Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2001-03-21
2002-12-03
Ngo, Hung N. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S035000, C385S089000
Reexamination Certificate
active
06488419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light emitting module.
2. Related Background Art
In 1.55 &mgr;m-band WDM systems, the wavelength spacing between adjacent channels is stipulated as 0.8 nm. This requires that the absolute accuracy of each channel wavelength should be controlled within the precision of ±0.1 nm or higher. DFB semiconductor lasers and DBR semiconductor lasers may be utilized for 1.55 &mgr;m-band WDM systems.
SUMMARY OF THE INVENTION
These semiconductor lasers provide a sharp oscillation spectrum, but their oscillation wavelength is determined by a diffraction grating fabricated in a laser chip at the manufacturing stage of semiconductor laser. It was not easy to yield a desired oscillation wavelength stably and accurately, because characteristics of the diffraction grating were affected by manufacturing process factors.
For implementation of it, there is the following attempt. A semiconductor laser chip is assembled to obtain a light emitting module. During operation of the module, output light from the light module is branched and this branch light is monitored by a large-scale apparatus like an optical spectrum analyzer. According to the monitor information, temperature or injection current of the semiconductor laser chip is adjusted.
However, in the wavelength division multiplexing (WDM) systems, it is not easy to realize a light emitting module applicable to the WDM systems because a plurality of wavelengths are used to transmit data in 16 channels or 32 channels.
It is, therefore, an object of the present invention to provide a light emitting module that permits easy adjustment of the wavelength of light generated in the light emitting module, without using any large-scale system like the optical spectrum analyzer.
In order to realize the light emitting module capable of attaining this object, the inventors conducted a variety of studies, e.g., on the light emitting modules incorporating the semiconductor laser. In order to adjust the oscillation wavelength of the light emitting module while operating the light emitting module, it is necessary to monitor the wavelength. For extracting oscillating light, an optical branching device, such as an optical coupler, needs to be coupled to output of the light emitting module. However, if the device having this function is used, the scale of the WDM systems will be large.
According to these studies, it became apparent that there were technical problems as follows. (1) There is a need for use of optical coupling means for obtaining monitor light to monitor light from the semiconductor light emitting element such as the semiconductor laser. (2) There is a need for use of separating means for separating the light from the coupling means into wavelength components. (3) There is a need for use of converting means for converting the light components from the separating means into electric signals.
In view of these problems, the inventors accomplished the present invention in structure as follows.
A light emitting module of the present invention comprises a semiconductor light emitting device, a photodetection device, an etalon device, and collimating means. The semiconductor light emitting device has first and second end faces. The photodetection device has first and second photodetectors optically coupled to the first end face of the semiconductor light emitting device. The etalon device has a first portion having a first thickness and a second portion having a second thickness. The first portion of the first thickness is provided so as to be located between the first end face of the semiconductor light emitting device and the first photodetector. The second portion of the second thickness is provided so as to be located between the first end face of the semiconductor light emitting device and the second photodetector. The first thickness of the etalon device is different from the second thickness of the etalon device. The collimating means functions to provide substantially collimated light for the etalon device that receives the light from the semiconductor light emitting device.
In the etalon device, the thickness of the portion located between the first end face of the semiconductor light emitting device and the first photodetector is different from that of the portion located between the first end face of the semiconductor light emitting device and the second photodetector. Light of different wavelength components passes through portions of the different thicknesses corresponding to the wavelength components in the etalon device. Therefore, if the wavelength components of light from the semiconductor light emitting device is changed, intensities of light passing through the particular portions of the etalon device varies in response to the change. This variation is converted into electric signals by the first photodetector and the second photodetector. Changes of these electric signals indicate the change of wavelengths in the light generated in the semiconductor light emitting device.
A difference signal between these electric signals represents a direction of the change of wavelengths in the light. By controlling the semiconductor light emitting device portion so as to keep this difference signal constant, it becomes feasible to keep the wavelength constant in the light generated in the semiconductor light emitting device.
The features according to the present invention as described below can be combined with the above-stated invention. The features according to the present invention as described below can be also combined with each other to enables the module to obtain actions and effects of the respective features and also obtain actions and effects achieved by the combination.
In the light emitting module, the etalon device has first and second surfaces. The first surface is arranged so as to be opposed to the second surface. The first and second surfaces are positioned so that an interval between them in the first portion is the first thickness. The etalon device has third and fourth surfaces. The third surface is provided so as to be opposed to the fourth surface. The third and fourth surfaces are located so that an interval between them in the second portion is the aforementioned second thickness. This configuration can provided the etalon device having the first and second thicknesses.
In the light emitting module of the present invention, the etalon device has a light receiving surface and a light outgoing surface. The light receiving surface is arranged so as to receive the light from the first end face of the semiconductor light emitting device, and the light outgoing surface is arranged so as to face the light receiving surface. The light receiving surface includes first and third faces. The light outgoing surface includes second and fourth faces. In the light emitting module of the present invention, the light receiving surface is inclined to the light outgoing surface. Because of this inclination, the distance between the light receiving surface and the light outgoing surface increases in a direction directed from the first portion to the second portion of the etalon device.
The etalon device has the light receiving surface and the light outgoing surface, the distance of which is changed in the first direction. When the etalon device is moved relative to the first and second photodetectors in the first direction, the transmission spectra achieved by the first and second portions of the etalon device is changed. This change results in changing the wavelength components of light received through the etalon device by the first and second photodetectors. The center wavelength of light generated in the semiconductor light emitting device can be adjusted by making use of this change. The transmitting peak wavelengths of the etalon device, which is utilized for adjusting the center wavelength of the light generated by the semiconductor light emitting device, can also be adjusted by rotating the etalon device. In the light emitting module, the etal
Kato Takashi
Kitayama Ken-ichi
Yamaguchi Akira
McDermott & Will & Emery
Ngo Hung N.
Sumitomo Electric Industries Ltd.
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