Pseudo-resistor circuits are used to mimic large value resistors and base their success on the reduction of occupied areas with respect to physical devices of equal value. This article presents an optimized architecture of pseudo-resistor, made in standard CMOS 0.35 µm technology to bias a low-noise transimpedance amplifier for high-sensitivity applications in the frequency range 100 kHz-10 MHz. The architecture was selected after a critical review of the different topologies to implement high-value resistances with MOSFET transistors, considering their performance in terms of linearity of response, symmetric dynamic range, frequency behavior, and simplicity of realization. The resulting circuit consumes an area of 0.017 mm 2 and features a tunable resistance from 20 M to 20 G, dynamic offset reduction due to a more than linear I-V curve, and a high-frequency noise well below the one of a physical resistor of equal value. This latter aspect highlights the larger perspective of pseudo-resistors as building blocks in very low-noise applications in addition to the advantage in occupied areas they provide.

Real‐time control of multiple cascaded devices is a key requirement for the development of complex silicon photonic circuits performing new sophisticated optical functionalities. This article describes how the dithering technique can be leveraged in combination with non‐invasive light probes to independently control the working point of many photonic components. The standard technique is extended by introducing the concept of orthogonal dithering signals to simultaneously discriminate the effect of different actuators, while the idea of frequency re‐use is discussed to limit the complexity of control systems in cascaded architectures. After a careful analysis of the problem, the article presents an automated feedback strategy to tune and lock photonic devices in the maxima/minima of their transfer functions with given response speed and sensitivity. The trade‐offs of this approach are discussed in detail to provide guidelines for the design of the feedback loop. Experimental demonstrations on a mesh of Mach‐Zehnder interferometers and on cascaded ring resonators are discussed to validate the proposed control architecture in different scenarios and applications.

A multichannel impedance-sensing CMOS chip for the readout of noninvasive light detectors in silicon photonics (SiP) is presented. The performance of the lock-in phase-sensitive demodulator is improved thanks to a capacitive feedback transimpedance amplifier (TIA) equipped with an active discharge network, able to keep a dc output offset lower than 3 mV for leakage currents up to 4 nA while injecting a noise lower than 40 fA/ √ Hz. The addition of a sensor capacitance compensation system at the input of the chip allows a 30-fold increase of the stimulation amplitude, enabling the tracking of sub-picoSiemens conductance variations on a baseline of few µS, with a bandwidth of 70 Hz. The chip performance opens the way to multipoint monitoring of complex photonic systems, addressing the challenges posed by the growing complexity of these architectures.

In technologies operating at light wavelengths for wireless communication, sensor networks, positioning, and ranging, a dynamic coherent control and manipulation of light fields is an enabling element for properly generating and correctly receiving free-space optical (FSO) beams even in the presence of unpredictable objects and turbulence in the light path. In this work, we use a programmable mesh of Mach–Zehnder (MZI) interferometers to automatically control the complex field radiated and captured by an array of optical antennas. The implementation of local feedback control loops in each MZI stage, without global multivariable optimization techniques, enables an unlimited scalability. Several functionalities are demonstrated, including the generation of perfectly shaped beams with nonperfect optical antennas, the imaging of a desired field pattern through an obstacle or a diffusive medium, and the identification of an unknown obstacle inserted in the FSO path. Compared to conventional devices used for the manipulation of FSO beams, such as spatial light modulators, our programmable device can self-configure through automated control strategies and can be integrated with other functionalities implemented onto the same photonic chip.

Many optoelectronic devices embedded in a silicon photonic chip, like photodetectors, modulators, and attenuators, rely on waveguide doping for their operation. However, the doping level of a waveguide is not always reflecting in an equal amount of free carriers available for conduction because of the charges and trap energy states inevitably present at the S i / S i O 2 interface. In a silicon-on-insulator technology with 10 15 c m − 3 p -doped native waveguides, this can lead to a complete depletion of the core from free carriers and to a consequently very high electrical resistance. This Letter experimentally quantifies this effect and shows how the amount of free carriers in a waveguide can be modified and restored to the original doping value with a proper control of the chip substrate potential. A similar capability is also demonstrated by means of a specific metal gate integrated above the waveguide that allows fine control of the conductance with high locality level. This paper highlights the linearity achievable in the conductance modulation that can be exploited in a number of possible applications.