Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-04-01
2004-08-31
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S034000, C385S089000, C385S093000
Reexamination Certificate
active
06785440
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an assembly for focusing and coupling the radiation produced by a semiconductor laser diode) into an optical fiber, in particular a multimode optical fiber, with a radiation-focusing element in the form of a cylinder lens being disposed in the area between a radiating surface of the laser and a light entrance side of the optical fiber, the cylinder lens being oriented substantially parallel to the multimode direction of the radiating surface of the semiconductor laser. The invention also relates to a laser module having a plurality of assemblies of the type defined above.
Finally the invention relates to an assembly for focusing and coupling the emissions produced by a semiconductor laser array (laser diode array) or a two-dimensional semiconductor laser structure (laser diode stack) into a corresponding number of individual optical fibers, in particular multimode optical fibers, with an optical system for focusing radiation being provided in the area between the radiating surface of the laser diode array or stack and the individual light entrance sides of the optical fibers.
DESCRIPTION OF BACKGROUND ART
The source “Applied Optics”, Vol. 16, no. 7, Jul. 1977, pp. 1966-1970, discloses an assembly having the features described in paragraph 1 of the “Technical field of the invention” above. This source (see in
FIG. 5
on p. 1968) describes a specially designed carrier element for coupling a semiconductor laser, e.g. a GaAs diode, and an optical fiber having a circular cross section, said element simultaneously carrying the cylinder lens for coupling the laser radiation produced by the GaAs diode into the subsequent optical fiber. This substantially cylindrical carrier element is provided on the top with a given number of V-groove recesses which are preshaped by mechanical, i.e. metal-removing, processing of the carrier element material, e.g. copper, in accordance with the intended coupling between laser, cylinder lens and optical fiber and in order to guarantee the necessary optical adjustment of these elements to one other. Due to this design of the carrier element the optical elements subsequent to the GaAs diode, i.e. the cylinder lens and the optical fiber, can be inserted into these above-mentioned recesses, the mutual adjustment of these elements being dependent on the precision with which the corresponding recesses have been machined in the carrier element. Very low tolerances are of course permissible here to allow for the necessary ultimate adjustment.
The mechanical requirements for the tolerances of such a carrier element, and in particular the required positioning accuracy for the GaAs diode relative to the subsequent optical elements, are thus extremely high since particularly this laser diode must be applied and fastened to the surface of the carrier element, for example by gluing or soldering. This means that the production and processing of such a carrier element is very elaborate to permit the necessarily very low tolerances to be met.
This known assembly is intended to focus as much as possible of the radiation emitted by one semiconductor diode into the core of the optical fiber, e.g. a multimode fiber with a circular cross section. There is no intention here to provide a laser module with the greatest possible power and radiation quality.
Further, “Applied Optics”, Vol. 17, No. 3, 1978, p. 479 ff., discloses an assembly wherein each individual laser of a monolithic laser diode array is coupled by means of a common cylinder lens to a great number of individual optical fibers. A carrier element in the form of a silicon substrate is likewise used here, a given number of V-shaped recesses being preshaped in this silicon substrate in accordance with the intended arrangement of cylinder lens and optical fibers for coupling between a laser diode and an optical fiber as in the known coupling assembly explained above.
Extremely low process tolerances are also permissible in this case. In addition, the direct contact between cylinder lens and laser diode array can drastically change the properties of the individual laser diodes, i.e. the laser diodes can very easily be mechanically destroyed when the cylinder lens is inserted into the V-shaped groove provided in the silicon substrate. In this latter assembly the manufacturing expenditure is therefore likewise considerable.
SUMMARY OF THE INVENTION
In view of the prior art described above the present invention is therefore based on the problem of providing an improved assembly for focusing and coupling the radiation produced by a semiconductor laser into an optical fiber, in particular a multimode optical fiber, primarily with the goal of realizing a highly efficient coupling between a multimode high-power laser diode and a multimode optical fiber. The invention is also based on the problem of providing a laser module, in particular a pumping module, with much greater power and maximum radiation quality as compared with known laser diode modules.
Finally there is also the requirement that assemblies utilizing the above-described type of coupling should be able to be produced in a much simpler and less expensive way compared with the prior art explained above, while ensuring all requirements for the precision of adjustment. The first mentioned problem is solved according to the invention by adapting a cylinder lens of the above-mentioned type to have a substantially equal to the width of a beam exit window defining the radiating surface of the semiconductor laser and whose diameter is substantially on the order of magnitude of the core diameter of the optical fiber, and preferably smaller than this core diameter, and by directly gluing the lens to, fusing the lens with or melting the lens onto the light entrance side of the optical fiber extending substantially at right angles to the orientation of the cylinder lens.
Further, the present invention makes it possible to obtain a laser module with high power and high radiation quality while having a small numerical aperture. A given number of individual assemblies designed according to the present invention are united into a module, the corresponding individual optical fibers being bunched such that the free ends, i.e. the light exit sides, of all optical fibers are disposed in a configuration that can be selected or predetermined at will.
A laser module of the type characterized above can be used in preferred fashion as a pumping laser for systems with pumped solid state lasers, the total laser radiation obtained on the light exit sides of the bunched optical fibers serving as the pumping energy for the subsequent pumped laser.
Such optical pumping (longitudinal and transversal) can be performed for example with or without frequency multiplication, for example for pumping a neodymium-YAG laser. It is also possible to use a laser module of the type characterized above as a laser particularly for medical applications or for materials processing. In such cases, the total laser radiation obtained on the light exit sides of the bunched optical fibers is utilized as the energy for the particular medical treatment process or the particular materials processing operation.
Furthermore the light exit sides of the bunched optical fibers can preferably be combined in a matrix-shaped assembly or a linear assembly. According to yet another feature of the invention any desired symbols can be applied in matrix form to an object as “laser marking” by a preferably selective and individual drive of the individual diode lasers and imaging on the object. In a corresponding way, machining places can be preselected in matrix form strictly by the electric drive of the individual diode lasers, which provides special advantages in particular for micromachining, e.g. when soldering, welding or drilling.
A further possibility of designing a laser module within the scope of the present invention is to couple and combine the radiating surfaces of laser diode arrays or of two-dimensional structures, so-called laser diode stacks, into co
Coherent Inc.
Sanghavi Hemang
Stallman & Pollock LLP
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