The present invention relates to a fiber-optic transmitting component in which, by means of an internal polarization filter, a defined proportion of the light output emitted by a light-emitting device can be set precisely and coupled into an optical fiber.
A specific class of fiber-optic transmitting components has a light-emitting component, a tubular or cylindrically shaped housing surrounding the component, and an adjusting sleeve that is fixed to the housing on the light output side. An optical fiber can be inserted and fixed in a suitable manner into the adjusting sleeve at its end facing away from the housing. Such a fiber-optic transmitting component is also referred to as a receptacle laser. The light-emitting device generally includes a semiconductor laser and optical elements, such as prisms and at least one lens, by means of which the beam of radiation emitted by the semiconductor laser can be deflected and focused onto the input end of the optical fiber fixed in the adjusting sleeve. By contrast, other fiber-optic transmitting components, specifically so-called pigtail lasers, do not have an adjusting sleeve but a fiber flange which includes a central passage opening in which an optical fiber is permanently mounted.
In the case of these fiber-optic transmitting elements, it is often desirable to ensure, during the manufacture, that only a defined proportion of the light output emitted by the light-emitting component is coupled into the optical fiber. However, without an adjustable distance between the optical fiber and the respective light-emitting component, it is very difficult or virtually impossible to set a defined, preselected input coupling level into the optical fiber during the adjusting stage, because a large number of variables determines this input coupling. Hitherto, in the case of receptacle lasers this problem has been solved by the light-emitting components, that is to say generally the semiconductor lasers, being measured and selected with regard to their emission characteristics (focal point, squint angle) and emitted power. For the purpose of the adjustment, the characteristic laser diode is assigned a suitable adjusting sleeve with the appropriate length to the fiber stop. Given the tolerances which occur in this case and which add up in each case, the respective input coupling can be set only over a wide tolerance band. The components with the desired input coupling then have to be selected by means of a measurement with a correspondingly low yield if a specific input coupling window is required in the application. In addition, a high logistical outlay for keeping stocks of different adjusting sleeves is necessary.
In order to make it possible to set the input coupling during the adjustment, some manufacturers use an additional connecting element (additional sleeve) and set the input coupling by means of axial displacement of the fiber guide. This is consequently possible only with an additional adjustment process and with the abovementioned additional sleeve as an additional mounting element. This impairs the overall mechanical stability of the component and increases the total manufacturing costs of the component as a result of the additional adjustment step and the additional mounting element.
It is accordingly an object of the invention to provide a fiber-optic transmitting component and a method for its assembly, which overcomes the above-mentioned disadvantages of the heretofore known devices and methods of this general type in which, during manufacture, it is possible to set a defined input coupling of the light output emitted by a light-emitting device into an optical fiber in a purposeful, precise manner and without any increased expenditure on adjustment, manufacture and costs.
With the foregoing and other objects in view there is provided, in accordance with the invention, a fiber-optic transmitting component from the class of receptacle lasers, having a light-emitting device, which is surrounded by a housing, and an adjusting sleeve which, at its one end, is connected to the housing and extends in the direction of a main emission direction of the beam of radiation emerging from the housing from the light-emitting device, and, at its other end, an optical fiber can be inserted and fixed in such a way that the beam of radiation can be coupled into the optical fiber, the adjusting sleeve having, at its one end, a base plate with a central opening, and a polarization filter that covers the opening being fixed indirectly or directly to the base plate.
In accordance with another object of the invention, there is provided a fiber-optic transmitting element from the classes of pigtail lasers, in which, instead of the aforementioned adjusting sleeve, a fiber flange is connected at its one surface to the housing and, at its other surface, an optical fiber is fixed in a central opening in the fiber flange in such a way that a beam of radiation emerging from the housing from the light-emitting device can be coupled into the optical fiber.
Accordingly, the fiber flange is shaped like the aforementioned base plate of an adjusting sleeve, but an optical fiber is permanently mounted in the central opening.
When setting the proportion of the light output that is coupled into the optical fiber, use is therefore made of the fact that the light-emitting device contains a semiconductor laser which emits a beam of radiation with a defined direction of polarization. The angular position of the polarization filter therefore determines the transmitted proportion of the beam of radiation through the polarization filter, and therefore the proportion of the radiation coupled into the optical fiber.
In accordance with an added object of the invention, there is provided a method of assembling a fiber-optic transmitting component. This method is based on the fact that the laser housing and the adjusting sleeve or the fiber flange with the polarization filter fixed to it are available as separate components and are then fixed to each other.
The method of assembling a fiber-optic transmitting component on the basis of the receptacle laser has the following method steps: manufacturing the light-emitting component and installing it in the housing; manufacturing the adjusting sleeve and fixing the polarization filter to the base plate of the sleeve; starting up the light-emitting device and aligning the adjusting sleeve axially with the main emission direction of the light-emitting device with the fiber plugged into the adjusting sleeve; measuring the light output of the optical radiation that has passed through the polarization filter in the glass fiber that is plugged in, as a function of an axial angular position of the adjusting sleeve; and fixing the adjusting sleeve to the housing at an axial angular position as soon as the light output assumes a previously determined value at this axial angular position.
The method of assembling a fiber-optic transmitting component on the basis of the pigtail laser differs from the abovementioned method in the fact that, instead of the adjusting sleeve, a fiber flange is manufactured, an optical fiber is mounted in the central opening of the fiber flange and a polarization filter that covers the central opening is fixed to the surface facing the light-emitting device.
It is preferable for the housing and the adjusting sleeve or the fiber flange to be cylindrically symmetrical, and for the axes of the cylinders and the main emission direction to coincide. An embodiment which is practical for fixing the housing and the adjusting sleeve consists in the housing and the adjusting sleeve each having a mounting flange, that is to say a fixing face that extends in the radial direction over the entire periphery and at which they can be fixed to each other. During the alignment and adjustment operation, the two components can be placed against each other at their mounting flanges and rotated in relation to each other until the desired light output has been achieved.
The polarization filter used can be, for example, a cost-effective grating or film polarizer or a crystal polarizer. The rotation of the adjusting sleeve or the fiber flange and of the polarization filter fixed to it relative to the housing and the light-emitting device configured in the latter causes rotation of the polarization direction of the laser radiation emitted by the light-emitting device and of the passage direction of the polarization filter in relation to each other. The polarization filter is designed in such a way that its plane of polarization is essentially parallel to the plane of oscillation of the laser beam. This therefore corresponds to the same design as is used for optical isolators.
In accordance with an additional object of the invention, the polarization filter is adhesively bonded to the base plate of the adjusting sleeve or to the fiber flange. In order to rule out any possible feedback to the laser radiation source, the polarization filter is preferably fixed in such a way that its main surfaces are inclined slightly with respect to the direction of incidence of the laser beam. For this purpose, suitable elements, such as projections, can be formed on the base plate of the adjusting sleeve or on the surface provided for this purpose on the fiber flange, or else an inclined fixing in an opening may be made possible, by means of which an appropriately inclined oblique face is formed, to which the polarization filter can be fitted.
In accordance with a further object of the invention, the polarization filter can also be fixed on a fixing element, such as a piece of curved metal sheet, which in turn is fitted to the adjusting sleeve or the fiber flange.
The fiber-optic transmitting component according to the invention, and the method for its assembly, solves the problem of the settable input coupling of the laser radiation in an elegant way. Without any additional mounting elements, the input coupling can be set by simply rotating the adjusting sleeve or the fiber flange, after which the fixing is performed at the determined angular position. The configuration according to the invention is of outstanding significance in particular for the applications which do not need the full light output emitted by the laser, but rather a precisely defined lower amount. This reduced light output may therefore be set precisely during adjustment by means of the rotary adjustment which is present in most automatic adjusters. This makes it possible, for example, to set a correspondingly fixed emitted light output in the fiber in relation to a predefined monitor current. This particular option makes it possible for the system manufacturer to incorporate these components completely mechanically and such that they can be operated directly without any costly retrimming of corresponding resistances by hand on the printed circuit board being needed.
A further advantage of the configuration according to the invention as compared with the prior art resides in the fact that, for the single-lens coupling optics which are normally used as part of the light-emitting device, the maximum convergence of the emitted beam of radiation can be set in such a way that it is optimally matched to the fiber aperture, permits specific coupling into the fiber and, at the same time, as a result of the corresponding divergence of the beam behind the focus, ensures virtually the same eye safety when the fiber is not plugged in as in the case of an open single-mode fiber, and therefore does not render any additional protective measures necessary.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a fiber-optic transmitting component with precisely settable input coupling, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.