Optical waveguides – With optical coupler – Input/output coupler
Patent
1997-03-14
1998-12-01
Palmer, Phan T. H.
Optical waveguides
With optical coupler
Input/output coupler
385 43, 65387, G02B 632
Patent
active
058450246
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
This invention relates to the optical coupling between a luminescent source and an optical fiber used in optical communication.
TECHNOLOGY IN THE BACKGROUND
Laser Diodes (called LD hereafter), Luminescent Diodes, and others are used as a luminescent source for optical communication. However, in order for light to enter into an optical fiber, which is the optical transmission path, coupling is generally performed by aligning the end of an optical fiber with the luminescent surface.
However, due to a considerable divergence in the angle of emission light from the luminescent surface, the coupling efficiency with optical fibers is poor. Consequently, there is a method to improve light entrance into the optical fiber by inserting a lens to improve coupling efficiency and focusing of the light.
In order to obtain optical coupling between an LD and an optical fiber, diverse combinations such as shown in FIG. 5(a)-(d) have been considered in the past. The light emitted from the LD does not form a circular Gaussian distribution but forms an elliptic beam having a large distribution difference in the vertical and horizontal directions.
FIG. 6 is a diagram that depicts the diverging angle of the incident beam point! is elongated along the X-axis, and the far-end light distribution NFP results in an elliptic beam distribution divergent along the Y-axis. Therefore, high coupling efficiency is not obtainable.
The method of coupling shown in FIG. 5(a) was an early concept. It attempts to increase the coupling efficiency by positioning a cylindrical lens 21 between LD 1 and optical fiber 20.
The methods of coupling shown in FIG. 5(c) and (d), both ignore ellipticity and both use a nonspherical lens 22, which take light beam aberrations into account, or in order to ease coupling tolerances during assembly, places two lenses 23 and 24 at the confocal positions.
In this case, the lenses cost more than the optical fiber type, but the merit of realizing equally good coupling is assured. However, since the lenses and fibers are separated in all examples of FIG. 5(a), (c), and (d), alignment of the beam axis becomes that much more difficult; since an interface occurs in the optical path, light will be lost as a consequence. In addition, although an antireflection coat is used, it is not beneficial because there are three surfaces in this case. Furthermore, the fact that there are numerous components raises the overall cost of the system.
On the other hand, in the case of FIG. 5(b) example, a curved surface 25 was formed at the end of the fiber 20 and symmetric to the Z axis, which is the optical axis. Although this alleviated the previously described shortcomings, the beam emitted from LD 1, in spite of its elliptical nature, is coupled to a circular core, which enables axial alignment only in an extremely narrow range and theoretically sets a limitation as well.
In particular, in the case of a distorted Lattice Type Quantum Well Laser, which is anticipated as an LD for optical excitation for light amplification, it becomes necessary to obtain a spacious active layer section in order to increase the inrush current. As a result, the light-emitting window formed on the side ends up in a horizontally extended (about 0.about.200 .mu.m) shape without a change in the thickness (about 0.about.2 .mu.m). This is a greater compression compared with the conventional LD, and in order to couple the beams more efficiently, an oblate lens matching the far-end distribution became necessary.
In view of the above-mentioned problems, the purpose of this invention is to offer an optical fiber with lens which, as opposed to the method of assembling special individual lenses, has a simple configuration, is capable of efficiently taking in flat beams, and has an improved optical coupling efficiency between an LD and a fiber.
DISCLOSURE OF THE INVENTION
This invention was made in order to solve the problems in conjunction with the above. The optical fiber with lens based on this invention is equipped with a diagonal section
REFERENCES:
patent: 3910677 (1975-10-01), Becker et al.
patent: 4370021 (1983-01-01), Khoe et al.
patent: 4490020 (1984-12-01), Sakaguchi et al.
Electronic Letters, vol. 17, No. 12, Jun. 11, 1981, H. Sakaguchi et al., "Power Coupling from Laser Diodes into Single-Mode Fibres with Quadrangular Pyramid-Shaped Hemiellipsoidal Ends", pp. 425-426.
Shibutani Michitomo
Tsushima Takuji
Ferguson Jr. Gerald J.
Namiki Precision Jewel Co. Ltd.
Palmer Phan T. H.
Robinson Eric J.
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