Optical radiation detection system

Comprising an electric parameter measuring circuit

The invention consists in a non-invasive technique for measuring the intensity of light radiation in an optical medium, without in any noise of the propagating optical field. The presence of light is detected locally in a quantitative way by two electrodes placed at a suitable distance from the optical medium, able to measure the electric impedance variation. The technique does not introduce any additional absorption, neither any disturbance of the optical signal phase. It has been successfully used in highly critical and sensitive devices such as interferometers and resonators. The technique is compatible with various materials such as silicon, indium phosphide and germanium. This non-invasive technique could be used in many scientific and industrial applications such as:
1) Management, control, automatic tuning, signal routing and dynamic reconfiguration of large scale integration photonic circuits;
2) Fault detection and real-time monitoring of the “health” status and working point of an optical circuit and device, both on-chip and bulk materials;
3) Automatic fiber-to-chip alignment requiring the alignment of only one optical fiber, thus overcoming the limitations of current complex active alignment techniques, which require the simultaneous alignment of two optical fibers;
4) Wafer-level testing: wafer “health check”, fabrication process testing, single device performance assessment without chip dicing and packaging.
In addition to the complete non-invasiveness of the system, other advantages are:
1) Miniaturization: the observation area can be reduced down to few tens of μm2;
2) Speed and sensitivity: detection of light power down to a fraction of microwatt in a few tens of microseconds has been achieved;
3) Multi-point observation: easily parallelizable in a large number of observation sites;
4) CMOS-compatibility: the electric impedance read-out circuit can be realized by standard CMOS micro-technology. 5) Direct integration in any photonic circuit: no additional steps of fabrication are required (no additional cost) and no change of the photonic layer is necessary (the photonic layer can be designed regardless of the electric detection system).

The technique has been certified for the control of industrial prototypes and the experimental demonstration of scientific concepts otherwise hardly usable.