Optical waveguides – With optical coupler – Input/output coupler
Patent
1994-04-22
1996-09-03
Lee, John D.
Optical waveguides
With optical coupler
Input/output coupler
359720, G02B 302, G02B 632
Patent
active
055531784
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an asymmetrical lens adapted to optically couple optical waveguides having different optical characteristics with a low optical loss level.
2. Prior Art
As the single mode optical fiber gains popularity in the field of optical telecommunications and other optical technologies, there has been an ever increasing demand for optically coupling an optical fiber and other optical waveguides having a configuration different from that of the optical fiber such as semiconductor laser devices and/or thin film optical waveguides particularly in the field of advanced optical telecommunications network.
Any two optical waveguides can be mutually connected by means of a rotatably symmetric lens such as a spherical lens or a nonspherical lens as long as they show an optical intensity distribution of waveguide mode which is rotatably symmetric relative to the optical axis that operates as the axis of symmetry on a plane perpendicular to the optical axis.
Such optical connection can be realized with a low optical loss level because the optical elements involved in the optical connection have an identical waveguide mode.
On the contrary, optical connection of any following combinations of optical waveguides has not been technically feasible without producing a significant optical loss: defined symmetry, e.g., an optical waveguide showing a rotatably symmetric circular beam pattern (axis of symmetry: optical axis), and an optical waveguide operational with a waveguide mode having no such symmetry, e.g., an optical waveguide showing an elliptic beam pattern which is not rotatably symmetric, are not similar to each other in terms of mode configuration, and horizontal directions of radiation pattern.
Currently, a cylindrical lens, a prism or another rotatably symmetric lens is used in such a way that the lens is inclined by a given angle relative to the optical axis in order to accommodate itself to the above described combinations of optical waveguides. However, such an arrangement is inevitably accompanied by a significant optical loss.
Technological proposals using a rotatably asymmetric lens in an attempt to minimize the optical loss in coupling two optical waveguides that fall in one of the above defined combinations are found in published papers including Japanese Patent Laid-open Publications Nos. 62-191803 (hereinafter referred to as Paper No. 1) and 3-172801 (hereinafter referred to as Paper No. 2). However, none of these known techniques has succeeded in reducing the optical loss in optical connection.
The reason for this lies in the fact that none of those proposals does not provide a theory for designing a lens to be used for optically coupling two optical waveguides as defined in any of the above combinations (1) through (3).
Hence, no lenses, lens systems nor lens devices have so far been designed to minimize the optical loss in coupling two optical waveguides that fall in any of the above defined combinations (1) through (3) and meet the demand of constructing an advanced optical telecommunications network.
Now, some of the currently available theories for designing a lens and the status quo of the technology for producing a lens will be briefly discussed.
Optical waveguides used in advanced optical telecommunications networks are normally designed to operate in a transversal direction only with a fundamental waveguide mode for optical transmission as in the case of single mode optical fibers and buried type semiconductor laser devices.
In optical transmission using such optical waveguides, the waveguide mode is defined as a function of the first order Gaussian beam, which provides a significantly favorable approximation as described in Paper 3 as listed below. Kunio Tada and Takeshi Kamiya, 1988, Maruzen K. K.
In an analysis using the first order Gaussian beams, equation [1] below provides a necessary and sufficient condition for a lens system of magnifying power m in order to establish an ideal connection between two optical wavegu
REFERENCES:
patent: 4961622 (1990-10-01), Gorman et al.
patent: 5159491 (1992-10-01), Richards
Lee John D.
The Furukawa Electric Co. Ltd.
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