Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2000-02-08
2001-05-29
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C250S208100, C250S208200, C372S029011
Reexamination Certificate
active
06239916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention lies in the field of light-emitting transmitting devices, in particular for purposes of optical data transmission, which are equipped with a so-called monitor unit for the purpose of power control. Specifically, it is desirable for many applications for the output power of a transmitter, which are usually lasers, to be kept as constant as possible—independently, for example, of temperature fluctuations and aging effects. In conventional edge-emitting or side-emitting lasers it is comparatively unproblematic to have a lateral arrangement of a monitor unit, because the monitor unit can be arranged to face the laser side or edge not provided for outputting useful radiation. The (lost) radiation emerging on this side is thus used for control purposes.
Recent developments and progress in production engineering have increasingly rendered possible the economic production of so-called vertically emitting transmitters (VCSEL=vertical cavity surface emitting laser). These transmitters, however, likewise require a control unit with a monitoring device if there is a high demand placed on the quality of a constant laser output power.
With regard to this problem, the introductory text of the international publication WO 95/18479 describes a basic design in which a fraction of the radiation emitted by a transmitter (VCSEL) with a vertically emitting emission zone is directed via a beam splitter onto a monitor unit in the form of a photodetector (photodiode). The output signal of the photodetector is applied to a control circuit which, in accordance with the photodetector output signal, influences the drive current of the laser in such a way that a desired transmitting output power is achieved. That design is relatively complex.
Against that background, WO 95/18479 describes an optical transmitting device in which a vertically emitting laser (VCSEL) has an integrated photodetector which evaluates radiation emerging at the underside of the laser. That design is also comparatively complicated and assumes an integral design of transmitter and monitor unit. It is therefore not possible for vertically emitting optical transmitters to be fitted subsequently or optionally with a monitor unit.
A further transmitting device is known from U.S. Pat. No. 5,809,050 (European patent application EP 0 786 838 A2). In that prior art transmitting device (FIG. 4E), provision is made for the purpose of implementing an integrated controlled laser light source of a vertically emitting laser (VCSEL) as an optical transmitter which has only a single emission zone emitting light vertically. Also provided is a monitor unit with an optically sensitive reception zone for controlling the power of the optical transmitter. A beam splitter which on the transmitter side splits up the emitted radiation into a fraction and a remaining part, is arranged between a coupling zone, which can be formed, for example, by an optical conductor connector receptacle, on the one hand, and the emission zone and reception zone on the other hand. The remaining part is output as useful radiation toward the coupling zone, while the fraction passes to the reception zone.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to create efficient coupling between an optical transmitter with a vertically emitting emission zone and the optically sensitive reception zone of a monitor unit, formation of the reflected radiation being rendered possible with only a small number of individual components, and in a compact design.
With the above and other objects in view there is provided, in accordance with the invention, an optical transmitting device, comprising:
an optical transmitter with a vertically emitting emission zone;
a monitor unit with an optically sensitive reception zone;
a lens body disposed between the emission zone and a coupling zone of a coupling partner, the lens body having a coupling zone side proximal to the coupling partner;
the emission zone emitting radiation into the lens body including a first radiation component traversing the lens body and striking the coupling zone, and a second radiation component reflecting at the coupling zone side and striking the reception zone of the monitor unit.
The above-noted objects of the invention are thus satisfied by the optical transmitting device having then optical transmitter with a vertically emitting emission zone, having a monitor unit with an optically sensitive reception zone and having a lens body. The lens body is arranged, on the one hand, between the emission zone and the reception zone and, on the other hand, a coupling zone of a coupling partner. There passes, via the lens body, a radiation component that strikes the coupling zone and a radiation component of the radiation reflected on the coupling zone side and striking the reception zone.
A first essential advantage of the transmitting device according to the invention consists in that the lens body has the double function both of coupling light into the coupling zone or coupling surface of the coupling partner, and of forming the radiation passing to the monitor unit—that is to say onto the optically sensitive surface thereof. Since these two functions are fulfilled by a single component, the transmitting device according to the invention can advantageously be designed with few components and in an extremely compact fashion. The reflection of the radiation component which is to be retroreflected onto the monitor unit can also be effected in principle by a reflecting element provided between the lens body and coupling zone.
However, in relation to this aspect a particularly preferred embodiment of the invention provides that a boundary surface on the coupling zone side reflects the component of the radiation toward the reception zone. Here, with its boundary surface on the coupling zone side, the lens body takes over a further function—specifically, that of a reflector—and thereby contributes to an even greater reduction in the required number of components, and to a yet more compact design of the transmitting device.
For many practical implementations, the reflection based on the difference between the refractive indices of the lens body and an external medium (for example air) on the coupling side can suffice to reflect an adequate radiation component to the monitor unit. According to a further preferred refinement of the transmitting device according to the invention, the boundary surface is partially silvered in order to ensure particularly favorable and defined reflection conditions. For this purpose, the boundary surface can be provided with a partially transparent reflective coating, and/or part of the boundary surface can be provided with a mirror.
In accordance with an advantageous feature of the invention, which is advantageous as regards the radial space requirement provides that the emission zone is situated inside the reception zone when seen projected against the emission direction.
In accordance with an alternative feature of the invention, which is preferred in terms of design and production engineering, provides that the emission zone and the reception zone are situated next to one another when seen projected against the emission direction.
In accordance with another feature of the invention, it is possible to implement a particularly compact design and a defined expansion of the radiation component applied to the reception zone by virtue of the fact that the radiation component reflected toward the reception zone has an intermediate focus. With regard to the physical size, the lens body geometry can preferably be designed in such a way that the intermediate focus is located in the lens body material.
In accordance with a concomitant feature of the invention, the boundary surface on the coupling zone side has the shape of a conical envelope. Consequently, it is advantageously possible to achieve symmetrical launching in relation to the Z axis (emission direction), and to irradiate an annular reception zone whose surface i
Epps Georgia
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Spector David N.
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