Abstract
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.
Highlights
The high integration density made possible by silicon photonics enables the design of increasingly complex photonic architectures in a very small footprint, where a cascade of several devices is exploited to perform different optical functionalities like modulation, multiplexing and routing [1]
The dithering technique can be effectively used to discriminate the effect of multiple actuators, while still using only a single detector. This feature is very useful in case of devices that require more than one heater to be operated, like Mach‐Zehnder interferometers (MZIs), or in cascaded structures where many actuators affect the output optical power, like arrays of coupled microring resonators
The advantages of the dithering technique were fully exploited by implementing orthogonal modulations to discriminate the effect of different actuators, while frequency re‐use allowed to keep the complexity of the control system low even when controlling many devices simultaneously
Summary
The high integration density made possible by silicon photonics enables the design of increasingly complex photonic architectures in a very small footprint, where a cascade of several devices is exploited to perform different optical functionalities like modulation, multiplexing and routing [1]. The standard technique is extended by introducing the concept of orthogonal dithering signals for the discrimination of multiple actuators, while the idea of frequency re‐use is presented as an effective way to limit the complexity of control systems These strategies allow to independently address each photonic device and track variations of the working conditions without requiring any calibration, making them suitable for high‐density architectures where a high number of sensors and control loops are needed. The dithering technique can be effectively used to discriminate the effect of multiple actuators, while still using only a single detector This feature is very useful in case of devices that require more than one heater to be operated, like MZIs, or in cascaded structures where many actuators affect the output optical power, like arrays of coupled microring resonators. The loop gain Gloop of the system and the error signal ɛD can be computed as: GloopðsÞ 1⁄4 À
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