The concept of point of darkness has received much attention for biosensing based on phase-sensitive detection and perfect absorption of light. The maximum phase change is possible at the point of darkness where the reflection is almost zero. To date, this has been experimentally realized using different material systems through the concept of topological darkness. However, complex nanopatterning techniques are required to realize topological darkness. Here, we report an approach to realize perfect absorption and extreme phase singularity using a simple metal-dielectric multilayer thin-film stack. The multilayer stack works on the principle of an asymmetric Fabry–Perot cavity and shows an abrupt phase change at the reflectionless point due to the presence of a highly absorbing ultrathin film of germanium in the stack. In the proof-of-concept phase-sensitive biosensing experiments, we functionalize the film surface with an ultrathin layer of biotin-thiol to capture streptavidin at a low concentration of 1 pM.

With the rapid advancement of the information age, the demand for multi-dimensional light information detection has significantly increased. Traditional Fourier-transform infrared (FTIR) spectrometers and pooptical power, andlarimeters, due to their bulky structure, are no longer suitable for emerging fields such as medical diagnostics, secure communications, and autonomous driving. As a result, there is a pressing need to develop new miniaturized on-chip devices. The abundant two-dimensional (2D) materials, with their unique light-matter interactions, offer the potential to construct high-dimensional spatial mappings of incident light, paving the way for the development of novel ultra-compact multi-dimensional deep optical sensing technologies. Here, we review the interconnections of multi-dimensional information and their relationship with 2D materials. We then focus on recent advances in the development of novel dimensional detectors based on 2D materials, covering dimensions such as intensity, time, space, polarization, phase angle, and wavelength. Furthermore, we discuss cutting-edge technologies in multi-dimensional fusion detection and highlight future technological prospects, with a particular emphasis on on-chip integration and future development.

One of the most exciting breakthroughs in physics is the concept of topology that was recently introduced to photonics, achieving robust functionalities, as manifested in the recently demonstrated topological lasers. However, so far almost all attention was focused on lasing from topological edge states. Bulk bands that reflect the topological bulk-edge correspondence have been largely missed. Here, we demonstrate an electrically pumped topological bulk quantum cascade laser (QCL) operating in the terahertz (THz) frequency range. In addition to the band-inversion induced in-plane reflection due to topological nontrivial cavity surrounded by a trivial domain, we further illustrate the band edges of such topological bulk lasers are recognized as the bound states in the continuum (BICs) due to their nonradiative characteristics and robust topological polarization charges in the momentum space. Therefore, the lasing modes show both in-plane and out-of-plane tight confinements in a compact laser cavity (lateral size ~3λ_laser). Experimentally, we realize a miniaturized THz QCL that shows single-mode lasing with a side-mode suppression ratio (SMSR) around 20 dB. We also observe a cylindrical vector beam for the far-field emission, which is evidence for topological bulk BIC lasers. Our demonstration on miniaturization of single-mode beam-engineered THz lasers is promising for many applications including imaging, sensing, and communications.