KR20100068155A - Apparatus and method for transmitting optical signal with enhanced reflection sensitivity in wavelength division multiplexing-passive optical network - Google Patents

Abstract

PURPOSE: An optical transmitting device at WDM-PON with improvement of reflection sensitivity and a method thereof are provided to improve stability and reliability of an optical link by making the optical link less sensitive to reflection. CONSTITUTION: A laser diode(10) produces an optical signal and uses the produced optical signal as seed light. A controller unit(20) extends line widen of an output spectrum of the laser diode by approving DC bias and RF signal to the laser diode on electricity of the laser diode. The controller unit comprises the input control part and the output control uniting the optical signal outputted by each wavelength, and uses the combined optical signal as the seed light.

Description

Apparatus and method for transmitting optical signal with enhanced reflection sensitivity in Wavelength Division Multiplexing-Passive Optical Network}

One aspect of the present invention relates to an optical transmission technology, and more particularly, to an optical transmission technology in a wavelength division multiplex based passive optical subscriber network.

This study is derived from the research conducted as part of the IT growth engine technology development project of the Ministry of Knowledge Economy and ICT. [Task Management Number: 2007-S-014-02, Project Name: Metro-Access All-optical Integrated Network Technology Development]

Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) is independent for each subscriber and has the advantage of providing a large capacity communication service. However, the wavelength division multiplexing-based passive optical subscriber network is a factor that increases the price because optical transmission modules having different wavelength characteristics are required as the number of subscribers.

In order to solve the above-mentioned difficulties, the downlink signal transmitted from the central office (CO) is modulated or remodulated by a reflective semiconductor optical amplifier (RSOA) without providing an independent light source to the subscriber. A loop-back scheme is proposed to send back to the central base station.

At this time, since the downlink signal transmitted from the central base station to the subscriber end must also have a distinct wavelength, seed light injection is performed so that the light wavelength of the light sources of the central base station can eliminate the distinction of individual wavelengths in order to solve the problem of price burden and equipment management. It is evolving toward the use of a see-light-injection reflective semiconductor optical amplifier.

In this case, the broadband light source (BLS) may be used as the sequential slicing of the broadband light source, but since the line width of the spectral sliced light source is wide, the transmission speed and the transmission distance of the downlink optical signal may be increased by dispersion. There is a limit.

As the optical subscriber network evolves in the high-speed, long-distance transmission direction, a single mode laser can be used to overcome the limitation due to dispersion. The single mode laser may be a Distributed Feedback Laser Diode Array (DFB-LD Array). However, when the above-described single mode laser is used as the optical transmitter, the optical link is very susceptible to reflection induced noise.

In accordance with an aspect, an optical transmission apparatus and an optical transmission method in a wavelength division multiplex based passive optical subscriber network controlling an optical link to be less sensitive to reflection are proposed.

According to an aspect of an exemplary embodiment, an optical transmitter generates an optical signal and outputs an optical signal by applying a DC bias and an RF signal to a laser diode at a threshold current of a laser diode and a laser diode using the generated optical signal as seed light. And a controller for extending the line width of the output spectrum of the laser diode.

On the other hand, the loop back type wavelength division multiplexing based passive optical subscriber network system according to the other aspect is a laser diode and output that extends the line width of the output spectrum as the optical signal is output by receiving a DC bias and RF signal at the threshold current of the laser diode It includes an optical line terminal including a reflective semiconductor optical amplifier for using the optical signal as a seed light and an optical receiver for receiving the optical signal from the outside.

Meanwhile, an optical transmission method according to another aspect includes inputting a threshold current of a laser diode and applying a DC bias and RF signal to the laser diode at the input threshold current to extend the line width of the output spectrum of the laser diode. do.

According to one embodiment, the linewidth of the output spectrum of the laser diode is extended, making the optical link less sensitive to reflection, thereby improving the stability and reliability of the optical link.

Furthermore, as the laser diode is operated at the threshold current, driving can be performed with low power RF power, thereby improving power efficiency.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention; In the following description of the present invention, if it is determined that detailed descriptions of related well-known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In addition, terms to be described below are terms defined in consideration of functions in the present invention, which may vary according to intention or custom of a user or an operator. Therefore, the definition should be made based on the contents throughout the specification.

1 is a block diagram illustrating a central base station of a loopback type wavelength division multiplexing based passive optical subscriber network system according to an embodiment of the present invention.

Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) is a next-generation optical subscriber network technology using Wavelength Division Multiplexing (WDM) technology. It overcomes the scalability and security weaknesses of) and provides high capacity and high quality service.

Meanwhile, the WDM-PON based Loop-back Reflective Semiconductor Optical Amplifier (Loop-back RSOA) is a downlink signal sent from the central base station (CO) without providing independent light sources to subscribers. Is modulated or remodulated by a reflective semiconductor optical amplifier and sent back to the central base station.

Referring to FIG. 1, a central office (CO) of a loopback wavelength division multiplexing-based passive optical subscriber network system is a seed light 310 and an optical line terminal OLT 320. The optical line terminal 320 includes a reflective semiconductor optical amplifier (RSOA) 324 and an optical receiver (RX) 324.

The seed light 110 may be used by spectral slicing a broadband light source (BLS). However, the method of using a spectral slice by using a broadband light source has a limitation in transmission speed and transmission distance of a signal due to dispersion.

Therefore, according to an embodiment of the present invention, a single mode laser may be used as the seed light 110 of the downlink signal or the uplink signal. The single mode laser may be a distributed feedback laser diode array (DFB-LD array).

However, when using a single mode laser as seed light, the optical link can be very sensitive to reflection induced noise. Therefore, when using a single mode laser, it is necessary to widen the line width of the output spectrum of the laser diode. Linewidth is the width on the wavelength spectrum of the light output from a light source.

According to an embodiment, the line width of the output spectrum is widened through a dithering technique using an RF signal so that the optical link is not sensitive to reflected noise, and a widened line diode is used as the seed light. Dithering refers to spreading the frequency to modulate the line width of the optical signal output spectrum.

Furthermore, according to one embodiment, the laser diode is operated near a threshold current (Ith). The threshold current is the current at which the light source starts to oscillate. As a result, the line width of the laser diode can be widened by only a small size of the RF signal near the threshold current.

Meanwhile, the subscriber station 330 includes an optical network unit (ONU) or an optical network terminal (ONT), and receives an optical signal from the optical line terminal 320. Furthermore, the wavelength division multiplexing-based passive optical subscriber network may further include an outdoor node (RN), which is an optical fiber between optical fiber termination devices of the optical line terminal 320 and the subscriber terminal 330. (fiber) 400 is connected to each other to relay.

2 is a configuration diagram of an optical transmission device 1 according to an embodiment of the present invention. Referring to FIG. 2, the optical transmitter 1 includes a laser diode 10 and a controller 20, and the controller 20 includes an input controller 200 and an output controller 210.

The laser diode 10 is a light emitting device for optical communication, and refers to a diode for generating light having a fine line width. The generated light signal is used as seed light. The laser diode 10 operates as a laser while rapidly increasing the light output when a current of more than a predetermined value called a threshold current (Ith) flows.

The controller 20 applies a DC bias and an RF signal together to the laser diode. Then, the applied RF signal is used to dither the optical signal to be output in a manner of extending the frequency of the optical signal. The controller 20 controls the laser diode to operate at the threshold current of the laser diode to output the dithered optical signal. This allows small RF dithering to extend the linewidth of the output spectrum of the laser diode.

Meanwhile, the input control unit 200 branches the RF signal generated from the RF signal generation source according to the number of optical channels, and applies the branched RF signal and the above-described DC bias to the threshold current of the laser diode.

The output control unit 210 combines the optical signal output for each wavelength according to the RF signal and the DC bias applied from the input control unit 200, and uses the combined optical signal as seed light.

3 is a block diagram of the input control unit 200 of the optical transmitter of FIG.

Referring to FIG. 3, the input controller 200 simultaneously applies the RF current I _RF and the bias current I _bias generated from the RF signal generation source to the laser diode 10. RF current (I _RF ) is a sinusoidal signal of arbitrary frequency and magnitude. When the DC bias current I _bias and the RF current I _RF are applied to the laser diode 10, the line width of the output spectrum is widened by the frequency chirp characteristic of the laser diode 10. As the line width widens, the optical link becomes less sensitive to reflection, thereby improving the stability and reliability of the optical link.

4 is a reference diagram for explaining a process of extending the line width of an output spectrum through an optical signal output at a threshold current of a laser diode according to an exemplary embodiment of the present invention.

In general, even if an RF signal having the same size is applied to the laser diode according to the type of the laser diode, the extent of the line width of the laser diode may be different. Furthermore, in order to widen the line width of the laser diode by dithering, the amplitude of the RF signal must be increased. However, as the size of the RF increases, the line width gradually increases, but it is not efficient to apply the RF signal having a large amplitude for each laser diode provided by the number of channels from the viewpoint of implementing the optical subscriber network.

Therefore, according to the present invention, the laser diode is operated at a threshold current to effectively widen the line width of the laser diode even with a small RF size. That is, the optical transmission apparatus according to the embodiment checks the threshold current of the laser diode, and generates an optical signal having a wide line width by applying a DC bias (I _bias ) and an RF current (I _RF ) near the threshold current.

For example, as shown in FIG. 4, when the x-axis is the driving current, the y-axis is defined as the optical output, and the optical output curve according to the operating current is graphically shown, the operating current The laser diode is operated 300 near 10 mA corresponding to the threshold current of to generate a light source. Therefore, the laser diode can be driven even with low power RF power, thereby improving efficiency of power consumption.

5 is a circuit diagram of an optical transmission device according to an embodiment of the present invention. Here, the circuit configuration will be described with reference to a single light source method, for example, a distributed feedback laser diode array (DFB-LD array).

Referring to FIG. 5, the DFB-LD array includes an RF signal generator 400, an RF distributor 410, a wavelength combiner 470, and an optical distributor 490. Furthermore, the RF amplifier 420 and the optical amplifier 480 may be further included.

The RF signal source 400 generates a sinusoidal signal having an arbitrary frequency and magnitude, for example, an RF signal. The RF signal generator 400 may be an oscillator. The RF splitter RF1 × N splitter 410 branches the output of the RF signal generator 400 by the number of wavelength channels N of the passive optical subscriber network. The branched RF current 450 is applied together with the DC bias current 460 generated from the bias voltage 440 to the laser diode 430 to widen the output line width of the single mode laser.

Furthermore, the laser array may further include an RF amplifier 420 having a small gain. In this case, the laser array may amplify the magnitude of the RF signal branched through the RF distribution unit 410 using an RF amplifier 420 having a small gain. The circuit is configured such that the amplified RF current 450 can be applied to the laser diode 430 together with the direct current 460.

Meanwhile, according to an embodiment, since the laser is operated at the threshold current of the laser diode 430, a small amount of direct current is required. Therefore, as illustrated in FIG. 5, the circuit can be easily configured by adjusting the resistance value.

On the other hand, the wavelength multiplexer (MUX) 470 combines the light output of the laser diode 430, each having a different output wavelength, and uses it as seed light.

Furthermore, the laser array may further include an optical amplifier 480. When the light output value coupled through the wavelength combiner 470 is small enough to be used as seed light, the light output unit 480 may be used to amplify the light output value. At this time, the amplified light output value is branched by the required number of systems (M) through the light distribution unit 490 is utilized as the seed light of the down signal or the up signal of the multiple system.

6 is an exemplary view showing that the line width of the output spectrum is expanded according to an embodiment of the present invention.

Referring to FIG. 6, when a laser diode, for example, DFB-LD is operated at a threshold current, the line width can be widened by only a small size of RF power. For example, when the bias current is 14 mA as shown in the graph shown on the right in FIG. 6, it can be seen that an RF current of 8 mA is applied to the laser diode along with the bias current to widen the line width.

FIG. 7 is an exemplary view illustrating a bit error rate (BER) when a laser diode having an extended line width of an output spectrum according to an embodiment of the present invention is used as seed light. At this time, the RSOA-based loop-back type WDM-PON using DFB-LD with wider line width as seed light will be described.

Referring to FIG. 7, a DFB-LD having a wider line width by applying an RF signal in an optical link having a reflection of about -32 dB is used as a seed light for RSOA, and when a DFB-LD having a general narrow line width is used as seed light. A bit error rate (BER) curve can compare downlink transmission quality.

Blocked squares and closed circles are when the transmission distance is 0 km, and empty squares and empty circles are the bit error rate curves after 60 km transmission. When using the DFB-LD having a narrow line width as the seed light in the reflective optical link (720, 730), it can be seen that an error flow occurs regardless of the transmission distance. In this situation, it can be seen that the transmission quality is improved when the line width is widened by applying the RF signal proposed in the present invention to the seed light DFB-LD (700, 710).

8 is a flowchart illustrating a light transmission method according to an embodiment of the present invention.

Referring to FIG. 8, the optical transmitter inputs the threshold current of the laser diode (S800). Subsequently, the optical transmitter may extend the line width of the output spectrum of the laser diode (S820) by applying the DC bias and RF signals to the laser diode at the input threshold current (S810). Here, the RF signal generated from the RF signal generation source may be branched according to the number of optical channels, and the branched RF signal and the DC bias may be applied to the laser diode.

The embodiments of the present invention have been described above. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 is a block diagram illustrating a central base station of a loopback type wavelength division multiplexing based passive optical subscriber network system according to an embodiment of the present invention;

2 is a block diagram of an optical transmitter according to an embodiment of the present invention;

3 is a configuration diagram of an input control unit of the optical transmission device of FIG.

4 is a reference diagram for explaining a process of extending the line width of an output spectrum through an optical signal output at a threshold current of a laser diode according to an embodiment of the present invention;

5 is a circuit diagram of an optical transmitter according to an embodiment of the present invention;

6 is an exemplary view showing that the line width of the output spectrum is expanded according to an embodiment of the present invention;

7 is an exemplary view illustrating a bit error rate when a laser diode having an extended line width of an output spectrum is used as seed light according to an embodiment of the present invention;

8 is a flowchart illustrating a light transmission method according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

1: light transmitting device 10: laser diode

20: control unit 200: input control unit

210: output control unit 400: RF signal generator

410: RF distributor 420: RF amplifier

450: RF current 460: bias current

470: wavelength combiner 480: optical amplifier

490: light distribution unit

Claims (14)

A laser diode generating an optical signal and using the generated optical signal as seed light; And And a control unit extending a line width of an output spectrum of the laser diode by applying a DC bias and an RF signal to the laser diode at the threshold current of the laser diode and outputting the optical signal. The method of claim 1, wherein the control unit, An input controller for branching an RF signal generated from an RF signal source according to the number of optical channels and applying the branched RF signal and the DC bias to a threshold current of the laser diode; And And an output control unit for combining the RF signals and the optical signals output for each wavelength based on the DC bias application and using the combined optical signals as the seed light. The method of claim 2, wherein the output control unit, And spreading the frequency of the optical signal to be output using the RF signal to extend the line width of the output spectrum. The method of claim 2, wherein the input control unit, It includes an RF amplifier for amplifying the branched RF signal, The input control unit And an RF signal amplified by the RF amplifier and the DC bias are applied at the threshold current of the laser diode. The method of claim 2, wherein the output control unit, It includes an optical amplifier for amplifying the combined optical signal, The output control unit, And an optical signal amplified by the optical amplifying unit as the seed light. The method of claim 1, wherein the laser diode, Light transmitting device, characterized in that the form of a single light source method is applied to independently configure one light source. The method of claim 6, wherein the laser diode, An optical transmission device, characterized in that the distributed feedback laser diode. A laser diode that receives a direct current bias and RF signal at a threshold current of the laser diode and outputs an optical signal to expand the line width of the output spectrum; And A loop back type wavelength division multiplexing passive optical subscriber network comprising a optical line terminal including a reflective semiconductor optical amplifier using the output optical signal as a seed light and an optical receiver receiving an optical signal from the outside system. The method of claim 8, wherein the laser diode, An RF signal generated from an RF signal source and branched according to the number of optical channels and the DC bias are applied at the threshold current of the laser diode to spread line frequency of the output spectrum as the frequency of the optical signal is spread-modulated. Loopback type wavelength division multiplexing based passive optical subscriber network system. The method of claim 8, wherein the laser diode, Loopback type wavelength division multiplexing passive optical subscriber network system, characterized in that the form of a single light source is applied independently constituting one light source. Inputting a threshold current of the laser diode; And And applying a DC bias and an RF signal to the laser diode at the input threshold current to extend the line width of the output spectrum of the laser diode. 12. The method of claim 11, wherein extending the line width of the output spectrum of the laser diode, And an RF signal generated from an RF signal source according to the number of optical channels, and applying the branched RF signal and the DC bias to the laser diode. 12. The method of claim 11, wherein extending the line width of the output spectrum of the laser diode, And combining the optical signal output for each wavelength based on the RF signal and the DC bias application, and using the combined optical signal as the seed light. The method of claim 11, wherein the laser diode, Light transmission method, characterized in that the form of a single light source method is applied to independently configure one light source.

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