Silicon photonics (SiPh) has emerged as the predominant platform across a wide range of integrated photonics applications, encompassing not only mainstream fields such as optical communications and microwave signal processing but also burgeoning areas such as artificial intelligence and quantum processing. A vital component in most SiPh applications is the optical phase shifter, which is essential for varying the phase of light with minimal optical loss. Historically, SiPh phase shifters have primarily utilized the thermo-optic coefficient of silicon for their operation. Thermo-optic phase shifters (TOPSs) offer significant advantages, including excellent compatibility with complementary metal–oxide–semiconductor technology and the potential for negligible optical loss, making them highly scalable. However, the inherent heating mechanism of TOPSs renders them power-hungry and slow, which is a drawback for many applications. We thoroughly examine the principal configurations and optimization strategies that have been proposed for achieving energy-efficient and fast TOPSs. Furthermore, we compare TOPSs with other electro-optic mechanisms and technologies poised to revolutionize phase shifter development on the SiPh platform.

Optical-resolution photoacoustic microscopy (OR-PAM) has rapidly developed and is capable of characterizing optical absorption properties of biological tissue with high contrast and high resolution (micrometer-scale lateral resolution). However, the conventional excitation source of rapidly diverging Gaussian beam imposes limitations on the depth of focus (DOF) in OR-PAM, which in turn affects the depth-resolving ability and detection sensitivity. Here, we proposed a flexible DOF, depth-invariant resolution photoacoustic microscopy (FDIR-PAM) with nondiffraction of Airy beams. The spatial light modulator was incorporated into the optical pathway of the excitation source with matched switching phase patterns, achieving the flexibly adjustable modulation parameters of the Airy beam. We conducted experiments on phantoms and intravital tissue to validate the effectiveness of the proposed approach for high sensitivity and high-resolution characterization of variable topology of tissue, offering a promising DOF of 926 μm with an invariant lateral resolution of 3.2 μm, which is more than 17-fold larger compared to the Gaussian beam. In addition, FDIR-PAM successfully revealed clear individual zebrafish larvae and the pigment pattern of adult zebrafishes, as well as fine morphology of cerebral vasculature in a large depth range with high resolution, which has reached an evident resolving capability improvement of 62% mean value compared with the Gaussian beam.