JPH04282603A - Optical multiplexer/demultiplexer - Google Patents

Abstract

PURPOSE:To obtain the low-loss optical multiplexer/demultiplexer which execute optical multiplexing and demultiplexing in a wide wavelength region with simple constitution without using dielectric filters. CONSTITUTION:This optical multiplexer/demultiplexer consists of two kinds of diffraction gratings 14, 15 varying in spectral characteristics, a lens 13 and plural pieces of optical fibers 11, 12a to 12f and is constituted to disperse the wavelengths of light of wavelengths lambdaa to lambdaf from one piece of optical fiber 11 with the two diffraction gratings 14, 15 via the lens 13 and to couple the desired light to plural pieces of the other optical fibers 12a to 12f. The light of the wavelength regions to lambdad, lambdaf reflected without being wavelength-dispersed by the 1st diffraction grating 14 is wavelength-dispersed by the 2nd diffraction grating 15.

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 at the input/output end of a wavelength division multiplexing optical communication system.

0002

2. Description of the Related Art In recent years, various forms of optical multiplexers and demultiplexers have been proposed and studied as key devices for wavelength division multiplexing optical communication systems. Optical multiplexers/demultiplexers using diffraction gratings are seen as promising for high-density wavelength division multiplexing optical communications with narrow wavelength spacing and a large number of multiplexes. However, there are generally no highly efficient diffraction gratings over a wide wavelength range, and an optical multiplexer/demultiplexer using two or more diffraction gratings with different spectral characteristics and a dielectric filter that separates each applicable wavelength range has been proposed.

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

FIG. 4 shows the configuration of a conventional optical multiplexer. In FIG. 4, 41 is an input fiber, 42a to 42
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 explained below. In the explanation, the operation of an optical demultiplexer will be explained, and for an optical multiplexer, the traveling direction of light may be reversed. It is also assumed that the wavelengths are λa, λb, λc, λd, λe, and λf from the short wavelength side, and that the dielectric filter 46 has a characteristic of transmitting wavelengths λa to λc and reflecting wavelengths λd to λf.

The wavelength λa~ emitted from the input fiber 41
The wavelength-multiplexed light of λf passes through the lens 43 and the light of wavelengths λa to λf is transmitted through the dielectric filter 46 and enters the first diffraction grating 44 . The incident light passes through the first diffraction grating 4
4, and are coupled to the light receiving fibers 42a to 42c via a dielectric filter 46 and a lens 43, respectively. On the other hand, the wavelength λ reflected by the dielectric filter 46
The light of d to λf enters the second diffraction grating 45, undergoes wavelength dispersion, is reflected again by the dielectric filter 46, and is coupled to the light receiving fibers 42d to 42f via the lens 43. The wavelength-multiplexed light is thus demultiplexed.

[0007]

[Problems to be Solved by the Invention] 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, and the multiplexed light is For any wavelength, two dielectric filters 46 are used.
Since the light is transmitted or reflected twice, the transmission loss or reflection loss of the dielectric filter 46 is multiplied by a factor of 2, resulting in a reduction in the insertion loss of the optical multiplexer/demultiplexer as a whole.

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

[0009]

[Means for Solving the Problems] In order to solve the above problems, the optical multiplexer/demultiplexer of the present invention consists of two types of diffraction gratings with different spectral characteristics, lenses, and a plurality of optical fibers, one of which The light from the optical fiber is wavelength-dispersed by two diffraction gratings via a lens, and the desired light is coupled to the other multiple optical fibers, and then reflected by the first diffraction grating without undergoing wavelength dispersion. The wavelength of the light is wavelength-dispersed by the second diffraction grating. Further, it is also possible to use a diffraction element in which the second diffraction grating is the same as the first diffraction grating and a dielectric layer is provided on the upper surface of the grating.

0010

[Operation] The present invention has a simple structure without using a dielectric filter, can be used in a wide wavelength range, and has low loss. Further, by bringing a dielectric material into close contact with the upper surface of the first diffraction grating in the second diffraction grating, it is no longer necessary to use two types of diffraction gratings. For example, this configuration is 0.
This is effective when transmitting simultaneously wavelength-multiplexed light in two wavelength bands, 8 μm and 1.3 μm.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 in 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, we will explain the operation of an optical demultiplexer, and the wavelengths at that time are λa, λb, λc, λd, λe from the short wavelength side.
, λf. FIG. 3 shows a conceptual diagram showing the relationship between light of each wavelength. In FIG. 3, 32a to 32f are lights with wavelengths λa to λf, respectively, 38 indicates a wavelength range that undergoes chromatic dispersion in the first diffraction grating, and 39 indicates a wavelength range that does not undergo chromatic dispersion and is totally reflected. .

The operation of the optical multiplexer/demultiplexer constructed as described above will be explained below with reference to FIGS. 1 and 3.

The wavelength-multiplexed light from the input fiber 11 with wavelengths λa to λf passes through the lens 13 to the first diffraction grating 1.
4. Since the first diffraction grating 14 has a wavelength dispersion ability for light in the wavelength range 38, light with wavelengths λa to λc undergoes chromatic dispersion and passes through the lens 13 to the receiving fiber 12a.
~12c, respectively. On the other hand, light having wavelengths λd to λf in the wavelength range 39 is not wavelength-dispersed by the first diffraction grating 14 and is totally reflected. The totally reflected light enters the second diffraction grating 15, undergoes wavelength dispersion, is totally reflected again by the first diffraction grating 14, and passes through the lens 13 to the receiving fibers 12d to 12.
f respectively. Assuming that the wavelength that undergoes wavelength dispersion in the first diffraction grating 14 is λ1, the wavelength that is totally reflected is λ2, and the grating interval of the first diffraction grating 14 is d, it is sufficient to satisfy λ2−λ1/2>d. For example, a diffraction grating with a grating groove number of 1200/mm is used as the first diffraction grating 14, a diffraction grating with a wavelength range 38 in the 0.8 μm band, and a diffraction grating with a grating groove number of 770/mm as the second diffraction grating 15. wavelength range 3
If wavelength multiplexing is performed such that 9 is in the 1.3 μm band, λ2-
This satisfies λ1/2>d.

As described above, according to this embodiment, the filter is inserted by dispersing the wavelength of light in the wavelength range that is totally reflected without undergoing wavelength dispersion in the first diffraction grating in the second diffraction grating. The configuration is simple, low loss, and wideband can be achieved without any interference.

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

FIG. 2 shows a configuration diagram of an optical multiplexer/demultiplexer in a second embodiment of the present invention. In FIG. 2, 21 is an input fiber, 22a to 22f are receiving fibers, 23 is a lens, 24a and 24b are diffraction gratings, 26 is a dielectric material, 2
7 is a diffraction element in which a dielectric material 26 is provided on a diffraction grating 24b. FIG. 3 shows a conceptual diagram showing the relationship between light of each wavelength. In FIG. 3, 32a to 32f are lights with wavelengths λa to λf, respectively, and 38 is a diffraction grating 24a in this case.
39 indicates a wavelength range that undergoes chromatic dispersion, and 39 indicates a wavelength range that does not undergo chromatic dispersion and undergoes total reflection.

The operation of the optical multiplexer/demultiplexer constructed as described above will be explained below with reference to FIGS. 2 and 3.

Light that has been wavelength-multiplexed into wavelengths λa to λf from the input fiber 21 enters the diffraction grating 24a via the lens 23. Since the diffraction grating 24a has wavelength dispersion ability for light in the wavelength range 38, the light in wavelengths λa to λc undergoes wavelength dispersion and is coupled to the light receiving fibers 12a to 12c via lenses, respectively. On the other hand, the wavelength λd~λ in the wavelength range 39
The light of f is not wavelength-dispersed and is totally reflected by the diffraction grating 24a. The totally reflected light enters the diffraction element 27 in which a dielectric material 26 is provided on the diffraction grating 24b, undergoes wavelength dispersion, is totally reflected again by the diffraction grating 24a, and is coupled to the light receiving fibers 12d to 12f via the lens 23, respectively. do. If the refractive index of the dielectric is n, then if the wavelength λ1 in the wavelength range 38 and the wavelength λ2 in the wavelength range 39 satisfy 1-1/2n>d/λ2, then the diffraction element 27 can measure the wavelengths λd to λf. Light undergoes wavelength dispersion. For example, using a diffraction grating with a grating groove count of 1200/mm as the diffraction gratings 24a and 24b,
Assuming that the dielectric has a refractive index of about 1.5 using glass, if wavelength multiplexing is performed such that the wavelength range 38 is a 0.8 μm band and the wavelength range 39 is a 1.3 μm band, λ2−λ1/2>d is obtained. It will be fulfilled.

As described above, according to this embodiment, the light in the wavelength range that is totally reflected without being subjected to wavelength dispersion by the diffraction grating is converted into wavelengths by the diffraction element provided with the dielectric layer on the top surface of the same type of diffraction grating. By dispersing, the configuration is simple without inserting a filter, and low loss and wide band can be achieved using the same type of diffraction grating. Preferably, an antireflection film is provided on the upper surface of the dielectric to further reduce the loss.

In the first and second embodiments, a simple diffraction grating is used, but if a Fourier diffraction grating with particularly high efficiency and less polarization dependence is used as the diffraction grating, the loss can be further reduced.

[0022]

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

[Brief explanation of the drawing]

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

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

FIG. 3 is a conceptual diagram showing the relationship between wavelengths λa to λf in an embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical multiplexer/demultiplexer in a conventional embodiment.

[Explanation of symbols]

11, 21, 41 input fibers 12a to 12f, 22a to 22f, 42a to 42f
Light receiving fiber 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)

[Claims] 1. A diffraction grating having two types of different spectral characteristics, a lens, and a plurality of optical fibers, the light passing from one optical fiber of the plurality of optical fibers through the lens being of the two types. A configuration is adopted in which the light is subjected to wavelength dispersion by the diffraction grating and is coupled to the other plurality of optical fibers via the lens, and the light incident on the first diffraction grating of the two diffraction gratings has a diffraction order. Only the wavelength range in which the wavelength range corresponds to the first diffraction grating undergoes wavelength dispersion, and the other light becomes reflected light, enters the second diffraction grating, undergoes wavelength dispersion, and is reflected again by the first diffraction grating. Optical multiplexer/demultiplexer. 2. The grating spacing of the first diffraction grating is d, and the first
Let the wavelength that undergoes wavelength dispersion in the first diffraction grating be λ1, and the wavelength that undergoes wavelength dispersion in the second diffraction grating as λ2, then λ2 - λ1
The optical multiplexer/demultiplexer according to claim 1, which satisfies /2>d. 3. The optical multiplexer/demultiplexer according to claim 1, wherein Fourier diffraction gratings are used for the first diffraction grating and the second diffraction grating. 4. The optical multiplexer/demultiplexer according to claim 1, wherein the first diffraction grating does not have a second or higher diffraction order for the incident light. 5. The second diffraction grating is of the same type as the first diffraction grating, and a diffraction element is used in which a dielectric layer is provided on the upper surface of the first diffraction grating. The optical multiplexer/demultiplexer according to claim 1. 6. The refractive index of the dielectric layer is n, and the wavelength of the light reflected by the first diffraction grating is λ2, satisfying 1-1/2n>d/λ2. optical multiplexer/demultiplexer. 7. The optical multiplexer/demultiplexer according to claim 5, wherein an antireflection film is provided on the upper surface of the dielectric. 8. The optical multiplexer/demultiplexer according to claim 5, wherein the first diffraction grating does not have a second or higher diffraction order for the incident light. 9. The optical multiplexer/demultiplexer according to claim 5, wherein a Fourier diffraction grating is used as the first diffraction grating.