The TDS technology can be summarized as a fusion of power-over-fiber and radio-frequency (RF) over fiber technologies. SPEAG has advanced these two technologies for integration into miniaturized fully isolated active optical probes for near electromagnetic field measurements.
The detailed functional principle of the TDS technology is summarized in the block diagram. Every TDS probe contains a sensor head and a sensor ID. The sensor head is located at the very tip of the probe and contains the actual electric- or magnetic-field sensor while the sensor ID is located in the rear of the probe body. The function of the sensor ID is to uniquely identify each probe to the remote unit and to provide a redundant optical link, which is continuously monitored for LASER safety.
The remote unit acts as the optical power supply in the power-over-fiber forward link. At the sensor head the photonic energy is converted into electrical energy from which the active elements in the sensor head are supplied. The sensor head uses electrically small transducers to pick up the electric (E-) or magnetic (H-)fields. The RF signal from the transducer is amplified by a low noise amplifier (LNA) and modulates the optical output of a high speed VCSEL (vertical cavity surface emitting LASER). The optical signal from the VCSEL is then transmitted to the remote unit over an optical fiber. At the remote unit, the optical signal is demodulated by means of a high speed photodiode (PD), amplified by a transimpedance amplifier (TIA), and made available over a standard 50Ω output to connect a standard measurement receiver such as an oscilloscope or spectrum analyser.
Basically, the TDS system can be regarded as a miniature, broad-band, optically isolated antenna. The antenna factor, the frequency dependent transfer function that converts the output from the remote unit in dBm to an H-field (in dBA/m) or an E-field (in dBV/m) is made available with the calibration certificate of each TDS probe.