JPH10227997A - Optical coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical coupler which can reduce the transmissivity or reflection factor polarization dependency of an optical film in inexpensive constitution through easy adjustment. SOLUTION: This optical coupler is constituted by including a 1st light input/ output terminal 11 and a 2nd light input/output terminal 12, and the optical film 13 and a glass plate 14 which are arranged in the optical path of light projecting from the 1st light input/output terminal 11 and made incident on the 2nd light input/output terminal 12. Then this optical coupler has a means which adjusts the tilt angle of the glass plate 14 to the optical path and then adjust the transmissivity polarization dependency of the optical film 13 on P-polarized light and S-polarized light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupler used for optical communication.

[0002]

2. Description of the Related Art In recent years, practical use of optical fiber amplifiers has been rapidly progressing. The optical fiber amplifier is composed of an in-line isolator, pump LD, WDM coupler, erbium-doped fiber, optical branch, monitor PD, etc.
In addition to the greatest feature that optical amplification can be performed without conversion into an electric signal as in the related art, there are features such as high gain, high output, and low noise, so that the performance of a transmission system can be dramatically improved.

[0003] In order to improve the characteristics of optical fiber amplifiers, to reduce the size, etc., these components have been actively combined and integrated. As a method of composite integration, a method of arranging a WDM film, an optical branching film, and an optical isolator formed of a dielectric multilayer film in the same housing is generally performed. The 1996 IEICE General Conference C -208,
In the 1994 IEICE Autumn Conference C-146, etc.
These composite integrated optical components are described in detail.

[0004] On the other hand, however, there is a problem that when multistage relay is performed by an optical fiber amplifier, the polarization dependence of loss is accumulated. Therefore, in order to maintain the quality of communication, it has become more important than ever to reduce the polarization dependence of the loss of the optical components constituting the optical fiber amplifier.

[0005] The loss polarization dependence of an optical component is mainly determined by the transmittance polarization or the reflectance polarization dependence of the built-in optical film. FIG. 8 is a graph showing the characteristics of a light branching film of the related art in which the dependency on the polarization of the reflectance is reduced. The optical film as in this conventional example is described in detail in Japanese Patent Application Laid-Open No. 3-94202.

[0006]

The conventional branched film has a small reflectance polarization dependence at the design value,
Since the value of the polarization dependence of the reflectance is sensitive to a change in the film thickness, there is a problem that it is difficult to obtain the characteristics as designed due to the film thickness variation at the time of manufacturing.

Further, even if the reflectance polarization dependence as designed is obtained, since the reflectance polarization dependence is sensitive to the change of the incident angle, it is necessary to adjust the incident angle with high precision. There is a problem that there is.

It is an object of the present invention to provide an optical coupler that can reduce the dependency of the transmittance or reflectance of an optical film on polarization with an inexpensive structure and simple adjustment.

[0009]

An optical coupler according to the present invention is an optical coupler used for optical communication, comprising a first optical input / output terminal, a second optical input / output terminal, and a first optical input / output terminal. Outgoing, second
An optical film and a glass plate disposed in an optical path incident on the optical input / output terminal of the optical disc, and means for adjusting the inclination angle of the glass plate with respect to the optical path.

[0010] The first and second optical input / output terminals may be optical fibers, the first optical input / output terminal may be an optical fiber,
The second light input / output terminal may be a light receiving element.

[0011] At least one of both surfaces of the glass plate has linearly polarized light (P-polarized light) perpendicular to the direction in which the glass plate is tilted.
And an optical film having a transmittance difference between horizontal and linearly polarized light (S-polarized light).

An optical coupler for use in optical communication, comprising: a first optical input / output terminal; an optical film for reflecting light emitted from the first optical input / output terminal; A second light input / output terminal on which light emitted from the terminal and reflected by the optical film is incident; a glass plate arranged in an optical path connecting the optical film and the second light input / output terminal; Means for adjusting the angle of inclination with respect to the optical path may be provided.

The first and second optical input / output terminals may be optical fibers, wherein the first optical input / output terminal is an optical fiber,
The second light input / output terminal may be a light receiving element.

[0014] At least one of both surfaces of the glass plate has linearly polarized light (P-polarized light) perpendicular to the direction in which the glass plate is tilted.
And an optical film having a transmittance difference between horizontal and linearly polarized light (S-polarized light).

An optical coupler according to the present invention is arranged in first and second optical input / output terminals and in an optical path emitted from the first optical input / output terminal and incident on the second optical input / output terminal. The optical film has a means for adjusting the inclination angle of the glass plate with respect to the optical path, thereby adjusting the transmittance polarization dependence of the P-polarized light and the S-polarized light of the optical film.

Here, the characteristics when the glass plate is inclined with respect to the optical path will be described. When light is obliquely incident on the glass plate, the reflectance (Rp, Rs) and transmittance (Tp, Ts) of polarized light (P-polarized light) and horizontal polarized light (S-polarized light) perpendicular to the direction in which the glass plate is tilted, It is represented by the following equation.

Rp = [｛n × cos (θ1) -cos
(Θ2)｝ / ｛n × cos (θ1) + cos (θ
2)｝] {2 Rs = [{cos (θ1) −n × cos (θ2)} /
{Cos (θ1) + n × cos (θ2)}] ＾ 2 Tp = 1−Rp Ts = 1−Rs where n: refractive index of glass plate, θ1: incident angle of light, θ
2 = Sin ^-1 {sin (θ1) / n2}.

FIG. 6 is a graph showing transmission characteristics when light is obliquely incident on a quartz plate (n = 1.46). In FIG. 6, reference numeral 61 denotes P-polarized light and 62 denotes S-polarized light. As shown in FIG. 6, the transmittance difference between the P-polarized light and the S-polarized light increases as the incident angle of the quartz plate increases. Therefore, it can be understood that the polarization dependence can be adjusted by adjusting the incident angle of the quartz plate.

[0019]

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the first embodiment of the present invention.
It is a schematic diagram which shows the structure of the optical coupler of 1st Embodiment, The code | symbol 10 in the figure is an optical coupler, 11 and 12 are optical input / output terminals, 1
3 is an optical film, 14 is a glass plate, and 16 is an optical axis.

The optical coupler 10 includes first and second optical input / output terminals 11 and 12, an optical film 13, and a glass plate 14. Light emitted from the first light input / output terminal 11 passes through the optical film 13 and the glass plate 14 and is incident on the second light input / output terminal 12.

By adjusting the inclination angle θ of the optical path of the glass plate 14 with respect to the optical axis 16 and the rotation angle φ about the optical axis 16, as described above, the transmittance polarization dependence of the P-polarized light and the S-polarized light of the optical film 13 is increased. Sex can be adjusted.

FIG. 2 is a schematic diagram showing the configuration of an optical coupler according to a second embodiment of the present invention. In the figure, reference numeral 20 denotes an optical coupler; 21, 22, and 25 optical input / output terminals; Is the optical film,
24 is a glass plate and 26 is an optical axis.

The optical coupler 20 includes first, second, and third optical couplers.
, Optical input / output terminals 21, 22, 25, an optical film 23, and a glass plate 24. First optical input / output terminal 2
The light emitted from 1 is separated into transmitted light and reflected light by the optical film 23, and the reflected light
And the transmitted light is incident on the third input / output terminal 25.

By adjusting the inclination angle θ of the optical path of the glass plate 24 with respect to the optical axis 26 and the rotation angle φ about the optical axis 26, the P-polarized light and the S-polarized light of the optical film 23 depend on the reflectance polarization as described above. Sex can be adjusted.

FIG. 3 is a schematic diagram showing the configuration of an optical coupler according to a third embodiment of the present invention. In the figure, reference numeral 30 denotes an optical coupler; 31, 32, and 35 optical input / output terminals; Is a long wavelength transmission filter, 34 is a quartz plate, and 36 is an optical axis.

The optical coupler 30 includes first, second, and third optical couplers.
, Optical input / output terminals 31, 32, and 35, a long wavelength transmission type filter 83, and a quartz plate. The light emitted from the first light input / output terminal 31 is transmitted to the long wavelength transmission type filter 3.
3. The transmitted light and the reflected light are separated by the
4, the light enters the second optical input / output terminal 32, and the reflected light enters the third optical input / output terminal 35.

FIG. 5 is a graph showing the transmission characteristics of the long-wavelength transmission type filter 33. In FIG. 5, reference numeral 51 denotes P-polarized light, and 52 denotes S-polarized light. The long-wavelength transmission filter 33 used as the present example has an incident angle of 22.5 degrees and a 1.55
It has a WDM (wavelength division multiplexing) function by transmitting signal light in the μm band and reflecting excitation light in the 1.48 μm band.

FIG. 6 is a graph showing transmittance characteristics (one side) when the quartz plate 34 is obliquely incident as described above. As shown in FIG. 5, the long-wavelength transmission filter 33 used in this embodiment has a transmittance of P-polarized light at about 1540 nm, which is almost 100%, while a transmittance of S-polarized light is 97%. Was. Therefore, transmittance polarization dependence is 0.1
About 3 dB was generated. However, the quartz plate 34 is moved 9 ° in the φ direction with respect to the direction in which the long-wavelength
By setting the angle in the 0 degree direction and the angle in the θ direction to 22 degrees,
The transmittance polarization dependence was able to be reduced to 0.01 dB or less.

FIG. 4 is a schematic diagram showing the structure of an optical coupler according to a fourth embodiment of the present invention. In the figure, reference numeral 40 denotes an optical coupler, 41 and 45 denote optical input / output terminals, and 42 denotes a light receiving terminal. Element, 43
Is a branch film, 44 is a quartz plate, and 46 is an optical axis.

The optical coupler 40 includes first and second optical input / output terminals 41 and 45, a branch film 43, a quartz plate 44, and a light receiving element 42.
It is composed of The light emitted from the first optical input / output terminal 41 is separated into transmitted light and reflected light by the branch film 43, and the reflected light is incident on the light receiving element 42 after passing through the quartz plate 44, and the transmitted light is Is input to the input / output terminal 45.

FIG. 7 is a graph showing the transmission characteristics of the branch film 43. In FIG. 7, reference numeral 71 denotes P-polarized light, and reference numeral 72 denotes S-polarized light.
The branch film 43 has an incident angle of 45 degrees, transmits about 90% of the 1.55 μm band signal light, and reflects the remaining 10%.

As shown in FIG. 7, the branch film 43 used in this embodiment has a reflectance of 10.1% for P-polarized light at around 1550 nm, and a reflectance of 10.5% for S-polarized light.
%Met. Therefore, the reflectance polarization dependence is 0.17 dB.
Occurred to a degree.

However, by setting the quartz plate in the same direction (0 degree) as the direction in which the branch film is inclined in the φ direction and 24.5 degrees in the θ direction, the reflectance polarization dependency is 0.01%.
It could be reduced to below dB.

In the third and fourth embodiments, a long wavelength transmission type filter and a branch film are used. However, when other optical films such as a short wavelength transmission type filter and an optical band pass filter are used, the present invention is not limited thereto. Obviously, a similar effect can be obtained.

Although quartz is used for the glass plate, the same applies when other materials are used or when an optical film having a transmittance difference between P-polarized light and S-polarized light is deposited on one or both surfaces of the glass plate. It is clear that various effects can be obtained.

[0036]

As described above, the optical coupler according to the present invention can easily reduce the polarization dependence of the optical film by adjusting the inclination angle of the glass plate disposed in the optical path. Having.

In addition, an inexpensive component such as a glass plate,
Moreover, there is an effect that the polarization dependency can be easily adjusted.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an optical coupler according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of an optical coupler according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a configuration of an optical coupler according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating a configuration of an optical coupler according to a fourth embodiment of the present invention.

FIG. 5 is a graph showing transmission characteristics of a long wavelength transmission type filter.

FIG. 6 is a graph showing transmission characteristics when light is obliquely incident on a quartz plate.

FIG. 7 is a graph showing transmission characteristics of a branch film 43;

FIG. 8 is a graph showing the characteristics of a conventional light-branching film having reduced reflectance polarization dependency.

[Explanation of symbols]

10, 20, 30, 40 Optical coupler 11, 12, 21, 22, 25, 31, 32, 35, 4,
1,45 Optical input / output terminal 13,23 Optical film 14,24 Glass plate 16,26,36 Optical axis 33 Long wavelength transmission filter 34 Quartz plate 42 Light receiving element 43 Branch film 51,61,71,81 P polarized light 52,62 , 72, 82 S polarized light

Claims (8)

[Claims] 1. An optical coupler used for optical communication, comprising:
A first and a second optical input / output terminal, an optical film and a glass plate which are arranged in an optical path emitted from the first optical input / output terminal and incident on the second optical input / output terminal; Means for adjusting a tilt angle of the glass plate with respect to the optical path. 2. The optical coupler according to claim 1, wherein said first and second optical input / output terminals are optical fibers. 3. The optical fiber according to claim 1, wherein the first optical input / output terminal is an optical fiber,
The optical coupler according to claim 1, wherein the second optical input / output terminal is a light receiving element. 4. An optical system in which at least one of both surfaces of the glass plate has a transmittance difference between linearly polarized light (P-polarized light) perpendicular to the direction in which the glass plate is inclined and horizontal linearly polarized light (S-polarized light). The optical coupler according to any one of claims 1 to 3, wherein a film is deposited. 5. An optical coupler for use in optical communication, comprising:
A first light input / output terminal, an optical film that reflects light emitted from the first light input / output terminal, and light emitted from the first light input / output terminal and reflected by the optical film. A second light input / output terminal to be incident, a glass plate disposed in an optical path connecting the optical film and the second light input / output terminal, and means for adjusting a tilt angle of the glass plate with respect to the light path. An optical coupler, comprising: 6. The optical coupler according to claim 5, wherein said first and second optical input / output terminals are optical fibers. 7. The optical fiber according to claim 1, wherein the first optical input / output terminal is an optical fiber,
The optical coupler according to claim 5, wherein the second optical input / output terminal is a light receiving element. 8. An optical system in which at least one of both surfaces of the glass plate has a transmittance difference between linearly polarized light (P-polarized light) perpendicular to the direction in which the glass plate is inclined and horizontal linearly polarized light (S-polarized light). The optical coupler according to any one of claims 5 to 7, wherein the film is deposited.