. Instead of the cylindrical shape, a structure in which the diameter of the cylindrical shape changes in the middle and a step is formed may be used. In the above embodiment, the main holder 9 is integrated. However, a structure of a main holder in which a plurality of separated holder parts are combined may be used. In this case, the assembly procedure of a plurality of holder parts is appropriately specified, and the order of alignment between the parts is arbitrarily determined. For example, one of the holder parts separated into the optical fiber array 2 or the aspherical lens 4 can be fixed in advance, and in this case, the relative position between the optical fiber array 2 and the aspherical lens 4 is optimized. Therefore, it is the remaining part of the separated holder part that is adjusted in position.

  In the above embodiment, the main holder 9 is fixed to the side surface of the optical fiber array 2 to which the optical isolator core 3 is fixed, and the main holder is attached to the end surface 4e of the aspherical lens 4 on which the total reflection mirror 5 is fixed. The end face 9c of 9 was fixed. However, the end surface 2b of the optical fiber array 2 in which the side on which the split 9a of the main holder 9 is formed is inserted and fixed to the side surface of the aspherical lens 4 on which the total reflection mirror 5 is fixed, and the optical isolator core 3 is fixed. Alternatively, the end face 9c of the main holder 9 may be fixed. However, in the case of this configuration, the end face 2b of the optical fiber array 2 is not inclined as shown in FIG. 1B, and needs to be perpendicular to the optical axes of the input / output fibers 6 and 7.

In the above embodiment, rutile is used as the polarization separation element. However, an optical birefringence material such as YVO ₄ or lithium niobate may be used.

  In the above embodiment, the self-magnetization maintaining garnet 13 is used as the non-reciprocal polarization plane rotating element for the simplification of the structure. May be used. In this case, the optical isolator core 3 is fixed inside the permanent magnet that is recessed a predetermined distance from the end surface of the hollow cylindrical permanent magnet, and a gap is formed between the end surface of the optical isolator core 3 and the end surface 2b of the optical fiber array 2. By providing it, the core spacer 8 can be substituted. A cylindrical permanent magnet may be fixed inside the main holder 9 around the garnet.

  In the above embodiment, the aspherical lens 4 is used as the light condensing means, but other lenses such as a gradient index lens may be used.

  In the above embodiment, each optical element for the optical isolator core 3 is laminated using the low melting point glass in the state of the core block 15, but the core that cuts out a hole through which an optical signal passes through the portion corresponding to the optical path. A plurality of thin films having a thickness of 100 μm or less formed according to the number of the optical element materials can be laminated by sandwiching the thin film between the strip-shaped optical element materials, and cut into each core. In this case, it is necessary to apply an antireflection coating for air on both surfaces of each optical element. In this case, since an optical signal does not pass through the portion other than the hole of the thin film, a heat resistant adhesive other than the inorganic optical adhesive can be used for bonding each optical element and the thin film.

  Further, in the above-described embodiment, after all the rectangular optical element materials to be a plurality of optical elements constituting the optical isolator core 3 are fixed to each other as shown in FIG. The core block 15 was cut to a desired size as shown in FIG. 6 to form a combination of a plurality of elements, and the optical isolator core 3 was manufactured. However, in the plurality of optical elements constituting the optical isolator core 3, at least a pair of adjacent optical element materials that are adjacent elements are fixed to each other to form a core block. The optical isolator core may be manufactured by cutting into a plurality of elements to form a combined body of a plurality of elements. In this case, the optical element material that has not been made into the core block is cut out individually, and then held in a combined body of the cut out elements after the core block is cut or fixed via a space. .

  In the above-described embodiment, the mutually facing surfaces of all the elements constituting the optical isolator core 3 are fixed to each other by an inorganic optical adhesive such as a low-melting glass, and if necessary, an inorganic optical adhesive. Anti-reflective coating is applied to the agent. However, at least one pair of mutually facing surfaces among the surfaces through which the optical signals of the plurality of optical elements constituting the optical isolator core 3 pass is fixed to each other by the inorganic optical adhesive, and at least one of these two surfaces An antireflective coating for the inorganic optical adhesive may be provided on one surface. That is, when the refractive index of the element material having one of the two surfaces and the refractive index of the inorganic optical adhesive are substantially the same, the non-reflective coating may not be applied to the one surface.

  In addition, in the case of stacking after cutting out individual optical elements, a holder for stacking is prepared, and each optical element is aligned, fixed, and reinforced while giving a slight space on the holder. An optical isolator core may be manufactured. In this case, an anti-reflection coating for air is applied to all surfaces through which optical signals of a plurality of optical elements constituting the optical isolator core pass, and these opposing surfaces are located between the respective surfaces. They are fixed to each other while holding the space.

  According to such an inline optical isolator 1 according to the best embodiment of the present invention, as described above, one optical input / output end surface 3a of the optical isolator core 3 faces the end surface 2b in the vicinity of the end surface 2b of the optical fiber array 2. Since the optical isolator core 3 is inserted in a place where the outer diameter of the optical signal spread is the smallest, the size of the optical isolator core 3 can be minimized.

  Further, since the polarization separation direction by the first rutile 11a and the second rutile 11b is substantially parallel to the boundary surface between the first half-wave plate 12a and the second half-wave plate 12b, the polarization separation is performed. Because there is no optical axis approach to this boundary surface due to, and there is no overlap between the light spreading end and this boundary surface, a special optical fiber array is not used, and processing accuracy and assembly accuracy are changed. Therefore, the product yield can be significantly improved as compared with the conventional method.

  In the above-described embodiment, the mutually facing surfaces of the elements constituting the optical isolator core 3 are fixed to each other by an inorganic optical adhesive such as low-melting glass, and, if necessary, to the inorganic optical adhesive. Anti-reflective coating is applied. Therefore, even when pumping light or the like of the optical amplifier is inserted, the optical isolator does not deteriorate.

  In the above-described embodiment, the optical isolator core 3 includes a plurality of rectangular optical element members fixed to each other and formed into the core block 15, and then the core block 15 is cut into a desired size. A combined body of these elements is formed. For this reason, the combination of the elements obtained by cutting the core block 15 becomes a plurality of optical isolator cores 3, and a plurality of optical isolator cores 3 are manufactured from one core block 15 at a time. For this reason, crystal axis orientation alignment of each element constituting the optical isolator core 3 is facilitated, so that the assembling process can be greatly simplified and the yield in manufacturing the optical isolator core 3 can be improved. Moreover, since each optical isolator core 3 is produced from the core block 15 using the large optical element material of each element, the material cost of the optical isolator core 3 is significantly reduced.

  In the above embodiment, the core block 15 is cut at an angle adjusted to the inclination angle of the end face 2 b of the optical fiber array 2. For this reason, a plurality of optical isolator cores 3 composed of respective elements having light input / output end faces that are inclined in the same manner as the end face 2b of the optical fiber array 2 are produced from one core block 15 in a lump. Since the size of 3 can be minimized, the material cost is further reduced.

  In the optical isolator 1 of the present embodiment, as described above, the relative positions of the optical fibers 6 and 7 in the optical axis direction are adjusted by moving the main holder 9 along the side surface of the optical fiber array 2. The thickness of the adhesive required to fix the end surface 9c of the main holder 9 and the end surface 4e of the aspherical lens 4 can always be minimized.

  Further, a split 9a is inserted in the length direction on the optical fiber array 2 side of the main holder 9, and the overlapping portions of the inner diameter of the main holder 9 and the outer diameter of the optical fiber 2 are always in close contact with each other. Since no adhesive layer is present, changes in characteristics due to changes in temperature or the like can be minimized. This characteristic stability is such that the axial centers of the two coincide with each other, and the shape effect that the influence of shrinkage and expansion due to the temperature of each material can be minimized is greatly contributed.

  As a result, the positional deviation caused by the curing of the adhesive can be minimized, the deterioration of the optical characteristics caused by the positional deviation can be suppressed, and the long-term reliability is also improved.

  As a result, the structure of the two-stage inline optical isolator can be simplified and downsized, and the product price can be reduced without deteriorating the optical characteristics, and the characteristics of the reflective optical isolator can be fully utilized. .

  The in-line optical isolator 1 according to the above embodiment can be applied to an optical communication system, an optical sensor system, and the like. Even in such a case, the same effect as the above-described embodiment can be obtained.

The structure of the in-line optical isolator by the best embodiment is shown, (a) is the top view, (b) is the side view. The structure of the main holder with which the inline optical isolator shown in FIG. 1 is shown is shown, (a) is the front view, (b) is the side view, and (b) is the back view. It is a figure which shows the structure of the optical isolator core with which the in-line optical isolator shown in FIG. 1 is provided, and the polarization state of the optical signal which advances to a forward direction. It is a figure which shows the structure of the optical isolator core with which the in-line optical isolator shown in FIG. 1 is provided, and the polarization state of the light which progresses in a reverse direction. It is a figure which shows the assembly structure of the core block for obtaining the optical isolator core with which the in-line optical isolator shown in FIG. 1 is equipped. It is the figure which showed the method of cutting out an optical isolator core from the core block shown in FIG. It is a figure which shows the modification which integrated the total reflection mirror and the aspherical lens of the aspherical lens with which the in-line optical isolator shown in FIG. 1 is equipped.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... In-line optical isolator 2 ... Optical fiber array 2a, 2b ... End surface 3 of optical fiber array 2 ... Optical isolator core 3a, 3b ... End surface 4, 16 of optical isolator core 3 ... Aspherical lens 4a, 16a ... Lens part 4b, 16b ... Lens barrel 4c, 16c ... Lens surface 4d, 16d of aspheric lens 4 End surface 5, 17 opposite to lens surface 4c of aspheric lens 4 Total reflection mirror 5a ... Mirror surface 6 ... Input optical fiber 7 ... Output Optical fiber 8 ... Core spacer 9 ... Main holder 10 ... Mirror holder 11a ... First rutile (first polarization separation element)
11b ... second rutile (second polarization separation element)
12a: first half-wave plate (first reciprocal polarization plane rotating element)
12b ... Second half-wave plate (second reciprocal polarization plane rotation element)
13 ... Garnet (non-reciprocal polarization plane rotating element)
14a ... 1st single polarized light 14b ... 2nd single polarized light 14c, 14d ... Higher order component 15 ... Core block

Claims (7)

Light including a first optical fiber disposed on the incident side and a second optical fiber disposed on the exit side, and optical axes of the first optical fiber and the second optical fiber being parallel to each other A fiber array,
A forward optical signal and a reverse light are introduced on both the incident side and the outgoing side, and a forward optical signal incident from the first optical fiber is emitted from the second optical fiber, and the second optical fiber is emitted. An optical isolator core that realizes an optical isolator function that does not emit light in the reverse direction from the optical fiber of the first optical fiber;
Condensing means for converting the condensing state of the light signal in the forward direction and the light in the reverse direction on both the incident side and the exit side;
The forward light signal introduced from the incident side of the condensing means is reflected and introduced to the outgoing side, and the reverse light introduced from the outgoing side of the condensing means is reflected and introduced to the incident side. These are polarization-independent in-line optical isolators in which the reflecting means to be introduced again into the light collecting means are aligned and fixed in this order,
The optical isolator core is
One light output / input surface is disposed near the end face of the optical fiber array in the vicinity of the end face of the optical fiber array including the end face of the first optical fiber and the end face of the second optical fiber,
The incident side portion and the emission side portion each function as an independent optical isolator core,
The optical element constituting the optical isolator core includes a first polarization separation element and a nonreciprocal polarization plane rotation element or a reciprocal polarization plane rotation element and a second polarization separation element,
These optical elements are held in a state arranged in this order and shared between the incident side portion and the emission side portion,
When the non-reciprocal polarization plane rotation element is provided, the first reciprocal polarization plane rotation is provided on the incident side of the optical isolator core between the first polarization separation element and the non-reciprocal polarization plane rotation element. A second reciprocal polarization plane rotation element on the output side of the element, the optical isolator core;
When the reciprocal polarization plane rotation element is provided, the first non-reciprocal polarization plane rotation element is provided between the first polarization separation element and the reciprocal polarization plane rotation element on the incident side of the optical isolator core. A second non-reciprocal polarization plane rotation element on the output side of the optical isolator core, and
The direction of polarization separation by the first polarization separation element and the second polarization separation element is perpendicular to a plane including the optical axis of the first optical fiber and the optical axis of the second optical fiber. An in-line optical isolator characterized by existing in a plane including the optical axis of each optical fiber. Anti-reflective coating for air is applied to all surfaces through which optical signals of a plurality of optical elements constituting the optical isolator core pass,
2. The inline optical isolator according to claim 1, wherein the optical elements are fixed to each other in a state in which the facing surfaces hold a space between the respective surfaces.   Among the surfaces through which optical signals of the plurality of optical elements constituting the optical isolator core pass, at least a pair of mutually facing surfaces are fixed to each other by an inorganic optical adhesive, and at least one of these two surfaces The in-line optical isolator according to claim 1, wherein a non-reflective coating is applied to the inorganic optical adhesive. A plurality of optical elements constituting the optical isolator core, at least a pair of adjacent elements that are rectangular optical elements are fixed to each other to form a core block, and then the core block is cut into a desired size. A plurality of combinations of the respective elements are formed, and
The angle at which the core block is cut is adjusted to the inclination angle of the end face of the optical fiber array facing the optical isolator core including the end face of the first optical fiber and the end face of the second optical fiber. The in-line optical isolator according to claim 3.   The end surface of the condensing unit opposite to the end surface facing the optical fiber array is located in the vicinity of the focal position of the condensing unit and is disposed substantially perpendicular to the optical axis of the condensing unit. The inline optical isolator according to any one of claims 1 to 4, wherein the reflection means is formed.   The main holder is fixed to one side surface of the light collecting means to which the optical fiber array or the reflecting means is fixed, and the end surface of the main holder is fixed to the other end surface. The inline optical isolator according to any one of claims 1 to 5. One or more splits are formed in the length direction in a portion fixed to at least one side surface of the optical fiber array or the light collecting means of the main holder, and
The in-line optical isolator according to claim 6, wherein at least a part of one side surface of either the optical fiber array or the condensing unit is in close contact with a part of the inner surface of the main holder.

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