Coherent light generators – Particular resonant cavity
Reexamination Certificate
2002-08-09
2004-11-16
Wong, Don (Department: 2828)
Coherent light generators
Particular resonant cavity
Reexamination Certificate
active
06819700
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing an external cavity semiconductor laser, an external cavity semiconductor laser, and a wavelength multiplex transmission system.
2. Related Background Art
A semiconductor laser generates light having a desired wavelength. Such a semiconductor laser is used as a light source for optical communications. In optical communications, WDM communication is implemented using a plurality of semiconductor lasers for generating optical signals having respective wavelength components.
SUMMARY OF THE INVENTION
An example of semiconductor lasers is an external cavity semiconductor laser. The external cavity semiconductor laser has a grating fiber and a semiconductor optical amplification element. In order to obtain a stable optical output, the external cavity semiconductor laser comprises a thermoelectronic element for temperature control and a control circuit for controlling the thermoelectronic element.
If an external cavity semiconductor laser does not include a Peltier element for controlling the temperature of the semiconductor optical amplification element, the length of the optical path, i.e., the optical cavity length, is changed due to variations of ambient temperatures or injected currents. This change causes a phenomenon, i.e., mode hopping, wherein the longitudinal mode discontinuously changes. Consequently, a so-called kink appears in the I-L characteristic (current vs. optical output characteristic). At the kink, the optical output of the semiconductor laser discontinuously changes, so that the use of such a semiconductor laser degrades the transmission quality.
Therefore, it is an object of the present invention to provide a method of manufacturing an external cavity semiconductor laser capable of reducing the occurrence of kinks, an external cavity semiconductor laser, and a wavelength multiplex transmission system.
An aspect of the present invention is a method of manufacturing an external cavity semiconductor laser. This method comprises the steps of: (a) providing an optical waveguide device and a semiconductor optical amplification element along a predetermined axis, the optical waveguide device having an optical waveguide and a Bragg grating exhibiting a maximum reflectivity at a frequency f
FG
; and (b) arranging the optical waveguide and the semiconductor optical amplification element while monitoring a frequency f
LD
and intensity of light from an optical system including the semiconductor optical amplification element and the optical waveguide device.
In this method, the step of providing the optical waveguide and the semiconductor optical amplification element can include a step of adjusting a distance along the predetermined axis between the optical waveguide device and the semiconductor optical amplification element such that the oscillation frequency f
LD
satisfies:
0
<f
FG
−f
LD
<20 GHz.
Another aspect of the present invention is a method of manufacturing an external cavity semiconductor laser. This method comprises the steps of: (a) preparing an optical waveguide device and a semiconductor optical amplification element, the optical waveguide device having an optical waveguide and a Bragg grating exhibiting a maximum reflectivity at a wavelength &lgr;
FG
; and (b) arranging the optical waveguide and the semiconductor optical amplification element while monitoring a wavelength &lgr;
LD
and intensity of light from an optical system including the semiconductor optical amplification element and the optical waveguide device.
In this method, the arrangement is carried out such that the wavelength &lgr;
LD
satisfies:
0<&lgr;
LD
−&lgr;
FG
<0.16 nanometers.
Still another aspect of the present invention is a method of manufacturing an external cavity semiconductor laser. The external cavity semiconductor laser comprises a grating fiber and a semiconductor amplification element. This method comprises the steps of (a) preparing a semiconductor optical amplification element and a grating fiber, the semiconductor optical amplification element being mounted on a stem, the grating fiber having a maximum reflectivity at a frequency f
FG
; and (b) arranging the semiconductor optical amplification element and the grating fiber while energizing the semiconductor optical amplification element through the stem and monitoring a frequency f
LD
and intensity of light from an optical system including the semiconductor optical amplification element and the grating fiber.
In this method, the arrangement can be carried out such that the oscillation frequency f
LD
satisfies:
0
<f
FG
−f
LD
<20 GHz.
Still another aspect of the present invention is a method of manufacturing an external cavity semiconductor laser. The external cavity semiconductor laser comprises a grating fiber and a semiconductor amplification element. This method comprises the steps of (a) preparing a semiconductor optical amplification element mounted on a stem and a grating fiber having a maximum reflectivity at a wavelength &lgr;
FG
; and (b) arranging the semiconductor optical amplification element and the grating fiber while energizing the semiconductor optical amplification element through the stem and monitoring a wavelength &lgr;
LD
and intensity of light from an optical system including the semiconductor optical amplification element and the grating fiber.
In this method, the arrangement is carried out such that the wavelength &lgr;
LD
satisfies:
0<&lgr;
LD
−&lgr;
FG
<0.16 nanometers.
Still another aspect of the present invention is an external cavity semiconductor laser. The external cavity semiconductor laser has a temperature-uncontrolled-type structure and is capable of generating light having an oscillation frequency f
LD
. The external cavity semiconductor laser comprises an optical waveguide device and semiconductor optical amplification element. The optical waveguide device has a Bragg grating and an optical waveguide, the Bragg grating having a reflection spectrum with a maximum reflectivity at a frequency f
FG
, and the Bragg grating being optically coupled to the optical waveguide. The semiconductor optical amplification element is optically coupled to the optical waveguide such that the oscillation frequency f
LD
satisfies:
0
<f
FG
−f
LD
<20 GHz.
An external cavity semiconductor laser of the present invention is capable of generating light having an oscillation frequency f
LD
. The external cavity semiconductor laser comprises a semiconductor substrate, a semiconductor optical amplification element, an optical waveguide device, and a Bragg grating. The semiconductor optical amplification element is provided on the semiconductor substrate. The optical waveguide device is provided on the semiconductor substrate and is optically coupled to the semiconductor optical amplification element. The Bragg grating is provided on the semiconductor substrate and is optically coupled to the optical waveguide. The Bragg grating has a spectrum exhibiting a maximum reflectivity at a frequency f
FG
. The semiconductor optical amplification element and the Bragg grating are arranged such that the oscillation frequency f
LD
satisfies:
0
<f
FG
−f
LD
<20 GHz.
An external cavity semiconductor laser of the present invention is capable of generating light having an oscillation frequency f
LD
. The external cavity semiconductor laser comprises a substrate, an optical waveguide, a Bragg grating, and a semiconductor optical amplification element. The substrate includes at least one of LiNbO
3
and LiTaO
3
. The optical waveguide is provided on the semiconductor substrate. The Bragg grating is provided on the semiconductor substrate and optically coupled to the optical waveguide. The Bragg grating has a spectrum exhibiting a maximum reflectivity at a frequency f
FG
. The semiconductor optical amplification element is optically coupled to the optical waveguide. The semiconductor optical amplification element and the Bragg grating are arranged s
Hashimoto Jun-ichi
Kato Takashi
Yamabayashi Naoyuki
Al-Nazer Leith A
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
Wong Don
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