JP2002311258A - Optical waveguide type diffraction grating element, multiplexing/demultiplexing module and optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide type diffraction grating element, which is short as a whole, reduces costs and improves reflection characteristics. SOLUTION: In an optical waveguide type diffraction grating element 100, diffraction gratings 113 based on refraction factor modulation are formed over a prescribed range W in a lengthwise direction in an optical fiber 110 of quartz adding GeO2 to a core area 111 including the center of an optical axis. The refraction factor modulation of each of diffraction gratings 113 is expressed as the sum of refraction factor modulations (1<=k<=K) in a fixed period Λk . A k-th refraction factor modulation forming area Wk is one part of the prescribed range W and the refraction factor modulation in the period Λk for reflecting the light of a reflection wavelength λk is formed. A k1 -st refraction factor modulation forming area Wk1 and a k2 -nd refraction factor modulation forming area Wk2 mutually overlap one part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type diffraction grating device having a diffraction grating formed by refractive index modulation over a predetermined range along the longitudinal direction of the optical waveguide, and includes this optical waveguide type diffraction grating device. The present invention relates to a multiplexing / demultiplexing module for multiplexing or demultiplexing light, and an optical transmission system including the multiplexing / demultiplexing module and performing optical transmission using multi-wavelength signal light.

[0002]

2. Description of the Related Art An optical waveguide type diffraction grating device has a diffraction grating formed by refractive index modulation over a predetermined range along the longitudinal direction of an optical waveguide (for example, an optical fiber). Light having a predetermined reflection wavelength of the guided light can be selectively reflected by the diffraction grating. In addition, the multiplexing / demultiplexing module including the optical waveguide type diffraction grating element can multiplex or demultiplex light by selectively reflecting light having a reflection wavelength by the optical waveguide type diffraction grating element. Wavelength division multiplexing (WDM) that performs optical transmission using a multi-wavelength signal light
ltiplexing) used in transmission systems and the like.

In general, an optical waveguide type diffraction grating device has a diffraction grating formed by refractive index modulation having a constant period Λ over a predetermined range along the longitudinal direction of the optical waveguide, and λ = 2N · Selectively reflects light with a reflection wavelength λ that satisfies the Bragg condition expressed by the following formula:
Transmits light of other wavelengths. Here, N is the average effective refractive index in the refractive index modulation region of the optical waveguide.

Further, by forming K diffraction gratings in different ranges along the longitudinal direction of the optical waveguide by forming K diffraction gratings with refractive index modulations having different periods Λ _k , the optical waveguide type diffraction grating device has K number of diffraction gratings. Light of each reflection wavelength λ _k (= 2N · Λ _k ) can be selectively reflected (1 ≦ k ≦ K,
K ≧ 2). However, such an optical waveguide type diffraction grating element that selectively reflects light having a plurality of reflection wavelengths has a plurality of diffraction gratings each formed in a different range along the longitudinal direction of the optical waveguide. As a result, the cost increases.

On the other hand, an optical waveguide type diffraction grating device in which a diffraction grating formed by refractive index modulation is formed over a predetermined range along the longitudinal direction of the optical waveguide, and a light guided through the optical waveguide is provided. Among them, one that selectively reflects light having a plurality of reflection wavelengths by a diffraction grating is known. For example,
Reference 1 "M. Ibsen, et al.," Sinc-Sampled Fiber Brag
g Gratings for Identical Multiple Wavelength Opera
tion ", IEEE Photon.Technol. Lett., Vol.10, No.6, p
842-844 (1998) ", the profile of refractive index modulation in the above-mentioned predetermined range is a sinc function type. Reference 2 “L.
A. Everall, et al., "Fabrication of multipassband m
oire resonators in fibers by the dual-phase-mask e
xposure method ", Opt. Lett., Vol.22, No.19, pp.147
The optical waveguide type diffraction grating element described in “3-1475 (1997)” is one in which a refractive index modulation with a period Λ _k (1 ≦ k ≦ K) is superimposed on the above-mentioned predetermined range. The optical waveguide type diffraction grating devices described in these documents have a short overall length and a low cost because the diffraction grating is formed by refractive index modulation only in one range along the longitudinal direction of the optical waveguide.

[0006]

However, the optical waveguide type diffraction grating device described in each of the above documents has the following problems. In other words, these optical waveguide type diffraction grating elements reflect light within a reflection wavelength band including the reflection wavelength λ _{k, but} have a reflectance outside the reflection wavelength band (ie, a transmission wavelength band through which light is to be transmitted). There is a peak wavelength band (side lobe), and since the reflectance in this side lobe is large, a part of the light having the wavelength to be transmitted is reflected.

Therefore, when a multiplexing / demultiplexing module including such an optical waveguide type diffraction grating element is used in a WDM transmission system, light having a wavelength to be transmitted but a part of light reflected by the optical waveguide type diffraction grating element is used. When the difference between the wavelengths of the light to be reflected and the light of the wavelength to be reflected which is actually reflected by the optical waveguide type diffraction grating element is small, crosstalk occurs and the reception error occurrence rate increases. .
In addition, since a part of the light having the wavelength to be transmitted is reflected by the optical waveguide type diffraction grating element, the light having the wavelength to be transmitted and actually transmitted by the optical waveguide type diffraction grating element causes a power loss. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an optical waveguide type diffraction grating element which is short as a whole, inexpensive, and has excellent reflection characteristics. It is another object of the present invention to provide a multiplexing / demultiplexing module including such an optical waveguide type diffraction grating element and an optical transmission system including the multiplexing / demultiplexing module.

[0009]

The optical waveguide type diffraction grating device according to the present invention has a diffraction grating formed by refractive index modulation over a predetermined range along the longitudinal direction of the optical waveguide.
Among the light guided through this optical waveguide, the reflection wavelength λ ₁ of the K wave
An optical waveguide type diffraction grating element that selectively reflects each light of λ _K by a diffraction grating, wherein a refractive index modulation in a predetermined range is _represented as a sum of refractive index modulations of a period Λ _k according to a reflection wavelength λ _k. is a refractive index modulation formed region of the k ₁ of the refractive index modulation of the periodic lambda _k1 is formed, the refractive index modulation forming areas of the k ₂ where the refractive index modulation of the periodic lambda _k2 is formed, a part from one another It is characterized by overlapping. In particular, it is preferable that the k ₁ -th refractive index modulation forming region and the k ₂ -th refractive index modulation forming region are partially shifted from each other by 1 mm or more. However, K ≧ 2, 1 ≦ k ≦ K, and 1 ≦ k
₁ <k ₂ ≦ K. This optical waveguide type diffraction grating element has a smaller maximum value of the reflectance in the transmission wavelength band than the conventional one. In addition, this optical waveguide type diffraction grating element
Since the diffraction grating formed by the refractive index modulation is formed only in one range along the longitudinal direction in the optical waveguide, the overall length is short and the cost is low.

Further, in the optical waveguide type diffraction grating device according to the present invention, the order of arrangement of the first to K-th refractive index modulation forming regions along the longitudinal direction of the optical waveguide is either ascending or descending with respect to the reflection wavelength. Preferably, it is not. In this case, the optical waveguide type diffraction grating element has a further smaller maximum value of the reflectance in the transmission wavelength band. Alternatively, since the optical waveguide type diffraction grating element has a small maximum value of the reflectance in the transmission wavelength band even if the displacement amount of each refractive index modulation forming region is small, the entire optical waveguide type diffraction grating element is further shorter and the cost is lower.

A multiplexing / demultiplexing module according to the present invention includes the above-described optical waveguide type diffraction grating element according to the present invention, and the K-wave reflection wavelengths λ _{1 to} λ _K are used by the optical waveguide type diffraction grating element. The light is selectively reflected to combine or split light. An optical transmission system according to the present invention is an optical transmission system that performs optical transmission using wavelength-multiplexed multi-wavelength signal light, and includes the multiplexing / demultiplexing module according to the present invention described above. A multi-wavelength signal light is multiplexed or demultiplexed by a module. According to this, even when the difference between the reflection wavelength and the transmission wavelength is small, crosstalk hardly occurs, the reception error occurrence rate is low, and the power loss of the light having the reflection wavelength is small.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, an embodiment of an optical waveguide type diffraction grating device according to the present invention will be described. FIG. 1 is an explanatory diagram of an optical waveguide type diffraction grating device 100 according to the present embodiment. This figure shows a sectional view of the optical waveguide type diffraction grating element 100 when cut along a plane including the optical axis. This optical waveguide type diffraction grating element 100 is composed of an optical fiber 11 serving as an optical waveguide.
The diffraction grating 113 is formed at 0. The optical fiber 110 is mainly composed of quartz glass,
GeO ₂ is added to the core region 111 including the center of the optical axis, and the core region 111 is surrounded by the clad region 1.
12 are provided. The refractive index modulation Δn over a predetermined range W along the longitudinal direction of the optical fiber 110
_The diffraction grating 113 is formed by _all .

When the z-axis is set along the longitudinal direction of the optical fiber 110, the refractive index modulation Δn of the diffraction grating 113
_all (z) is within a predetermined range W

(Equation 1)It is represented by the following formula. K is an integer of 2 or more, and the diffraction grating
Refractive index modulation Δn of 113 _all(z) is a constant period Λ_kRefraction
Rate modulation Δn_k(z) (1 ≦ k ≦ K). Λ
_kIs the reflection wavelength λ_kIs the period of the refractive index modulation according to φ
_kIs the k-th refractive index modulation Δn_kAt the origin (z = 0)
Phase. Δn (z) is the refractive index modulation Δn_kShake
The width, which is represented by a Gaussian function of the variable z. Note that this
In the figure, K = 4.

The k-th refractive index modulation forming region W _k (z _k
−Δz ≦ z ≦ z _k + Δz) is a part of the predetermined range W, and forms a refractive index modulation Δn _k (z) with a period Λ _k that reflects light having a reflection wavelength λ _k . Further, the k ₁ -th refractive index modulation forming region W _k1 (z _k1 −Δz ≦ z ≦ z _k1 + Δz) and the k-th refractive index modulation forming region W _k1
2 refractive index modulation forming region W _k2 (z _k2 −Δz ≦ z ≦ z _k2 +
Δz) partially overlap each other. In particular, the k ₁
Refractive index modulation forming area W _k1 and the refractive index modulation forming area W _k2 of the k _2, it is preferable that the overlap part offset from one another 1mm or more. That is,

(Equation 2) It is preferable that the following relationship be established. Here, k, is k ₁ and k _2, respectively, an arbitrary integer of 1 K or less, k ₁ ≠ k _2.

Further, the reflection wavelength lambda _k in the refractive index modulation forming area W _k of the k

(Equation 3) When the following relational expression is satisfied, the k-th refractive index modulation forming region W
_k is the center position z _k of

(Equation 4) The following relational expression may be satisfied. However, the optical fiber 11
It is preferable that the arrangement order of the refractive index modulation forming regions W _{1 to} W _K along the longitudinal direction of 0 is neither ascending order nor descending order with respect to the reflection wavelength (the relationship of the above formula (4) is not satisfied). .

FIG. 2 is a diagram showing the reflection characteristics of the optical waveguide type diffraction grating device 100 according to this embodiment. here,
K = 4. As shown in this figure, the reflection wavelength band is divided into four wavelength bands including each of the reflection wavelengths λ _{1 to} λ ₄ . The band other than the reflection wavelength band is a transmission wavelength band through which light is to be transmitted. Within this transmission wavelength band, there is a wavelength band (side lobe) where the reflectance peaks. Since the optical waveguide type diffraction grating element 100 according to the present embodiment has the above-described configuration, the maximum value of the reflectance in the side lobe in the transmission wavelength band is −20 dB or less (more preferably, −). 30dB
Below).

Such an optical waveguide type diffraction grating device 100
Then, when light of multiple wavelengths propagates through the core region of the optical fiber 110 and reaches the diffraction grating 113, of the light that has reached, the refractive index modulation Δn _k (1 ≦ k ≦ K) having a constant period Λ _k.
Wavelength λ _k (= 2
Light N · lambda _k) is reflected by the diffraction grating 113, the light of other wavelengths is transmitted through the diffraction grating 113. The optical waveguide type diffraction grating element 100 has a smaller reflectance in the transmission wavelength band than the conventional one because the respective refractive index modulation forming regions _Wk have the above relationship, and has a higher reflection characteristic. Is excellent. The optical waveguide type diffraction grating device 1
00 is a diffraction grating 113 with refractive index modulation Δn _{all in} only one range W in the optical waveguide direction in the optical fiber 110.
Are formed, so that the overall length is short and the cost is low.

Next, a method of manufacturing the optical waveguide type diffraction grating device 100 according to this embodiment will be described. First, a quartz optical fiber 110 in which GeO ₂ is added to the core region 111 is prepared. For this optical fiber 110,
For example, a wavelength 24 output from a KrF excimer laser light source through a phase mask having phase modulation of a predetermined period.
By irradiating 8nm ultraviolet laser beam, to form a refractive index modulation [Delta] n ₁ constant period lambda _1. While sequentially replacing the phase mask, by repeating such an ultraviolet laser beam irradiation, sequentially superimposed to form a refractive index modulation [Delta] n _k a constant period _{Λ k (1 ≦ k ≦ K} ). The arrangement of the respective phase masks in each of the K times of irradiation of the ultraviolet laser light is based on the respective refractive index modulation forming regions W _k.
Are arranged as described above.

Next, an example of the optical waveguide type diffraction grating device according to this embodiment will be described. Here, assuming K = 4, λ ₁ = 1531.116 nm and λ ₂ = 1532.6.
81 nm, λ ₃ = 1534.250 nm, λ ₄ = 153
5.822 nm. Amplitude [Delta] n of the refractive index modulation [Delta] n _k
The parameter a appearing in the function of (z) was 9.4 × 10 ⁻⁴ , the parameter b was 4.3 mm, and the parameter α was 2.5. Each phase φ _k was set to 0. Further, the length 2Δz of each refractive index modulation forming area W _k was 18 mm.

FIG. 3 is a diagram showing the reflection characteristics of the optical waveguide type diffraction grating device of the first embodiment. In the first embodiment,
Center position z _k of the refractive index modulation forming area W _k is

(Equation 5) And the reflection wavelengths were arranged in ascending or descending order with respect to the reflection wavelength. The displacement amount d of each refractive index modulation formation region W _k is 0 mm in FIG. 6A, 5 mm in FIG. 6B, and 6 mm in FIG.
mm, and 15 mm in FIG.

As can be seen from FIG. 3, when the displacement d is 0 mm (ie, when there is no displacement), the local maximum value of the reflectance in the side lobe in the transmission wavelength band is about -20 dB. there were. The displacement d is 5mm
In the case of, the maximum value of the reflectance in the side lobe in the transmission wavelength band was about -37 dB. When the displacement d was 6 mm, the maximum value of the reflectance in the side lobe in the transmission wavelength band was about -41 dB. When the displacement d was 15 mm, no side lobe was observed in the transmission wavelength band. Further, the transmittance at each reflection wavelength was −60 dB regardless of the value of the displacement amount.

FIG. 4 is a diagram showing the reflection characteristics of the optical waveguide type diffraction grating device of the second embodiment. In the second embodiment,
Center position z _k of the refractive index modulation forming area W _k is

(Equation 6) And the reflection wavelengths were arranged in an order other than the ascending order or the descending order with respect to the reflection wavelength. The position shift amount d of each refractive index modulation forming region W _k is 0 mm in FIG. 10A, 5 mm in FIG. 10B, 6 mm in FIG. 10C, and FIG. Then 15
mm.

As can be seen from FIG. 4, when the displacement d is 0 mm (that is, when there is no displacement), the maximum value of the reflectance in the side lobe in the transmission wavelength band is about -20 dB. there were. The displacement d is 5mm
In the case of, the maximum value of the reflectance in the side lobe in the transmission wavelength band was about -47 dB. When the displacement d was 6 mm, the maximum value of the reflectance in the side lobe in the transmission wavelength band was about -52 dB. When the displacement d was 15 mm, no side lobe was observed in the transmission wavelength band. Further, the transmittance at each reflection wavelength was −60 dB regardless of the value of the displacement amount.

FIG. 5 is a diagram showing the relationship between the maximum value of the reflectance in the side lobe in the transmission wavelength band and the displacement d in each of the first embodiment and the second embodiment. As can be seen from this figure, each refractive index modulation forming region W
_The larger the displacement amount d of _k is, the smaller the maximum value of the reflectance in the side lobe in the transmission wavelength band is. Even when the displacement d is 1 mm, the maximum value of the reflectance in the side lobe in the transmission wavelength band is small. Further, if the displacement amount d of each refractive index modulation forming region Wk is _{substantially} the same, the maximum value of the reflectance in the side lobe in the transmission wavelength band is larger in the case of the second embodiment than in the case of the first embodiment. Is smaller. If the maximum value of the reflectance in the side lobe in the transmission wavelength band is substantially the same, each refractive index modulation forming region W _k
May be smaller in the case of the second embodiment than in the case of the first embodiment. That is, the optical waveguide type diffraction grating device of the second embodiment, even a small position thread amount d of the refractive index modulation forming area W _k, since the maximum value of the reflectance within the transmission wavelength band is small, furthermore, the whole As short and cheap.

Next, an embodiment of the multiplexing / demultiplexing module according to the present invention will be described. The multiplexing / demultiplexing module of each embodiment described below includes the optical waveguide type diffraction grating element 100 according to the above embodiment. Hereinafter will be described as to transmit light of wavelength lambda _{2m + 1} While the diffraction grating device 100 reflects light of wavelength lambda _2m. Here, m is an integer of 1 or more and M or less, and each wavelength is

(Equation 7) It is assumed that the following relational expression is satisfied.

FIG. 6 is an explanatory diagram of the multiplexing / demultiplexing module 10 according to the first embodiment. This multiplexing / demultiplexing module 10
The optical circulator 210 is connected to one end of the optical waveguide type diffraction grating element 100, and the optical waveguide type diffraction grating element 10
The optical circulator 220 is connected to the other end of the zero. The optical circulator 210 is connected to the first terminal 21.
1, a second terminal 212 and a third terminal 213. The light input to the first terminal 211 is output from the second terminal 212 to the optical waveguide type diffraction grating device 100, and the second terminal 21
2 is output from the third terminal 213. Also,
The optical circulator 220 has a first terminal 221, a second terminal 222, and a third terminal 223.
The light input to 21 is output from the second terminal 222 to the optical waveguide type diffraction grating device 100, and the light input to the second terminal 222 is output from the third terminal 223.

In the multiplexing / demultiplexing module 10, when light having a wavelength λ _{2m + 1} is input to the first terminal 211 of the optical circulator 210, these lights are transmitted from the second terminal 212 of the optical circulator 210 to the optical waveguide type diffraction grating. The light is output to the element 100, transmitted through the optical waveguide type diffraction grating element 100, input to the second terminal 222 of the optical circulator 220, and output from the third terminal 223 of the optical circulator 220. The wavelength λ is applied to the first terminal 221 of the optical circulator 220.
_{When 2 m} of light is input, these lights are transmitted from the second terminal 222 of the optical circulator 220 to the optical waveguide type diffraction grating device 1.
00, is reflected by the optical waveguide type diffraction grating element 100, is input to the second terminal 222 of the optical circulator 220, and is output from the third terminal 223 of the optical circulator 220. That is, in this case, the multiplexing / demultiplexing module 10 operates as a multiplexer, and the optical circulator 21
And light of the wavelength lambda _{2m + 1} inputted to the first terminal 211 of 0, the wavelength inputted to the first terminal 221 of the optical circulator 220 lambda
Multiplexes the _2m of light, and outputs the thus multiplexed wavelengths lambda ₁ to [lambda] _2M from the third terminal 223 of the optical circulator 220. When the multiplexing / demultiplexing module 10 is used only as a multiplexer, the optical circulator 210 is unnecessary.

In the multiplexing / demultiplexing module 10, wavelengths λ ₁ to λ are applied to the first terminal 211 of the optical circulator 210.
_{When 2M} light is input, these lights are transmitted from the second terminal 212 of the optical circulator 210 to the optical waveguide type diffraction grating element 1.
Output to 00. And of these lights, the wavelength λ
_2m light is reflected by the optical waveguide type diffraction grating element 100,
The signal is input to the second terminal 212 of the optical circulator 210 and output from the third terminal 213 of the optical circulator 210. On the other hand, the light having the wavelength λ _{2m + 1} is transmitted through the optical waveguide type diffraction grating element 100, enters the second terminal 222 of the optical circulator 220, and receives the third terminal 2 of the optical circulator 220.
23. That is, in this case, the multiplexing / demultiplexing module 10 operates as a demultiplexer, and outputs the wavelengths λ ₁ to λ ₁ input to the first terminal 211 of the optical circulator 210.
λ _2M is demultiplexed and the light of wavelength λ _2m is
The light having the wavelength λ _{2m + 1} is output from the third terminal 223 of the optical circulator 220. When the multiplexing / demultiplexing module 10 is used only as a demultiplexer, the optical circulator 220 is unnecessary.

Further, the multiplexing / demultiplexing module 10 is
Works as a duplexer and also acts as a duplexer
As a result, optical ADM (Add-Drop Multiplexer)
Also works. That is, this multiplexing / demultiplexing module 10
Wave input to first terminal 211 of optical circulator 210
Long λ₁~ Λ_2MWavelength λ_2mLight circulator 2
Output (Drop) from the third terminal 213 of No. 10 and
Wavelength λ that carries other information _2mLight circulator 220
(Add) from the first terminal 221. And light sa
Wavelength λ input to the first terminal 211 of the calculator 210
₁~ Λ_2MWavelength λ of_{2m + 1}Light and an optical circulator
Wavelength λ input to the first terminal 221_2mWith the light of
Wave and its combined wavelength λ₁~ Λ_2MThe light of the light circu
The signal is output from the third terminal 223 of the generator 220.

FIG. 7 is an explanatory diagram of a multiplexing / demultiplexing module 20 according to the second embodiment. This multiplexing / demultiplexing module 20
The optical fiber 110A and the optical fiber 110B are optically coupled via optical couplers 114A and 114B, respectively, and a diffraction grating 113A is formed in a predetermined range of the optical fiber 110A between the optical coupler 114A and the optical coupler 114B. The diffraction grating 113B is formed in a predetermined range of the optical fiber 110B between the optical coupler 114A and the optical coupler 114B to form the optical waveguide diffraction grating 100B. I have. These optical waveguide type diffraction grating elements 100A and 10A
0B is the optical waveguide type diffraction grating element 10 described above.
It is equivalent to 0.

In the multiplexing / demultiplexing module 20, the optical fiber
The wavelength λ is applied to the first end 115A of the bus 110A._{2m + 1}Light enters
Then, these lights are branched by the optical coupler 114A.
And transmitted through the optical waveguide type diffraction grating elements 100A and 110B.
Then, they are multiplexed by the optical coupler 114B, and the optical fiber 1
It is output from the second end 116A of 10A. Optical fiber
The wavelength λ is applied to the second end 116B of the_2mLight enters
Then, these lights are branched by the optical coupler 114B.
And reflected by the optical waveguide type diffraction grating elements 100A and 110B.
Then, they are multiplexed by the optical coupler 114B, and the optical fiber 1
It is output from the second end 116A of 10A. That is,
In this case, the multiplexing / demultiplexing module 20 is used as a multiplexer.
Operates and enters the first end 115A of the optical fiber 110A.
Wavelength λ_{2m +1}And the second end 1 of the optical fiber 110B.
Wavelength λ input to 16B_2mWith the light of
Wavelength λ₁~ Λ_2MAt the second end of the optical fiber 110A.
Output from 116A.

Further, in the demultiplexing module 20, when light of wavelength lambda ₁ to [lambda] _2M to the first end 115A of the optical fiber 110A is inputted, these lights, the light is branched by the coupler 114A diffraction grating Element 100A, 110B
Output to Then, of these lights, the light having the wavelength λ _2m is reflected by the optical waveguide type diffraction grating elements 100A and 110B, multiplexed by the optical coupler 114A, and output from the first end 115B of the optical fiber 110B. On the other hand, the light having the wavelength λ _{2m + 1} is transmitted to the optical waveguide type diffraction grating elements 100A and 11A.
0B, is multiplexed by the optical coupler 114B, and output from the second end 116A of the optical fiber 110A. That is, in this case, the multiplexing / demultiplexing module 20
The first end 11 of the optical fiber 110A operates as a duplexer.
The wavelengths λ _{1 to} λ _2M input to 5A are demultiplexed, and light having a wavelength of λ _2m is output from the first end 115B of the optical fiber 110B.
The light having the wavelength λ _{2m + 1} is transmitted to the second end 116A of the optical fiber 110A.
Output more.

Further, the multiplexing / demultiplexing module 20 is
Works as a duplexer and also acts as a duplexer
Thus, the optical ADM also operates. That is,
Of the optical fiber 110A.
Wavelength λ input to end 115A ₁~ Λ_2MWavelength λ_2mof
Light is output from the first end 115B of the optical fiber 110B (Dr
op) and the wavelength λ that carries other information_2mThe light of the light
Input (Add) from the second end 116B of the fiber 110B.
You. Then, it enters the first end 115A of the optical fiber 110A.
Wavelength λ₁~ Λ_2MWavelength λ of_{2m + 1}Light and light
The wavelength λ input to the second end 116B of the fiber 110B_2mof
Multiplexed with light, and the multiplexed wavelength λ₁~ Λ_2MThe light of the light
The light is output from the second end 116A of the fiber 110A.

FIG. 8 is an explanatory diagram of a multiplexing / demultiplexing module 30 according to the third embodiment. This multiplexing / demultiplexing module 30
The optical fiber 110C and the optical fiber 110D in the optical coupler 114C are optically coupled via the optical coupler 114C.
A diffraction grating 113C is formed in a predetermined range of a fusion part with 0D, and thus, an optical waveguide type diffraction grating element 100C is obtained. This optical waveguide type diffraction grating element 100C is equivalent to the optical waveguide type diffraction grating element 100 described above. However,
The diffraction grating 113C is formed in both the core region of the optical fiber 110C and the core region of the optical fiber 110D.

In the multiplexing / demultiplexing module 30, when light having a wavelength λ _{2m + 1} is input to the first end 115C of the optical fiber 110C, these lights are converted into the optical waveguide type diffraction grating element 100C.
And is output from the second end 116C of the optical fiber 110C. Also, the second end 116 of the optical fiber 110D
When light of wavelength λ _2m is input to D, these lights are reflected by the optical waveguide type diffraction grating element 100C, and
It is output from the second end 116C of OC. That is, in this case, the multiplexing / demultiplexing module 30 operates as a multiplexer, and the light of the wavelength λ _{2m + 1} input to the first end 115C of the optical fiber 110C and the second end 11
6D is multiplexed with the light having the wavelength λ _2m and the multiplexed light having the wavelengths λ _{1 to} λ _2M is transmitted to the second end 1 of the optical fiber 110C.
Output from 16C.

Further, in the demultiplexing module 30, when light of wavelength lambda ₁ to [lambda] _2M to the first end 115C of the optical fiber 110C is input, these light reaches the diffraction grating device 100C. Then, of these lights, light having a wavelength of λ _2m is reflected by the optical waveguide type diffraction grating element 100C and output from the first end 115D of the optical fiber 110D. On the other hand, the light having the wavelength λ _{2m + 1} is transmitted through the optical waveguide type diffraction grating element 100C, and the second end 11 of the optical fiber 110C.
Output from 6C. That is, in this case, the multiplexing / demultiplexing module 30 operates as a demultiplexer, and the wavelengths λ _{1 to} λ _2M input to the first end 115C of the optical fiber 110C are used.
And the light having the wavelength λ _2m is converted into the first light of the optical fiber 110D.
The light of wavelength λ _{2m + 1} output from the end 115D is
Output from the second end 116C of 10C.

Further, the multiplexing / demultiplexing module 30 is
Works as a duplexer and also acts as a duplexer
Thus, the optical ADM also operates. That is,
Of the optical fiber 110C.
Wavelength λ input to end 115C ₁~ Λ_2MWavelength λ_2mof
Light is output from the first end 115D of the optical fiber 110D (Dr
op) and the wavelength λ that carries other information_2mThe light of the light
Input (Add) from the second end 116D of the fiber 110D.
You. Then, it enters the first end 115C of the optical fiber 110C.
Wavelength λ₁~ Λ_2MWavelength λ of_{2m + 1}Light and light
The wavelength λ input to the second end 116D of the fiber 110D_2mof
Multiplexed with light, and the multiplexed wavelength λ₁~ Λ_2MThe light of the light
The light is output from the second end 116C of the fiber 110C.

Each of the multiplexing / demultiplexing modules 10, 20, and 30 includes the optical waveguide type diffraction grating element 100 according to the above-described embodiment, and is therefore small and inexpensive. Further, in the optical waveguide type diffraction grating element 100, the transmittance in the reflection wavelength band is small, and
Since the reflectance outside the reflection wavelength band is small, even if the difference between the reflection wavelength λ _2m and the transmission wavelength λ _{2m + 1} is small, any of
Difficult crosstalk occurs, the reception error occurrence rate is low and is small power loss of the light having the reflection wavelength lambda _2m.

Next, an embodiment of the optical transmission system according to the present invention will be described. FIG. 9 is a schematic configuration diagram of the optical transmission system 1 according to the present embodiment. The optical transmission system 1 includes an optical fiber transmission line 5 between a transmitting station 2 and a relay station 3.
, The relay station 3 and the receiving station 4 are also connected by the optical fiber transmission line 6, and the relay station 3 is provided with a multiplexing / demultiplexing module 10.

The transmitting station 2 wavelength multiplexes the signal light of wavelengths λ _{1 to} λ _2M and sends out the signal light to the optical fiber transmission line 5. Relay station 3
Are the wavelengths λ _{1 to} λ _2M transmitted through the optical fiber transmission line 5.
, And are demultiplexed by the multiplexing / demultiplexing module 10 so that the signal light having the wavelength λ _{2m + 1} is
To transmit the signal light having the wavelength λ _2m to another optical fiber transmission line. In addition, the relay station 3 uses the multiplexing / demultiplexing module 10 to transmit the signal light having the wavelength λ _2m input through another optical fiber transmission line to the optical fiber transmission line 6. The receiving station 4
The signal light of wavelengths λ _{1 to} λ _2M that has propagated through the optical fiber transmission line 6 is input, and is demultiplexed into each wavelength and received.

The optical transmission system 1 multiplexes or demultiplexes signal light of wavelengths λ _{1 to} λ _2M using the multiplexing / demultiplexing module 10 including the optical waveguide type diffraction grating element 100 according to the present embodiment. Is what you do. Therefore, the reflection wavelength λ _2m
And the transmission wavelength λ _{2m + 1} is small, crosstalk is unlikely to occur, the reception error occurrence rate is low, and
The power loss of light having a reflection wavelength of λ _2m is small. Note that the multiplexing / demultiplexing module 20 or 3
0 may be provided.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, the optical waveguide type diffraction grating device of the above embodiment has a diffraction grating formed by refractive index modulation on an optical fiber which is an optical waveguide. However, the present invention is not limited to this, and a diffraction grating formed by refractive index modulation may be formed in an optical waveguide formed on a flat substrate.

[0044]

Effect of the Invention] above, as explained in detail, the optical waveguide type diffraction grating device according to the present invention, the refractive index modulation in the predetermined range, as the sum of the refractive index modulation of the periodic lambda _k corresponding to the reflected wavelength lambda _k represented, the refractive index modulation forming areas of the k ₁ of the refractive index modulation of the periodic lambda _k1 is formed, the refractive index modulation forming areas of the k ₂ where the refractive index modulation is formed of a period lambda _k2 is one with one another Overlapping. In particular, it is preferable that the k ₁ -th refractive index modulation forming region and the k ₂ -th refractive index modulation forming region are partially shifted from each other by 1 mm or more. However, K ≧ 2, 1 ≦ k ≦ K, and 1 ≦ k ₁ <k ₂ ≦ K. The optical waveguide type diffraction grating element thus configured has a smaller maximum value of the reflectance in the transmission wavelength band than the conventional one. In addition, this optical waveguide type diffraction grating element has a diffraction grating formed by refractive index modulation only in one range along the longitudinal direction of the optical waveguide, so that it is short as a whole and inexpensive.

Further, the first to the first along the longitudinal direction of the optical waveguide.
It is preferable that the arrangement order of the respective K-th refractive index modulation forming regions is not ascending or descending with respect to the reflection wavelength. In this case, this optical waveguide type diffraction grating element
The maximum value of the reflectance in the transmission wavelength band is even smaller.
Alternatively, since the optical waveguide type diffraction grating element has a small maximum value of the reflectance in the transmission wavelength band even if the displacement amount of each refractive index modulation forming region is small, the entire optical waveguide type diffraction grating element is further shorter and the cost is lower.

A multiplexing / demultiplexing module according to the present invention includes the above-described optical waveguide type diffraction grating element according to the present invention, and the K-wave reflection wavelengths λ _{1 to} λ _K are respectively transmitted by the optical waveguide type diffraction grating element. Selectively reflects to combine or split light. An optical transmission system according to the present invention is an optical transmission system that performs optical transmission using wavelength-multiplexed multi-wavelength signal light, and includes the multiplexing / demultiplexing module according to the present invention described above. The multi-wavelength signal light is multiplexed or demultiplexed by the module. According to this, even when the difference between the reflection wavelength and the transmission wavelength is small, crosstalk hardly occurs, the reception error occurrence rate is low, and the power loss of the light having the reflection wavelength is small.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an optical waveguide type diffraction grating device according to an embodiment.

FIG. 2 is a diagram showing reflection characteristics of the optical waveguide type diffraction grating element according to the embodiment.

FIG. 3 is a view showing the reflection characteristics of the optical waveguide type diffraction grating device of the first embodiment.

FIG. 4 is a view showing the reflection characteristics of the optical waveguide type diffraction grating device of the second embodiment.

FIG. 5 is a diagram illustrating a relationship between a local maximum value of a reflectance in a side lobe in a transmission wavelength band and a displacement amount d in each of the first embodiment and the second embodiment.

FIG. 6 is an explanatory diagram of the multiplexing / demultiplexing module according to the first embodiment.

FIG. 7 is an explanatory diagram of a multiplexing / demultiplexing module according to a second embodiment.

FIG. 8 is an explanatory diagram of a multiplexing / demultiplexing module according to a third embodiment.

FIG. 9 is a schematic configuration diagram of an optical transmission system according to the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical transmission system, 2 ... Transmitting station, 3 ... Relay station, 4 ... Receiving station, 5, 6 ... Optical fiber transmission line, 10, 20, 30 ...
Multiplexing / demultiplexing module, 100 ... optical waveguide type diffraction grating element,
110: optical fiber (optical waveguide), 111: core region,
112: cladding region, 113: diffraction grating, 210, 2
20 ... optical circulator.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Satoshi Inoue 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries Co., Ltd. Yokohama Works (72) Inventor Manabu Shiozaki 1, Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Ki Kogyo Co., Ltd. Yokohama Works F-term (reference) 2H047 LA02 LA19 RA00 TA11 2H050 AC72 AC82 AC84 AD03 5K002 BA05 DA02 FA01

Claims (5)

[Claims] [Claim 1] A diffraction grating according to the refractive index modulation over a predetermined range along the longitudinal direction of the optical waveguide is formed, reflection wavelength lambda ₁ of the K-wave of the light guided through the optical waveguide to [lambda] _K
(Where K ≧ 2) an optical waveguide type diffraction grating element for selectively reflecting each light by the diffraction grating, wherein the refractive index modulation in the predetermined range is a reflection wavelength λ _k
Expressed as the sum of the refractive index modulation of the periodic lambda _k corresponding to (although, 1 ≦ k ≦ K), and refractive index modulation forming areas of the k ₁ where the refractive index modulation of the periodic lambda _k1 is formed, the period lambda _k2 K ₂ in which the refractive index modulation of
And a refractive index modulation forming region partially overlaps with each other (where 1 ≦ k ₁ <k ₂ ≦ K). 2. A light waveguide as claimed in claim 1 wherein said the first k ₁ of the refractive index modulation forming region and the refractive index modulation forming areas of the k ₂ are partially overlapped offset 1mm or more from each other Type diffraction grating element. 3. The optical waveguide according to claim 1, wherein said first optical waveguide extends along a longitudinal direction of said optical waveguide.
2. The optical waveguide type diffraction grating device according to claim 1, wherein the order of arrangement of each of the K-th refractive index modulation forming regions is not any of ascending order and descending order with respect to the reflection wavelength. 4. An optical waveguide type diffraction grating device according to claim 1, wherein said optical waveguide type diffraction grating device selectively reflects light of each of said K-wave reflection wavelengths λ _{1 to} λ _K , Multiplexing / demultiplexing module. 5. An optical transmission system for performing optical transmission using wavelength-multiplexed multi-wavelength signal light, comprising: the multiplexing / demultiplexing module according to claim 4, wherein said multiplexing / demultiplexing module uses said multi-wavelength signal. An optical transmission system characterized by multiplexing or demultiplexing light.