JP2576408B2 - Optical splitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multiplexer for splitting an incident first light and multiplexing one of the split lights with a second light.

[0002]

2. Description of the Related Art In an optical communication system for performing long-distance optical communication, it is necessary to amplify an optical signal weakened in a transmission cable. Conventionally, when amplifying an optical signal, the optical signal is converted into an electric signal, electrically amplified, and then converted into an optical signal again. In recent years, an optical fiber amplifier for directly amplifying an optical signal has been proposed.

FIG. 10 shows the configuration of a conventionally proposed optical fiber amplifier. Optical fiber amplifier 11
Is a first optical splitter 1 that splits an input optical signal 12
3, a multiplexer 15 for multiplexing the pumping light 14, and an optical isolator 16 connected in series to the input side of the rare-earth ion-doped fiber 17, and an optical isolator 18 and a second optical splitter 19 on the output side. Are connected in series. First
The optical signal 21 split by the optical splitter 13 is detected by the first monitor photodiode 22 for monitoring, and the signal 23 split by the second optical splitter 19,
24 is detected by the second monitor photodiode 25 for monitoring. The other optical signal 24 is the output of the optical fiber amplifier 11. In such an optical fiber amplifier 11, a pumping light source 26 is connected to the multiplexer 15 and a pumping light 14
Is injected into the rare-earth ion-doped fiber 17, and the optical signal 27 passing through the first optical splitter 13 is directly amplified.

FIG. 7 specifically shows a configuration of a first optical splitter as an example of an optical splitter used in the conventional optical fiber amplifier. The configuration of the second optical splitter 19 is substantially the same as that of the first optical splitter 13.

[0005] The first optical splitter 13 includes a first input / output terminal 311, a second input / output terminal 312 arranged in a direction orthogonal to the traveling direction of the optical signal 32 coming from the first input / output terminal 311, and a first input / output terminal 311. It has three input / output terminals 311 to 313 of a third input / output terminal 313 arranged in the traveling direction of the optical signal 32 incident from the input / output terminal 311. First optical splitter 13
Inside, a glass plate 33 is disposed so as to be inclined at a predetermined angle with respect to the traveling direction of the optical signal 32.
A branch film 34 is formed on the surface on the incident side, and an antireflection film 35 is formed on the opposite surface.

In the first optical splitter 13, for example, when an optical signal 32 having a wavelength λ1 enters from a first input / output terminal 311, a part thereof is split by a splitting film 34,
From the input / output terminal 312. The remaining optical signal passes through the glass plate 33 and is emitted from the third input / output terminal 313.

FIG. 8 specifically shows the structure of a conventional multiplexer used in the optical fiber amplifier shown in FIG. The multiplexer 15 has a first input / output terminal 411,
The three input / output terminals 411 of the second input / output terminal 412 arranged in the traveling direction of the incoming optical signal 27 and the third input / output terminal 413 arranged in the direction orthogonal to the traveling direction of the optical signal 27 To 413. This multiplexer 1
5, a glass plate 43 is disposed so as to be inclined at a predetermined angle with respect to the traveling direction of the optical signal 27.
7, an anti-reflection film 44 is formed on the incident side surface, and a wavelength synthesizing film 45 is formed on the opposite surface.

In the multiplexer 15, a first input / output terminal 41
It is assumed that an optical signal 27 having a wavelength of λ1 is incident from 1 and an excitation light 14 having a wavelength of λ2 is incident from a third input / output terminal 413. The optical signal 27 passes through the anti-reflection film 44, the glass plate 43, and the wavelength synthesizing film 45 in this order and passes through the second input / output terminal 41.
It is led to 2. The other excitation light 14 is reflected by the wavelength synthesizing film 45 and similarly guided to the second input / output terminal 41 2.

As described above, in the conventional optical fiber amplifier,
On the input side of the rare earth ion-doped fiber 17, the first optical splitter 13 and the optical multiplexer 15 are separately arranged as physically different parts. For this reason, not only the number of parts increases, but also the first optical splitter 13 and the multiplexer 15 need to be relatively positioned. Therefore, an optical multiplexer in which the two are combined and integrated has been proposed.

FIG. 9 specifically shows the configuration of the proposed optical demultiplexer. The optical multiplexer 51 includes a first input / output terminal 521, a second input / output terminal 522 arranged in one direction orthogonal to the traveling direction of the optical signal 12 having the wavelength λ1 that enters therefrom, and an optical signal 12 A third input / output terminal 523 and a second input / output terminal
Scene 4 of the fourth input / output terminal disposed at a position facing
It has two input / output terminals 521 to 524.

In the optical path connecting the first optical input / output terminal 521 and the third optical input / output terminal 523 in the optical multiplexer 51,
The first glass plate 53 and the fourth glass plate 54 are arranged at a predetermined interval at the same inclination angle. First
A branch film 55 is formed on the surface on the incident side of the glass plate 53, and an antireflection film 56 is formed on the other surface. An antireflection film 57 is provided on the incident side surface of the second glass plate 54.
Further, a wavelength synthesizing film 58 is formed on each of the other surfaces.

In such an optical multiplexer 51, the optical signal 21 reflected by the optical branching film 55 of the first glass plate 53
Are output from the second input / output terminal 522 as monitor light, and the first monitor photodiode 2 shown in FIG.
2 will be incident. The optical signals transmitted through the branch film 55, the first glass plate 53, and the antireflection film 56 respectively transmit the other antireflection film 57, the second glass plate 54, and the wavelength combining film 58. Since the excitation light 14 of the wavelength λ2 incident from the fourth input / output terminal 524 is reflected by the wavelength synthesizing film 58, the lights of both wavelengths λ1 and λ2 are multiplexed and guided to the third input / output terminal 523. Will be.

[0013]

In the optical multiplexer 51 shown in FIG. 9, since the branch film 55 and the wavelength synthesizing film 58 are formed on separate glass plates 53 and 54, they are formed on the same glass plate. It cannot be shared as parts. Therefore, there is still a problem that the number of components is still large and the size of the optical multiplexer 51 is larger than that of a conventional branching device or a multiplexer. In addition, there is a problem that the structure as the optical multiplexer 51 is complicated.

Japanese Patent Application Laid-Open No. 3-225304 discloses an optical multiplexer / demultiplexer having another configuration, which is an optical element for separating light having two wavelengths λ1 and λ2 mixed. , And is different from an optical multiplexer that performs both branching and multiplexing, and is not directly related to the present invention.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical multiplexer having a simple configuration and a small size.

[0016]

An optical / optical multiplexer according to the present invention comprises:
A first optical input / output terminal for inputting / outputting light of wavelength λ1 and an optical branching film for transmitting part of light of wavelength λ1 output from the first optical input / output terminal and reflecting the rest are formed on one surface. The wavelength λ is formed on the surface opposite to the surface on which the light branching film is formed.
A substrate that transmits light with a light multiplexing film that transmits light of one wavelength and reflects light of wavelength λ2 is used. The light passes through the second optical input / output terminal to which the light of wavelength λ1 output from the first optical input / output terminal and reflected by the optical branching film is input, the optical branching film, the substrate, and the optical multiplexing / demultiplexing film. Wavelength λ1
A third light input / output terminal to which the light is input, and a fourth light that reflects light from the optical multiplexing film and outputs light of wavelength λ2 arranged at a position where light is input to the third light input / output terminal. It is characterized by having an input / output terminal.

An optical branch film for partially reflecting light of the first wavelength emitted from the first optical input / output terminal and guiding the light to the second optical input / output terminal is formed on one surface of the substrate. I have. The light transmitted through the light branching film is transmitted and guided to the third light input / output terminal, and the light of the second wavelength emitted from the fourth light input / output terminal is reflected to form the third light input / output terminal. Is formed on the other surface of the substrate. Here, the substrate can be composed of, for example, a single transparent glass plate.

That is, in the present invention, the light branching film is formed on one surface of the substrate, and the optical multiplexing film is formed on the other surface. Light of the first wavelength is incident on the light branching film, a part of which is branched, and the remaining light passes through the light branching film and the optical multiplexing film. On the other hand, the light of the second wavelength enters the optical multiplexing film, is multiplexed with the light of the first wavelength transmitted through the optical multiplexing film, and is output.

The present invention also provides a first optical input / output terminal and a second optical input / output terminal.
The third optical input / output terminal, the third optical input / output terminal, and the fourth optical input / output terminal have means for condensing input / output light. Here, further, the refractive index of the substrate is n, the beam diameter of the light of wavelength λ2 output from the fourth optical input / output terminal is w, and the incident angle from the fourth optical input / output terminal to the light transmitting substrate is θ. Then, the thickness t of the substrate becomes

[0020]

(Equation 3)

It is characterized by satisfying.

According to the present invention, in particular, a light branching film is formed on one surface of a substrate that transmits light, and an optical multiplexing film is formed on the other surface, so that the functions of the optical branching device and the optical multiplexer are combined and integrated. Thus, miniaturization is achieved. In addition, the signal light output from the first optical input / output terminal is transmitted through one substrate, the monitor side is branched, and the pump light is multiplexed. Therefore, the effect that the optical loss of the signal light is reduced as compared with the conventional configuration can be obtained.

Here, as described above, when the optical branching film and the optical multiplexing film are formed on both surfaces of one substrate, the excitation light of wavelength λ2 output from the optical input / output terminal on the excitation light source side is In some cases, not all light is reflected by the optical multiplexing film, and some light is transmitted. Then, since the signal is leaked and input to the optical input / output terminal on the monitor arranged opposite to the substrate, a part of the high intensity excitation light is mixed with the weak signal light to be received. Therefore, the noise of the monitor light may increase, and sufficient monitoring may not be performed. Therefore, in the present invention, even when the optical branching device and the optical multiplexer are combined and integrated, the thickness of the substrate is set to be equal to or greater than the thickness defined by the above equation so that such a problem does not occur. I have.
That is, by increasing the thickness of the substrate, even if a part of the excitation light passes through the optical demultiplexing film, the light transmitted through the substrate is shifted from the optical axis to the optical input / output terminal on the monitor side.

Further, the present invention is characterized in that a film for blocking excitation light is formed on a part of the surface on which the light branching film is formed. By blocking the excitation light with the blocking film, leakage to the monitor side can be further reduced.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows the configuration of an optical multiplexer according to an embodiment of the present invention. The optical multiplexer according to the present invention shown in FIG.
It is applied to an optical amplifier for a 1.55 μm band optical communication system. It has a function of branching a part of the input signal light having a wavelength of 1.55 μm to a monitor PD, and multiplexing the remaining signal light with a pump light having a wavelength of 1.48 μm. In FIG. 1, the same portions as those in FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

The optical multiplexer 61 includes a first input / output terminal 5
The board 62 is arranged so as to be inclined with respect to a straight line connecting the third input / output terminal 21 and the third input / output terminal 523. A branch film 63 is deposited on the surface of the substrate 62 on the side where the first light (optical signal 12) of the wavelength λ1 is incident. Further, the second light (excitation light 1) having the wavelength λ2 incident from the second input / output terminal 524 is used.
An optical multiplexing film 64 is deposited on the surface reflecting 4).

The light branch film 63 is made of Ti deposited on the substrate 1.
It is composed of a multilayer film composed of O2 and SiO2, and has a characteristic of transmitting about 90% of incident light and reflecting the remaining 10%. On the other hand, the optical multiplexing film 64 has a wavelength of 1.55 μm.
m has a characteristic of transmitting signal light of m and reflecting excitation light having a wavelength of 1.48 μm, and is formed of a multilayer film similar to the light branching film 2. The substrate 1 is made of the same BK7 glass as the conventional one.

A part of the optical signal 12 incident on the branch film 63 is reflected and guided toward the second input / output terminal 522.
The remaining optical signal 12 passes through the branch film 63, the glass plate 62, and the optical multiplexing film 64, and is guided to the third input / output terminal 523. Further, the excitation light 14 incident from the second input / output terminal 524 is reflected by the optical multiplexing film 64, and
Are connected to the input / output terminal 523.

Assuming that the optical multiplexer 61 of this embodiment is used in an optical fiber amplifier as shown in FIG. 10 as an example, the light enters the first monitor photodiode 22 from the second input / output terminal 522. Monitor light is obtained. From the third input / output terminal 523, the combined light of the wavelength λ1 and the wavelength λ2 which enters the rare earth ion-doped fiber 17 via the optical isolator 16 is emitted.

In this embodiment, the branch film 63 has a wavelength of 1.55 μm.
The optical multiplexing film 64 has a function of branching the optical signal 12 of wavelength m (wavelength λ1) in a 9 to 1 ratio. It has a function of reflecting light 14. For this reason, the optical signal having a wavelength of 1.55 μm emitted from the first input / output terminal 522 is reflected by the branch film 63 by 10%, guided to the second input / output terminal 522, transmitted by 90%, and transmitted by 90%. 3 to the input / output terminal 523. In addition, a fourth input / output terminal 524
The excitation light 14 having a wavelength of 1.48 μm emitted from is reflected by the optical multiplexing film 64 and guided to the third input / output terminal 523.

Each of the first to fourth optical input / output terminals 521
Reference numerals 524 to 524 each include an aspherical lens (not shown) that converts light emitted from the optical fiber into parallel light at the distal end of the optical fiber end where the end surface of the optical fiber is terminated. About 10% of the signal light 12 output from the first light input / output terminal 521 is reflected by the branch film 63. The reflected light is input to the second optical input / output terminal 522 and input to the monitor PD outside the optical multiplexer 61. The remaining signal light that has passed through the branch film 63 passes through the substrate 62 and the optical multiplexing film 64, is input to the third optical input / output terminal 523, and is transmitted to an external optical amplification optical fiber.

On the other hand, the wavelength 1.
The 48 μm pump light 14 is output from the fourth optical input / output terminal 524, reflected by the multiplexing film 64, and input to the third optical input / output terminal 523. The signal light 12 output from the first optical input / output terminal 521 is multiplexed with the signal light 12 and transmitted to the optical amplification optical fiber.

As described above, according to the present invention, a single glass plate or the like is used in contrast to the conventional case where one glass plate is required for splitting and combining light. Is sufficient, the volume of the optical multiplexer is reduced to about one half of the conventional one. In addition, since positioning of the substrates is not required as compared with the case where two substrates are used, the number of optical axis adjustment and fixing portions is reduced, and the productivity can be improved. Furthermore, since the branching device is formed on one side of the substrate and the optical multiplexing film is formed on the other side, the number of components is greatly reduced, and the cost required for manufacturing and storing individual components can be reduced.

Next, the configuration for improving the characteristics of the optical multiplexer of the present invention will be described in detail. The isolation (stopband attenuation) of the optical multiplexing film 64 formed of the multilayer film in the reflection stopband is usually only about 25 dB. That is, in the above-described embodiment, 99% or more of the excitation light 5 having a wavelength of 1.48 μm output from the fourth optical input / output terminal 524 is reflected by the optical multiplexing film 64. However, a small amount of 0.2 to 0.3% of the light passes through the optical multiplexing film 64, and is input to the second optical input / output terminal 522 disposed at a position opposed to the substrate 62. . The signal light 12 is branched from the second light input / output terminal 52.
The monitor light to be input to 2 is weak light attenuated by being transmitted. On the other hand, the excitation light 14 leaking from the fourth light input / output terminal 524 has a very high intensity. For this reason, if even a small percentage of the light is input to the second optical input / output terminal 522, accurate monitoring of the signal light 12 cannot be performed.

In the optical multiplexer 61 of the present invention, in order to avoid the above problem, the thickness of the substrate 62 is made larger than a certain amount. In the optical path of the light transmitted through the optical multiplexing film 63, the optical path taken for inputting the signal light to the second optical input / output terminal 522 is shifted. Here, the shifted pump light 1 with respect to the optical path of the signal light 12 input to the second optical input / output terminal 522
The separation distance d of the optical path No. 4 is represented by the equation (1).

[0037]

(Equation 4)

Here, t is the thickness of the substrate 1, θ is the incident angle of the signal light or the excitation light on the substrate, and n is the refractive index of the substrate 1. Assuming that the beam diameter of the signal light 12 and the excitation light 14 is 0.5 mm, the incident angle on the substrate 62 is 45 degrees, the refractive index of the substrate 64 is 1.5, and the thickness of the substrate 64 is 3.0 mm, the separation is performed. The distance d is 2.26 mm, and the optical path of the pump light 14 can be sufficiently separated from the optical path of the signal light 12.

FIG. 2 shows the separation distance from the optical axis to the second light input / output terminal 522 and the first light emitted from the fourth light input / output terminal 523 when the beam diameter is 0.5 mm. 3 shows the relationship with the isolation of light emitted from the light input / output terminal. If the separation distance is set to about 2 mm, the isolation becomes approximately 70 dB, so that the leakage light from the fourth optical input / output terminal can be sufficiently reduced.

With such a configuration, an optical multiplexer according to the present invention is actually manufactured, and the pumping light 14 is connected to the fourth optical input / output terminal 524.
Output. At this time, no excitation light was detected from the second optical input / output terminal 522 within the range of the measurement sensitivity, and it was confirmed that the isolation was 80 dB or more. For example, the intensity of the signal light 12 output from the first optical input / output terminal 521 is −20 dBm, and the intensity of the pump light 14 output from the fourth optical input / output terminal 14 is +15 dBm. Then, the intensity of the signal light 12 input to the second optical input / output terminal 522 is −30 dBm, whereas the intensity of the pump light is −65 dBm or less. Therefore,
The pump light component does not affect the monitoring of the signal light 12.

Generally, if the optical path is separated from the beam diameter, sufficient isolation can be secured. Therefore, if the thickness t of the substrate 1 is set to a value satisfying the expression (2) from the expression (1), it is possible to sufficiently prevent the excitation light from being input to the optical input / output terminal on the monitor side.

[0042]

(Equation 5)

As described above, the light branching film and the light multiplexing film are formed on both sides of the same substrate, and the light is branched by transmission and reflection on the side where the light branching film is formed. By adopting a configuration in which light of two different wavelengths is multiplexed on the side where the optical multiplexing film is formed, the optical splitter and the optical multiplexer can be combined and integrated. The volume ratio can be reduced to less than half of the conventional one. Moreover, the signal light emitted from the optical fiber of the first optical input / output terminal is made parallel by an aspheric lens,
The light passes through the light branching film and the light combining film at one time. As a result, the number of times of converting light into parallel light or condensing light is reduced, and the number of times light is transmitted through the substrate is also reduced as compared with the conventional configuration, so that the passage loss is reduced. Further, an antireflection film is not required on the end face of the substrate. Further, since the number of optical input / output terminals is reduced from six to four as compared with the conventional case, the number of components is reduced, and the manufacturing process is simplified.

Further, by setting the thickness of the substrate to a certain value or more and shifting the optical path of the leakage light of the excitation light from the optical path of the signal light to the monitor side, the excitation light leaks to the monitor side even when integrated. And the signal light can be monitored without being affected by the pump light.

In the above-described embodiment of the present invention, the light branching film is formed of a multilayer film, but is not limited to this.
Other means such as a grating may be used. Further, the angle of incidence on the optical branching film and the optical multiplexing film is 45 degrees, but it goes without saying that the angle can be freely selected.

Next, another embodiment in which the characteristics in the embodiment of the present invention shown in FIG. 1 are further improved will be described. FIG. 3 shows a perspective view of a substrate used in the improved embodiment. The substrate 72 shown in FIG. 3 has a light branching film 63 formed on a surface that receives light emitted from the first light input / output terminal 521, similarly to the substrate 62 shown in FIG. In addition to the light branching film 63, the substrate 72 has an aperture 75 made of a metal film having a hole formed only near the center.
It has.

The diameter of the hole provided in the aperture 75 is about 800 μm, which is slightly larger than the beam diameter of the light 12 emitted from the first light input / output terminal 521. First
The light 12 emitted from the light input / output terminal 521 passes through this hole and partially passes through the light branching film 63. The remaining light is reflected to the second light input / output terminal 522 side. Also,
As the metal film, chromium and gold are directly deposited on the upper surface of the light branching film 63. The hole constituting the aperture 75 is formed by lifting off after the vapor deposition. Since the aperture 75 has a high reflectivity, even if a part of the emitted light 12 from the first optical input / output terminal hits the metal film, the light is reflected toward the second optical input / output terminal 522, so that light loss and Not be.

On the other hand, as shown in FIG. 4, the leakage light λ2 ′ transmitted through the optical multiplexing film 64 among the excitation light 14 incident from the fourth light input / output 524 side is located at the position where the hole is provided. And arrive at a position that is off. Therefore, this leakage light λ
2 ′ is reflected by the aperture 75. Therefore, it is possible to prevent the excitation light 14 from leaking and entering the second optical input / output terminal 522.

Apart from adding an aperture having a hole on the upper surface of the light branching film 63, only the side where the second light input / output terminal 522 is arranged with respect to the center of the substrate as shown in FIG. The same effect can be obtained by using an aperture on which a metal film is formed. The aperture 75 is not limited to a metal film, but may be any as long as it blocks light.

As shown in FIG. 6, a monitoring photodiode 80 may be directly arranged at the optical input / output terminal on the monitor side without using an optical fiber. In this case, if an aperture 81 having a hole having a size substantially equal to the beam diameter is added to the front surface of the photodiode, light leakage can be reduced. Further, as shown in FIG.
An isolator 82 may be built in the optical multiplexer 61. Similarly, an excitation light source can be directly disposed at the optical input / output terminal on the excitation light source side without using an optical fiber.

As described above, according to the optical multiplexer of the present invention, it is possible to greatly reduce the size and to reduce the insertion loss by combining and integrating the optical splitter and the optical multiplexer. Has an effect. Further, the number of parts is reduced, the manufacturing process is simplified, and the effect of greatly contributing to lower prices is obtained.

[0052]

As described above, according to the present invention, a single glass plate or the like is conventionally used for splitting and combining light. Since the use of the optical multiplexer is sufficient, the volume of the optical multiplexer is reduced to about half that of the conventional optical multiplexer, which greatly contributes to downsizing. Further, as compared with the case where two substrates are used, positioning of the substrates is not required, and the number of adjustment or fixing portions is reduced, so that productivity can be improved. Furthermore, since the branching device is formed on one side of the substrate and the wavelength synthesizing film is formed on the other side, the number of parts is greatly reduced, and the cost required for manufacturing and storing individual parts can be reduced.

[Brief description of the drawings]

FIG. 1 is a principle diagram showing a configuration of an optical multiplexer according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between separation distance and isolation in the optical multiplexer according to one embodiment of the present invention.

FIG. 3 is a perspective view of a substrate used in another embodiment of the present invention.

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

FIG. 5 is a perspective view showing another configuration of a substrate used in another embodiment of the present invention.

FIG. 6 is a top view showing an embodiment in which the light receiving element and the isolator are integrated in the optical multiplexer according to the present invention.

FIG. 7 is a schematic configuration diagram of a conventional optical fiber amplifier configured to perform splitting and multiplexing of light using a splitter and a multiplexer.

8 is a principle diagram showing an example of the configuration of the conventional branch shown in FIG.

9 is a principle diagram showing an example of the configuration of the conventional multiplexer shown in FIG.

FIG. 10 is a principle diagram showing the principle of a conventionally proposed optical multiplexer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Optical fiber amplifier 12 Optical signal 13 Optical splitter 14 Pumping light 15 Optical multiplexer 16 Isolator 17 Erbium-doped fiber 18 Isolator 19 Optical splitter 21 Monitor light 22 Monitoring photodiode 23 Monitor light 24 Amplified light 25 Monitor photodiode 26 Excitation semiconductor laser 27 Optical signal 51 Optical fiber amplifier 521 to 524 First to fourth input / output terminals 62 Substrate 63 Optical branching film 64 Optical multiplexing film 72 Substrate 75 Aperture 80 Light receiving element 81 Aperture 82 Isolator λ1 Optical signal wavelength λ2 Excitation light wavelength

Claims (15)

(57) [Claims] An optical branching film for partially reflecting light of a first wavelength emitted from a first terminal and guiding the light to a second terminal is formed on one surface of a substrate. A wavelength synthesizing film that transmits the transmitted light and guides the light to the third terminal and reflects the light of the second wavelength emitted from the fourth terminal to guide the light to the third terminal is provided on the other surface of the substrate. An optical multiplexer characterized by being formed. 2. The method according to claim 1, wherein the substrate is a single transparent glass plate, and the substrate transmits light of the second wavelength to the second terminal.
The optical multiplexer according to claim 1, wherein the optical multiplexer has a thickness that does not optically couple . 3. A first optical input / output terminal for inputting / outputting light having a wavelength of λ1, a portion of light having a wavelength of λ1 output from the first optical input / output terminal, and transmitting the remaining light. A light in which a light branching film to be reflected is formed on one surface, and a wavelength synthesizing film is formed on a surface opposite to the surface on which the light branching film is formed, to transmit the light having the wavelength λ1 and reflect the light having the wavelength λ2. A second optical input / output terminal to which light having a wavelength of λ1 output from the first optical input / output terminal and reflected by the optical branching film is input; and a light transmitting film and the substrate. And a third optical input / output terminal to which the light of wavelength λ1 transmitted through the wavelength synthesizing film is input; and a position where the light is reflected by the wavelength synthesizing film and input to the third optical input / output terminal. An optical multiplexer comprising: a fourth optical input / output terminal for outputting light having a wavelength of λ2. 4. The first light input / output terminal, the second light input / output terminal, the third light input / output terminal, and the fourth light input / output terminal.
4. The optical multiplexer according to claim 3, wherein the light input / output terminal includes a condensing lens for converting the emitted light into parallel light at an emission end. 5. A first optical input / output terminal for inputting / outputting light having a wavelength of λ1, a part of light having a wavelength of λ1 output from the first optical input / output terminal, and transmitting the remaining light. A light in which a light branching film to be reflected is formed on one surface, and a wavelength synthesizing film is formed on a surface opposite to the surface on which the light branching film is formed, to transmit the light having the wavelength λ1 and reflect the light having the wavelength λ2. A light-receiving element that receives light having a wavelength of λ1 output from the first optical input / output terminal and reflected by the light branching film, and converts the light of the wavelength λ1 into an electric signal; A third light input / output terminal to which light having a wavelength of λ1 transmitted through the light branching film, the substrate, and the wavelength combining film is input; and a light reflected by the wavelength combining film and transmitted to the third light input / output terminal. it but having a fourth optical input-output terminal for outputting the arranged wavelength lambda ₂ of light at a position that is input Optical multiplexer and butterflies. 6. The first light input / output terminal, the third light input / output terminal, and the fourth light input / output terminal each include a condensing lens for converting an output light into a parallel light at an output end. 6. The optical multiplexer according to claim 5, wherein the light receiving element includes a condenser lens in front of a light receiving surface. 7. When the refractive index of the substrate is n, the beam diameter of output light from a fourth optical input / output terminal is w, and the incident angle from the fourth optical input / output terminal to the substrate is θ, 7. The optical multiplexer according to claim 6, wherein the thickness t of the light transmitting substrate satisfies the following expression. 8. The optical multiplexer according to claim 4, wherein the substrate has a film for blocking or reflecting light formed on a part of the surface on which the light branching film is formed. . 9. The optical coupling device according to claim 6, wherein the substrate has a light blocking film for blocking or reflecting light formed on a part of the surface on which the light branching film is formed. Waver. 10. The light blocking film has an inner diameter substantially equal to a beam diameter of light emitted from the first light input / output terminal at a position irradiated with light emitted from the first light input / output terminal. The optical multiplexer according to claim 8, wherein the optical multiplexer has a hole. 11. The light blocking film has an inner diameter substantially equal to a beam diameter of light emitted from the first light input / output terminal at a position irradiated with light emitted from the first light input / output terminal. The optical multiplexer according to claim 9, further comprising a hole. 12. The light blocking film is formed in a substantially half area on the side of the second light input / output terminal centering on a position irradiated with light emitted from the first light input / output terminal. The optical multiplexer according to claim 8, wherein: 13. The light blocking film is formed in a substantially half area on the side of the second light input / output terminal with respect to a position irradiated with light emitted from the first light input / output terminal. The optical multiplexer according to claim 9, wherein: 14. The optical multiplexer according to claim 3, wherein an isolator is disposed between said substrate and said third optical input / output terminal. 15. The optical multiplexer according to claim 5, wherein an isolator is arranged between said substrate and said third optical input / output terminal. ## EQU2 ## w t ≧ {cos θ × tan [sin ^{- 1} ｛(sin θ) / n}]