KR20130085559A - Apparatus and mehod for controlling optical transmitter - Google Patents

Abstract

PURPOSE: An apparatus and method for controlling an optical transmitter are provided to uniformly maintain an extinction ratio by controlling the operation of a laser diode of an optical transmitter. CONSTITUTION: An apparatus for controlling an optical transmitter comprises a light source and a control unit (24). The control unit monitors the intensity of light outputted from the light source and maintains the light output by controlling bias currents. The control unit sets modulation currents as a ratio of the bias currents and controls the ratio using a temperature. [Reference numerals] (201) Injected light; (202) Light output; (23) APC circuit; (24) Control unit; (AA) Modulated currents; (BB) Bias currents

Description

Optical transmitter control device and method {APPARATUS AND MEHOD FOR CONTROLLING OPTICAL TRANSMITTER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical subscriber transmission system, and more particularly, to an apparatus and a method capable of controlling a laser diode (LD) driving of an optical transmitter to maintain a constant extinction ratio according to a change in temperature and injected light intensity. will be.

WDM-PON (WAVELENGTH DIVISION MULTIPLEXED PASSIVE OPTICAL NETWORK) transmits and receives optical signals of different wavelengths from multiple optical transmitters and receivers through optical fiber using a wavelength division multiplexing device. By using the wavelength division multiplexing method, it is possible to transmit a large amount of data at the same time, thereby increasing the bandwidth between transmission intervals, and the cost of renting an optical line by transmitting data using one optical fiber instead of using multiple optical fibers. And there is an advantage to save the maintenance cost.

In the control design of an optical transmission device including a laser diode (LD), the main goal is to control the zero level and one level of the light output to an optimal value. At this time, APC (Automatic Power Control) and AMC (Automatic Modulation Control) control technology has been commonly used.

APC controls the intensity of light output by controlling the bias current according to the current of the monitoring photo diode (mPD) of the laser diode, and AMC controls the current with a predefined optimized modulation current according to the temperature. To control. Furthermore, a method of controlling the modulation current according to the bias current has been proposed.

APC and AMC control methods can guarantee a constant output and attenuation rate according to temperature and device aging, but like injection seeding-type optical transmitters, signal quality can be changed when the injection light intensity, temperature, device aging, or both change simultaneously. The disadvantage is that it is difficult to maintain. For example, when the optimized light transmission module changes the injected light, changes the temperature, or both at the same time, the LI curve of the laser diode changes, which changes the crossing point to cause signal jitter or extinction. ratio, making it difficult to guarantee stable signal quality. In addition, the conventional APC control circuit is suitable for outputting light of a certain intensity, but in the optical subscriber transmission system in which the transmission distance / loss is not constant, it is not possible to automatically adjust the light intensity according to the light transmission distance / light loss.

In conclusion, in the APC control method, since the zero level of the output signal is changed according to the bias current, the resultant light ratio is changed. Various methods have been proposed to maintain the chain light ratio, but the AMC control method of controlling the modulation current according to the dual temperature has a problem that the chain light ratio cannot be kept constant according to the intensity change of the external injection light, and the modulation current according to the bias current. The control method has a problem in that the chain light ratio cannot be kept constant when the temperature and the injected light intensity are simultaneously changed.

No. 6,859,473 (registered Feb. 22, 2005)

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus and method for controlling the LD driving of an optical transmitter to maintain a constant chain light ratio according to changes in temperature and injected light intensity.

Another object of the present invention is to provide an apparatus and method for automatically adjusting the intensity of light output according to the optical transmission distance / light loss in an optical subscriber transmission system in which transmission distance / loss is not constant.

According to an aspect of the present invention, an apparatus and method are disclosed that are capable of maintaining a constant chain light ratio according to a change in temperature and injected light intensity by controlling LD driving of an optical transmitter. According to the present invention, the optical transmitter monitors the output intensity of the light source, controls the bias current to maintain a constant light output, sets the modulation current as the ratio of the bias current, and adjusts the ratio by temperature. In addition, the intensity of the optical signal output from the optical transmitter provided in one optical node is adjusted according to the intensity of the optical signal or injection light received from another optical node.

According to the present invention, when the temperature and the injected light intensity are changed at the same time, there is an advantage in that the chain light ratio can be kept constant. In addition, in the optical subscriber transmission system in which the transmission distance / loss is not constant, there is an advantage of automatically adjusting the intensity of light output according to the optical transmission distance / light loss.

1 is a diagram showing the configuration of an optical subscriber transmission system to which the present invention can be applied.
2 is a diagram showing the configuration of an optical transmitter according to an embodiment of the present invention.
3 shows a change in the proportional function required with temperature in accordance with an embodiment of the invention.
4 is a view showing a change in light output according to the injected light intensity.
5 is a view comparing the intensity of the received optical signal according to the present invention compared to the prior art.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

1 is a diagram showing the configuration of an optical subscriber transmission system to which the present invention can be applied.

The optical subscriber transmission system (WDM-PON system) includes an optical line terminal (OLT: 100), an optical transmitter (110, 310), an optical splitter (120), and an injection light source of a central office (CO). 131, 132, an optical circulator 140, a single mode fiber 210, a remote node 200, and an optical network unit 300 (ONU) 300. .

The optical transmitter 310 located in the optical subscriber terminal 300 receives the light source transmitted from the injection light source 1 131, and the optical transmitter 110 located in the central base station 100 receives the light source from the injection light source 2 132. Receive the input. In the optical transmitter 110 of the central base station 100 and the optical transmitter 310 of the optical subscriber terminal 300, the light output signal intensity decreases due to the increase in the intensity of the light sources input from the respective injection light sources 131 and 132. Occurs. The reduction of the optical output signal strength may occur in both the optical transmitters 310 and 110 located in the central base station 100 and the optical subscriber terminal 300, and in particular, in the optical transmitter 310 located in the optical subscriber terminal 300. Occurs more severely. This is because the intensity distribution of the injected light input to the optical transmitter 310 located in each optical subscriber terminal 300 is wide because the distance from the central base station 100 to the optical subscriber terminal 300 varies.

The optical transmitters 110 and 310 used in the optical subscriber transmission system (WDM-PON system) use an automatic output control (APC) technique to maintain the quality of the output optical signal.

Looking at the configuration of the optical transmitter (110,310) with reference to Figure 2 as follows.

The laser diode (LD) 21 outputs an optical signal having a predetermined optical power to the front portion based on the modulation current, the bias current, and the injection light 317 applied from the LD driving circuit, and also the rear portion. Outputs an optical signal having optical power. In one embodiment, the optical power ratio of the optical signal output to the front portion and the optical signal output to the rear portion may be 9: 1. However, the optical power ratio of the optical signal output to the front part and the rear part of the laser diode 21 is not limited thereto. The laser diode 21 is a diode that generates an optical signal using a forward semiconductor junction as an active medium, and gallium arsenide (GaAs) or the like may be used as the material. The higher the temperature of the laser diode 21 requires a higher intensity current.

The photodiode 22 receives the optical signal output to the rear portion of the laser diode 21 and converts it into a monitoring current. The converted monitoring current is proportional to the power of the optical signal received by the photodiode 22. Therefore, in the photodiode 22, when the injection light 201 increases and the optical signal output to the rear portion of the laser diode 21 increases, the monitoring current also increases proportionally.

An automatic output control (APC) circuit 23 forms a control signal for controlling the bias current based on the monitoring current delivered from the photodiode 22.

The laser diode (LD) 21 included in the optical transmitter 20 may be manufactured in a photodiode (mPD) 22 and one package (for example, a transmitter optical sub-assembly (TOSA)). The photodiode 22 is configured to receive an optical signal by using a mirror and simultaneously output a signal having a predetermined ratio to the rear surface. The photodiode 22 outputs a current proportional to the intensity of the optical signal input. The photodiode 22 outputs a current in proportion to the control signal (control signal for controlling the bias current) of the automatic output control (APC) circuit 23. The amount of bias current flowing through the laser diode 21 is adjusted so that the output current amount of the diode 22 always maintains a constant value. For example, when the output optical signal intensity of the laser diode 21 is higher than the reference value, the output current of the photodiode 22 also increases, and the control unit 24 controls the laser according to the control signal of the automatic output control (APC) circuit 23. The bias current input to the diode 21 is reduced to reset the output optical signal strength to a reference value. That is, the controller 24 reduces the bias current input to the laser diode 21 to lower the output optical signal intensity of the laser diode 21 to reduce the output current of the photodiode 22. On the other hand, if the output optical signal intensity of the laser diode 21 is lower than the reference value, the output current of the photodiode 22 is also reduced. According to the control signal of the automatic output control (APC) circuit 23, the controller 24 controls the laser. The bias current input to the diode 21 is increased to increase the output optical signal intensity of the laser diode 21 to increase the output current of the photodiode 22.

In addition, the controller 24 forms a modulation current applied to the laser diode 21. In one embodiment, the modulation current is to receive data including information to be transmitted from the outside to the optical signal output from the laser diode (21).

In particular, the controller 24 controls the modulation current in proportion to the bias current. At this time, the ratio of the modulation current to the bias current is changed according to the temperature. As such, by controlling the ratio of the modulation current to the bias current according to the temperature, it is possible to maintain a constant chain light ratio to the change in temperature and the injected light intensity.

The ratio of the modulation current to the bias current changes with temperature, and the change in the proportional function K (T) required with temperature is shown in FIG. The control unit 24 controls the bias current and the modulation current based on this proportional function K (T). For example, if the bias current A for adjusting the output optical signal intensity of the laser diode 21 is known, the optimum modulation current B is calculated and applied at an arbitrary temperature (for example, 20 degrees) based on the proportional function K (T). can do.

The proportional function K (T) of FIG. 3 measures the bias current and the modulation current to maintain the required output light (0 dBm) and the chain light ratio (13 dB) according to the change in the injected light intensity and temperature, and calculates LD characteristics thereof. As a parameter, it is calculated in advance and stored.

In addition, the controller 24 may adjust the light output intensity of the laser diode 21 according to the light transmission distance / light loss.

Therefore, the control unit 24 monitors the light output intensity of the laser diode 21 and controls the bias current to maintain a constant light output, in which the modulation current is set as a ratio of the bias current, which is dependent on the temperature. By adjusting.

The optical transmitter 20 for the WDM-PON using the injection seeding method has a characteristic of changing the light intensity output according to the injection light intensity as shown in FIG. 4. For example, when the intensity of the injection light 201 is increased, the photodiode 22 is affected by the injection light 201 so that the current of the photodiode 22 is relatively increased, and the APC circuit 23 is increased. The control unit 24 reduces the output light intensity by decreasing the bias current in order to keep the current of the photodiode 22 constant according to the control signal of. On the contrary, when the intensity of the injection light 201 is decreased, the photodiode 22 is affected by the injection light 201, so that the current of the photodiode 22 is relatively decreased, and the control signal of the APC circuit 23 is reduced. Accordingly, the control unit 24 increases the output light intensity by increasing the bias current to keep the current of the photodiode 22 constant. That is, the output light of the optical transmitter 20 in which the injection light 201 is injected relatively strongly is adjusted to be relatively low, and the output light of the optical transmitter 20 in which the injection light 201 is relatively weak is injected relatively strongly. Adjust. 4 is a view showing a change in light output according to the injected light intensity. The FP-LD used in the experiment has a total reflectance of 0.4% with a total antireflection coating to improve the efficiency of the injected light.

As a result, the optical transmitter of the ONU, which is located far from the central base station CO, is injected with light of weaker intensity, and the output signal is strongly controlled to transmit to the central base station CO. The optical transmitter of the ONU, which is located close to the CO), is injected with a stronger signal to weakly regulate the output signal and transmit it to the central base station (CO). Therefore, the receiving end of the central base station (CO) receives the light of uniform intensity, there is an advantage that can reduce the signal interference between channels.

As such, the output intensity of the optical signal output from one optical node (for example, CO or ONU) may be adjusted according to the intensity of the optical signal received from another optical node (ONU or CO). In one embodiment, when the central base station (CO) delivers the injected light of a predetermined wavelength to the optical subscriber end device (ONU) in the optical subscriber transmission system (WDM-PON system), the optical subscriber end device (ONU) is a central base station The optical signal of the same wavelength as the injection light of the predetermined wavelength received from the (CO) is transmitted to the central base station (CO), wherein the output intensity of the optical signal output from the optical subscriber end device (ONU) is from the central base station (CO) The intensity of the injected light is adjusted. In another embodiment, when the central base station (CO) transmits an optical signal to the optical subscriber end device (ONU) in the optical subscriber transmission system (WDM-PON system), the central base station (CO) at the optical subscriber end device (ONU) The output strength of the optical signal transmitted to is adjusted according to the intensity of the signal light received from the central base station (CO).

5 is a diagram comparing a conventional light control method having a fixed light output and a reception power level according to the proposed method. Considering the WDM-PON network with a fixed optical output (-5 to 0 dBm), when the optical terminal experiences an optical path loss of 7.5 dB to 13.5 dB depending on insertion loss and transmission distance, the reception power level of the central station is -18.5 to -7.5 dBm. On the other hand, in the proposed light source control scheme, as the path loss decreases from 13.5dB to 7.5dB, the injected light intensity also decreases by 6dB, and the output decreases from -5 to 0dBm to -8.9 to -3.9dBm (light output intensity / When the injected light intensity slope = -0.65 dB / dB, see FIG. 4), the received power level difference is reduced from -18.5 to -7.5 dB to -18.5 to -11.4 dB.

Although the method has been described through particular embodiments, the method may also be implemented as computer readable code on a computer readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and may be implemented in the form of a carrier wave (for example, transmission over the Internet) . In addition, the computer-readable recording medium may be distributed over network-connected computer systems so that computer readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the above embodiments can be easily deduced by programmers of the present invention.

Although the present invention has been described in connection with some embodiments thereof, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention as understood by those skilled in the art. something to do. It is also contemplated that such variations and modifications are within the scope of the claims appended hereto.

20: optical transmitter 21: laser diode (LD)
22: Photodiode (mPD) 23: Automatic Output Control (APC) Circuit
24:

Claims (9)

As an optical transmitter adjusting device,
Light source; And
An optical transmitter control device including a control unit for monitoring an output intensity of the light source, controlling a bias current to maintain a constant light output, setting a modulation current as a ratio of the bias current, and adjusting the ratio by temperature . The method of claim 1,
The intensity of the optical signal output from the optical transmitter provided in one optical node is adjusted according to the intensity of the optical signal received from another optical node, optical transmitter control device. The method of claim 1,
The intensity of the optical signal output from the optical transmitter provided in one optical node is adjusted according to the intensity of the injection light received from the other optical node, optical transmitter control device. The method of claim 3,
And the optical signal is an optical signal having the same wavelength as the injected light. 5. The method according to any one of claims 1 to 4,
And the ratio is a proportional function calculated from a bias current and a modulation current measured to maintain an output light and a chain light ratio required according to a change in injected light intensity and temperature. As a method of adjusting the optical transmitter,
And adjusting the intensity of the optical signal output from the optical transmitter provided in one optical node according to the intensity of the optical signal or injection light received from another optical node. The method according to claim 6,
Monitoring the output intensity of the light source at the optical transmitter, controlling the bias current to maintain a constant light output, setting a modulation current as the ratio of the bias current, and adjusting the ratio by temperature Optical transmitter control method to do. The method according to claim 6,
And the optical signal is an optical signal having the same wavelength as the injected light. 9. The method according to any one of claims 6 to 8,
And the ratio is a proportional function calculated from a bias current and a modulation current measured to maintain an output light and a chain light ratio required according to a change in injected light intensity and temperature.

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