Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-07-14
2001-10-30
Kim, Ellen E. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S038000, C385S031000
Reexamination Certificate
active
06310997
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ferrule assembly and an optical module having the ferrule assembly, specifically serving as a light source of optical communication, optical fiber amplifiers, and the like.
2. Related Background Art
Laser modules are basically composed of a light-emitting device as a light source and an optical resonator comprising a pair of reflectors mutually reflecting the light emitted from the light-emitting device.
In the laser modules mentioned above, one of the reflectors constituting the resonator is one facet (back facet) of the light-emitting device itself or dielectric films having a high reflectivity formed on this back facet. A Bragg grating disposed near an end portion of the optical fiber opposing the light-emitting device is utilized as the other reflector. The Bragg grating is formed within the optical fiber by providing a periodic refractive index alteration, and reflects specific light determined by the Bragg diffraction condition. The optical fiber in which a Bragg grating is formed is described as grating faiber and is advantageous that the desirable oscillation wavelength can easily be selected by the specification of the Bragg grating.
In case of an optical resonator constituted by one facet of the light-emitting device and a grating fiber, a ferrule is attached to an end portion of the grating fiber, and a ferrule assembly constituted by the grating fiber and the ferrule is secured at a predetermined position. An optical coupling between the light-emitting device and the grating fiber can be realized by disposing an optical element (lens) between the facet of the light-emitting device and the end face of the grating fiber facing each other. The optical coupling can also be realized by rounding the facet of the grating fiber instead of providing the optical element.
In a typical configuration of the ferrule assembly, it is common that the optical axis of the light-emitting device and the grating fiber are aligned to each other. In order to prevent the light reflected by the front facet of the light-emitting device back into the waveguide of the light-emitting device again, however, the front facet of the light-emitting device is vertically inclined off the optical axis by a predetermined angle.
In case where the facet of the grating fiber is rounded, the ferrule assembly has such a configuration that the end portion of the grating fiber protrudes from the end surface of the ferrule. It is due to the fact that, while the facet of the light-emitting device and the end face of the grating fiber must be installed close to each other, it is structurally difficult for the ferrule to approach the light-emitting device. Hence, a part of the end of the grating fiber including the rounded facet thereof protrudes from the end surface of the ferrule.
As a result of detailed studies concerning the above-mentioned resonator, the inventor has found that the resonator characteristic is attributed to the structure of the ferrule assembly.
The first factor affecting to the resonator characteristic lies in tightly securing the whole portion of fiber grating to the inner wall of the ferrule with an adhesive. In this case, due to deformations, thermal expansions, and the like of the ferrule, a stress is directly applied to the fiber grating. The reflection characteristic of the fiber grating would change. The second factor is, when the grating fiber and the ferrule are not firmly fixed to each other, the installed position of the grating fiber may shift gradually due to the environment conditions. As a result, the coupling efficiency between the light-emitting device and the grating fiber deteriorates.
SUMMARY OF THE INVENTION
In order to overcome the problems mentioned above, it is an object of the present invention to provide a ferrule assembly which is not influenced by manufacture and environment conditions, and an optical module equipped with the ferrule assembly.
For achieving the object, the ferrule assembly of the present invention comprises a grating fiber and a ferrule attached to an end portion of the grating fiber. The grating fiber includes a Bragg grating disposed apart from one end face by a predetermined distance. The ferrule comprises a securing portion for securing the grating fiber and an accommodating portion for accommodating the grating region in which the Bragg grating is disposed.
In particular, the ferrule assembly is characterized in that, while the portion of the grating fiber excluding the grating region is secured to the securing portion, the grating region is accommodated in the accommodating portion of the ferrule in a state apart from the inner wall without being secured to the ferrule.
As a consequence, the grating region would not receive any stress from the ferrule even when the ferrule is mechanically or thermally deformed. Stable optical characteristics, i.e., stable resonance characteristics, can be attained.
Further, the ferrule assembly of the present invention may have a configuration in which an opening end of the insertion bore of the ferrule is provided with a tapered portion. The grating fiber and the ferrule are secured to each other with solder at the tapered portion. Since the solder can appropriately be lead to a desirable securing position, scattering of the securing strength between the grating fiber and ferrule among products can be suppressed. The member to be secured to the ferrule is not needed to be a grating fiber such as that mentioned above but may be a standard single-mode fiber without a Bragg grating. This configuration is widely applicable to technologies in which a ferrule and an optical fiber are secured to each other with solder.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from 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.
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“Narrow Line Semiconductor Laser Using Fibre Grating”, Electronics Letters, Jun. 20, 1991, vol. 27, No. 13, pp. 1115-1116.
“Reduction of Optical-Feedback-Induced Frequency Noise in Pigtailed Laser Diodes”, Electronics Letters, Jun. 22, 1989, vol. 25, No. 13, pp. 863-864.
Kato Takashi
Nakaya Hiroyuki
Kim Ellen E.
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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