JP2006047812A - Optical isolator and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical isolator for facilitating the assembling to a small-sized laser diode module, and to provide its manufacturing method. <P>SOLUTION: A plate of a first polarizer 2, a plate of a magnetic garnet thick film 3, and a plate of a lens array 1 are cut and separated into individual optical isolators, after respective optical surface is made to face and adhere, and integrate. Here, the substance of the lens array 1 is optical glass or silicon, and the aspheric lens surface is formed on the surface. In addition, a ring band is formed to make a diffraction optical element having image forming effect. At this time, mold molding, etching or a laser ablating method is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical isolator mainly used for optical fiber communication.

  In optical fiber communication, an optical isolator is used to prevent return light to a laser diode as a light source. This optical isolator combines a polarizer and a Faraday rotator, transmits a laser beam emitted from a laser diode, and shields a beam entering the laser diode from an optical waveguide such as an optical fiber, thereby blocking the laser diode. Stable oscillation can be ensured.

  As an example of such an optical isolator, there is an optical isolator disclosed in Patent Document 1.

JP 2004-170540 A

  In the case of the optical isolator according to Patent Document 1 described above, a separate lens is prepared to couple the light beam emitted from the laser diode to the optical waveguide. However, since this lens is separate from the optical isolator, When incorporated in a laser diode module, it is necessary to align the lens and the optical isolator, which causes an increase in man-hours when incorporating the optical isolator. Further, since it is difficult to make the lens and the optical isolator closely contact each other, it has been difficult to reduce the total length of the laser diode module.

  The present invention has been made to solve such problems, and a technical problem thereof is to provide an optical isolator that can be easily assembled and contribute to downsizing of a laser diode module, and a method for manufacturing the same.

  According to the first invention, in an optical isolator including at least two polarizers and at least one Faraday rotator, a lens is integrated on the entire incident side, the emission side, or both. An optical isolator is obtained. With this configuration, an optical isolator that is small in the optical path direction and can be easily incorporated into a laser diode module or the like.

  According to a second invention, there is obtained an optical isolator according to the first invention, wherein the lens is manufactured from a lens array made of optical glass. In this configuration, a lens array plate made of optical glass that can be processed by molding or the like is used.

  According to a third invention, in the optical isolator of the first invention, an optical isolator is obtained in which the lens is manufactured from a silicon substrate. In this configuration, a lens array formed on a silicon substrate having a high refractive index capable of high-precision surface processing is used.

  According to a fourth invention, there is provided an optical isolator according to any one of the first to third inventions, wherein the lens is a diffractive optical element having an imaging effect. In this configuration, a diffractive optical element having an imaging effect is used as a lens.

  According to the fifth invention, after integrating at least two plates of the polarizer, at least one plate of the Faraday rotator, and the plate of the lens array so that the optical surfaces of the plates face each other, A method for manufacturing an optical isolator, characterized by cutting, is obtained. By this method, a large number of optical isolator chips are obtained by cutting and separating from several integrated plates.

  In the case of the optical isolator of the present invention, by integrating the optical isolator and the lens, position adjustment between the lens and the optical isolator can be omitted, and the optical isolator can be easily incorporated into the laser diode module. Further, the close contact between the lens and the optical isolator can contribute to shortening the overall length of the laser diode module.

  The optical isolator according to the best mode of the present invention is an optical isolator comprising at least a polarizer and a Faraday rotator as optical elements, and a lens is attached to the incident side, the reflection side, or both of the optical isolator. In this case, the lens is preferably made of optical glass or silicon, and is made of an aspherical lens or a diffractive element having an imaging function.

  Furthermore, if the lens is arrayed, and the polarizer and magnetic garnet thick plate (plate) constituting the optical isolator element are integrated, the arrayed lens is integrated into a single process. An optical isolator can be manufactured.

  Hereinafter, the optical isolator of the present invention will be described in detail with reference to the drawings with some embodiments.

  FIG. 1 is a perspective view showing an outline of a manufacturing process of an optical isolator according to Embodiment 1 of the present invention, and FIG. 2 is a side view of a lens array used in the optical isolator according to Embodiment 1 of the present invention.

  In FIG. 1, reference numeral 1 denotes a lens array, in which an aspherical lens having a diameter of 0.8 mm is formed in an array on M-NbFD83 (manufactured by HOYA), which is an optical glass. The aspheric shape is expressed by the following equation.

In Equation 1, Z: displacement in the optical axis direction (so-called sag amount) with respect to the surface apex at the periphery of the optical surface that is an aspheric surface, c: curvature near the center, k: cone coefficient, r: from the surface apex , A ₁ : r quadratic coefficient, a ₂ : r fourth coefficient, a ₃ : r sixth coefficient, a ₄ : r eighth coefficient. In the aspherical surface of Example 1, c = 1.759547, k = −0.046336, a ₁ = 0.414119, a ₂ = −2.7728137, a ₃ = −0.194329, a ₄ = 1. 140452. The thickness of the central portion (the thickness from the top of the surface to the opposite plane) is 0.2 mm.

  The lens array 1 is obtained by molding optical glass M-NbFD83 (manufactured by HOYA Co., Ltd.) into a plate shape and the above shape by injection molding. 2 is a first polarizer, and 4 is a CUPO (trade name of HOYA Co., Ltd.) as a second polarizer. The forward direction (from the lens array 1 to the polarizer) depends on the polarization rotation direction of the Faraday rotator. The angle of the transmitted polarization direction is 45 degrees so that the incident beam passes in the direction of propagation of the light beam to 4). The thickness of both the first polarizer 2 and the second polarizer 4 is 0.2 mm.

  Reference numeral 3 denotes a magnetic garnet thick film that constitutes a Faraday rotator. When a magnetic field that saturates an internal magnetic field is applied, the magnetic garnet thick film has an effect of rotating the incident polarization direction. The thickness of the magnetic garnet thick film 3 is 0.5 mm so that the incident polarization direction is rotated 45 degrees at 1550 nm.

  When the isolator according to the first embodiment is manufactured, first, the first polarizer 2, the magnetic garnet thick film 3, and the second polarizer 4 are bonded together. In this case, when importance is attached to the optical characteristics, a light beam having a working wavelength is incident from the second polarizer 4 side, and the leakage light emitted to the first polarizer 2 side is minimized. In addition, the relative angle between the first polarizer 2 and the second polarizer 4 is adjusted. On the other hand, when priority is given to shortening the manufacturing tact, the edges of the three members of the first polarizer 2, the magnetic garnet thick film 3, and the second polarizer 4 may be aligned and bonded.

  After bonding the three members constituting the optical isolator, the lens array 1 is bonded and fixed, and the composite 5 is created. After bonding and fixing, although not shown, a dicing saw, a wire cutter or the like is used to cut and separate the optical isolator chip 6 so that one aspherical lens constituting the lens array 1 is combined with one optical isolator element. To manufacture. Although not shown, the optical isolator chip 6 operates as an optical isolator by adding a permanent magnet for applying a magnetic field to the magnetic garnet thick film 3.

  In the first embodiment, by using a molding optical glass having a high refractive index as a lens material, aberrations of the lens system can be favorably corrected, and a laser diode having a numerical aperture 0.4 of the emitted beam Is coupled to a single mode fiber having a numerical aperture of 0.1, the distance from the laser diode end surface to the lens surface is 0.6 mm, and the distance from the exit surface of the second polarizer 4 to the single mode fiber is 1.8 mm. By adjusting the position of the azimuth perpendicular to the beam propagation direction, the distance from the laser diode to the single mode fiber was shortened to 3.5 mm, and a coupling efficiency of 80% was obtained at a wavelength of 1550 nm.

  In the first embodiment, the lens is arranged on the laser diode side (incident side of the optical isolator). However, when the distance between the laser diode and the lens can be increased, the second polarizer side (optical isolator) is used. The same effect can be obtained even if a lens having an optimized optical surface shape is disposed on the light exit side.

  In this example, CUPO (manufactured by HOYA) was used as the polarizer, but a polar core (manufactured by Corning), which is a similar absorption polarizer, or rutile, which is a separate polarizer, was used. However, the same effect can be obtained.

  FIG. 3 is a perspective view showing an outline of a manufacturing process of an optical isolator according to Embodiment 2 of the present invention. In FIG. 3, reference numeral 7 denotes a first lens array, in which a diffractive element having an imaging function is formed on a silicon substrate by etching. FIG. 4 is a schematic cross-sectional view of the central portion of the first lens array 7, and 8 is the central portion of the diffractive element constituting the first lens array. Each annular zone of each lens constituting the lens array gives a phase difference to the incident light wavefront. The phase difference given by the lenses constituting the first lens array 7 is given by the following equation.

In Equation 2, Φ is a phase difference (radian), A _i is an i-th order coefficient, and ρ is a surface radius (mm). In the second embodiment, A ₁ = −8103.315706 and A ₂ = 15419.85.

  9 is a polar core (manufactured by Corning), which is a first polarizer, and its thickness is 0.2 mm. Reference numeral 10 denotes a so-called hard magnetic garnet thick film that exhibits a Faraday effect by an internal magnetic field, and has a thickness of 0.5 mm. 11 is a polar core (manufactured by Corning) as a second polarizer, and its thickness is 0.2 mm.

Reference numeral 12 denotes a second lens array. Like the first lens array, a diffractive element having an imaging function is formed on a silicon substrate by etching. Since the structure is the same as that of the first lens array 7, the description thereof is omitted. Each annular zone of each lens constituting the second lens array gives a phase difference to the incident light wavefront. The phase difference given by the lenses constituting the second lens array 12 is given by the same formula as in the case of the first lens array 7. In the case of the second lens array 12, A ₁ = −2027.515737 , A ₂ = 16150.13.

  When assembling the isolator according to the second embodiment, first, the first polarizer 9, the hard magnetic garnet thick film 10, and the second polarizer 11 are bonded together. In this case, when importance is attached to the optical characteristics, the light beam having the working wavelength is incident from the second polarizer 11 side, and the leakage light emitted to the first polarizer 9 side is minimized. In addition, the relative angle between the first polarizer 9 and the second polarizer 11 is adjusted. On the other hand, when priority is given to shortening the manufacturing tact, the edges of the three members of the first polarizer 9, the hard magnetic garnet thick film 10, and the second polarizer 11 may be aligned and bonded.

  After bonding the three members constituting the optical isolator, the first lens array 7 and the second lens array 12 are bonded and fixed, and the composite 13 is manufactured. After bonding and fixing, although not shown, a dicing saw, a wire cutter or the like is used so that one diffractive element constituting the first lens array 7 and the second lens array 12 is combined with one optical isolator element. Then, the optical isolator chip 14 is manufactured.

  In the second embodiment, a diffraction element having an imaging function is formed on a silicon substrate having a thickness of 0.3 mm, so that a laser diode with a numerical aperture of 0.4 is used as a single mode with a numerical aperture of 0.1. In the case of coupling to a fiber, the distance from the laser diode end surface to the lens surface is 0.25 mm, the distance from the exit surface of the second polarizer 4 to the single mode fiber is 0.9 mm, and the position is in the direction perpendicular to the beam propagation direction. By adjusting the distance, the distance from the laser diode to the single mode fiber was shortened to 3.5 mm, and a coupling efficiency of 90% was obtained at a wavelength of 1550 nm.

  In this embodiment, the total length of the optical isolator can be further shortened by using a diffractive element having an imaging function as a coupling lens.

  FIG. 5 is a perspective view showing an outline of the manufacturing process of the optical isolator according to the third embodiment of the present invention. In FIG. 5, reference numeral 15 denotes a lens array, which is an aspherical lens formed on a silicon substrate by laser ablation with a carbon dioxide laser. The aspheric shape is expressed by the following formula.

Since the meaning of each coefficient in Equation 3 is the same as that in the first embodiment, the description thereof is omitted. In the third embodiment, c = −1.031137, k = −2.39681, a ₁ = −0.052863, a ₂ = 0.027988, and a ₃ = a ₄ = 0.

  Reference numeral 16 denotes a polar core (manufactured by Corning) as a first polarizer, and its thickness is 0.2 mm. Reference numeral 17 denotes a magnetic garnet thick film having a thickness of 0.5 mm. 18 is a polar core (manufactured by Corning), which is a second polarizer, and its thickness is 0.2 mm.

  When assembling the optical isolator of Example 3, first, the first polarizer 16, the magnetic garnet thick film 17, and the second polarizer 18 are bonded together. In this case, when importance is attached to the optical characteristics, the light beam having the working wavelength is incident from the second polarizer 18 side, and the leakage light emitted to the first polarizer 16 side is minimized. In addition, the relative angle between the first polarizer 16 and the second polarizer 18 is adjusted. On the other hand, when priority is given to shortening the manufacturing tact, the edges of the three members of the first polarizer 16, the magnetic garnet thick film 17, and the second polarizer 18 may be aligned and bonded.

  After the three members constituting the optical isolator are bonded to produce the composite 19, the lens array 15 is bonded and fixed to the first polarizer 16. In this case, as shown in the drawing, the surface of the lens array 15 on which the aspheric lens shape is formed is bonded to the incident surface of the first polarizer 16. In this case, an adhesive is filled between the lens array 15 and the first polarizer 16, but in Example 3, an epoxy adhesive having a refractive index of 1.539 at a wavelength of 1550 nm. Is used.

  After bonding and fixing, although not shown, using a dicing saw, a wire cutter or the like, the optical isolator chip 20 is manufactured by cutting and separating so that one lens is combined with one optical isolator element. Although not shown, a permanent magnet for applying a magnetic field to the magnetic garnet thick film 17 is added to the isolator chip 20 to operate as an optical isolator.

  In the third embodiment, an aspherical shape is formed on a silicon substrate having a thickness of 0.3 mm, so that a laser diode having a numerical aperture of 0.4 is coupled to a single mode fiber having a numerical aperture of 0.1. In this case, the distance from the laser diode end surface to the lens surface is 0.48 mm, the distance from the exit surface of the second polarizer 4 to the single mode fiber is 1.81 mm, and the position of the azimuth perpendicular to the beam propagation direction is adjusted. As a result, a coupling efficiency of 95% was obtained at a wavelength of 1550 nm.

  In the third embodiment, the aspherical surface portion formed on the silicon substrate is opposed to the optical isolator element side, so that the plane side of the substrate is opposed to the laser diode side. By doing so, particularly high coupling efficiency could be achieved.

  The optical isolator according to the present invention has been described based on the above three embodiments. In the three embodiments, each of the optical isolator elements is a so-called single-stage optical isolator composed of a first polarizer, a magnetic garnet thin film, and a second polarizer. 2 are arranged in series, or a so-called two-stage optical isolator, or a magnetic garnet thin film and a third polarizer are further arranged on the emission side of the one-stage optical isolator. Even if it is a five-stage optical isolator, the effect of the present invention is exhibited similarly.

The perspective view which shows the outline of the manufacturing process of the optical isolator which concerns on Example 1 of invention. 1 is a side view of a lens array used in an optical isolator according to Embodiment 1 of the present invention. The perspective view which shows the outline of the manufacturing process of the optical isolator which concerns on Example 2 of this invention. Sectional drawing of the center part of the 1st lens array 7 which concerns on Example 2 of this invention. The perspective view which shows the outline of the manufacturing process of the optical isolator which concerns on Example 3 of this invention.

Explanation of symbols

1,15 Lens array 2,9,16 First polarizer 3,17 Magnetic garnet thick film 4,11,18 Second polarizer 5,13,19 Composite 6,14,20 Optical isolator chip 7 First Lens array 8 Central portion 10 of diffraction element Hard magnetic garnet thick film 12 Second lens array

Claims (5)

  An optical isolator comprising at least two polarizers and at least one Faraday rotator, wherein a lens is integrated on the entire incident side, the emission side, or both.   2. The optical isolator according to claim 1, wherein the lens is manufactured from a lens array made of optical glass.   2. The optical isolator according to claim 1, wherein the lens is manufactured from a silicon substrate.   4. The optical isolator according to claim 1, wherein the lens is a diffractive optical element having an imaging effect.   The at least two plates of the polarizer, the at least one plate of the Faraday rotator, and the lens array plate are integrated so that the optical surfaces of the plates face each other, and then cut. Manufacturing method of optical isolator.

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