Coherent light generators – Particular component circuitry – Optical pumping
Reexamination Certificate
1998-12-07
2001-06-26
Font, Frank G. (Department: 2877)
Coherent light generators
Particular component circuitry
Optical pumping
C372S029011, C372S030000, C372S031000
Reexamination Certificate
active
06252893
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to an optical transmitting device having a number of semiconductor lasers situated next to one another.
An optical transmitting device of this type is described in Published, Non-Prosecuted British Patent Application GB 2 276 493 A. In the case of the known transmitting device, each semiconductor laser is constructed as an edge-emitting laser having a lens and a monitor diode associated with it. The monitor diode is used to produce an electrical variable that is proportional to the optical power output by the respectively associated laser. By an electronic circuit configuration which is not described in more detail in the publication, the electrical signal can be used to ensure that the respective semiconductor laser always outputs a constant light power in the event of temperature changes and as it ages. The configuration of the known optical transmitting device is comparatively complex inasmuch as each individual semiconductor laser has a monitor diode associated with it.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an optical transmitting device which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is of relatively simple construction and which can be produced inexpensively.
With the foregoing and other objects in view there is provided, in accordance with the invention, an optical transmitting device, including: a plurality of semiconductor lasers disposed next to one another; a monitor diode; at least one monitor laser outputting an optical power received by the monitor diode, the monitor diode converting the optical power into an electrical signal; and an electronic circuit connected to the monitor diode and receiving the electrical signal: the electronic circuit controlling the at least one monitor laser and driving the plurality of semiconductor lasers in parallel; the electronic circuit controlling the at least one monitor laser such that the electrical signal constantly has a preset value corresponding to a specified maximum permissible optical power of the at least one monitor laser; the electronic circuit forming a correction variable from the preset value of the electrical signal and a nominal signal corresponding to a nominal value of the optical power of the at least one monitor laser; the electronic circuit having current measuring inputs for detecting currents through the plurality of semiconductor lasers and through the at least one monitor laser; and the electronic circuit outputting a control signal received by the plurality of semiconductor lasers for reducing a power output of a respective one of the plurality of semiconductor lasers if a magnitude of a current flowing through the respective one of the plurality of semiconductor lasers reaches that of a current through the at least one monitor laser weighted by the correction variable.
To achieve this object, in an optical transmitting device having a number of semiconductor lasers situated next to one another, the invention provides at least one monitor laser whose optical power is converted into an electrical signal by a monitor diode associated with the monitor laser. The monitor diode is connected to an electronic circuit that controls the monitor laser. The electronic circuit correspondingly drives the semiconductor lasers in parallel, such that the electrical signal constantly has a preset value corresponding to a specified maximum permissible optical power of the monitor laser. A correction variable is formed in the electronic circuit using the preset value of the electrical signal and a nominal signal corresponding to the nominal value of the optical power of the monitor laser. The electronic circuit uses current measuring inputs to detect the currents through the semiconductor lasers and through the monitor laser, and reduces the power of a semiconductor laser if the magnitude of the current flowing through the semiconductor laser reaches that of the current flowing through the monitor laser, weighted by the correction variable.
A substantial advantage of the transmitting device according to the invention is that not all of its semiconductor lasers are provided with a monitor diode, but a single monitor diode is associated merely with the monitor laser for the entire configuration of semiconductor lasers. As a result of this, the transmitting device according to the invention is comparatively easy to construct, which also results in reduced production costs. Furthermore, when constructing the transmitting device according to the invention, there is no need to consider the respective type of semiconductor lasers, because the configuration of the transmitting device according to the invention demands merely that attention be paid to the semiconductor lasers being able to readily output their light. In terms of circuitry, the transmitting device according to the invention creates no appreciable increase in complexity, as compared with the known device, because the wiring complexity created by connecting the current measuring inputs to the semiconductor lasers merely corresponds to the complexity required for connecting the monitor diodes used in the known transmitting device. Furthermore, the electronic circuit in the transmitting device according to the invention may easily be an ASIC, one or two additional circuit details of which are unimportant, as is known.
Any desired semiconductor laser may be used as the monitor laser in the transmitting device according to the invention. It is regarded as advantageous if the monitor laser is a semiconductor laser whose electro-optical behavior is virtually the same as that of the semiconductor lasers. This requirement can easily be met by virtue of the fact that the monitor laser and the semiconductor lasers are a constituent part of an array originating from one wafer. Consequently, it is a relatively simple matter to assess the current through the monitor laser.
It is regarded as particularly advantageous if the semiconductor lasers and the monitor laser are components (VCSEL—Vertical Cavity Surface Emitting Laser) which emit light on a single component side, because it would be a particularly complex matter to mount monitor diodes on every laser of this type.
When forming the correction variable in the electronic circuit, the bias current of the semiconductor laser diodes and also their differential gradient may also be taken into account besides the preset value, corresponding to a specified maximum permissible optical power of the monitor laser, and the nominal signal. With a sufficient approximation of the circumstances actually specified, a correction variable may be used which is obtained in the electronic circuit by forming the quotient of the preset value and the nominal value. The measured current through the respective semiconductor laser is weighted by forming the product of the correction variable and the measured current through the monitor laser.
In the transmitting device according to the invention, the current measuring inputs of the electronic circuit device are advantageously connected to resistors connected in series with the semiconductor lasers. Such resistors are generally always present, so that this type of current detection causes no additional complexity.
The transmitting device according to the invention may advantageously be a constituent part of an optical coupling point in which the transmitting device is opposite an optical reception element having a number of light-sensor elements situated next to one another and associated with the semiconductor lasers. A transmitting device of such a construction is disclosed per se in the above-mentioned British laid-open specification.
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 an optical transmitting device it is nevertheless not intended to be limited to the details shown, since various mod
Font Frank G.
Greenberg Laurence A.
Lerner Herbert L.
Rodriguez Armando
Siemens Aktiengesellschaft
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