JP2600507B2 - Optical multiplexer / demultiplexer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit used for an input / output terminal of a wavelength division multiplexing optical communication system.

[0002]

2. Description of the Related Art In recent years, various types of optical multiplexer / demultiplexers have been proposed and studied as key devices of a wavelength division multiplexing optical communication system. An optical multiplexer / demultiplexer using a diffraction grating is expected to be used in high-density wavelength division multiplexing optical communication having a narrow wavelength interval and a large number of multiplexes. However, there is generally no high-efficiency diffraction grating in a wide wavelength range, and an optical multiplexer / demultiplexer using two or more diffraction gratings having different spectral characteristics and a dielectric filter for separating each of the application wavelength ranges has been proposed.

An example of the above-described conventional optical multiplexer / demultiplexer will be described below with reference to the drawings.

FIG. 4 shows a configuration of a conventional optical multiplexer. In FIG. 4, 41 is an input fiber, 42a to 42a.
f is a light receiving fiber, 43 is a lens, 44 is a first diffraction grating, 45 is a second diffraction grating, and 46 is a dielectric filter.

The operation of the optical multiplexer / demultiplexer configured as described above will be described below. In the description, the operation of the optical demultiplexer is performed, and the light traveling direction of the optical demultiplexer may be reversed. The wavelength lambda _a from the short wavelength _{side, λ b, λ c, λ} d, and λ _e, λ _f, a dielectric filter 4
6 is a wavelength lambda _a to [lambda] _c transmitted, the wavelength lambda _d to [lambda] _f and has a characteristic of reflecting.

The wavelength λ _a emitted from the input fiber 41 is
The wavelength multiplexed light of λ _f is transmitted through the lens 43 by the dielectric filter 46, and the light of wavelengths λ _a to λ _f is transmitted and enters the first diffraction grating 44. The incident light enters the first diffraction grating 44.
Filter 46 and the lens 4
3, the light receiving fibers 42a to 42c are respectively coupled. On the other hand, the wavelength λ _d reflected by the dielectric filter 46
Light to [lambda] _f is through the lens 43 and reflected again by the dielectric filter 46 receives the wavelength dispersion enters the second diffraction grating 45, is coupled to the receiving fiber 42D～42f. In this way, the wavelength-multiplexed light is split.

[0007]

However, the above configuration has a complicated configuration in which a dielectric filter 46 is inserted between the lens 43 and the first diffraction grating 44. For any wavelength, two dielectric filters 46
Since the light is transmitted or reflected twice, the transmission loss or reflection loss of the dielectric filter 46 is squared and affected, and the insertion loss of the entire optical multiplexer / demultiplexer is reduced.

The present invention has been made in view of the above problems, and provides an optical multiplexer / demultiplexer that can be used in a wide wavelength range without inserting a dielectric filter.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, an optical multiplexer / demultiplexer according to the present invention comprises two types of diffraction gratings, lenses, and a plurality of optical fibers having different spectral characteristics. The structure is such that light from an optical fiber is wavelength-dispersed by two diffraction gratings via a lens and desired light is coupled to a plurality of other optical fibers, and is reflected by the first diffraction grating without being subjected to wavelength dispersion. The light to be dispersed is wavelength-dispersed by the second diffraction grating. A diffraction element having the same structure as the first diffraction grating and having a dielectric layer provided on the upper surface of the grating can also be used as the second diffraction grating.

[0010]

According to the present invention, the above-described structure can be used with a simple structure without using a dielectric filter, can be used in a wide wavelength range, and has low loss. In addition, it is not necessary to use two types of diffraction gratings by attaching a dielectric to the second diffraction grating on the upper surface of the first diffraction grating. This configuration is effective, for example, in the case where wavelength-division multiplexed light is simultaneously transmitted in two wavelength bands of 0.8 μm and 1.3 μm.

[0011]

An optical multiplexer / demultiplexer according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of an optical multiplexer / demultiplexer according to a first embodiment of the present invention. In FIG. 1, 11 is an input fiber, 12a to 12f are light receiving fibers, 13 is a lens, 14 is a first diffraction grating, and 15 is a second diffraction grating. Here, the operation of the optical demultiplexer will be described. At this time, the wavelengths are λ _a , λ _b , λ _c , λ _d , λ _e , and λ _f from the short wave side.
And FIG. 3 is a conceptual diagram showing the relationship between light of each wavelength. In FIG. 3, 32a to 32f _denote light having wavelengths λ _{a to} λ _f , respectively, 38 denotes a wavelength range in which the first diffraction grating receives chromatic dispersion, and 39 denotes a wavelength range in which no chromatic dispersion is received and total reflection occurs. ing.

The operation of the optical multiplexer / demultiplexer configured as described above will be described below with reference to FIGS.

Light multiplexed at wavelengths λ _a to λ _f from the input fiber 11 is passed through a lens 13 to a first diffraction grating 14.
Incident on. Since the first diffraction grating 14 has a wavelength dispersion capability for the light in the wavelength range 38, the light of the wavelengths λ _{a to} λ _c receives the chromatic dispersion and passes through the lens 13 to the light receiving fibers 12 a to 1.
2c. On the other hand, light of wavelengths λ _{d to} λ _{f in} the wavelength region 39 is totally reflected by the first diffraction grating 14 without being wavelength-dispersed. Totally reflected light enters the second diffraction grating 15,
Upon receiving the wavelength dispersion, the light is totally reflected again by the first diffraction grating 14 and coupled to the light receiving fibers 12d to 12f via the lens 13. The wavelength lambda ₁ that receives the chromatic dispersion in the first diffraction grating 14, ₂ wavelength lambda to be totally reflected, the lattice spacing of the first diffraction grating 14 as d, meet the λ ₂ -λ _1/2> d Just do it. For example, a diffraction grating having the number of grating grooves of 1200 / mm as the first diffraction grating 14, a wavelength range 38 of 0.8 μm band, and a diffraction grating of the number of grating grooves 770 / mm as the second diffraction grating 15. Used, wavelength range 3
9 will satisfy the λ ₂ -λ _1/2> d by performing wavelength multiplexing, such as a 1.3μm band.

As described above, according to this embodiment, the filter is inserted by dispersing the wavelength in the wavelength region that is totally reflected without undergoing wavelength dispersion by the first diffraction grating by the second diffraction grating. The structure can be simplified, the loss can be reduced, and the band can be widened without any problem.

Next, an optical multiplexer / demultiplexer according to a second embodiment of the present invention will be described with reference to the drawings.

FIG. 2 shows a configuration diagram of an optical multiplexer / demultiplexer according to a second embodiment of the present invention. In FIG. 2, 21 is an input fiber, 22a to 22f are light receiving fibers, 23 is a lens, 24a and 24b are diffraction gratings, 26 is a dielectric,
Reference numeral 7 denotes a diffraction element in which a dielectric 26 is provided on the diffraction grating 24b. FIG. 3 is a conceptual diagram showing the relationship between light of each wavelength. In FIG. 3, reference numerals 32a to 32f _denote light beams having wavelengths λ _{a to} λ _f , respectively, 38 denotes a wavelength region which receives chromatic dispersion by the diffraction grating 24a, and 39 denotes a wavelength region which receives no chromatic dispersion and undergoes total reflection. ing.

The operation of the optical multiplexer / demultiplexer configured as described above will be described below with reference to FIGS.

Light multiplexed at wavelengths λ _a to λ _f from the input fiber 21 enters the diffraction grating 24 a via the lens 23. Since the diffraction grating 24a has the wavelength dispersion capability for light in the wavelength region 38, light of wavelength lambda _a to [lambda] _c is respectively coupled to the receiving fiber 12a~12c through the lens receiving wavelength dispersion. On the other hand, light of wavelengths λ _{d to} λ _{f in} the wavelength range 39 is totally reflected without being wavelength-dispersed by the diffraction grating 24a. The total reflected light enters a diffraction element 27 having a dielectric 26 provided on a diffraction grating 24b, receives wavelength dispersion, and
Is totally reflected again by the light receiving fiber 1 through the lens 23.
2d to 12f, respectively. Let n be the refractive index of the dielectric
Tosureba wavelength lambda ₁ in the wavelength range 38, if they meet the wavelength lambda ₂ at 1-1 / 2n> d / λ ₂ of the wavelength range 39, light of wavelength lambda _d to [lambda] _f by the diffraction element 27 Receives chromatic dispersion. For example, as the diffraction gratings 24a and 24b, a diffraction grating having the number of grating grooves of 1200 / mm is used, and the refractive index of the dielectric is about 1.5 when glass is used, the wavelength range 38 is the 0.8 μm band, and the wavelength range 39 is by performing the wavelength multiplexing as a 1.3μm band will satisfy the _{λ 2 -λ 1/2> d} .

As described above, according to the present embodiment, light in a wavelength region that is totally reflected without undergoing wavelength dispersion by the diffraction grating is converted into a wavelength by the diffraction element in which a dielectric layer is provided on the upper surface of the same type of diffraction grating. By dispersing, the structure can be simplified without inserting a filter, and low loss and wide band can be achieved by using the same kind of diffraction grating. Desirably, the loss can be further reduced by providing an antireflection film on the upper surface of the dielectric.

In the first and second embodiments, the diffraction grating is merely used. However, if a Fourier diffraction grating having high efficiency and little polarization dependence is used, the loss can be reduced.

[0022]

As described above, according to the present invention, light in a wavelength range that is not wavelength-dispersed by the first diffraction grating is wavelength-dispersed by the second diffraction grating, thereby achieving low loss without inserting a dielectric filter. Broadband optical multiplexing / demultiplexing is possible. Especially 0.8
It is useful for wavelength-division multiplexed optical communication with a large number of multiplexes in the μm band and the 1.3 μm band.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of an optical multiplexer / demultiplexer according to a second embodiment of the present invention.

FIG. 3 is a conceptual diagram showing a relationship between wavelengths λ _{a to} λ _f in one embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical multiplexer / demultiplexer according to a conventional example.

[Explanation of symbols]

11, 21, 41 Input fibers 12a to 12f, 22a to 22f, 42a to 42f Light receiving fibers 13, 23, 43 Lens 14, 44 First diffraction grating 15, 45 Second diffraction grating 24a, 24b Diffraction grating 26 Dielectric Layer 46 Dielectric filter

Claims (9)

(57) [Claims] An optical fiber comprising two types of diffraction gratings having different spectral characteristics, a lens, and a plurality of optical fibers, wherein one of the plurality of optical fibers transmits light from the one optical fiber through the lens. Receives the wavelength dispersion by the diffraction grating, and couples to the other plurality of optical fibers via the lens. The light incident on the first diffraction grating of the two diffraction gratings has a diffraction order. Only the wavelength region where the light is subjected to wavelength dispersion, the other light becomes reflected light, enters the second diffraction grating, receives the wavelength dispersion, and is reflected again by the first diffraction grating. Optical multiplexer / demultiplexer. 2. The wavelength interval of the first diffraction grating is d, the wavelength of the first diffraction grating that receives chromatic dispersion is λ ₁ , and the wavelength of the second diffraction grating that receives chromatic dispersion is λ ₂ , where λ ₂ − 2. The optical multiplexer / demultiplexer according to claim _{1, wherein} λ 1/2> d is satisfied. 3. The optical multiplexer / demultiplexer according to claim 1, wherein a Fourier diffraction grating is used as the first diffraction grating and the second diffraction grating. 4. A method according to claim 1, wherein the first diffraction grating receives two light beams.
2. The method according to claim 1, wherein the first and second diffraction orders have no diffraction order.
An optical multiplexer / demultiplexer as described in the above. 5. A diffraction element, wherein the second diffraction grating is of the same type as the first diffraction grating, and a diffraction element having a dielectric layer provided on the grating upper surface of the first diffraction grating is used. The optical multiplexer / demultiplexer according to claim 1. 6. The optical system according to claim 1, wherein the refractive index of the dielectric layer is n, and the wavelength of light reflected by the first diffraction grating is λ ₂ , wherein 1-1 / 2n> d / λ ₂ is satisfied. 5. The optical multiplexer / demultiplexer according to 5. 7. The optical multiplexer / demultiplexer according to claim 5, wherein an antireflection film is provided on the upper surface of the dielectric. 8. The first diffraction grating has two incident light beams.
6. The method according to claim 5, wherein the diffraction order is not higher than the first order.
An optical multiplexer / demultiplexer as described in the above. 9. The optical multiplexer / demultiplexer according to claim 5, wherein a Fourier diffraction grating is used as the first diffraction grating.