The detection electronics consisted of two identical channels, schematically presented in
Figure 3. Each channel comprises a photodiode (BPW34, Osram Opto Semiconductors, Regensburg, Germany) followed by transimpedance amplifier (current-to-voltage converter), a low-pass filter, consisting of resistor
RLP and capacitor
CLP, and a buffer. The transimpedance amplifier, built using an operational amplifier (AD8627, Analog Devices, Norwood, MA, USA), converts the current
I from the photodiode into voltage
U according to:
where
RF—transimpedance (
RF = 100 kΩ). Capacitor
CF improves stability of the transimpedance amplifier. The low-pass filter, with cut-off frequency of 10 kHz, filters out the broadband noise. The filter is followed by a buffer (AD8641, Analog Devices) driving a sixteen-bit data acquisition card (
NI-9215, National Instruments, Austin, TX, USA) or an oscilloscope (
TDS3032, Tektronix, Beaverton, OR, USA).
The detection electronics was built on a printed circuit board. It was powered by a ±12 V stabilized laboratory power supply.
, & Wierzba P. (2016). Interferometric Sensor of Wavelength Detuning Using a Liquid Crystalline Polymer Waveplate. Sensors (Basel, Switzerland), 16(5), 633.