Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2003-01-29
2004-12-14
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S033000, C385S037000, C385S090000
Reexamination Certificate
active
06832021
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a configuration for coupling radiation into an optical fiber. The configuration contains a semiconductor laser having a radiation exit window, and an optical fiber having a radiation entry end. The radiation exit window of the semiconductor laser faces the radiation entry end of the optical fiber. A resonator is provided and has an end mirror and an output mirror, between which the semiconductor laser is disposed. An optical device is disposed between the semiconductor laser and the optical fiber and serves for imaging only the fundamental mode of the radiation of the semiconductor laser onto the radiation entry end of the optical fiber.
In the present context, the term “end mirror” relates to a resonator mirror which is of a highly reflective configuration and reflects radiation that is generated in the semiconductor laser and impinges on it back into the semiconductor laser as far as possible completely or with the exception of a slight residue, which can be utilized for laser monitoring, for example. In the present context, the term “output mirror” relates to a resonator mirror which is of a partly reflective configuration such that a part of the radiation that impinges on it, which part is provided for engendering and maintaining laser activity, is reflected back into the semiconductor laser and a residue of the radiation is output from the semiconductor laser configuration.
In particular in applications which require a particularly high radiation power, such as, for example, in communications technology, as a pump laser or for materials processing (welding, soldering and the like), it is necessary to couple the radiation emitted by a semiconductor laser into an associated optical fiber as far as possible without radiation losses and with a high intensity. Therefore, the use of the fundamental mode is usually required in such applications on account of its intensity distribution and its better focusability.
The prior art has already disclosed various configurations and devices for efficiently coupling radiation into optical fibers.
Thus, by way of example, German Patent DE 37 05 408 C1 discloses a device for optically coupling a laser to an optical waveguide, between which an optical collimator is disposed and which are all disposed in corresponding receptacles in a housing. In this case, the receptacles of the laser and of the collimator are constructed in such a way that the laser can be displaced laterally with respect to the main beam propagation direction and the collimator can be displaced along the main beam propagation direction, so that a low-loss coupling of the radiation emitted by the laser into the optical waveguide can be set despite manufacturing and mounting tolerances.
A further configuration for efficiently coupling radiation into an optical waveguide is disclosed in European Patent EP 0 366 320 B1, corresponding to U.S. Pat. No. 4,877,300. In this case, a so-called mode field modifier is provided between a light source and an optical waveguide or between two optical waveguides. The mode field modifier essentially contains an expanded fiber piece with specially chosen refractive indices of core and cladding of the optical waveguide in the expanded fiber piece in order to achieve a beam expansion that is as large as possible. In this way, the coupling-in becomes less sensitive to a lateral misalignment of the components.
Furthermore, German Patent DE 195 35 526 C1 (corresponding to U.S. Pat. No. 5,864,645) and U.S. Pat. No. 5,508,842 disclose two different constructions of optical fiber amplifiers which in each case have an efficiency that is as high as possible. In the case of DE 195 35 526 C1 this is achieved by as far as possible complete absorption of the pump light in the laser core of the double-core fiber by the pump core which surrounds the laser core being partly ground away or chamfered away, so that as far as possible the entire pump light is directed onto the laser core. In the case of the optical fiber amplifier of U.S. Pat. No. 5,508,842, by contrast, the fiber core is tapered in the direction of propagation of the pump light, so that, despite the attenuation of the pump light with the propagation thereof, a maximum proportion of the pump light always contributes to the amplification of the signal light.
While the above-described configurations are concerned with the object of efficient, i.e. low-loss coupling of radiation into an optical fiber, Published, Non-Prosecuted German Patent Application DE 100 09 379 A1, for example, describes an optical fiber amplifier that amplifies essentially only the fundamental mode of the signal radiation. For this purpose, the fiber amplifier has a central active laser core and a pump core surrounding the latter within a fiber cladding, thereby forming a so-called double-core fiber. An element for transverse mode selection is additionally provided in order to amplify essentially only the fundamental mode and to suppress higher modes than the fundamental mode. This element is configured for example as adiabatic tapering of the fiber or as a so-called mode scrambler.
Furthermore, Published, Non-Prosecuted German Patent Application DE 196 28 068 A1 discloses a laser with a so-called fundamental mode determinator in order to emit only light in the transverse fundamental mode and to mask out other modes. The fundamental mode determinator, which essentially contains two screens, is disposed together with the active laser material between the two resonator mirrors.
The above-described conventional configurations for efficiently coupling radiation into an optical fiber all exhibit a relatively complicated construction of either the laser configuration, the optical fiber or the coupling-in system. Therefore, there is a need for a configuration that is as simple and compact as possible and nevertheless enables highly efficient coupling-in of radiation.
For this purpose, a configuration has already been developed, as is described in Published, Non-Prosecuted German Patent Application DE 42 38 434 A1.
Published, Non-Prosecuted German Patent Application DE 42 38 434 A1 discloses a configuration for focusing and coupling the radiation generated by a semiconductor laser into a multimode optical fiber. A radiation-focusing element in the form of a cylindrical lens is disposed between the radiation exit side of the semiconductor laser and the radiation entry side of the optical fiber. In this case, the longitudinal axis of the cylindrical lens is oriented essentially parallel to the multimode direction of the radiation emitted by the semiconductor laser in order that only the fundamental mode of the radiation of the semiconductor laser is imaged onto the radiation entry side of the optical fiber. In order to achieve a simplified assembly, the cylindrical lens is adhesively bonded directly onto the radiation entry side of the optical fiber or is melted together with it or is melted onto the latter.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a configuration for coupling radiation into an optical fiber that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which the coupling-in of radiation is as efficient as possible and is ensured despite a more compact construction.
With the foregoing and other objects in view there is provided, in accordance with the invention, a configuration for coupling radiation. The configuration contains a semiconductor laser having a radiation exit window formed therein, and an optical fiber having a radiation entry end. The radiation exit window of the semiconductor laser faces the radiation entry end of the optical fiber. A resonator is provided and has an end mirror and an output mirror. The semiconductor laser is disposed between the end mirror and the output mirror, and the output mirror is formed in or at the optical fiber. An optical device is disposed between the semiconductor laser and the optical fiber and serves for imaging o
Greenberg Laurence A.
Locher Ralph E.
OSRAM Opto-Semiconductors GmbH
Palmer Phan T. H.
Stemer Werner H.
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