JP2006228790A - Optical isolator and optical fiber amplifier using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical isolator of a simple structure which is easy to be assembled, can be manufactured by a low cost and miniaturized. <P>SOLUTION: This optical isolator is constituted by arranging a first birefringence crystal 1, a Faraday rotor 2, a second birefringence crystal 3, and a third birefringence crystal 4 in this order, unifying them as a spherical object, and having a tube ferrule 5 with an incidence photometry fiber, and a tube ferrule 6 with an outgoing photometry fiber. The interface of the birefringence crystal 1 and the Faraday rotor 2 and the interface of the Faraday rotor 2 and the birefringence crystal 3 are inclined substantially in the same direction to the advancing direction of a signal light which is incident, and the direction of the optical axis of the birefringence crystal 3 is directed in the direction which performs the amount of the revolution mostly in the same direction as the Faraday rotation by the Faraday rotor 2 from the direction of the optical axis of the birefringence crystal 1, and the optical surface having the refractivity at the incidence side of the birefringence crystal 1 and the emitting side of the birefringence crystal 4 is arranged integrally. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical isolator used mainly in an optical communication system such as an optical amplifier and an optical fiber amplifier using the optical isolator.

  Conventionally, an erbium-doped optical fiber amplifier (hereinafter referred to as EDFA) is generally used as an optical amplifier used for optical communication. Since the EDFA has an amplification band in the 1.55 μm band, which is the lowest loss of a single mode fiber (SMF), the chance of being widely used in a wavelength division multiplexing (WDM) system for long-distance optical transmission is increasing. As an amplification method, basically, a rare earth element such as erbium (Er) is optically excited, an inversion distribution is formed by keeping electrons in the upper rank, and optical amplification of signal light is obtained by stimulated emission. Therefore, the basic components of an EDFA are an erbium-doped optical fiber (EDF) that is an optical fiber for amplification, a pumping light source (having a wavelength of 0.98 μm or 1.48 μm), and pumping light. And a wavelength division multiplexing filter (WDM filter) that performs wavelength multiplexing of signal light.

  Incidentally, other optical fiber amplifiers include praseodymium (Pr) in the 1.3 μm band, thulium (Tm) in the 1.4 μm band, and other systems include Raman amplifiers that utilize the nonlinear effects of optical fibers, or Semiconductor optical amplifiers (SOA) and the like have been developed. Among them, although Raman amplifiers are attracting attention as commercialized systems, they require a high-power excitation light source compared to EDFAs, or the number of parts associated therewith tends to increase. However, it has not been spread as much as the recent EDFA whose price has been reduced.

  Incidentally, a distributed feedback semiconductor laser (hereinafter referred to as a DFB laser) is generally used as a signal light source amplified by an EDFA. This DFB laser has the characteristic that the oscillation spectrum is narrow and has excellent dispersion characteristics, but on the other hand, it is very sensitive to the return light from the reflected light, and from the coupling end face to the optical fiber and other discontinuous interfaces. When the reflected light returns, the characteristic becomes unstable. Therefore, in the EDFA, in order to prevent the reflected light from returning to the light-emitting element that is the signal light source, a one-way transmission function of light (transmits forward light and reverse light) between the signal light source and the EDF. An in-line type optical isolator having a function of blocking light is arranged to block the return light of reflected light from the optical fiber in the direction of the signal light source, so that stable operation can always be performed.

  As described above, the amplification unit serving as the core in the EDFA is an EDF, an excitation light source, and a WDM filter that performs wavelength multiplexing of signal light and excitation light, and these optical components cannot be omitted in principle. In the case of an optical isolator, the return light from the reflection point is prevented and greatly contributes to the stable oscillation of the signal light source, but the influence of the return light is determined by the product of the reflectance from the reflection point and the gain, When the reflectance is low or the gain is small (for example, the gain is about 10 dB), it can be made unnecessary. Recently, EDFA prices have been reduced, and there is a movement to omit parts. However, such omission of parts greatly limits the transmission capacity and transmission distance of signal light. Therefore, there is a demand for hybridizing parts and lowering the price of a single part. Among the optical passive devices that attract attention, in-line optical isolators in which wavelength multiplexing / demultiplexing filters and optical isolators are hybridized, in-line optical isolators in which WDM filters and optical isolators are hybridized (so-called WDM optical isolators) Thing).

  As an example of such an in-line type optical isolator, signal light is incident on a first optical fiber in one optical waveguide, and a part of the first reflective material is transmitted through a first lens for monitoring. , And after passing through the first lens again, is incident on the second optical fiber, and other signal light is sequentially supplied to the second lens, the independent optical isolator, the third lens, the second reflective material, When the excitation light from the excitation light source is incident on the second optical fiber in the second optical waveguide in addition to being transmitted through the fourth lens and incident on the first optical fiber in the other optical waveguide, the excitation light Is emitted from the second optical fiber, is emitted from the fourth lens, is reflected by the second reflecting material, is transmitted through the fourth lens again, and is then incident on the first optical fiber. The so-called forward excitation light Of the type made it possible to enter the EDF together with the signal light (see Patent Document 1).

JP 2001-174665 A (Page 3, FIG. 1)

  In the case of the in-line type optical isolator disclosed in Patent Document 1, a fiber coupling lens, a reflective material (wavelength demultiplexing / multiplexing device such as a WDM filter), and an independent optical isolator, which are the main parts of various optical components, are independent of each other. In addition to the problem that it takes time to assemble because of the configuration deployed in the device, the spatial dimensions of the device and the optical fiber amplifier package are limited, and the number of parts is large, so miniaturization is realized. There is a problem that it is difficult to reduce the manufacturing cost.

  The present invention has been made to solve such problems, and its technical problem is that an optical isolator having a small and simple structure that can be easily assembled and manufactured at low cost, and an optical isolator using the same. It is to provide a fiber amplifier.

  According to the present invention, the first birefringent crystal, the first Faraday rotator, the second birefringent crystal, and the third birefringent crystal are arranged in this order from the incident side. The interface of the first birefringent crystal and the first Faraday rotator and the interface of the first Faraday rotator and the second birefringent crystal are approximately the same with respect to the traveling direction of the incident signal light. The orientation of the optical axis of the second birefringent crystal is the same direction as the Faraday rotation by the first Faraday rotator from the orientation of the optical axis of the first birefringent crystal. Oriented in substantially the same amount of direction, and an optical surface having refraction or an optical element having refraction is integrated on the incident side of the first birefringent crystal and the exit side of the third birefringent crystal. Optically arranged isolators can be obtained.

  According to the present invention, in the optical isolator, at least one of the vicinity of the interface between the first birefringent crystal and the first Faraday rotator and the vicinity of the interface between the first Faraday rotator and the second birefringent crystal. Thus, an optical isolator having a wavelength division multiplexing filter provided with a pumping light input port for allowing pumping light to enter can be obtained.

  Furthermore, according to the present invention, in any of the above optical isolators, the optical element having a refractive property is a planoconvex spherical lens or a planoconvex aspherical surface having a plane opposite to the incident surface of the first birefringent crystal. Any one of a lens, a diffractive lens, a gradient index lens, and a planoconvex spherical lens, a planoconvex aspherical lens, a diffractive lens, and a refractive index whose surface facing the exit surface of the second birefringent crystal is a plane. An optical isolator that is any one of distributed lenses is obtained.

  In addition, according to the present invention, in any one of the above optical isolators, the optical surface having the refractive properties is a surface on the incident side of the first birefringent crystal processed into a substantially spherical shape and the second birefringent crystal. An optical isolator that is a surface on the emission side is obtained. In this optical isolator, it is preferable that the outer periphery of the first birefringent crystal, the first Faraday rotator, the second birefringent crystal, and the third birefringent crystal integrated into a substantially spherical shape.

  On the other hand, according to the present invention, from the incident side, the first birefringent crystal, the first Faraday rotator, the second birefringent crystal, the third birefringent crystal, the second Faraday rotator, and the fourth A birefringent crystal is arranged in this order, and the interface between the first birefringent crystal and the first Faraday rotator, and the interface between the first Faraday rotator and the second birefringent crystal. Are inclined by substantially the same amount in the same direction with respect to the traveling direction of the incident signal light, and the interface between the third birefringent crystal and the second Faraday rotator, the second Faraday rotator, and The interface of the fourth Faraday rotator is inclined in substantially the same direction with respect to the traveling direction of the incident signal light, and the orientation of the optical axis of the second birefringent crystal is the first Faraday by the first Faraday rotator from the orientation of the optical axis of the birefringent crystal The direction of the optical axis of the fourth birefringent crystal is directed from the direction of the optical axis of the third birefringent crystal to the second Faraday. The direction of the optical axis of the third birefringent crystal is substantially the same as the direction of the optical axis of the second birefringent crystal. An optical surface having a refractive property or an optical element having a refractive property is integrally disposed on the incident side of the first birefringent crystal and the exit side of the third birefringent crystal that is oriented in an orthogonal direction. An optical isolator is obtained.

  According to the present invention, in the optical isolator, in the vicinity of the interface between the first birefringent crystal and the first Faraday rotator, in the vicinity of the interface between the first Faraday rotator and the second birefringent crystal, the third Provided with an excitation light input port for making excitation light incident on at least one of the vicinity of the interface of the birefringent crystal and the second Faraday rotator and the vicinity of the interface of the second Faraday rotator and the fourth birefringence crystal An optical isolator having a wavelength division multiplex filter is obtained.

  Furthermore, according to the present invention, in any of the above optical isolators, the optical element having a refractive property is a planoconvex spherical lens or a planoconvex aspherical surface having a plane opposite to the incident surface of the first birefringent crystal. Any one of a lens, a diffractive lens, and a gradient index lens, and a planoconvex spherical lens, a planoconvex aspherical lens, a diffractive lens, a refractive index whose surface facing the exit surface of the fourth birefringent crystal is a plane An optical isolator that is any one of distributed lenses is obtained.

  In addition, according to the present invention, in any one of the above optical isolators, the optical surface having the refractive properties is a surface on the incident side of the first birefringent crystal processed into a substantially spherical shape and the second birefringent crystal. Of the first birefringent crystal processed into a substantially spherical shape, the surface of the third birefringent crystal, the surface of the third birefringent crystal on the incident side, the surface of the fourth birefringent crystal on the output side. And an optical isolator which is a surface on the emission side of the fourth birefringent crystal. In this optical isolator, the outer periphery of the first birefringent crystal, the first Faraday rotator, and the second birefringent crystal integrated into a substantially spherical shape, the third birefringent crystal, the second birefringent crystal, The outer periphery of the integrated Faraday rotator and fourth birefringent crystal is processed into a substantially spherical shape, or the first birefringent crystal, the first Faraday rotator, the second birefringent crystal, the third It is preferable that the outer periphery of the integrated birefringent crystal, the second Faraday rotator, and the fourth birefringent crystal is processed into a substantially spherical shape.

  On the other hand, according to the present invention, an optical fiber amplifier using any one of the above optical isolators can be obtained.

  In the case of the optical isolator according to the present invention, the outer periphery of the integrated main part of various optical elements is processed into a substantially spherical shape, and the optical isolator is provided with an optical isolator and a wavelength multiplexing / demultiplexing filter (wavelength division multiplexing filter). On the other hand, since it has a refractive lens function, it is easy to assemble with a small number of parts, and has a simple and compact structure that can be manufactured at low cost. The degree of freedom of the spatial dimensions of the amplifier package is increased, and a small-sized structure can be easily formed at low cost even when an optical fiber amplifier is constructed.

  One of the optical isolators according to the best mode of the present invention includes a first birefringent crystal, a first Faraday rotator, a second birefringent crystal, and a third birefringent crystal in this order from the incident side. The interface of the first birefringent crystal and the first Faraday rotator and the interface of the first Faraday rotator and the second birefringent crystal are respectively the traveling directions of the incident signal light. The orientation of the optical axis of the second birefringent crystal is the same as the Faraday rotation by the first Faraday rotator from the orientation of the optical axis of the first birefringent crystal. The optical surface having refraction or the optical element having refraction is integrated on the incident side of the first birefringent crystal and the exit side of the third birefringent crystal. Are arranged. With such a configuration, the lens for converging the laser beam emitted from the core of the optical fiber and the so-called one-stage polarization-independent optical isolator can be integrated to reduce the size of the device.

  Another optical isolator according to the best mode of the present invention includes a first birefringent crystal, a first Faraday rotator, a second birefringent crystal, a third birefringent crystal, a second birefringent crystal from the incident side. The Faraday rotator and the fourth birefringent crystal are arranged in this order, and the interface between the first birefringent crystal and the first Faraday rotator, the first Faraday rotator, and the second birefringent crystal. The refraction crystal interface is inclined by substantially the same amount in the same direction with respect to the traveling direction of the incident signal light, and the interface between the third birefringence crystal and the second Faraday rotator and the second Faraday rotator. And the interface of the fourth Faraday rotator are inclined in substantially the same direction with respect to the traveling direction of the incident signal light, and the orientation of the optical axis of the second birefringent crystal is the first birefringence. From the orientation of the optical axis of the crystal, the first Faraday rotator causes The direction of the optical axis of the fourth birefringent crystal is directed from the direction of the optical axis of the third birefringent crystal to the second Faraday rotator. The direction of the optical axis of the third birefringent crystal is oriented almost perpendicular to the direction of the optical axis of the second birefringent crystal. The optical surface having the refractive property or the optical element having the refractive property is integrally disposed on the incident side of the first birefringent crystal and the outgoing side of the third birefringent crystal. With such a configuration, the lens for converging the laser beam emitted from the core of the optical fiber and the so-called two-stage polarization-independent optical isolator can be integrated, and the device can be similarly reduced in size.

  However, in the former optical isolator, at least one of the vicinity of the interface between the first birefringent crystal and the first Faraday rotator and the vicinity of the interface between the first Faraday rotator and the second birefringent crystal is compared with the latter. In the optical isolator, near the interface between the first birefringent crystal and the first Faraday rotator, near the interface between the first Faraday rotator and the second birefringent crystal, the third birefringent crystal, and the second Wavelength division multiplex filter provided with excitation light input ports for making excitation light incident on at least one of the vicinity of the interface of the Faraday rotator and the vicinity of the interface of the second Faraday rotator and the fourth birefringent crystal, respectively. It is preferable to arrange a (WDM filter). According to this configuration, the device for making the excitation light incident on the amplification optical fiber and the optical isolator can be integrated.

  Further, in the former optical isolator, the optical surface having the refractive property is set as the surface on the incident side of the first birefringent crystal processed into a substantially spherical shape and the surface on the output side of the second birefringent crystal, The outer periphery of the first birefringent crystal, the first Faraday rotator, the second birefringent crystal, and the third birefringent crystal is processed into a substantially spherical shape. In the latter optical isolator, The incident side surface of the first birefringent crystal and the exit side surface of the second birefringent crystal, the incident side surface of the third birefringent crystal, and the fourth The surface of the birefringent crystal on the exit side, or the surface on the incident side of the first birefringent crystal processed into a substantially spherical shape and the surface on the exit side of the fourth birefringent crystal, Of the birefringent crystal, the first Faraday rotator, and the second birefringent crystal The outer periphery of the third birefringent crystal, the second Faraday rotator, and the fourth birefringent crystal integrated into a substantially spherical shape, or the first birefringent crystal, It is preferable that the outer periphery of the integrated first Faraday rotator, second birefringent crystal, third birefringent crystal, second Faraday rotator, and fourth birefringent crystal is processed into a substantially spherical shape. . According to this configuration, the lens for converging the laser beam emitted from the optical fiber can be omitted, the size can be further reduced, and the outer periphery of the integrated birefringent crystal is substantially spherical. It is possible to realize both downsizing and facilitating processing by processing into a single shape.

  Furthermore, in the former optical isolator, as a refractive optical element, a plano-convex spherical lens, a plano-convex aspheric lens, a diffractive lens, a refractive index, and the like are planes opposite to the incident surface of the first birefringent crystal. Any one of a distributed lens and any one of a plano-convex spherical lens, a plano-convex aspherical lens, a diffractive lens, and a gradient index lens whose surface facing the exit surface of the second birefringent crystal is a plane. In the latter optical isolator, as a refractive optical element, the refractive optical element is a plano-convex spherical lens having a plane opposite to the incident surface of the first birefringent crystal. , Any one of a plano-convex aspheric lens, a diffractive lens, and a gradient index lens, and a plano-convex spherical lens having a plane opposite to the exit surface of the fourth birefringent crystal, a plano-convex aspheric lens, Diffraction lens, gradient index lens It is preferable assumed to be one of. According to this configuration, it is possible to integrate the functions of a lens for converging a laser beam emitted from an optical fiber, an optical isolator, and a wavelength division multiplexing filter (WDM filter) for allowing excitation light to enter.

  In addition, in both the former and the latter optical isolators, if a device in which these functions are integrated is incorporated into an optical fiber amplifier package, a smaller and higher performance optical fiber amplifier can be constructed.

  Hereinafter, some examples will be given, and the optical isolator of the present invention and the optical fiber amplifier using the optical isolator will be specifically described including the manufacturing process thereof.

  FIG. 1 is a schematic diagram showing a basic configuration of an optical isolator according to Embodiment 1 of the present invention.

The optical isolator according to Example 1 uses a first birefringent crystal 1 using rutile (TiO ₂ ), a Faraday rotator 2 using a GdBi iron garnet film (GdBiIG thick film), and rutile (TiO ₂ ). The second birefringent crystal 3 and the third birefringent crystal 4 arranged in this order and integrated as a spherical shape having an outer diameter of 2 mm are different from those of the first birefringent crystal 1 on the incident side. A ferrule 5 with an incident side optical fiber that emits signal light to the vicinity is disposed, and an output side for allowing the signal light transmitted therethrough to enter the vicinity of the third birefringent crystal 4 on the output side. A ferrule 6 with an optical fiber is arranged. Note that the Faraday rotator 2 has a polarization direction of a laser beam incident due to the Faraday effect viewed from the first birefringent crystal 1 side in a state where a magnetic field is applied in a direction parallel to the beam traveling direction by a magnet (not shown). Thus, it has a function of rotating 45 degrees counterclockwise.

  As thicknesses of various optical members, the thickness of the central portion is 0.6 mm for the first birefringent crystal 1, 0.5 mm for the Faraday rotator 2, 0.15 mm for the second birefringent crystal 3, The birefringent crystal 4 is 0.75 mm. Also, the interface between the first birefringent crystal 1 and the Faraday rotator 2 and the interface between the Faraday rotator 2 and the second birefringent crystal 3 are the central axes of the integrated devices as shown in FIG. It is inclined 4 degrees from the plane orthogonal to.

  FIG. 2 is a schematic diagram showing the orientations of the optical axes of the birefringent crystals 1, 3, and 4 provided in the optical isolator.

  Here, when viewed from the first birefringent crystal 1 side, the optical axis is the direction of arrow C1, the optical axis of the second birefringent crystal 3 is the direction of arrow C2, and the optical axis of the third birefringent crystal 4 is Each direction is directed to the direction of the arrow C3, and the relationship between the three is as shown in FIG. 2, in which the orientation of the optical axis of the second birefringent crystal 3 is counterclockwise to the orientation of the first birefringent crystal 1. This indicates that the direction of the optical axis of the third birefringent crystal 4 is orthogonal to the direction of the optical axis of the second birefringent crystal 3.

  In the case of this optical isolator, when the signal light emitted from the optical fiber core portion of the ferrule 5 with the incident side optical fiber is incident on the first birefringent crystal 1, the incident surface is processed into a spherical surface. It propagates in the refractive crystal 1 as a substantially parallel beam. Thereafter, the signal light beam is converted into two beams of an ordinary light component and an extraordinary light component corresponding to the optical axis of the first birefringent crystal 1 at the interface between the first birefringent crystal 1 and the Faraday rotator 2. The angles determined by the ordinary light refractive index and the extraordinary light refractive index and Snell's law (for example, when the wavelength of the signal light is 1550 nm, the emission angle is 4.246 degrees for the ordinary light component, and 4 for the extraordinary light component). .690 degrees), the first birefringent crystal 1 exits and enters the Faraday rotator 2.

  The polarization directions of the two signal light beams are rotated approximately 45 degrees in the counterclockwise direction when viewed from the side of the first birefringent crystal 1 inside the Faraday rotator 2 due to the Faraday effect. The two beams that have reached the interface between the Faraday rotator 2 and the second birefringent crystal 3 correspond to the ordinary light refractive index and the extraordinary light refractive index corresponding to the orientation of the optical axis of the second birefringent crystal 3, respectively. The light is refracted at an angle determined by Snell's law and is incident on the second birefringent crystal 3. The orientation of the optical axis of the second birefringent crystal 3 is counterclockwise from the orientation of the optical axis of the first birefringent crystal 1 as shown in FIG. The rotation direction and the rotation amount are the same as the rotation direction and the rotation amount in the polarization direction by the Faraday rotator 2. Whether it becomes an ordinary light component or an extraordinary light component when incident is coincident with the state when the first birefringent crystal 1 is emitted.

  That is, the signal light beam on the side emitted as the ordinary light component when emitted from the first birefringent crystal 1 is also incident as the ordinary light component when incident on the second birefringent crystal 3. The signal light beam on the side emitted as the extraordinary light component when the birefringent crystal 1 is emitted also enters the second birefringent crystal 3 as the extraordinary light component. Accordingly, the two signal light beams are refracted in the same amount as that emitted from the first birefringent crystal 1 (the emission angle is 4.246 degrees for the ordinary light component and 4.690 degrees for the extraordinary light component). Is incident on the second birefringent crystal 3 in the direction opposite to the direction of emission of the first birefringent crystal 1. Therefore, the two signal light beams propagate inside the second birefringent crystal 3 in a state of being parallel to each other.

  The optical distances of the paths through which the two signal light beams propagate are different when they reach the interface between the second birefringent crystal 3 and the third birefringent crystal 4, and at the wavelength of 1550 nm, the two birefringent crystals are different. The optical distance of the propagation path of the beam that has propagated inside the 3,4 as normal light is 3.509 mm, and the optical distance of the propagation path of the beam that has propagated as extraordinary light is 3.701 mm. If there is such a difference in the optical distance between the paths of the two beams, polarization dispersion becomes a problem when the signal light enters the core portion of the ferrule 6 with the outgoing-side optical fiber, but the third birefringent crystal 4 Solves this problem and compensates for the difference in optical distance between the paths of the two signal light beams. Since the optical axis of the third birefringent crystal 8 is orthogonal to the optical axis of the second birefringent crystal 3 as shown in FIG. 2, the optical distance difference between the two signal light beams is corrected. In addition, at the time of exiting the third birefringent crystal 4, the optical distances of the propagation paths of the two signal light beams are both 5.538 mm, and the difference therebetween is eliminated, and the problem of polarization dispersion is solved.

  When the third birefringent crystal 4 is emitted, the two beams are converged by the spherical refraction (lens function) of the exit surface, but the two signal light beams are converted into parallel light beams parallel to each other. Since it propagates through the inside of the refracting crystal 4, it converges to the same position after exiting the third birefringent crystal 4. If the arrangement of the ferrule 6 with the outgoing optical fiber is adjusted so that the core portion of the optical fiber of the ferrule 6 with the outgoing optical fiber is positioned at the convergence point of the two beams, the signal light is the optical isolator according to the first embodiment. Will pass.

  Next, the operation when the reflected light generated at the connection point on the propagation path is emitted from the end face of the ferrule 6 with the outgoing side optical fiber will be described. The light beam emitted from the ferrule 6 with the outgoing side optical fiber is incident on the third birefringent crystal 4, but becomes a parallel beam due to the refraction (lens function) of the spherical entrance surface. 4 propagates inside. At this time, when propagating by separating into an ordinary light component and an extraordinary light component in a form corresponding to the azimuth of the optical axis and exiting the second birefringent crystal 3, if the wavelength is 1550 nm, the emission angle of the ordinary light component is The incident light component exits at 4.246 degrees and 4.690 degrees, and enters the Faraday rotator 2.

  In the Faraday rotator 2, the polarization directions of the two beams are rotated 45 degrees in the clockwise direction when viewed from the second birefringent crystal 2 side in accordance with the nonreciprocity of the Faraday rotation. As a result, when two beams are emitted from the Faraday rotator 2 and incident on the first birefringent crystal 1, the beam transmitted as an ordinary light component when passing through the second birefringent crystal 3 is When the light is incident on the birefringent crystal 1, it is incident as an extraordinary light component, but the beam that has passed through the second birefringent crystal 3 as an extraordinary light component is incident on the first birefringent crystal 1 as an ordinary light component. As a result, the outgoing angle after refracting at the interface between the Faraday rotator 2 and the first birefringent crystal 1 is 3.621 degrees for ordinary light and 4.418 degrees for extraordinary light. The incident angle when the signal light emitted from the ferrule 5 with the incident side optical fiber passes through the inside of the first birefringent crystal 1 and enters the interface between the first birefringent crystal 1 and the Faraday rotator 2 is 4. Therefore, the propagation angle differs from that in the case where the signal light propagates from the left to the right in FIG.

  The two parallel beams propagated through the first birefringent crystal 1 at such an angle become convergent beams due to the refraction (lens function) of the optical surface having the spherical shape of the first birefringent crystal 1 and are incident on the incident side. Although propagating to the ferrule 5 with fiber, the propagation angle inside the first birefringent crystal 1 is different from that at the time of propagation of signal light, so that it deviates from the optical fiber core portion of the ferrule 5 with incident side optical fiber. It converges at the point.

  As described above, the beam emitted from the ferrule 6 with the outgoing side optical fiber does not enter the optical fiber core portion of the ferrule 5 with the incoming side optical fiber, and operates as an optical isolator.

  FIG. 3 is a schematic diagram showing a basic configuration of an optical isolator according to Embodiment 2 of the present invention.

The optical isolator according to Example 2 includes a first birefringent crystal 11 using a yttrium vanadate (YVO ₄ ) single crystal, a first Faraday rotator 12 using a GdBi iron garnet film (GdBiIG thick film), A second birefringent crystal 13 using a yttrium vanadate (YVO ₄ ) single crystal arranged in this order and integrated into a spherical shape having an outer diameter of 2 mm, and a yttrium vanadate (YVO ₄ ) single crystal A third birefringent crystal 21 used, a second Faraday rotator 22 made of a GdBi iron garnet film (GdBiIG thick film), a fourth birefringent crystal 23 using a yttrium vanadate (YVO ₄ ) single crystal, Are arranged in this order and arranged in parallel as a spherical shape having an outer diameter of 2 mm, and the first birefringence crystal on the incident side in these is arranged. The ferrule 15 with an incident-side optical fiber that emits signal light is disposed near the area 11, and the signal light transmitted therethrough is incident on the vicinity of the fourth birefringent crystal 23 on the emission side. An output-side ferrule 16 with an optical fiber is arranged. The first Faraday rotator 12 changes the polarization direction of the laser beam incident by the Faraday effect in a state where a magnetic field is applied in a direction parallel to the beam traveling direction by a magnet (not shown). The second Faraday rotator 22 has a function of rotating 45 degrees in the counterclockwise direction when viewed from the side. It has a function of rotating the polarization direction of the incident laser beam by the Faraday effect by 45 degrees counterclockwise as viewed from the third birefringent crystal 21 side.

  As thicknesses of various optical members, with respect to the thickness of the central portion, the first birefringent crystal 11 in the first spherical body is 0.75 mm, the first Faraday rotator 12 is 0.5 mm, and the second birefringent crystal. 13 is 0.75 mm, the third birefringent crystal 21 in the second spherical body is 0.75 mm, the second Faraday rotator 22 is 0.5 mm, and the fourth birefringent crystal 23 is 0.75 mm. is there. Further, the interface between the first birefringent crystal 11 and the first Faraday rotator 12, the interface between the first Faraday rotator 12 and the second birefringent crystal 13, the third birefringent crystal 21 and the second Faraday. The interface of the rotor 22 and the interfaces of the second Faraday rotator 22 and the fourth birefringent crystal 23 are inclined by 4 degrees from the plane orthogonal to the central axis of each integrated device as shown in FIG. ing.

  FIG. 4 is a schematic diagram showing the orientation of the optical axes of the birefringent crystals 11, 13, 21, 23 provided in the optical isolator.

  Here, as viewed from the first birefringent crystal 11 side, the optical axis is the direction of the arrow C1, the optical axis of the second birefringent crystal 13 is the direction of the arrow C2, and the third birefringent crystal 21 is the direction of the arrow. The orientation of C3 and the orientation of the fourth birefringent crystal 23 are respectively directed to the orientation of the arrow C4, and the relationship between the four is that the orientation of the optical axis of the second birefringent crystal 13 is as shown in FIG. The orientation of the first birefringent crystal 11 is oriented 45 degrees counterclockwise, and the orientation of the optical axis of the third birefringent crystal 21 is that of the optical axis of the second birefringent crystal 13. The azimuth of the optical axis of the fourth birefringent crystal 23 is orthogonal to the azimuth and is directed to a direction obtained by rotating the azimuth of the optical axis of the third birefringent crystal 21 by 45 degrees counterclockwise. It is shown that.

  In the case of this optical isolator, the propagation process of the beam emitted from the optical fiber core part of the ferrule 15 with the incident side optical fiber is described in the first embodiment until the signal light is incident on the second birefringent crystal 13. Since it is the same, description is abbreviate | omitted. When the signal light beam obtained by splitting the second birefringent crystal 13 into two beams is emitted, the second birefringent crystal 13 becomes a convergent beam due to the refraction (lens function) of the spherically shaped optical surface. The two beams which are emitted from the birefringent crystal 13 and become convergent beams once form a beam waist and then diverge and enter the third birefringent crystal 21. Since the azimuth of the optical axis is orthogonal to the azimuth of the optical axis of the second birefringent crystal 13, the signal light beam propagated through the first birefringent crystal 11 and the second birefringent crystal 13 as ordinary light, The third birefringent crystal 21 is propagated as extraordinary light.

  The relationship between the rotation direction and the rotation amount in the polarization direction of the second Faraday rotator 22 and the orientation of the optical axis of the fourth birefringent crystal 23 is the same as in the first Faraday rotator 12 and the second birefringent crystal 13. Since the relationship is the same, the signal light beam that has propagated through the third birefringent crystal 21 as extraordinary light propagates through the fourth birefringent crystal 23 as extraordinary light. Similarly, the signal light beam propagated through the first birefringent crystal 11 and the second birefringent crystal 13 as extraordinary light propagates through the third birefringent crystal 21 and the fourth birefringent crystal 23 as ordinary light. become. Therefore, for the signal light beam, two of the four birefringent crystals 11, 13, 21, 23 on the propagation path are transmitted as ordinary light, and two are transmitted as abnormal light. Polarization dispersion will not occur.

  The signal light beam transmitted through the fourth birefringent crystal 23 becomes convergent light due to the refractive property (lens function) of the optical surface having the spherical shape of the fourth birefringent crystal 23, and passes through the fourth birefringent crystal 23. Exit. Since the two signal light beams are parallel light beams propagated through the fourth birefringent crystal 23, they converge at the same position after exiting the fourth birefringent crystal 23. If the arrangement of the ferrule 16 with the output side optical fiber is adjusted so that the core portion of the ferrule 16 with the output side optical fiber is positioned at the convergence point of the two beams, the signal light is the optical isolator according to the second embodiment. Will pass.

  Next, the operation when the reflected light generated at the connection point on the propagation path is emitted from the end face of the ferrule 16 with the outgoing optical fiber will be described. The light beam emitted from the ferrule 16 with the emission side optical fiber enters the fourth birefringent crystal 23, but propagates through the inside of the crystal as a parallel beam due to the refractive property (lens function) of the spherical incident surface. At this time, when propagating by separating into an ordinary light component and an extraordinary light component in a form corresponding to the azimuth of the optical axis and exiting the fourth birefringent crystal 23, the same angle as in the case of the first embodiment is used. 2 enters the Faraday rotator 22.

  Subsequent beams emitted from the end face of the ferrule 16 with the outgoing-side optical fiber propagate in the optical isolator according to the second embodiment from the right to the left in FIG. 3 in the same manner as in the first embodiment. However, since the orientation of the optical axis of the third birefringent crystal 21 and the orientation of the optical axis of the second birefringent crystal 13 are orthogonal to each other as shown in FIG. The polarization states at 13 and 11 are separated into extraordinary light and ordinary light in the fourth birefringent crystal 23, and the extraordinary light is ordinary light in the third birefringent crystal 21 and the second birefringent crystal 13. The extraordinary light becomes ordinary light in the first birefringent crystal 11, and the ordinary light becomes extraordinary light in the third birefringent crystal 21, ordinary light in the second birefringent crystal 13, and extraordinary light in the first birefringent crystal 11.

  The beam emitted from the ferrule 16 with the outgoing-side optical fiber is split into two and propagates in such a polarization state, and then, depending on the refractive property (lens function) of the spherical optical surface of the first birefringent crystal 11. Although it becomes a convergent beam and is emitted toward the ferrule 15 with the incident side optical fiber, the propagation angle when the propagation angle in the first birefringent crystal 11 propagates with respect to the beam emitted from the ferrule 15 with the incident side optical fiber Therefore, the light beam converges at a point deviated from the optical fiber core portion of the ferrule 15 with the incident side optical fiber.

  As described above, the beam emitted from the ferrule 16 with the outgoing optical fiber does not enter the optical fiber core portion of the ferrule 15 with the incoming optical fiber, and operates as an optical isolator. Note that the optical isolator according to the second embodiment has a so-called two-stage configuration using four birefringent crystals and two Faraday rotators as a polarizer, and therefore, compared with the optical isolator of the first embodiment. Higher isolation can be obtained, and the polarization dispersion can be compensated without adding new parts by adjusting the orientation of the optical axis of each birefringent crystal.

  FIG. 5 is a schematic diagram showing a basic configuration of an optical isolator according to Embodiment 3 of the present invention.

The optical isolator according to the third embodiment includes silicon oxide (SiO ₂ ) and tantalum pentoxide (Ta ₂ ) by ion-assisted deposition between the first birefringent crystal 1 and the Faraday rotator 2 in the optical isolator according to the first embodiment. O ₅ ) and 71 layers are laminated so that a 1550 nm band light beam is transmitted and a 1480 nm band beam is reflected, and the WDM filter 19 is arranged so as to form a similar spherical shape. Furthermore, a ferrule 35 with an optical fiber for excitation light incidence, which includes a PANDA fiber, which is a kind of polarization maintaining fiber, is provided on the ferrule 5 side with the incident side optical fiber. Here, the ferrule 35 with an optical fiber for excitation light incidence here has the polarization direction of the PANDA fiber that holds the polarization direction of the emitted excitation light so that it propagates as an ordinary light component inside the first birefringent crystal 1. A laser module (not shown) that emits excitation light having a wavelength of 1480 nm is connected to the PANDA fiber that has been adjusted in advance.

  Here, the first birefringent crystal 1, the Faraday rotator 2, the second birefringent crystal 3, the third birefringent crystal 4, the ferrule 5 with the incident side optical fiber, and the ferrule 6 with the outgoing side optical fiber In the same manner as in Example 1, the signal light emitted from the ferrule 5 with the incident side optical fiber enters the ferrule 6 with the outgoing optical fiber, and the return light emitted from the ferrule 6 with the outgoing optical fiber Since the process of not entering the optical fiber core portion of the ferrule 5 with the incident side optical fiber is the same as that in the first embodiment, the description thereof is omitted. Incidentally, since the WDM filter 19 disposed in the propagation path transmits a beam having a wavelength of 1550 nm, it does not affect the propagation of the signal light and the propagation of the return light.

  In the case of this optical isolator, the excitation light emitted from the laser module is emitted from the PANDA fiber of the ferrule 35 with an optical fiber for excitation light input and is incident on the first birefringent crystal 1. Due to the refraction (lens function) of the optical surface having a spherical shape, it becomes a parallel beam and propagates inside and enters the WDM filter 19.

  Therefore, since the WDM filter 19 reflects a light beam having a wavelength of 1480 nm, the excitation light incident on the WDM filter 19 is reflected here and propagates to the ferrule 5 side with the incident-side optical fiber. The birefringent crystal 1 is converted into a convergent beam by the refraction (lens function) of the optical surface having a spherical shape, and is incident on the optical fiber core portion of the ferrule 5 with the incident side optical fiber. In the actual manufacturing process, the position of the ferrule 35 with an optical fiber for excitation light incidence is adjusted and fixed so that the excitation light accurately enters the ferrule 5 with an incident side optical fiber.

  In the optical isolator according to the third embodiment, the excitation light emitted from the ferrule 35 with an optical fiber for exciting light incidence can be incident on the ferrule 5 with an incident-side optical fiber for emitting signal light. It is arranged on the output side of the amplifying optical fiber in the optical fiber amplifier to prevent the return light from returning to the amplifying optical fiber and to a so-called backward pumping method in which the pumping light is incident from the output side of the amplifying optical fiber. It is possible to apply. In addition, a WDM filter 19 is provided at the interface between the Faraday rotator 2 and the second birefringent crystal 3, and the ferrule 35 with an optical fiber for excitation light incidence is reflected by the WDM filter 19 and then the ferrule with an output side optical fiber is reflected. If it is configured to be arranged at a position where it is incident on the optical fiber core 6, it can be applied by changing to a so-called forward pumping system.

  FIG. 6 is a schematic diagram showing a basic configuration of an optical isolator according to Embodiment 4 of the present invention.

The optical isolator according to the fourth embodiment includes silicon oxide (SiO ₂ ) and tantalum pentoxide by ion-assisted vapor deposition between the fourth birefringent crystal 23 and the second Faraday rotator 22 in the optical isolator according to the second embodiment. By laminating 71 layers of (Ta ₂ O ₅ ), a WDM filter 29 made to transmit a light beam in the 1550 nm band and reflect a beam in the 1480 nm band is arranged to form a similar spherical shape. Further, a ferrule 45 with an optical fiber for pumping light incident is provided on the side of the ferrule 6 with an optical fiber on the output side, which includes a PANDA fiber that is a kind of polarization maintaining fiber. Here, the ferrule 45 with an optical fiber for exciting light incident here has the polarization direction of the PANDA fiber that holds the polarization direction of the emitted excitation light so that it propagates as an ordinary light component in the first birefringent crystal 1. A laser module (not shown) that emits excitation light having a wavelength of 1480 nm is connected to the PANDA fiber that has been adjusted in advance.

  The first birefringent crystal 11, the first Faraday rotator 12, the second birefringent crystal 13, the third birefringent crystal 21, the second Faraday rotator 22, and the fourth birefringent crystal 23 here. The ferrule 15 with the incident side optical fiber and the ferrule 16 with the output side optical fiber are the same as in the second embodiment, and the signal light emitted from the ferrule 15 with the incident side optical fiber is the ferrule 16 with the output optical fiber. And the process in which the return light emitted from the ferrule 16 with the output-side optical fiber is not incident on the optical fiber core portion of the ferrule 15 with the input-side optical fiber are the same as those in the second embodiment. Description of is omitted. Incidentally, since the WDM filter 29 arranged in the propagation path transmits a beam having a wavelength of 1550 nm, it does not affect the propagation of the signal light and the propagation of the return light.

  In the case of this optical isolator, the excitation light emitted from the laser module is emitted from the PANDA fiber of the ferrule 45 with an optical fiber for excitation light input and is incident on the fourth birefringent crystal 23. Due to the refraction (lens function) of the optical surface having a spherical shape, it becomes a parallel beam and propagates inside and enters the WDM filter 29.

  Therefore, since the WDM filter 29 reflects a light beam having a wavelength of 1480 nm, the excitation light incident on the WDM filter 29 is reflected here and propagates to the ferrule 16 side with the incident side optical fiber. The fourth birefringent crystal 23 becomes a convergent beam due to the refraction (lens function) of the optical surface having a spherical shape, and is incident on the optical fiber core portion of the ferrule 16 with the output side optical fiber. In the actual manufacturing process, the position of the ferrule 45 with an optical fiber for excitation light incidence is adjusted and fixed so that the excitation light accurately enters the ferrule 16 with an output-side optical fiber.

  In the optical isolator according to the fourth embodiment, the excitation light emitted from the ferrule 45 with an optical fiber for exciting light incident can be made incident on the ferrule 16 with an output-side optical fiber for entering signal light. It is arranged on the input side of the amplification optical fiber in the optical fiber amplifier so as to prevent the return light from returning to the signal source on the near side of the optical fiber amplifier and to make the excitation light incident from the input side of the amplification optical fiber. It can be applied to the forward excitation scheme. In addition, a WDM filter 29 is provided at the interface between the first birefringent crystal 11 and the Faraday rotator 12, and the ferrule 45 with an optical fiber for excitation light incidence is reflected by the WDM filter 29 and then a ferrule with an incident side optical fiber is provided. If it is arranged at a position where it is incident on the 15 optical fiber cores, it can be applied by changing to a so-called forward pumping system.

  FIG. 7 is a schematic diagram showing a basic configuration of an optical isolator according to Embodiment 5 of the present invention.

The optical isolator according to Example 5 includes a refractive index distribution type lens 41 using a SELFOC lens manufactured by Nippon Sheet Glass Co., Ltd., a first birefringent crystal 31 using a rutile (TiO ₂ ) single crystal, a GdBi iron garnet film ( Faraday rotator 32 by GdBiIG thick), rutile (TiO ₂₎ second birefringent crystal 33 using a single crystal, as well as rutile (third birefringent crystal 34 with TiO ₂₎ single crystal, and Japan The refractive index distribution type lens 42 made of plate glass manufactured by Plate Glass Co., Ltd. is arranged in this order and integrated so that the outer shape is a square shape with a cross section of 2 mm square and a cube shape with a length of 4 mm. A ferrule 25 with an incident-side optical fiber that emits signal light is disposed in the vicinity of a gradient-index lens 41 that becomes a refractive index distribution-type lens 42 is constructed by arranging the emission-side optical fiber ferrule 26 to be incident signal light transmitted through it against the vicinity of. Note that the Faraday rotator 32 has a polarization direction of a laser beam incident due to the Faraday effect viewed from the first birefringent crystal 1 side in a state where a magnetic field is applied in a direction parallel to the beam traveling direction by a magnet (not shown). Thus, it has a function of rotating 45 degrees counterclockwise.

  As for the thicknesses of various optical members, the thicknesses of the central portions are 1 mm for the gradient index lenses 41 and 42, 0.6 mm for the first birefringent crystal 31, 0.5 mm for the Faraday rotator 32, and the second compound. The refractive crystal 33 is 0.15 mm, and the third birefringent crystal 34 is 0.75 mm. Also, the interface between the first birefringent crystal 31 and the Faraday rotator 32 and the interface between the Faraday rotator 32 and the second birefringent crystal 33 are 4 degrees from the plane orthogonal to the central axis of the device as shown in FIG. It is inclined. Further, the positional relationship among the orientation of the optical axis of the first birefringent crystal 31, the orientation of the optical axis of the second birefringent crystal 33, and the orientation of the optical axis of the third birefringent crystal 34 is as in Example 1. The relationship is the same as that described with reference to FIG.

  In the case of the optical isolator of Example 5, the signal light emitted from the ferrule 25 with the incident-side optical fiber enters the first birefringent crystal 31 as a parallel beam due to refraction within the gradient index lens 41. Since the process from entering the first birefringent crystal 31 to exiting the third birefringent crystal 34 is the same as in the first embodiment, description thereof is omitted.

  The signal light beam emitted from the third birefringent crystal 34 is incident on the gradient index lens 42 as a parallel beam, and the incident signal beam is converted into a convergent beam by the refraction of the gradient index lens 42. Then, the light is emitted to the ferrule 26 side with the outgoing side optical fiber. The position of the ferrule 26 with output side optical fiber is adjusted in advance so that the signal light beam enters the optical fiber core portion of the ferrule 26 with output side optical fiber.

  Next, the return light emitted from the ferrule 26 with the outgoing-side optical fiber is incident on the gradient index lens 42, converted into a parallel beam by the refractive index inside the gradient index lens 42, and third birefringence. Incident on the crystal 34. The subsequent process until the return light is emitted from the first birefringent crystal 31 is the same as that in the first embodiment, and a description thereof will be omitted. The two return light beams emitted from the first birefringent crystal 31 enter the gradient index lens 41. At this time, the refractive index distribution type lens 41 becomes a convergent beam due to the refractive index inside the gradient index lens 41. The incident angle when the return light beam is incident on the gradient index lens 41 is that when the signal light emitted from the ferrule 25 with the incident side optical fiber exits the gradient index lens 41. As a result, the two return light beams operate as an optical isolator by converging at a position deviated from the optical fiber core portion of the ferrule 25 with the incident side optical fiber.

  In the optical isolator of the fifth embodiment, the basic operation portion is a so-called one-stage type light composed of three birefringent crystals 31, 33, 34 and one Faraday rotator 32 as in the first embodiment. Although it is configured to be an isolator, it may be configured to be a so-called two-stage type optical isolator composed of four birefringent crystals and two Faraday rotators as in the case described in the second embodiment. There is no problem. In addition, the optical isolator of the fifth embodiment has been described with a configuration in which the ferrule 25 with an incident-side optical fiber that is a signal light input port and the ferrule 26 with an output-side optical fiber that is a signal light output port are described. In the same manner as described in the third and fourth embodiments, a WDM filter is provided at the interface between the birefringent crystal and the Faraday rotator, and a ferrule with an optical fiber for pumping light incident, which is a pumping light input port, is added. It is also possible to adopt a configuration modified so as to have an excitation light introducing function. Furthermore, in the optical isolator of the fifth embodiment, the example in which the refractive index distribution type lenses 41 and 42 using the SELFOC lens are used as the optical element having the refractive property has been described. However, the first birefringent crystal 31 and the third If the shape of the surface facing the birefringent crystal 34 is a flat surface, other types of lenses such as plano-convex spherical lenses, plano-convex aspheric lenses, and diffractive lenses can be substituted.

  FIG. 8 is a schematic diagram showing a basic configuration of an optical fiber amplifier according to Example 6 of the present invention using the optical isolator according to Example 2 and the optical isolator according to Example 3.

  In this optical fiber amplifier, an excitation laser module 52 for outputting laser excitation light having a wavelength of 1480 nm is coupled to the ferrule 35 with an optical fiber for excitation light incidence in the optical isolator according to the third embodiment, and erbium is added as an amplification medium. One end of the optical fiber 51 is coupled to the ferrule 5 with the incident side optical fiber in the optical isolator according to the third embodiment, and the other end of the erbium-doped optical fiber 51 is connected to the ferrule 16 with the outgoing side optical fiber in the optical isolator according to the second embodiment. It is constituted by being connected to.

  In the optical fiber amplifier according to the sixth embodiment, the internally generated return light is cut so as not to reach the signal source by the optical isolator according to the third embodiment disposed on the input side of the erbium-doped optical fiber 51 and output. The return light from the side is cut so as not to enter the erbium-doped optical fiber 51 by the optical isolator according to the second embodiment arranged on the output side of the erbium-doped fiber 51, and the excitation light is further erbium-doped light. An optical isolator according to the third embodiment disposed on the input side of the fiber 51 is input from the ferrule 35 with an optical fiber for pumping light incident, which is a port for introducing pumping light, and enters the erbium-doped fiber 51 through the WDM filter 19. It is like that. According to the configuration of the optical fiber amplifier according to the sixth embodiment, it can be easily constructed with a downsized configuration.

  In the optical fiber amplifier according to Example 6, the configuration using the erbium-doped optical fiber 51 as a pumping medium has been described. However, a fiber doped with praseodymium (Pr) for signal light in the 1300 nm band may be used, or It is possible to use a fiber doped with thulium (Tm) for signal light in the 1400 nm band, as well as to a Raman amplifier using the nonlinear effect of an optical fiber, and as an optical isolator, According to the NF and gain of the optical fiber amplifier, and the pumping method, it is possible to appropriately select and use each of the embodiments from the first embodiment to the fifth embodiment.

It is the schematic diagram which showed the basic composition of the optical isolator which concerns on Example 1 of this invention. It is the schematic diagram which showed the azimuth | direction of the optical axis in the birefringent crystal with which the optical isolator shown in FIG. 1 is equipped. It is the schematic diagram which showed the basic composition of the optical isolator which concerns on Example 2 of this invention. It is the schematic diagram which showed the azimuth | direction of the optical axis in the birefringent crystal with which the optical isolator shown in FIG. 3 is equipped. It is the schematic diagram which showed the basic composition of the optical isolator which concerns on Example 3 of this invention. It is the schematic diagram which showed the basic composition of the optical isolator which concerns on Example 4 of this invention. It is the schematic diagram which showed the basic composition of the optical isolator which concerns on Example 5 of this invention. FIG. 6 is a schematic diagram illustrating a basic configuration of an optical fiber amplifier according to a sixth embodiment of the present invention including the optical isolator illustrated in FIG. 3 and the optical isolator illustrated in FIG. 5.

Explanation of symbols

1,3,4,11,13,21,23,31,33,34 Birefringent crystal 2,12,22,32 Faraday rotator 5,15,25 Ferrule with incident side optical fiber 6,16,26 Outgoing side Ferrule with optical fiber 19, 29 WDM filter 35, 45 Ferrule with optical fiber for excitation light incidence 41, 42 Gradient index lens 51 Erbium-doped optical fiber 52 Laser module for excitation

Claims (11)

  The first birefringent crystal, the first Faraday rotator, the second birefringent crystal, and the third birefringent crystal are arranged in this order from the incident side, and the first birefringent crystal The interface of the first Faraday rotator and the interface of the first Faraday rotator and the second birefringent crystal are approximately the same amount in the same direction with respect to the traveling direction of the incident signal light. Tilted, and the orientation of the optical axis of the second birefringent crystal was swung from the orientation of the optical axis of the first birefringent crystal in the same direction as the Faraday rotation by the first Faraday rotator. The optical surface having refraction or the optical element having refraction is integrally disposed on the incident side of the first birefringent crystal and the exit side of the third birefringent crystal. A characteristic optical isolator.   2. The optical isolator according to claim 1, wherein at least one of the vicinity of the interface between the first birefringent crystal and the first Faraday rotator, and the vicinity of the interface between the first Faraday rotator and the second birefringent crystal. An optical isolator comprising a wavelength division multiplex filter provided with a pumping light input port for allowing pumping light to be incident on the optical isolator.   3. The optical isolator according to claim 1, wherein the optical element having refractive properties includes a plano-convex spherical lens, a plano-convex aspheric lens, a diffraction surface, and a plane opposite to the incident surface of the first birefringent crystal. Any one of a lens, a refractive index distribution type lens, and a plano-convex spherical lens, a plano-convex aspheric lens, a diffractive lens, and a refractive index distribution type whose surface opposite to the exit surface of the second birefringent crystal is a plane. An optical isolator characterized by being one of lenses.   3. The optical isolator according to claim 1, wherein the refractive optical surface includes an incident side surface of the first birefringent crystal processed into a substantially spherical shape and an output side of the second birefringent crystal. An optical isolator characterized in that it is a flat surface.   5. The optical isolator according to claim 4, wherein an outer periphery of the first birefringent crystal, the first Faraday rotator, the second birefringent crystal, and the third birefringent crystal integrated is substantially spherical. An optical isolator characterized by being processed into   The first birefringent crystal, the first Faraday rotator, the second birefringent crystal, the third birefringent crystal, the second Faraday rotator, and the fourth birefringent crystal are arranged in this order from the incident side. And the interface between the first birefringent crystal and the first Faraday rotator and the interface between the first Faraday rotator and the second birefringent crystal are respectively incident signal light. Of the third birefringent crystal and the second Faraday rotator, and the second Faraday rotator and the fourth Faraday rotator. The interface is inclined substantially in the same direction with respect to the traveling direction of the incident signal light, and the orientation of the optical axis of the second birefringent crystal is the orientation of the optical axis of the first birefringent crystal. To approximately the same direction as the Faraday rotation by the first Faraday rotator. The orientation of the optical axis of the fourth birefringent crystal is the same direction as the Faraday rotation by the second Faraday rotator from the orientation of the optical axis of the third birefringent crystal. The direction of the optical axis of the third birefringent crystal is directed to the direction substantially orthogonal to the direction of the optical axis of the second birefringent crystal. An optical isolator comprising a refractive optical surface or a refractive optical element integrally disposed on the incident side of the first birefringent crystal and the outgoing side of the third birefringent crystal.   7. The optical isolator according to claim 6, wherein an interface between the first birefringent crystal and the first Faraday rotator, an interface between the first Faraday rotator and the second birefringent crystal, the third Excitation light input for making excitation light incident on at least one of the vicinity of the interface of the birefringent crystal and the second Faraday rotator and the vicinity of the interface of the second Faraday rotator and the fourth birefringent crystal An optical isolator comprising a wavelength division multiplexing filter having a port.   8. The optical isolator according to claim 6, wherein the optical element having refractive properties is a plano-convex spherical lens, a plano-convex aspheric lens, a diffractive lens having a plane opposite to the incident surface of the first birefringent crystal. Any one of a lens, a refractive index distribution type lens, and a plano-convex spherical lens, a plano-convex aspheric lens, a diffractive lens, a refractive index distribution type whose surface facing the exit surface of the fourth birefringent crystal is a plane An optical isolator characterized by being one of lenses.   8. The optical isolator according to claim 6, wherein the optical surface having refractive properties is an incident side surface of the first birefringent crystal processed into a substantially spherical shape and an output side of the second birefringent crystal. , The surface on the incident side of the third birefringent crystal, the surface on the output side of the fourth birefringent crystal, or the incident side of the first birefringent crystal processed into a substantially spherical shape An optical isolator characterized in that the optical isolator is a surface on the emission side of the fourth birefringent crystal.   10. The optical isolator according to claim 9, wherein an outer periphery of an integrated body of the first birefringent crystal, the first Faraday rotator, and the second birefringent crystal is processed into a substantially spherical shape, and the third The outer periphery of the integrated birefringent crystal, the second Faraday rotator, and the fourth birefringent crystal is processed into a substantially spherical shape, or the first birefringent crystal, the first Faraday rotation The outer periphery of the integrated element, the second birefringent crystal, the third birefringent crystal, the second Faraday rotator, and the fourth birefringent crystal is processed into a substantially spherical shape. Optical isolator. An optical fiber amplifier using the optical isolator according to claim 1.

Images