Very high‐sensitivity tunable phase detection of light power variations using electrical modulation of Si‐photodiode in photovoltaic regime

Abstract

The use of a silicon (Si)-photodiode (Si-PD) operating in photovoltaic mode as a tunable very high-sensitivity phase detector of light power variations is demonstrated. This result is reached by applying to the Si-PD an electrical modulation through an AC excitation signal without a DC reverse bias. This allows employing the synchronous demodulation technique for phase detection that shows much better performances with respect to the conventional amplitude measurements, mainly overcoming the issues related to the electrical noise and the resolution limitation due to the selected full scale. The phase variations to be detected occur between the modulating signal and the one provided by the Si-PD as a function of the light power variations on its sensitive area. The proposed approach notably simplifies both the electronic circuitry and the optical setup, minimising the detection system complexity and size. Experimental results demonstrate that it is possible to achieve phase detection sensitivity, with respect to light power variations, of up to 410°/μW as a function of the Si-PD settable operating conditions. Using a standard commercial lock-in amplifier with a 0.01°phase resolution is possible to obtain a light power resolution of up to 25 pW.

High-Sensitivity High-Resolution Optical Phase Shift Detection Technique Using a Si Photodiode Operating in Photovoltaic Mode

“…Considering the best results presented in [21] that have been achieved for the minimum modulating frequency f 0 =7.7Hz and the maximum load resistor R L2 =10MΩ, in this paper we will explore and report the optimisation and maximisation of the system detection sensitivity and resolution in terms of the minimum detectable light power variation. In this sense, we have performed a complete electrical characterisation of the proposed phase shift detection technique, employing the Si PD operating in photovoltaic mode, by varying the frequency f 0 of the sinusoidal modulating bias voltage V BIAS (f 0 ) and fixing the load resistance R L2 at the best standard value of 10MΩ.…”

“…Recently, it has been demonstrated that variations of the light power due to any kind of interaction with matter can be evaluated by measuring the phase shift between the electrical signal generated by the Si PD (i.e., the input signal) and a suitable reference signal at a specific modulating frequency with the Si PD operating in both photoconductive and photovoltaic regimes [19][20][21]. This novel detection method has the advantage to be independent from the amplitude of both the input and reference signals and does not suffer of any fullscale limitations.…”

One-Decade Frequency Range, In-Phase Auto-Aligned 1.8 V 2 mW Fully Analog CMOS Integrated Lock-In Amplifier for Small/Noisy Signal Detection

“…Obviously, by changing R NOISE value, the input (and the output) noise can be changed. However, the chosen component values allow to demonstrate the capability of the designed LIA to recover very small-amplitude and noisy signals as well as its suitability for low-frequency modulated sensor applications [6], [34], [35]. All the measurements have been performed by employing the laboratory electronic instrumentations reported above (i.e., the digital oscilloscope and the DMM).…”

“…In order to overcome the above mentioned limitations, we have developed and fabricated a new fully-analog integrated LIA, in a standard CMOS technology (AMS 0.35μm), suitable for accurate measurements of very small signals, for example coming from thermally-modulated gas chemical resistive sensors [34] improving their sensitivity and selectivity and, more in general, generated from specific applications where a low-frequency modulation (in mHz-Hz range) of signals is operated as in optical sensing solutions [6], [35]. The system operates, automatically and continuously, through appropriate internal feedbacks, on both the relative phase alignment and the operating frequency tuning of input noisy and reference signals, allowing the correct detection of the AC input signal amplitude.…”

Experimental characterization towards an in-fibre integrated silicon slab based all-optical modulator

“…Today, most optical modulations are achieved through the use of electrical circuits controlling the voltage applied on the modulator [1,2]. Nevertheless, due to the industrially increasing interest in optics communication the field of all-optical modulation is becoming more and more popular [3][4][5][6][7].…”