Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1999-12-02
2001-12-04
Healy, Brian (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S123000, C385S027000, C385S028000, C385S141000, C359S341430
Reexamination Certificate
active
06327412
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical fiber for receiving light emitted from a semiconductor light-emitting device and guiding thus received light, a light-emitting module comprising this optical fiber and the semiconductor light-emitting device, and an optical fiber type optical amplifier, which is named as optical fiber amplifier, using this light-emitting optical module.
BACKGROUND ART
As an apparatus for amplifying signal light in optical communications, an optical fiber amplifier has been known. As disclosed in each of Japanese Patent Application Laid-Open No. HEI 10-56227 and Japanese Patent Application Laid-Open No. HEI 10-90547, such an optical fiber amplifier is configured such that signal light is propagated through an amplifying optical fiber doped with a rare-earth element; and pumping light, having a predetermined wavelength different from that of the signal light and causing the doped rare earth to release light having a wavelength identical to that of the signal light, is input into the amplifying optical fiber from both ends thereof, so as to amplify the signal light.
Semiconductor light-emitting devices such as light-emitting diode (LED) and laser diode (LD) are in common use for the pumping light source. The light emitted from one such semiconductor light-emitting devices is guided to the amplifying optical fiber by a waveguide optical fiber.
In general, the output face of the light-emitting region (active region) of a semiconductor light-emitting device has a rectangular form, and the length L of the longer side of the output face of the light-emitting region is longer as its optical output power is greater. As the semiconductor light-emitting device favorably usable for the pumping light source, those having an L of 100 &mgr;m or 50 &mgr;m and the like have been known. In order to favorably guide the light emitted from such a kind of semiconductor light-emitting device to a waveguide optical fiber, while facilitating the positional adjustment between the semiconductor light-emitting device and the optical fiber, it has conventionally been a common practice to make the core diameter D of the waveguide optical fiber not shorter than the length L of the longer side of the output face of the light-emitting region of the semiconductor light-emitting device (see catalogs of LD modules MLD100-FC and MLD300-FC manufactured by Mitsui Chemicals, Inc., catalog of LD module AOC980-120-HHL200 manufactured by Applied Optics Corp., and catalog of LD module SDLO-4000 manufactured by SDL, Inc., for example).
DISCLOSURE OF THE INVENTION
In such an optical fiber amplifier, it is required that not only the light incident on the waveguide optical fiber and guided thereby have a high power, but also the optical power per unit cross-sectional area in its core region, i.e., light intensity, be high. Conventionally, however, the light intensity has not been sufficient since the core diameter D of the waveguide optical fiber is large, though the power of light incident on and guided by the optical fiber has been high. As a consequence, in such a conventional optical fiber amplifier employing a semiconductor light-emitting device and a waveguide optical fiber, even when a semiconductor light-emitting device having a high optical output power is used, since the light intensity of the guided pumping light is insufficient, the pumping efficiency of the element to be excited in the amplifying optical fiber is low, thus yielding a low optical amplification factor.
In view of such a problem, it is an object of the present invention to provide an optical fiber which can guide light having a sufficient light intensity and optical output power, a light-emitting module using the same, and an optical fiber amplifier using this light-emitting module.
For achieving the above-mentioned object, the optical fiber in accordance with the present invention is characterized in that a core cross section at an end face has a maximum width of 50 &mgr;m or less, and the product of this maximum width and a numerical aperture thereof is 5.2 &mgr;m or greater.
The inventors have studied conditions to be satisfied by the optical fiber in order to transmit light having a high output power therethrough with a high light intensity. Then, the inventors have found it preferable to reduce the core diameter D while keeping the coupling efficiency with respect to the light source on the entrance side substantially at 100%. Even when the beam diameter of the light incident on the optical fiber end face is made narrower than the core diameter D, light having a higher mode number cannot be guided through the optical fiber unless the core diameter and the numerical aperture satisfy a predetermined relationship therebetween, whereby the coupling efficiency will deteriorate accordingly. Also, increasing the core diameter in excess is unfavorable since it decreases the light intensity. The inventors have found that, when application to an optical fiber amplifier or the like is taken into consideration, the core diameter preferably should not exceed 50 &mgr;m from the viewpoints of matching with the amplifying optical fiber, maintenance of light intensity, and the like, and that the incident high-output beam can be guided with a high coupling efficiency while maintaining a high light intensity when the core diameter is set to the above-mentioned range. When this optical fiber is utilized as an optical fiber for guiding pumping light in the optical fiber amplifier, pumping light having a high output and high intensity can be guided to the amplifying optical fiber, whereby the efficiency of amplification can be enhanced. In particular, when a high-output LD or the like is used as the light source, substantially the whole light emitted from the LD can be guided to the core portion and transmitted therethrough while maintaining a high light intensity.
Alternatively, the optical fiber in accordance with the present invention is characterized in that it has two core portions, the product of the maximum width of a core cross section at an end face and a numerical aperture thereof being 2.6 &mgr;m or less in each of the core portions, the two core portions being provided with respective cladding portions independent from each other at one end thereof, and at the other end thereof the two core portions being disposed at least near or adjacent to each other and provided with a common cladding portion, the maximum distance between outer peripheries of the two core portions being 50 &mgr;m or less.
Also in this optical fiber, a high-output light beam can be input therein from the side where the core portions are disposed near each other, so as to be split into two, whereby the light beams having a high output power and high intensity can be emitted to both of branched end faces. If this optical fiber is used as the waveguide optical fiber in the optical fiber amplifier, then, while using a single semiconductor laser as its pumping light source, the pumping light incident on the optical fiber from its unified one end can easily be guided to both ends of the amplifying optical fiber, whereby the efficiency of amplification can be enhanced. When a high-output LD or the like is used as the light source, substantially the whole light emitted from the LD can be guided to the core portions and transmitted therethrough while maintaining a high light intensity.
On the other hand, the light-emitting module in accordance with the present invention comprises a semiconductor light-emitting device for emitting light having a predetermined wavelength; a light-collecting optical system for collecting the light emitted from the semiconductor light-emitting device; and an optical fiber for receiving the light guided by the light-collecting optical system, guiding thus received light through a core region, and emitting thus guided light, the optical fiber being disposed such that a maximum width direction of the core region at an input face thereof aligns with a maximum width direction of an incident beam, the maximum width D [&m
Ishikawa Shinji
Kakui Motoki
Sasaki Takashi
Healy Brian
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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