JPH10148792A - Wavelength multiplexing light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a function efficiently multiplexing plural lights of narrow intervals between wavelengths and different wavelengths by providing a wavelength band selector and multiplexing the wavelength of light from pieces of light sources so as to output the wavelength-multiplexed light from an output port. SOLUTION: Light outputted from a light source 111 enters the port 1 of an optical circulator 20, is outputted from a port 2 to be reflected by a band reflecting filter 31 and is inputted to the port 2 again. Light from a light source 112 passes through the filter 31 and inputted to the port 2 of the circulator 20. Consequently, the synthesized light of output light from the light sources 111 and 112 is inputted to the port 2 of the circulator 20. Light from a light source 113 passed through a band reflecting filter 32 and is outputted to the port 4 from the port 3. After all, output light of the light sources 111 to 113 are superimposed and outputted from the port 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The wavelength multiplex light source of the present invention is a transmission light source applied to an optical communication system, and more particularly to a wavelength multiplex light source for transmitting a plurality of signal lights having different wavelengths using one optical fiber. The present invention relates to a transmission light source for an optical communication system.

[0002]

2. Description of the Related Art Conventionally, as main technical means for multiplexing light having different wavelengths, a wavelength combining coupler that multiplexes light using a wavelength difference of light and multiplexing using a difference in polarization direction of light are used. There is a method using a polarization combining coupler or an optical branching coupler.

[0003] Wavelength combining couplers are formed by melting two optical fibers with their cores brought close to each other (optical fiber fusion type WDM coupler), or by forming a dielectric multilayer film coated on a glass substrate. One using wavelength dependency of transmittance (reflection) and one using optical coupling phenomenon between two optical waveguides arranged close to each other on an optical substrate (waveguide WDM coupler) Etc.

As the polarization combining coupler, there are basically those using a prism made of a birefringent optical material and those utilizing the birefringence of the transmittance or the reflectance of a dielectric multilayer film coated on glass. In addition, a birefringent prism is arranged in the light output unit so that the phase difference between the two multiplexed lights becomes an integral multiple of π, and the multiplexed light is output as linearly polarized light. (For example, see Japanese Patent Laid-Open No. 5-164)
990).

Further, as an optical branching coupler, one manufactured by the same configuration as the above-mentioned optical fiber fusion WDM coupler (optical fiber fusion branching coupler), the transmittance of a dielectric multilayer film coated on a glass substrate is used. There are a type utilizing characteristics, and a type in which an optical waveguide is formed in a Y-shape on an optical substrate.

[0006]

In general, a transmission light source used for optical communication needs to maintain a good signal-to-noise ratio of the transmitted light. Therefore, a semiconductor laser or other light source element needs to be connected to an optical fiber transmission line. It is desired to minimize the loss of light to the input end of the device.

[0007] In a wavelength division multiplexing optical communication system, there is an increasing demand for a large capacity, and it is desired to transmit as much signal light as possible to an optical fiber transmission line. However, at the same time, for the purpose of transmitting over long distances,
In many cases, a plurality of optical amplifiers are inserted into an optical transmission line. In this case, the operating wavelength band of the optical amplifier is limited, so that the wavelength band that can be used as a transmission light source is limited.
For this reason, in order to increase the number of wavelengths of the signal light, all the signal lights must be within the operating wavelength band of the optical amplifier.
There is a need to set the wavelength interval of the signal light source to be extremely narrow, 1 nm or less.

[0008] In the case where a wavelength multiplexed light source is formed by the above-described conventional technique under such requirements, the following problems occur.

WDM that combines light using the wavelength difference of light
In any of the above-mentioned couplers, the limit is to combine light having a wavelength interval of about 1 nm. At wavelength intervals smaller than this, the refractive index fluctuation of the optical member used with respect to the environmental temperature change. , The multiplexing characteristics fluctuate significantly. That is, it is difficult for a WDM coupler currently used to multiplex light having a wavelength interval on the order of 0.1 nm.

In a polarization combining coupler that multiplexes light by utilizing the difference in the polarization direction of light, only two linearly polarized lights whose polarization directions are orthogonal to each other are subject to multiplexing. Light cannot be multiplexed. A polarization combining coupler in which a birefringent prism is arranged at an output portion of a polarization combining coupler to output output light as linearly polarized light (Japanese Patent Laid-Open No. 5-164990)
Japanese Patent Application Laid-Open No. H11-187, it seems that these can be connected in multiple stages and multiplexed. However, the polarization combining coupler uses a plurality of lights having the same wavelength as input conditions. Such a wavelength multiplexing light source that combines a plurality of lights having different wavelengths cannot be used.

[0011] In the optical branch coupler, the input light receives a distribution loss corresponding to the number of branches of the optical branch coupler in principle. For example, in the case of using an optical splitting coupler that splits and outputs four optical fibers, in principle, each input light has a power of 1/4 or less, so that the pass loss may be 6 dB or less. Not theoretically possible. That is, as the number of lights to be combined increases, the transmission loss also increases. When this is used for a wavelength division multiplexed light source, the signal-to-noise ratio of the transmitted light is significantly deteriorated.

It is an object of the present invention to provide a wavelength division multiplexing light source capable of efficiently multiplexing a plurality of lights having different wavelengths with different wavelength intervals.

[0013]

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, the wavelength multiplexed light source of the present invention comprises first to n-th (n is a natural number of 2 or more) n input / output ports and output ports. A light input from an m-th (m is a natural number of 1 or more and n-1) input / output port in the forward direction.
The light is output to the first input / output port to prevent light in the direction opposite to the forward direction from passing therethrough, and light input from the nth input / output port in the forward direction is output to the (m + 1) th input / output port. An optical circulator for outputting and blocking the passage of light in the direction opposite to the forward direction is provided. The optical circulator is connected to each of the first to n-th input / output ports with n light sources that output light of different wavelengths. A wavelength band selection for transmitting light having the wavelength of the light source and reflecting light having the wavelength of the light source other than the light source between the n input / output ports and the light sources connected to the input / output ports. And a reflector for wavelength-multiplexing the light output from the n light sources and outputting the wavelength-multiplexed light from the output port.

Here, the wavelength band selective reflector includes an interference film band reflection filter or an optical fiber grating. K-th (k is a natural number not less than 2 and not more than n)
Is characterized in that it includes an optical fiber grating that reflects light of a wavelength of a light source with a number smaller than the first k-th light source.

A wavelength division multiplexed light source according to the present invention comprises a plurality of the above wavelength division multiplexed light sources, further connected to output ports of the wavelength division multiplexed light sources, and further multiplexes the wavelength division multiplexed light output from the output ports. It is characterized by having an optical multiplexer for outputting the same. Here, the optical multiplexer is
An optical coupler that combines a plurality of input lights and outputs a combined light, or a wavelength combining coupler that combines a plurality of inputted lights having different wavelengths and outputs a combined light, or an input mutually polarized light It is characterized in that it is a polarization combining coupler that combines a plurality of lights in different states by polarization and outputs combined light.

Further, the wavelength multiplexed light source of the present invention comprises at least two wavelength multiplexed light sources, and one output port of the wavelength multiplexed light source has one of the other input / output ports of the wavelength multiplexed light source. It is characterized by being connected to one.

The operation of each component of the wavelength division multiplex light source of the present invention will be described below.

The first to k-th light sources output light having different wavelengths. Light input from the first light source to the first port of the optical circulator is output from the second port of the optical circulator, is reflected by the first band reflection filter connected to the second port, and is reflected again. Input to the second port. The output light from the second light source connected to the second port of the optical circulator via the first band reflection filter passes through the first band reflection filter and enters the second port of the optical circulator. Is done. Therefore, the light of the first light source and the light of the second light source are superimposed and input to the second port of the optical circulator. Similarly, a third band-pass filter for reflecting light from the third port of the optical circulator, the first light source, and the second light source and inputting the reflected light to the third port again is connected. Light from the third light source passes through the second band reflection filter and is input to the port 3 of the optical circulator. Therefore, port 3 of the optical circulator
, The output lights of the first to third light sources are superimposed and input.

The lights sequentially combined as described above are finally output from the ports of the optical circulator to which no light source is connected.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the wavelength division multiplex light source of the present invention will be described with reference to FIG.

The three light sources 111 to 113 have different wavelengths λ1 to λ3, respectively. The light source 111 is connected to the port 1 of the optical circulator 20 having four input / output ports. A light source 112 is connected to the port 2 of the optical circulator via a band reflection filter 31 that reflects λ1. Also, the optical circulator 20
Port 3 is connected to a light source 113 via a band reflection filter 32 that reflects λ1 and λ2.

The output light of the light source 111 is the optical circulator 2
The light enters port 1 of port 0, is output from port 2, is reflected by band reflection filter 31, and is input to port 2 again. Light from the light source 112 passes through the band reflection filter 31 and is input to the port 2 of the optical circulator. Therefore, the combined light of the output lights of the light source 111 and the light source 112 is input to the port 2 of the optical circulator and output to the port 3.

By the same operation, the light sources 111 and 11
2 (combined light of the wavelengths λ1 and λ2) is reflected by the band reflection filter 32 connected to the port 3 of the optical circulator 20 and reflecting the λ1 and λ2.
And output to port 4. Light from the light source 113 passes through the band reflection filter 32 and is output from the port 3 to the port 4. After all, from port 4, light source 1
Output lights 11 to 113 are superimposed and output.

The optical circulator can be realized by utilizing the magneto-optical effect (for example, see Japanese Patent No.
No. 36074). Further, as the band reflection filter, an optical fiber grating (for example, Japanese Patent Application Laid-Open No. H7-140311) in which a core portion of an optical fiber is periodically changed in refractive index so as to reflect a specific wavelength is used. be able to.

Although the case of three light sources has been illustrated here, it goes without saying that the number of light sources can be increased by using a similar configuration according to the number of ports of the optical circulator.

The first embodiment will be described with reference to FIG.

The output light wavelengths of the signal light sources 111 to 113 are:
1550.0, 1550.5, and 155, respectively
1.0.

The optical circulator 20 utilizes the magneto-optical effect. An optical fiber grating 41 that reflects 1550 nm is used as a device corresponding to the band reflection filter 31 of FIG. As the band reflection filter 32 of FIG. 1, an optical fiber grating 42 that reflects 1550 nm and an optical fiber grating 43 that reflects 1550.5 nm are connected in series.

Light loss in the reflection path at the reflection wavelength of the optical fiber grating is 0.5 dB, and transmission loss at the transmission wavelength is 0.5 dB. The light passing loss from the port 1 to the port 2, the port 2 to the port 3, and the port 3 to the port 4 of the optical circulator are 1.0 dB, respectively. Therefore, even with the output light of the light source 111 passing through the largest number of paths, the passage loss up to the optical circulator output port (port 4) is 4 dB, which is the lowest in principle in the wavelength multiplex light source constituted only by the optical branching coupler. The loss is smaller than 6 dB, and by using this configuration, a wavelength division multiplexed light source having a good signal-to-noise ratio can be realized.

A second embodiment of the wavelength division multiplexed light source of the present invention is as follows.
As shown in FIG.

In the second embodiment, two wavelength multiplexed light sources according to the first embodiment are used, and the outputs of the respective wavelength multiplexed light sources are multiplexed by an optical coupler 50 and output.

The output light wavelengths of the light sources 111 to 116 are different from each other. The reflection wavelength of the optical fiber gratings 44 and 45 is the light source 115, and the reflection wavelength of the optical fiber grating 46 is the wavelength of the light source 116. As the optical coupler 50, an optical branching coupler, a wavelength combining coupler, or a polarization combining coupler can be used.

When a wavelength combining coupler is used, the first
It is necessary to select the wavelength of the light source to be used so that the wavelength bands of the wavelength multiplexed light output from the second wavelength multiplexed light source do not overlap. Further, in this case, the wavelength interval between the respective wavelength bands depends on the performance of the WDM coupler and needs to be increased to about 1 nm as described above.

When a polarization combining coupler is used, the path of the light is composed of a polarization maintaining optical fiber or the like so that the polarization of the light is not disturbed from each light source to the polarization combining coupler. This can be achieved by performing

A third embodiment of the wavelength division multiplexed light source of the present invention is as follows.
As shown in FIG.

The third embodiment relates to a wavelength division multiplex light source obtained by connecting the wavelength division multiplex light sources shown in the first embodiment in cascade.

The output port of the wavelength division multiplexed light source shown in the first embodiment is connected to the port 3 of the optical circulator 21 via the optical fiber gratings 45 and 46, and the port 1 and the port 2 are connected to the light source 114 and the light source. 11
5 are connected to each other. The wavelength of the output light from the light sources 114 and 115 is λ4 = 1551.
5 nm and λ5 = 1552.0 nm.

The light source 115 and the optical circulator 21
Between them, an optical fiber grating 44 for reflecting light of λ4 is inserted. The reflection wavelengths of the optical fiber gratings 45 and 46 connected to the optical circulator are λ4 and λ5, respectively.

Thus, the light from the light sources 111 to 113 synthesized by the optical circulator 20 is superimposed on the output light from the light sources 114 and 115 by the optical circulator 21 and output from the port 4 of the optical circulator 21. Become.

[0040]

As described above, in the wavelength division multiplexing light source according to the present invention, since the wavelength multiplexing function is realized by the optical circulator and the band reflection filter, the optical fiber grating having a steep reflection characteristic is used as the band reflection filter. By using the above, it is possible to output wavelength-division multiplexed light arranged at a narrow wavelength interval, exceeding the wavelength interval limit of input light of the conventional WDM coupler as a whole.

Also, since no optical branching coupler is used, a wavelength multiplexing light source with extremely low loss can be constructed. Further, since the wavelength of the light source can be increased by cascade-connecting the wavelength multiplexed light sources, the number of signal light wavelengths can be increased or decreased according to the increase or decrease of the amount of transmission information after the wavelength multiplex transmission system is installed. That is, there is an advantage that the flexibility of the optical transmission device with respect to the number of signal lights can be increased.

[0042]

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an embodiment of a wavelength division multiplexed light source according to the present invention.

FIG. 2 is a configuration diagram showing a first embodiment.

FIG. 3 is a configuration diagram showing a second embodiment.

FIG. 4 is a configuration diagram showing a third embodiment.

[Explanation of symbols]

 111 to 116 signal light source 20, 21 optical circulator 31, 32 band reflection filter 41 to 46 optical fiber grating 50 optical coupler

Claims (9)

[Claims] 1. An apparatus comprising n input / output ports and output ports from a first to an n-th (n is a natural number of 2 or more), and an m-th (m is a natural number of 1 to n-1) The light input from the input / output port in the forward direction is output to the (m + 1) th input / output port to prevent the light in the direction opposite to the forward direction from passing therethrough. An optical circulator that outputs light input in a direction to the (m + 1) th input / output port of the output port and blocks passage of light in a direction opposite to the forward direction; and N light sources that are connected to the n-th input / output port and output light of different wavelengths, respectively, between the n input / output ports and the light sources connected corresponding to the input / output ports When light of the wavelength of the light source is transmitted, And a wavelength band selective reflection means for reflecting light of the wavelength of the light source other than the light source, wherein the light output from the n light sources is wavelength-multiplexed and wavelength-multiplexed light is output from the output port. Wavelength multiplexed light source. 2. A wavelength division multiplexed light source according to claim 1, wherein said wavelength band selective reflection means includes an interference film band reflection filter. 3. The wavelength multiplexed light source according to claim 1, wherein said wavelength band selective reflection means includes an optical fiber grating. 4. The wavelength band selecting / reflecting means connected to a k-th input / output port (k is a natural number not less than 2 and not more than n) among the input / output ports, 4. The wavelength division multiplexed light source according to claim 3, further comprising an optical fiber grating that reflects light having a wavelength of the light source. 5. A plurality of the wavelength multiplexing light sources according to claim 1, 2 or 3, further connected to each of the output ports of the plurality of wavelength multiplexing light sources, and output from the output ports. A wavelength multiplexing light source, further comprising an optical multiplexing means for multiplexing and outputting the wavelength multiplexed light. 6. The wavelength division multiplexed light source according to claim 5, wherein said optical multiplexing means is an optical coupler that combines a plurality of input lights and outputs a combined light. 7. The wavelength multiplexing light source according to claim 5, wherein said optical multiplexing means is a wavelength multiplexing coupler that wavelength-combines a plurality of light beams having different wavelengths and outputs a combined light. 8. The wavelength multiplexing means according to claim 5, wherein said optical multiplexing means is a polarization combining coupler that combines a plurality of input lights having different polarization states with each other and outputs a combined light. Multiple light sources. 9. The wavelength multiplexed light source according to claim 1, further comprising at least two of the wavelength multiplexed light sources, wherein the output port of one of the wavelength multiplexed light sources is the other of the wavelength multiplexed light sources. Characterized in that the wavelength division multiplexed light source is connected to any one of the input / output ports.