JP2002202420A - Optical wavelength coupling/branching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature independent optical wavelength coupling/ branching device in which a demultiplexing characteristic is not deteriorated and a branched wavelength is correctly controlled. SOLUTION: In the optical wavelength coupling/branching device which is provided with an array waveguide diffraction grating 3 consisting of a plurality of channel waveguides, an input side slab waveguide 2 which is connected to the array waveguide diffraction grating, and an output side slab waveguide 5 which is connected to the array waveguide diffraction grating and in which a changing quantity of the branched wavelength does not depend on temperature but almost is constant, a refractive index control region 55 is provided in the input side slab waveguide 2 or the output side slab waveguide 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength multiplexer / demultiplexer used in a wavelength division multiplex system in the field of optical communication.

[0002]

2. Description of the Related Art In the field of optical communication, there has been proposed a wavelength division multiplexing system in which a plurality of signals are put on lights of different wavelengths and transmitted through one optical fiber to increase the information capacity. In this system, an optical wavelength multiplexer / demultiplexer that multiplexes / demultiplexes light of different wavelengths plays a major role. In particular, an optical wavelength multiplexer / demultiplexer using an arrayed waveguide diffraction grating has the advantages of realizing the multiplexing / demultiplexing at narrow wavelength intervals and increasing the multiplexing number of the communication capacity.

FIG. 4 shows an optical circuit of a conventional arrayed waveguide diffraction grating type optical wavelength multiplexer / demultiplexer. This optical wavelength multiplexer / demultiplexer
An arrayed waveguide diffraction grating 3 is provided on a quartz substrate 7, an input side slab waveguide 2 and an input channel waveguide 1 are connected to an input side of the arrayed waveguide diffraction grating 3, and an output of the arrayed waveguide diffraction grating 3 is provided. The output side slab waveguide 5 and the output channel waveguide 6 are connected to the side. The array waveguide diffraction grating 3 includes a plurality of channel waveguides 4 (hereinafter, referred to as an array waveguide).

[0004] This type of device has a problem that the wavelength of the demultiplexed light is shifted by a maximum of 0.6 nm when used at an environmental temperature of, for example, 0 to 60 ° C.

In order to solve this problem, the temperature of the optical circuit is generally controlled by a heater or a Peltier element. However, a practical system for eliminating the wavelength shift due to temperature without performing this temperature control is known. Proposed.

In this system, as shown in FIG. 5 or FIG. 6, a groove 9 or a groove 10 is provided in a part of the array waveguide 4, the input side slab waveguide 2, or the output side slab waveguide 5, and is provided therein. A method has been proposed in which a material having a temperature coefficient of a refractive index different from that of an optical circuit is filled to cancel the inclination of the equal phase surface due to temperature and to make the temperature independent (Y. In).
"Athermal silica-based arrayed-wave"
guide grating (AWG) multiplexer ”, ECOC 97 technic
al digest, pp. 33-36, 1997).

In an optical wavelength multiplexer / demultiplexer actually manufactured, a deviation occurs between a split wavelength and a desired wavelength to be split due to fluctuations in an optical circuit manufacturing process. It is important to eliminate this deviation and make the demultiplexed wavelength coincide with the desired wavelength. In an optical wavelength multiplexer / demultiplexer that is not temperature-independent because a wavelength-demultiplexing wavelength shifts due to temperature, the temperature dependence of the wavelengths of the wavelengths of the wavelength-multiplexing / demultiplexing device is positively utilized, and a heater or a Peltier element is used. By accurately adjusting the temperature of the optical circuit, it is possible to eliminate the deviation caused in the process of manufacturing the optical circuit and to make the demultiplexed wavelength coincide with the desired wavelength.

However, the optical wavelength multiplexer / demultiplexer whose demultiplexing wavelength is made temperature-independent as described above does not have means for adjusting the temperature of a heater or a Peltier element, so that this method cannot be used. Therefore, in order to control the demultiplexing wavelength, as shown in FIG. 7, a method of directly connecting the optical fiber 21 to the end of the input side slab waveguide 2 and controlling the demultiplexing wavelength by the connection position of the optical fiber 21 is proposed. Have been.

[0009]

However, in this method, even if the connection position of the optical fiber 21 is slightly shifted, a shift occurs between the demultiplexed wavelength and a desired wavelength. Therefore, it has been difficult to accurately adjust the demultiplexing wavelength to a desired wavelength.

The input side slab waveguide 2 shown in FIG.
Is required to be accurately controlled on the order of several μm. If manufactured out of the desired edge position,
There is a possibility that the demultiplexing characteristic is deteriorated as compared with the desired characteristic, and the crosstalk is increased.

Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology, and to provide a temperature-independent device capable of accurately controlling the wavelength of demultiplexed light without deteriorating the demultiplexing characteristics. An optical wavelength multiplexer / demultiplexer is provided.

[0012]

According to the first aspect of the present invention,
Light having an arrayed waveguide grating composed of a plurality of channel waveguides, an input slab waveguide connected to the arrayed waveguide grating, and an output slab waveguide connected to the arrayed waveguide grating In the optical wavelength multiplexer / demultiplexer having a circuit and a change amount of the demultiplexed wavelength substantially constant regardless of the temperature, a refractive index control region is provided in the input-side slab waveguide or the output-side slab waveguide. It is characterized by having.

According to a second aspect of the present invention, there is provided an arrayed waveguide grating composed of a plurality of channel waveguides, an input slab waveguide connected to the arrayed waveguide grating, and connected to the arrayed waveguide grating. An output side slab waveguide, and a groove is formed in any of the input side slab waveguide, the output side slab waveguide or the arrayed waveguide diffraction grating, and the light is formed in the groove. By inserting a material having a temperature gradient with a refractive index different from that of the circuit constituting the circuit, the change amount of the demultiplexed wavelength is substantially constant regardless of the temperature. A waveguide or the output side slab waveguide is provided with a refractive index control region.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the above description, the core material in the refractive index control region has a larger refractive index than the core material other than the refractive index control region.

The invention described in claim 4 is the first to third aspects of the present invention.
Wherein the refractive index control region has a wedge shape.

[0016] The invention according to claim 5 provides the invention according to claims 1 to 4.
The refractive index of a core material in the refractive index control region is controlled by light irradiation.

The invention described in claim 6 is the first to fourth aspects of the present invention.
The refractive index of the core material in the refractive index control region is controlled by applying a stress based on a photoelastic effect.

The invention according to claim 7 is the invention according to claims 1 to 6
5. The material according to claim 1, wherein the material forming the optical circuit is a quartz-based material, and the core portion contains germanium.

The invention according to claim 8 is the invention according to claims 5 to 7
5. The method according to claim 1, wherein a carbon dioxide laser, an excimer laser, or an Ar ion laser is used as a light source for the light irradiation.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical wavelength multiplexer / demultiplexer according to the present invention will be described below.

FIG. 1 shows an optical circuit of an arrayed waveguide diffraction grating type optical wavelength multiplexer / demultiplexer. This optical wavelength multiplexer / demultiplexer is manufactured on a quartz substrate 7. On the quartz substrate 7, a core made of a quartz-based material is formed, and this core constitutes an optical circuit. The core and the surface of the quartz substrate 7 are covered with a cladding film made of a quartz-based material. The optical circuit includes an arrayed waveguide grating 3, an input side slab waveguide 2 is connected to an input side of the arrayed waveguide grating 3, and an output side of the arrayed waveguide grating 3 is connected to an output side. The side slab waveguide 5 is connected. The input channel waveguide 1 is connected to the input slab waveguide 2, and the output channel waveguide 6 is connected to the output slab waveguide 5. The arrayed waveguide diffraction grating 3 includes a plurality of channel waveguides 4.

In the middle of the input side slab waveguide 2, a groove 8 is provided.
Is formed, and an optical resin is inserted into the groove 8 so that the wavelength of the demultiplexed light is made independent of the temperature. A wedge-shaped refractive index control region 55 is provided in the middle of the output side slab waveguide 5, and the core material in the refractive index control region 55 has a larger refractive index than the core material other than the refractive index control region 55. Have. The refractive index of the core material in the refractive index control region 55 is controlled so that the demultiplexed wavelength matches a desired wavelength.

FIG. 2 shows a refractive index control device of the refractive index control area 55. This device controls the refractive index of the core material of the refractive index control region 55 of the output side slab waveguide 5 so that the demultiplexed wavelength of the element matches the desired wavelength.

The refractive index is changed by reflecting the excimer light output by the KrF excimer laser 31 on the mirror 32 and irradiating the mirror on the output side slab waveguide 5. By changing the irradiation time of the excimer light, the refractive index can be changed. A mask 35 for excimer light blocking is used so that the excimer light is applied to a part of the output side slab waveguide 5 in a wedge shape. During excimer light irradiation,
The demultiplexing characteristics of the optical wavelength multiplexer / demultiplexer are monitored by the optical spectrum analyzer 34, and the excimer light irradiation is stopped when the demultiplexed wavelength reaches a desired wavelength. In this method, the demultiplexing wavelength can be set to a desired wavelength. Further, since the refractive index in the refractive index control region 55 can be made substantially uniform, the demultiplexing characteristics are almost the same as before excimer light irradiation, and there is almost no increase in crosstalk.

When the light from the broadband light source 33 is input through the input optical fiber 12 and the input channel waveguide 1, this light wave propagates in the input side slab waveguide 2, and the arrayed waveguide diffraction grating 3 To reach the border. The arriving light wave is coupled and propagated to each array waveguide 4 at a power ratio according to the electric field distribution at the boundary, and reaches the boundary between the array waveguide 4 and the output side slab waveguide 5.

The length of the array waveguide 4 is Δ
It is designed to be longer for every constant length of L. Accordingly, the amount of phase change φ ^′ _i (λ) received by the light wave propagating through the i-th array waveguide 4 from the inside is determined with reference to the innermost array waveguide 4.

[0027]

(Equation 1) Becomes Here, lambda light wave wavelengths in vacuum, n _a is the effective refractive index of the arrayed waveguide 4. Therefore, the equal phase plane of the light wave near the boundary between the array waveguide 4 and the output side slab waveguide 5 is inclined depending on the wavelength. The light waves that have undergone a phase change by each array waveguide 4 cause interference in the output side slab waveguide 5, and this interference wave is extracted from the output channel waveguide 6.

Here, since the direction of the equal phase plane differs for each wavelength, when the wavelength changes, the light condensing position shifts at the boundary between the output side slab waveguide 5 and each output channel waveguide 6. For this reason, it is possible to take out only the light wave having a unique demultiplexing wavelength from each output channel waveguide 6, and a multiplexing / demultiplexing function of the light wave is realized.

The wavelength λ of the light wave output from the output channel waveguide 6 disposed on the axis of symmetry 11 (FIG. 1 or 3) of the output side slab waveguide is:

[0030]

(Equation 2) It is expressed as Here, m is the diffraction order.

[0031] Here, in the case of constituting the optical circuit using conventional materials, when the temperature changes, the refractive index of the material by thermo-optic effect is changed, n _a is changed by this. Further, the length of the arrayed waveguide 4 changes due to thermal expansion, and accordingly, ΔL also changes. Therefore, the equal phase plane of the light wave near the boundary between the arrayed waveguide 4 and the output side slab waveguide 5 is inclined due to the temperature, and the output demultiplexed wavelength changes. In the case of a light wave output from the output channel waveguide 6 arranged on the axis of symmetry 11 of the output side slab waveguide 5, the wavelength change amount Δλ when the temperature T changes by ΔT is given by the following equation (2). By differentiating with T

[0032]

(Equation 3) Becomes Here, consider the case of being made of a quartz-based material, and d
n _a / dT is, if equal to the temperature coefficient of the refractive index of the silica-based _{material, dn a / dT ≒ 1 ×} 10 -5, 1 / ΔL · d
(ΔL) / dT ≒ 5 × 10 -7, for a n _a ≒ 1.45, when the λ = 1550nm, Δλ / ΔT ≒ 0.0
It becomes 1 nm / ° C. Therefore, for example, when used at an environmental temperature of 0 to 60 ° C., the wavelength of the demultiplexed light is shifted by a maximum of 0.6 nm. Therefore, in the present embodiment, in order to cancel the shift of the split wavelength, the groove 8 is formed as described above, and the groove 8 has a temperature gradient of a refractive index different from that of the material forming the optical circuit. A material is inserted to make the demultiplexed wavelength independent of temperature, and the refractive index control region 55 is formed.

In this embodiment, the refractive index control region 55
By adjusting the refractive index of the above, it is possible to eliminate the deterioration of the demultiplexing characteristic and to control the demultiplexing wavelength accurately in accordance with the following demultiplexing wavelength control principle.

FIG. 3 shows the principle of wavelength division control. Light is emitted from the array waveguide 4 in various directions in the output side slab waveguide 5, but only light of a specific wavelength λ (θ) is emitted at a certain emission angle θ. This relationship is

[0035]

(Equation 4) It is expressed as Here, _ns is the refractive index of the output side slab waveguide 5, and d is the distance between the arrayed waveguides 4 at the end of the output side slab waveguide 5.

Since the refractive index control region 55 is wedge-shaped, the light is refracted by the refractive index control region 55 and reaches one output channel waveguide 66 among the plurality of output channel waveguides 6. According to the shape of the wedge of the refractive index control region 55 and the refractive index n, only light emitted at a certain angle θ reaches the output channel waveguide 66. Therefore, the wavelength λ (θ)
Only reaches the output channel waveguide 66.

This wavelength λ (θ) becomes the split wavelength in the output channel waveguide 66. Here, the refractive index control region 5
When the refractive index of the core material of No. 5 is changed from n to n ′, the angle of refraction of light in the refractive index control region 55 changes, and light having a different radiation angle θ ′ reaches the output channel waveguide 66. Accordingly, the demultiplexed wavelength of the output channel waveguide 66 is also λ (θ).
To λ (θ ′). According to this, by adjusting the refractive index of the refractive index control region 55, the demultiplexing wavelength can be adjusted.

As a method of controlling the refractive index shown in FIG. 2, a change in the refractive index by applying a stress based on the photoelastic effect may be used in addition to excimer light irradiation. When a carbon dioxide laser is irradiated or a stress applying material is loaded on the upper part of the clad, the stress applied to the core material changes, and the refractive index of the core material changes due to the photoelastic effect. Thereby, the refractive index of the refractive index control region 55 can be adjusted, and the demultiplexing wavelength can be adjusted.

It is desirable that the core material be a material whose refractive index can be easily changed by light irradiation. In the case of a quartz material, the core of the optical circuit preferably contains germanium. As a light source for light irradiation, a carbon dioxide laser or a KrF laser capable of generating a wavelength having a high optical power and a high sensitivity to germanium is used.
An excimer laser such as that described above, or an Ar ion laser is desirable.

Although the present invention has been described based on one embodiment, it is apparent that the present invention is not limited to this. In the above embodiment, the refractive index control region 55 is provided in the output side slab waveguide 5, but it is possible to provide the refractive index control region in the input side slab waveguide 2. The present invention relates to an optical wavelength multiplexer / demultiplexer used in an optical multiplex transmission system, an M × N frequency routing device, and Add / Drop.
The present invention is also applicable to filters and the like and methods for manufacturing them.

[0041]

According to the present invention, it is possible to provide a temperature independent optical wavelength multiplexer / demultiplexer in which the demultiplexing wavelength is accurately controlled without deteriorating the demultiplexing characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an optical wavelength multiplexer / demultiplexer according to the present invention.

FIG. 2 is a diagram showing a refractive index control device.

FIG. 3 is a diagram for explaining a principle of wavelength division control.

FIG. 4 is a diagram showing an optical circuit of a conventional optical wavelength multiplexer / demultiplexer.

FIG. 5 is a diagram showing an optical circuit of a conventional optical wavelength multiplexer / demultiplexer.

FIG. 6 is a diagram showing an optical circuit of a conventional optical wavelength multiplexer / demultiplexer.

FIG. 7 is a diagram illustrating an optical circuit of a conventional optical wavelength multiplexer / demultiplexer.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input channel waveguide 2 input side slab waveguide 3 arrayed waveguide diffraction grating 4 arrayed waveguide 5 output side slab waveguide 6 output channel waveguide 7 substrate 8 groove 12 input optical fiber 31 KrF excimer laser 34 optical spectrum Analyzer 35 Mask 55 Refractive index control area

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Naoto Uezuka 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture F-term in Opto-Systems Research Laboratory, Hitachi Cable, Ltd. 2H047 KA03 KA12 KA12 LA19 MA05 PA11 RA08 TA31 TA42 TA44

Claims (8)

[Claims] 1. An arrayed waveguide grating composed of a plurality of channel waveguides, an input slab waveguide connected to the arrayed waveguide grating, and an output slab waveguide connected to the arrayed waveguide grating. In an optical wavelength multiplexer / demultiplexer having an optical circuit having a waveguide and a change amount of a demultiplexing wavelength substantially constant regardless of temperature, a refractive index control is performed on the input-side slab waveguide or the output-side slab waveguide. An optical wavelength multiplexer / demultiplexer, wherein a region is provided. 2. An arrayed waveguide grating comprising a plurality of channel waveguides, an input slab waveguide connected to the arrayed waveguide grating, and an output slab waveguide connected to the arrayed waveguide grating. An optical circuit having a waveguide, wherein a groove is formed in one of the input side slab waveguide, the output side slab waveguide or the arrayed waveguide diffraction grating, and a material forming the optical circuit in the groove. By inserting materials with different refractive index temperature gradients,
In an optical wavelength multiplexer / demultiplexer in which the amount of change in demultiplexed wavelength is substantially constant regardless of temperature, a refractive index control region is provided in the input slab waveguide or the output slab waveguide. An optical wavelength multiplexer / demultiplexer. 3. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein a core material in the refractive index control region has a larger refractive index than a core material other than the refractive index control region. 4. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein said refractive index control region is wedge-shaped. 5. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein the refractive index of the core material in the refractive index control region is controlled by light irradiation. 6. The optical wavelength multiplexing / demultiplexing device according to claim 1, wherein the refractive index of the core material in the refractive index control region is controlled by applying a stress based on a photoelastic effect. vessel. 7. The optical wavelength combining device according to claim 1, wherein the material constituting the optical circuit is a quartz-based material, and the core portion contains germanium. Waver. 8. The optical wavelength multiplexer / demultiplexer according to claim 5, wherein a carbon dioxide gas laser, an excimer laser, or an Ar ion laser is used as a light source used for the light irradiation.