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The performance of LiNb03 waveguide devices, e.g. switches and modulators, is impaired by drift in the output light characteristics when they are subject to temperature changes or DC voltages are applied to the electrodes 1,2,3,4,5. The latter phenomenon, known as DC drift, arises from free charge carriers present in the crystal, which move in the applied field and change the "effective" electric field experienced by the light. Since the "effective" field will change in time due to charge carrier motion, the light output of the device will be time dependent. The magnitude and time constants of the described behaviour depends on several parameters. Some of them are: the crystal quality and cut, the buffer layer material, the electrode configuration and in general the processing of the chip. As the DC drift will impair the crosstalk of a switch, it is desirable to minimize its magni-tude. Depending on the application, it can also be an advantage to adjust the time constants for the drift to suitable values. All this can be done through careful design and manufacturing of the switch. However, it is difficult to get rid of the DC and temperature drift problems completely that way, and if the application requires extremely low crosstalk values it might be necessary to stabilize the switch with some kind of feed-back control system. A LiNb03 chip that is subject to temperature changes will to some extent alter its characteristics. That is due to electric fields set up through the pyro-electric effect. The described phenomenon will affect the transfer function of a switch, and appear as a temperature drift in the crosstalk characteristic. The parameters that determine the drift magnitude, are related to those of the DC drift. Another important factor is the packaging of the chip, so careful design of the package is required in order to get a small temperature dependence for the packaged switch. The most interesting parameter, when characterizing a LiNb03 switch under various conditions, is the extinction ratio or crosstalk between the output ports. It is shown here how the crosstalk deteriorates due to drift problems (DC and temperature drift), and how to overcome those problems through stabilization by means of feed-back control signals.
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