JP3611842B2 - Manufacturing method of wavelength demultiplexer - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a wavelength demultiplexer that demultiplexes light having a plurality of different wavelengths.Manufacturing methodIn particular, a signal transmitted on a carrier having a different wavelength via an optical fiber is demultiplexed into a signal for each carrier.I didThe present invention relates to a method of manufacturing a wavelength demultiplexer.
[0002]
[Prior art]
In recent years, research and development of systems that perform high-speed and large-volume data communication by optical communication have been active. In particular, in order to send a large amount of data at once, a wavelength division multiplexing optical transmission system has been developed in which an optical signal is transmitted on a carrier wave having a different wavelength in one optical fiber.
[0003]
As described above, when an optical signal placed on a carrier having a plurality of different wavelengths is transmitted through one optical fiber, the optical signal having the different wavelengths is demultiplexed into the respective wavelengths on the receiving side. Must be detected.
[0004]
Therefore, the receiving characteristics of the optical signal are greatly influenced by the accuracy of wavelength demultiplexing on the receiving side. If the wavelength demultiplexing accuracy on the receiving side is poor, even if many signals are transmitted on carrier waves of different wavelengths on the transmitting side, these signals cannot be received. A duplexer is desired.
[0005]
There are various types of wavelength demultiplexing methods known in the art. For example, as a method for separating two wavelengths, a filter using a multilayer interference film and an interferometer such as a Fabry-Perot type or a Michelson type are known.
[0006]
FIG. 8 is a schematic view of an apparatus to which the method for separating the two wavelengths is applied.
FIG. 8A shows an example of a filter using a multilayer interference film. The multilayer interference film 81 is formed on the transparent substrate 80, and the incident light 82 that has been converted into parallel rays by a lens or the like is incident thereon. Incident light 82 incident on the multilayer interference film 81 is repeatedly reflected inside the multilayer interference film 81. At this time, only the light 84 having the wavelength λ 2 that satisfies the condition for transmitting through the multilayer interference film 81 can pass through the multilayer interference film 81. The light 83 with the wavelength λ 1 that does not satisfy the transmission condition cannot be transmitted through the multilayer interference film 81 and is reflected. In this way, the use of a multilayer interference film filter can separate light of two different wavelengths.
[0007]
FIG. 8B is a schematic diagram of a Fabry-Perot interferometer. The Fabry-Perot interferometer has reflectors 85 and 86 having high reflectivity arranged in parallel at a predetermined interval. Also in this case, as in the case of the multilayer interference film filter, the incident light 82 converted into parallel rays enters from the back surface of the reflecting plate 85 and is reflected between the reflecting plates 85 and 86 many times. Then, the light 84 having the wavelength λ2 that satisfies the transmission condition is transmitted through the Fabry-Perot interferometer, and the light 83 having the wavelength λ1 that does not satisfy the condition is reflected to separate the light having two different wavelengths.
[0008]
FIG. 8C is a schematic diagram of a Michelson interferometer. A half mirror 89 is installed at the center, and the incident light 82 which is a parallel light beam is separated in two orthogonal directions. Reflecting mirrors 87 and 88 are provided in the traveling direction of the separated light, respectively, and reflect the light traveling toward the respective surfaces at right angles. The distances from the half mirror 89 to the reflecting mirrors 87 and 88 are different so as to produce an appropriate optical path difference. The respective lights reflected by the reflecting mirrors 87 and 88 return to the same location of the half mirror 89 and cause interference, and the lights 83 and 84 having different wavelengths λ1 and λ2 are separated.
[0009]
On the other hand, as a method for separating a plurality of wavelengths simultaneously, there is practically a diffraction grating and an arrayed waveguide grating using an optical waveguide as a modification thereof.
FIG. 9 is a schematic diagram of a duplexer that employs a method of simultaneously separating a plurality of wavelengths.
[0010]
FIG. 9A is a schematic diagram of a diffraction grating. As is well known, the diffraction grating is used as a spectroscope, and when irradiated with incident light 90 of parallel rays including light of a plurality of wavelengths, it is reflected by the unevenness of the surface. Incident light 90 reflected by each unevenness interferes with each other, and light of different wavelengths is emitted at different angles.
[0011]
FIG. 9B is a schematic configuration diagram of an arrayed waveguide grating using an optical waveguide.
Light including light of a plurality of wavelengths is incident from the incident port 93 and branched into a large number of waveguides 94. A light exit 91 is provided at the tip of each waveguide 94, and incident light is emitted as emitted light 92. Each of the waveguides 94 is different in length and the like, and is configured to have different optical path lengths in which light propagates through the waveguide 94 until light is emitted from the exit port 91. The lights that have passed through the waveguide 94 have different phases from each other, and thus interfere with each other when exiting from the exit port 91. Thereby, the light of a different wavelength is radiate | emitted to a different direction with the effect | action similar to a diffraction grating.
[0012]
[Problems to be solved by the invention]
By the way, in a demultiplexer that only separates two different wavelengths, if it is used for receiving an optical signal in an optical multiplex communication in which a large number of different wavelengths of light are multiplexed, the demultiplexing is performed to demultiplex each light. It is necessary to connect the receivers in several stages, and the size of the receiver cannot be increased.
[0013]
On the other hand, in a diffraction grating or the like, light having different wavelengths is deflected and demultiplexed in a direction corresponding to the wavelength. . In an optical multiplex communication, if as much information as possible is transmitted at once, the difference in wavelength between different signal waves must be reduced. When a diffraction grating having a small dispersion angle is used as a duplexer for a receiver, there is a high possibility that such a signal wave is erroneously received. Therefore, the reliability of the receiver is significantly impaired. Further, the diffraction grating is easily influenced by the polarization state of incident light, and tends to have unstable characteristics. Furthermore, the diffraction grating has a problem in that fine irregularities on the surface thereof must be manufactured regularly and a manufacturing process for obtaining a diffraction grating with good performance becomes difficult.
[0014]
In addition, the arrayed waveguide grating can adjust the dispersion angle to some extent depending on the way the waveguide is configured, but the adjustment of the configuration to obtain the desired configuration is very subtle, and is easily affected by temperature changes, There is a drawback of poor environmental resistance.
[0015]
Therefore, the present invention can separate a plurality of lights at the same time, has a relatively large dispersion angle, has a simple structure, and has good environmental resistance.wavelengthDuplexerManufacturing methodThe purpose is to provide. In particular, the wavelength of light propagating in one optical propagation path isDifferentA wavelength demultiplexer that can multiplex optical transmission by separating multiple lights for each wavelength and receiving them with light propagation paths or light receiving elements at spatially different positions.Manufacturing methodI will provide aAimed at.
[0016]
[Means and Actions for Solving the Problems]
In order to solve the above problems, the present invention has opposing first and second reflecting surfaces that are parallel to each other, and is on or near one of the first and second reflecting surfaces. A light beam that radiates radially from the line segment set in parallel to the one surface is incident between the first and second reflection surfaces, and the first and second reflections are performed for each of the multiple reflections. A method of manufacturing a wavelength demultiplexer configured to transmit light through one of the reflecting surfaces and to form a light flux whose traveling direction differs depending on the wavelength of the light as a result of the interference, A reflective film is formed on each of parallel surfaces of a transparent parallel plate having at least two surfaces parallel to each other, and the respective reflective films are used as the first and second reflective surfaces, and the reflective film A part with low reflectivity is formed on a part of the reflective film And forming a transparent body on the surface on which at least the low-reflectivity part is formed, with the low-reflectance part being the incident region of the light beam between the first and second reflective surfaces. It is a feature.
According to another aspect of the present invention, a first reflecting surface that reflects light and a second reflecting surface that has a reflectance of less than 100% and transmits part of the light are formed on a parallel plate, and incident Providing a first lens for converging the emitted light so as to spread radially while repeating reflection between the first and second reflecting surfaces, and providing the first lens This is a method of manufacturing a wavelength demultiplexer that demultiplexes light while interfering with light emitted through the second reflecting surface in a process.
FIG. 1 shows the present invention.Wavelength demultiplexer obtained by the manufacturing method ofIt is a figure explaining the principle ofthisIt is sectional drawing which looked at the duplexer from the horizontal direction.
[0017]
In the present invention, the two reflecting surfaces 12 and 13 are arranged in parallel with a distance d. The reflectivities of the reflecting surfaces 12 and 13 should be determined appropriately. However, here, for convenience of explanation, the reflectance of one of the reflecting surfaces 12 and 13 is almost 100%, and the other has a transmittance of several percent, or the reflectance is smaller than 100%. It is assumed that a part of light is transmitted from the surface 12.
[0018]
However, which of the reflecting surfaces 12 and 13 is configured to have a reflectance of approximately 100% is arbitrary. For example, the reflecting surface 13 has a transmittance of several percent, or less than 100%. Further, the reflection surface 12 may have a reflectance that allows a part of light to pass therethrough, and the reflection surface 12 may have a reflectance of approximately 100%.
[0019]
In FIG. 1, it is assumed that the reflecting surface 13 has a reflectance of approximately 100% and the reflecting surface 12 has a reflectance smaller than 100% and is configured to transmit a part of light. .
[0020]
A part of the reflection surface 12 may be provided with an irradiation window 11 that reflects little or no light, and the light may enter from here. Although this irradiation window 11 is not necessarily required, it is desirable to provide it in view of light loss.
[0021]
Incident light 10 is focused on one line using a cylindrical lens or the like. A line segment in which light is collected by a cylindrical lens or the like in this way is hereinafter referred to as a focal line. The point indicated by i in the figure is a view of the focal line of the incident light 10 from the side.
[0022]
In the figure, the focal line i is described on the assumption that it exists in the plane where the irradiation window 11 is provided, but in reality, the focal line is not necessarily provided with the irradiation window 11. It does not have to be in the plane. However, there is a possibility that a slight change occurs in the demultiplexing characteristics of the wavelength demultiplexer of the present invention by shifting the position of the focal line in this way.
[0023]
The incident light 10 converged on the focal line i then spreads radially about the focal line i and reaches the reflecting surface 13. On the reflecting surface 13, the incident light 10 spreads to a width between points (precisely lines) indicated by 1). Then, the light is reflected by the reflecting surface 13 toward the reflecting surface 12. Since the reflecting surface 12 has a property of partially transmitting light, a part of the light reflected from 1) is emitted to the outside as 1) '.
[0024]
On the other hand, the light that has not been transmitted is reflected by the reflecting surface 12 and reaches the range indicated by 2) of the reflecting surface 13. As is clear from the figure, since the incident light 10 is a light beam that gradually spreads radially about the focal line i, the width of the light beam is gradually expanded while repeating reflection between the reflection surface 13 and the reflection surface 12. This is shown by the wider interval between 2) than the interval between 1).
[0025]
Similarly, the light reflected from 2) is reflected by the reflecting surface 12, and a part thereof is emitted to the outside as 2) '. Similarly, among the light reflected by 2), the light reflected by the reflecting surface 12 was reflected by the reflecting surface 12 out of the two lights reflected by 3) within the range indicated by 3). The light is reflected in the range on the reflecting surface 13 indicated by two 4).
[0026]
The light reflected in the ranges indicated by 3) and 4) is reflected by the reflecting surface 12, and part thereof is emitted to the outside as 3) ', 4)'. As described above, reflection is performed many times between the reflection surface 13 and the reflection surface 12 (multiple reflection), and a part of the light is emitted from the reflection surface 12 to the outside whenever it is reflected. The light 1) 'to 4)' etc. emitted to the outside interfere with each other and form a light beam. Light beams made of light of different wavelengths have different traveling directions and are emitted from the reflecting surface 12 at different angles.
[0027]
FIG. 2 replaces the principle of multiple reflection of the present invention with an equivalent model.
The light emitted from the focal line i is reflected by the reflecting surface 13, but the reflecting surface 13 is the same as the mirror, and when the reflecting surfaces 12 and 13 are not provided, the light is emitted from the focal line i0. Is equivalent to In addition, the light that has been subjected to multiple reflection once (the light that has been reflected by the reflecting surface 12, reflected again by the reflecting surface 13, and emitted to the outside) is twice the distance d from the focal line i0 to the reflecting surfaces 12, 13. Equivalent to light emitted from a focal line far away. Similarly, light that has been twice reflected twice is equivalent to light emitted from the focal line i2, light that has been multiple reflected three times is equivalent to the focal line i3, and light that has been multiple reflected four times is equivalent to light emitted from the focal line i4.
[0028]
Here, in fact, the light emitted from the focal line i and repeatedly emitted to the outside becomes weaker each time the reflection is repeated, so the light emitted from each focal line is the focal line. The light intensity gradually decreases as it goes from i1 to the focal line i4.
[0029]
The distance between the focal lines i0 to i4 is always equal to twice the distance d between the reflecting surfaces 12 and 13.
As is clear from the figure, the light emitted from the respective focal lines overlap each other and interfere with each other. Here, it is assumed that the light emitted from the focal line i includes light of a plurality of wavelengths. Since the light emitted from the focal line i is light that spreads radially at an angle, it includes many Fourier components, that is, light having many different traveling directions with respect to light having the same wavelength. The conditional expression for strengthening the light is that the wavelength is λ, the distance between the reflecting surfaces 12 and 13 is d, and the angle of the light traveling direction when the direction perpendicular to the reflecting surfaces 12 and 13 is 0 ° is θ.
2d × cos θ = mλ (1)
It can be expressed. Here, m is an arbitrary integer. Therefore, if d and λ are constant, the direction θ in which the light of wavelength λ is emitted is determined by taking a certain value of m.
[0030]
If the light incident between the reflecting surfaces 12 and 13 is a parallel light beam including a plurality of wavelengths, the light of all wavelengths travels in the same direction (since θ is determined) ) And light having a wavelength satisfying the formula (1) is limited to at most one. Therefore, in this case, the two wavelengths can only be separated (this corresponds to a Fabry-Perot interferometer or the like).
[0031]
On the other hand, in the case of the present invention, since the light emitted from the focal line i spreads radially at a certain angle, light of each wavelength is superposed with light having different traveling directions. In (1), light having different λ acts so that only a component having a traveling direction θ satisfying the expression (1) is extracted to form a light beam. Accordingly, light including a plurality of light beams having different wavelengths can be emitted in different directions for each wavelength, and a plurality of light beams can be demultiplexed at a time.
[0032]
【Example】
FIG. 3 is a perspective view of one embodiment of the present invention.
In the figure, for example, reflective multilayer films 31 and 32 which are multilayer interference films having high reflectivity are applied to both surfaces of a parallel plate 30 made of glass having a thickness of 100 μm. Here, as thickness d of the parallel plate 30, about 50-100 micrometers is practically preferable.
[0033]
The reflectivity of the reflective multilayer films 31 and 32 with respect to light having a vertical incidence and an incident angle close thereto, for example, 20 degrees or less, is approximately 100% for one surface and approximately 95% for the other surface. However, the reflectance of the other surface is not particularly required to be 95%, and it is sufficient that the incident light can perform sufficient multiple reflection between the reflective multilayer films 31 and 32, which is practically 80%. There is no particular problem as long as the value is smaller than 100%. Therefore, for convenience, the reflectance of the other surface is assumed to be 95%.
[0034]
Further, it is completely arbitrary which of the reflective multilayer films 31 and 32 is a film having a reflectance of approximately 100%, but in FIG. 3, the reflective multilayer film 32 has a reflectance of approximately 100%. It has the composition to have.
[0035]
A part of the reflective multilayer film 31 provided with an interference film having a reflectivity of 95% is provided with an area provided with an interference film (or antireflection film) having a reflectivity of approximately 0% instead of the interference film. The irradiation window 33 is configured so that the boundary between the reflective multilayer film 31 and the irradiation window 33 is a straight line.
[0036]
For example, the incident light exits from an optical fiber (not shown), is converted into parallel rays by the collimator lens 34, and is then collected on one line segment by the cylindrical lens 35. Such a line segment on which light is collected is referred to as a focal line 36. The reason for not condensing the light at one point is that interference due to multiple reflection does not occur in the direction parallel to the boundary between the reflective multilayer film 31 and the irradiation window 33.
[0037]
The condensed light enters the reflective multilayer films 31 and 32 through the portion of the irradiation window 33 having a reflectance of approximately 0% as incident light 38. At this time, the focal line 36 is set so as to be parallel and sufficiently close to the boundary between the reflective multilayer film 31 and the irradiation window 33. In addition, the optical axis of the incident light 38 is inclined from the vertical incidence so that the light spread by one reciprocation between the reflective multilayer films 31 and 32 does not leak from the irradiation window 33.
[0038]
The inclination angle of the incident optical axis at this time is determined by the thickness of the light beam and the condensing position of the incident light 38 (that is, the focal line 36) at a position where the light travels through the parallel plate 30 twice as long as its thickness. The ratio between the average value of the thickness of the light beam and twice the thickness d of the glass plate is multiplied by the refractive index of the glass.
[0039]
The inclination of the incident optical axis will be described with reference to FIG.
The thickness of the light beam at the position where the light travels through the parallel plate 30 by a distance twice as large as its thickness is the width of the light beam represented by b in FIG. The condensing position of the incident light 38, that is, the thickness of the light beam at the focal line 36 is indicated by a in FIG. This a is, for example, as large as the diffraction limit of light when the incident light 38 is collected by a cylindrical lens. These average values represent the distance between the points a1 and b1 where the optical axis 41 when the length represented by c in FIG. 5 is 0 intersects the surface on which the reflective multilayer film 31 is provided. When c is 0, it is the minimum condition that the incident light 38 does not leak from the irradiation window 33 when the incident light 38 is reflected from the reflective multilayer film 32 and returned.
[0040]
By the way, the inclination θ1 of the optical axis can be obtained from the value obtained by dividing the distance between the points a1 and b1 by the value obtained by doubling the thickness d of the parallel plate 30. Are known. Therefore, the condition of the inclination of the optical axis 41 so that the incident light 38 is not leaked from the irradiation window 33 when the incident light 38 is reflected by the reflective multilayer film 32 and returned is refracted when light enters a medium having a different refractive index. Can be expressed as the following equation.
[0041]
Optical axis inclination θ1 ≧ n (a + b) / 4d (2)
Here, n is the refractive index of the parallel plate 30.
Returning to FIG. 3, the embodiment of the present invention will be described.
[0042]
The light that enters the parallel plate 30 repeats multiple reflections. At this time, 5% of light passes through this surface and goes out every time it is reflected by the surface of the reflective multilayer film 31 having a reflectance of 95%. The transmitted lights exiting from the parallel plate 30 interfere with each other to form one light beam 37. The traveling direction of the light beam 37 depends on the wavelength of the light. As a result, when the light beam 37 is condensed at one point by the lens, the condensing position moves on a straight line as the wavelength changes. If a plurality of light receivers 40 are arranged on this straight line, they can be received by different light receivers 40 for each wavelength.
[0043]
It will be described in more detail with reference to FIG. 4B that the traveling direction of the light flux varies depending on the wavelength of light.
As described above, in the present invention, light including a plurality of wavelengths is condensed on the focal line 36 and then incident between the reflecting surfaces 44 and 45 so as to spread radially around the focal line 36. Here, the reflective surface 44 corresponds to the reflective multilayer film 31, and the reflective surface 45 corresponds to the reflective multilayer film 32.
[0044]
By making light including a plurality of wavelengths incident as light that spreads radially from the focal line 36 at a certain angle, light of each wavelength is superimposed with various traveling directions. That is, many Fourier components are included.
[0045]
Accordingly, when attention is paid to light of one wavelength, light of the same wavelength enters the parallel plate 30 at various angles. In the figure, light having three different traveling directions is shown.
[0046]
In order for the light reflected in the parallel plate 30 to be emitted to the outside to cause interference and strengthen each other to form a light beam, it is necessary to satisfy the formula (1), but the thickness d of the parallel plate 30 is When fixed, the incident angle must satisfy the condition in order for light of a certain wavelength to form a light beam. In particular, when the incident light is a parallel light beam, the traveling direction of the light is fixed, so that only a light beam having a wavelength determined by the incident angle and the thickness d of the parallel plate 30 can form a light beam.
[0047]
However, as in the present invention, by using incident light that spreads radially around the focal line 36, even light of the same wavelength can be a collection of light in different traveling directions. That is, even if the incident angles are not set one by one, the light that has different traveling directions always includes light that is incident at an angle that satisfies the conditions that are strengthened by interference.
[0048]
As shown in the figure, light of the same wavelength is incident at a time at angles of 1), 2) and 3). Of these, when the light of 2) satisfies the conditions for strengthening each other, the light of 1) and 3) does not satisfy the conditions, so after being emitted to the outside, they are weakened by interference and do not produce a light beam. On the other hand, since the light of 2) strengthens each other, a light beam is formed in the direction indicated by the arrow of 2).
[0049]
In the case of light of other wavelengths, it may happen that the light of 1) and 2) does not satisfy the conditions, and the light of 3) satisfies the conditions. Then, in the case of this wavelength, a light beam is produced in the direction indicated by the arrow 3).
[0050]
As described above, when a plurality of light beams having different wavelengths are superimposed and incident, as described above, light beams are formed in different directions for each wavelength.
With the above operation, the wavelength multiplexed signal can be demultiplexed at different wavelengths simultaneously. Furthermore, since the dispersion angle can be adjusted by the thickness d of the parallel plate 30, the dispersion angle can be increased. That is, in the case of a diffraction grating, in order to increase the dispersion angle, it is necessary to narrow the interval between the concaves and convexes. Arise. On the other hand, in the present invention, it is only necessary to change the thickness of the parallel plate 30, so that it is easy to manufacture and the dispersion angle can be increased.
[0051]
Moreover, since the phase difference of the multiple reflected light can be accurately shifted by a predetermined value only by making the parallel plates 30 in parallel, the environment resistance is also excellent. In addition, the configuration of this embodiment has little change in characteristics due to the polarization state of light.
[0052]
FIG. 5 is a block diagram of another embodiment of the present invention.
In the figure, the reflectance of the reflective multilayer film 31 'is approximately 100%, and the reflectance of the reflective multilayer film 32' is 95%. In this case, the operation is the same as that described with reference to FIGS. 3 and 4 except that a light beam 37 ′ generated by multiple reflection of light is formed on the side opposite to the incident light 38.
[0053]
That is, the light converted into parallel rays by the collimating lens 34 becomes incident light 38 that is condensed on the focal line 36 by the cylindrical lens 35. Incident light 38 incident on the parallel plate 30 undergoes multiple reflections between the reflective multilayer films 31 ′ and 32 ′. In this embodiment, since the reflectance of the reflective multilayer film 31 'is approximately 100%, light is not emitted from the reflective multilayer film 31' side, but is emitted from the reflective multilayer film 32 'side. The emitted light interferes with each other and forms a light beam 37 'whose traveling direction depends on its wavelength. This is condensed by the lens 39 and detected by the light receiver 40.
[0054]
FIG. 6 shows an example of a method of manufacturing the duplexer according to the present invention.
First, in FIG. 6A, a parallel plate 30 having as good parallelism as possible is formed of glass or the like, and reflection films 60 and 61 are formed on both surfaces by a method such as vacuum deposition or ion sputtering. At this time, one of the reflection films 60 and 61 is set to have a reflectance close to 100%, and the other is set to have a reflectance smaller than 100%, preferably 80% or more. Form it.
[0055]
Next, in FIG. 6B, a part of either one of the reflective films 60 and 61 is scraped off. In FIG. 5, the side of the reflective film 60 is scraped off, but the surface to be scraped may be any, and the configuration of the embodiment of FIG. It only changes whether it becomes a structure like an Example.
[0056]
Further, as this scraping method, etching or the like may be used, but mechanical scraping is most inexpensive. However, when scraping mechanically, care must be taken not to damage the parallel plate 30 so much. That is, the portion where the reflective film is cut off is a portion that becomes the irradiation window 33 in the embodiment of FIG. 3 or FIG. Because there is.
[0057]
In addition, it is not necessary to use the method of first forming and scraping the reflective film as in the above method to form the irradiation window portion. It is also possible to prevent the reflective film from being formed on only a part.
[0058]
In the step of FIG. 6C, a transparent adhesive 62 is applied on the reflective film 60 and the portion where it has been removed. Since the adhesive 62 is also applied to the irradiation window portion, it is preferable that the adhesive 62 does not cause light loss as much as possible.
[0059]
In FIG. 6D, a transparent transparent protective plate 63 is attached on the transparent adhesive 62 to protect the reflective film and the like from being damaged. At this time, since the transparent adhesive 60 is filled to fill the step formed by scraping off the reflective film 60, the transparent protective plate 63 can be adhered in parallel to the upper surface of the parallel plate 30.
[0060]
Similarly, although not shown, in order to protect the reflective film 61, it is also possible to apply an adhesive to this surface and attach a protective plate. In the case of the figure, if the reflective film 61 has a reflectance of about 100%, the irradiation window 33 is not provided, so that light does not pass through this surface, and the adhesive and the protective plate are not necessarily transparent. It doesn't have to be a thing.
[0061]
Furthermore, an antireflection film may be provided on the transparent protective plate on the surface on which light enters or exits. For example, since the transparent protective plate 63 in FIG. 6D has the irradiation window 33 on this surface, an antireflection film 64 is provided.
[0062]
FIG. 7 is a diagram of a configuration example in which the wavelength demultiplexer 73 of the present invention is applied to a waveguide demultiplexer.
A waveguide made of lithium niobate or the like is provided on the substrate 65. Light from an optical fiber or the like enters from the incident waveguide 70. This light includes optical signals carried on a plurality of carrier waves having different wavelengths. In general, light comes out of an optical fiber or the like so that its width is widened, so that incident light from the optical fiber or the like is converted into parallel rays by a collimating lens 71.
[0063]
Incident light converted into parallel rays is condensed by a cylindrical lens 72 only in a direction parallel to the surface of the drawing of FIG. And the incident light condensed on the focal line perpendicular to the surface of the drawing of the same figure is made to enter the wavelength demultiplexer 73 from the irradiation window 76.
[0064]
In this configuration example, the wavelength demultiplexer 73 is provided with the reflection film 74 on one surface of the parallel plate 79 and the reflection film 75 and the irradiation window 76 on the other surface as described above. In addition, the light flux that has been multiple-reflected by the parallel plate 79 is configured to be emitted to the side opposite to the irradiation window 76. That is, the reflectivity of the reflective film 75 is about 100%, the reflectivity of the reflective film 74 is smaller than 100%, and a part of the light that is multiply reflected in the parallel plate 79 is emitted to the outside. Yes.
[0065]
The light that has passed through the wavelength demultiplexer 73 is emitted as a light beam in different traveling directions for each wavelength and is focused by the lens 77. Then, as shown in FIG. 7, the light exiting the wavelength demultiplexer 73 at different angles by being condensed by the lens 77 is condensed at different points. That is, for example, the light beams having the wavelengths λ1, λ2, and λ3 are collected at points as illustrated.
[0066]
A plurality of light receiving waveguides 78 for receiving the light collected for each wavelength is provided at a place where the light is collected by the lens 77. Each of the light receiving waveguides 78 is provided so as to guide an optical signal carried on a carrier wave having a single wavelength, and simultaneously receives the signals of the respective channels transmitted by the wavelength multiplexing method.
[0067]
The light guided by each light receiving waveguide 78 is detected by a light receiver such as a photodiode provided in the subsequent stage in a one-to-one correspondence with each light receiving waveguide 78 and processed as a signal.
[0068]
In the above-described embodiment, the description has been made on the assumption that the focal line is included in the surface of the irradiation window. Moreover, the structure by which incident light is condensed on a focal line before an irradiation window may be sufficient.
[0069]
In the above embodiment, only the configuration in which the reflectance of one of the two reflective multilayer films is almost 100% is shown, but the configuration is not necessarily limited thereto. That is, for example, when the reflectance of both reflective multilayer films is 95%, the same effect can be obtained. In this case, light leaks from both reflective multilayer films to the outside, and as a result of interference, a light flux whose traveling direction depends on the wavelength is formed on both sides of the parallel plate.
[0070]
【The invention's effect】
According to the present invention, since light of a plurality of wavelengths can be separated at a time, a receiver in optical multiplexing optical communication can be reduced in size.
[0071]
Compared to a receiver using a diffraction grating, the dispersion angle with respect to a change in wavelength is large, so that an optical signal can be accurately received even in optical multiplex communication with a large multiplicity. Also, the structure is simple and can be inexpensive. Furthermore, since multiple reflection is used, the phase difference of each light beam is always constant, the characteristics are stable, and changes in characteristics due to polarized light that cannot be avoided when a diffraction grating is used can be reduced.
[0072]
Compared to an arrayed waveguide grating, the structure is simple, the characteristics are stable by using multiple reflections, and the environment resistance is excellent.
[Brief description of the drawings]
FIG. 1 is a diagram (part 1) for explaining the principle of the present invention;
FIG. 2 is a diagram (part 2) for explaining the principle of the present invention;
FIG. 3 is a perspective view showing an embodiment of the present invention.
FIG. 4 is a diagram illustrating the configuration and operation of an embodiment.
FIG. 5 is a perspective view showing another embodiment of the present invention.
FIG. 6 is a diagram showing a manufacturing process of the wavelength demultiplexer of the present invention.
FIG. 7 is a front view in which the wavelength demultiplexer of the present invention is applied to a waveguide type wavelength demultiplexer.
FIG. 8 is a diagram (part 1) illustrating a conventional wavelength demultiplexer.
FIG. 9 is a diagram (part 2) illustrating a conventional wavelength demultiplexer.
[Explanation of symbols]
10, 38 Incident light
11, 33, 76 Irradiation window
12, 13, 44, 45 Reflecting surface
30 parallel plates
31, 32, 31 ', 32' reflective multilayer film
34, 71 Collimating lens
35, 72 Cylindrical lens
36
37, 37 'luminous flux
39, 77 lenses
40 Receiver
41 optical axis
60, 61, 74, 75 Reflective film
62 Transparent adhesive
63 Transparent protective plate
64 Anti-reflective coating
65 substrates
70 Incident waveguide
73 wavelength demultiplexer
78 Receiving waveguide
79 Parallel plate
80 Transparent substrate
81 Multilayer interference film
85, 86 Reflector
87, 88 Reflection mirror
89 half mirror
91 Outlet
93 Entrance
94 Waveguide

Claims (10)

The first and second reflecting surfaces are parallel to each other, and are set parallel to the one surface on or near one of the first and second reflecting surfaces. A light beam that spreads radially from the line segment in a direction perpendicular to the line segment is incident between the first and second reflection surfaces, and is transmitted through one of the first and second reflection surfaces for each multiple reflection. outputting light, the result of their interference, the traveling direction is a configuration process for the preparation of a wavelength demultiplexer to form different light flux with the wavelength of light,
Forming a reflective film on each parallel surface of a transparent parallel plate having at least two parallel surfaces , and making each of the reflective films the first and second reflective surfaces ;
A part having a low reflectivity is formed in a part of one of the reflective films , and the low reflectivity part is used as an incident region of the light beam between the first and second reflective surfaces ,
A method of manufacturing a wavelength demultiplexer, comprising forming a transparent body on a surface on which at least the low reflectance portion is formed. 2. The method of manufacturing a wavelength demultiplexer according to claim 1, wherein the low reflectance part is formed by mechanically scraping a part of the reflective film. 2. The method of manufacturing a wavelength demultiplexer according to claim 1, wherein the low reflectance portion is formed by removing a part of the reflective film by etching. 2. The method of manufacturing a wavelength demultiplexer according to claim 1, wherein the low reflectance portion is formed by masking in advance so that a reflective film is not formed on this portion. Forming a first reflecting surface that reflects light and a second reflecting surface that has a reflectance of less than 100% and transmits a part of the light on a parallel plate;
Providing a first lens for converging the incident light so as to spread radially while repeating reflection between the first and second reflecting surfaces; and
A method of manufacturing a wavelength demultiplexer that demultiplexes light while interfering with light transmitted through the second reflecting surface and interfering with the step of providing the first lens. 6. The method of manufacturing a wavelength demultiplexer according to claim 5, wherein the first lens condenses the incident light into a line segment. 6. The method of manufacturing a wavelength demultiplexer according to claim 5, wherein the first lens condenses the incident light into a line segment on an irradiation window provided on the flat plate. The method further comprises a step of providing a second lens that demultiplexes light emitted through the second reflecting surface while interfering, and converges the demultiplexed light for each wavelength. Item 6. A method for manufacturing a wavelength demultiplexer according to Item 5. 9. The method of manufacturing a wavelength demultiplexer according to claim 8, further comprising a step of providing a plurality of light receivers that receive the demultiplexed light converged by the second lens. 9. The method of manufacturing a wavelength demultiplexer according to claim 8, further comprising a step of providing an optical waveguide for receiving demultiplexed light converged by the second lens.

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