KR20160022178A - Optical device for wavelength division multiplexing communication - Google Patents

Abstract

The present invention relates to an optical device for a wavelength multiplexing communications method, provided to block cross talk between channels in an optical communications system having a wavelength multiplexing structure. According to the present invention, the optical device for a wavelength multiplexing communications method, comprising a DFB-LD light source and a light receiving device in an optical communications system of a WDM method, is provided to manufacture a WDM optical device for two-way communications, in which a wavelength selection filter for preventing cross talk, which passes ″1″ signals and blocks ″0″ signals and signals with a wavelength longer than that of the ″0″ signals, is arranged between the DFB-LD and a wavelength selection filter for setting an optical path, which determines the optical path, and thus the transmission optical power of the ″1″ signals is sufficient and the shake of wavelengths occurs less by effectively blocking the ″0″ signals and the signals with a wavelength longer than that of the ″0″ signals, thereby achieving better signal transmission quality.

Description

[0001] OPTICAL DEVICE FOR WAVELENGTH DIVISION MULTIPLEXING COMMUNICATION [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device using a wavelength division multiplexing communication method, and more particularly, to an optical device for a wavelength division multiplexing communication method capable of blocking crosstalk between channels in an optical communication system having a wavelength multiplexing structure.

2. Description of the Related Art In recent years, optical communications using light as a medium for information transmission have been popularized for high-capacity information transmission and high-speed information communication. Particularly, WDM (Wavelength Division Multiplexing) technique is widely used for next generation optical communication. WDM technology is a technology that focuses on the fact that even if optical information having various wavelengths is mixed into one optical fiber, optical information having different wavelengths due to non-coherence of the laser does not occur, have.

Currently, various wavelength intervals are being standardized, and WDM schemes of 100 GHz (~ 0.8 nm spacing) or 50 GHz (~ 0.4 nm spacing) are widely studied. 1 shows an example of a TWDM (Time Division Multiplexing) scheme called NG-PON2, which is a combination of TDM (Time Division Multiplexing) and WDM (Wavelength Division Multiplexing). This TWDM scheme is currently adopted as standardization. The TWDM scheme refers to a method in which multiple subscribers simultaneously form one optical communication network by performing time division multiplexing (TDM) on each wavelength using four wavelengths.

In the TWDM system shown in FIG. 1, the OLT (optical line terminal) optical module of the office of the telephone company operates only at respective independent wavelengths, and the ONU (Optical Network Unit) As shown in FIG. The number of ONUs corresponding to one OLT optical module of the telephone company of Korea is several, and a plurality of ONU optical modules performing communication with one OLT optical module use the optical network in a time division manner. In this structure, a maximum of 64 ONU optical modules correspond to one OLT optical module, and up to 256 ONU optical modules correspond to all four OLT optical modules, so that the optical network can be efficiently used.

Since a plurality of ONU optical modules communicating with one OLT optical module in the TWDM system operates in a time division manner, if there is optical output from another ONU optical module when one ONU is operating, it acts as crosstalk in communication . Therefore, among the ONU optical modules which are simultaneously connected to one OLT, the state changes to the operating state by the time division procedure without operating. Currently, ONU optical devices mainly use DFB-LD (Distributed FeedBack Laser Diode) as a light source, and this DFB-LD results in a severe wavelength change depending on the injection current state.

As shown in FIG. 1, in the telephone company, wavelengths of four OLTs are bundled to transmit a signal to a subscriber ONU through a single optical fiber. An optical signal transmitted from the subscriber ONU to the four wavelengths is responsible for each wavelength OLT optical receiver. Therefore, each wavelength assigned to an ONU must be very precisely controlled. If the light emitted by one assigned ONU has a wavelength other than one, this signal is incident on a different optical receiver than the pre- Which causes the signal to be confused. However, since several ONUs have the same wavelength, if any one of the ONUs having the same wavelength is in an operating state, there is no light output from another ONU. Therefore, when the ONU in an unoperated state is switched to the operating state over time, the laser diode of the ONU increases the optical power until the output of the operating state is completely turned off.

Currently, low-cost ONU optical transmitters that are commonly used use DFB-LDs, and these DFB-LDs have wavelength-dependent characteristics depending on the injection current.

In order to use it as an optical communication signal, the laser light emitted from the ONU must be received by the optical receiver more than a certain power. In the digital communication, the "1" signal and the "0" . At present, the "1" state output of the ONU optical device must have an optical output of at least 3dBm and the "0" signal of the ONU optical device should be at least -5dB less than the "1" signal power. This condition means that the current for the "1" state signal of the laser diode chip must be equal to or higher than a specific current. Normally, a current exceeding 50 mA must be supplied to obtain the light output required for the "1" Therefore, when the ONU is switched from the non-operating state to the operating state, a very large current change is required, which causes a serious fluctuation of the output laser wavelength of the optical element of the ONU set to a specific wavelength. The fluctuation of such a wavelength acts as crosstalk to the channel using the other wavelength, which causes the quality of the optical communication to deteriorate.

Meanwhile, it is preferable that the optical device of the ONU is fabricated in the form that the wavelength variable laser light source and the wavelength tunable optical receiver are directly connected. In the optical module for bidirectional communication composed of the optical transmitter operating in the burst mode and the wavelength tunable optical receiver, A method for effectively eliminating crosstalk caused by a fluctuation of the wavelength of an optical transmitter operating as a light source has not been proposed, thereby making it difficult to develop a next-generation optical communication optical device.

Korean Patent Registration No. 10-0532307 (November 23, 2005)

It is an object of the present invention to provide a wavelength multiplexing optical communication system capable of reducing wavelength fluctuation of a DFB-LD operating in a burst mode to prevent crosstalk between channels. And an optical device for a wavelength division multiplexing communication method.

In accordance with another aspect of the present invention, there is provided an optical element for a wavelength division multiplexing communication system including a DFB-LD light source and a light receiving element in a WDM optical communication system, Quot; 0 "signal or a signal of a longer wavelength than the" 0 "signal, is disposed between the wavelength selective filters for optical path setting for determining the optical path according to the wavelengths .

Here, the -10 dB line width of the wavelength selective filter for crosstalk is preferably 4 GHz or more and 1/2 or less of the WDM channel spacing.

It is preferable that a collimating lens for collimating the laser light emitted from the DFB-LD is further disposed on the optical path between the DFB-LD and the crosstalk-canceling wavelength selective filter.

The wavelength selective filter for crosstalk may comprise a wavelength selective filter having an etalon structure.

In addition, the free spectral range (FSR) of the wavelength selective filter for crosstalk of the etalon structure preferably matches the channel frequency interval of the communication system.

On the other hand, it is preferable that the mobility of the transmission band wavelength of the wavelength selective filter for blocking the crosstalk of the etalon structure is 1 pm / C.

According to the present invention, in the optical communication system of the wavelength multiplexing structure, the "1" signal of the optical signal of the ONU is efficiently transmitted, and sufficient optical power is transmitted to the optical receiving end of the OLT. . As a result, the transmission power of the "1" signal is sufficient, and the signal of a longer wavelength than the "0" signal and the "0" signal is effectively blocked to reduce the fluctuation of the wavelength, thereby improving the signal transmission quality of the TWDM system. It will be possible to make a character.

The present invention can be effectively used in a burst mode of a TWDM system in which a wavelength change is severe, but the wavelength difference between the "1" state and the "0" state occurs at a considerable level even when the burst mode operation is not performed. The present invention can be effectively applied to any WDM system having narrower channel spacing than 100 GHz WDM, especially 50 GHz WDM as well as TWDM.

1 is a conceptual diagram of an NG-PON2 system, which is a kind of a conventional WDM communication system,
FIG. 2 is a diagram illustrating an example of transmission spectrum pattern and transmission eye pattern when DFB-LD is operated in a bidirectional communication mode,
FIG. 3 shows an example of spectrum and eye pattern when the DFB-LD of the ONU is driven at 5mA to 55mA corresponding to the burst mode driving,
4 is a conceptual diagram of an optical device for bidirectional communication WDM with a wavelength selective filter for crosstalk according to the present invention inserted therein.
5 shows an example of an optical signal spectrum and an eye pattern when a wavelength selective filter for crosstalk having a bandwidth of 25 GHz according to the present invention is inserted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 shows a spectrum and a transmission eye pattern according to the operation of the DFB-LD when the optical fiber for bidirectional communication WDM does not operate in the burst mode. FIG. 2 shows an example of driving the DFB-LD at 25 mA to 75 mA.

In the spectrum of FIG. 2, the optical power ratio of the "1" signal corresponding to the driving current of 75 mA and the "0" signal corresponding to the driving current of 25 mA corresponds to 5.18 dB, and the wavelength difference corresponds to 0.196 nm. In FIG. 2, when the DFB-LD is driven at 75 mA and 25 mA, the extinction ratio of the eye pattern is 4.94 dB, which is a difference in magnitude between the "1" and the "0"

3 shows an example of a spectrum and an eye pattern when the DFB-LD of the ONU is driven at 5 mA to 55 mA corresponding to the burst mode driving.

As shown in FIG. 3, it can be seen that the wavelength difference between the signal corresponding to the "0" signal and the signal corresponding to the "1" signal increases to 0.296 nm in the burst mode. In the burst mode, the difference between the light intensity of the "1" signal and the light intensity of the "0" signal increases to 14.9 dB since the output light power becomes very small. In the eye pattern, the extinction ratio reaches 11.85 dB, so that the optical receiver of the OLT can sufficiently discriminate the signal.

However, in the TWDM optical communication, four wavelengths with a wavelength interval of 100 GHz (0.8 nm) or 50 GHz (0.4 nm) are used as optical signals. Therefore, if a signal of "1" is fixed to one of four predetermined wavelengths in FIG. 3, for example, in the case of TWDM using an interval of 50 GHz (0.4 nm) So that the "0" signal is mostly transmitted to the adjacent channel, so that it is impossible to proceed to the normal channel. This phenomenon leads to serious crosstalk, which is a factor that hinders the quality of communication.

This phenomenon does not occur only in the burst mode. For example, when the ONU optical module is operating at 25 mA to 75 mA in FIG. 2, the wavelength difference between the "1" signal and the "0" signal is 0.196 nm, Quot; 0 "signal of the " 0 "

In accordance with this problem, in the present invention, a crosstalk cancellation wavelength selective filter for passing a predetermined "1 " signal effectively and blocking a signal longer than a" 0 & So that crosstalk can be prevented.

FIG. 4 is a conceptual diagram of an optical device for WDM into which the wavelength selective filter for crosstalk can be inserted according to the embodiment of the present invention.

4, in the embodiment of the present invention, a light transmitting element 100 including a DFB-LD 110 and a light receiving element 200 including a tunable photo diode are arranged so that their optical axes are perpendicular to each other. And the wavelength selective filter 300 for optical path setting is disposed at the intersection of the optical axes. The optical path-setting wavelength selective filter 300 plays a role of adjusting the path of the transmission and reception light wavelengths.

In addition, it is preferable to transmit the "1" wavelength mainly emitted from the DFB-LD 110 between the DFB-LD 110 and the optical path setting wavelength selective filter 300, and to transmit the "0" A crosstalk preventing wavelength selective filter 500 for blocking a signal of a wavelength is disposed as a trace. The "1" wavelength signal 610 emitted via the DFB-LD 110 and traveling via the crosstalk wavelength selective filter 500 and the optical path setting wavelength selective filter 300 is transmitted to the optical fiber 400 Conversely, the optical reception signal 620 transmitted from the optical fiber 400 is reflected by the optical path setting wavelength selective filter 300 and is incident on the optical receiving element 200.

5 shows the spectrum and the eye pattern of the optical signal when the wavelength selective filter for crosstalk having the band width of 25 GHz is inserted. In FIG. 5, the optical signal transmission device is driven with 5 mA to 55 mA as shown in FIG. 3 Respectively.

3, the optical output intensity ratio of the "1" signal and the "0" signal was 14.9 dB and the wavelength difference was 0.296 nm. On the other hand, when the crosstalk canceling wavelength selective filter 500 was further added , The light output intensity ratio of the "1" signal and the "0" signal is 28dB, which is about 13dB, and the wavelength difference is almost 0.28nm.

Therefore, in the optical device for bidirectional communication of TWDM operating in the burst mode with the structure of FIG. 4, a wavelength selective filter 500 for crosstalk interception is additionally inserted between the DFB-LD 110 and the optical path setting wavelength selective filter 300 Thus, the crosstalk between the wavelength channels can be effectively blocked. In the embodiment of the present invention, it is preferable that the wavelength selective filter 500 for crosstalk can be composed of a wavelength selective filter having a narrow wavelength line width. Here, the wavelength selective filter having a narrow wavelength line width is referred to as an optical path setting wavelength This means that the selectivity filter 300 has a relatively narrow transmission bandwidth compared to the point at which the bandwidth of the pass or reflection corresponds to at least a few hundred GHz and this effectively separates wavelength channels having wavelength intervals of typically 100 GHz or 50 GHz It is possible to perform the function. According to the experiment of the present invention, it is preferable that the -10 dB band width of the crosstalk-intercepting wavelength selective filter 500 is less than half of the WDM wavelength channel, but it is preferably at least 4 GHz. This is because the insertion loss increases sharply for a wavelength selective filter with a -10dB bandwidth too narrow, and a too wide -10dB bandwidth does not sufficiently block crosstalk to a side channel. That is, the -10 dB band width is preferably at least 1/2 of the WDM channel spacing frequency, which is -10 dB band width of 50 GHz or less for 100 GHz wavelength spacing, and the wavelength selective filter 500 for crosstalk interception for 50 GHz wavelength spacing WDM -10dB A bandwidth of 25 GHz or less is appropriate.

In the embodiment of the present invention, all the laser beams traveling to the crosstalk-canceling wavelength selective filter 500 having a narrow transmission bandwidth must have the same incident angle. Therefore, the DFB-LD 110 of FIG. 4 and the crosstalk It is preferable that a collimating lens is disposed on the optical path between the wavelength selective filter 500 for shielding. Further, it is preferable that a lens for converging the collimated laser light to the optical fiber 400 is further provided on the optical path after being emitted from the DFB-LD 110 and transmitted through the wavelength selective filter 300 for optical path setting . The lens disposed between the optical path determining wavelength selective filter 300 and the optical fiber 400 serves to collimate the laser beam emitted from the optical fiber 400 and proceeding to the optical receiving element 200.

In the present invention, the characteristics of the DFB-LD 110 vary very sensitively depending on the presence or absence of light incident on the DFB-LD. Therefore, the DFB-LD 110 and the optical path setting wavelength selective filter 300 It is also possible to add an optical isolator which passes the laser light only in one direction.

Meanwhile, it is preferable that the crosstalk-intercepting wavelength selective filter 500 is set to an etalon structure, which is for producing an optical module for bidirectional communication corresponding to various channels. The FSR (free spectral range) of the etalon-crosstalk wavelength selective filter 500 is preferably set to the set channel frequency interval of the TWDM system. In addition, it is preferable that the crosstalk-canceling wavelength selective filter 500 does not change the transmission wavelength band according to the temperature change of the optical module. Accordingly, the crosstalk wavelength of the crosstalk- Is preferably 1 pm / ° C or less. In addition, in the present invention, the position of the wavelength selective filter 500 for crosstalk can be adjusted by changing the position of the optical path between the lens for collimating the laser beam emitted from the DFB-LD 110 and the wavelength- It is natural that any location is possible.

Meanwhile, the wavelength tunable light receiving device can be applied to the optical receiving device applied to the present invention.

It is to be understood that the present invention is not limited to the above-described embodiment, and that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention. Of course, can be achieved.

100: optical transmission element
200: Light receiving element
300: wavelength selective filter for optical path setting
400: Optical fiber
500: wavelength selective filter for crosstalk
610: Optical path of optical transmission signal
620: optical path of the optical reception signal

Claims (6)

An optical device for a wavelength division multiplexing communication system including a DFB-LD light source and a light receiving element in a WDM optical communication system,
Quot; 1 "signal is passed between the DFB-LD and the optical path setting wavelength selective filter for determining the optical path in accordance with the wavelength, and the signal of & And a wavelength selective filter is disposed on the optical element.
The method according to claim 1,
Wherein the -10 dB line width of the crosstalk-intercepting wavelength selective filter is 4 GHz or more and 1/2 or less of the WDM channel spacing.
The method according to claim 1,
And a collimating lens for collimating the laser light emitted from the DFB-LD is disposed on the optical path between the DFB-LD and the crosstalk canceling wavelength selective filter.
The method according to claim 1,
Wherein the wavelength selective filter for crosstalk is a wavelength selective filter of an etalon structure.
5. The method of claim 4,
Wherein the free spectral range (FSR) of the wavelength selective filter for crosstalk of the etalon structure is equal to the channel frequency interval of the communication system.
5. The method of claim 4,
Wherein the mobility of the transmission band wavelength according to the temperature of the crosstalk-inhibiting wavelength selective filter of the etalon structure is 1 pm / 占 폚.

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