filters, [3] polarizers with embedded photon emitters, [4] label-free optical biosensors, [5,6] fluorophore enhancers, [7] and amplifiers for surface-enhanced Raman scattering (SERS). [8] Many of these applications would benefit from increasing the interaction between surface-confined resonant electromagnetic fields and the materials being probed such as biomolecules, [9] cells, [10] viral particles, [11] Raman tags, [8] liquid crystals, and fluorophores [7] that reside on the PC surface. Open-faced PC slabs that interface with liquid media, such as those used for label-free biosensing applications, are generally comprised of a subwavelength, periodic surface structure within a low refractive index material (such as polymer or SiO 2 ) that is subsequently coated with a layer of high refractive index material (such as TiO 2 or Si 3 N 4 ), which is then immersed into the sensing medium. [12] The spatial electromagnetic field profile of the device mainly resides within the higher refractive index regions, but exponentially decays into its lower refractive index surroundings. Modulation of the PC's resonant wavelength derives from perturbations of the local refractive index (for example, displacing water with cells/biomolecules, or changing the orientation of a liquid crystal film) within the evanescent tail of the electromagnetic field. However, the short penetration depth of the electromagnetic field leaves the device sensitive to change only in close proximity to the surface. [13] In order to increase the penetration depth of the evanescent field profile into the sensing medium, which is desirable for improved sensitivity to bulk refractive index changes, a thinner waveguide layer can be used to weaken the confinement of the mode and enhance the leakage of the evanescent field into the sensing medium. Meanwhile, a drastic reduction of the refractive index of the cladding layer such that it is less than that of the sensing medium works in a more straightforward and universal manner. Our hypothesis is that if the grating structure is comprised of a cladding material with a lower refractive index than the media coving the PC surface, then the mode structure of the electromagnetic standing wave will relocate its spatial distribution to reside mainly in the sensing medium, and thus a greater degree of resonant wavelength modulation can be achieved for a given change of refractive index in the surrounding medium. In order to achieve this more sensitive optical architecture, conventional low refractive index bulk materials utilized for the PC cladding can be Porous SiO 2 (PSiO 2 ) with ultralow refractive index (n = 1.09) is incorporated as the cladding of a photonic crystal (PC) refractive index sensor with enhanced sensitivity through the establishment of resonant modes that principally reside in the liquid medium covering the PC surface. PSiO 2 , obtained by thermal oxidation of porous Si that has been transferred to a transparent substrate, is transparent at visible and near infrared wavelengths with a refractive ind...
Strain-engineered diffusion masks deposited via plasma-enhanced chemical vapor deposition are demonstrated to control the curvature of the zinc diffusion front and, hence, disordering front, in disorder-defined vertical-cavity surface-emitting lasers (VCSELs) for enhanced high-power single-mode operation. Tensilely strained silicon nitride diffusion masks are applied to limit the lateral undercut of the disordering front, thereby minimizing the interaction between the disordered region of the distributed Bragg reflector and the fundamental mode. This results in higher threshold modal gain and absorption losses from the disordered region for higher-order modes while enabling greater output powers for fundamental-mode operation in single-mode impurity-induced disordered VCSEL designs. Using this technique, 850 nm AlGaAs VCSELs are shown to operate in a single fundamental mode with record optical output powers in excess of 10 mW and side-mode suppression ratios greater than 35 dB. Electrical and optical performances of these devices are presented in addition to near-field images confirming single-fundamental-mode lasing.
A compact analysis platform for detecting liquid absorption and emission spectra using a set of optical linear variable filters atop a CMOS image sensor is presented. The working spectral range of the analysis platform can be extended without a reduction in spectral resolution by utilizing multiple linear variable filters with different wavelength ranges on the same CMOS sensor. With optical setup reconfiguration, its capability to measure both absorption and fluorescence emission is demonstrated. Quantitative detection of fluorescence emission down to 0.28 nM for quantum dot dispersions and 32 ng/mL for near-infrared dyes has been demonstrated on a single platform over a wide spectral range, as well as an absorption-based water quality test, showing the versatility of the system across liquid solutions for different emission and absorption bands. Comparison with a commercially available portable spectrometer and an optical spectrum analyzer shows our system has an improved signal-to-noise ratio and acceptable spectral resolution for discrimination of emission spectra, and characterization of colored liquid’s absorption characteristics generated by common biomolecular assays. This simple, compact, and versatile analysis platform demonstrates a path towards an integrated optical device that can be utilized for a wide variety of applications in point-of-use testing and point-of-care diagnostics.
Monolithically combining silicon nitride ( S i N x ) photonics technology with III-V active devices could open a broad range of on-chip applications spanning a wide wavelength range of ∼ 400 − 4000 n m . With the development of nitride, arsenide, and antimonide lasers based on quantum well (QW) and quantum dot (QD) active regions, the wavelength palette of integrated III-V lasers on Si currently spans 400 nm to 11 µm, with a crucial gap in the red-wavelength regime of 630–750 nm. Here, we demonstrate red I n 0.6 G a 0.4 P QW and far-red InP QD lasers monolithically grown on CMOS-compatible Si (001) substrates with continuous-wave operation at room temperature. A low-threshold current density of 550 A / c m 2 and 690 A / c m 2 with emission at 680–730 nm was achieved for QW and QD lasers on Si, respectively. This work represents a step toward the integration of visible red lasers on Si, allowing the utilization of integrated photonics for applications including biophotonic sensing, quantum computing, and near-eye displays.
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