KR20060067801A - System and method for forming channel using tunable laser diode - Google Patents

Abstract

The present invention combines a wide wavelength tunable laser with a TDM data structure and appropriately utilizes the optical components required to add a channel switching function to a WDM-PON system, which is a local optical network, and greatly expands the potential transmission speed. In addition, if there is a wavelength transition between the light source and the AWG, the loop-back network structure is used to track the wavelength without additional bypass line and optimize the size of the transmitted signal. In addition, the use of a wavelength variable laser that changes the wavelength electrically minimizes the number of temperature controllers (TEC) required for temperature stabilization of the optical line terminal (OLT).

Tunable Laser, Channel Switching, WDM-PON

Description

System and method for forming channel using tunable laser diode

1 shows a basic network structure of a WDM-PON network.

2 (a) and 2 (b) show an example in which predetermined channels among N channels are channel exchanged in the channel exchange unit of the present invention as a preferred embodiment of the present invention.

FIG. 3 illustrates a WDM-PON system having a channel switching function by modifying an ONU portion of the channel switching WDM-PON system of FIG. 1.

Figure 4 shows a micrograph of the DBR-LD used in one embodiment of the present invention.

5 is a graph measuring wavelength tunable characteristics of the DBR-LD used in an embodiment of the present invention.

Figure 6 shows a micrograph of the SGDBR-LD used in one embodiment of the present invention.

7 is a graph measuring wavelength tunable characteristics of SGDBR-LD used in an embodiment of the present invention.

  The present invention relates to a short-range optical communication network and a technology for an optical communication network structure using passive elements between a base station of a consumer and a communication operator. Currently, high-tech optical communication technology is widely applied in the back-bone network, but coaxial cable is the main means of communication in the local area network (access base), that is, the base station or the office. Staying in

However, because the local area network has many consumers, it is expected that if the technology matures, it will provide a sufficiently large optical communication market. Therefore, much research is being conducted to preempt the necessary technology and secure intellectual property rights.

The most influential means of communication in local area networks is WDM-PON (wavelength division multiplexing passive optical network), which uses passive devices to simultaneously communicate multiple channels assigned to multiple optical wavelengths through a single fiber. to be.

The present invention improves transmission efficiency in a wavelength division multiplexing passive optical network (WDM-PON) by exchanging channels using a wavelength tunable laser and combining the time division multiplexing (TDM) concept with the channel transmission. It is to track.

Representative WDM-PON structures currently proposed or reported include P. Healey et al, "Spectral slicing WDM-PON using wavelength-seeded reflective SOAs," IEE Electron. Lett., Vol. 37, No. 19, pp 1181-1182, 2001. The light of an EDFA or LED is split into multiple wavelengths using an arrayed waveguide grating (AWG), followed by spectrum slicing, assigning a channel to each wavelength and reflecting semiconductor RSOA. Amplified and modulated by optical amplifiers to generate and send data signals, and reported the experimental results of transmitting 25km, 1.25GHz, and 8channels through these methods.

Another representative WDM-PON structure currently proposed or reported is Hyun Deok Kim. et al, "A Low-cost WDM source with an ASE injected Fabry-Perot semiconductor laser," IEEE Photon. Technol. Lett., Vol. 12, No. 8, pp. 1067-1069, 2000. After dividing the light of the light source into several wavelengths, it is incident on a Fabry-Parot laser diode (FP-LD) to make a wavelength-selective FP LD, which generates a data signal. It has been reported that the 155Mb / s, 120km transmission results through this method has been reported.

In addition, M. Zirngibl. et al, "LARNet, a Local Access Router Network," IEEE Photon. Technol. Lett., Vol. 7, No. 2, pp. In 215-217, 1995, a method of generating a multi-frequency laser (MFL) by incorporating a distributed Bragg reflector (DBR) grating on each channel waveguide of an AWG is provided. In this way, transmission results for 200 Mb / s, 10 km, and 9 channels were reported.

In the above-described conventional method, the improvement of the transmission rate through the channel switching and wavelength tracking function proposed by the present invention is not proposed. Accordingly, an object of the present invention is to provide a channel switching method and system for improving transmission efficiency through channel switching and wavelength tracking in a WDM-PON.

The present invention is to improve the transmission speed by exchanging the wavelength of the generated channel using a laser having a wavelength variable characteristic.

More specifically, the present invention improves transmission efficiency in a wavelength division multiplexing passive optical network (WDM-PON) by exchanging channels using a laser having a wide wavelength tunable characteristic and combining the time division multiplexing (TDM) concept with the channel transmission. It is for.

And if there is a wavelength transition between the light source and the AWG, the appropriate network structure is used to track the wavelength and optimize the size of the transmitted signal. In addition, the use of wavelength-tunable lasers that change the wavelength electrically minimizes the number of thermo-electric controllers (TECs) required for temperature stabilization of optical line terminals (OLTs).

In order to achieve the above object, a channel switching system using a tunable laser in a WDM-PON according to the present invention is a wavelength division multiplexing passive optical subscriber network system, using each light source including a laser having a tunable characteristic. A signal generator for generating signals in N channels; A channel variable unit configured to exchange channels by varying a wavelength of the laser so that a predetermined number of channels among the N channels have the same wavelength; And a TDM setting unit configured to time multiplex the predetermined number of channels having the same wavelength.

In order to achieve the above object, in the WDM-PON according to the present invention, a channel switching system using a wavelength tunable laser is N in each wavelength including multiple lasers having wavelength tunable characteristics in a wavelength division multiplexing passive optical subscriber network system. A channel exchange unit for exchanging two channels; A detector that receives and detects a wavelength optical signal of a channel generated by the signal generator and transmitted downward to the ONU and then upwardly transmitted to the OLT; and changes in relative magnitudes of the signal detector 162 signal and the light source state detector 111 signal. And a tracking unit that optimizes the signal detector 162 signal by appropriately changing the wavelength of the light source and the temperature of the temperature controller 162 when the signal of the signal detector 162 is degraded.

In order to achieve the above object, a channel switching method using a wavelength tunable laser in the WDM-PON according to the present invention is a wavelength division multiplexing passive optical subscriber network system, using each light source including a laser having a wavelength tunable characteristic. Generating signals on the N channels; Exchanging channels by varying the wavelength of the laser such that a predetermined number of channels among the N channels have the same wavelength; and time multiplexing the predetermined number of channels having the same wavelength.

In order to achieve the above object, a channel switching method using a wavelength tunable laser in the WDM-PON according to the present invention includes (a) each light source including a laser having a wavelength tunable characteristic in a wavelength division multiplexing passive optical subscriber network system. (B) receiving and detecting an optical signal of a channel generated in the step (a) and transmitted downward to the ONU and then transmitted upward to the OLT; Observe the relative magnitude change of the signal detector 162 signal and the light source condition detector 111 signal, and when the signal of the signal detector 162 degenerates, changes the wavelength of the light source and the temperature of the temperature control device 162 appropriately. 162 optimizing the signal.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same elements among the drawings are denoted by the same reference numerals and symbols as much as possible even though they are shown in different drawings.

In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

In addition, in order to be more faithful to the present invention, it is noted that changes or modifications can be made by those skilled in the art without departing from the spirit of the present invention.

As used herein, "channel exchange" means that each channel generates a wavelength of a light source other than the wavelength it generates. For example, when there are N light sources L1, L2, ... Ln-1, Ln, and generate wavelengths λ1, λ2, ..λn-1, λn, respectively, the light source L2 does not generate λ2 but λ1. When it happens, it means that the channel has been exchanged.

1 shows a basic network structure of a WDM-PON network.

WDM-PON is a structure in which multiple ONUs are connected to a central office through multiple optical links by using a wavelength division multiplexing (WDM) method for multiplexing wavelengths by subscriber or service. terminal, 100), RN (Remote Node, Remote Detector) 180, and ONU ((Optical Network Units, 190)).

The base station is also referred to as a feeder network, generates an optical signal having a plurality of different wavelengths and transmits it to a remote detector (180, hereinafter referred to as "RN"), and on the contrary, transmits from the ONU 190, which is a multiple subscriber network, to the RN 180 It consists of a part for receiving a signal to the base station.

The OLT 100, which is a transmitter, is usually located in a base station of a telecommunications operator, and includes a signal generator 120, a channel variable unit 130, a TDM setup unit 140, and a light source including N light sources 121. The state signal detector 111, the temperature controllers 112 and 161, the molded optical coupler 150, an arrayed waveguide grating 160, a signal detector 162, and a tracer 170 are included.

The ONU 190 is also referred to as a distribution network, and receives each WDM signal distributed by the RN 180 and transmits it at the subscriber, or transmits multiple SCM (Sub-carrier Multiplexing) signals from each subscriber to the base station. To RN 180.

The ONU 190 installed in the individual receiver includes an RSOA (191, reflective semiconductor optical amplifier) and a signal detector 192 for detecting a transmitted signal.

The RN 180 is located between the base station and the ONU 190 and uses a passive optical device such as an arrayed waveguide grating (AWG) to demultiplex and route optical signals of various wavelengths from the base station to the ONU 190, and vice versa. Each WDM channel destined for the base station in the ONU 190 of the multiplexed to the base station.

Under the network structure as shown in FIG. 1, the present invention uses a transmission signal in the form of a loop-back signal as a preferred embodiment. This signal structure does not require light generating devices such as lasers or light emitting diodes, and requires only an optical amplifier (eg RSOA or SOA), which not only lowers the price of the ONU installed in the receiver but also manages and maintains it. Is easy. Such local area networks typically operate within a distance of about 20 km.

The channel switched WDM-PON communication network of FIG. 1 operates as follows.

The N-channel wavelength optical signal from the light source 121 in the OLT 100 is extracted by a shape coupler 150 which extracts the wavelength optical signal from the optical path, so that individual channels are branched at the RN 180, respectively. Is passed to the receiver's ONU (downstream).

The signal transmitted to the ONU is partially detected by the signal detector 192 and the rest is amplified by going to the reflective semiconductor optical amplifier (RSOA, 191), and the ONU data is loaded on the corresponding portion of the loopback signal and transmitted to the OLT (upstream). ).

Each ONU signal is combined at RN 180 and separated back at AWG 160 of the base station to be read by signal detector 162 in the base station.

At this time, OLT and ONU use Loop-Back signal as transmission signal. The Loop-Back signal consists of two parts (193 and 194).

The front part of the loop-back signal has the same structure as a normal digital modulation signal 193, and the rear part is a constant-sized optical signal 194 without a modulation signal, which is sent from the ONU to the OLT in the rear part. Load the signal.

The channel exchanger 110 of FIG. 1 includes a signal generator 120, a channel variable unit 130, and a TDM setup unit 140.

The signal generator 120 generates signals for N channels using N light sources.

The light source 121 generates a wavelength optical signal carrying downlink transmission data transmitted from the OLT in the wavelength division multiplexing passive optical subscriber network system to each ONU using a laser having a wavelength variable characteristic, and the laser generates a current. It is characterized by changing the wavelength electrically.

N light sources L ₁ , L2, ... Ln-1, Ln default to generate wavelengths lambda 1, lambda 2, .lambda n-1, and lambda n, respectively. However, since each of the N light sources generates a wavelength optical signal of a channel using a wavelength tunable laser, a light source that generates λ1 in L1 can also generate a variable wavelength optical signal of λ2, .. λn-1, λn. .

As a preferred embodiment of the laser, for example, the distributed Bragg Reflector laser diode (DBR-LD) and the sampled grating reflector laser diode (SGDBR-LD), the DBR-LD has a variable region of up to 8-10 nm and the SGDBR-LD Has a wide variable region of 35nm or more. That is, when the channel spacing is 100 GHz (0.8 nm), the DBR-LD can generate 10 channels and the SGDBR-LD can generate signals of 40 channels or more with the same laser.

In the case of a wavelength variable laser or a DFB-LD (distributed feedback laser) that changes the wavelength with temperature, the temperature controller has a complicated problem because the same number of temperature controllers as the number of light sources are required and they must be operated independently of each other.

However, in the present invention, when the light source 121 entering the OLT uses a DBR-LD or SGDBE-LD wavelength tunable laser, the current is injected into the DBR portion to electrically change the wavelength, thereby requiring a temperature controller (TEC, thermo- The number of electric controllers 112 can be reduced. Therefore, at least one temperature controller may be used depending on the capacity.

The channel variable unit 130 changes the wavelength of a predetermined channel among the N channels by using a wavelength tunable laser as needed to convert the wavelength optical signal of the channel generated by the signal generator 120 as necessary. .

The TDM setting unit 140 transmits a channel by time multiplexing a wavelength of a predetermined channel changed by the channel variable unit.

The channel exchanger 110 of FIG. 1 will be described in more detail in the relevant part of FIG. 2.

The shaping optical coupler 150 extracts the wavelength optical signal from the optical path and combines the optical signals of the N channels generated from the N light sources 121 and time-multiplexed by the TDM setting unit and transmitted to the ONU 190.

In the network structure of FIG. 1, in a preferred embodiment of the present invention, the ONU 190 uses a loop-back signal and downwards to an ONU and a signal amplifier 191 for amplifying a wavelength optical signal of a channel transmitted downward in the OLT. And a signal detector 192 for detecting the transmitted signal. The signal amplifier includes a reflective semiconductor optical amplifier (RSOA) or a semiconductor optical amplifier (SOA).

The reflective semiconductor optical amplifier 191 is utilized in a loop-back form in the WDM-PON method. That is, the reflective semiconductor optical amplifier 191 amplifies the signal transmitted to the ONU, and loads the ONU data in the rear portion 113 of the loop-back signal to the OLT.

The RN 180 combines the signal amplified by the reflective semiconductor optical amplifier 191 and transmits the signal amplified by the reflective semiconductor optical amplifier 191 to the AWG 160 in the base station. The AWG 160 transmits the wavelength optical signal of the channel transmitted upward from the ONU to the OLT. Separate and detect.

Since WDM-PON uses many different wavelengths, the wavelength of the light source may change little by little due to temperature change and deterioration with time. Since the RN 180 is normally installed outdoors, the wavelength of the RN 180 may shift according to the outdoor temperature change.

In this case, the upstream signal 181 from the ONU to the OLT detected in the base station is compared with the light source state detector signal 111 in order to track the transition wavelength.

When the wavelength of the AWG 160 in the base station and the wavelength of the RN 180 do not match, the signal detector 162 may detect that the intensity of light passing through the AWG 160 decreases.

The tracking unit 170 compares the magnitude of the signal passing through the AWG 160 and the light source state detector signal 111 when the wavelength of the AWG 160 in the base station and the wavelength of the RN 180 do not coincide with each other. Control each controller so that it has the initial size.

 First, by adjusting the temperature controller 161 that controls the temperature of the base station AWG, the temperature of the controller 161 is changed little by little in the direction of increasing the optical signal, and at the same time, the wavelength of the light source is also changed little by little in the direction of increasing the optical signal. Is the maximum value.

That is, when the wavelength shift of the RN 180 occurs, the tracking unit 170 adjusts the signal detected by the signal detector 162 to have a maximum value by simultaneously changing the AWG temperature of the base station and the wavelength of the light source.

2 (a) and 2 (b) show an example in which predetermined channels among N channels are channel exchanged in the channel exchange unit of the present invention as a preferred embodiment of the present invention.

When there are N light sources L1, L2, ... Ln-1, Ln, and generate wavelengths λ1, λ2, ..λn-1, and λn, respectively, in the present invention, the meaning of "channel switching" means that each channel has its own. This means generating a wavelength of a light source other than the generated wavelength. For example, it means that the channel is switched when the light source L2 does not generate λ2 but rather λ1.

Looking at the process of channel exchange between four channels as an embodiment of the present invention as shown in Figure 2- (1). If the receivers of channels 1, 2, and 3 do not have a large amount of data and the receivers of channel 4 require high-speed data transmission, the light source of channel 1 divides the signals of channels 1, 2, and 3 into time bands and transmits respective wavelengths. .

For example, t1, t2 and t3 are divided into λ1 for t1, λ2 for t2, and λ3 for t3. At this time, since the light source uses a tunable laser, the light source can be changed in wavelength as described above.

The light sources of channels 2, 3, and 4 generate the signal of channel 4, and time-multiplex the wavelength optical signal of the channel transmitted downward from the OLT to the ONU.

More specifically, when described with reference to Figure 2- (2) as follows.

If the wavelength of the three channels of channel 2, channel 3, and channel 4 of the optical signal generated by the channel exchanger is changed to λ 4 to generate the signal 101010 in the TDM setting unit, the OLT is transmitted downward to the ONU. Divide the downlink transmission time of the optical signal into six, time multiplexing by assigning 1 to channel 2, 0 to channel 3, 1 to channel 4, then 0 to channel 2, 1 to channel 3, and 0 to channel 4. To transmit the signal.

In this case, the system's potential maximum communication speed is increased by three times. The technical feasibility required for this is as follows. If the maximum communication speed per channel is 2.5Gbps, the maximum communication speed becomes 7.5Gbps.

In this case, when the DBR-LD is used as the wavelength tunable laser and the channel spacing is 100 GHz (0.8 nm), it is possible to exchange over 10 channels and the maximum transmission speed is 22.5 Gbps or more.

Since the switching speed of the DBR-LD or SGDBR-LD used as the preferred embodiment of the present invention is in the unit of completed ms, channel switching is also possible in ms unit. You can also use an external cavity tunable laser (ECTL) or wavelength-tunable laser using MEMS, although the switching speed is a bit slow.

Currently, the DBR-LD is reported in the paper by direct modulation up to 40 GHz, and the SGDBR-LD is selling 2.5 Gbps by electro-absorption modulator integration.

FIG. 3 illustrates a WDM-PON system having a channel switching function by modifying an ONU portion of the channel switching WDM-PON system of FIG. 1.

In the WDM-PON system of FIG. 3, an optical circulator 303 is additionally included in the ONU using a light generating device 301 such as a laser or a light emitting diode (LED).

Compared to FIG. 1, the modified channel-switched WDM-PON system of FIG. 3 uses a conventional signal structure instead of a loop-back signal structure, and has only one strand of optical fiber 302 between the base station and the RN. have.

However, the channel switching is possible in the modified channel switching WDM-PON system of FIG. 3, but does not have a wavelength tracking function as shown in FIG. 1. That is, in the structure of FIG. 1, since the wavelength of the light source generated by the light source in the OLT is returned to the signal detector as it is, there is an advantage that wavelength tracking can be performed without adding a separate bypass line.

Figure 4 shows a micrograph of the DBR-LD used in one embodiment of the present invention.

The DBR-LD of FIG. 4 outputs 5 to 10 mW when the total length is 700 to 1000 mm and the output intensity is 80 mA. In FIG. 4, 401 is an active region, 402 is a phase control region, and 403 is a DBR region.

5 is a graph measuring wavelength tunable characteristics of the DBR-LD used in an embodiment of the present invention. As shown in the figure, it can be seen that the wavelength of the output light changes by changing the magnitude of the current injected into the DBR region.

Figure 6 shows a micrograph of the SGDBR-LD used in one embodiment of the present invention.

The SGDBR-LD of FIG. 6 has an overall length of about 1 to 1.5 mm and the light output intensity is slightly lower than or similar to that of the DBR-LD of FIG. 4. In FIG. 6, 602 is an active region, 603 is a phase control region, and 601 and 604 at both ends are SGDBR regions.

7 is a graph measuring wavelength tunable characteristics of SGDBR-LD used in an embodiment of the present invention. 7 shows that the variable region of the wavelength is 35 nm from 1520 nm to 1555 nm.

The invention can also be embodied as computer readable code on a computer readable recording medium. Computer-readable recording media include all kinds of recording devices that store data that can be read by a computer system.

Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, which are also implemented in the form of carrier waves (for example, transmission over the Internet). It also includes. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

The best embodiments have been disclosed in the drawings and specification above. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims.

Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

The present invention uses a tunable laser to vary the wavelength generated by each light source, to enable channel exchange by time multiplexing the channel transmitted from the OLT to the ONU, and to increase the transmission efficiency.

In addition, the use of the tunable laser in the light source, when the reflective semiconductor optical amplifier or semiconductor optical amplifier is used in the ONU, the wavelength can be traced to produce an effect of matching the AWG channel wavelength to the RN channel wavelength in the OLT.

In addition, the wavelength tunable laser has the characteristic of changing the wavelength by the current, the effect of simplifying the complicated circuit by the temperature controller, and the economical efficiency effect occurs by reducing the use of a plurality of temperature controllers .

Claims (15)

A system for switching channels in a wavelength division multiplexing passive optical subscriber network. A signal generator for generating signals in N channels using respective light sources including a laser having a wavelength tunable characteristic; A channel variable unit configured to exchange channels by varying a wavelength of the laser so that a predetermined number of channels among the N channels have the same wavelength; And And a TDM setting unit for time multiplexing the predetermined number of channels having the same wavelength. The method of claim 1, The laser having the wavelength tunable characteristics is a distributed bragg reflector laser diode (DBR-LD) or a sampled grating reflector laser diode (SGDBR-LD). The method of claim 1, The wavelength of the laser is variable by current. The method of claim 1, wherein the light source And a wavelength optical signal carrying downlink transmission data transmitted from each OLT to each ONU in the wavelength division multiplexing passive optical subscriber network system using the laser having the wavelength tunable characteristic. A system for switching channels in a wavelength division multiplexing passive optical subscriber network. A channel exchanger for exchanging wavelengths in N channels using respective light sources including lasers having wavelength tunable characteristics; A detector configured to receive and detect a wavelength optical signal of a channel generated by the signal generator and transmitted downward to the ONU and then transmitted upward to the OLT; And a tracking unit observing a relative magnitude change of the signal detector signal and the light source condition detector signal and optimizing the signal detector signal by changing the wavelength of the light source and the temperature of the temperature controller when the signal of the signal detector is degraded. Channel switching system. The method of claim 5, And the ONU uses a loop-back signal and amplifies an optical signal of a wavelength of a channel transmitted downward in the OLT. The method of claim 5, The ONU includes a reflective semiconductor optical amplifier (RSOA) or a semiconductor optical amplifier (SOA) using a loop-back signal. The method of claim 5, The laser having the wavelength tunable characteristics is a distributed bragg reflector laser diode (DBR-LD) or a sampled grating reflector laser diode (SGDBR-LD). The method of claim 5, The wavelength of the laser is variable by current. The method of claim 5, And a remote detector for detecting a wavelength optical signal of a channel transmitted downward from the OLT to the ONU. 6. The apparatus of claim 5, wherein the channel exchange unit A channel varying unit for exchanging channels by changing a wavelength of the laser so that a predetermined number of channels among the N channels have the same wavelength; And And a TDM setting unit for time multiplexing the predetermined number of channels having the same wavelength. A method of switching channels in a wavelength division multiplexing passive optical subscriber network, Generating a signal in the N channels using each light source including a laser having wavelength tunable characteristics; Exchanging channels by varying the wavelength of the laser such that a predetermined number of channels of the N channels have the same wavelength; and Time multiplexing the predetermined number of channels having the same wavelength. The method of claim 12, The laser having the wavelength tunable characteristic is a distributed bragg reflector laser diode (DBR-LD) or a sampled grating reflector laser diode (SGDBR-LD). The method of claim 12, The wavelength of the laser is a channel switching method characterized in that the variable by the current. The method of claim 12, wherein the light source Channel exchange, characterized in that for generating a channel by generating a wavelength optical signal carrying the downlink transmission data transmitted to each ONU in the OLT in the wavelength division multiplexing passive optical subscriber network system using the laser having the wavelength tunable characteristics Way.

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