JP2003121789A - Optical isolator, laser module, optical amplifier, and polarizing filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that dielectric multi-layered film elements which are arranged in parallel to each other increase the wavefront aberration of passing laser light. SOLUTION: This optical isolator is equipped with a Faraday rotator 7 which rotates the polarization of laser light by a >=45 deg. angle of rotation around the optical axis 11 and projects it, a parallel flat plate type polarizer 6 which is arranged obliquely to the optical axis 11 and projects the laser light made incident along the optical axis 11 through a polarization transmission characteristic in a first polarizing direction, and a parallel flat plate type analyzer 8 which is arranged reversely obliquely to the polarizer 6 opposite the polarizer 6, across the Faraday rotator 7, has a polarization transmission characteristic in a second polarizing direction rotated by a 45 deg. angle of rotation from the first polarizing direction, and projects the laser light having passed through the Faraday rotator 7 through the polarization transmission characteristic in the second polarizing direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator which passes only light traveling in one direction and blocks light traveling in the opposite direction, and a laser module using the optical isolator. The present invention also relates to an optical amplifier, and further relates to a polarization filter having a dielectric multilayer film.

[0002]

2. Description of the Related Art FIG. 22 is a diagram showing a structure of a dielectric multilayer film element applied to a conventional optical isolator, and FIG. 23 is a view showing a structure of a conventional optical isolator. This conventional optical isolator is disclosed in Japanese Patent Application Laid-Open No. 8-166656.

In FIG. 22, 101 is an optical element and 10 is an optical element.
2 is, for example, a Faraday effect element plate such as yttrium iron garnet (YIG) crystal or LPE garnet film, 10
3 is an antireflection film formed on one surface of the Faraday effect element plate 102, and 104 is a polarization separation film formed on the other surface of the Faraday effect element plate 102. Also, FIG.
In the above, reference numeral 105 denotes a polarizer formed by forming a polarization separation film made of a dielectric multilayer film coating on one surface of a ½ wavelength plate, and 106 is a Faraday rotator formed by the optical element 101 having a magnet 106M. The polarization separation film 104 functions as an analyzer. The polarizer 105 is formed by disposing a polarization separation film on a half-wave plate.

In this conventional optical isolator, as shown in FIG. 23, a polarizer 105 and a Faraday rotator 106 are arranged in parallel with each other. In this way, the laser light emitted from the semiconductor laser to the optical isolator performs polarization separation of the P-polarized component and the S-polarized component by the polarizer 105, and the P-polarized component is 45 degrees around the optical axis by the Faraday rotator 106. And the rotated P-polarized component is coupled to an optical fiber (not shown). When the P-polarized component rotated from the optical fiber returns to the optical isolator, the rotated P-polarized component of the return light is rotated again by 45 degrees around the optical axis by the Faraday rotator 106, and the rotated P-polarized component of the return light is returned. The polarization direction of is different from the polarization direction of the laser light emitted from the semiconductor laser by 90 degrees. Then, the rotated P-polarized component of the return light is reflected by the polarizer 10.
Even if the light beam enters the light source 5, it cannot pass through the polarizer 105. Therefore, the conventional optical isolator functions as an optical isolator.

Although not shown, the above-mentioned Japanese Patent Laid-Open No. 8-1
In addition to the above-mentioned conventional technique, Japanese Patent No. 66561 discloses another optical isolator using two Faraday effect element plates 102 shown in FIG. This optical isolator uses the dielectric multilayer film 104 formed on each Faraday effect element plate 102 as a polarizer and an analyzer, respectively. Further, this optical isolator sets the Faraday rotation angle of each Faraday effect element plate 102 to 2
It is set to 2.5 degrees. Then, the two Faraday effect element plates in this optical isolator are respectively inclined by a predetermined angle with respect to the incident light so that the polarization of the incident light is finally rotated by 45 degrees.

[0006]

Since the conventional optical isolator is constructed as described above, the dielectric multilayer film elements arranged in parallel with each other increase the wavefront aberration of the passing laser light. There were challenges.

FIG. 24 (a) is a diagram showing the wavefront aberration that generally occurs in a parallel plate. FIG. 24B is a diagram showing the wavefront aberration that is generated and amplified in the conventional optical isolator. Figure 2
As shown in FIG. 4 (a), when an incident wave (or plane wave) is incident on a parallel plate that is inclined with respect to the traveling direction of the incident wave (or plane wave), this incident wave (or plane wave) causes wavefront aberration. Then, the light is emitted from the parallel plate.

In view of this, in the conventional optical isolator shown in FIGS. 22 and 23, the polarizer 105 and the Faraday rotator 106 are inclined and arranged in parallel as shown in FIG. 24 (b). In addition, the wavefront aberration generated in the polarizer 105 is further increased by the Faraday rotator 106.

The present invention has been made to solve the above problems, and an object thereof is to construct an optical isolator capable of reducing the wavefront aberration of passing laser light.

Another object of the present invention is to construct a laser module and an optical amplifier using the above optical isolator.

A further object of the present invention is to provide a polarizing filter having a dielectric multilayer film suitable for the polarizer and analyzer of the above optical isolator.

[0012]

An optical isolator according to the present invention comprises an optical rotator having an optical rotatory action about an optical axis and a parallel optical axis arranged so as to be inclined with respect to the optical axis. A flat plate type polarization means and a parallel plate type detection means arranged on the optical axis and arranged so as to sandwich the optical rotation means together with the polarization means so as to reduce the wavefront aberration generated in the polarization means. It was done like this.

The optical isolator according to the present invention is provided with an optical rotation means for rotating the polarized light of the passing light around the optical axis by a predetermined rotation angle and emitting the polarized light, and a tilting direction with respect to the optical axis. To the parallel plate type polarizing means inclined by a first angle to the optical axis and sandwiching the optical rotating means with the polarizing means so as to face each other, and a second angle in the opposite inclination direction with respect to the polarizing means. The parallel plate type light detecting means is arranged so as to be inclined only.

The optical isolator according to the present invention is an optical isolator having an optical axis, a parallel plate type polarizing means intersecting with the optical axis, and a parallel plate detector which intersects with the optical axis and sandwiches the optical rotating means together with the polarizing means so as to face each other. Optical means, wherein the virtual light detecting means is placed in a relationship perpendicular to the optical axis of the virtual optical rotating means, and the first polarization plane of the polarized light passing through the virtual polarizing means is virtual. The virtual polarization means is placed so as to be parallel to the second plane of polarization of the polarized light that passes through the conventional light detection means, and the first line of intersection between the virtual polarization means and the first plane of polarization is The virtual polarization means and the virtual polarization means with respect to the optical axis of the virtual optical rotation means are arranged to face each other in a substantially V shape with respect to the second line of intersection between the virtual light detection means and the second polarization plane. Of the first polarization plane and the second polarization plane with respect to the second polarization plane. The virtual light detecting means is rotated around the optical axis of the virtual optical rotating means so as to be 45 °, and the rotation angle of the virtual optical rotating means is the angle at which the polarization plane of the polarized light rotates around the optical axis. As a result, the arrangement substantially the same as the arrangement of the virtual polarization means, the virtual light detection means and the virtual optical rotation means arranged under the condition that they are set at about 45 ° is used. And the light detecting means.

In the optical isolator according to the present invention, the absolute value of the inclination arrangement angle of the light detecting means from the normal line of the light incident surface of the light detecting means to the electric field vector of the light is the light from the normal line of the light incident surface of the polarizing means. The absolute values of the tilted arrangement angles of the polarization means with respect to the electric field vector of 1 are the same, and they are arranged at the inclined arrangement angle of the opposite sign.

In the optical isolator according to the present invention, the light detecting means has a reverse inclination arrangement angle having the same absolute value as the inclination arrangement angle of the polarization means formed by the normal line of the light incident surface of the polarization means and the optical axis and having the opposite sign. The normal line of the light emitting surface and the optical axis are arranged so as to be arranged in a reverse inclination.

In the optical isolator according to the present invention, the polarizing means or the light detecting means is arranged so as to be inclined so that the inclined arrangement angle formed by the normal line of the light incident surface and the optical axis becomes the Brewster angle. It is a thing.

In the optical isolator according to the present invention, the polarizing means or the light detecting means is such that the absolute value of the inclined arrangement angle formed by the normal line of the light incident surface and the optical axis is from 50 ° to 60 °. It is arranged so as to be inclined.

In the optical isolator according to the present invention, the optical rotation means sets the predetermined rotation angle to 45 ° and outputs the polarized light of the passing light after rotating it about the optical axis by the predetermined rotation angle. , 4 around the optical axis from the first polarization direction of the polarization means
It has a polarization transmission characteristic in the second polarization direction in the direction rotated by 5 °.

In the optical isolator according to the present invention, the polarizing means or the light detecting means has one plane on which the multilayer film is formed and the other plane parallel to the one plane, and one plane to the other plane. A parallel plate type light transmission medium having a thickness up to a plane of up to 0.5 mm is used.

In the optical isolator according to the present invention, the polarizing means or the light detecting means is a parallel plate type light transmitting medium having a multilayer film formed on one plane without using an adhesive layer. is there.

In the optical isolator according to the present invention, the polarizing means or the light detecting means is a parallel plate type having a multilayer film formed on one plane by electron beam evaporation with oxygen ion assist or electron beam evaporation with oxygen plasma assist. The light transmitting medium is used.

In the optical isolator according to the present invention, the polarizing means or the analyzing means is a parallel plate type light transmitting medium having an antireflection film formed on the other plane.

In the optical isolator according to the present invention, the polarizing means or the light detecting means is provided with a long-wavelength transmission type filter having a multilayer film in which a low refractive index medium is sandwiched by a high refractive index medium.

In the optical isolator according to the present invention, a parallel plate type dielectric multilayer film is formed by combining with a dielectric thin film material having a low refractive index in which the deposition rate of the dielectric substance on the film formation surface is lower than 80%. The formed polarizing filter is used as a polarizing means or a light detecting means.

In the optical isolator according to the present invention, the dielectric thin film material having a high refractive index is combined with Si, and the dielectric thin film material having a low refractive index is combined with SiO ₂ or MgF ₂ to form a parallel plate type dielectric multilayer film. The polarizing filter is used as a polarizing means or an analyzing means.

A laser module according to the present invention is a parallel plate type having an optical rotating means having an optical rotating action around an optical axis and a parallel plate type which is arranged inclined with respect to the optical axis and has a polarization transmission characteristic in a first polarization direction. A polarizing means and a parallel-plate type detecting means which is arranged so as to sandwich the optical rotation means together with the polarizing means so as to reduce the wavefront aberration generated in the polarizing means, and which has polarization transmission characteristics in the second polarization direction; And an optical isolator including a laser light source means for emitting laser light, and a parallel light converting means for converting the laser light emitted from the laser light source means into parallel light and entering the parallel light.

The laser module according to the present invention is provided with an optical transmission means for transmitting laser light and an optical coupling means for coupling the laser light emitted from the optical isolator to the optical transmission means.

The optical amplifier according to the present invention includes a laser module, signal light input means for inputting signal light, signal light input to the signal light input means, and laser light as pumping light emitted from the laser module. And a signal light amplification path for receiving the signal light and the excitation light from the signal light / pumping light coupling means, amplifying the signal light with the excitation light, and emitting the amplified signal light. Is an optical rotation means having an optical rotation effect around the optical axis, a parallel plate type polarizing means arranged obliquely with respect to the optical axis and having polarization transmission characteristics in the first polarization direction, and an optical rotation means together with the polarizing means. Are disposed so as to face each other and are arranged so as to reduce the wavefront aberration generated in the polarization means, and an optical isolator including a parallel plate type analysis means having polarization transmission characteristics in the second polarization direction, and a laser beam Out A laser light source means for, in which so as to comprise a parallel light transforming means for entering the optical isolator converts the laser beam emitted from the laser light source means into parallel light.

An optical amplifier according to the present invention comprises a second optical isolator on at least one of an input side and an output side of a signal light amplification path, and the second optical isolator has optical rotation means having an optical rotation effect around an optical axis. And a parallel plate type polarization means having a polarization transmission characteristic in the first polarization direction and inclined with respect to the optical axis, and an optical rotation means together with the polarization means, and the wavefront generated by the polarization means. And a parallel plate type analyzer arranged to reduce the aberration and having a polarization transmission characteristic in the second polarization direction.

An optical amplifier according to the present invention is an optical rotating means having an optical rotating action around an optical axis, and a parallel plate type which is arranged inclined with respect to the optical axis and has a polarization transmission characteristic in a first polarization direction. A polarizing means and a parallel-plate type detecting means which is arranged so as to sandwich the optical rotation means together with the polarizing means so as to reduce the wavefront aberration generated in the polarizing means, and which has polarization transmission characteristics in the second polarization direction; An optical isolator, a laser light source means for emitting pumping light, a signal light inputting means for inputting signal light, and a signal light / pumping light for coupling the signal light and pumping light input to the signal light inputting means An input side or an output side of the signal light amplification path, which includes a coupling means and a signal light amplification path that receives the signal light and the excitation light from the signal light / pumping light coupling means, amplifies the signal light by the excitation light, and emits the signal light. To at least one of the It is obtained so as to include the data.

The optical amplifier according to the present invention is configured by adding a rare earth element to an optical fiber, and a rare earth element-doped optical fiber that is excited by pumping light and amplifies the signal light is used as a signal light amplification path. .

The optical isolator according to the present invention comprises a parallel plate type polarizing means having a first polarization direction parallel to the first plane of polarization of polarized light passing through the polarizing means, and polarized light passing through the analyzing means. Parallel plate-shaped analyzer having a second polarization direction that is parallel to the second plane of polarization, and an optical axis that is placed between the polarizer and the analyzer and intersects the polarizer and the analyzer. And the optical rotation means for rotating the polarization of the polarized light beam around the optical axis at a rotation angle of about 45 ° in the rotation direction, wherein the second polarization direction of the light detecting means is the first polarization direction of the polarization means. The virtual light detecting means is placed in parallel relationship with the virtual light polarizing means so as to be the same as the polarization direction, and the virtual light detecting means has a rotation angle of approximately 225 ° in the rotation direction of the light rotating means. Virtual polarization means and virtual detector arranged under the condition of rotating around the optical axis at The polarizing means and the analyzing means have an arrangement which is substantially the same as the arrangement of the light means.

The optical isolator according to the present invention comprises a parallel plate type polarizing means having a first polarization direction parallel to the first polarization plane of polarized light passing through the polarizing means, and polarized light passing through the analyzing means. Parallel plate-shaped analyzer having a second polarization direction that is parallel to the second plane of polarization, and an optical axis that is placed between the polarizer and the analyzer and intersects the polarizer and the analyzer. And the optical rotation means for rotating the polarization of the polarized light beam around the optical axis at a rotation angle of about 45 ° in the rotation direction, wherein the second polarization direction of the light detecting means is the first polarization direction of the polarization means. In the process in which the light detecting means is placed in a parallel relationship with the polarizing means so as to be the same as the polarization direction, and the light detecting means is rotated around the optical axis at a rotation angle of approximately 225 ° in the rotation direction of the light rotating means. Arrangement of polarization means and analysis means which is substantially the same as the arrangement made and consequently To have.

The polarization filter according to the present invention is formed by making the dielectric thin film material having a low refractive index a deposition filling rate of the dielectric substance on the deposition surface lower than 80%. .

In the polarization filter according to the present invention, the high refractive index dielectric thin film material is Si, and the low refractive index dielectric thin film material is SiO ₂ or MgF ₂ .

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. Embodiment 1. 1 is a diagram showing a structure of a dielectric multilayer filter applied to an optical isolator according to Embodiment 1 of the present invention. In FIG. 1, 1 is a dielectric multilayer film filter, 2 is a parallel plate type light transmission medium such as optical glass BK7, and 3 is a dielectric multilayer film provided on the light incident surface of the parallel plate type light transmission medium 2. is there. Further, m1 is a normal line of the light incident surface of the parallel plate type light transmission medium 2, Lin is a laser beam incident on the dielectric multilayer filter 1, and θ is a normal line of the light incident surface of the dielectric multilayer filter 1. And laser beam Li
It is an inclined arrangement angle formed by n and corresponds to the incident angle of the laser beam Lin to the substrate.

As shown in FIG. 1, the P-polarized component reflection band is set to be narrower than the S-polarized component reflection band with respect to the laser beam Lin obliquely incident on the light incident surface of the parallel plate type light transmission medium 2. The long-wavelength transmission type dielectric multilayer filter 1 having the dielectric multilayer 3 formed thereon is manufactured. FIG. 2 is a diagram showing a configuration example of the dielectric multilayer filter 1 of FIG.
This shows an example of the dielectric multilayer film 3 made of a combination of O ₂ / SiO ₂ .

Here, H is a quarter of the wavelength and has a thickness of 1/4.
It represents the product of λ and the refractive index n _H of the high refractive index medium. L represents the product of the thickness ¼λ of a quarter of the wavelength and the refractive index n _L of the low refractive index medium. (0.505H1.146L
0.505H) indicates a situation in which the layer of the low refractive index medium is sandwiched between the layers of the high refractive index medium, the thickness of the layer of the low refractive index medium is 1.146 * 1 / 4λ * n _L , and The layer thickness of the refractive index medium is 0.505 * 1 / 4λ * n _H. In this case, since the layer thickness depends on the reference wavelength of the laser light, the layer thickness changes depending on the filter characteristics. In addition, (0.505
H1.146L0.505H) ³ has three layers (0.505
H1.146L0.505H) is stacked three times. Therefore, 66 layers (3 * 3 + 3 *) with each low refractive index medium layer sandwiched between high refractive index medium layers
16 + 3 * 3) are stacked with the dielectric multilayer film 3. Further, as the reference wavelength λ serving as a reference for the thickness of one wavelength λn, in this example, the wavelength of a light beam traveling in a vacuum at a wavelength of 927 nm is selected. However, λn = λv / n (n is the refractive index of the medium).

FIG. 3 is a diagram showing polarized light transmission characteristics of the configuration example of the dielectric multilayer filter 1 of FIG. The horizontal axis represents the wavelength [nm] of the incident laser beam and the vertical axis represents the transmittance [%], and the light incident angle of the laser beam is θ = 52.5.
It is supposed to be °. As can be seen from FIG. 3, the transmittance Ts of the S-polarized component shows a numerical value of several% or less on the dotted line, while
The transmittance Tp of the P-polarized component shown by the solid line shows a numerical value of 75% or more. Thus, the dielectric multilayer filter 1
Indicates high polarization separation characteristics.

The structure of an optical isolator using this dielectric multilayer filter 1 will be described below. FIG. 4 is a diagram showing the structure of the optical isolator according to the first embodiment of the present invention. In FIG. 4, 4 is a semiconductor laser (laser light source means) that emits laser light, 5 is a collimator lens (parallel light conversion means) that converts the laser light into parallel light, and 6 is a polarizer by the dielectric multilayer filter 1 ( Polarizing means) 7 is a Faraday rotator (optical rotation means) composed of a Faraday effect element 7F and a magnet 7M. Faraday rotator 7
Has an optical rotation effect of rotating the polarization plane of the incident laser light around the optical axis by 45 ° around the optical axis and emitting the light in accordance with the direction of the magnetic field generated by the magnet 7M.

Reference numeral 8 is an analyzer (light detecting means) by the dielectric multilayer filter 1, 9 is an optical fiber (light transmitting means) for transmitting laser light, and 10 is laser light emitted from the analyzer 8 to the optical fiber 9. It is a coupling lens (optical coupling means) for coupling. Further, 11 is an optical axis of the Faraday rotator 7. Here, the parallel movement of the optical axis due to the refraction by the polarizer or the analyzer is extremely small, and therefore the description is omitted.

The dielectric multilayer filter 1 shown in FIGS.
It is used as a polarizer 6 and an analyzer 8. And Figure 4
As shown in Table 1, the optical isolator according to the first embodiment has a predetermined inclination angle θ with respect to the optical axis 11 (in the case of the dielectric multilayer film 3 shown in Table 2, the light incident angle is near the Brewster angle). Angle θ = 50 ° to 60 °) and the polarization direction of the polarizer 6 (first polarization direction, polarization plane of polarization that can pass through the polarizer 6) Second polarization plane which is the polarization plane of the polarization that can be transmitted through the analyzer 8 (the second polarization direction, which is rotated by 45 ° around the optical axis 11 with respect to the polarization transmission characteristic of the polarization plane of the second polarization plane). ), And has the same inclination arrangement angle θ opposite to the polarizer 6 in the opposite direction.
The Faraday rotator 7 is arranged so as to be opposed to and sandwiched by the analyzer 8 which is reversely inclined by (that is, -θ). The first polarization plane of the polarized light passing through the polarizer 6 and the traveling direction (optical axis direction) of the polarized light determine the first polarization plane of the polarized light, and the second polarization direction of the polarized light passing through the analyzer 8 and The second polarization plane of the polarized light is determined by the traveling direction of the polarized light (optical axis direction).

Here, the polarizer 6 and the analyzer 8 shown in FIG.
The positional relationship with and can be understood as follows, for example. 5 to 8 are views for explaining the positional relationship between the polarizer 6 and the analyzer 8, and FIGS. 5 (a) to 8 (a) are side views of the optical isolator, and FIGS. FIG. 8B is a front view of the optical isolator. The same reference numerals as those in FIG. 1 and FIG. 4 indicate the corresponding configurations, and the illustration of other than the main components is omitted. 5 to 8, the Z axis is taken in the direction of the optical axis 11 of the Faraday rotator 7, and the X axis and the Y axis orthogonal to each other are taken in two directions orthogonal to the optical axis 11, respectively.

In the states shown in FIGS. 5A and 5B, the light incident surface and the light emitting surface of the polarizer 6 and the analyzer 8 are arranged so as to be orthogonal to the optical axis 11 of the Faraday rotator 7. In addition, the polarization directions of the polarizer 6 and the analyzer 8 are all aligned with the Y-axis direction of FIG. 5B (first step). The operation example from the state of FIGS. 5 (a) and 5 (b) to the arrangement relationship of the polarizer 6 and the analyzer 8 in the optical isolator of FIG. 4 is as follows.

First, in FIGS. 5 (a) and 5 (b),
The polarizer 6 is tilted by an angle θ about a rotation axis that is parallel to the X-axis direction and penetrates the center of the polarizer 6, and the normal line m1 of the light incident surface of the polarizer 6 and the optical axis 11 of the Faraday rotator 7 The angle of the inclined arrangement is θ. FIG. 6A and FIG. 6B show the state at this time. The inclination arrangement angle θ is not particularly limited as long as it is an angle capable of exhibiting a function as a polarizer and an analyzer. For example, if a value near the Brewster angle is selected as the inclination arrangement angle θ, as will be described later. The polarization separation characteristics of the P-polarized component and the S-polarized component in the polarizer 6 can be improved.

Then, in the state shown in FIGS. 6A and 6B, the analyzer 8 is tilted in the direction opposite to that of the polarizer 6. That is, the analyzer 8 is tilted by the angle −θ about the rotation axis that is parallel to the X-axis direction and passes through the center of the analyzer 8, and the normal line m2 of the light emission surface of the analyzer 8 and the optical axis 11 of the Faraday rotator 7 are arranged. The inclination arrangement angle formed by and is set to −θ (second step). The state at this time is as shown in FIGS. 7 (a) and 7 (b), and the analyzer 8 is arranged in the reverse inclination with respect to the polarizer 6. This state is defined by the first line of intersection L1 which is the line of intersection between the polarizer 6 and the first plane of polarization (first polarization direction), the analyzer 8 and the plane of polarization of the laser light passing through the analyzer 8. The second line of intersection L2, which is the line of intersection with the (second polarization direction), faces in a substantially V shape.

Finally, the analyzer 8 is rotated about the optical axis 11 of the Faraday rotator 7 so that the linearly polarized light which has passed through the polarizer 6 is rotated by 45 ° by the Faraday rotator 7 just passing through the analyzer 8. It is rotated by 45 ° to shift the polarization direction of the analyzer 8 by 45 ° with respect to the polarization direction of the polarizer 6 (third step). The states at this time are shown in FIGS. 8A and 8B, and the positional relationship between the polarizer 6 and the analyzer 8 in the optical isolator shown in FIG. 4 can be obtained.

The positional relationship between the polarizer 6 and the analyzer 8 shown in FIG. 8 can be expressed as follows. That is, the first surface PL1 including the exit surface of the polarizer 6, the second surface PL2 including the entrance surface of the analyzer 8, and the intersection point P2 between the plane PL1 including the exit surface of the polarizer 6 and the optical axis 11. When a third surface PL3 including the line P3 and including a cross point P2 between the second surface and the optical axis 11 and perpendicular to the optical axis 11 is assumed, The line of intersection between the surface PL1 and the second surface PL2 is the third
So as to pass between the surface PL3 and the fourth surface PL4 of
The polarizer 6 and the analyzer 8 are arranged.

The positional relationship between the polarizer 6 and the analyzer 8 shown in FIG. 8 can be expressed as follows. That is, first
The analyzer 8 shown in FIG. 6 is arranged so as to be parallel to the polarizer 6 inclined at the inclined arrangement angle θ. That is, like the polarizer 6, the analyzer 8 is also rotated about the rotation axis parallel to the X-axis direction by the same inclination arrangement angle θ. At this time, the analyzer 8 is arranged so that the second polarization direction of the analyzer 8 is parallel to the first polarization direction of the analyzer 6.

Next, in this state, the analyzer 8 is rotated around the optical axis of the Faraday rotator 7 in the rotation direction of the Faraday rotator 7 (the direction in which the Faraday rotator 7 rotates the polarization plane of the polarized light transmitted according to the direction of the magnetic field). ) Rotate 180 degrees. As a result, the polarizer 6 and the analyzer 8 have the positional relationship shown in FIG. Then, from this state, the analyzer 8 is further rotated about the optical axis of the Faraday rotator 7 by 45 degrees in the rotation direction of the Faraday rotator 7. That is, in total, the analyzer 8 is placed around the optical axis of the Faraday rotator 7 and
225 degrees in the direction of rotation. As a result, the polarizer 6
And the analyzer 8 has the arrangement relationship shown in FIG.

Note that this operation example is merely an example. Of course, even if the analyzer 8 is rotated around the optical axis of the Faraday rotator 7 by 135 degrees in the direction opposite to the rotation direction of the Faraday rotator 7, the same result is obtained. Becomes That is, a Faraday rotator 7 having an optical axis, a parallel plate type polarizer 6 intersecting the optical axis,
A parallel plate analyzer 8 that intersects the optical axis and sandwiches the Faraday rotator 7 together with the polarizer 6 so as to face each other, and the virtual analyzer 8 is perpendicular to the optical axis of the virtual Faraday rotator 7. And the virtual polarizer 6 is placed so that the first plane of polarization of the polarized light passing through the virtual polarizer 6 is parallel to the second plane of polarization of the polarized light passing through the virtual analyzer 8. The first line of intersection between the virtual polarizer 6 and the first plane of polarization is placed approximately V-shaped with respect to the second line of intersection between the virtual analyzer 8 and the second plane of polarization. So as to face each other, the virtual polarizer 6 and the virtual analyzer 8 are tilted with respect to the optical axis of the virtual Faraday rotator 7 to form a first polarization plane and a second polarization plane. The virtual analyzer 8 is rotated around the optical axis of the virtual Faraday rotator 7 so that the angle between them is approximately 45 ° with respect to the second polarization plane. , The virtual Faraday rotator 7 is arranged under the condition that the rotation angle of the virtual Faraday rotator 7 is set to about 45 °, which is the angle at which the polarization plane of the polarized light rotates around the optical axis. The first embodiment is that the Faraday rotator 7, the polarizer 6 and the analyzer 8 have an arrangement that is substantially the same as the arrangement of the analyzer 8 and the virtual Faraday rotator 7. This is a feature of the optical isolator. That is, it suffices that the positional relationship between the polarizer and the analyzer of the present invention shown in FIG. 8 be obtained as a result, and an operation example using a virtual polarizer, an analyzer, and a Faraday rotator is for explanation. Was only used for. That is, these operation examples do not limit the production method of the polarizer and the analyzer shown in FIG.

Of course, the operation procedure until the arrangement relationship of FIG. 4 is obtained is not limited to that of FIGS. 5 to 8, and the arrangement relationship of the polarizer 6 and the analyzer 8 of FIG. 4 may be obtained. In addition, in FIG. 5 to FIG. 8, in order to make the drawings easy to see, the light incident / exiting surface shapes of the polarizer 6 and the analyzer 8 are square, and the polarizer 6 is
Although the analyzer 8 has a larger shape than that, the size and shape of the polarizer 6, the Faraday rotator 7, and the analyzer 8 are not particularly limited as long as the light flux passing through the optical isolator is not eclipsed. Further, even if + θ and −θ have an error with each other, a certain reduction effect can be recognized.

Next, the operation will be described. In FIG. 4, the laser light emitted from the semiconductor laser 4 is converted into parallel light by the collimator lens 5 and enters the polarizer 6 along the optical axis 11. As described with reference to FIGS. 5 to 8, since the polarizer 6 is tilted at the tilt angle θ with the optical axis 11, the laser light traveling along the optical axis 11 is polarized at the light incident angle θ. It is incident on the child 6.

9 (a) and 9 (b) are views showing how the laser light incident on the optical isolator in the forward direction and the backward direction respectively passes therethrough. In FIG. 9A, the laser light from the semiconductor laser 4 is linearly polarized light with a polarization extinction ratio of about 20 dB, and the P-polarized component has a high transmittance for the polarizer 6 having the polarization transmission characteristic in the first polarization direction. The S-polarized component passes through and is reflected by the polarizer 6. The P-polarized light component transmitted through the polarizer 6 is incident on the analyzer 8 after its plane of polarization is rotated by 45 ° around the optical axis 11 by the Faraday rotator 7.

Since the polarization direction of the analyzer 8 is rotated by 45 ° with respect to the polarization direction of the polarizer 6, the P-polarized component passing through the polarizer 6 passes through the Faraday rotator 7. The light passes through the analyzer 8 having the polarization transmission characteristic in the second polarization direction as it is. After that, as shown in FIG. 4, the laser light that has passed through the analyzer 8 becomes emitted light from the optical isolator and is coupled to the optical fiber 9 via the coupling lens 10 in FIG.

On the other hand, due to the reflection from the optical fiber 9 and the coupling lens 10 in FIG. 4, a return laser beam which is incident on the analyzer 8 in the opposite direction is generated. As shown in FIG. 9B, in this return laser light, the S-polarized component is reflected by the dielectric multilayer film 3 on the analyzer 8, and only the P-polarized component passes through the analyzer 8. Since the polarization plane of the P-polarized light component that has passed through the analyzer 8 is rotated by 45 ° when passing through the Faraday rotator 7, the polarization plane of the return laser light passes through the Faraday rotator 7 and becomes the first polarization of the polarizer 6. It becomes orthogonal to the polarization transmission characteristic in the polarization direction of, and enters the polarizer 6 as an S-polarized component.
Therefore, this S-polarized component is reflected by the polarizer 6 and cannot go backward any more, so that the semiconductor laser 4 is isolated.

Next, it will be described that the optical isolator of FIG. 4 can reduce wavefront aberration. FIG. 10 is a diagram for explaining the effect of the optical isolator according to the first embodiment of the present invention, and conceptually shows generation and reduction of wavefront aberration. The same reference numerals as those in FIG. 4 indicate the corresponding configurations. here,
Since the Faraday rotator 7 is arranged parallel to the wavefront, the Faraday rotator 7 is not shown in the figure regardless of the wavefront aberration.

As shown in FIG. 10, in the optical isolator according to the first embodiment, the analyzer 8 is arranged so as to be oppositely inclined with respect to the polarizer 6, so that the wavefront aberration generated in the polarizer 6 is detected by the analyzer 8. The laser light having the reduced wavefront can be emitted from the analyzer 8.

FIG. 11 is a diagram showing a result of simulating the relationship between the inclination arrangement angle and the occurrence of the wavefront aberration by calculation.
A parallel plate having a thickness of m is used as the polarizer 6 and the analyzer 8. In FIG. 11, the horizontal axis represents the tilted arrangement angle of the polarizer 6, and the vertical axis represents the wavefront aberration having a coefficient with the wavelength used of 1480 nm as a unit. That is, FIG.
Shows the dependence of the wavefront aberration on the inclination angle of the polarizer.
The broken line shows the occurrence of the wavefront aberration when only the polarizer 6 is tilted, while the solid line tilts the same angle by making the polarizer 6 and the analyzer 8 face each other in opposite directions as shown in FIG. The occurrence of wavefront aberration when arranged is shown.

As is clear from FIG. 11, a polarizer 6 and an analyzer 8 having the same characteristics are arranged so as to face each other with the Faraday rotator 7 in between, and the inclination arrangement angle is 60 ° or less. Angle θ = 50 ° to 6 around the star angle
The wavefront aberration generated in the polarizer 6 on the incident side can be reduced by the analyzer 8 by setting it to 0 ° and arranging it in the opposite direction. The intensity due to the wavefront aberration at a certain point A is expressed by the following equation (1)
It is known to be represented by. Here, i (A) is the normalized intensity at an arbitrary point A, λ is the wavelength, and ΔΦ is the wavefront aberration.

I (A) = 1− (2π / λ) ² · (ΔΦ) ² (1)

The normalized intensity i shown in equation (1)
When (A) is 0.8 or more, it can be considered that the system is sufficiently reduced. Under this condition, the wavefront aberration is λ / 14
(≈0.07λ) or less. From this condition and FIG. 11, it can be seen that the inclination arrangement angle is limited to about 60 °. As is clear from FIG. 11, the polarizer 6 and the analyzer 8 having the same characteristics are arranged so as to face each other with the Faraday rotator 7 sandwiched therebetween, and the inclination arrangement angle is 60 ° or less near the Brewster angle. Angle θ = 50 ° -60
By setting the angle to 0 ° and tilting in the opposite direction, the wavefront aberration generated in the polarizer 6 on the incident side can be reduced by the analyzer 8.

Even if + θ and −θ have an error with each other, a certain reduction effect can be recognized. Also,
The polarizer 6 and the analyzer 8 are the dielectric multilayer filter 1 having the same characteristics, but the parallel plate type light transmission medium (eg, glass substrate) 2 may be a normal optical glass thin plate such as BK7. it can. Further, the thickness of the parallel plate type light transmitting medium 2 is less than 1 mm (from a thickness of about 0.2 mm in view of distortion generated at the time of vapor deposition on the substrate and handling in manufacturing, and from the viewpoint of reducing the occurrence of wavefront aberration, 0 Since it is possible to make the thickness up to about 0.5 mm),
The occurrence of wavefront aberration can be reduced as compared with a thick polarizer such as a polarization beam splitter.

Further, in a polarizer such as a polarization beam splitter in which a thin film is sandwiched between high-refractive-index materials and bonded, there is a possibility that the deterioration of the transmittance due to the heat deterioration of the adhesive layer may occur, but this embodiment 1 Dielectric Multilayer Filter 1
Since it does not have an adhesive layer, it is possible to prevent a decrease in transmittance due to thermal deterioration.

Further, the dielectric multilayer film 3 formed on the polarizer 6 and the analyzer 8 is made of TiO ₂ and Si shown in FIG.
A long-wavelength transmissive filter in which a low refractive index medium is sandwiched by a high refractive index medium such as a multilayer film in combination with O ₂ is used, and thus a short refractive index medium is sandwiched by a high refractive index medium. Since the number of multilayer films to be configured is smaller than that of a wavelength transmission type filter, the overall layer thickness can be made thinner, which reduces wavefront aberrations that occur when light passes and also leads to a reduction in material costs. Further, it is possible to reduce the surface strain due to thermal stress and the like, and further, it is possible to shorten the time required for forming the multilayer film, which leads to an improvement in workability of film formation.

Further, by forming the dielectric multilayer film 3 as a thin film polarizing filter by oxygen beam assisted electron beam or oxygen plasma assisted electron beam vapor deposition, the film thickness is more accurate and robust than conventional vapor deposition. The membrane can be realized. A transmission wavelength shift can be reduced by forming an accurate film thickness, and environment resistance can be improved by forming a robust film.

Although not shown, an antireflection film for the P-polarized light component may be formed on the surface of the dielectric multilayer filter 1 opposite to the surface on which the dielectric multilayer 3 is formed. As a result, P in the dielectric multilayer filter 1 is
Since the return laser light of the polarization component can be reduced, noise generation of the laser output light can be reduced.

Further, when the dielectric multilayer filter 1 is arranged, the inclination arrangement angle formed by the normals m1 and m2 and the optical axis 11 is defined as Brewster's angle (an optical transmission medium 2 of a parallel plate type). In the case of the glass BK7, it may be 56.7 °). This eliminates the need for an antireflection film for the P-polarized component, reduces the generation of noise in the laser output light, and reduces the material cost and man-hours for manufacturing the dielectric multilayer filter 1.

Further, as shown in FIG. 4, the optical isolator according to the first embodiment and the semiconductor laser 4 may be combined by a collimator lens 5 to form a module. As a result, the return laser light to the semiconductor laser 4 is reduced, and a laser module in which the increase in noise of the output of the semiconductor laser 4 due to the return laser light is reduced can be configured.

Further, a laser module in which the optical isolator and the semiconductor laser 4 are combined to form a module may be used as a pumping light source for an optical amplifier. FIG. 12 is a diagram showing the configuration of the optical amplifier according to the first embodiment of the present invention, and shows an EDFA (abbreviation of erbium-doped optical fiber amplifier). The same reference numerals as those in FIG. 4 indicate the corresponding configurations.

In FIG. 12, reference numeral 12 is the first embodiment.
Optical isolator, 13 is a signal light input terminal (signal light input means) to which signal light is input, and 14 is a signal light input terminal 13
Signal light / pumping light multiplexer / demultiplexer (signal light / pumping light coupling means) for multiplexing the signal light from the optical fiber and the pumping light from the optical fiber 9,
Reference numeral 15 denotes an EDF in which erbium is added to an optical fiber (abbreviation of erbium-doped optical fiber, signal light amplification path, rare earth-doped optical fiber). The EDF 15 is excited by the excitation light emitted from the semiconductor laser 4 as the excitation light source,
The gain is given to the passing signal light.

Since the return light to the semiconductor laser 4 is isolated by the optical isolator according to the first embodiment, an optical amplifier equipped with a low noise pumping light source can be constructed, which results in low noise. It becomes possible to realize a high efficiency optical amplifier. Not only the EDF 15 but also other rare earth-doped optical fibers are used as signal light amplification paths to configure an optical amplifier, and similar effects can be obtained.

Further, in FIG. 12, at least one of the input side and the output side of the EDF 15 is provided with the first embodiment.
The optical isolator may be coupled. For example, in FIG. 13, the second optical isolator 16 is connected to the EDF 15
It is arranged on the input side of. By doing so, it becomes possible to prevent oscillation in the optical amplifier.

Further, as shown in FIG. 14, E of FIG.
Optical fiber (signal light amplification path) 17 instead of DF15
, The optical isolators 12 and 16 may be applied to an optical amplifier using Raman amplification, and the same effect can be obtained. The excitation directions in FIGS. 13 and 14 may be forward excitation, backward excitation, or bidirectional excitation.

As described above, according to the first embodiment, the Faraday rotator 7 which rotates the polarized light of the laser light around the optical axis 11 and emits it, and the inclination arrangement angle θ with respect to the optical axis 11.
And a parallel plate type polarizer 6 which emits the laser light incident along the optical axis 11 along the optical axis 11 to the Faraday rotator 7 through the polarization transmission characteristic in the first polarization direction, and the polarizer 6 Along with the Faraday rotator 7 facing each other, the Faraday rotator 7 and the Faraday rotator 7 are arranged so as to be opposite to each other with the opposite inclination angle -θ having the same absolute value and the opposite sign as the optical axis 11. Since the laser light passing through the rotator 7 is provided with the parallel plate type analyzer 8 which emits the laser light via the polarization transmission characteristic in the second polarization direction, the wavefront aberration of the laser light passing through the polarizer 6 is provided. Can be reduced by the analyzer 8, and the effect of reducing the occurrence of wavefront aberration can be obtained.

Further, according to the first embodiment, the polarizer 6 or the polarizer 6 is arranged so that the inclined arrangement angle (light incident angle) θ formed by the normal line m1 of the light incident surface and the optical axis 11 becomes the Brewster angle. Since the analyzer 8 is arranged so as to be inclined, it is possible to reduce the returning laser light without requiring a means for preventing reflection, and it is possible to obtain the effect of reducing the number of manufacturing steps of the optical isolator and the manufacturing cost. .

Further, according to the first embodiment, the inclined arrangement angle (light incident angle) θ formed by the normal line m1 of the light incident surface and the optical axis 11 is an angle of 50 ° to 60 °. Since the polarizer 6 or the analyzer 8 is arranged so as to be inclined, there is an effect that it is possible to configure an optical system in which the wavefront aberration is sufficiently reduced while satisfying the Brewster angle incidence condition.

Further, according to the first embodiment, the Faraday rotator 7 is rotated around the optical axis 11 of the polarization of the passing laser light by a predetermined rotation angle of 45 ° with the predetermined rotation angle being 45 °. Since the analyzer 8 has a polarization transmission characteristic in the second polarization direction in the direction rotated by 45 ° around the optical axis 11 from the first polarization direction of the polarizer 6, the analyzer 8 The first polarization component of the return laser light that has passed through 8 is
Since it becomes orthogonal to the polarization transmission characteristics in the polarization direction of, the effect that optimum optical isolation can be realized is obtained.

Further, according to the first embodiment, the dielectric multilayer film 3 is formed on one plane having two planes parallel to each other, and the thickness from one plane to the other plane is maximum. Since the parallel plate type light transmission medium 2 up to 0.5 mm is used as the polarizer 6 and the analyzer 8, the parallel plate type light transmission medium 2 can be thinly formed. The effect that the wavefront aberration of the laser light generated by the passage of the light transmitting medium 2 can be reduced.

Further, according to the first embodiment, the parallel plate type light transmitting medium 2 having the dielectric multilayer film 3 formed on one plane is used as the polarizer 6 and the analyzer 8 without using an adhesive layer. As a result, deterioration of the adhesive layer due to heat does not occur, and the effect of preventing a decrease in transmittance of the optical isolator can be obtained.

Further, according to the first embodiment, the parallel plate type light transmitting medium having the dielectric multilayer film 3 formed on one plane by electron beam evaporation with oxygen ion assist or electron beam evaporation with oxygen plasma assist. 2 is the polarizer 6
Since the analyzer and the analyzer 8 are used, the effect that the dielectric multilayer film 3 can be formed robustly can be obtained, and the accuracy of forming the dielectric multilayer film 3 can be improved, and the deviation of the transmission wavelength can be reduced. The effect of being able to be obtained is obtained.

Further, according to the first embodiment, since the parallel plate type light transmission medium 2 having the antireflection film formed on the other plane is used as the polarizer 6 and the analyzer 8, the return laser The effect that the influence of light can be reduced can be obtained.

Further, according to the first embodiment, the long wavelength transmission type filter including the dielectric multilayer film 3 in which the low refractive index medium is sandwiched by the high refractive index medium is used as the polarizer 6 and the analyzer 8.
Since the number of multilayer films to be configured is smaller than that of a short wavelength transmission type filter in which a high refractive index medium is sandwiched between low refractive index media, the dielectric multilayer film 3 can be made thin. Therefore, it is possible to obtain the effect that the surface strain due to thermal stress can be reduced, and the time required for forming the dielectric multilayer film 3 can be shortened.

Further, according to the first embodiment, the semiconductor laser 4 for emitting the laser light and the collimator lens 5 for converting the laser light emitted from the semiconductor laser 4 into parallel light and making the collimator lens 5 incident on the optical isolator are provided. Because I chose
The effect that the noise characteristic of the laser light emitted from the laser module can be improved is obtained.

Further, according to the first embodiment, the optical fiber 9 for transmitting the laser light and the coupling lens 10 for coupling the laser light emitted from the optical isolator to the optical fiber 9 are provided. The effect that the low-noise laser light can be efficiently incident on the optical fiber 9 can be obtained.

Further, according to the first embodiment, a laser module including the semiconductor laser 4, the optical isolator 12, the coupling lens 10 and the optical fiber 9, the signal light input terminal 13 to which the signal light is input, and the signal light input terminal 13 are provided. A signal light / pumping light multiplexer / demultiplexer 14 for coupling the signal light input to the optical input terminal 13 and the laser light for pumping light emitted from the laser module, and a signal light from the signal light / pumping light multiplexer / demultiplexer 14 Since it is provided with the signal light amplification path such as the EDF 15 that receives the excitation light, amplifies the signal light by the excitation light, and emits the signal light, the effect that low noise and high efficiency optical amplification can be realized is obtained.

Further, according to the first embodiment, since the optical isolator 16 is provided on at least one of the input side and the output side of the signal light amplification path, it is possible to obtain the effect of preventing oscillation in the optical amplifier. .

Further, according to the first embodiment, the semiconductor laser 4 which emits the pumping light, the signal light input terminal 13 into which the signal light is input, and the signal light input into the signal light input terminal 13 and the pumping Signal light / pumping light multiplexer / demultiplexer 1 for coupling light
4 and a signal light amplification path such as an EDF 15 that receives the signal light and the pump light from the signal light / pump light multiplexer / demultiplexer 14 and amplifies the signal light by the pump light and emits the signal light. Since the optical isolator 16 is provided on at least one of the output side and the output side, the effect of preventing oscillation in the optical amplifier can be obtained.

Embodiment 2. In the second embodiment, another mode of the polarization filter used for the polarizer and the analyzer of the optical isolator and passing only the unidirectional polarization of the traveling light will be described.

FIG. 15 is a diagram showing another example of the film configuration of the polarization filter using the dielectric substance described in the first embodiment, and here the reference wavelength λv is 927 nm. In FIG. 15, the dielectric substance forming the multilayer film is
TiO ₂ is generally used as the high refractive index material, and SiO ₂ is used as the low refractive index material. When the film structure shown in FIG. 15 is formed by using these dielectric materials, the polarization transmission characteristics are as shown in FIG. 16, and as shown in FIG. 17, the P polarization component and the S polarization component are -30 dB or more (P Ratio of S-polarized light component transmittance to polarized light component transmittance) Separable wavelength range is 1250
Only about 90 nm from 1 nm to 1340 nm can be obtained,
It becomes difficult to separate polarized light over a wide wavelength band of 100 nm or more.

FIG. 18 is a diagram showing a film configuration example of a polarization filter of a dielectric multilayer film according to the second embodiment of the present invention.
Si as the high refractive index material and SiO as the low refractive index material
₂ is adopted. Where H and L are the quarter wavelength thicknesses of the high refractive index material film and the low refractive index material film, n _S ,
n _H , n _L , and n _A represent the refractive indexes of the substrate, Si, SiO ₂ , and air, respectively, and the reference wavelength serving as the reference for the thickness of one wavelength is 927 nm. The incident angle of the incident light ray is 52.5 °. Also, for example, 0.505
The optical thickness of the Si layer of H is (0.505 × 927) /
(4 × 3.4) = 34.422 nm.

FIG. 19 is a diagram showing the spectral polarization characteristics of the polarization filter of the dielectric multilayer film having the film configuration example shown in FIG. The horizontal axis represents the wavelength of the incident light beam in the unit of nm, and the vertical axis represents the transmittance in the unit of%. 1250 nm
From 1 to 1360 nm, the P-polarized component shows a high transmittance of about 95% or more, and the S-polarized component shows a low transmittance of several% or less.

FIG. 20 shows the spectral polarization characteristics of the polarization filter of the dielectric multilayer film having the film configuration example shown in FIG. 18, evaluated by the polarization separation characteristics of the P polarization component and the S polarization component. The value obtained by dividing the transmittance of the component by the transmittance of the S-polarized component is expressed in dB format. From 1250 nm to 1
-30 dB in the 110 nm wavelength band over 360 nm
It has the above polarization separation ability.

In the second embodiment, MgF ₂ may be used as the low refractive index material in addition to SiO ₂ described above.

Further, by lowering the filling temperature of the vapor deposition by lowering the substrate temperature during vapor deposition and lowering the effective refractive index of the low refractive index substance, the high refractive index substance and the low refractive index substance can be reduced. Since the difference in the refractive index between and can be widened, it is possible to realize a wide band polarization filter. It should be noted that lowering the filling density of vapor deposition (forming by lowering the vapor deposition filling rate of the dielectric substance on the film formation surface) means that the vapor deposition filling rate is 80% or more in ordinary thin film formation. Filling rate is 8
This corresponds to making it less than 0%.

As described above, by combining the dielectric thin film material having a higher refractive index than the conventional one and the dielectric thin film material having a lower refractive index than the conventional one, polarization separation can be performed in a wavelength band wider than the conventional one. .

FIG. 21 is a diagram showing the structure of a semiconductor laser module in which an optical isolator and a semiconductor laser are combined. The polarization filter of the second embodiment is incorporated as a polarizer and an analyzer of the optical isolator. Figure 2
1, reference numeral 21 is a polarizer (polarizing means) using the polarization filter of the second embodiment, 22 is an analyzer (analysis means) using the polarization filter of the second embodiment, and 23 is a Faraday effect element. Reference numeral 24 is a magnet, 25 is a Faraday rotator (optical rotation means), 26 is a semiconductor laser, 27 is a collimator lens, 28 is a coupling lens, and 29 is an optical fiber.

As described above, in the optical isolator shown in FIG. 21, the polarization filter according to the second embodiment is used as the polarizer 2.
1 and the analyzer 22, high optical isolation can be realized, and by combining this optical isolator and a semiconductor laser,
The return light to the semiconductor laser is reduced, and the increase in noise of the semiconductor laser output due to the return light can be reduced.

As described above, according to the second embodiment, a parallel plate type dielectric multilayer film is formed by combining a high refractive index dielectric thin film material and a low refractive index dielectric thin film material. Since the polarizing filter is used as the polarizing filter, it is possible to obtain the effect that the polarized light can be separated in a wider wavelength band than the conventional one.

Further, according to the second embodiment, the dielectric thin film material having a low refractive index is formed by setting the deposition filling rate of the dielectric substance on the deposition surface to be lower than 80%. Therefore, as compared with the related art, it is possible to obtain the effect that the polarized light can be separated in a wider wavelength band.

Further, according to the second embodiment, the dielectric thin film material having a high refractive index is Si, and the dielectric thin film material having a low refractive index is SiO ₂ or MgF _2. Thus, it is possible to obtain the effect that the polarized light can be separated in a wide wavelength band.

[0103]

As described above, according to the present invention, the optical rotator having the optical rotatory action about the optical axis and the polarization transmission characteristic in the first polarization direction, which are arranged to be inclined with respect to the optical axis. The parallel plate type polarization plate having the parallel plate type polarization plate and the polarization plate having the polarization plate and the polarization plate are arranged so as to reduce the wavefront aberration generated in the polarization plate, and have a polarization transmission characteristic in the second polarization direction. Since the light detecting means is provided, the wavefront aberration of the light passing through the polarizing means can be reduced by the light detecting means, and the effect of reducing the occurrence of wavefront aberration can be obtained.

According to the present invention, the optical transmission means for transmitting the laser light and the optical coupling means for coupling the laser light emitted from the optical isolator to the optical transmission means are provided. The effect that the light can be efficiently incident on the optical transmission means is obtained.

According to the present invention, a dielectric thin film material having a high refractive index and a dielectric thin film material having a low refractive index are combined to form a parallel plate type dielectric multilayer film. Then, the effect that polarized light can be separated in a wide wavelength band can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a dielectric multilayer filter applied to an optical isolator according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a dielectric multilayer filter 1 of FIG.

FIG. 3 is a diagram showing polarization transmission characteristics of a configuration example of the dielectric multilayer filter 1 of FIG.

FIG. 4 is a diagram showing a configuration of an optical isolator according to the first embodiment of the present invention.

FIG. 5 is a diagram for explaining a positional relationship between a polarizer and an analyzer.

FIG. 6 is a diagram for explaining a positional relationship between a polarizer and an analyzer.

FIG. 7 is a diagram for explaining a positional relationship between a polarizer and an analyzer.

FIG. 8 is a diagram for explaining a positional relationship between a polarizer and an analyzer.

FIG. 9 is a diagram showing how laser light is incident on the optical isolator in the forward direction and in the reverse direction, respectively.

FIG. 10 is a diagram for explaining the effect of the optical isolator according to the first embodiment of the present invention.

FIG. 11 is a diagram showing a result obtained by simulating a relationship between an inclined arrangement angle and generation of wavefront aberration by calculation.

FIG. 12 is a diagram showing the configuration of the optical amplifier according to the first embodiment of the present invention.

FIG. 13 is a diagram showing the configuration of the optical amplifier according to the first embodiment of the present invention.

FIG. 14 is a diagram showing the configuration of the optical amplifier according to the first embodiment of the present invention.

FIG. 15 is a diagram showing another example of the film configuration of the polarization filter using the dielectric substance described in the first embodiment.

FIG. 16 is a diagram showing the spectral polarization characteristics of a polarization filter using the dielectric substance described in the first embodiment.

FIG. 17 is a diagram showing polarization separation characteristics of a polarization filter using the dielectric substance described in the first embodiment.

FIG. 18 is a diagram showing an example of a film configuration of a polarization filter according to a second embodiment of the present invention.

19 is a diagram showing spectral polarization characteristics of the polarization filter of FIG.

20 is a diagram showing polarization separation characteristics of the polarization filter shown in FIG.

FIG. 21 is a diagram showing a configuration of a semiconductor laser module in which the polarization filter of the present invention is incorporated as a polarizer and an analyzer of an optical isolator and combined with a semiconductor laser.

FIG. 22 is a diagram showing a configuration of a dielectric multilayer film element applied to a conventional optical isolator.

FIG. 23 is a diagram showing a configuration of a conventional optical isolator.

FIG. 24 is a diagram showing a wavefront aberration generally generated by a parallel plate and a wavefront aberration generated and amplified by a conventional optical isolator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 dielectric multilayer film filter, 2 parallel plate type light transmitting medium, 3 dielectric multilayer film, 4 semiconductor laser (laser light source means), 5 collimator lens (parallel light converting means), 6
Polarizer (polarizing means), 7 Faraday rotator (optical rotation means), 7F Faraday effect element, 7M magnet, 8 analyzer (analysis means), 9 optical fiber (optical transmission means), 1
0 coupling lens (optical coupling means), 11 optical axis,
12 optical isolator, 13 signal light input terminal (signal light input means), 14 signal light / pumping light multiplexer / demultiplexer (signal light /
Excitation light coupling means), 15 EDF (erbium-doped optical fiber; optical amplification path, rare-earth-doped optical fiber), 16
Optical isolator, 17 optical fiber (signal light amplification path), 21 polarizer (polarizing means), 22 analyzer (analyzing means), 23 Faraday effect element, 24 magnet, 25
Faraday rotator (optical rotation means), 26 semiconductor laser, 27 collimator lens, 28 coupling lens, 29 optical fiber, Lin laser beam, m1, m
2 normal, θ inclined arrangement angle (light incident angle).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hidekazu Kodera             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 2H037 AA01 BA03 CA14 DA03 DA04                       DA05 DA06                 2H038 AA21 BA35                 2H049 BA02 BA05 BA07 BA08 BA43                       BB03 BB06 BC25                 2H099 AA02 BA02 CA00 CA08                 5F072 JJ20 KK30 YY17

Claims (25)

[Claims] 1. An optical rotation means having an optical rotation effect around an optical axis, a parallel plate type polarization means arranged on the optical axis so as to be inclined with respect to the optical axis, and an optical axis on the optical axis. An optical isolator, comprising: a parallel plate type analyzer arranged so as to sandwich the optical rotating means together with the polarizing means so as to face each other and reduce the wavefront aberration generated in the polarizing means. 2. An optical rotation means for rotating and emitting polarized light of passing light around the optical axis by a predetermined rotation angle, and a first angle in an inclination direction with respect to the optical axis, which is arranged on the optical axis. Parallel plate-shaped polarization means inclined only by the angle, and arranged on the optical axis so as to sandwich the optical rotation means together with the polarization means, and to incline by a second angle in the opposite inclination direction with respect to the polarization means. An optical isolator, which is provided with a parallel plate type light detecting means. 3. An optical rotating means having an optical axis, a parallel plate type polarizing means intersecting with the optical axis, and a parallel plate detecting means intersecting with the optical axis and sandwiching the optical rotating means together with the polarizing means so as to face each other. Where the virtual light detecting means is placed in a relationship perpendicular to the optical axis of the virtual optical rotating means, and the first plane of polarization of the polarized light passing through the virtual polarizing means is virtual. The virtual polarization means is placed so as to be parallel to the second polarization plane of the polarized light that passes through the analysis means, and the first line of intersection between the virtual polarization means and the first polarization plane is virtual. A virtual polarization means and a virtual polarization means with respect to the optical axis of the virtual optical rotation means so as to face each other in a substantially V shape with respect to a second line of intersection between the optical analysis means and the second plane of polarization. The different light detecting means are inclined with respect to each other, and the angle between the first plane of polarization and the second plane of polarization is the second plane of polarization. Then, the virtual light detecting means is rotated around the optical axis of the virtual optical rotating means so as to be approximately 45 °, and the rotation angle of the virtual optical rotating means is the angle at which the polarization plane of the polarized light rotates around the optical axis. The arrangement that is substantially the same as the arrangement of the virtual polarization means, the virtual light detection means, and the virtual optical rotation means arranged under the condition that they are set at about 45 ° is An optical isolator comprising the polarizing means and the light detecting means. 4. The absolute value of the inclined arrangement angle of the light detecting means from the normal line of the light incident surface of the light detecting means to the electric field vector of light is the polarization from the normal line of the light incident surface of the polarizing means to the electric field vector of light. 2. The optical isolator according to claim 1, wherein the means have the same absolute value of the inclination arrangement angles and are arranged at the inclination arrangement angles of opposite signs. 5. The light detecting means has a reverse inclination arrangement angle having an absolute value equal to the inclination arrangement angle of the polarizing means formed by the light incident surface of the polarization means and the optical axis and having an opposite sign to the normal line of the light emitting surface. 3. The optical isolator according to claim 1, wherein the optical isolator and the optical axis are arranged so as to be reversely inclined. 6. The polarizing means or the light analyzing means is tilted so that the tilted arrangement angle formed by the normal line of the light incident surface and the optical axis is the Brewster angle. Optical isolator. 7. The polarizing means or the light detecting means is arranged so that the absolute value of the inclination arrangement angle formed by the normal line of the light incident surface and the optical axis is 50 ° to 60 °. The optical isolator according to claim 1 or 2, characterized in that. 8. The optical rotator has a predetermined rotation angle of 45 ° and outputs the polarized light of the passing light by rotating the light about its optical axis by the predetermined rotation angle, and outputs the polarized light. 45 around the optical axis from the polarization direction of 1
The optical isolator according to claim 2, wherein the optical isolator has a polarization transmission characteristic of a second polarization direction in a direction rotated by an angle of °. 9. The polarization means or the light analysis means has one plane on which a multilayer film is formed and the other plane parallel to the one plane, and the plane from the one plane to the other plane. The optical isolator according to claim 2, wherein the light transmission medium is a parallel plate type having a thickness of up to 0.5 mm. 10. The light according to claim 9, wherein the polarizing means or the light detecting means is a parallel plate type light transmitting medium having a multilayer film formed on one plane without using an adhesive layer. Isolators. 11. The polarizing means or the analyzing means is a parallel plate type light transmitting medium having a multilayer film formed on one plane by electron beam evaporation with oxygen ion assist or electron beam evaporation with oxygen plasma assist. The optical isolator according to claim 9, characterized by: 12. The optical isolator according to claim 9, wherein the polarizing means or the light detecting means is a parallel plate type light transmitting medium having an antireflection film formed on the other plane. 13. The optical isolator according to claim 9, wherein the polarizing means or the light detecting means comprises a long-wavelength transmission type filter having a multilayer film in which a low refractive index medium is sandwiched by a high refractive index medium. 14. A polarizing filter comprising a parallel plate type dielectric multilayer film formed by combining with a dielectric thin film material having a low refractive index in which a deposition rate of a dielectric substance on a film forming surface is lower than 80%. The optical isolator according to any one of claims 1 to 3, wherein the optical isolator is a means or a light detecting means. 15. A polarizing filter formed by combining a high refractive index dielectric thin film material as Si and a low refractive index dielectric thin film material as SiO ₂ or MgF ₂ to form a parallel plate type dielectric multilayer film as a polarizing means or 15. The optical isolator according to claim 14, wherein the optical isolator is a light detecting means. 16. An optical rotator having an optical rotatory action about an optical axis, a parallel plate type polarizer arranged obliquely with respect to the optical axis and having polarization transmission characteristics in a first polarization direction, The polarizing means and the optical rotation means are sandwiched so as to face each other, and arranged so as to reduce the wavefront aberration generated in the polarizing means,
An optical isolator provided with a parallel plate type analyzer having polarization transmission characteristics in the second polarization direction, a laser light source means for emitting laser light, and a laser light emitted from the laser light source means for converting into parallel light. Then, the laser module is provided with a parallel light converting means for entering the optical isolator. 17. The laser module according to claim 16, further comprising: an optical transmission unit that transmits a laser beam; and an optical coupling unit that couples the laser beam emitted from an optical isolator to the optical transmission unit. 18. A laser module, signal light input means for inputting signal light, signal for coupling the signal light input to the signal light input means and laser light as pumping light emitted from the laser module. An optical / pumping light coupling means; and a signal light amplification path for receiving the signal light and the pumping light from the signal light / pumping light coupling means, amplifying the signal light by the pumping light, and emitting the amplified signal light. The laser module includes an optical rotator having an optical rotatory action about an optical axis, a parallel plate type polarizing means arranged to be inclined with respect to the optical axis and having polarization transmission characteristics in a first polarization direction, and the above-mentioned polarized light. Means for sandwiching the optical rotation means in opposition to each other, and arranged so as to reduce the wavefront aberration generated in the polarization means, and having a parallel plate type analysis means having polarization transmission characteristics in the second polarization direction. Isolator and a laser light source means for emitting a laser beam, an optical amplifier, characterized in that it comprises a parallel light conversion means for converting the laser beam emitted from said laser light source means into parallel light incident on the optical isolator. 19. A second optical isolator is provided on at least one of an input side and an output side of a signal light amplification path, and a second optical isolator is provided.
Is an optical isolator having an optical rotation effect around an optical axis, a parallel plate type polarizing means arranged obliquely with respect to the optical axis and having polarization transmission characteristics in a first polarization direction, And a parallel plate type analyzer having a polarization transmission characteristic in the second polarization direction, which is disposed so as to sandwich the optical rotation unit with the polarization unit so as to face each other and reduce the wavefront aberration generated in the polarization unit. 19. The method according to claim 18, wherein
The optical amplifier described. 20. An optical rotation means having an optical rotation effect around an optical axis, a parallel plate type polarization means arranged obliquely with respect to the optical axis and having polarization transmission characteristics in a first polarization direction, The polarizing means and the optical rotation means are sandwiched so as to face each other, and arranged so as to reduce the wavefront aberration generated in the polarizing means,
An optical isolator including a parallel plate type analyzer having polarization transmission characteristics in the second polarization direction, a laser light source unit for emitting pumping light, a signal light input unit for inputting signal light, and the above-mentioned signal. A signal light / pumping light coupling means for coupling the signal light input to the light inputting means and the pumping light, and the signal light and the pumping light received from the signal light / pumping light coupling means, and the An optical amplifier comprising: a signal light amplification path that amplifies and outputs the signal light; and the optical isolator is provided on at least one of an input side and an output side of the signal light amplification path. 21. The optical amplifier according to claim 18, wherein a rare earth-doped optical fiber which is configured by adding rare earth to an optical fiber and is excited by pumping light to amplify the signal light is used as a signal light amplification path. . 22. A parallel plate type polarizing means having a first polarization direction parallel to a first polarization plane of a polarized light beam passing through the polarizing means, and a second polarization plane of the polarized light beam passing through the analyzing means. And a parallel plate-shaped light detecting means having a second polarization direction parallel to the light receiving means, and an optical axis which is placed between the light polarizing means and the light detecting means and intersects with the light polarizing means and the light detecting means. At the rotation angle of about 45 °, the optical polarization means rotates the polarization of the polarized light beam about the optical axis, wherein the second polarization direction of the light detection means is the same as the first polarization direction of the polarization means. As described above, the virtual light detecting means is placed in a parallel relationship with the virtual polarizing means, and the virtual light detecting means is approximately 22 in the rotation direction of the optical rotation means.
As a result, an arrangement substantially the same as the arrangement of the virtual polarizing means and the virtual analyzing means arranged under the condition that they are rotated around the optical axis at a rotation angle of 5 ° is adopted. An optical isolator having means. 23. A parallel plate type polarizing means having a first polarization direction parallel to a first polarization plane of polarized light passing through the polarizing means, and a second polarization plane of polarized light passing through the analyzing means. And a parallel plate-shaped light detecting means having a second polarization direction parallel to the light receiving means, and an optical axis which is placed between the light polarizing means and the light detecting means and intersects with the light polarizing means and the light detecting means. At the rotation angle of about 45 °, the optical polarization means rotates the polarization of the polarized light beam about the optical axis, wherein the second polarization direction of the light detection means is the same as the first polarization direction of the polarization means. As described above, the analyzing means is placed in a parallel relationship with the polarizing means, and the analyzing means is rotated about the optical axis at a rotation angle of about 225 ° in the rotation direction of the optical rotating means. Light having substantially the same arrangement of polarizing means and analyzing means Isolator. 24. A polarizing filter characterized in that a dielectric thin film material having a low refractive index is formed by making a deposition filling rate of a dielectric substance on a film forming surface lower than 80%. 25. A polarization filter, wherein the high refractive index dielectric thin film material is Si, and the low refractive index dielectric thin film material is SiO ₂ or MgF ₂ .