inside or outside a Fabry−Pérot (FP) cavity to control the optical properties of laser emission. [8][9][10][11][12][13] Most studies focused on either the tunability of laser modes or switching of lasing wavelengths. However, the capability to control both lasing spectra and laser modes in a microresonator remains challenging due to the lack of efficient mechanisms to overcome mode competitions. Conventional FP cavity relies on two highly reflected planar mirrors to form a resonator, in which whole-body interactions between the electromagnetic field and the gain medium can be utilized for intracavity detection and manipulation. [14][15][16][17][18] The structure of within the FP cavity can also alter the lasing output characteristics sensitively (e.g., laser mode, threshold, and lasing spectrum). Herein, we developed a tunable laser by configuring the optical confinement, chirality, and polarization at the nanoscale with liquid crystals (LCs) in FP microcavity. LCs have received emerging attention owing to its tunability, in which the orientation of the elongated LC molecules will change under an external stimulus. Additionally, anisotropic optical characteristics can be manipulated dynamically by changing the internal structures in cholesteric LC (CLC). Based on the unique features, LCs have been extensively used in biosensing, temperature detection, and whispering-gallery mode (WGM) laser resonators. [19][20][21][22][23][24] As the chiral dopant increases in CLC droplets, the number of periodic refractive index variation (periodic shells) increases to form higher structural confinement and chirality. Recent studies have further applied CLC microdroplets to obtain spherical or lateral confinement of optical modes. [25][26][27] In this work, we explored the lasing properties of a hybrid FP cavity by modulating light confinement and interactions in a FP resonator. Different configurations of micro-/nanostructured CLC−WGM droplet allowed the versatile design of optical confinement, chirality, and molecular orientation. Taking advantage of the vast complexity and tunability of CLCs, this novel concept provides a simple yet highly versatile method to manipulate laser modes and lasing wavelengths. Three representative CLC structures were prepared and analyzed in this work, with the pitch length (p o ) designed to be larger (p o >> λ), close to (p o ∼ λ), and smaller (p o < λ) than the lasing wavelength (λ). Figure 1a shows that as the pitch length becomes smaller, Manipulation of laser emission offers promising opportunities for the generation of new spatial dimensions and applications, particularly in nanophotonics, super-resolution imaging, and data transfer devices. However, the ability to control laser modes and wavelength in a microcavity remains challenging. Here, a novel approach is demonstrated to control laser modes by manipulating the 3D-optical confinement, chirality, and orientations in a Fabry−Pérot microcavity with cholesteric liquid crystal droplets. Different configurations of intracavity micro-/nanost...

We report on the design, fabrication, and characterization of mass-producible, sensitive, intensity-detection-based planar waveguide sensors for rapid refractive index (RI) sensing; the sensors comprise suspended glass planar waveguides on glass substrates, and are integrated with microfluidic channels. They are facilely and cost-effectively constructed via vacuum-less processes. They yield a high throughput, enabling mass production. The sensors respond to solutions with different RIs via variations in the transmitted optical power due to coupling loss in the sensing region, facilitating real-time and simple RI detection. Experiments yield a good resolution of 5.65 × 10−4 RIU. This work has major implications for several RI-sensing-based applications.

We demonstrate silicon-based p - n - p floating-base GeSn heterojunction phototransistors with enhanced optical responsivity for efficient short-wave infrared (SWIR) photodetection. The narrow-bandgap GeSn active layer sandwiched between the p - G e collector and n - G e base effectively extends the photodetection range in the SWIR range, and the internal gain amplifies the optical response by a factor of more than three at a low driving voltage of 0.4 V compared to that of a reference GeSn p - i - n photodetector (PD). We anticipate that our findings will be leveraged to realize complementary metal-oxide-semiconductor-compatible, sensitive, low driving voltage SWIR PDs in a wide range of applications.

The rapid and sensitive detection of human C-reactive protein (CRP) in a point-of-care (POC) may be conducive to the early diagnosis of various diseases. Biosensors have emerged as a new technology for rapid and accurate detection of CRP for POC applications. Here, we propose a rapid and highly stable guided-mode resonance (GMR) optofluidic biosensing system based on intensity detection with self-compensation, which substantially reduces the instability caused by environmental factors for a long detection time. In addition, a low-cost LED serving as the light source and a photodetector are used for intensity detection and real-time biosensing, and the system compactness facilitates POC applications. Self-compensation relies on a polarizing beam splitter to separate the transverse-magnetic-polarized light and transverse-electric-polarized light from the light source. The transverse-electric-polarized light is used as a background signal for compensating noise, while the transverse-magnetic-polarized light is used as the light source for the GMR biosensor. After compensation, noise is drastically reduced, and both the stability and performance of the system are enhanced over a long period. Refractive index experiments revealed a resolution improvement by 181% when using the proposed system with compensation. In addition, the system was successfully applied to CRP detection, and an outstanding limit of detection of 1.95 × 10−8 g/mL was achieved, validating the proposed measurement system for biochemical reaction detection. The proposed GMR biosensing sensing system can provide a low-cost, compact, rapid, sensitive, and highly stable solution for a variety of point-of-care applications.

In this article, we report the process induced variation in the characteristics of PECVD deposited and thermally grown silicon dioxide (SiO 2 ) thin film. We find key differences in the porosity, arrangement of the nano-pores, surface roughness, refractive index and electrical resistivity of the SiO 2 thin films obtained by the two methods. While the occurrence of the nanoporous structure is an inherent property of the material and independent of the process of film growth or deposition, the arrangements of these nano-pores in the oxide film is process dependent. The distinct arrangements of the nano-pores are signatures of the deposition/growth processes. Morphological analysis has been carried out to demonstrate the difference between oxides either grown by thermal oxidation or through PECVD deposition. The tunable conductive behavior of the metal filled nano-porous oxides is also demonstrated, which has potential to be used as conductive oxides in various applications.