GB2025121A - Improvements in or relating to the stabilisation of injection lasers - Google Patents
Improvements in or relating to the stabilisation of injection lasers Download PDFInfo
- Publication number
- GB2025121A GB2025121A GB7829069A GB7829069A GB2025121A GB 2025121 A GB2025121 A GB 2025121A GB 7829069 A GB7829069 A GB 7829069A GB 7829069 A GB7829069 A GB 7829069A GB 2025121 A GB2025121 A GB 2025121A
- Authority
- GB
- United Kingdom
- Prior art keywords
- laser
- output
- low frequency
- signal
- threshold
- 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.)
- Granted
Links
Classifications
-
- 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
- H04B10/564—Power control
-
- 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
-
- 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
- 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
- H01S5/06812—Stabilisation of laser output parameters by monitoring or fixing the threshold current or other specific points of the L-I or V-I characteristics
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Semiconductor Lasers (AREA)
Abstract
An injection laser 24 has drive circuitry which includes a generator 25 for superimposing a low frequency signal on the drive signal to the laser. The light output of the laser is sensed by a photodetector 33. A rectifier 36 rectifies the low frequency component of the photodetector output and the rectified signal is compared with a reference signal in a comparator 38. The output of the comparator 38 is fed to the drive circuitry to maintain the d.c. bias of the laser close to the laser threshold, thereby stabilising the output intensity of the laser. <IMAGE>
Description
SPECIFICATION
Improvements in or relating to the stabilisation of injection lasers
This invention relates to the stabilisation of the optical output characteristics of an injection laser.
Semiconductor injection lasers (e.g. gallium arsenide lasers) have been proposed for use in optical communication systems to convert either digital or analogue electrical signals into optical signals. A problem in such applications is that the output characteristics of a semiconductor laser change with temperature and passage of time. The output characteristics which can vary are: 1q the laser threshold current,
the laser efficiency a when the current applied to the laser is greater than the threshold current, and
the spontaneous efficiency ss when the current applied to the laser is less than the threshold current where P is the optical output power of the laser and I the current applied to the laser.
In addition there is an unwanted switch-on time delay for lasing action between the application of the input modulating current and the appearance of the optical output pulse when the bias current 1b applied to the laser is below the threshold current I This is usually of importance as it is preferable to operate the laser with its bias current 1b below 1q for two reasons in most digital systems:
(i) to optimise the ratio between the 'on' and 'off' pulses within the limits permitted by the unwanted switch-on delay and the maximum permitted peak optical output power.
For low speed digital systems e.g. 8 Mbits/s, the d.c. bias current may be zero.
(ii) as ss < a, a less sensitive control of the bias current is required in order to maintain the optical output power in the 'off' state at or substantially at a predetermined level.
For intensity modulated, frequency modulated and very high speed digital systems it may be preferable to apply a bias current at a value that is greater than the threshold current.
The switch-on delay (td) can be approximately represented by the equation
wherein I m is the modulating current 1b is the bias current 1q is the threshold current and 7 is the carrier lifetime (typically of the order of 1 ns to 4ns).
Thus it can be seen that if the threshold current varies the switch-on delay td will also vary unless an adjustment is made to the d.c.
bias current lb. A change in the switch-on delay td can be important in an optical communication system particularly if td increases to such an extent that it becomes significant compared to the shortest desired input pulse length.
It has been proposed to use high speed circuits to monitor the light output of the laser and either by direct detection of the light level corresponding to a logic zero using a trough detector or by measurement of the switch-on delay to maintain the d.c. bias of the laser close to threshold.
The present invention provides a monitoring arrangement which does not require high frequency components. The present invention makes use of the fact that the slope of the output light-current characteristic of a laser changes close to threshold. If a low frequency signal is superimposed on the bias signal applied to the laser, a low frequency signal can be detected in the light output of the laser. Some parameters of the low frequency component have different valuels depending upon whether the laser is biassed just above threshold or just below threshold. By monitoring such parameters of the low frequency component it is possible to adjust the bias of the laser in such a way that it is biassed close to threshold. Examples of parameters which can be monitored are amplitude and, in the case of a sine wave, the ratio of the detected fundamental to the detected second harmonic.
According to the present invention there is provided apparatus for stabilising the output characteristics of an injection laser comprising means for applying a drive signal to the laser, means for applying a low frequency to the laser, means for producing an electrical signal indicative of the light output of the laser, means for detecting the low frequency component, means for comparing a parameter of the low frequency component with a predetermined reference signal, the output of the comparing means being used to maintain the d.c. bias of the laser at or near threshold. The parameter may be the amplitude of the low frequency component.
The means for producing said electrical signal may be a photodiode.
The detecting means may comprise a rectifier coupled to the photodiode by a capacitor.
The comparing means may comprise a differential amplifier.
The output of the comparing means may be connected to a field effect transistor which is connected in parallel with the laser, the output of the comparing means being arranged to vary the current through said transistor such that the laser is biassed at or near threshold.
The means for applying the low frequency signal may comprise a low frequency generator and a diode gate so arranged that it transmits the low frequency signal only when the drive signal of the laser is at logic 'zero' level.
The apparatus may include means for monitoring the mean optical power output of the laser to provide a feedback signal for controlling the laser such that said mean optical power remains substantially constant.
The invention will be described now by way of example only with particular reference to the accompanying drawings. In the drawings:
Figure 1 is a graph illustrating the variation of optical output power with current for an injection laser;
Figures 2a and 2b illustrate the principle of the present invention;
Figure 3 is a schematic circuit diagram of apparatus according to the present invention;
Figure 4 is a circuit diagram showing in more detail part of the apparatus of Fig. 3;
Figure 5 is a circuit diagram illustrating a modification of the arrangement of Fig. 3, and
Figure 6 shows another embodiment of apparatus in accordance with the present invention.
The characteristics of an injection laser which can vary with temperature and time are the laser threshold current Iq, the laser efficiency
and the spontaneous efficiency
These characteristics are illustrated in Fig. 1 of the drawings. In addition there is a switchon time delay for lasing action between the application of an input modulating current to the laser and the appearance of the output of light from the laser when the bias current applied to the laser is below the threshold current q The switch-on delay td can be approximately represented by the following equation
where Im is the modulating current is is the bias current 1q is the threshold current and T is the carrier lifetime (typically in the order of 1 nS to 4nS).
Thus the switch-on delay will vary with variation in the threshold current of the laser.
This can be important since, although it may be desirable to bias the laser below the threshold current (for digital systems), the switch-on delay may represent a limitation in the speed of operation of the laser. The switch-on delay is of importance when the laser is used in optical comunication systems to transmit information in digital form. The switch-on delay can be important in such systems when it becomes significant compared to the shortest desired input pulse duration. For intensity and frequency modulated optical communication systems, the variation of threshold current and slope efficiency a with temperature and the passage of time is important.
We propose to maintain the d.c. bias applied to the laser close to threshold by applying a low frequency modulation to the laser drive, detecting the modulation in the light output from the laser, and controlling the bias applied to the laser on the basis of the detected modulation. The principle is illustrated in Figs. 2a and 2 b. Fig. 2a illustrates the situation when data pulses are applied to a laser which is biassed slightly above the threshold and Fig. 2b illustrates the situation when data pulses are applied to the laser which is biassed slightly below threshold. A low frequency ripple is shown as being applied to the zero level. It will be seen that if the laser is biassed above threshold the ripple appears in the light output of the laser as a much greater signal than if the laser is biassed below threshold. This feature can be used as a means of controlling the bias applied to the laser so that the bias is close to threshold.
Referring now to Fig. 3 of the drawings a laser level control arrangement has a data input line 20 along which data pulses can be fed to the gate of a field effect transistor 22.
The source electrode of the field effect transistor 22 is connected to one terminal of a laser 24 whose light output is to be controlled and the drain electrode is connected by a capacitor 23 to the other electrode. The arrangement includes a 1 kHz square wave generator 25 which is connected by a diode gate 26 to the laser 24. The data input line 20 is connected by a line 28 to the diode gate.
The light output from the laser 24 is fed via a beam splitter 30 to an optical fibre 32. The beam splitter 30 directs some of the light emitted by the laser to a photo diode 33 which is connected across the inputs of a differential amplifier 34. The output of the amplifier 34 is connected to two feedback loops. The first feedback loop includes a coupling capacitor 35 which is connected via a rectifier 36 to the inverting input of a differential amplifier 38. The non-inverting input of the differential amplifier 38 is connected to receive a reference input. The output of the amplifier 38 is connected to the drain electrode of the field effect transistor 22.
The second feedback loop comprises a connection from the output of the amplifier 34 to the inverting input of the differential amplifier 44. The non-inverting input of the differential amplifier 44 is connected to receive a reference voltage. The output of the amplifier 44 is connected to a voltage to current converter 46 which provides a d.c. bias along line 48 for the laser 24. The reference voltage applied to the non-inverting input of the amplifier 38 has a magnitude representative of a predetermined amplitude of ripple voltage in the light output of the laser. The reference voltage applied to the non-inverting input of the amplifier 44 is indicative of a predetermined mean optical output from the laser.
The diode gate 26 is shown in more detail in Fig. 4 of the drawings. The diode gate comprises a transistor 50 which is switched on or off according to whether the data pulse applied along line 20 is a O or a 1. The emitter of the transistor 50 is connected by two resistors 51, 52 to the laser 24. The junction of the two resistors 51 and 52 is connected by a diode 54 to the 1 kHz square wave generator 25. The arrangement is such that the 1 kHz square wave signal is only applied to the laser when a data 0 signal is applied to the laser. If a 1 is being applied to the laser no ripple signal is applied.
In operation the light signal from the laser is detected by the photo diode 33 and amplified by the amplifier 34. The a.c. component of the amplified signal is passed by the capacitor 35 to the rectifier 36. The rectifier 36 produces a d.c. signal which is indicative of the amplitude of the ripple in the light output of the laser. This signal is applied to the inverting input of the amplifier 38 where it is compared with the reference signal. The output of the amplifier 38 is used to control the current passing through the field effect transistor 22. The field effect transistor shunts the laser 24 and in the arrangement shown the output of the amplifier 38 varies the drain to source voltage across the field effect transistor to thereby change the mutual conductance of the transistor.The arrangement is such that the current through the transistor 22 is varied to maintain the bias of the laser 24 close to threshold. In this way the field effect transistor 22 controls the light level (see
Figs. 2a and 2b) of the laser corresponding to logic zero.
The other feedback loop including the amplifier 44 is used to control the logic 'one' level bias current of the laser. The output signal from the amplifier 34 is compared with the mean power reference signal by the amplifier 44. The output of the amplifier 44 is used to control the d.c. bias level applied to the laser 24 in such a manner that the mean power output of the laser 24 remains constant.
As shown in the arrangement of Fig. 3 the low frequency ripple is a square wave of about 1 kHz. The depth of modulation of the ripple is between 1 % and 10% of the 'one' light output level. In practice other shapes of ripple could be used.
Also as shown in Fig. 3 the output of the amplifier 38 is used to vary the drain source voltage of the field effect transistor. An alternative arrangement which can be used is shown in Fig. 5. In this arrangement a double gate field effect transistor is used and the output of the amplifier 38 is connected to the second gate of the field effect transistor.
For coding systems with zero disparity the averaged mean power detected by the feedback photo diode remains constant. However, for codes without zero disparity it is necessary to control the peak power to prevent damage to the laser. This can be done by monitoring the incoming data stream and using the mean level as the reference signal in the mean power feedback loop.
As an alternative arrangement to the diode gate, the ripple signal can be injected into the gate or drain of the shunt field effect transistor. This arrangement relies on the transistor switching off completely during light output 'ones'.
In the arrangement described with reference to Figs. 3 and 4 the amplitude of the low frequency signal is monitored. If the low frequency signal is a sine wave it is possible to detect the second harmonic which is generated because of the non-linearity near threshold. By monitoring the ratio of the detected fundamental and the detected second harmonic it is possible to derive a signal for maintaining the laser close to threshold. An arrangement for achieving this is shown in
Fig. 6. In this arrangement the generator 25 is arranged to generate a sine wave of frequency f1. The output of the amplifier 34 is fed to two filters 70, 71.The filter 70 is arranged to pass signals with frequency f, and the filter 71 signals with frequency 2f1. The filter 70 is connected by a rectifier 73 to the non-inverting input of an amplifier 75 and the filter 71 is connected by a rectifier 76 to the inverting input of the amplifier 75. The output of the amplifier is connected to the laser drive 22. The amplifier 75 compares the 2f1 signal with the f signal and provides a signal to adjust the laser drive so that the laser remains biassed close to threshold. In this arrangement the low frequency signal is applied to both the zero and one levels.
The arrangement shown in Fig. 6 is useful when the injected ripple signal is a function of the data, i.e. return to zero pulses with nonzero disparity, or in certain multilevel or linear transmission schemes. Furthermore it may also be possible to dispense with the gate in the ripple injection circuit.
If very low values of injected ripple were required in the Fig. 3 arrangement, for example to prevent excessive modulation of switchon delay of the laser by L.F. ripple causing jitter, it would be necessary to use a phase sensitive detector or active filter in the first feedback loop to overcome sensitivity limitations caused by laser noise.
Claims (9)
1. Apparatus for stabilising the output characteristics of an injection laer comprising means for applying a drive signal to the laser, means for applying a low frequency to the laser, means for producing an electrical signal indicative of the light output of the laser, means for detecting the low frequency component, and means for comparing a parameter of the low frequency component with a predetermined reference signal, the output of the comparing means being used to maintain the d.c. bias of the laser at or near threshold.
2. Apparatus as claimed in claim 1 wherein said parameter is the amplitude of the low frequency component.
3. Apparatus as claimed in claim 1 or claim 2 wherein the means for producing said electrical signal is a photodiode.
4. Apparatus as claimed in claim 3 wherein the detecting means comprises a rectifier coupled to the photodiode by a capacitor.
5. Apparatus as claimed in any preceding claim wherein the comparing means comprises a differential amplifier.
6. Apparatus as claimed in any preceding claim wherein the output of the comparing means is connected to a field effect transistor which is connected in parallel with the laser, the output of the comparing means being arranged to vary the current through said transistor such that the laser is biassed at or near threshold.
7. Apparatus as claimed in any preceding claim wherein the means for applying the low frequency signal comprises a low frequency generator and a diode gate so arranged that it transmits the low frequency signal only when the drive signal of the laser is at logic "zero" level.
8. Apparatus as claimed in any preceding claim including means for monitoring the mean optical power output of the laser to provide a feedback signal for controlling the laser such that said optical power remains substantially constant.
9. Apparatus for stabilising the output characteristics of an injection laser substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7829069A GB2025121B (en) | 1978-07-06 | 1978-07-06 | Stabilisation of injection lasers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7829069A GB2025121B (en) | 1978-07-06 | 1978-07-06 | Stabilisation of injection lasers |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2025121A true GB2025121A (en) | 1980-01-16 |
| GB2025121B GB2025121B (en) | 1982-05-19 |
Family
ID=10498290
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7829069A Expired GB2025121B (en) | 1978-07-06 | 1978-07-06 | Stabilisation of injection lasers |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2025121B (en) |
Cited By (26)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4347610A (en) * | 1979-10-18 | 1982-08-31 | U.S. Philips Corporation | Control circuit for the drive current of a laser |
| EP0075295A2 (en) * | 1981-09-21 | 1983-03-30 | Siemens Aktiengesellschaft | Optical transmission system for high-frequency digital signals |
| FR2524230A1 (en) * | 1982-03-26 | 1983-09-30 | Lignes Telegraph Telephon | Information transmission system for optical fibre link - uses generator to modulate information signal with service signals, and low pass filter to maintain constant output of laser diode |
| FR2526554A1 (en) * | 1982-05-06 | 1983-11-10 | Telecommunications Sa | METHOD FOR REGULATING LIGHT INFORMATION TRANSMITTING MEANS AND THE SYSTEM FOR IMPLEMENTING THE SAME |
| FR2532802A1 (en) * | 1982-09-07 | 1984-03-09 | Lignes Telegraph Telephon | Information transmission system comprising a device for regulating the levels of information. |
| DE3242481A1 (en) * | 1982-11-18 | 1984-05-24 | ANT Nachrichtentechnik GmbH, 7150 Backnang | Laser controller |
| DE3312044A1 (en) * | 1983-04-02 | 1984-10-04 | ANT Nachrichtentechnik GmbH, 7150 Backnang | Method for regulating the output signal of a semiconductor laser |
| US4516242A (en) * | 1981-06-18 | 1985-05-07 | Tokyo Shibaura Denki Kabushiki Kaisha | Output stabilizing device |
| US4580294A (en) * | 1983-04-27 | 1986-04-01 | U.S. Philips Corporation | Optical transmitter |
| EP0237922A2 (en) * | 1986-03-18 | 1987-09-23 | Alcatel SEL Aktiengesellschaft | Regulation process for the optical power of a laser, and circuit for carrying out the process |
| US4862466A (en) * | 1986-09-25 | 1989-08-29 | Minolta Camera Kabushiki Kaisha | Laser emitting apparatus with temperature intensity control |
| EP0331304A2 (en) * | 1988-03-04 | 1989-09-06 | BRITISH TELECOMMUNICATIONS public limited company | Amplification of optical signals |
| GB2219165A (en) * | 1988-05-27 | 1989-11-29 | Stc Plc | Optical transmission systems |
| EP0347202A2 (en) * | 1988-06-14 | 1989-12-20 | Brother Kogyo Kabushiki Kaisha | Excitation system for a semiconductor laser device |
| US4918681A (en) * | 1986-12-25 | 1990-04-17 | Kabushiki Kaisha Toshiba | Data reproducing apparatus using idling current |
| GB2231714A (en) * | 1989-05-17 | 1990-11-21 | Basf Ag | Pulsed laser |
| EP0407919A2 (en) * | 1989-07-11 | 1991-01-16 | Harmonic Lightwaves, Inc. | Optical transmitters linearized by means of parametric feedback |
| EP0412830A2 (en) * | 1989-08-10 | 1991-02-13 | Tektronix Inc. | Apparatus and method for reduction of intermodulation distortion in an optical fiber network |
| AT393016B (en) * | 1988-06-14 | 1991-07-25 | Vaillant Gmbh | Gas burner |
| GB2245756A (en) * | 1990-06-23 | 1992-01-08 | Stc Plc | Digital driving of injection lasers |
| DE4127421A1 (en) * | 1990-08-17 | 1993-01-07 | Roman Koller | Safety circuit for medical laser scalpel - detects parameters of test oscillation applied to all circuit components e.g. relay shutter, and power supply cut=off switch |
| GB2260667A (en) * | 1991-10-19 | 1993-04-21 | Northern Telecom Ltd | Optical transmitters |
| GB2286920A (en) * | 1994-02-25 | 1995-08-30 | Fujitsu Ltd | Power control of laser diodes in optical signal transmitters |
| US5579328A (en) * | 1995-08-10 | 1996-11-26 | Northern Telecom Limited | Digital control of laser diode power levels |
| US5953690A (en) * | 1996-07-01 | 1999-09-14 | Pacific Fiberoptics, Inc. | Intelligent fiberoptic receivers and method of operating and manufacturing the same |
| US7792166B2 (en) | 2005-06-24 | 2010-09-07 | Lockheed Martin Corporation | Apparatus and method for driving laser diodes |
-
1978
- 1978-07-06 GB GB7829069A patent/GB2025121B/en not_active Expired
Cited By (43)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4347610A (en) * | 1979-10-18 | 1982-08-31 | U.S. Philips Corporation | Control circuit for the drive current of a laser |
| US4516242A (en) * | 1981-06-18 | 1985-05-07 | Tokyo Shibaura Denki Kabushiki Kaisha | Output stabilizing device |
| EP0075295A3 (en) * | 1981-09-21 | 1984-08-01 | Siemens Aktiengesellschaft | Optical transmission system for high-frequency digital signals |
| EP0075295A2 (en) * | 1981-09-21 | 1983-03-30 | Siemens Aktiengesellschaft | Optical transmission system for high-frequency digital signals |
| FR2524230A1 (en) * | 1982-03-26 | 1983-09-30 | Lignes Telegraph Telephon | Information transmission system for optical fibre link - uses generator to modulate information signal with service signals, and low pass filter to maintain constant output of laser diode |
| FR2526554A1 (en) * | 1982-05-06 | 1983-11-10 | Telecommunications Sa | METHOD FOR REGULATING LIGHT INFORMATION TRANSMITTING MEANS AND THE SYSTEM FOR IMPLEMENTING THE SAME |
| US4504976A (en) * | 1982-05-06 | 1985-03-12 | Societe Anonyme De Telecommunications | Device for regulating a laser diode |
| FR2532802A1 (en) * | 1982-09-07 | 1984-03-09 | Lignes Telegraph Telephon | Information transmission system comprising a device for regulating the levels of information. |
| DE3242481A1 (en) * | 1982-11-18 | 1984-05-24 | ANT Nachrichtentechnik GmbH, 7150 Backnang | Laser controller |
| DE3312044A1 (en) * | 1983-04-02 | 1984-10-04 | ANT Nachrichtentechnik GmbH, 7150 Backnang | Method for regulating the output signal of a semiconductor laser |
| US4580294A (en) * | 1983-04-27 | 1986-04-01 | U.S. Philips Corporation | Optical transmitter |
| EP0237922A2 (en) * | 1986-03-18 | 1987-09-23 | Alcatel SEL Aktiengesellschaft | Regulation process for the optical power of a laser, and circuit for carrying out the process |
| EP0237922A3 (en) * | 1986-03-18 | 1991-02-27 | Alcatel SEL Aktiengesellschaft | Regulation process for the optical power of a laser, and circuit for carrying out the process |
| US4862466A (en) * | 1986-09-25 | 1989-08-29 | Minolta Camera Kabushiki Kaisha | Laser emitting apparatus with temperature intensity control |
| US4918681A (en) * | 1986-12-25 | 1990-04-17 | Kabushiki Kaisha Toshiba | Data reproducing apparatus using idling current |
| EP0331304A3 (en) * | 1988-03-04 | 1989-12-20 | British Telecommunications Public Limited Company | Amplification of optical signals |
| EP0331304A2 (en) * | 1988-03-04 | 1989-09-06 | BRITISH TELECOMMUNICATIONS public limited company | Amplification of optical signals |
| US4995100A (en) * | 1988-03-04 | 1991-02-19 | British Telecommunications Public Limited Company | Amplication of optical signals |
| GB2219165A (en) * | 1988-05-27 | 1989-11-29 | Stc Plc | Optical transmission systems |
| GB2219165B (en) * | 1988-05-27 | 1992-10-21 | Stc Plc | Optical transmission systems |
| EP0347202A2 (en) * | 1988-06-14 | 1989-12-20 | Brother Kogyo Kabushiki Kaisha | Excitation system for a semiconductor laser device |
| EP0347202A3 (en) * | 1988-06-14 | 1991-03-20 | Brother Kogyo Kabushiki Kaisha | Excitation system for a semiconductor laser device |
| AT393016B (en) * | 1988-06-14 | 1991-07-25 | Vaillant Gmbh | Gas burner |
| GB2231714A (en) * | 1989-05-17 | 1990-11-21 | Basf Ag | Pulsed laser |
| EP0407919A2 (en) * | 1989-07-11 | 1991-01-16 | Harmonic Lightwaves, Inc. | Optical transmitters linearized by means of parametric feedback |
| EP0407919A3 (en) * | 1989-07-11 | 1992-12-09 | Harmonic Lightwaves, Inc. | Optical transmitters linearized by means of parametric feedback |
| EP0412830A2 (en) * | 1989-08-10 | 1991-02-13 | Tektronix Inc. | Apparatus and method for reduction of intermodulation distortion in an optical fiber network |
| EP0412830A3 (en) * | 1989-08-10 | 1992-07-08 | Tektronix, Inc. | Apparatus and method for reduction of intermodulation distortion in an optical fiber network |
| GB2245756A (en) * | 1990-06-23 | 1992-01-08 | Stc Plc | Digital driving of injection lasers |
| GB2245756B (en) * | 1990-06-23 | 1994-06-08 | Stc Plc | Digital driving of injection lasers |
| DE4127421A1 (en) * | 1990-08-17 | 1993-01-07 | Roman Koller | Safety circuit for medical laser scalpel - detects parameters of test oscillation applied to all circuit components e.g. relay shutter, and power supply cut=off switch |
| GB2260667B (en) * | 1991-10-19 | 1995-10-25 | Northern Telecom Ltd | Optical transmitters |
| GB2260667A (en) * | 1991-10-19 | 1993-04-21 | Northern Telecom Ltd | Optical transmitters |
| EP0539038A2 (en) * | 1991-10-19 | 1993-04-28 | Nortel Networks Corporation | Optical transmitters |
| EP0539038A3 (en) * | 1991-10-19 | 1993-09-22 | Northern Telecom Limited | Optical transmitters |
| US5311005A (en) * | 1991-10-19 | 1994-05-10 | Northern Telecom Limited | Optical transmitters |
| GB2286920A (en) * | 1994-02-25 | 1995-08-30 | Fujitsu Ltd | Power control of laser diodes in optical signal transmitters |
| US5557445A (en) * | 1994-02-25 | 1996-09-17 | Fujitsu Limited | Optical signal transmitter having an apc circuit with automatic bias current control |
| GB2286920B (en) * | 1994-02-25 | 1997-11-05 | Fujitsu Ltd | An optical transmitter having an APC circuit with automatic bias current control |
| US5579328A (en) * | 1995-08-10 | 1996-11-26 | Northern Telecom Limited | Digital control of laser diode power levels |
| US5953690A (en) * | 1996-07-01 | 1999-09-14 | Pacific Fiberoptics, Inc. | Intelligent fiberoptic receivers and method of operating and manufacturing the same |
| US7792166B2 (en) | 2005-06-24 | 2010-09-07 | Lockheed Martin Corporation | Apparatus and method for driving laser diodes |
| US8170075B1 (en) | 2005-06-24 | 2012-05-01 | Lockheed Martin Corporation | Method and apparatus for driving laser diodes |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2025121B (en) | 1982-05-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19950706 |