JPH1031121A - Waveguide type composing/branching filter using grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composing/branching filter in configuration, which can deal with the wavelength fluctuation of light to be transmitted and further gets suitable for mass production, concerning the composing/branching filter utilizing Bragg reflection. SOLUTION: This composing/branching filter has a three-dimensional optical waveguide 21 for enclosing light in breadthwise direction and thicknesswise direction and propagating light orthogonally to these directions and gratings 4 and 24 provided on the optical waveguide 21 along the propagating direction of light in order to reflect light 6 of specified wavelength in light 5 propagated through the optical waveguide 21. At such a time, since the optical waveguide 21 at the section provided with the gratings 4 and 24 is equipped with a section to continuously change either the width or the thickness of the optical waveguide 21 along the propagating direction of light at least so that the wavelength of reflectable light can be made into wide band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for combining light having a plurality of wavelengths into one optical transmission medium or extracting light having an arbitrary wavelength from an optical transmission medium in which light having a plurality of wavelengths is propagated. Related to duplexers.

[0002]

2. Description of the Related Art In the field of optical communication, a method of transmitting a plurality of signals on lights of different wavelengths and transmitting the signals through a single optical fiber (wavelength division multiplex transmission system) has been studied in order to expand the communication capacity. I have. In this system, a multiplexer / demultiplexer that multiplexes or demultiplexes light of different wavelengths plays an important role.

[0003] In the trunk line of optical communication, it is desired to increase the number of multiplexed communication capacities at narrow wavelength intervals in order to dramatically increase the amount of transmission. Therefore, a multiplexer / demultiplexer capable of multiplexing and demultiplexing a plurality of signal lights at a narrow wavelength interval is required.

As described above, while there is a demand for an increase in the number of multiplexed trunk lines, a plan for optically multiplexing a subscriber network in which an optical fiber is laid to each home and audio and video signals are transmitted by a wavelength division multiplex system has been proposed. In Japan, since only light having two wavelengths of 1.3 μm and 1.55 μm is used, there is currently no request to increase the multiplexing number. For this reason, the multiplexer / demultiplexer for subscriber optical communication may have a function of multiplexing / demultiplexing light of two wavelengths. There is a problem that the wavelength of light to be transmitted varies due to variations in wavelength between lots and variations in the oscillation wavelength of the semiconductor laser being used, and the multiplexer / demultiplexer must be able to cope with this variation. In addition, since the equipment for the subscriber optical communication is installed in each home, a thorough cost reduction is required. Therefore, as a multiplexer / demultiplexer for subscriber optical communication, it is desired to be able to cope with fluctuations in the wavelength of light and to achieve a thorough cost reduction.

[0005] As a typical example of a conventional multiplexer / demultiplexer for optical communication equipment and modules, a waveguide type Mach-Cheander interferometer is known. In addition, the optical waveguide
A structure in which a Bragg reflector is formed by forming a reflector and used as a multiplexer / demultiplexer is described in "Optical Integrated Circuit" by Hiroshi Nishihara et al. (Ohmsha).

[0006] Japanese Patent Application Laid-Open No. 61-6605 discloses that
By gradually changing the thickness of the planar waveguide on which the diffraction grating is mounted in the traveling direction of the light, the wavelength-multiplexed signal light is emitted upward from different positions of the diffraction grating for each wavelength. A wave device is described.

[0007]

However, the multiplexer / demultiplexer composed of the above-mentioned Mach-Cheander interferometer has a large element length, and the number that can be obtained from one wafer is small. Therefore, it cannot respond to the demand for lower prices.

Further, since the Bragg reflector has a very sharp wavelength selectivity, it is very difficult to use it as a multiplexer / demultiplexer in a system in which the transmitted wavelength is not stable, such as subscriber optical communication. It is. In addition, if the optical waveguide has birefringence, the center wavelength of reflection shifts depending on the polarization, and if the waveguide is made of a birefringent material, the Bragg reflector cannot be used. There was also. The birefringence depends on the material to be used and the method of manufacturing the optical waveguide. In the case of an anisotropic crystal material, it is natural that the material has birefringence, but glass that should be isotropic in nature should be used. A system optical waveguide may also have birefringence depending on the manufacturing method. For example, it is known that a quartz optical waveguide manufactured on a silicon substrate by a flame deposition method has birefringence. Even though there is a difference in size, it is necessary to consider that all optical waveguides that are currently in practical use have birefringence, and thus, Bragg reflectors have not been put to practical use.

In the duplexer described in Japanese Patent Application Laid-Open No. 61-6605, the demultiplexed light is radiated from the optical waveguide. Instead, a condensing optical system is required, and the loss of light increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multiplexer / demultiplexer utilizing Bragg reflection, which can cope with fluctuations in the wavelength of light to be transmitted and which has a configuration suitable for mass production. .

[0011]

In order to achieve the above object, the present invention provides the following multiplexer / demultiplexer.

That is, in order to confine light in the width direction and the thickness direction and propagate light in a direction orthogonal to the three-dimensional optical waveguide, and to reflect light of a specific wavelength among light propagating through the optical waveguide, A grating provided on the optical waveguide along the light propagation direction, wherein at least one of the width and the thickness of the optical waveguide is provided at a portion where the grating is provided. Is a multiplexer / demultiplexer provided with a portion that continuously changes along the propagation direction of the optical multiplexer / demultiplexer.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.

According to the present invention, in a multiplexer / demultiplexer using a Bragg reflector, the wavelength selectivity of the Bragg reflector is relaxed,
This is to broaden the reflection wavelength range.

As a method of relaxing the wavelength selectivity of the Bragg reflector and widening the band, a method of continuously changing the grating pitch can be considered. However, the grating pitch is extremely small and moreover. Must change continuously. It is extremely difficult to manufacture a grating in which the pitch is minutely and continuously changed, and it is almost impossible to actually manufacture the grating. For this reason, in the present invention, the grating pitch is constant, and the structure and dimensions of the waveguide are continuously changed so that the Bragg wavelength has a distribution. This relaxes the wavelength selectivity of the Bragg reflector and broadens the reflection wavelength range. This operating principle will be described first, and then specific embodiments will be described with reference to the drawings.

When the grating is formed on the optical waveguide,
Operates as a reflector under certain conditions (Bragg conditions). Assuming that the traveling direction of light propagating through the optical waveguide as a coordinate system is z, the forward wave is B (z), and the backward wave is A (z), the following mode coupling equation is established near the Bragg condition. I do.

[0017]

(Equation 1)

[0018]

(Equation 2)

Here, α is a coefficient representing the loss of the optical waveguide. If the loss of the optical waveguide is negligible, α = 0
It can be. χ is a coupling coefficient, which is an important parameter that indicates the strength of the coupling that generates the propagating light in the opposite direction due to the interaction between the signal light and the grating. Also, χ *
Represents the complex conjugate of χ.

Where δ is

[0021]

(Equation 3)

Is a parameter indicating the degree of detuning from the Bragg condition. Here, β is A (z) and B
The propagation constant of (z), K is a lattice vector, λ is the wavelength of light propagating in the optical waveguide, Λ is the pitch of grating, m is the order of Bragg diffraction, and N _eff (λ) is the light guide. The effective refractive index of the wave path.

If the Bragg condition is completely satisfied, δ = 0 and mK = 2β (4).

Equations (1) and (2) are expressed as A (L)
Solving under the boundary condition of = 0,

[0025]

(Equation 4)

[0026]

(Equation 5)

## EQU1 ## Therefore, the amplitude reflectance r is

[0028]

(Equation 6)

## EQU1 ## Here, γ ² = | χ | ² + (α + iδ) ² (8) The reflectance R is

[0030]

(Equation 7)

## EQU1 ## Here, it is assumed that the loss of the optical waveguide is negligible, and α = 0 hereinafter. At this time,

[0032]

(Equation 8)

## EQU1 ##

The result is shown in FIG.
If the wavelength of the light changes and deviates from the design wavelength, the degree of detuning δ from the Bragg condition increases from equation (3). δ
Increases, the reflectance R decreases as can be seen from FIG. The band at this time also changes depending on the coupling coefficient χ and the length L of the grating, and the band becomes wider as | と | L increases.

The coupling coefficient χ is determined by the depth of the grating,
It depends on the refractive index of the core and cladding of the optical waveguide. In order to obtain a large reflectance even if the length L of the grating is reduced, it is necessary to increase the coupling coefficient 反射. 100
When L and χ are determined and the grating is designed so as to obtain a reflectance close to 0.1%, for example, if a band is defined where the reflectance is reduced to １ ／, the band is converted into a wavelength of 0. It was usually as narrow as several nm to several nm.

However, for light having a wavelength of 1.55 μm used in subscriber optical communication, ± 20 nm, that is, ± 1.3%
Since a degree of wavelength variation is expected, it has been difficult to use a multiplexer / demultiplexer using a Bragg reflector until now.

In order to overcome this problem and increase the bandwidth of the Bragg reflector, it is conceivable to increase | χ |. However, as described above, | χ | is the depth of the grating and the core and cladding of the optical waveguide. There is a limit in increasing | χ | because it depends on the refractive index and the like. Therefore, |
It is necessary to find parameters other than χ | L.

Therefore, according to the present invention, N
We focused on _eff (λ). That is, in equation (3), since the wavelength dependence of δ is largely determined by the term of 2π / λ, 2π due to the wavelength fluctuation of the signal light of the subscriber optical communication.
It was considered that if N _eff could be changed so as to cancel the fluctuation of / λ, it would be possible to cope with the wavelength fluctuation of the signal light. Since N _eff (λ) is a function of λ and a function of the refractive index of the core and the cladding of the optical waveguide, and the function of the dimensions of the optical waveguide, in the present invention, the refractive index of the core and the cladding of the optical waveguide, By changing the dimensions of the optical waveguide, N _eff (λ) is changed.

Since N _eff (λ) is also a function of λ, it varies depending on the wavelength fluctuation of the signal light in the subscriber optical communication. However, it is impossible that N _eff (λ) is a function of λ in the first place. ,
It depends on the refractive index of the core and the cladding having wavelength dispersion.
The wavelength fluctuation of the signal light of the subscriber network is ± 20 nm as described above.
The wavelength dispersion of the refractive index of the core and the cladding due to this wavelength variation is very small, as in the present invention,
When considering only the wavelength fluctuation of the signal light, N _eff can be regarded as not depending on λ.

As described above, in the present invention, N _eff (λ) is changed by changing the refractive index of the core and the clad of the optical waveguide and the dimension of the optical waveguide, but the refractive index of the core and the clad is changed. Since it is difficult to determine the basic design of the optical waveguide and change it continuously along the light propagation direction, in the present embodiment, by changing the width of the three-dimensional optical waveguide, N _eff is continuously changed. Change.

It is not easy to find N _eff of a three-dimensional optical waveguide, and no analytical expression can be presented here. Normally, it is calculated by an approximate solution such as the Mart-Cutley method or the equivalent refractive index method, or a numerical solution such as the finite element method. However, the following points can be clarified from the results obtained by these known methods. That is, the refractive index of the core is n ₁ and the refractive index of the cladding is n ₂
If (n ₁ > n ₂ ), then n ₁ > N _eff > n _2, and if the width of the optical waveguide is increased, N _eff will gradually _approach n ₁ . That is, by changing the width of the optical waveguide, N _eff can be set to a desired value.

According to this fact, the present invention is implemented as follows.

As a precondition, the wavelength fluctuation width of light having a wavelength to be selected from light of a plurality of wavelengths is known in advance, and λ
It is assumed that it has a wavelength width of _{i, 1 to} λ _{i, 2} . Further, a material used for the core and a material used for the clad are determined in advance. Further, here, a single-mode waveguide having only the zero-order mode as the waveguide mode is used.

First, an optical waveguide is designed for a wavelength λ _{i, 1} , and the thickness T and width W ₁ of the optical waveguide are determined from the refractive index n _{1 of the} core and the refractive index n _{2 of the} clad. _Assuming that the _effective refractive index of the optical waveguide at this time is N _{eff, 1} , the period を_{満 た す of the} grating satisfying the Bragg condition with respect to N _{eff, 1} is given by (1)
1) Determined from the equation.

[0045]

(Equation 9)

Next, the width of the optical waveguide is widened in a range where the single mode is obtained, and the width W _{2 of the} optical waveguide is obtained. Although W ₂ cannot be unconditionally increased, as known from the results of known results, for example, “Optical Integrated Circuit” by Hiroshi Nishihara et al. Waveguide conditions are relatively mild, and it is relatively easy to change N _eff by a few percent under single mode conditions.

Then, the width of the optical waveguide at both ends of the grating having a length L determined from the design of the grating is represented by W
It defined ₁ and W _2, defined as the width in between the optical waveguide is changed continuously. The width of the optical waveguide may be designed to change linearly from W ₁ to W ₂ , but if possible, the width of the optical waveguide may be curved so that N _eff changes linearly. It can also be designed to change dynamically.

Here, in order to design a Bragg reflector of a single-mode optical waveguide, W ₂ is designed within the range of the width of a single mode, but two optical waveguides intersect. In the case of a configuration in which the light is split between the crossed optical waveguides, it is conceivable to locally manufacture the optical fiber on the assumption of a multimode optical waveguide. In the case of such a multimode optical waveguide, W _{2 is set} within a range in which an allowable number of modes can be obtained.
Can be designed.

Specifically, by designing an optical waveguide and a grating, an example of a multiplexer / demultiplexer using a Bragg reflector as shown in FIGS. 2A, 2B and 2C can be shown. .

Here, it is assumed that the optical waveguide 21 is made of quartz glass, and the refractive index of the core n ₁ = 1.4.
8. The refractive index of the cladding n ₂ is set to 1.46. Wavelength λ _{i, 1}
When a three-dimensional optical waveguide that becomes a single mode with respect to 1.54 μm is designed, for example, a thickness T = 2.5 μm and a width W ₁
= 3 μm. When the effective refractive index in this case is approximately obtained by the equivalent refractive index, N _{eff, 1} = 1.44659. Substituting N _{eff, 1} into the equation (11) and setting the grating period Λ ₁ to 0.526 μm, the wavelength λ _{i, 1} = 1.5
The Bragg diffraction condition of order m = 1 is satisfied for 4 μm. Next, if the width of the optical waveguide is increased to W ₂ = 6.5 μm in a range where a single mode is obtained, N _{eff, 2} = 1.469
3, and the Bragg diffraction condition is satisfied by performing phase matching with λ _{i, 2} = 1.546 μm. Therefore, by changing the width of the optical waveguide from W ₁ to W ₂ at the grating portion, the wavelength λ _{i, 1} = 1.54 μm to λ _{i, 2} = 1.5
A Bragg reflector that can handle light having a wavelength of 46 μm can be configured.

On the other hand, by designing the depth of the grating 4 and the like, | χ | L = 3 and | χ | = 0.006.
(1 / μm), the detuning degree δ ≒ ± 1.25 | χ
| Reduces the reflectivity to about 1/2. When this detuning degree δ is converted into a wavelength, it becomes ± 0.003 μm, and the band is 0.006 μm if a band is defined where the reflectance becomes １ ／.

Therefore, the width of the optical waveguide is changed from W ₁ to W ₂ , and the grating 4
Λ _{i, 1} and λ _{i, 2} are obtained by adding λ _{i, 1} = 1.537 μ
m and λ _{i, 2} = 1.549 μm, and the reflectivity becomes に な る or more in this band.

Specifically, | χ | = 0.006 (1 / μm)
In order to make | χ | L = 3 at this time, L may be set to 500 μm. Therefore, as shown in FIG.
Between 00 μm, the width of the optical waveguide is 3 μm to 6.5 μm.
And by providing a grating 4 with ＝ ₁ = 0.526 μm in this portion, the wavelength λ _{i, 1} = 1.53
The band from 7 μm to λ _{i, 2} = 1.549 μm is 0.012
A multiplexer / demultiplexer using a μm Bragg reflector can be configured.

Further, as shown in FIG. 2C, the width of the optical waveguide is further changed from the width of 3 μm to 6.5 μm with the length L = 500 μm at the end of the optical waveguide having the changed width. When a grating 24 having a period Λ ₂ = 0.529 μm is formed at the wavelength λ _{i, 1} = 1.537 μm, λ _{i, 2} = 1.
A multiplexer / demultiplexer using a Bragg reflector having a 561 μm band of 0.024 μm can be configured.

In order to further widen the band, this configuration may be further multi-staged. However, since the coupling coefficient 若干 slightly changes depending on the width W of the optical waveguide, it is necessary to consider it strictly, but the description of the present invention ignores the change χ.

Further, as shown in FIG. 2B, the width of the second-stage optical waveguide can be changed in a direction in which the width becomes smaller. In the case of FIG. 2B, a band similar to that of FIG. 2C is obtained.

The operation of the multiplexer / demultiplexer shown in FIGS. 2A, 2B and 2C will now be described. The wavelength-multiplexed signal light 5 is made incident on the optical waveguide 21. Here, the signal light 5 having wavelengths of 1.3 μm and 1.55 μm is incident. When the signal light 5 reaches the multiplexer / demultiplexer, a wavelength of 1.55
The light of μm is reflected and split, and travels in the optical waveguide 21 in the opposite direction as reflected light 6. The light having a wavelength of 1.3 μm passes through the multiplexer / demultiplexer and travels as it is as the transmitted light 7 through the optical waveguide 21. When the reflected light 6 and the transmitted light 7 are respectively incident on the optical waveguide 21 in opposite directions, they are multiplexed by the multiplexer / demultiplexer, and the signal light 5 in the opposite direction is obtained.

At this time, even if the wavelength of the signal light 3 having a wavelength of 1.55 μm fluctuates, in the case of the multiplexer / demultiplexer of FIG. 2A of the present invention, λ _{i, 1} = 1. 537 μm and λ _{i, 2} =
The fluctuation of the signal light can be handled in the band of 0.012 μm of 1.549 μm, and the light in this band can be demultiplexed. In the case of the multiplexer / demultiplexer shown in FIGS. 2B and 2C, the wavelength λ _{i, 1} = 1.537 μm to λ _{i, 2} = 1.561.
It is possible to cope with the fluctuation of the signal light in the 0.024 μm band of μm, and the light in this band can be split.

FIG. 1A shows the structure of a multiplexer / demultiplexer for splitting the reflected light 26 into an optical waveguide 27 different from the signal light 6. When such a multiplexer / demultiplexer is designed, β ′ is used instead of β in the above-described equation (4), so that the multiplexer / demultiplexer shown in FIGS. 2A, 2B, and 2C is used. It can be designed like a vessel. Where β ′ = βcos θ, θ:
The angle between the optical waveguide 27 and the optical waveguide 21 is divided by two.

Next, FIGS. 1 (a), 2 (a),
The method for manufacturing the multiplexer / demultiplexer of (b) or (c) will be described.
Here, the optical waveguides 21 and 27 and the gratings 4 and 24 are configured as shown in FIG. That is, the optical waveguides 21 and 27 are formed by sequentially laminating the lower clad layer 3, the core layer 1, and the upper clad layer 2 on the substrate 23. The gratings 4 and 24 are formed by processing the upper surface of the core layer 1 into irregularities.

First, Si is used as the substrate 23,
A quartz glass is formed as the lower cladding layer 3 on the substrate 23. As a film forming method, a method such as flame deposition, EB vapor deposition, or CVD can be used. In the case of the flame deposition method, after the film is formed, a vitrification treatment is further performed at a temperature of about 1200 ° C. to form a clad layer. The core layer 1 is formed in the same manner, but several percents of TiO ₂ or GeO ₂ are added to quartz glass. The refractive index is controlled by the amount added.

A resist is applied to the upper surface of the formed core layer 1 by a spin coating method, a grating pattern is formed on the resist, and the upper surface of the core layer 1 is processed by dry etching. In the case where first-order diffraction is used as a method of forming a grating pattern on a resist, since the pitch of the grating is extremely small as described above, patterning is performed by known two-beam interference or an interference method using a phase grating. When the gratings having different periods are continuous as shown in FIGS. 2B and 2C, the drawing area is limited by the size of the light beam, and the light beam is drawn while being shifted by a certain amount.

After the dry etching, a resist is again applied to the core layer 1 by spin coating, and the optical waveguide 21
The pattern 27 is drawn, and the core layer 1 is processed into the shape of the optical waveguides 21 and 27 by dry etching.

Then, by forming an upper clad layer on the core layer 1, a multiplexer / demultiplexer can be manufactured.

Although the gratings 4 and 24 are formed on the upper surface of the core layer 1 in the structure of FIG. 1B, the structure may be such that the gratings are formed on the upper surfaces of the lower cladding layer 3 and the upper cladding layer 2. is there.

In this case, the grating is of the refractive index modulation type. However, the present invention is not limited to this, and it is also possible to use a grating having another configuration.

In this embodiment, a quartz glass material is used as a material constituting the optical waveguide. However, other glass materials of different glass types, semiconductor materials, polymethyl methacrylate, fluorinated polyimide, etc. Can be used.

Although the above-described manufacturing method is suitable for mass production, an optical waveguide manufactured by such a manufacturing method usually has a birefringence value of 1 × 10 ⁻⁴ or more. When the optical waveguide has such birefringence, a phenomenon in which the wavelength of the transmitted light shifts depending on the polarization occurs, but the multiplexer / demultiplexer of the present embodiment has a wide wavelength band as described above. Therefore, it is possible to cope with wavelength fluctuation due to birefringence. Therefore, since the multiplexer / demultiplexer according to the present embodiment can be manufactured by a method suitable for mass production, it can be manufactured at low cost.

Next, an optical circuit module using the multiplexer / demultiplexer according to the present embodiment will be described with reference to FIGS. 4 and 5. FIG.

The optical module shown in FIG. 4 has an optical waveguide 21 mounted on a substrate 23. In the middle of the optical waveguide 21,
A multiplexer / demultiplexer 201 is provided. In addition, the optical waveguide 21
Is connected to a branch portion 21. Branch 21
Are connected to an optical waveguide 112 and an optical waveguide 113. A light receiving element 101 for detecting light of 1.3 μm is attached to an end of the optical waveguide 112.
One end of the semiconductor laser 102 that emits light of 1.3 μm is connected to an end of the optical waveguide 113. In addition, the opposite emission end of the semiconductor laser 102 includes:
A light receiving element 103 for monitoring is arranged via an optical waveguide. These are all mounted on the substrate 23.

The multiplexer / demultiplexer 201 is formed by changing the width of the optical waveguide 21 and mounting a grating on that portion. As a specific configuration of the multiplexer / demultiplexer 201, one of the multiplexers / demultiplexers 201 shown in FIGS. 2A, 2B, and 2C is selected according to a required band.

Here, the operation of the optical circuit module of FIG. 4 will be described.

An external optical waveguide is connected to the optical waveguide 21, and signal light is made to enter from the external optical waveguide. For example, when the signal light 5 is a signal light in which a wavelength of 1.55 μm and a light of 1.3 μm are multiplexed, the multiplexer / demultiplexer 201 reflects and reflects the light of 1.55 μm. The light 6 is returned to the external optical waveguide. In addition, the multiplexer / demultiplexer 201 includes:
Light having a wavelength of 1.3 μm is transmitted as transmitted light 7. The transmitted light 7 is branched by the branching unit 111, and the transmitted light 7 incident on the optical waveguide 112 is detected by the light receiving element 101. Further, the light 10 having a wavelength of 1.3 μm emitted from the semiconductor laser 102.
4 is transmitted through the multiplexer / demultiplexer 201 and enters an external optical waveguide. When only light having a wavelength of 1.55 μm is incident as signal light from an external optical waveguide, the light having a wavelength of 1.3 μm emitted from the semiconductor laser 102 is multiplexed with the multiplexer / demultiplexer 201. The multiplexed light travels in the opposite direction to the signal light 5 and reaches an external optical waveguide.

In the optical circuit module as shown in FIG.
By using the multiplexer / demultiplexer shown in FIGS. 2A, 2B, and 2C of the present embodiment, the wavelength 1.55
Even when the wavelength of the light of μm fluctuates, the light can be demultiplexed in accordance with the fluctuation.

The optical circuit module of FIG. 5 has the same configuration as the optical circuit module of FIG.
The light demultiplexed by the optical waveguide 2 is converted into an optical waveguide 2 different from the optical waveguide 21.
7 is branched. In the case of FIG.
2 is configured as the multiplexer / demultiplexer shown in FIG. Of the external signal light 5, light having a wavelength of 1.55 μm is branched as reflected light 26 into an optical waveguide 27. Other configurations are the same as those in FIG.

Also in the optical circuit module of FIG. 5, by using the multiplexer / demultiplexer of FIG. 1A of this embodiment,
Even when the wavelength of light having a wavelength of 1 and 55 μm included in the signal light 5 has a fluctuation, the light can be demultiplexed in accordance with the fluctuation.

As described above, in the present embodiment, in the multiplexer / demultiplexer using Bragg reflection, the N _eff is changed by continuously changing the width of the three-dimensional optical waveguide along the light propagation direction. Can be done. As a result, the band of the reflection wavelength can be widened, so that it is possible to provide a multiplexer / demultiplexer having a configuration that can cope with wavelength fluctuations of light to be transmitted and that is suitable for mass production.

As described in the above-described manufacturing method,
Since the structure in which the width of the three-dimensional optical waveguide is modulated can be easily formed by the steps of film formation and etching, the multiplexer / demultiplexer of the present invention is suitable for mass production and can be manufactured at low cost.

In the above-described embodiment, a multiplexer / demultiplexer for multiplexing / demultiplexing light of two or more wavelengths in optical communication has been described. Because it can reflect light of a specific wavelength,
Of course, it can be used as a filter.

[0080]

As described above, according to the present invention, a multiplexer / demultiplexer utilizing Bragg reflection, which can cope with wavelength fluctuations of light to be transmitted and which is suitable for mass production. Can be provided.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram and FIG. 1B is a cross-sectional view illustrating a configuration of a multiplexer / demultiplexer according to an embodiment of the present invention.

FIGS. 2A, 2B, and 2C are explanatory diagrams illustrating a configuration of a multiplexer / demultiplexer according to an embodiment of the present invention.

FIG. 3 is a graph showing reflection characteristics of a duplexer using a Bragg reflector.

FIG. 4 is an explanatory diagram showing a configuration of an optical circuit module using the multiplexer / demultiplexer of the present invention.

FIG. 5 is a perspective view showing a configuration of an optical circuit module using the multiplexer / demultiplexer of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Core layer, 2 ... Upper clad layer, 3 ... Lower clad layer, 4, 24, 24 ... Grating,
5 ... wavelength multiplexed signal light, 6, 26 ... demultiplexed reflected light of specific wavelength, 7 ... transmitted light, 21, 27 ...
..Optical waveguide, 23 substrate, 101 light receiving element, 102 semiconductor laser, 103 light receiving element for monitoring, 111 branch part, 112, 113
-Optical waveguides, 201, 202 ... multiplexer / demultiplexer.

Claims (11)

[Claims] 1. A three-dimensional optical waveguide for confining light in a width direction and a thickness direction and propagating light in a direction orthogonal thereto.
And a grating provided on the optical waveguide along a light propagation direction to reflect light of a specific wavelength among the light propagating through the optical waveguide, wherein the grating is provided. Wherein the optical waveguide has a portion in which at least one of the width and the thickness of the optical waveguide continuously changes along the light propagation direction. 2. The optical waveguide according to claim 1, wherein the portion of the optical waveguide where the grating is provided has a plurality of portions where the shape of the optical waveguide changes continuously. Multiplexer / demultiplexer. 3. The multiplexer / demultiplexer according to claim 2, wherein the portion where the shape of the optical waveguide continuously changes is provided periodically and repeatedly. 4. The multiplexer / demultiplexer according to claim 2, wherein the gratings provided in each of the portions where the shapes of the plurality of optical waveguides change continuously have different periods. 5. The optical waveguide according to claim 1, wherein the optical waveguide is a single mode waveguide, and a change in the shape of the optical waveguide is within a range satisfying a condition of the single mode waveguide. Multiplexing / demultiplexing device. 6. The optical waveguide according to claim 1, wherein another portion of the optical waveguide provided with a grating is connected to another optical waveguide for guiding light reflected by the grating in another direction. Characteristic multiplexer / demultiplexer. 7. The multiplexer / demultiplexer according to claim 1, wherein said optical waveguide comprises a core and a clad, and said grating is formed on at least one of said core and said clad. 8. A multiplexer / demultiplexer according to claim 1, wherein said optical waveguide is an optical waveguide formed by film formation and etching. 9. A multiplexer / demultiplexer according to claim 1, wherein said optical waveguide has a birefringence value of 1 × 10 ⁻⁴ or more. 10. Light is confined in the width direction and the thickness direction,
A three-dimensional optical waveguide for propagating light in a direction perpendicular to the three-dimensional optical waveguide; The optical waveguide of the portion where the grating is provided is provided with a portion where at least one of the width and the thickness of the optical waveguide continuously changes along the light propagation direction. A grating filter. 11. An optical waveguide, a detector for detecting light propagated through the optical waveguide, a light source for causing light to enter the optical waveguide, and a multiplexer / demultiplexer for light having different wavelengths transmitted through the optical waveguide. An optical circuit module comprising a multiplexer / demultiplexer on a substrate, wherein the multiplexer / demultiplexer confine the light in the width direction and the thickness direction, and propagates the light in a direction orthogonal thereto. And a grating provided on the optical waveguide along the light propagation direction to reflect light of a specific wavelength among the light propagating through the optical waveguide, wherein the grating is provided. The optical circuit module according to claim 1, wherein at least one of the width and the thickness of the optical waveguide is continuously changed along the light propagation direction.