JPH08110497A - Four wavelength multiplexing method - Google Patents

Abstract

PURPOSE: To multiplex four light waves having different wavelengths with a small light loss in a wavelength region capable of amplification of an optical fiber amplifier. CONSTITUTION: P-polarization light having a wavelength of 1,530μm from a first light source 301 and S-polarization light having a wavelength of 1,535μm from a second light source 302 are multiplexed by a polarized wave multiplexer 305 and P-polarization light having a wavelength of 1,550μm from a third light source 303 and S-polarization light having a wavelength of 1,555μm from a fourth light source 304 are multiplexed by a polarized wave multiplexer 309. The light outputs multiplexed by the polarized wave multiplexers 305, 309, respectively, are multiplexed by a multiplexer 313 and outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wavelength multiplexing method, and more particularly to a method for injecting light waves of four different wavelengths into one optical fiber. The present invention relates to a 4-wavelength multiplexing method required for 4-wavelength multiplex communication, which is a method used for light waves.

[0002]

2. Description of the Related Art It is called to combine two or more light waves into one optical fiber, and four methods described below are well known as a method for combining two light waves. ing.

The first method is to use an optical coupler called a 3 dB coupler. This optical coupler is a 4-terminal optical component obtained by, for example, melting and adhering a fixed portion of two optical fibers, and has an advantage that the wavelength of the combined optical wave is loosely limited, but It has the drawback that half of the optical power is wasted.

The second method is to use a special mirror called a diffraction grating. This mirror has several hundred lines / mm
A v-shaped groove is engraved at a ratio of, and has a property that the angle of the light wave reflected by the mirror differs depending on the wavelength. Therefore, by adjusting the incident angles of the light waves of different wavelengths on the mirror, the incident angles can be set so that the reflected light waves overlap. By this method, it is possible to multiplex several tens of light waves having different wavelengths. However, the optical loss of the mirror is as large as about 6 dB, and the incident angle is not easily set.

The third method is a method called a polarization multiplexing system. Polarization refers to the way the entire spatial change occurs when a light wave propagates, but linear polarization is suitable for multiplexing. Linearly polarized light is also called linearly polarized light. In the case of linearly polarized light, the direction of overall change is on one straight line, and the output light from the semiconductor laser is generally linearly polarized light. When linearly polarized light is obliquely incident on the dielectric plane, a light wave whose polarization direction is in the plane of incidence is called p-polarized light, and a light wave whose polarization direction is perpendicular to the plane of incidence is called s-polarized light. The incident surface is a surface including the normal line of the dielectric plane and the traveling direction of the incident light wave.

Since the s-polarized light and the p-polarized light have greatly different reflection and transmission characteristics of the dielectric film, only the s-polarized light can be reflected by properly selecting the incident angle. Further, when a dielectric multilayer film having different optical properties is sandwiched by the oblique surfaces of two triangular prisms, it is possible to have a property of reflecting s-polarized light and transmitting p-polarized light in the wavelength range. Such an optical component is already known as a prism type polarizer, and a commercial item can be easily obtained.

FIG. 2 is a schematic view for explaining the function of the prism type polarizer, and is an example in which the input / output terminal of light is composed of a polarization maintaining optical fiber to which an optical connector is attached. In FIG. 2, an optical connector 102 that serves as a common optical fiber terminal is coupled to a prism type polarizer 101 via a lens 107, and an optical connector 103 that serves as an s-polarized input / output terminal is coupled via a lens 105. Lens 1
Optical connector 10 serving as p-polarized input / output terminal via 06
4 are connected. When the output light from one semiconductor laser is incident on the optical connector 103 so as to be s-polarized and the output light from the other semiconductor laser is incident on the optical connector 104 to be p-polarized, the optical connector 102 is obtained.
, The light waves of these two semiconductor lasers are combined and extracted. The lenses 105 and 106 polarize the light wave output from the optical fiber into a polarized beam, and the lens 107 focuses the polarized beam onto the optical fiber. Such polarization multiplexing
It has the advantages that the restriction on the wavelength is loose and that the optical loss can be 1 dB or less, but it has the drawback that it can basically be applied only to multiplexing of two light waves.

The fourth method is a wavelength multiplexing method which utilizes the fact that the transmission and reflection characteristics of the dielectric multilayer film differ depending on the wavelength. This principle and characteristics are known. An example of the wavelength characteristics is shown in FIG. In FIG. 3, the horizontal axis represents wavelength and the vertical axis represents optical loss during transmission. Characteristic 20
1 is the optical loss between the common terminal and the terminal of the light wave whose wavelength is around 1.53 μm, and the characteristic 202 is the optical loss between the common terminal and the terminal of the light wave whose wavelength is around 1.55 μm.

Such wavelength multiplexing has the advantage that the optical loss can be 1 dB or less, but the wavelengths of the optical waves to be combined must be separated by a certain distance or more. The example of the characteristic shown in FIG. 3 is an example in which two wavelengths are closest to each other. The wavelength range suitable for optical fiber communication is a sufficiently wide wavelength range, but when an erbium-doped optical fiber amplifier (hereinafter referred to as an optical fiber amplifier) is applied, the wavelength range is from 1.525 μm to 1.25 μm. Limited to 57 μm. When wavelength multiplexing is performed in a wavelength range in which this optical amplification is possible, there is a drawback that the combined value of the characteristics shown in FIG. 3 can basically be applied only to the multiplexing of two combined waves.

[0010]

A plurality of light waves having different wavelengths in the amplifiable wavelength range of an optical fiber amplifier are used.
In the case of combining and entering the two optical fibers, conventionally, it was possible to combine two light waves with small optical loss, but for four combining waves, a diffraction grating type multiplexer with large optical loss must be used. I had to do it.

Therefore, a main object of the present invention is to provide a four-wavelength multiplexing method capable of combining four light waves having different wavelengths with a small optical loss in the wavelength range in which the optical fiber amplifier can amplify.

[0012]

According to the present invention, a first light wave having a wavelength of λ1 and a second light wave having a wavelength of λ2 larger than λ1 are used.
Is a four-wavelength multiplexing method for combining a third light wave having a wavelength of λ3 larger than λ2 and a fourth light wave having a wavelength of λ4 larger than λ3.
2 is greater than 1.528 μm and 1.538 μm
Is smaller than 1.54 and the wavelengths λ3 and λ4 are 1.54.
The value is larger than 5 μm and smaller than 1.57 μm, and the first light wave and the second light wave are combined by the polarization multiplexing method in which the polarization planes are orthogonal to each other, and the third light wave and the fourth light wave are combined. Are combined by a polarization multiplexing method in which the planes of polarization are orthogonal to each other and combined, and a light wave in which the first and second light waves are multiplexed and a light wave in which the third and fourth light waves are multiplexed It is configured to be multiplexed by wavelength division multiplexing.

[0013]

In the four-wavelength multiplexing method according to the present invention, two light waves are combined with a smaller optical loss in polarization multiplexing with an optical loss of 1 dB or less, and two such combined optical waves are further increased by 1 dB.
Since they are combined with the following optical loss, four optical waves having different wavelengths are combined with an optical loss of 2 dB or less.

[0014]

FIG. 1 is a diagram showing an embodiment of the present invention.
In FIG. 1, the first light source 301 has a wavelength of 1.530 μm.
The second light source 302 has an output of s-polarized light at a wavelength of 1.535 μm, and has a p-polarized output of m.
The light source 303 has a wavelength of 1.550 μm and outputs p-polarized light, and the fourth light source 304 has a wavelength of 1.555 μm and outputs s-polarized light. The p-polarized light from the first light source is incident on the polarization-multiplexed wave multiplexer 305 via the p-polarized light input connector-attached optical cord 306, and the s-polarized light from the second light source 302 is the s-polarized input connector-attached optical cord 307. It is incident on the polarization-multiplexing wave device 305 via the, and the polarization-multiplexing wave device 305 multiplexes the incident p-polarized light and s-polarized light, and outputs the multiplexed light to the optical code 308 with a connector for combined light output. The combined optical output connector-attached optical cord 308 is connected to the short wavelength lightwave input connector-attached optical cord 314.

The p-polarized light from the third light source 303 is incident on the polarization-multiplexing wave device 309 through the optical code 310 with a p-polarization input connector, and the s-polarized light from the fourth light source 304 is s-polarized light.
It is incident on the polarization-multiplexing wave multiplexer 309 via the polarization input connector-attached optical code 311. The polarization polarization-multiplexing wave device 309 multiplexes these p-polarized light and s-polarized light, and outputs them to the combined light-output connector attached optical code 312. Output. The optical cord 312 with a connector for combined light output is the optical cord 3 with a connector for long-wavelength lightwave input.
It is connected to 15. The wavelength multiplex wave multiplexer 313 combines light waves in the short wavelength range of 1.528 μm or more and 1.538 μm or less and light waves in the long wavelength range of 1.545 μm or more and 1.570 μm or less. The combined light wave is output to the optical code 316 with a light wave light output connector.

In the configuration shown in FIG. 1, the first light source 3
The light wave from 01 and the light wave from the second light source 302 are combined by the polarization multiplexing compound wave device 305 and output from the combined optical output connector-equipped optical cord 308 with an optical loss of 1 dB or less. The light wave is input to the wavelength division multiplexing wave device 313 via the optical code 314 with a connector for inputting a short wavelength light wave, but since the wavelength is in the transmission range of the short wavelength band, the combined light output connector has an optical loss of 1 dB or less. It is output to the optical code 316. The light wave from the third light source 303 and the fourth light source 304
The optical waves from are combined by the polarization multiplexing wave device 309 and 1 dB
The two light waves output from the combined optical output connector-attached optical cord 312 with the following optical loss and output are transmitted through the long-wavelength lightwave input connector-attached optical cord 315 to the wavelength multiplex wave multiplexer 31.
Although the wavelength is in the transmission range of the long wavelength band, it is output to the combined optical output connector optical code 316 with an optical loss of 1 dB or less. Therefore, the first, second and third
And the light waves output from the fourth light sources 301, 302, 303, 304 are combined with an optical loss of 2 dB or less.

In FIG. 1, a semiconductor laser is not used as the first to fourth light sources 301 to 304, and if the light source has stable polarization, it can be linearly polarized by using a polarization adjuster together. Therefore, the semiconductor laser can be replaced.

Further, in FIG. 1, the first light source 301 and the second light source 302 are optical cords with connectors 306 and 307.
The output light from the light source can be incident on the prism-type polarizer through the lens system. By doing so, the size of the multiplexing device can be reduced.

[0019]

As described above, according to the present invention, the erbium optical fiber amplifier is in the amplifiable wavelength range,
Light waves of four different wavelengths can be multiplexed with a light loss of 2 dB or less.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the function of a conventional prism type polarizer.

FIG. 3 is an example of measuring the optical loss of a wavelength division multiplexer.

[Explanation of symbols]

301 1st light source 302 2nd light source 303 3rd light source 304 4th light source 305,309 Polarization multiple wave multiplexer 306-308,310-312,314-316 Optical code with connector 313 Wavelength multiple wave multiplexer

Claims (1)

[Claims] 1. A first lightwave having a wavelength of λ1, a second lightwave having a wavelength of λ2 larger than λ1, a third lightwave having a wavelength of λ3 larger than λ2, and a wavelength of 4 to combine with a fourth light wave having λ4 larger than λ3
A wavelength multiplexing method, wherein the wavelengths λ1 and λ2 have a value larger than 1.528 μm and smaller than 1.538 μm, and the wavelength λ3
And λ4 is greater than 1.545 μm and 1.57 μm
The value is smaller than m, and the first light wave and the second light wave are combined by a polarization multiplexing method in which polarization planes are orthogonal to each other, and the third light wave and the fourth light wave are combined. A light wave obtained by multiplexing the first and second light waves and a light wave obtained by multiplexing the third and fourth light waves are multiplexed by a polarization multiplexing method in which polarization planes are orthogonal to each other and are combined. A four-wavelength multiplexing method characterized in that multiplexing is performed by multiplexing.