CA1229653A - Laser differential quantum efficiency control circuit - Google Patents
Laser differential quantum efficiency control circuitInfo
- Publication number
- CA1229653A CA1229653A CA000474044A CA474044A CA1229653A CA 1229653 A CA1229653 A CA 1229653A CA 000474044 A CA000474044 A CA 000474044A CA 474044 A CA474044 A CA 474044A CA 1229653 A CA1229653 A CA 1229653A
- Authority
- CA
- Canada
- Prior art keywords
- laser
- signal
- low pass
- quantum efficiency
- pass filter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/068—Stabilisation of laser output parameters
- H01S5/0683—Stabilisation of laser output parameters by monitoring the optical output parameters
- H01S5/06835—Stabilising during pulse modulation or generation
Landscapes
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Semiconductor Lasers (AREA)
Abstract
LASER DIFFERENTIAL QUANTUM EFFICIENCY CONTROL CIRCUIT
Abstract of the Disclosure In an injection laser drive arrangement, variations in differential quantum efficiency are compensated by means of a feedback loop which includes a low pass filter and the usual PIN diode on the rear face of the laser diode. A second low pass filter, having characteristics identical to the first, filters the input signal. The outputs of the two low pass filters are compared and integrated to provide a control signal for varying the amplitude of the signal applied to the laser diode. With this arrangement, laser output variations due to patterns of bits in the input signal are cancelled out in the control signal, which consequently compensates the differential quantum efficiency.
- i -
Abstract of the Disclosure In an injection laser drive arrangement, variations in differential quantum efficiency are compensated by means of a feedback loop which includes a low pass filter and the usual PIN diode on the rear face of the laser diode. A second low pass filter, having characteristics identical to the first, filters the input signal. The outputs of the two low pass filters are compared and integrated to provide a control signal for varying the amplitude of the signal applied to the laser diode. With this arrangement, laser output variations due to patterns of bits in the input signal are cancelled out in the control signal, which consequently compensates the differential quantum efficiency.
- i -
Description
~2~53 LASER DIFFERENTIAL QUANTUM EFFICIENCY CONTROL CIRCUIT
This invention relates to injection laser drive arrangements and in particular to controlling the AC drive current to the laser to compensate for differential quantum efficiency variations.
Background of the Invention As described in Canadian patent application No. 474,043 entitled Peak Optical Power Control Circuit for Laser Driver by Go Burley, filed concurrently herewith and having the same assignee as this application, to which the reader is directed for reference, the typical injection laser light/drive current characteristic shows little light output (L) until a threshold current, Ilk, is exceeded.
Thereafter the light output increases at a rate LOWE, which is known as the slope efficiency or differential quantum efficiency.
Temperature and aging cause variations in the threshold and the slope efficiency with concomitant variations in the mean and peak output power of the injection laser.
In seeking to compensate for such variations in slope 2Q efficiency or differential quantum efficiency, G. Burley proposes to monitor the light output from the laser using a PIN diode having a lower bandwidth than the input signal. The PIN diode is in a feedback loop including a low pass filter having a bandwidth even lower than that of the PIN diode. The power output of the low pass filter is proportional to the amplitude of the laser output signal. Such an arrangement is generally satisfactory so long as the input signal is random, at least over a prescribed period. However, in some cases the ~2~g~;~
signal is not random or cannot be considered random over a short period of time. In such a signal, therefore, sequences of 1's and O's will occur which have a definite pattern, i.e. will repeat regularly.
For satisfactory operation, the bandwidth of the low pass filter should encompass several lines of the frequency spectrum of the output signal. Since the line spacing in the frequency spectrum is inversely proportional to the interval between pattern repeats, such a low pass filter arrangement is not entirely satisfactory if the pattern repeats after a short time interval. In such a case, the pattern would cause fluctuations in the output of the low pass filter. Consequently, the pattern in the input signal will produce a correction just as if the pattern were a variation in the differential quantum efficiency of the laser diode.
The present invention seeks to eliminate or at least mitigate this problem and provide a laser drive arrangement with drive current compensation which compensates for differential quantum efficiency variations while differentiating laser output variations which are attributable to pattern in the input data signal.
Summary of the Invention According to the present invention, there is provided an injection laser drive arrangement comprising:-means for deriving from a digital input signal two signals each having a power spectrum that is substantially the same as the power spectrum of said input signal;
drive means for supplying to said injection laser a drive signal dependent upon a control signal and one of said two signals;
96~i3 detector means a detecting a light output signal from said laser;
filter means having a bandwidth significantly less than that of said output signal for filtering the output of said detector means, second filter means having characteristics substantially identical to the first-mentioned low pass filter means and serving to filter to the other of said two signals; and comparator means for comparing respective outputs of the first-mentioned filter means and the second filter means to provide said control signal.
Brief Description of the Drawing The attached drawing illustrates schematically a laser diode and associated drive arrangement. This embodiment of the lo invention will now be described by way of example only.
As shown in the drawing, a laser drive arrangement comprises input means in the form of a D-type flip-flop 10, the output of which is applied to a power splitter 12. A digital input signal, comprising high speed data at, say, 135 Mb/sec. or 565 Mb/sec., is retimed by flip-flop 10 to maintain constant amplitude. The power splitter 12 splits the input signal into two similar signals each having the same power spectrum as the input signal. One of the two similar signals is applied to a variable gain drive amplifier 14, the output of which drives a laser diode 16.
A PIN diode 18, mounted upon the back face of the laser diode 16, detects the output of the laser diode and provides a corresponding signal to a low pass filter 20. The instantaneous 6~3 amplitude of the output of the low pass filter 20 depends upon the cut-off frequency of the filter and the statistics of the input signal. Generally, the output of the low pass filter will be pattern-dependent, although for a well-randomized input signal, it is a slowly-varying analog signal.
The output of low pass filter 20 is applied to the non-inverting input of a comparator 22, the inverting input of which is connected to a fixed reference. The output of the comparator 22 is a pulse train whose pulse width is proportional to the amplitude and pattern of the signal applied to the low pass filter. This output is connected to the inverting input of a differential amplifier 24. A
second comparator 26, similar to comparator 22, has its output connected to the non-inverting input of differential amplifier 24.
The inverting input of comparator 26 is connected to a fixed reference and its non-inverting input connected to the output of a second low pass filter 28 which filters the second of the two similar signals from the power splitter 12. The two fixed references applied to comparators 22 and 26, respectively, are a DC voltage which is about 70 percent of that which would produce a continuous stream of 1's from the comparators.
The two loops comprising, respectively, low pass filter 28 and comparator 26, and low pass filter 20 and comparator 22 have substantially identical transfer functions. Thus, relative variations between the averages of the two signals applied to the differential amplifier 24, one derived from the input and the other from the laser diode's output, are detected by the differential amplifier 24. The resultant error signal is integrated by integrator 30 which provides a control signal to control the gain of drive amplifier 14 and to compensate for variations in the laser diode differential quantum efficiency Because the two signals fed to the differential amplifier are derived ultimately from the same source, namely the input signal, pattern dependent effects in the feedback signal from the low pass filter 20 will be canceled by those in the signal from the low pass filter 28. Thus, the control signal will compensate for the residual part of the feedback signal which represents variations in differential quantum efficiency of the laser diode.
The foregoing description is of an arrangement for controlling the peak power, which primarily affects the slope efficiency. A conventional mean power control circuit may be employed in parallel, as indicated in the drawing as item 32 connected between the output of PIN diode and the drive to the laser diode 16.
An advantage of embodiments of the present invention, being independent of pattern effects, is that the integrator can have a short time constant yet the control loop will still track the quantum efficiency variations. Also, such short time constant leads to increased agility.
This invention relates to injection laser drive arrangements and in particular to controlling the AC drive current to the laser to compensate for differential quantum efficiency variations.
Background of the Invention As described in Canadian patent application No. 474,043 entitled Peak Optical Power Control Circuit for Laser Driver by Go Burley, filed concurrently herewith and having the same assignee as this application, to which the reader is directed for reference, the typical injection laser light/drive current characteristic shows little light output (L) until a threshold current, Ilk, is exceeded.
Thereafter the light output increases at a rate LOWE, which is known as the slope efficiency or differential quantum efficiency.
Temperature and aging cause variations in the threshold and the slope efficiency with concomitant variations in the mean and peak output power of the injection laser.
In seeking to compensate for such variations in slope 2Q efficiency or differential quantum efficiency, G. Burley proposes to monitor the light output from the laser using a PIN diode having a lower bandwidth than the input signal. The PIN diode is in a feedback loop including a low pass filter having a bandwidth even lower than that of the PIN diode. The power output of the low pass filter is proportional to the amplitude of the laser output signal. Such an arrangement is generally satisfactory so long as the input signal is random, at least over a prescribed period. However, in some cases the ~2~g~;~
signal is not random or cannot be considered random over a short period of time. In such a signal, therefore, sequences of 1's and O's will occur which have a definite pattern, i.e. will repeat regularly.
For satisfactory operation, the bandwidth of the low pass filter should encompass several lines of the frequency spectrum of the output signal. Since the line spacing in the frequency spectrum is inversely proportional to the interval between pattern repeats, such a low pass filter arrangement is not entirely satisfactory if the pattern repeats after a short time interval. In such a case, the pattern would cause fluctuations in the output of the low pass filter. Consequently, the pattern in the input signal will produce a correction just as if the pattern were a variation in the differential quantum efficiency of the laser diode.
The present invention seeks to eliminate or at least mitigate this problem and provide a laser drive arrangement with drive current compensation which compensates for differential quantum efficiency variations while differentiating laser output variations which are attributable to pattern in the input data signal.
Summary of the Invention According to the present invention, there is provided an injection laser drive arrangement comprising:-means for deriving from a digital input signal two signals each having a power spectrum that is substantially the same as the power spectrum of said input signal;
drive means for supplying to said injection laser a drive signal dependent upon a control signal and one of said two signals;
96~i3 detector means a detecting a light output signal from said laser;
filter means having a bandwidth significantly less than that of said output signal for filtering the output of said detector means, second filter means having characteristics substantially identical to the first-mentioned low pass filter means and serving to filter to the other of said two signals; and comparator means for comparing respective outputs of the first-mentioned filter means and the second filter means to provide said control signal.
Brief Description of the Drawing The attached drawing illustrates schematically a laser diode and associated drive arrangement. This embodiment of the lo invention will now be described by way of example only.
As shown in the drawing, a laser drive arrangement comprises input means in the form of a D-type flip-flop 10, the output of which is applied to a power splitter 12. A digital input signal, comprising high speed data at, say, 135 Mb/sec. or 565 Mb/sec., is retimed by flip-flop 10 to maintain constant amplitude. The power splitter 12 splits the input signal into two similar signals each having the same power spectrum as the input signal. One of the two similar signals is applied to a variable gain drive amplifier 14, the output of which drives a laser diode 16.
A PIN diode 18, mounted upon the back face of the laser diode 16, detects the output of the laser diode and provides a corresponding signal to a low pass filter 20. The instantaneous 6~3 amplitude of the output of the low pass filter 20 depends upon the cut-off frequency of the filter and the statistics of the input signal. Generally, the output of the low pass filter will be pattern-dependent, although for a well-randomized input signal, it is a slowly-varying analog signal.
The output of low pass filter 20 is applied to the non-inverting input of a comparator 22, the inverting input of which is connected to a fixed reference. The output of the comparator 22 is a pulse train whose pulse width is proportional to the amplitude and pattern of the signal applied to the low pass filter. This output is connected to the inverting input of a differential amplifier 24. A
second comparator 26, similar to comparator 22, has its output connected to the non-inverting input of differential amplifier 24.
The inverting input of comparator 26 is connected to a fixed reference and its non-inverting input connected to the output of a second low pass filter 28 which filters the second of the two similar signals from the power splitter 12. The two fixed references applied to comparators 22 and 26, respectively, are a DC voltage which is about 70 percent of that which would produce a continuous stream of 1's from the comparators.
The two loops comprising, respectively, low pass filter 28 and comparator 26, and low pass filter 20 and comparator 22 have substantially identical transfer functions. Thus, relative variations between the averages of the two signals applied to the differential amplifier 24, one derived from the input and the other from the laser diode's output, are detected by the differential amplifier 24. The resultant error signal is integrated by integrator 30 which provides a control signal to control the gain of drive amplifier 14 and to compensate for variations in the laser diode differential quantum efficiency Because the two signals fed to the differential amplifier are derived ultimately from the same source, namely the input signal, pattern dependent effects in the feedback signal from the low pass filter 20 will be canceled by those in the signal from the low pass filter 28. Thus, the control signal will compensate for the residual part of the feedback signal which represents variations in differential quantum efficiency of the laser diode.
The foregoing description is of an arrangement for controlling the peak power, which primarily affects the slope efficiency. A conventional mean power control circuit may be employed in parallel, as indicated in the drawing as item 32 connected between the output of PIN diode and the drive to the laser diode 16.
An advantage of embodiments of the present invention, being independent of pattern effects, is that the integrator can have a short time constant yet the control loop will still track the quantum efficiency variations. Also, such short time constant leads to increased agility.
Claims (2)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An injection laser drive arrangement comprising:-means for deriving from a digital input signal two signals each having a power spectrum that is substantially the same as the power spectrum as said input signal;
drive means for supplying to said injection laser a drive signal dependent upon a control signal and one of said two signals;
detector means for detecting a light output from said laser;
filter means having a bandwidth with a maximum significantly less than that of said output signal for filtering the output of said detector means;
second low pass filter means having a transfer function substantially identical to that of the first-mentioned filter means and serving to filter the other of said two signals; and comparator means for comparing respective outputs at the first-mentioned and second filter means to provide said control signal.
drive means for supplying to said injection laser a drive signal dependent upon a control signal and one of said two signals;
detector means for detecting a light output from said laser;
filter means having a bandwidth with a maximum significantly less than that of said output signal for filtering the output of said detector means;
second low pass filter means having a transfer function substantially identical to that of the first-mentioned filter means and serving to filter the other of said two signals; and comparator means for comparing respective outputs at the first-mentioned and second filter means to provide said control signal.
2. An injection laser drive arrangement as defined in claim 1, wherein each said filter means comprises a low pass filter.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000474044A CA1229653A (en) | 1985-02-11 | 1985-02-11 | Laser differential quantum efficiency control circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000474044A CA1229653A (en) | 1985-02-11 | 1985-02-11 | Laser differential quantum efficiency control circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1229653A true CA1229653A (en) | 1987-11-24 |
Family
ID=4129814
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000474044A Expired CA1229653A (en) | 1985-02-11 | 1985-02-11 | Laser differential quantum efficiency control circuit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1229653A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0497270A2 (en) * | 1991-01-31 | 1992-08-05 | Sumitomo Electric Industries, Ltd. | Semiconductor laser device driving circuit |
| EP0649201A1 (en) * | 1993-10-14 | 1995-04-19 | AT&T Corp. | Amplitude detection scheme for optical transmitter control |
| WO2013079904A1 (en) * | 2011-12-02 | 2013-06-06 | Nanotech Semiconductor Limited | Closed loop optical modulation amplitude control |
| CN104426611A (en) * | 2013-08-27 | 2015-03-18 | 塞姆泰克股份有限公司 | Closed loop optical modulation amplitude control |
| US9300405B2 (en) | 2011-12-02 | 2016-03-29 | Semtech Corporation | Closed loop optical modulation amplitude control |
-
1985
- 1985-02-11 CA CA000474044A patent/CA1229653A/en not_active Expired
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0497270A2 (en) * | 1991-01-31 | 1992-08-05 | Sumitomo Electric Industries, Ltd. | Semiconductor laser device driving circuit |
| EP0497270A3 (en) * | 1991-01-31 | 1993-01-20 | Sumitomo Electric Industries, Ltd. | Semiconductor laser device driving circuit |
| US5224112A (en) * | 1991-01-31 | 1993-06-29 | Sumitomo Electric Industries, Ltd. | Semiconductor laser device driving circuit |
| AU646921B2 (en) * | 1991-01-31 | 1994-03-10 | Sumitomo Electric Industries, Ltd. | Semiconductor laser device driving circuit |
| EP0649201A1 (en) * | 1993-10-14 | 1995-04-19 | AT&T Corp. | Amplitude detection scheme for optical transmitter control |
| US5448629A (en) * | 1993-10-14 | 1995-09-05 | At&T Corp. | Amplitude detection scheme for optical transmitter control |
| WO2013079904A1 (en) * | 2011-12-02 | 2013-06-06 | Nanotech Semiconductor Limited | Closed loop optical modulation amplitude control |
| US8548336B2 (en) | 2011-12-02 | 2013-10-01 | Semtech Corporation | Closed loop optical modulation amplitude control |
| CN104137443A (en) * | 2011-12-02 | 2014-11-05 | 塞姆泰克股份有限公司 | Closed loop optical modulation amplitude control |
| US9300405B2 (en) | 2011-12-02 | 2016-03-29 | Semtech Corporation | Closed loop optical modulation amplitude control |
| CN104426611A (en) * | 2013-08-27 | 2015-03-18 | 塞姆泰克股份有限公司 | Closed loop optical modulation amplitude control |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP0539038B1 (en) | Optical transmitters | |
| US4277846A (en) | Circuit for stabilizing the output of an injection laser | |
| CA1081801A (en) | Regenerator for an optical transmission system | |
| US4796266A (en) | Laser driver circuit with dynamic bias | |
| JP2932100B2 (en) | Laser diode control circuit | |
| US4344173A (en) | Stabilization circuit for a digitally operated laser | |
| EP0574816B1 (en) | Laser bias and modulation circuit | |
| CN1012927B (en) | Binary data regenarator with adaptive threshold level | |
| CA1149021A (en) | Control circuit for the drive current of a laser | |
| US5153765A (en) | Optical transmitter comprising a laser diode | |
| US20030039328A1 (en) | Timing circuit | |
| GB1559511A (en) | Injection lasers | |
| US5754577A (en) | Compensation for variations in temperature and aging of laser diode by use of small signal, square-law portion of transfer function of diode detection circuit | |
| US20020027689A1 (en) | Fiber optic transceiver employing front end level control | |
| CA1229653A (en) | Laser differential quantum efficiency control circuit | |
| US4101847A (en) | Laser control circuit | |
| US7492797B2 (en) | Laser driver circuit | |
| US5187713A (en) | Nonlinear device control methods and apparatus | |
| US6975658B1 (en) | Gain normalization for automatic control of lightwave emitters | |
| EP0528569B1 (en) | Injection laser modulation | |
| US4543664A (en) | Direct current coupled data transmission | |
| US20080101795A1 (en) | Data signal amplitude and cross-point detectors in an optical modulator control system | |
| US5739937A (en) | Optical unit for restoring a pulse pattern, receiver suitable for use in a transmission system comprising such a unit | |
| US5302860A (en) | Circuit arrangement for automatic gain control | |
| JPH0318079A (en) | Semiconductor laser driver |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |