EP0357799A1
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EP
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Method and apparatus for modulating a semiconductor laser
Assignee: Fujitsu Ltd
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Filing: 1989-03-02
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Granted: —
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Expires: 2009-03-02
Abstract
Abstract A method of modulating a semiconductor laser used for various optical communication systems, a method of stabilizing a light interference device based on the self-homodyne, and a light modulating apparatus using a semiconductor laser. To eliminate adverse effects of chirping on a semiconductor laser and to realize high-speed modulation based on direct modulation, a particular short-pulse current is superposed on a bias current to drive the semiconductor laser such that high-speed phase modulation is effected to the optical output. In order to eliminate phase deviation on the output side of the light interference device caused by self-homodyne and to obtain stable output, furthermore, an average intensity of optical output is found, a feedback is applied to the wavelength of the input light or to the difference of optical path length of the light interference device depending upon the average intensity of the optical output thereby to correct phase bias at the time of intensity modulation. Further, to effect the light intensity modulation stably and at high speeds, the transmission data are converted into codes ac. cording to predetermined rules and are differentiated, the differentiated signals are superposed as modulated current pulses onto a predetermined bias current to drive the semiconductor laser, and the optical output is subjected to the intensity modulation by the self-homodyne via the light interference device.
Inventors
- 👤 Masataka Shirasaki
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 18:16
CPC Classifications
H; H04; H04B; H04B10/00; H04B10/50; H04L; H04L27/00; H04L27/10; H04L27/12; H04L27/18; H04L27/20; H04L27/2096; H01; H01S; H01S5/00; H01S5/06; H01S5/068; H01S5/0683; H01S5/06832
Claims Analysis
Total Claims: 26
Claim 1
Independent Claim
67 words
1) A semiconductor laser apparatus for driving a semiconductor laser by superimposing a modulating current pulse on a constant bias current, wherein said modulating current pulse is formed such that an integral of the oscillation frequency which is varied by the modulating current pulse becomes π or -π in terms of a phase amount, thereby applying a phase modulation to the output light of said semiconductor laser.
Claim 2
Dependent Claim
67 words
1) A semiconductor laser apparatus for driving a semiconductor laser by superimposing a modulating current pulse on a constant bias current, wherein said modulating current pulse is formed such that an integral of the oscillation frequency which is varied by the modulating current pulse becomes π or -π in terms of a phase amount, thereby applying a phase modulation to the output light of said semiconductor laser.
Claim 3
Dependent Claim
36 words
2) The semiconductor laser according to claim 1 wherein the integral of the varying oscillation frequency is a product of a time integral of said modulating current pulse for one time slot and a chirping coefficient.
Claim 4
Dependent Claim
23 words
3) The semiconductor laser apparatus according to claim 1 wherein said modulating current pulse corresponds to 1 or 0 of the transmission data.
Claim 5
Dependent Claim
19 words
4) The semiconductor laser according to claim 1 wherein said modulating current pulse is of a 6 function type.
Claim 6
Dependent Claim
34 words
5) The semiconductor laser apparatus according to claim 2 wherein the phase-modulated output light from the semiconductor laser is converted to a light pulse by a self-homodyne-type detecting circuit to provide an intensity modulation.
Claim 7
Dependent Claim
33 words
6) The semiconductor laser apparatus according to claim 5 wherein said self-homodyne detecting circuit comprises a Mach-Zehnder-type interferometer circuit for providing a difference of one time slot which is caused by a delay.
Claim 8
Dependent Claim
33 words
7) The semiconductor laser apparatus according to claim 5 wherein said self-homodyne detecting circuit comprises a Michelson-type interferometer circuit for providing a difference of one time slot which is caused by a delay.
Claim 9
Dependent Claim
19 words
8) The semiconductor laser apparatus according to claim 5 wherein said self-homodyne detecting circuit comprises a Fabry-Perot-type interferometer circuit.
Claim 10
Dependent Claim
30 words
9) The semiconductor laser apparatus according to claim 2 wherein a self-homodyne interference circuit is provided at the output from the semiconductor laser which is subject to a phase modulation.
Claim 11
Dependent Claim
60 words
10) The semiconductor laser apparatus according to claim 2 wherein the output light from the semiconductor laser which is subject to the phase modulation is applied to an optical fiber for transmission and the output light is converted to a light pulse of 0 or 1 at the output terminal of the transmission optical fiber by a self-homodyne detecting circuit.
Claim 12
Dependent Claim
123 words
11) The semiconductor laser apparatus according to claim 2 comprising a light interfering circuit for dividing said input light to enable the divided input light to pass through two light paths which have different light path lengths, and for combining the divided input light thereafter to provide an intensity modulated output light based on the phase difference between the two lights to be combined, wherein a feedback is applied to a light wavelength of said input light using an average intensity obtained by integrating the intensity of the output light from said light interfering circuit in a time interval corresponding to a speed which is slower than that of said phase modulation, thereby correcting the phase bias at the time of intensity modulation.
Claim 13
Dependent Claim
157 words
12) The semiconductor laser apparatus according to claim 2 comprising an optical interference circuit, said optical interference circuit comprising means for receiving an input light comprising a phase-modulated light signal obtained from the output light from said semiconductor laser, means for combining a divided signal which is obtained by dividing said input light and which passes along two optical paths which have different optical path lengths, and means for providing an output light which is subject to an intensity modulation based on the phase difference between the two lights to be combined, wherein a feedback is applied to the difference in optical path lengths of the two optical paths by using an average light intensity obtained by integrating the intensity of the output signal light from said optical interference circuit in a time interval corresponding to a speed which is slower than that of said modulation, and wherein a phase bias is corrected during the. intensity modulation.
Claim 14
Dependent Claim
70 words
13) The semiconductor laser apparatus according to claim 1 equipped with a driving circuit comprising means for converting a sign of the transmission data only when the transmission data comprises either 1 or 0, a differentiating circuit for differentiating a conversion output signal from the sign converting means, driving means for superimposing the differentiated output signal from the differentiating circuit on a constant bias current as a modulating pulse current.
Claim 15
Dependent Claim
59 words
14) The semiconductor laser apparatus according to claim 13 comprising a self-homodyne interferometer having an optical delay circuit for making the relative phase difference between one and the other of the divided lights 0 or π , the divided lights being obtained by dividing the output light from the semiconductor laser and making the relative delay one time slot.
Claim 16
Dependent Claim
18 words
15) The semiconductor laser apparatus according to claim 13 wherein said differentiating circuit is equipped with a stub.
Claim 17
Dependent Claim
143 words
16) A semiconductor laser apparatus comprising a semiconductor laser and means for modulating an output light therefrom, wherein said modulating means comprises an optical interferometer circuit for dividing an input light into two, enabling the divided input lights to pass along two light paths capable of modulating the difference in optical path lengths, thereafter recombining the divided input, and providing an intensity-modulated output light based on the phase difference produced by the difference in the light path length of the two lights to be combined, a feedback being applied to the light wavelength of the input light by using an average intensity obtained by integrating an intensity of the output light from the optical interference circuit in a time interval corresponding to a speed which is slower than that of the modulation, thereby correcting the phase bias at the time of intensity modulation.
Claim 18
Dependent Claim
143 words
16) A semiconductor laser apparatus comprising a semiconductor laser and means for modulating an output light therefrom, wherein said modulating means comprises an optical interferometer circuit for dividing an input light into two, enabling the divided input lights to pass along two light paths capable of modulating the difference in optical path lengths, thereafter recombining the divided input, and providing an intensity-modulated output light based on the phase difference produced by the difference in the light path length of the two lights to be combined, a feedback being applied to the light wavelength of the input light by using an average intensity obtained by integrating an intensity of the output light from the optical interference circuit in a time interval corresponding to a speed which is slower than that of the modulation, thereby correcting the phase bias at the time of intensity modulation.
Claim 19
Dependent Claim
154 words
17) A semiconductor laser apparatus comprising a semiconductor laser and a means for modulating an output light from said semiconductor laser, wherein said modulating means comprises an optical interference circuit, which divides an input light into two, enabling the divided input lights to pass along two optical paths capable of modulating the difference in an optical path length and recombining the divided input lights thereafter and providing an output light which is intensity-modulated based on the phase difference caused by the difference in the light path length of the two lights to be combined and a feedback is applied to the light path difference between the two light paths by using an average intensity obtained by integrating the intensity of the output light of said light interfering circuit in a time interval corresponding to a speed which is slower than that of the modulation, thereby correcting a phase bias at the time of intensity-modulation.
Claim 20
Dependent Claim
154 words
17) A semiconductor laser apparatus comprising a semiconductor laser and a means for modulating an output light from said semiconductor laser, wherein said modulating means comprises an optical interference circuit, which divides an input light into two, enabling the divided input lights to pass along two optical paths capable of modulating the difference in an optical path length and recombining the divided input lights thereafter and providing an output light which is intensity-modulated based on the phase difference caused by the difference in the light path length of the two lights to be combined and a feedback is applied to the light path difference between the two light paths by using an average intensity obtained by integrating the intensity of the output light of said light interfering circuit in a time interval corresponding to a speed which is slower than that of the modulation, thereby correcting a phase bias at the time of intensity-modulation.
Claim 21
Dependent Claim
64 words
18) A method for modulating a semiconductor laser comprising a step of driving the semiconductor laser by using a modulating current pulse superimposed on a constant bias current, wherein the product of a time integral of said modulating current pulse with regard to one time slot and a chirping coefficient is π or -π , to phase-modulate the output light from the semiconductor laser.
Claim 22
Dependent Claim
64 words
18) A method for modulating a semiconductor laser comprising a step of driving the semiconductor laser by using a modulating current pulse superimposed on a constant bias current, wherein the product of a time integral of said modulating current pulse with regard to one time slot and a chirping coefficient is π or -π , to phase-modulate the output light from the semiconductor laser.
Claim 23
Dependent Claim
42 words
19) The method of modulating a semiconductor laser according to claim 18, wherein the output light from the semiconductor laser which is subject to a phase modulation is converted to a light pulse by a self-homodyne-type method to provide an intensity-modulated output.
Claim 24
Dependent Claim
70 words
20) A semiconductor device for driving the semiconductor laser (23) by a modulating current pulse superimposed on a constant bias current, wherein a phase modulation is applied to an output light from the semiconductor laser according to existence or nonexistence of a modulating current pulse, by producing a phase difference based on an integral of an oscillation integration frequency which varies according to an application of the modulating current pulse.
Claim 25
Dependent Claim
70 words
20) A semiconductor device for driving the semiconductor laser (23) by a modulating current pulse superimposed on a constant bias current, wherein a phase modulation is applied to an output light from the semiconductor laser according to existence or nonexistence of a modulating current pulse, by producing a phase difference based on an integral of an oscillation integration frequency which varies according to an application of the modulating current pulse.
Claim 26
Dependent Claim
29 words
21) A semiconductor laser apparatus according to claim 20 wherein the phase-modulated output light of the semiconductor laser is converted to an intensity modulation by using a self-homodyne detector.
References Cited (Backward Citations)
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