Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-04-13
2001-12-11
Leung, Quyen (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S026000, C359S237000, C359S248000, C385S001000
Reexamination Certificate
active
06330266
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for selecting a semiconductor integrated optical modulator/laser light source device comprising a modulator section and a laser section.
There would be coming attractive a semiconductor optical modulator integrated laser light source device having an integration of a laser device such as a distributed feed back laser or a distributed reflection laser and a modulator such as an electroabsorption modulator on account of this light source device shows a small chirping when the modulator shows a modulation. The property of the small chirping of the laser device is suitable for a long-distance and large capacitance optical signal transmission. In the semiconductor optical modulator integrated laser light source device, the laser section is driven by a direct current and the modulator section is driven by pulse signals having binary levels wherein when one level is applied onto the modulator section, the modulator performs an attenuation function thereby the laser beam is absorbed in the modulator, resulting in almost no laser emission being obtained. By contrast, another level is applied onto the modulator section, the modulator shows no attenuation function thereby the laser beam pass through in the modulator without any attenuation, resulting in a laser emission being obtained.
This semiconductor optical modulator integrated laser light source device is, however, engaged with problems in generation of bit error due to the following reasons.
A first reason for generation of the bit error associated with the semiconductor optical modulator integrated laser light source device is concerned with a generation of wavelength chirping which is caused by optical and electrical interference between the laser section and the modulator section in the semiconductor optical modulator integrated laser light source device. The optical and electrical interference between the laser section and the modulator section may often be generated when an isolation resistance between the laser section and the modulator section is small or when the modulator section has a facet showing an insufficient reflective suppression function.
A second reason for generation of the bit error associated with the semiconductor optical modulator integrated laser light source device is concerned with a variation in optical power due to an influence of an electrical multiplication reflection which is caused by an impedance mismatching between the modulator and a modulator driver circuit for driving the modulator.
A third reason for generation of the bit error associated with the semiconductor optical modulator integrated laser light source device is concerned with an increase of the wavelength chirping of the modulator section due to rising an efficient of the phase modulation of the which is caused by a carrier accumulation. The carrier accumulated is generated by an optical absorption into the modulator section.
Therefore, it is required to verify whether the semiconductor optical modulator integrated laser light source device is available to be free from the above described problem with the bit error. In the prior art, the verifying process is accomplished by making a complicated measurement of a property of the transmission bit error rate associated with the semiconductor integrated optical modulator/laser light source device wherein the measurement of the transmission bit error rate property requires conducting an optical signal transmission test under the same conditions as the practical use and further confirming whether or not there exists a bit error for each of an extremely large numbers of bits as signals having transmitted in the test. Thus, it has been required to develop a quite novel method for selection thereof free from the above problem.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel convenient method for selecting a semiconductor integrated optical modulator/laser light source device comprising a modulator section and a laser section free from any problems as described above.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.
The present invention provides a method for selecting a semiconductor integrated optical modulator/laser light source device comprising a modulator section and a laser section. The method comprises the following steps. The laser section is supplied with a direct current which is equal to or larger than a threshold current for allowing the laser section to show a laser emission when the modulator section is supplied with a pulse signal for allowing the modulator section to show a pulse modulation so as to allow a light emitted directly from a facet of the laser section to show a transmission through a light wavelength dispersion medium within which the light on transmission shows a dispersion in wavelength. An intensity of the light having shown the dispersion in wavelength is measured to find a coefficient of variation in intensity of the light, wherein the variation is due to a wavelength chirping. There is verified the fact that the coefficient of variation in intensity of the light be below a predetermined reference level.
The present invention also provides a method for selecting a semiconductor integrated optical modulation/laser light source device comprising a modulator section and a laser section. The method comprises the following steps. The laser section is supplied with a direct current which is equal to or larger than a threshold current for allowing the laser section to show a laser emission when the modulator section is supplied with a binary pulse signal both with first and second voltage levels and with a frequency which is within a practically available range for allowing the modulator section to show a pulse modulation where the modulator section performs no light attenuation function in the first voltage level of the binary pulse signal and the modulator section performs a light attenuation in the second voltage level. Any of first and second lights emitted from facets of the laser section and the modulator section respectively is caused to show spectra with first and second peaks in intensity versus frequency, provided that the first peak appears only in the first voltage level of the binary pulse signal and the second peak appears only in the second voltage level of the binary pulse signal. There is verified the fact that a difference in frequency between the first and second peaks be below a predetermined reference value.
The present invention also provides a method for selecting a semiconductor integrated optical modulator/laser light source device comprising a modulator section and a laser section. The method comprises the following steps. The laser section is supplied with a direct current which is equal to or larger than a threshold current for allowing the laser section to show a laser emission when the modulator section is reverse-biased with first and second direct-current voltages respectively corresponding to first and second voltage levels of a binary pulse signal to be practically used for a pulse modulation of the modulator section wherein the modulator section performs no light attenuation function in the first direct-current voltage and the modulator section performs a light attenuation in the second direct-current voltage. A light emitted from a facet of the laser section is caused to show spectra with first and second peaks in intensity versus frequency, provided that the first peak appears only in the first direct-current voltage and the second peak appears only in the second direct-current voltage. There is verified the fact that a difference in frequency between the first and second peaks be below a predetermined reference value.
The present invention also provides a method for selecting a semiconductor integrated optical modulator/laser light source device comprising a modulator section and a laser section. The method comprises the following steps
Leung Quyen
Menefee James
NEC Corporation
Young & Thompson
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