Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
1999-07-09
2001-12-25
Ullah, Akm E. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S147000
Reexamination Certificate
active
06332721
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a laser diode (hereinafter referred to as “LD”) module and, more particularly, to an LD module capable of improving optical coupling efficiency between an LD chip and an optical fiber without reducing life span reliablity on a CAN-packaged LD chip.
2. Description of Related Art
LD module is a module for optical telecommunication in which an LD light source incorporating an LD chip is optically coupled to an optical fiber. As the LD light source, an LD light source having a structure, as a CAN package, that an LD chip is mounted with an LD preservation gas having a main component of an inert gas has been known to improve the life span reliability.
With such an LD module, LD light emitted from the LD chip is polarized in a prescribed direction, and is radiated in an elliptical shape to one end of the optical fiber. The optical coupling efficiency between the LD light source and the optical fiber is therefore generally low, and to compensate this, the LD chip has to be used with a large output. When the LD chip is used with a large output, however, the life span of the LD chip is shortened as a current status, thereby raising a problem of low life span reliablity in the LD module.
As a means for improving the optical coupling efficiency of the LD module without using the LD chip with a large output, forming a convex fiber lens on one end of the optical fiber for effectively condensing the LD light by correcting an aspect ratio of the LD light has been proposed (see, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 8-86,923 or Japanese Unexamined Patent Publication (KOKAI) Heisei No. 8-5,865). With an LD module of this kind, the LD chip can be used with a lower output, so that the chip can keep the life span reliability.
A following problem, however, may occur where an optical fiber having a convex fiber lens is coupled to an LD light source having a CAN package structure. That is, because the convex fiber lens has a very short focal distance, the lens must be ordinarily placed in proximity of 1 to 20 microns from the LD chip. Accordingly, the one end of the optical fiber, together with the convex fiber lens, must be inserted in the above CAN package. However, it is very difficult with the current technical level to maintain an adequately gas-sealed state where the one end of the optical fiber is inserted in the above structure.
This invention is devised in consideration of the above problems. It is an object of the invention to provide an LD module capable of improving optical coupling efficiency between an LD chip and an optical fiber without reducing life span reliability on a CAN-packaged LD chip. Other objects of the invention can be understood from the description of this specification as below.
SUMMARY OF THE INVENTION
As a consequence that the inventors of this invention made extensive researches to accomplish the above objects, the inventors reached an LD module including: an LD light source having a CAN package structure in which an LD chip is incorporated with an LD preservation gas; an optical fiber on one end of which a convex fiber lens for condensing light is formed; and a lens system for coupling placed between the LD light source and the convex fiber lens, wherein the lens system is constituted to be capable of forming an image by condensing the LD light from the LD chip, and wherein the convex fiber lens is located so that a focal point coincides with the image forming point of the LD light.
In a preferred embodiment of the invented LD module, the optical fiber may be a polarized plane maintaining fiber; a polarization maintaining axis of the polarization maintaining fiber may be placed to coincide with the polarization direction; the LD light source, the optical fiber, and the lens system may be so located that a polarization extinction ratio of the LD light transmitting through the polarization maintaining fiber is equal to or greater than 10 dB; the polarization extinction ratio may be equal to or greater than 20 dB; the convex fiber lens may be formed to have an opening angle in a vertical axis direction perpendicular to the optical axis direction of the optical fiber and an opening angle in a horizontal axis direction perpendicular to the optical axis direction of the optical fiber wherein the opening angle in the horizontal axis direction is different from the opening angle in the vertical axis direction; an angle between the vertical axis direction and a through axis as a polarization maintaining axis perpendicular to the optical axis direction of the optical fiber may be set 20 degrees or less; the angle between the vertical axis direction and the through axis may be zero degree; the convex fiber lens may be in a shape having an apex; the convex fiber lens may be made of two inclined planes which come closer to each other as approaching to a tip of the optical fiber; a ridgeline between the two inclined planes may not overlap on the vertical axis; the convex fiber lens may be made of a tip end surface and two inclined continuation planes which intersect with the tip end surface and come closer to each other as approaching to a tip of the optical fiber; the tip end surface may be a curving surface; the tip end surface may be a flat surface; the tip end surface may not intersect the optical axis direction of the optical fiber with right angle; at least one of the two inclined continuation planes may include a curving surface; the two inclined continuation planes may include only flat surfaces; each of the two inclined continuation planes may include an inclined flat surface; a difference between an angle formed between one of the inclined flat surface of the convex fiber lens and the optical axis of the optical fiber and an angle formed between the other of the inclined flat surface of the convex fiber lens and the optical axis of the optical fiber may be equal to or less than 10 degrees; a distance between a line formed by intersecting the two inclined flat planes of the convex fiber lens with each other and the optical axis of the optical fiber may be equal to or less than 1 micron; an angle between the tip end surface of the convex fiber lens and a plane perpendicular to the optical axis of the optical fiber may be of 6 to 15 degrees; an intersecting line between one inclined continuation plane of the convex fiber lens and the tip end surface and another intersecting line between the other inclined continuation plane of the convex fiber lens and the tip end surface may be parallel to each other; an intersecting line between one inclined continuation plane of the convex fiber lens and the tip end surface may be located on a tip side more than another intersecting line between the other inclined continuation plane of the convex fiber lens and the tip end surface; a ridgeline exists which is formed by the two inclined continuation planes of the convex fiber lens; any ridgeline may not exist which is formed by the two inclined continuation planes of the convex fiber lens; a width of the tip end surface of the convex fiber lens may be narrower than a diameter of a mode field of the optical fiber; the convex fiber lens may have an anti-reflecting coating on a surface of the lens; the optical fiber may be a single mode optical fiber; a part of the lens system may be incorporated in the light transmission window of the LD light source; an image forming magnification of the LD light of the lens system may be of 0.5 to 10; the optical fiber may serve as an external resonator for stabilizing a center wavelength of the LD light by Bragg reflection of the LD light emitted form the LD chip; effective reflection factor K
2
Rg may be greater than reflection factor R of a front end surface of the LD light source where reflection factor of the external resonator is Rg and coupling efficiency of the LD light source and the optical fiber is K; the center wavelength of the LD light may be of 500 to 1400 nm; the center wavelength of the LD light may be of 700 to 1000 nm.
In another aspec
Armstrong Westerman Hattori McLeland & Naughton LLP
Mitsubishi Chemical Corp.
Ullah Akm E.
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