JP2632119B2 - Polarization independent filter device with built-in optical isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter in which a dielectric multilayer film is formed after a polarization-independent optical isolator having a non-reciprocal portion in which birefringent plates are arranged on both sides of a Faraday rotator. The present invention relates to a polarization-independent filter device having a built-in optical isolator that is arranged obliquely with respect to the above.

[0002]

2. Description of the Related Art An optical demultiplexer or an optical multiplexer is a device that separates light of different wavelengths for each wavelength or combines light of different wavelengths in a wavelength multiplexing system such as optical communication. This is a device for selecting light of an arbitrary wavelength from light of a wide band to light of a narrow band or light of a different wavelength. Generally, in an optical communication system, an optical isolator is combined with an optical demultiplexer, an optical multiplexer, or an optical wavelength selector, and for example, the reflected light is blocked by an optical fiber amplifier or the like, and at the same time, the signal light and the pumping light for amplification are simultaneously output. Separation,
Used for coupling or wavelength selection.

There are an optical fiber type and a filter type in the optical demultiplexer and the optical multiplexer. The optical fiber type mainly uses a single mode optical fiber, closes the cores of two optical fibers sufficiently compared to the core diameter, and obtains a desired demultiplexing characteristic by the distribution of light guided to each optical fiber. Is obtained. This type is the mainstream because simple connection is possible, but there is a problem that the power of the output light fluctuates because the branching ratio changes due to the change in the polarization state of the incident light.

On the other hand, the filter type uses a filter in which a dielectric multilayer film is formed, and obtains a predetermined wavelength characteristic by interference between transmitted light and reflected light generated at the interface of each layer film. By changing the film configuration and the film thickness, a long-wavelength pass filter and a short-wavelength pass filter used in a demultiplexer or a multiplexer can be realized in an arbitrary wavelength range. However, if the filter is arranged obliquely to the incident light, the reflected light does not depend much on the polarization state of the incident light, and the power fluctuation is relatively small, but the transmitted light has a large power fluctuation depending on the polarization state of the incident light. . Therefore, in the prior art, a duplexer having a structure in which signal light is reflected by a filter and taken out, or a multiplexer having a structure in which signal light is taken in is used for optical fiber amplification.

Further, the optical wavelength selector uses a filter having a dielectric multilayer film formed thereon, and obtains a predetermined wavelength characteristic by interference between transmitted light and reflected light generated at the interface of each layer film. By changing the film configuration and the film thickness, a band-pass filter used in the optical wavelength selector can be realized in an arbitrary wavelength range. If incident light is incident on this filter vertically, the transmitted light does not depend on the polarization state of the incident light, and no power fluctuation occurs. Therefore, in the prior art, an LD having a center wavelength that is not constant over a wide band is used.
(Semiconductor laser) A wide variety of wavelength selectors have a structure that selects signal light with a constant center wavelength in a narrow band from light beams or selects signal light by combining signal light and pumping light for amplification. Used in the system.

FIG. 7 shows an example of a conventional optical fiber amplifying duplexer in which an optical isolator and an optical duplexer are connected. An optical demultiplexer 54 using a filter 52 is disposed downstream of the optical isolator 50. Here, the filter 52 is a short wavelength pass filter having a dielectric multilayer film formed on the surface. Optical splitter 5
A reflection plate 56 that further reflects the light reflected by the filter 52 and emits the light in a desired direction is provided in 4. The optical isolator 50 and the optical demultiplexer 54 are connected by a connector 57 and an optical fiber 58.

[0007] When wavelength multiplexed light of 1550 nm wavelength signal light and 1480 nm wavelength excitation light is incident, this light beam passes through the optical isolator 50 and reaches the filter 52 from the connector 57. The filter 52 is a short wavelength pass filter,
The excitation light having a wavelength of 1480 nm is transmitted, and the signal light having a wavelength of 1550 nm is reflected. The signal light is used by being reflected by the reflector 56 in a direction to be taken out, and the excitation light is used up and removed.

FIG. 8 shows an example of a conventional optical fiber amplifying multiplexer in which an optical isolator and an optical multiplexer are connected. An optical isolator 6 is provided after the optical multiplexer 64 using the filter 62.
Place a 0. Here, the filter 62 is a long wavelength pass filter having a dielectric multilayer film formed on the surface. Optical filter 60
And the optical multiplexer 64 are connected by a connector 67 and an optical fiber 68.

The filter 62 is a long-wavelength pass filter, which allows signal light having a wavelength of 1550 nm to pass therethrough and reflects excitation light having a wavelength of 1480 nm to produce wavelength multiplexed light. This light beam reaches the optical isolator 60 from the connector 67.

FIG. 9 shows an example of a conventional optical fiber amplifier wavelength selector in which an optical isolator and an optical wavelength selector are connected. An optical wavelength selector 74 using a filter 72 is disposed downstream of the optical isolator 70. Here, the filter 72 is a band-pass filter having a dielectric multilayer film formed on the surface. The optical isolator 70 and the optical wavelength selector 74 are connected by a connector 77 and an optical fiber 78.

When wavelength-division multiplexed light consisting of a signal light having a wavelength of 1550 nm and an excitation light having a wavelength of 1480 nm is incident, this light passes through an optical isolator 70 and is transmitted from a connector 77 to a filter 72.
To reach. Filter 72 is a bandpass filter,
The signal light having a wavelength of 1550 nm is transmitted, and the excitation light having a wavelength of 1480 nm is reflected.

[0012]

The filters of the optical demultiplexer and the optical multiplexer are arranged obliquely with respect to the incident light, and even when an optical wavelength selector selects an arbitrary wavelength in a wide band, the filter is used for the incident light. Are arranged obliquely with respect to. Therefore, when the incident angle of the light beam with respect to the filter is large, the Brewster condition is different between the S-polarized light component and the P-polarized light component with respect to the filter. In the short wavelength pass filter, the long wavelength pass filter, and the band pass filter, the reflectance of the P-polarized component and the S-polarized component is almost constant at each wavelength in the reflection wavelength range, but the P-polarized component and S The transmittance of the polarized light component varies greatly at each wavelength.

For example, FIG. 10 shows an example of measuring the characteristics of P-polarized light and S-polarized light of a long wavelength pass filter. Here, the filter is arranged at an angle of 22.5 degrees to a plane perpendicular to the incident light. FIG. 10A shows transmission loss, and FIG. 10B shows reflection loss. In the figure, a portion between the P-polarized light and the S-polarized light is a fluctuation portion of the transmission loss and the reflection loss with respect to each incident polarization plane. This filter clearly has a greater polarization dependence on transmitted light than on reflected light. Therefore, the polarization state of the light incident on the filter is not uniquely determined, and the branching ratio between the P-polarized component and the S-polarized component changes. Here, when the incident light has a certain wavelength within the transmission wavelength range, the transmission of the P-polarized component and the S-polarized component is different, so that the transmitted light undergoes power fluctuation according to the polarization state.

FIG. 11 is a schematic diagram showing the characteristics of P-polarized light and S-polarized light of, for example, a band-pass filter. Here, the filter is arranged to be inclined with respect to the incident light in order to obtain an arbitrary selected wavelength. In the drawing, a portion between the P-polarized light and the S-polarized light is a portion where the transmittance varies with respect to the incident polarization plane. Therefore, the polarization state of the light incident on the filter is not uniquely determined, and the branching ratio between the P-polarized component and the S-polarized component changes. Here, since the transmittance of the P-polarized light component and the transmittance of the S-polarized light component of the incident light are different, the transmitted light fluctuates in power according to the polarization state.

Therefore, this type of filter has a drawback that all of the optical demultiplexer, the optical multiplexer, and the optical wavelength selector fluctuate in power depending on the polarization state.

In an optical demultiplexer, in this type of filter, reflected light has less power fluctuation than transmitted light as described above. Therefore, as signal light for which power fluctuations need to be suppressed as much as possible, reflection at the filter must be used. However, using reflected light complicates the optical path,
Even if a reflecting mirror is required or an optical fiber is used, there is a disadvantage that the outer diameter of the device is increased. Further, there is a disadvantage that the excitation light, which is transmitted light, cannot be reused.

In the prior art, an optical isolator and an optical demultiplexer, an optical multiplexer, or an optical wavelength selector are separately manufactured and connected by an optical fiber and a connector.
Also in that respect, there is a problem that the number of parts is large and the shape becomes large.

An object of the present invention is to provide a multiplexed light or a wavelength-selective light having a constant and stable power without depending on the polarization state of the incident light. It is an object of the present invention to provide a polarization-independent filter device with a built-in optical isolator that can be obtained as transmitted light instead of light and can be downsized.

[0019]

SUMMARY OF THE INVENTION The present invention provides a filter having a dielectric multi-layer film formed after a polarization-independent optical isolator having a non-reciprocal portion in which wedge-shaped birefringent plates are arranged on both sides of a Faraday rotator. This is a polarization-independent filter device with a built-in optical isolator arranged obliquely to incident light. Here, the optical axis of the wedge-shaped birefringent plate adjacent to the filter is adjusted such that when projected onto the filter, the projected image is rotated by 45 degrees from the S-polarized direction of the filter to the P-polarized direction.

The filter of the polarization independent filter device is a long wavelength pass filter or a short wavelength pass filter. An input port is provided on the optical path of the incident light in front of the non-reciprocal portion of the filter device, a first output port is provided on the optical path of the output light passing through the filter, and on the optical path of the output light reflected by the filter. An optical demultiplexer is provided by providing a second output port.

Further, the filter is a long-wavelength pass filter or a short-wavelength pass filter, and the first filter is disposed on the optical path of the incident light in front of the non-reciprocal portion of the polarization independent filter device.
And an output port is provided on the optical path of the output light behind the filter, and a second input port is provided on the optical path of the input light reflected by the filter and output to the output port. Filter. Further, a second non-reciprocal part is disposed between the second input port and the filter, and the optical axis of the birefringent plate of the second non-reciprocal part adjacent to the filter is:
When projected onto the filter, the projected image
The optical multiplexer may be adjusted so as to be rotated by 45 degrees from the polarization direction to the P polarization direction.

Alternatively, the filter of the polarization-independent filter device is a band-pass filter, and an input port is provided on the optical path of the incident light in front of the non-reciprocal portion of the filter device, and the filter is provided on the optical path of the output light transmitted through the filter. Is provided with an emission port to provide an optical wavelength selector.

[0023]

A light beam is incident on a polarization independent filter device having a built-in optical isolator according to the present invention. The light beam passes through the optical isolator, is separated into ordinary light and extraordinary light by the birefringent plate, becomes parallel, and reaches the filter. Here, when the optical axis of the birefringent plate adjacent to the filter is projected onto the filter, the projected image is adjusted so as to be rotated by 45 degrees from the S-polarized direction of the filter to the P-polarized direction. The split ratio of transmission and reflection in the filter is the same. If the ordinary light and the extraordinary light are received together, the power of the transmitted light or the reflected light becomes constant even if the polarization plane of the incident light changes and the branching ratio between the ordinary light and the extraordinary light changes. The combination of the filter and the birefringent plate of the optical isolator adjacent thereto functions as a polarization-independent filter device.

A wavelength division multiplexed light having two different wavelengths is incident on an optical demultiplexer using this polarization independent filter device. The wavelength-division multiplexed light is composed of a light beam in a transmission wavelength region and a light beam in a reflection wavelength region in the filter. First, the wavelength multiplexed light passes through the optical isolator, is separated into ordinary light and extraordinary light, becomes parallel, and reaches the filter. The ordinary light and the extraordinary light in the transmission wavelength range pass through the filter and couple to the first port, while the ordinary light and the extraordinary light in the reflection wavelength range are reflected by the filter and couple to the second port, and are independent of the polarization. As described in the type filter device, the power is constant and stable. Thus, the combination of the filter and the birefringent plate of the optical isolator adjacent thereto functions as a polarization-independent optical demultiplexer.

Light in the transmission wavelength range of the filter is incident on an optical multiplexer using this polarization independent filter device. This light beam passes through the optical isolator, is separated into ordinary light and extraordinary light by the birefringent plate, becomes parallel, and reaches the filter. As described above, after passing through the filter, by receiving the ordinary light and the extraordinary light together, even if the polarization plane of the incident light changes and the branching ratio between the ordinary light and the extraordinary light changes, the power of the transmitted light is kept constant. Become. On the other hand, light rays in the reflection wavelength range are reflected when they enter the filter, but the reflected light has sufficiently small polarization dependence as compared with the transmitted light. Therefore, the ordinary light and the extraordinary light in the transmission wavelength range pass through the filter, and the ordinary light and the extraordinary light in the reflection wavelength range are reflected by the filter. These wavelength multiplexed lights are coupled to the output port, and the power is constant and stable. . Thus, the combination of the filter and the birefringent plate of the optical isolator adjacent thereto functions as a polarization-independent optical multiplexer.

In the optical multiplexer, when the polarization dependence of the light beam in the reflection wavelength range in the filter is sufficiently large that it cannot be ignored, a second non-reciprocal portion is provided between the entrance port of the light beam in the reflection wavelength region and the filter. Deploy. When the optical axis of the birefringent plate at the second non-reciprocal portion adjacent to the filter is projected onto the filter, the projected image is shifted from the S-polarized direction of the filter by P
Since the adjustment is performed so as to be rotated by 45 degrees in the polarization direction, the power of the wavelength multiplexed light coupled to the output port is constant and more stable.

A light beam with a wide wavelength band is incident on an optical wavelength selector using this polarization independent filter device. This light beam passes through the optical isolator, is separated into ordinary light and extraordinary light by the birefringent plate, becomes parallel, and reaches the filter. As described above, after passing through the filter, by receiving the ordinary light and the extraordinary light together, even if the polarization plane of the incident light changes and the branching ratio between the ordinary light and the extraordinary light changes, the power of the transmitted light is kept constant. Become. Therefore, the ordinary light and the extraordinary light in the transmission wavelength range pass through the filter and are coupled to the output port, and the power is constant and stable. Thus, the combination of the filter and the birefringent plate of the optical isolator adjacent thereto functions as a polarization-independent optical wavelength selector.

[0028]

FIG. 1 is an explanatory diagram showing an embodiment of an optical demultiplexer using a polarization-independent filter device incorporating an optical isolator according to the present invention. The polarization-independent filter device 40 with a built-in optical isolator has a polarization-independent type optical isolator having the non-reciprocal portion 16 and is disposed obliquely to the incident light (for example, a plane perpendicular to the incident light and a 22.5. This is a structure in which the filter 20 arranged in (degree) is provided. Here, the non-reciprocal portion 16 has a 45-degree Faraday rotator 14 disposed between the two wedge-shaped birefringent plates 10 and 12 and is integrally connected.
Both wedge-type birefringent plates 10 and 12 are made of, for example, a rutile single crystal, and the thick and thin portions thereof are Faraday rotators 14.
Are combined to face each other. The filter 20 is a long-wavelength pass filter in which a dielectric multilayer film is formed on the surface (incident side surface 22) of a parallel plate of glass by vapor deposition or the like. In this optical demultiplexer, an input port Pi is provided on the optical path of the incident light in front of the non-reciprocal portion 16, and the filter 2 is provided.
A first outgoing port P _O1 is provided on the optical path of the outgoing light passing through 0, and a second outgoing port P _O2 is provided on the optical path of the outgoing light reflected by the filter 20. In each port, spherical lenses 35, 36, and 37 for collimating the single mode optical fibers 30, 31, and 32 are arranged.

Next, the positional relationship between the filter 20 and the adjacent wedge-shaped birefringent plate 12 will be described. As shown in FIG. 2, the optical axis Ax of the wedge-shaped birefringent plate 12 adjacent to the filter 20 is in a plane perpendicular to the incident light, and when the optical axis Ax is projected on the filter 20, The image is adjusted and arranged so that the image is rotated by 45 degrees from the S polarization direction to the P polarization direction of the filter. Therefore, filter 2
When the S polarization direction and the P polarization direction of 0 are projected on a plane perpendicular to the optical axis, the projected image in the S polarization direction is the X axis, the projected image in the P polarization direction is the Y axis, and the optical axis direction is the Z axis. Then, the optical axis Ax of the birefringent plate is inclined by 45 degrees (clockwise as viewed from the incident side) with respect to the X axis. At this time, as shown in FIG. 2, the polarization plane of the ordinary light is tilted at −45 degrees (counterclockwise as viewed from the incident side) with respect to the X axis, and the polarization plane of the extraordinary light is 45 degrees with respect to the X axis.
Degrees (clockwise as viewed from the incident side).

The operation of this optical demultiplexer is as follows. From the input port Pi, for example, a signal light having a wavelength of 1550 nm and a wavelength
Wavelength multiplexed light consisting of 1480 nm excitation light is incident. The wavelength-division multiplexed light passes through the non-reciprocal portion 16, is separated into ordinary light and extraordinary light by the wedge-shaped birefringent plates 10 and 12, becomes parallel light, and reaches the filter 20. In the filter 20, the signal light having a wavelength of 1550 nm is in the transmission wavelength range.
Through. Here, the split ratio of transmission and reflection in the filter 20 is determined by the angle between the polarization plane of the light beam and the X-axis direction. Since the polarization planes of the ordinary light and the extraordinary light are orthogonal to each other, they form an angle of 45 degrees with respect to the X-axis direction, and have the same branch ratio between transmission and reflection. That is, the wavelength 1550
Since the transmittance of the ordinary light and the extraordinary light of nm is the same, by receiving these two rays together, even if the polarization plane of the incident light changes and the branching ratio between the ordinary light and the extraordinary light changes, The power of the transmitted light is constant. Thus, the light having the wavelength of 1550 nm passes through the filter 20 and is coupled to the first output port _PO1 .

On the other hand, the excitation light having a wavelength of 1480 nm is in the reflection wavelength range and is reflected by the filter 20. Similarly to the above, since the reflectance of the ordinary light and the extraordinary light becomes the same, by receiving these two rays together, even if the polarization plane of the incident light changes, the branching ratio of the ordinary light and the extraordinary light changes. However, the power of the reflected light is constant. Thus, the excitation light having the wavelength of 1480 nm is reflected by the filter 20 and is coupled to the second output port P _O2 .

FIG. 6 is a characteristic diagram showing the measured insertion loss of this optical demultiplexer at wavelengths from 1470 nm to 1580 nm. This includes, in addition to the transmission and reflection losses of the filter,
Includes insertion loss for each component. The shaded portions indicate the values of insertion loss that can be taken when the polarization state of the incident light changes in various ways. In particular, it shows that the value of the insertion loss is almost constant around the wavelength of 1550 nm or around the wavelength of 1480 nm, and has almost no polarization dependence.

FIG. 3 is an explanatory view showing an embodiment of an optical multiplexer using a polarization-independent filter device with a built-in optical isolator according to the present invention. The polarization-independent filter device 42 with a built-in optical isolator is inclined (for example, a plane perpendicular to the incident light at 22.5 degrees) with respect to the incident light subsequent to the polarization-independent optical isolator having the non-reciprocal portion 16. This is a structure in which the filter 20 arranged in is provided. The basic structure of the polarization-independent filter device 42 is the same as that shown in FIG. 1, and a detailed description thereof will be omitted. This optical multiplexer has a first incident port P _i1 on the optical path of incident light in front of a polarization-independent filter device 42 with a built-in optical isolator, and an output port on the optical path of emitted light transmitted through the filter 20. Po is provided, and a second incident port P _i2 is provided on the optical path of incident light that is reflected by the filter 20 and exits to the exit port Po.

The operation of this optical multiplexer is as follows. A signal light of, for example, 1550 nm is incident from the first incident port P _i1 . This signal light passes through the polarization independent filter device 42 with a built-in optical isolator, and is coupled to the output port Po, and the power becomes constant. On the other hand, the second input port P
_When excitation light having a wavelength of, for example, 1480 nm is incident from _i2 , this excitation light is in a reflection wavelength range with respect to the filter 20, and therefore has relatively small polarization dependence and is coupled to the output port Po as shown in FIG. Is done. Accordingly, the value of the insertion loss is approximately constant near the wavelength of 1550 nm or 1480 nm, and has almost no polarization dependence.

FIG. 4 is an explanatory view showing another embodiment of the optical multiplexer according to the present invention. A second non-reciprocal portion 17 is inserted between the second input port P _i2 of the optical multiplexer and the filter 20. The configuration of the second non-reciprocal part 17 is the same as that of the non-reciprocal part 16, and the optical axis of the birefringent plate 12 of the second non-reciprocal part 17 adjacent to the filter 20 is the projected image when projected onto the filter 20. Is adjusted so as to be rotated 45 degrees from the S polarization direction of the filter 20 to the P polarization direction. Therefore, the wavelength 15
The insertion loss around 50 nm and around the wavelength 1480, especially around the wavelength 1480 in the reflection wavelength region is more constant, and the polarization dependence is eliminated.

FIG. 5 is an explanatory view showing an embodiment of an optical wavelength selector using a polarization independent filter device having a built-in optical isolator according to the present invention. The polarization-independent filter device 44 with a built-in optical isolator has a band-pass filter 25 fixed to a substrate 26 at a stage subsequent to the polarization-independent optical isolator having the non-reciprocal portion 16. The movable structure 26 rotates so that the incident nucleus of the filter 25 can be selected according to the selected wavelength for the incident light. This optical wavelength selector has a configuration in which an input port Pi is provided on an optical path of incident light in front of a polarization independent filter device 44 with a built-in optical isolator, and an output port Po is provided on an optical path of output light.

The operation of the optical wavelength selector is as follows. For example, a broadband light having a center wavelength of 1550 nm is incident from the incident port Pi. The filter 25 is designed to select a wavelength of 1560 nm at normal incidence, for example, and
By rotating the substrate 26 about the pin 27 so as to select the signal light of nm, the filter 25 is arranged obliquely with respect to the incident light. The signal light that has passed through the polarization independent filter device 44 is coupled to the output port Po, and the power is constant. Therefore, at a wavelength of 1552 nm, the value of the insertion loss is almost constant and there is almost no polarization independence.

The present invention is not limited to only such a configuration. The optical demultiplexer or the optical multiplexer may use a short wavelength pass filter instead of the long wavelength pass filter depending on the wavelength of the light beam to be used. The optical wavelength selector is not limited to the presence or absence of the wavelength tuning function, the configuration of the wavelength tuning mechanism, and the like.

[0039]

[0040]

According to the present invention, a filter having a dielectric multilayer film formed obliquely with respect to incident light is provided downstream of a polarization-independent optical isolator having a non-reciprocal portion in which birefringent plates are arranged on both sides of a Faraday rotator. And the polarization directions of the ordinary light and the extraordinary light are 45
As a result, the branching ratio of transmission and reflection of ordinary light and extraordinary light becomes the same. Therefore, when the ordinary light and the extraordinary light are received together, a light beam having a constant and stable power can be emitted without depending on the polarization state of the incident light. Therefore, the optical demultiplexer, the optical multiplexer and the optical wavelength selector using the polarization-independent filter device having the built-in optical isolator can stabilize the insertion loss and emit a light beam having a constant and stable power.

Also, unlike the prior art, the optical demultiplexer uses the transmitted light of the filter as signal light, so that a reflector or the like is not required, and the number of parts is reduced because the optical isolator and the optical demultiplexer are integrated. it can. Therefore, the size of the device can be reduced. Further, in the optical demultiplexer, it is possible to reuse the excitation light of the reflected light. Also, in the optical multiplexer and the optical wavelength selector, the size of the device can be similarly reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an optical demultiplexer using a polarization-independent filter device with a built-in optical isolator according to the present invention.

FIG. 2 is a partial explanatory view showing a polarization independent filter device having a built-in optical isolator according to the present invention.

FIG. 3 is an explanatory view showing an optical multiplexer according to the present invention.

FIG. 4 is an explanatory view showing another embodiment of the optical multiplexer according to the present invention.

FIG. 5 is an explanatory diagram showing one embodiment of an optical wavelength selector according to the present invention.

FIG. 6 is a diagram illustrating a polarization dependence characteristic measurement of the optical demultiplexer according to the present invention.

FIG. 7 is an explanatory view of a conventional combination of an optical isolator and an optical demultiplexer.

FIG. 8 is an explanatory view of a conventional combination of an optical isolator and an optical multiplexer.

FIG. 9 is an explanatory diagram of a combination of a conventional optical isolator and an optical wavelength selector.

FIG. 10 is a diagram illustrating characteristics of transmission and reflectance of P-polarized light and S-polarized light of a long wavelength pass filter.

FIG. 11 shows transmission of P-polarized light and S-polarized light of a band-pass filter.
FIG. 4 is a schematic diagram of a characteristic of reflectance.

[Explanation of symbols]

10 tapered birefringent plate 12 wedge-shaped birefringent plate 14 Faraday rotator 16 non-reciprocal unit 20 filter 40 optical isolator internal polarization independent-type filter device P _i input port P _o1 first output port P _o2 second output port

Claims (5)

(57) [Claims] 1. A filter in which a dielectric multilayer film is formed is disposed obliquely with respect to incident light after a polarization independent optical isolator having a non-reciprocal portion in which wedge-shaped birefringent plates are disposed on both sides of a Faraday rotator. The optical axis of the birefringent plate of the wedge-shaped birefringent plate adjacent to the filter is such that when projected onto the filter, the projected image is P from the S-polarized direction of the filter.
A polarization-independent filter device with a built-in optical isolator that is adjusted to rotate by 45 degrees in the polarization direction. 2. The polarization-independent filter device with a built-in optical isolator according to claim 1, wherein the filter is a long-wavelength pass filter or a short-wavelength pass filter, and an incident port is provided on an optical path of incident light in front of the non-reciprocal portion. An optical demultiplexer provided with a first output port on an optical path of output light transmitted through the filter and a second output port on an optical path of output light reflected by the filter. 3. The polarization-independent filter device with a built-in optical isolator according to claim 1, wherein the filter is a long-wavelength pass filter or a short-wavelength pass filter, and the first filter is disposed on an optical path of incident light in front of the non-reciprocal portion. An entrance port of
An output port is provided on the optical path of the output light behind the filter,
An optical multiplexer having a second incident port on an optical path of incident light which is reflected by a filter and exits to the exit port. 4. A second input port between the second input port and the filter.
And the optical axis of the birefringent plate of the second non-reciprocal portion adjacent to the filter is such that when projected onto the filter, the projected image is 45 degrees from the S-polarized direction of the filter to the P-polarized direction. 4. The optical multiplexer according to claim 3, wherein the optical multiplexer is adjusted to rotate. 5. The polarization-independent filter device with a built-in optical isolator according to claim 1, wherein the filter is a band-pass filter, an incident port is provided on an optical path of incident light in front of the non-reciprocal portion, and the light passes through the filter. An optical wavelength selector having an output port on the optical path of the output light to be emitted.