KR20180111269A - Time and wavelength division multiplexing system - Google Patents

Abstract

The present invention relates to a time and wavelength division multiplexing system which allows normal communication without a separate temperature maintaining device even if a wavelength of an optical signal changes. A plurality of users (101, 102, ..., 10m) including light sources generating multi-channel laser lights are connected to a receiving end (300) including three arrayed waveguide gratings (310a, 310b), two optical detectors (330a, 330b), and a multi-input/output device (350) by a single-mode optical fiber (200). The plurality of users (101, 102, ..., 10m) have a plurality of light sources (LS1, LS2, ..., LSl) generating laser lights of different wavelengths. The arrayed waveguide gratings (310) use a Gaussian form with a corresponding wavelength order of 2. The number of filters is set to allow a 3 dB bandwidth to be equal to intervals of n filters making up the arrayed waveguide gratings to form an all-pass filter of a form in which the plurality of filters are combined.

Description

[0001] TIME AND WAVELENGTH DIVISION MULTIPLEXING SYSTEM [0002]

The present invention relates to time and wavelength division multiplexing systems, and more particularly to a time and wavelength division multiplexing system in which a drop in optical signal transmission does not occur without using a temperature holding device.

(Hereinafter, simply referred to as " TDMA ") technology and wavelength division multiplexing (hereinafter, also simply referred to as " WDM ") technology in a time division multiple access (Time & Wavelength Division Multiplexing; hereinafter, simply referred to as " TWDM ") scheme in which a plurality of optical signals of different wavelengths are transmitted through one optical fiber via one communication network Is a widely used communication method because of the possibility of large-capacity communication.

The WDM system, which is the basic in the TWDM system, uses different optical signals of different wavelengths from different users. Therefore, it is necessary to precisely control the wavelength interval for each user and also to maintain the wavelength of each channel accurately and stably There is a need to do.

On the other hand, for example, in a laser light source such as a DFB LD (Distributed FeedBack Laser Diode), the wavelength of the output laser light output from the laser light source changes when the temperature changes. For this reason, in a system using the WDM system, A temperature holding device such as a thermo-electric cooler (TEC) is used as a device for keeping constant.

2 (a) showing the operation of the AWG when the temperature holding device is not used in the WDM system, when the temperature holding device is not used in a general WDM system, due to a wavelength change of the optical signal due to a temperature change, Between the pass band PB of each filter of the arrayed waveguide grating (hereinafter sometimes simply referred to as " AWG ") and the pass band PB The signal is not properly detected by any of the filters of the AWG, so that a problem arises that the communication becomes virtually impossible. To prevent such a problem, a temperature holding device is used.

However, in the case of using the temperature holding device, the configuration of the system is complicated and the installation cost is increased. Particularly, since the temperature holding device such as TEC is a device consuming a large amount of power, . Therefore, researches on a method of not using a temperature holding device have been conducted recently. For example, there is a technique of Patent Document 1 filed by the present applicant.

1 is a diagram showing a system configuration of a WDM system not using the conventional temperature holding device disclosed in Patent Document 1. The conventional WDM system disclosed in Patent Document 1 has a transmitting end including a light source that outputs two or more multi- 210), two or more arrayed waveguide gratings 221, 222, and two or more optical detectors 231, 232 connected to each of two or more AWGs are connected to a single mode fiber Quot; SMF "), and the passband (PB) of the filters constituting two or more AWGs have different center wavelengths and overlap each other at certain portions, So that there is no wavelength to be missed.

More specifically, as shown in Fig. 2 (b) showing the operation of the WDM system according to the prior art of Patent Document 1, in the method of Patent Document 1, when one AWG is used by using two AWGs Filters F1, F2, ... , F1 ', F2' ... , And Fn ', respectively. Therefore, even when the wavelength of the optical signal according to the temperature change is located, for example, between the pass band PB and the pass band PB of each filter of the AWG, the additional filters F1 ', F2', ... , Fn ', it is possible to perform the communication without using the temperature holding device.

However, in the prior art of Patent Document 1, the pass band PB that can be detected by the two AWGs 221 and 222 is determined. In Fig. 2 (b), for example, between F1 and F1 ', between F2 and F2' between, … There is a band which can not detect any AWG out of the two AWGs 221 and 222. Therefore, according to the conventional technique of Patent Document 1, the band pass filter Pass filter can not be achieved. As a result, the wavelength of the optical signal changed by the temperature change exists in a band where no AWG of the two AWGs 221 and 222 can be detected There is a problem that communication becomes difficult in practice.

Open Patent Publication No. 10-2016-0081847 (published on June 7, 2016)

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and it is an object of the present invention to provide an all-pass filter capable of detecting a signal of all wavelength bands by keeping the sum of pass- And a wavelength division multiplexing system capable of performing normal communication even when the wavelength of an optical signal transmitted from a transmitting terminal changes according to a temperature change without a separate temperature maintaining device.

According to an aspect of the present invention, there is provided a time and wavelength division multiplexing (TDM) system comprising: a transmitter including a plurality of users having a light source for generating laser light; Two arrayed waveguide gratings (AWGs) connected in parallel with the transmitting end by a single mode optical fiber, two photodetectors connected to the two arrayed waveguide gratings, two photodetectors connected to the two photodetectors Wherein the two arrayed waveguide gratings are of a Gaussian type with a degree of a corresponding wavelength of 2, and the 3db bandwidth of the two arrayed waveguide gratings The number of filters is set so as to coincide with the intervals of the plurality of filters constituting the arrayed waveguide grating.

Preferably, the light source is composed of a plurality of light sources that generate laser beams of different wavelengths.

Preferably, when the wavelength of the laser light transmitted from a specific user or a specific user group among the plurality of users changes due to a temperature change, the MIMO apparatus controls a user or a user group whose wavelength of laser light has changed, So that the communication can be continued.

Preferably, when the wavelength of the laser light transmitted from a specific user or a specific user group among the plurality of users changes due to a temperature change, the MIMO apparatus controls a user or a user group whose wavelength has changed, To a light source that outputs laser light having the same wavelength as the wavelength before the temperature change at the changed temperature.

Preferably, the number n of the plurality of filters constituting the arrayed waveguide grating is larger than the number m of the plurality of users (n > m).

Preferably, the number m of the plurality of users is greater than the number of the plurality of light sources (m> l).

According to the present invention, the sum of the pass band (PB) of each filter constituting the AWG is always maintained at a constant value. Therefore, even when the wavelength of the optical signal transmitted from the transmitting end changes in accordance with the temperature change, Communication effect can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a system configuration of a conventional WDM system not using a temperature holding device, Fig.
2 is a diagram for explaining the operation of the prior art,
3 is a diagram showing a system configuration of a TWDM system not using a temperature holding device according to a preferred embodiment of the present invention,
4 is a diagram showing the operation of a TWDM system according to a preferred embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 3 is a diagram showing a system configuration of a TWDM system not using the temperature holding device according to the preferred embodiment of the present invention.

3, the TWDM system not using the temperature holding device according to the preferred embodiment of the present invention includes a transmitting end 100 composed of a plurality of users 101, 102, ..., 10m, two arrayed waveguide gratings A receiving end 300 composed of two optical detectors 310a and 310b and two optical detectors 330a and 330b and a multiple input multiple output (hereinafter simply referred to as " MIMO " And are connected in a state in which they can communicate with each other by the SMF 200. [

Each of the plurality of users 101, 102, ..., and 10m is a light source that generates a laser beam, and the plurality of users 101, 102, ..., The present invention differs from the conventional system of Patent Document 1 using a light source of one wavelength per user in this respect.

The plurality of light sources LS1, LS2, ..., LS1 may be laser diodes outputting laser beams of different wavelengths, and may be, for example, DFB LDs (Distributed FeedBack Laser Diodes).

The number m (m is an integer of 2 or more) of the users 101, 102, ..., 10m constituting the transmitting terminal 100 is larger than the number l of each light source LS1, LS2, ..., > l.

It is preferable to distribute the light sources that output light of the same wavelength among a plurality of light sources that output laser beams of different wavelengths to a plurality of users. For example, a plurality of users 101, 102, ..., If the number of light sources LS1, LS2, ..., LS1 is 4, and the light sources of four different wavelengths are distributed equally to 32 users, , And the number of users per each group using light sources of the same wavelength is 8 each.

That is, for example, the light source LS1 for outputting the laser light of the wavelength? 1, the light source LS2 for outputting the laser light of the wavelength? 2, the light source LS3 for outputting the laser light of the wavelength? 3, and the light source LS4 for outputting the laser light of the wavelength? When four light sources LS1, LS2, LS3 and LS4 are equally distributed to 32 users, eight users are used together for each light source.

Here, to meanly distribute the light sources that output light of the same wavelength among a plurality of light sources outputting laser beams of different wavelengths to a plurality of users means that the total number of 32 users is divided by the number of light sources LS2, LS3, and LS4, respectively, by allocating each of the four user groups to use one of the four light sources LS1, LS2, LS3, and LS4, as a result of dividing the four light sources LS1, LS2, For example, if the number of light sources is 4 and the number of users is 30, then two of the light sources are the same number of light sources. Including a case where the light is distributed substantially evenly, even though it is not a perfectly even distribution, such as distributing to eight persons each and distributing the remaining two light sources to seven persons respectively.

Of course, in the present embodiment, the number of users using the light source LS1, the number of users using the light source LS2, the number of users using the light source LS3, And 8 users each of 8 users using the light source LS4), communication is performed by the TDMA method.

The SMF 200 is an optical transmission line for transmitting the optical signal output from the transmitting end 100 to the receiving end 300. In this embodiment, The laser light is coupled and multiplexed by an optical coupler (not shown) and transmitted to the receiving end 300 through the SMF 200.

The optical signal transmitted from the transmitting end 100 through the SMF 200 is input to the two AWGs 310a and 310b connected in parallel to the SMF 200 and the AWG 310a and the AWG 310b, (Demultiplexed) the optical signals transmitted from the transmitting end 100 through the SMF 200 to the optical detectors 330a and 330b, respectively.

3, the AWG 310a of the two AWGs 310a and 310b has n / 2 filters F1, F3, ..., Fn-1, and the AWG 310b has n / 2 (N is an integer of 2 or more) filters F2, F4, ..., Fn.

In this embodiment, two AWGs 310a and 310b use a Gaussian-type AWG having a corresponding wavelength of 2, and the AWG 310a and the AWG 310b have a 3-dB bandwidth corresponding to an interval of n filters constituting the AWGs 310a and 310b Is set. Therefore, the AWGs 310a and 310b of the present embodiment form an all-pass filter in the form of a combination of n filters, Even if the wavelength deviates from the initial setting value, it is possible to continuously detect the wavelength without the temperature holding device.

This will be described in more detail with reference to FIG. 4 is a diagram showing the operation of the AWG 310a and 310b of the TWDM system according to the preferred embodiment of the present invention.

The operation when the temperature holding device is not used in the general WDM system and the operation of the conventional WDM system described in Patent Document 1 are the same as described above. As described above, according to the technology of Patent Document 1, The wavelength of the optical signal changed by the temperature change is different from that of the two AWGs 221 and 222. In this case, There is a problem that communication becomes difficult in practice when any of the AWGs is present in a band that can not be detected.

On the other hand, in the preferred embodiment of the present invention, two AWGs 310a and 310b of the Gaussian type having a corresponding wavelength of 2 are used, and the n filters (n = The sum of the passbands PB of the filters forming the AWGs 310a and 310b is always maintained at a constant value as shown in FIG. 4 Therefore, even when the wavelength of the optical signal transmitted from the transmitting terminal 100 changes in accordance with the temperature change, normal communication becomes possible without a separate temperature maintaining device.

The optical detectors 330a and 330b detect the number of photodetectors PD1, PD3, ..., PDn-1 and PD2, PD4, ..., PDn The AWG 310a and the AWG 310b convert the optical signals of the respective wavelengths, which are spectrally divided and transmitted, into electrical signals and output them to the MIMO 350. [

The number of the plurality of filters F1, F3, ..., Fn-1 and F2, F4, ..., Fn constituting the two AWGs 310a, 310b and the number of the two optical detectors 330a, The number n of the plurality of photodetectors PD1, PD3, ..., PDn-1 and PD2, PD4, ..., PDn constituting the photodetector is larger than the number m of the plurality of users 101, 102, ..., > m. < / RTI >

The MIMO 350 outputs a plurality of optical signals input from the two optical detectors 330a and 330b to an output terminal and is transmitted from a specific one of the plurality of users 101, 102, ..., When the wavelength of the optical signal changes and the number of users using the same wavelength increases in the light source of a certain wavelength and the number of users using the same wavelength decreases in the other light sources, And controls the user whose wavelength of the optical signal has changed so that normal communication can be performed.

Specifically, as in the above-described example, for example, a light source LS1 for outputting a laser beam having a wavelength? 1, a light source LS2 for outputting a laser beam having a wavelength? 2, a light source LS3 for outputting a laser beam having a wavelength? When a user is assigned to each of the four light sources of the light source LS4 for outputting light and communication is performed, for example, the light source LS2 for outputting the laser light of the wavelength? It is assumed that the MIMO 350 confirms that the optical signal having the wavelength of? 3 other than? 2 is output by this temperature change.

In this case, although there is no change in the light source actually used by each user, in view of the wavelength of the optical signal output from the light source and recognized by the MIMO 350, eight light sources that are uniformly assigned to each light source that outputs the same wavelength The number of users is changed. That is, the number of users who use the light source LS1 for outputting the laser light of the wavelength? 1 and the light source LS4 for outputting the laser light of the wavelength? 4 remains unchanged, but the light source LS2 for outputting the laser light of the wavelength? The number of users who use the light source LS3 decreases from 8 to 7, and the number of users increases from 8 to 9 using the light source LS3 that outputs the laser light of the wavelength? 3, resulting in an imbalance in the number of users.

As a control method in this case, in the first method, the MIMO 350 controls the communication to be continuously performed even by the wavelength changed for the user or the user group whose wavelength of the optical signal output by the temperature change changes. That is, in the above example, the MIMO 350 controls the user group using the light source LS2 that outputs the laser beam of the wavelength? 2 and the light source LS3 that outputs the laser beam of the wavelength? 3, So that communication can be continuously performed.

In the second method, the MIMO 350 uses the light source used by the user among the plurality of light sources LS1, LS2, ..., LS1 for a user whose wavelength of the optical signal output by the temperature change is changed, The light source is redistributed so as to switch to a light source that outputs laser light having the same wavelength as before.

In this embodiment, each of the plurality of users 101, 102, ..., 10m uses any one specific light source among the plurality of light sources LS1, LS2, ..., LS1, and in the example described above, Assuming that the wavelength of the optical signal output by the user 105 using the light source LS2 outputting the laser light of the light source LS2 changed from? 2 to? 3 before the temperature change, in this case, the light sources LS1, LS3, LS4 It is natural that the wavelength of the optical signal that the light sources LS1, LS3, LS4 can output at the temperature after the change also changes.

In this case, when the light source LS1 that outputs the laser light of? 1 at the temperature before the change among the light sources LS1, LS2, LS3, and LS4 outputs the laser light of the wavelength? 2 at the temperature after the change, the MIMO 350, The light source LS2 used before the temperature change is redistributed by a method of redistributing the light source to the light source LS1 which outputs the laser light of the wavelength? 2 at the changed temperature or the like so that the communication is continuously performed.

While the present invention has been described with reference to the preferred embodiments, it is to be understood that the present invention is not limited to the above-described embodiments, and various changes and modifications are possible within the scope of the present invention.

100 transmitter
101, 102, ... , 10m users
LS1, LS2, ... , LSℓ light source
200 single mode fiber
300 receiver
310 array type waveguide grating
330 photodetector
PD1, PD2, ... , PDn photodetector
350 Multiple Input / Output Devices

Claims (6)

Time and wavelength division multiplexing (" TWDM ") system,
A transmitting end including a plurality of users having a light source for generating laser light;
Two arrayed waveguide gratings (AWGs) connected in parallel with the transmitting end by a single mode optical fiber, two photodetectors connected to the two arrayed waveguide gratings, and two photodetectors connected to the two photodetectors And a receiving end including a multiple input multiple output (MIMO)
Wherein the two arrayed waveguide gratings have a Gaussian shape with a corresponding wavelength of 2 and the number of filters is set such that the 3db bandwidth of the two arrayed waveguide gratings coincides with the interval of the plurality of filters constituting the arrayed waveguide grating Set time and wavelength division multiplexing system. The method according to claim 1,
Wherein the light source comprises a plurality of light sources for generating laser beams of different wavelengths. The method of claim 2,
Output device controls a user or a group of users whose wavelengths of laser light have changed when the wavelength of the laser light transmitted from a specific user or a specific user group among the plurality of users changes due to a temperature change, Time multiplexing and wavelength division multiplexing system. The method of claim 2,
Output device controls a user or a group of users whose wavelengths of laser light have changed when a wavelength of the laser light transmitted from a specific user or a specific user group of the plurality of users changes due to a temperature change, To a light source for outputting a laser beam having the same wavelength as the wavelength before the temperature change at a changed temperature, and a wavelength division multiplexing system. The method according to claim 1,
Wherein the number n of the plurality of filters constituting the arrayed waveguide grating is greater than the number m of the plurality of users (n > m). The method of claim 2,
(M) of the plurality of users is greater than the number (l) of the plurality of light sources (m >

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