JPH1022914A - Optical communication method - Google Patents

Abstract

(57) [Summary] [Problem] Deterioration of signal quality due to optical attenuator. A light source that oscillates in multiple modes is used as a signal source.
When the levels of the optical signals of a plurality of modes oscillated therefrom are different, those optical signals are separated according to the mode, and an appropriate mode optical signal is selected from the separated optical signals according to the transmission loss to a receiving point. And receive it. The signal is light source 1
Is transmitted by externally modulating single-mode light or multi-mode light output from the light source 1. When there are a plurality of optical receivers, the single mode light or the multimode light output from the light source 1 is changed to two or more, and each of them is externally modulated to optically transmit a desired signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication method, and uses a Fabry-Perot laser (FP-L) as a light source.
This is suitable for optical communication when using a multi-mode oscillation laser as in D).

[0002]

2. Description of the Related Art FIG. 8 shows a conventional example of an optical communication apparatus using an FP-LD which oscillates in multiple modes as a light source. This optical communication apparatus modulates the multi-mode light output from the FP-LD 1 as it is by the modulator 3 and transmits it to the optical transmission path 4, and converts the multi-mode light transmitted to the transmission path 4 as it is to the optical receiver 2. Is what you receive. An optical attenuator 5 is inserted in front of the optical receiver 2. The optical attenuator 5 is replaced according to the amount of transmission loss of the optical transmission line 4 to change the attenuation thereof. Light is received.

[0003]

In the optical communication system shown in FIG. 8, it is necessary to replace the optical attenuator 5 according to the amount of transmission loss of the optical transmission line 4, so that the operation is troublesome. In some cases, there is a problem that the attenuation of the optical signal by the optical attenuator 5 causes deterioration of the quality of the transmission signal.

An object of the present invention is to provide an optical communication method that does not require an attenuator for adjusting light level.

[0005]

According to the optical communication method of the present invention, as shown in FIGS. 1 and 2, a light source 1 which oscillates in multiple modes is used as a signal source, and a plurality of modes oscillated therefrom are used. When the optical signal levels are different, these optical signals are separated by mode, and the mode light suitable for the output level is selected and received from the separated optical signals according to the transmission loss to the receiving point. To send to the side.

In the optical communication method according to the second aspect of the present invention, as shown in FIGS. 1, 2, and 5, a light source 1 that oscillates in multiple modes is used as a signal source, and the level of an optical signal of a plurality of modes oscillated therefrom. Are different from each other, and the desired wavelength is limited, the temperature-level characteristic in the oscillation mode is adjusted so that the mode light having the desired oscillation wavelength becomes the transmission level suitable for the transmission loss to the receiving point. , And separates the mode light from other moat lights into a single mode light, which is transmitted to the receiving side.

In the optical communication method according to the third aspect of the present invention, as shown in FIGS. 3 and 4, a light source 1 which oscillates in multiple modes is used as a signal source, and the levels of optical signals of a plurality of modes oscillated therefrom are different. In such a case, the multi-mode light is transmitted to the receiving side, and the center wavelength of the wavelength filter is adjusted on the receiving side to the wavelength of the mode light having a level corresponding to the transmission loss to the receiving point, and the single wavelength is passed through the wavelength filter. And receives the selected mode light.

In the optical communication method according to a fourth aspect of the present invention, as shown in FIGS. 1 to 4, the light source 1 is directly modulated to optically transmit a desired signal.

In the optical communication method according to a fifth aspect of the present invention, as shown in FIGS. 6 and 7, a single mode light or a multi-mode light output from the light source 1 is externally modulated to optically transmit a desired signal. Is what you do.

In the optical communication method according to the sixth aspect of the present invention, as shown in FIGS. 6 and 7, the single mode light or the multimode light output from the light source 1 is changed to two or more, and each of them is externally modulated. Optical transmission of a desired signal.

[0011]

According to the optical communication method of the present invention,
When the levels of the optical signals of a plurality of modes oscillated from the light source 1 are different, the optical signals are separated for each mode, and the output level is determined from the separated optical signals according to the transmission loss to the receiving point. Is selected and transmitted to the receiving side, so that the reception level in the optical receiver 2 can be set to an appropriate value without providing an optical attenuator between the light source 1 and the receiver 2. . Extraction of single-mode light from multi-mode light can be performed without attenuating the light level by a diffraction grating or the like, so that communication with low quality can be performed.

In the optical communication method according to the second aspect of the present invention, when the levels of the optical signals of a plurality of modes oscillated from the light source 1 are different and the transmitted wavelength is limited to a desired wavelength, The temperature-level characteristics in the oscillation mode are controlled so that the mode light having the desired oscillation wavelength has a transmission level suitable for the transmission loss to the receiving point, and the mode light is separated from other moat lights to form a single light. Mode light,
Since the signal is transmitted to the receiving side, the reception level in the optical receiver 2 can be set to an appropriate value without providing an optical attenuator between the light source 1 and the receiver 2 even for light having a limited wavelength. .

In the optical communication method according to the third aspect of the present invention, when the levels of optical signals of a plurality of modes oscillated from the light source 1 are different, the multimode light is transmitted to the receiving side, and In the above, the center wavelength of the wavelength filter is adjusted to the wavelength of the mode light having a level corresponding to the transmission loss to the receiving point, and a single mode light is selected and received through the wavelength filter, so that an optical attenuator is not required. The reception level in the optical receiver 2 can be set to an appropriate value.

In the optical communication method according to the fourth aspect of the present invention, a desired signal can be optically transmitted by directly modulating the light source 1.

In the optical communication method according to the fifth aspect of the present invention, a desired signal can be optically transmitted by externally modulating the single mode light or the multimode light output from the light source 1.

In the optical communication method according to the sixth aspect of the present invention, the single mode light or the multi-mode light output from the light source 1 is made two or more, and each of them is externally modulated to optically transmit a desired signal. Therefore, a plurality of optical receivers 2 as shown in FIGS.
, Information can be transmitted by the single light source 1.

[0017]

FIG. 1 shows an optical communication method according to a first embodiment of the present invention, in which an FP-LD (Fabry-Perot laser) oscillating in multiple modes is used as a light source 1. . The light source 1 is a multi-mode light having a mode-to-mode level deviation as shown on the left side of the drawing (the wavelength of each mode light is λ
1, .lambda.2, .lambda.3, .lambda.4, and .lambda.5), and the multimode light is directly modulated by the modulator 3 provided in the light source 1 to become modulated multimode light. The modulator 3 performs modulation based on various information such as a video signal and a data signal input thereto, and superimposes various information on multi-mode light. In this case, since the multi-mode light of the light source 1 is subjected to the same modulation in every single mode light, receiving any one of the mode light is the same as receiving the multi-mode light collectively. It is possible to receive information superimposed on light.

The multimode light of the light source 1 is made to enter the optical transmission path 4 through a mode selection block 6 provided on the light source 1 side and transmitted therethrough. After being cut, only one desired single mode light enters the optical transmission line 4 and is transmitted, and is received by the optical receiver 2 at the terminal side of the transmission line 4. The right side in FIG. 1 shows the state of the single mode light received by the optical receiver 2.

In this optical communication method, the transmission loss of the optical transmission line 4 between the light source 1 and the optical receiver 2 is evaluated in advance, or the light receiving level of the single mode light received by the optical receiver 2 A single mode light suitable for reception by the optical receiver 2 is found by a method such as actual monitoring, and the mode selection block 6 selects and attaches a device capable of outputting the single mode light. When the transmission loss of the optical transmission line 4 between the light source 1 and the optical receiver 2 fluctuates, the light receiving level in the optical receiver 2 is monitored at a desired time interval or in real time, and the mode selection block It is also possible to exchange 6 for a suitable one.

[0020]

Second Embodiment FIG. 2 shows a second embodiment of the optical communication method according to the present invention, in which a wavelength filter 7 is provided instead of the mode selection block 6 in FIG.
The wavelength filter 7 having a center wavelength suitable for the wavelength of the single-mode light appropriate for the transmission loss of the optical transmission line 4 is prepared from the plurality of single-mode lights.

[0021]

Third Embodiment FIG. 3 shows a third embodiment of the optical communication method according to the present invention, in which the wavelength filter 7 in FIG. 2 is disposed not on the light source 1 side but on the optical receiver 2 side. It is like that. Also in this embodiment, a wavelength filter 7 capable of outputting a mode light matching the transmission loss of the optical transmission line 4 is used similarly to the above two.

[0022]

Fourth Embodiment FIG. 4 shows a fourth embodiment of the optical communication method of the present invention, which has the same configuration as that of FIG. 3, but the wavelength of light used for communication is limited. Have been.
For example, the light source 1 shown in FIG.
In the case of emitting multimode light of 3, λ4, λ5,
In the case where the use of the mode light having the wavelength λ2 is restricted, the wavelength filter 7 should be one that can output the mode light having the wavelength λ2 from among the multi-mode lights.
Amplifies the mode light of wavelength λ2 to a desired level corresponding to the transmission loss of the optical transmission line 4. In this case, utilizing the temperature dependence of the wavelength-gain characteristics of the light source 1 as shown in FIG.
Raise or lower the temperature of the light source 1 to raise the gain peak to the wavelength λ.
2 so that the mode light of wavelength λ2 in the multimode light is mainly amplified.

[0023]

Embodiment 5 FIG. 6 shows a fifth preferred embodiment of the optical communication method according to the present invention. This is an application to a communication system in which a plurality of optical receivers 2 are provided, and a light source on the transmission side for the plurality of optical receivers 2 can be realized by one light source 1 that oscillates in one multimode. In this device, the multi-mode light of the light source 1 is divided into three by an optical coupler 8, each of which is individually modulated by a modulator (optical external modulator) 3, and an information signal is placed thereon. An efficient system without a single light source and no optical attenuator is constructed by selecting a mode light having a wavelength suitable for the amount of transmission loss of the optical transmission line 4 up to 2 by the wavelength filter 7.

[0024]

Sixth Embodiment FIG. 7 shows a sixth embodiment of the optical communication method according to the present invention, in which a single light source 1 transmits signals to a plurality of optical receivers 2 as in FIG. It was made possible. In this example, a wavelength separation filter 9 is provided in front of the light source 1, and the wavelength separation filter 9 allocates single mode light suitable for the amount of transmission loss of the optical transmission path 4 to each optical receiver 2. The modulator (optical external modulator) 3 is provided in front of the wavelength separation filter 9 and can transmit individual signals to the individual optical receivers 2.

[0025]

The optical communication method of the present invention has the following effects. 1. Since an optical communication device that does not require an optical attenuator can be realized, there is no need to replace an optical attenuator according to the amount of transmission loss in an optical transmission line as in the related art. 2. Since an optical attenuator is not required, signal quality degradation that may occur when the optical attenuator is inserted is also prevented. 3. In particular, according to the invention of claim 6, signal transmission to a plurality of optical receivers can be performed with a single light source, and the number of light sources can be reduced, thereby greatly reducing the cost of the system.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the optical communication method of the present invention.

FIG. 2 is a schematic diagram showing a second embodiment of the optical communication method according to the present invention.

FIG. 3 is a schematic diagram showing a third embodiment of the optical communication method according to the present invention.

FIG. 4 is a schematic diagram showing a fourth embodiment of the optical communication method according to the present invention.

FIGS. 5A and 5B are explanatory diagrams showing wavelength-gain characteristics of a light source in the communication method of FIG. 4;

FIG. 6 is a schematic view showing a fifth embodiment of the optical communication method according to the present invention.

FIG. 7 is a schematic diagram showing a sixth embodiment of the optical communication method of the present invention.

FIG. 8 is a schematic diagram showing a conventional example of an optical communication method using an FP-LD as a light source.

[Explanation of symbols]

 1 light source 2 optical receiver 3 modulator

Claims (6)

[Claims] A light source (1) that oscillates in multiple modes is used as a signal source, and when the levels of optical signals of a plurality of modes oscillated therefrom are different, those optical signals are separated for each mode,
An optical communication method characterized in that mode light suitable for an output level is selected from the separated optical signals according to a transmission loss to a receiving point and transmitted to a receiving side. 2. A light source (1) which oscillates in multiple modes is used as a signal source. When the levels of optical signals of a plurality of modes oscillated from the light source are different and a desired wavelength is transmitted, oscillation occurs. The temperature-level characteristics in the mode are controlled so that the mode light having the desired oscillation wavelength has a transmission level suitable for the transmission loss to the receiving point, and the mode light is separated from other moat lights to form a single mode. An optical communication method, wherein the light is transmitted to a receiving side. 3. A multi-mode oscillating light source (1) is used as a signal source. When the levels of optical signals of a plurality of modes oscillated therefrom are different, the multi-mode light is transmitted to a receiving side, and the receiving side transmits the multi-mode light. The center wavelength of the wavelength filter is adjusted to the wavelength of the mode light having a level corresponding to the transmission loss to the receiving point, and a single mode light is selected and received through the wavelength filter. Optical communication method. 4. The optical communication method according to claim 1, wherein a desired signal is optically transmitted by directly modulating the light source. 5. The optical system according to claim 1, wherein a single mode light or a multi-mode light output from the light source is externally modulated to transmit a desired signal. Optical communication method. 6. The method according to claim 1, wherein the single-mode light or the multi-mode light output from the light source is made two or more, and each of them is externally modulated to optically transmit a desired signal.
The optical communication method according to claim 3.