Mingsen Pan

Cytochrome c oxidase (CCO) is widely regarded as the primary photoacceptor underlying photobiomodulation (PBM), in which light absorption stimulates mitochondrial respiration by promoting electron transfer through CCO. Single-molecule plasmonic nanopore measurements were used to examine cytochrome c (CC)–CCO interactions across three excitation wavelengths spanning the near-infrared range, which is preferred for PBM studies in vivo due to increased tissue penetration. Wavelength-dependent measurements of CC–CCO interactions were performed under normoxic, hypoxic, and allosterically inhibited conditions, revealing distinct interaction populations that are obscured in ensemble measurements. CC–CCO interactions were resolved into short-duration, long-duration, and heterogeneous populations for all wavelengths and oxygenation conditions. The short-duration population was selectively and substantially depleted by both hypoxia and ADDA5-mediated allosteric inhibition, supporting its assignment as a distinct, putative electron-transfer-associated interaction state. Allosteric inhibition strongly favored the long-duration population, whereas hypoxia predominantly increased heterogeneous duration interactions, consistent with non-specific binding. Under normoxia, 820 nm and 905 nm produced statistically comparable population fractions of the putative electron-transfer-active population, whereas the corresponding population fraction at 1064 nm was significantly lower but remained substantial. The short-duration binding population kinetics remained largely unchanged across wavelength and oxygenation states, indicating that these conditions primarily altered access to the CCO binding site rather than affecting its binding lifetime. These findings reveal the previously unresolved heterogeneity in CC–CCO interactions and provide a single-molecule framework for understanding how the excitation wavelength and oxygenation state may influence molecular interactions relevant to PBM efficiency.

Scaling up the area of photonic-crystal surface-emitting lasers (PCSELs) to produce higher output power while maintaining single-mode operation has been a longstanding objective in photonics and laser physics. Achieving this goal requires two fundamental physics: the difference between the modal losses of the fundamental and higher-order modes, and the mode competition between them. Both physics contribute to the lasing threshold difference between the fundamental and higher-order modes and have been considered individually in past works. But there has not been a theoretical study that treats both physics together for the design of PCSELs. Here we provide a theoretical framework to elucidate the interplay between differential modal losses and mode competition in PCSELs. Based on this framework, we introduce designs based on spatial engineering of photonic-crystal slabs to simultaneously control the modal properties and mode competition. Compared to designs that focus on only one of these physics, our designs can increase the difference between the lasing thresholds of the fundamental and higher-order modes by orders of magnitude. Our findings provide new insights into realizing scalable PCSELs for large-area single-mode lasing.

We report a novel ultra-thin metalens design based on photonic crystal slab (PCS) resonance modes. We experimentally verified with a metalens structure based on amorphous silicon on a quartz material platform by implementing the optical guided resonance on the PCS. The PCS metalens designs feature an ultra-thin device layer of about 160 nm at an operation wavelength of 940 nm. A full 2π transmission phase transition is realized by varying the air hole sizes at the design wavelength. Metalens devices with different phase change gradients were designed and fabricated to achieve different NAs. A maximum of 86.4% focusing efficiency is achieved. Imaging capabilities are characterized, and clear images are observed within the field of view. The PC resonance-based phase modulation design can be applied to optical beam manipulation, phase plate design, imaging, and laser beam formation applications.

In recent decades, photonic crystal surface-emitting lasers (PCSELs), a novel design of semiconductor light sources, have shown huge performance improvement. Based on compact semiconductor heterostructures, PCSELs have not only achieved near diffraction limit beam divergence but have also realized single-mode lasing from a broad emission area. Thanks to its planar cavity design, PCSEL cavities can integrate confinement structures laterally, which can potentially achieve performances otherwise unachievable in the current semiconductor lasers. This paper reviews recent advances in PCSELs, including the high-power PCSELs, laterally confined PCSEL design, PCSEL cavity size scaling for high speed, narrow laser linewidth, and coherent PCSEL arrays.

As a new type of semiconductor laser, photonic crystal surface-emitting lasers (PCSELs) feature large-area single-mode surface emission with high power and high beam quality. The unique features of single-mode lasing over a large area active region are implemented by the in-plane optical feedback from two-dimensional (2D) photonic crystal cavities. In larger PCSEL cavities, the lasing gain threshold becomes similar for the fundamental and high-order modes, which degrades single-mode operation. Here, we investigate the impact of carrier injection on PCSEL modes by controlling the injection area and the gain mode interaction. Optical and electrical simulations are carried out to calculate the gain mode overlapping factor for different p electrode designs. We fabricated 250 × 250 µm2 photonic crystal cavities with different p electrode sizes for injection area control. The PCSEL device characterization results show that devices with an electrode size to cavity side length ratio of 0.6 have the maximum slope efficiency and a lower lasing threshold with a single lobe beam profile. Such selective carrier injection can also provide gain-guided resonance in the PCSEL cavities and enhance optical gain in the fundamental mode while suppressing gain in the high-order modes.

We propose and investigate a novel coherent laser array design based on laterally coupled photonic crystal surface-emitting lasers (PCSELs). As a new type of semiconductor laser technology, PCSELs have field confinement in a planar cavity and laser beam emission in the surface normal direction. By engineering lateral couplings between PCSELs with heterostructure photonic crystal designs, we can achieve coherent operations from an array of PCSELs. In this paper, we demonstrate coherent operation from a passively coupled PCSEL array design. We fabricated PCSEL array devices on a GaAs-based quantum well heterostructure at a target wavelength of 1040 nm. Experimental results show that the 2-by-2 PCSEL arrays have spectral linewidth of 0.14–0.22 nm. Beam combining performance was characterized by self-interference experiments. Similar coherency between the PCSEL array and single PCSEL device was observed. Our compact PCSEL array designs by passive lateral coupling have potential applications in fields of on-chip photonic computing, quantum, and information processing.

We report frequency response characterization for the high-power photonic crystal surface-emitting lasers (PCSELs). Power-bandwidth results for our fabricated GaAs 1040 nm lasers are presented and discussed.

Semiconductor lasers are the heart for the development of technologies in many fields. In recent decades, a new type of large-area surface-emitting lasers based on the in-plane photonic crystal modulation and feedback have emerged to show superior advantages of high output power, low-divergence, high beam quality and brightness, and compact and monolithic structure. In this paper, we review the design and development of photonic crystal surface-emitting laser and discuss the future investigation and improvements.

Topological effects in photonic non-Hermitian systems have recently led to extraordinary discoveries including nonreciprocal lasing, topological insulator lasers, and topological metamaterials, to mention a few. These effects, although realized in non-Hermitian systems, are all stemming from their Hermitian components. Here we experimentally demonstrate the topological skin effect and boundary sensitivity, induced by the imaginary gauge field in a two-dimensional laser array, which are fundamentally different from any Hermitian topological effects and intrinsic to open systems. By selectively and asymmetrically injecting gain into the system, we have synthesized an imaginary gauge field on chip, which can be flexibly reconfigured on demand. We show not only that the non-Hermitian topological features remain intact in a nonlinear nonequilibrium system, but also that they can be harnessed to enable persistent phase locking with intensity morphing. Our work lays the foundation for a dynamically reconfigurable on-chip coherent system with robust scalability, attractive for building high-brightness sources with arbitrary intensity profiles.