Semiconductor light emitting module

Details Semiconductor light emitting module Semiconductor light emitting module

1999-08-27

2001-08-14

Palmer, Phan T. H. (Department: 2874)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S037000, C372S006000

Reexamination Certificate

active

06273620

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser module with a grating fiber within which a Bragg grating is formed, and particularly relates to a module with an excellent high frequency performance.
2. Related Background Art
Wavelength division multiplex (WDM) systems for optical communication have been attractive because of abrupt increasing of information to be transmitted. Minimum interval to the neighboring wavelength in the WDM system is set to be 0.8 nm by ITU standard (International Telecommunication Unit). Distributed feedback laser diodes (DFB-LD) with an Mach-Zender type external modulator made of lithium niobate have been used as a light source for such a WDM system because of its sharp oscillation spectrum. In DFB-LD, the oscillation wavelength is determined by the Bragg grating formed within the laser chip.
A semiconductor optical amplifier with a grating fiber, which is called fiber grating laser, has been also attractive. The device comprises a semiconductor optical amplifier and a grating fiber within which a Bragg grating is formed in its core portion. The amplifier and the grating fiber are arranged so that the one facet of the amplifier and the Bragg grating make an optical resonator.
In the WDM system, the wavelength interval is set to be 0.8 nm as mentioned above, then the fiber grating laser is superior to the DFB-LD because the oscillation wavelength is primarily defined by the fiber grating and is adjusted independently of the semiconductor optical amplifier. However, the fiber grating laser has less performance than DFB-LD at high operating frequencies because the length of the optical resonator is longer than that of DFB-LD.
In the semiconductor optical amplifier driven with a high frequency signal, carriers in the active layer of the semiconductor is also affected by the signal. The variation of the carrier density causes the alteration of the refractive index in the active layer, the effective length of the optical resonator, and the oscillation wavelength responds dynamically to the signal frequency. Consequently, the width of oscillation spectrum (FWHM: Full width at Half Maximum) increase. This phenomenon is known as chirping. An optical source with a wider oscillation spectrum is inappropriate for the WDM system.
SUMMARY OF THE INVENTION
In order to solve the problem above mentioned, it is an object of the present invention to provide a fiber grating laser module which has a stable oscillation wavelength at high frequencies and an improved chirping characteristics.
A fiber grating laser module according to the present invention comprises a semiconductor optical amplifier and an optical fiber in which the Bragg grating is formed. The semiconductor optical amplifier provides an optical wave-guide in which light is generated and is amplified by the carrier injection and the optical wave-guide provides a light emitting facet and a light reflecting facet opposing to the emitting facet. A light incident facet of the optical fiber is optically coupled to the light emitting facet of the semiconductor optical amplifier. Therefore, the Bragg grating in the optical fiber and the light reflecting facet forms an optical resonator so as to resonate the light generated and amplified in the optical wave-guide of the semiconductor optical amplifier. The subject of the present invention is that the reflectance of the Bragg grating is larger than 60% at the Bragg diffraction wavelength.
It is preferred in the present invention that the optical wave-guide extends along the axis connecting the light emitting facet and the light reflecting facet of the semiconductor optical amplifier, and the angle between the axis and the normal of the light emitting facet is a predetermined value larger than zero.
The fiber grating laser module of the present invention is preferable to form the light incident facet of the optical fiber so as to focus the light from the light emitting facet of the semiconductor optical amplifier onto the fiber core.
Further scope of applicability of the present invention will become apparent form the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.


REFERENCES:
patent: 5485481 (1996-01-01), Ventrudo et al.
patent: 5659559 (1997-08-01), Ventrudo et al.
patent: 5715263 (1998-02-01), Ventrudo et al.
patent: 5717804 (1998-02-01), Pan et al.
patent: 5724377 (1998-03-01), Huang
patent: 5845030 (1998-12-01), Sasaki et al.
patent: 5930430 (1999-07-01), Pan et al.

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