Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2003-01-31
2004-11-23
Nguyen, Chau N. (Department: 2831)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S093000, C385S088000
Reexamination Certificate
active
06821030
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optical coupling apparatus including a semiconductor light emitting device and an optical fiber that are optically connected to each other. More particularly, the invention relates to a single lens optical coupling apparatus that attains optical coupling by use of a single lens.
A known optical coupling apparatus allows an outgoing beam from a semiconductor laser to be incident into an end face of an optical fiber through a lens, and optical coupling is attained between the semiconductor laser and the optical fiber through the single lens, as described in JP-A-05-150146. This reference discloses a construction in which the semiconductor laser, the lens and a light reception device are mounted onto a substrate having thick portions on both sides thereof that are parallel to an optical axis to suppress the change of optical coupling in the optical axis direction and to reduce an optical axis error.
Another reference, JP-A-11-330564, describes optical coupling between an optical semiconductor device and an optical fiber by use of a single lens. The optical semiconductor device and the lens are mounted onto a block. The block is arranged on a heat sink and is encompassed by a package. An optical fiber is inserted and fixed into a cylindrical optical fiber fixing portion disposed on a side surface of the package. Fixing members capable of deformation are interconnected to a package main body to prevent an optical axis error of the package resulting from thermal expansion of the heat sink when the heat sink is screw-fixed to mount an optical communication appliance. Still another reference, JP-A-2001-284699, discloses a construction in which two lenses are used to optically couple a semiconductor laser and an optical fiber, and the semiconductor laser and a first lens are mounted onto a base and are disposed on a bottom plate of a package through a Peltier device. A fitting cylinder is so fitted as to protrude from inside and outside of the package, and a second lens and the optical fiber are disposed inside the cylinder and at an end portion, respectively.
BRIEF SUMMARY OF THE INVENTION
The inventors of this invention have found that the constructions of the known references are not yet satisfactory as a construction of a single lens optical coupling apparatus that is very susceptible to influences of thermal deformation of a base and surrounding portions when service life of the apparatus is extended or when the apparatus is applied to long-distance optical transmission.
Evaluation items of performance of an optical coupling apparatus include optical coupling temperature characteristics (hereinafter called “tracking error”) relating to stability of optical coupling in a temperature range from a low temperature to a high temperature. The tracking error occurs mainly as an operating temperature of the optical coupling apparatus changes to invite thermal deformation, and this thermal deformation in turn invites a change of the optical coupling state between a semiconductor light emitting device and an optical fiber.
JP-A-2001-284699 as the known reference described above employs a confocal optical system that uses two lenses and suppresses the change of optical coupling due to thermal deformation. The confocal optical system has a feature in that tolerance of a positioning error on the change of optical coupling becomes greater between the two lenses. The optical coupling apparatus makes the most of this feature, exhibits a small change of optical coupling even when thermal deformation develops, and makes it easier to satisfy the tracking error specification. However, the confocal optical system using the two lenses increases the number of components and the number of assembly steps and is likely to invite the increase of the production cost.
It is more advantageous to establish optical coupling by using one lens in order to reduce the number of components as well as the number of assembly steps and to lower the production cost. However, because the optical coupling system using one lens does not have a broad tolerance portion of the positioning error of the confocal optical system, the change of optical coupling unavoidably occurs due to very limited thermal deformation. Therefore, the optical coupling apparatus of the one-lens optical system must employ a component construction that makes the difference of the thermal expansion ratios smaller than that of the component construction of the confocal optical system to suppress thermal deformation. Because the optical coupling apparatus is constituted by a plurality of materials having mutually different thermal expansion ratios, however, it is extremely difficult to completely eliminate thermal deformation unless specific materials are used to form the components. When such specific components are employed, the production cost increases with the result that the effect of lowering the cost of production by using one lens is lost.
It has been found that the form of JP-A-05-150146 and JP-A-11-330564 occupies a large ratio to the length of a so-called “base portion” of the housing, and is greatly susceptible to deformation of the base. Therefore, it is believed difficult to sufficiently reduce the tracking error. In addition, because JP-A-11-330564 does not mount the Peltier device, temperature control by the Peltier device is not possible. When any temperature change occurs, thermal expansion and thermal deformation of the block further increase the positioning error between the semiconductor light emitting device and the lens in the direction of height. Consequently, the position of the laser beam to be condensed to the optical fiber greatly changes, and the tracking error specification cannot be satisfied easily.
It is therefore an object of the invention to provide an optical coupling apparatus that can solve the problems described above.
To accomplish this object, the invention employs a construction that can insure long service life and can be applied to long distance optical communication even in a form susceptible to influences of thermal deformation of a base and surrounding components such as in the case of a single lens optical coupling apparatus.
For example, a construction capable of satisfying an optical coupling change of ±0.5 dB within a temperature range from −20° C. to 75° C. as a tracking error specification can be accomplished at a low cost of production.
The invention can specifically take the following forms, for example.
(1) An optical coupling apparatus including a base; a temperature controlling device disposed on the base; a substrate arranged on the temperature controlling device and having mounted thereto a semiconductor light emitting device and a lens into which rays of light from the semiconductor light emitting device are introduced while being diffused; a through-hole portion formed in a housing wall portion installed on the base, penetrating through the housing wall portion and having a wall surface portion longer than a thickness of the housing wall portion; and an optical fiber communicated with the through-hole portion and receiving converged light from the lens introduced thereto; wherein a length of the substrate in a direction connecting the light emitting device to the optical fiber is within a range from 0.1 to 0.25 with respect to a length of the base sandwiched by the housing walls of the substrate.
(2) The optical coupling apparatus described in the construction (1) further comprises an optical isolator which communicates with the through-hole portion and into which converged light is introduced on the side of the lens from an end portion of the optical fiber, wherein the optical isolator and at least a part of the optical fiber are arranged inside a region of the through-hole portion encompassed by the housing walls, and the end portion of the optical fiber is arranged at a position within three times the thickness of the housing wall from an outer or inner side surface of the housing wall in a direction connecting the ligh
Fukuda Kazuyuki
Kuwano Hideyuki
Matsushima Naoki
Niwa Yoshiaki
Antonelli Terry Stout & Kraus LLP
Nguyen Chau N.
OpNext Japan, Inc.
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