KR20160107029A - Apparatus and method for optimizing bias of laser diode in analog optical signal transmission - Google Patents

Apparatus and method for optimizing bias of laser diode in analog optical signal transmission Download PDF

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KR20160107029A
KR20160107029A KR1020150029937A KR20150029937A KR20160107029A KR 20160107029 A KR20160107029 A KR 20160107029A KR 1020150029937 A KR1020150029937 A KR 1020150029937A KR 20150029937 A KR20150029937 A KR 20150029937A KR 20160107029 A KR20160107029 A KR 20160107029A
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South Korea
Prior art keywords
amplitude
signal
bias
digital
laser
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KR1020150029937A
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Korean (ko)
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KR102025200B1 (en
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한찬교
조승현
정환석
이종현
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한국전자통신연구원
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/504—Laser transmitters using direct modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H04B10/505—Laser transmitters using external modulation
    • H04B10/5057—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output
    • H04B10/50572—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output to control the modulating signal amplitude including amplitude distortion
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/58—Compensation for non-linear transmitter output

Abstract

A laser bias optimization apparatus is disclosed. The device comprises a laser module, an analog / digital converter for converting the analog feedback signal of the laser module to digital, a first digital / analog converter for converting the bias current control signal to digital and outputting it to the laser module, A second digital-to-analog converter for outputting to the laser module, and a digital signal processor for controlling the amplitude of the bias current and the modulation signal based on the digital feedback signal.

Figure P1020150029937

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser bias optimizing apparatus for an analog optical transmission,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog optical transmission system, and more particularly to an optical transmitter for directly modulating a laser diode in an analog optical transmission system.

Generally, in an optical transmitter, a laser diode (LD) is directly modulated to convert an electrical modulation signal into an optical signal. The laser diode has a characteristic in which the output optical power is almost not output until the forward current in the applied direction exceeds the threshold current, but the optical power linearly increases when the current exceeds the threshold current. 1 shows the current-optical power response characteristics of a laser. When a modulated signal having an excessive amplitude is input, the signal is cut off due to the phenomenon of clipping as shown in FIG. 1, and distortion of the signal due to the clipping occurs. In order to convert a modulated signal into an optical signal without distortion, it is necessary to set the bias current of the laser to an appropriate point. That is, it is necessary to appropriately set the value of the bias current. The response characteristic of the laser diode changes with temperature as shown in Fig. Therefore, it is necessary to adjust the bias current value and the magnitude of the modulation signal according to the temperature of the laser module in order to maintain the output optical power and modulation degree constant.

Korean Patent Laid-Open Publication No. 10-2012-0133159 (published on Dec. 10, 2012)

An object of the present invention is to provide a technical solution for minimizing distortion of a signal caused by a modulation characteristic of a laser diode when an analog signal is optically modulated and transmitted.

According to an aspect of the present invention, there is provided a laser bias optimization apparatus including a laser module, an analog / digital converter for converting an analog feedback signal of a laser module into a digital signal, a first digital / analog converter for converting a bias current control signal to a digital signal, A second digital-to-analog converter for converting the signal to digital and outputting it to the laser module, and a digital signal processor for controlling the amplitude of the bias current and the modulation signal based on the digital feedback signal.

According to an aspect, a digital signal processor may include a bias control unit for sweeping a bias current to obtain a response characteristic between the current and the optical power of the laser module, and to set a bias current at a point where predetermined optical power is generated have. Further, the digital signal processor sweeps the amplitude of the test modulation signal at a point where the bias current is set to determine the amplitude at which clipping occurs, defines the optical modulation index at the detected amplitude as '1' And a modulation signal amplitude controller for setting the amplitude of the modulation signal such that the optical modulation index is a predetermined optical modulation index based on '1'.

According to an aspect, the modulated signal amplitude control unit may send the test modulation signal primarily and correct the feedback response thereto, and then sweep the amplitude of the test modulation signal to detect the amplitude at which the clipping occurs.

Meanwhile, a laser bias optimization method for analog optical transmission performed by a digital signal processor of a laser bias optimizing apparatus according to an aspect includes a step of sweeping a bias current to obtain a response characteristic between a current of the laser diode and optical power, And setting a bias current at a point where optical power is generated.

According to an aspect, a method of optimizing a laser bias includes the steps of sweeping an amplitude of a test modulation signal at a point where a bias current is set to determine an amplitude at which clipping occurs, defining a light modulation index at a detected amplitude as '1' , And setting the amplitude of the modulated signal such that the optical modulation index is a predetermined optical modulation index based on the defined optical modulation index '1'.

According to an aspect, a method of optimizing a laser bias further comprises the step of calibrating a feedback response after sending a test modulated signal to a laser module at a point where a bias current is set, . ≪ / RTI >

According to the present invention, the amplitude of the laser bias and modulation signal can be controlled by one digital controller. An accurate correction through the digital feedback loop has the advantage that the user can flexibly set the optical modulation index within a range that does not cause distortion due to clipping.

FIG. 1 is a graph showing current-optical power response characteristics of a laser. FIG.
2 is a graph showing current-optical power response characteristics of a laser according to temperature.
3 is a block diagram of a laser bias optimizer according to one embodiment.
4 is a flowchart of a laser bias optimization method according to an embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and further aspects of the present invention will become more apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram of a laser bias optimizer according to one embodiment. The laser bias optimizer is applied to an optical transmitter that uses a light source direct modulation scheme in an analog optical transmission system and optimizes the laser bias current of the optical transmitter and the amplitude of the modulated signal through digital control so that transmission signal distortion does not occur. 3, the laser bias optimization apparatus includes a laser module 100, an analog-digital converter (ADC) 200, a first digital-to-analog converter (DAC 1) 2 digital-to-analog converter (DAC 2) 400 and a digital signal processor (DSP)

The laser module 100 includes a laser diode (LD) 110 and a monitor photodiode (mPD) The front face of the LD 110 is coupled to the optical fiber and the back face of the LD 110 is input to the monitor PD 120. The LD 110 outputs an optical signal having a predetermined optical power to a front facet based on a bias current and a modulation current, and outputs an optical signal having a predetermined optical power even to the rear portion. The optical power of the optical signal output to the front portion and the optical power of the optical signal output to the rear portion have a certain ratio, for example, a ratio of 9: 1 or 8: 2. The monitor PD 120 converts the optical signal input from the rear portion of the LD 110 into an electric signal and outputs the electric signal to the digital signal processor 500.

The analog-to-digital converter 200 is located in a feedback loop from the laser module 100 to the digital signal processor 500. The first amplifier 600 may be formed at the front end of the A / D converter 200. The first amplifier 600 amplifies and outputs the analog feedback signal input from the monitor PD 120. The analog-to-digital converter 200 converts the input analog feedback signal into a digital feedback signal and outputs the digital feedback signal to the digital signal processor 500. The first digital-to-analog converter 300 is for controlling the bias current of the LD 110, converts the bias current control signal input from the digital signal processor 500 into an analog signal, and outputs the analog signal to the laser module 100 . The second digital-to-analog converter 400 is inserted into the output terminal of the digital signal processor 500 to reproduce the modulated signal of the LD 110, converts the LD modulated signal input from the digital signal processor 500 into an analog signal And outputs it to the laser module 100.

The digital signal processor 500 digitally controls the bias current based on the digital feedback signal and also digitally controls the amplitude of the digitally modulated signal. According to an aspect, the digital signal processor 500 includes a bias control unit 510, and may further include a modulation signal amplitude control unit 520. The bias control unit 510 controls the current of the LD 110 and the optical power of the LD 110 based on the digital feedback signal from the monitor PD 120 while sweeping the bias current from the lowest point to continuously vary the bias current value. . Then, a bias current value generated by the predetermined optical power is detected, and a bias current control signal is outputted so that a bias current is set to the detected bias current value. The output bias current control signal is converted into an analog signal by the first digital-to-analog converter 300 and input to the laser module 100. Thereby, a bias current is set at a point where predetermined optical power is generated. Here, the predetermined optical power may be optical power preset by the user.

When the bias current is set, the modulation signal amplitude controller 520 outputs a test modulation signal to the LD 110 at the set bias point. The output test modulated signal is converted into an analog signal through the second digital-to-analog converter 400 and input to the LD 110. In one embodiment, the test modulated signal is a sinusoidal wave of amplitude and low frequency that is sufficiently smaller than the amplitude at which clipping occurs, i.e., when the optical modulation index (OMI) is '1'. And the amplitude sufficiently smaller than the amplitude when the OMI is " 1 " may be, for example, about 1/10 of the amplitude. For reference, the optical modulation index is a measure indicating the degree of modulation of the laser diode, and is defined as shown in Equation 1 below.

Figure pat00001

I bias is the bias current of the laser, I th is the critical current of the laser, and ΔI is the half of the peak-to-peak amplitude of the input signal. When OMI is '1', it becomes the maximum input amplitude that does not exceed the laser's threshold current lower limit.

The modulation signal amplitude control unit 520 sweeps the amplitude of the test modulation signal at the bias point set by the bias control unit 510 from the lowest width, that is, continuously. Then, the amplitude of the test modulation signal is analyzed to determine the amplitude at which the clipping occurs. The optical modulation index at the amplitude at which the clipping occurs is defined as " 1 " and is stored in the memory. Next, the amplitude of the modulated signal is controlled so as to be a predetermined optical modulation index based on the defined optical modulation index '1'. The predetermined optical modulation index may be preset by the user.

In one embodiment, the modulation signal amplitude controller 520 limits the output range of the second digital-to-analog converter 400 to control the amplitude of the modulation signal. In another embodiment, the modulation signal amplitude controller 520 controls the second amplifier 700 located at the rear end of the second digital-to-analog converter 400 to be a variable gain amplifier (VGA) And controls the amplitude of the modulation signal by adjusting the gain of the VGA. In another embodiment, a variable attenuator 800 is disposed downstream of the second amplifier 700, and the modulation signal amplitude control unit 520 limits the degree of attenuation of the variable attenuator 800 to control the amplitude of the modulation signal.

According to a further aspect, the modulation signal amplitude control unit 520 sends a test modulation signal to the LD 110 at a bias point set by the bias control unit 510 and processes the response of the feedback loop to signal correction After doing so, you can sweep the test modulation signal secondarily to determine the amplitude at which clipping occurs. The primary reason for correcting the response of the feedback loop is to limit the input amplitude so as to suppress the nonlinear response that may occur in the LD 110 and correct the nonlinear response of the monitor PD 120, The accuracy of the characteristic is increased and the optical modulation index can be accurately set.

4 is a flowchart of a laser bias optimization method according to an embodiment. First, the user sets the output optical power and also sets the optical modulation index. The digital signal processor 500 sweeps the bias current to obtain the current-optical power response characteristic of the LD 110 (S100). A bias current is set at a point where the optical power set by the user is generated (S200). When the bias current is set, the digital signal processor 500 outputs a test modulation signal to the LD 110, which is a sinusoidal wave having an amplitude sufficiently smaller than the amplitude at which the clipping occurs at the set bias point (S300). Then, the signal response fed back from the monitor PD 120 is corrected (S400). S300 and S400 for correcting the response of the feedback loop may be omitted.

When the response of the feedback loop is corrected or the bias current is set, the digital signal processor 500 sweeps the amplitude of the test modulation signal to determine the amplitude at which the clipping occurs (S500). Then, the optical modulation index at the detected amplitude is defined as '1' (S600). Next, the digital signal processor 500 sets the amplitude of the modulation signal to be the optical modulation index set by the user (S700).

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

100: laser module 110: laser diode
120: monitor photodiode 200: analog-to-digital converter
300: first digital-to-analog converter 400: second digital-to-
500: digital signal processor 510: bias control unit
520: Modulation signal amplitude control unit 600: First amplifier
700: second amplifier 800: variable attenuator

Claims (7)

Laser module;
An analog / digital converter for converting an analog feedback signal of the laser module into a digital signal;
A first digital-to-analog converter converting the bias current control signal into a digital signal and outputting the digital signal to a laser module;
A second digital-to-analog converter for converting the modulated signal into a digital signal and outputting the modulated signal to a laser module; And
A digital signal processor for controlling the amplitude of the bias current and the modulation signal based on the digital feedback signal;
/ RTI > wherein said laser bias optimizer is a laser bias optimizer for analog optical transmission.
The digital signal processor of claim 1, further comprising:
A bias controller for sweeping a bias current to obtain a response characteristic between the current and the optical power of the laser module and setting a bias current at a point where predetermined optical power is generated;
/ RTI > wherein said laser bias optimizer is a laser bias optimizer for analog optical transmission.
3. The digital signal processor of claim 2, further comprising:
The amplitude of the test modulation signal is swept at the point where the bias current is set to determine the amplitude at which the clipping occurs, the optical modulation index at the detected amplitude is defined as '1', and the defined optical modulation index '1' A modulation signal amplitude controller for setting the amplitude of the modulation signal such that the optical modulation index is a predetermined optical modulation index;
Further comprising: a laser bias optimizer for analog optical transmission.
The method of claim 3,
The modulated signal amplitude control unit sends a test modulation signal primarily and corrects the feedback response thereto, and thereafter sweeps the amplitude of the test modulation signal to ascertain the amplitude at which the clipping occurs.
A laser bias optimization method for analog optical transmission performed by a digital signal processor of a laser bias optimizer according to claim 1,
Sweeping the bias current to obtain a response characteristic between the current and the optical power of the laser diode; And
Setting a bias current at a point where a predetermined optical power is generated;
/ RTI > The method of claim 1,
6. The method of claim 5,
Sweeping the amplitude of the test modulation signal at a point where the bias current is set to determine the amplitude at which the clipping occurs;
Defining a light modulation index at the detected amplitude as '1'; And
Setting an amplitude of the modulated signal such that the optical modulation index is a predetermined optical modulation index based on the defined optical modulation index '1';
Wherein the laser bias optimization method further comprises:
The method according to claim 6,
And correcting the feedback response after sending the test modulated signal to the laser module at a point where the bias current is set,
The step of determining the amplitude at which the clipping occurs is performed after the response correction step.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20180077926A (en) * 2016-12-29 2018-07-09 세종대학교산학협력단 Methods and systems for reduciing nonliearity over fronthaul optical fiber networis

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5402433A (en) * 1994-01-05 1995-03-28 Alcatel Network Systems, Inc. Apparatus and method for laser bias and modulation control
KR20060065865A (en) * 2004-12-10 2006-06-14 한국전자통신연구원 Temperature compensated optical transmitter of analog/digital mixed mode
KR20120133159A (en) 2011-05-30 2012-12-10 한국전자통신연구원 Apparatus and Method for Controlling Current in Optical Transmitter

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5402433A (en) * 1994-01-05 1995-03-28 Alcatel Network Systems, Inc. Apparatus and method for laser bias and modulation control
KR20060065865A (en) * 2004-12-10 2006-06-14 한국전자통신연구원 Temperature compensated optical transmitter of analog/digital mixed mode
KR20120133159A (en) 2011-05-30 2012-12-10 한국전자통신연구원 Apparatus and Method for Controlling Current in Optical Transmitter

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20180077926A (en) * 2016-12-29 2018-07-09 세종대학교산학협력단 Methods and systems for reduciing nonliearity over fronthaul optical fiber networis

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