Subnanometer Linewidths Research Articles

Classical electromagnetically-induced transparency in hybrid metal-dielectric meta-structures with sub-nanometer linewidth

Classical electromagnetically-induced transparency in hybrid metal-dielectric meta-structures with sub-nanometer linewidth

Compact Quantum-Dot Microbeads with Sub-Nanometer Emission Linewidth.

Fluorescent microbeads are widely used for applications in life sciences and medical diagnosis. The spectral contrast and sharpness of photoluminescence are critical in the utilities of microbeads for imaging and multiplexing. Here, we demonstrate microbeads capable of generating single-peak laser emission with a sub-nanometer linewidth. The microbeads are made of quantum dots that are tightly packed and crosslinked via ligand exchange for high optical gain and refractive index as well as material stability. Bright single-mode lasing with no photobleaching is achieved with particle diameters as small as 1.5 μm in the air. Sub-nm lasing emission is maintained even inside high-index surroundings, such as organic solvents and biological tissues. Feasibility of intracellular tagging and multi-color imaging in vivo is demonstrated.

Resonant random laser emission from graphene quantum dots doped dye solution

In this letter, we report on the fabrication of dye doped graphene quantum dots (GQDs) random lasers with resonant feedback that are optically pumped with nanosecond pulses. GQDs, synthesized by the pyrolysis of citric acid, are used as the scattering elements in an ethylene glycol solution of rhodamine B dye. It is experimentally demonstrated that using GQDs instead of titania nanoparticles not only results in the multimode random lasing emission, but also increases the operating lifetime, significantly. We observe discrete lasing modes with subnanometer linewidths at the pump fluences above the threshold. Furthermore, the dependences of the random lasing emission characteristics on the pumping position and concentration of GQDs are investigated, experimentally.

Lasing in Ni Nanodisk Arrays.

We report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.

Random lasing emission tailored by femtosecond and picosecond pulsed polymer ablation.

We report the realization of random lasers with spatially localized feedback in which the average number of lasing modes is tuned via the fabrication process. The scattering elements required for optical feedback are obtained by short-pulsed laser ablation. By varying the pulse parameters, we control the scattering properties of the induced defects and, thus, the emission spectra. We demonstrate a large variety of spectral signatures typical of resonant random lasing with sub-nanometer linewidths, low thresholds (about 40 pJ/μm2), and single-to-multimode emission. Our simple approach allows us to obtain optical resonators with sharp linewidths at frequencies covering the entire gain window for multiple applications.

Spectral broadening in narrow linewidth, continuous-wave high power fiber amplifiers

We present an investigation on the spectrum broadening in continuous-wave, sub-nanometer linewidth high power fiber amplifiers caused by the multiple four-wave mixing (FWM) process. The spectrum broadening employing two different types of narrow linewidth seeds, including the multi-longitudinal-mode seed and the broadened single frequency seed generated by high speed phase modulation, is studied. It is shown both theoretically and experimentally that the multi-longitudinal-mode seed experiences serious spectrum broadening induced by the FWM among various longitudinal modes, while the modulated seed can maintain the spectrum profile during the amplifying process even with some noise fluctuation. The different broadening results are mainly caused by the random phase distribution of the multiple waves. It is further explained by an exact solution of the degenerate FWM with three waves. The theoretical predictions on the spectrum and power dependence of the output laser linewidth are in quantitative agreement with the experimental results up to kilowatt.

Temperature-independent optical transition with sub-nanometer linewidth in thermally diffused Gadolinium in GaN.

We have demonstrated temperature-independent optical transitions from thermally diffused Gd in GaN. The emission wavelength is sub-bandgap with respect to GaN. The origin of photon generation is identified as atomic transitions in Gd hosted in the weak interaction field of GaN. The emission linewidth remains sub-nanometer (0.1-0.6nm) from 19 to 300K for all the optical pumping intensities. The shift in wavelength with temperature and optical pumping is negligible (∼0.8 nm) for the entire temperature window. The output intensity is found to scale linearly with the pumping power. The magnetic, electrical, and physical characterizations indicate that Gd acts as an electron trap in GaN. Transient absorption spectroscopy discovers a major nonradiative parallel path for carrier leaking. The observed characteristics may find potential applications in narrow linewidth optical sources.

Sub-nanometer linewidth perfect absorption in visible band induced by Bloch surface wave

We demonstrate the unity absorption of visible light with an ultra-narrow 0.1 nm linewidth. It arises from the Bloch surface wave resonance in alternating TiO2/SiO2 multilayers. The total absorption and narrow linewidth are explained from the radiative and absorptive damping, which are quantitatively determined by the temporal coupled mode theory. When a silver film with proper thickness is added to the absorber, the perfect absorption is achieved with only 3 structural bilayers, in contrast with 8 bilayers required without Ag. Furthermore, significant field enhancement and an ultrahigh 2600/RIU sensing figure-of-merit are simultaneously obtained at resonance, which might facilitate applications in nonlinear optical devices and high resolution refractive index sensing.

Design of a hybrid As₂S₃-Ti:LiNbO₃ optical waveguide for phase-matched difference frequency generation at mid-infrared.

Based on arsenic tri-sulfide films on titanium-diffused lithium niobate, we designed a hybrid optical waveguide for efficient mid-infrared emission by phase-matched difference frequency generation (DFG). The hybrid waveguide structure possesses a low-index magnesium fluoride buffer layer sandwiched between two high-index As(2)S(3) slabs, so that pump and signal waves are tightly confined by titanium-diffused waveguide while the DFG output idler wave at mid-infrared is confined by the whole hybrid waveguide structure. On a 1 mm-long hybrid waveguide pumped at 50 mW powers, a normalized power conversion efficiency of 20.52%W(-1)cm(-2) was theoretically predicted, which is the highest record for mid-infrared DFG waveguides based on lithium niobate crystal, to the best of our knowledge. Using a tunable near-infrared pump laser at 1.38-1.47 µm or a tunable signal laser at 1.95-2.15 µm, a broad mid-infrared tuning range from 4.0 µm to 4.9 µm can be achieved. Such hybrid optical waveguides are feasible for mid-infrared emission with mW powers and sub-nanometer linewidths.

Multiwavelength generation in a random distributed feedback fiber laser using an all fiber Lyot filter

Multiwavelength lasing in the random distributed feedback fiber laser is demonstrated by employing an all fiber Lyot filter. Stable multiwavelength generation is obtained, with each line exhibiting sub-nanometer line-widths. A flat power distribution over multiple lines is obtained, which indicates that the power between lines is redistributed in nonlinear mixing processes. The multiwavelength generation is observed both in first and second Stokes waves.

Sub-Nanometer Line Width and Line Profile Measurement Using STEM Images with Metal Coating

The novel method of sub-nanometer uncertainty for the line width and line profile measurement using STEM (Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement. In accordance with the proposed method, the traceability and reference metrology of line width measurements are established using Si lattice structures. The interface of SiO2-Air is defined using image intensity of STEM image after metal coating. The edge positions of the Si line from top to bottom are detected. Then, the pixel size of the images is evaluated using 2D Fourier analysis for Si lattice structures. Using the proposed method, the line profile and line width of 50 nm are measured with expanded uncertainty less than 0.3 nm.

Subnanometer Linewidth Uniformity in Silicon Nanophotonic Waveguide Devices Using CMOS Fabrication Technology

We report subnanometer linewidth uniformity in silicon nanophotonics devices fabricated using high-volume CMOS fabrication tools. We use wavelength-selective devices such as ring resonators, Mach-Zehnder interferometers, and arrayed waveguide gratings to assess the device nonuniformity within and between chips. The devices were fabricated using 193 or 248 nm optical lithography and dry etching in silicon-on-insulator wafer technology. Using 193 nm optical lithography, we have achieved a linewidth uniformity of 2 nm (after lithography) and 2.6 nm (after dry etch) over 200 mm wafer. Furthermore, with the developed fabrication process, using wavelength-selective devices, we have demonstrated a linewidth control better than 0.6 nm within chip and better than 2 nm chip-to-chip. The necessity for high-resolution optical lithography is demonstrated by comparing device nonuniformity between the 248 and 193 nm optical lithography processes.

Whispering-gallery modes and light emission from a Si-nanocrystal-based single microdisk resonator

We report on visible light emission from Si-nanocrystal based optically active microdisk resonators. The room temperature photoluminescence (PL) from single microdisks shows the characteristic modal structure of whispering-gallery modes. The emission is both TE and TM-polarized in 300 nm thick microdisks, while thinner ones (135 nm) support only TE-like modes. Thinner disks have the advantage to filter out higher order radial mode families, allowing for measuring only the most intense first order modal structure. We reveal subnanometer linewidths and corresponding quality factors as high as 2800, limited by the spectral resolution of the experimental setup. Moreover, we observe a modification of mode linewidth by a factor 13 as a function of pump power. The origin of this effect is attributed to an excited carrier absorption loss mechanism.

Strong light confinement in microporous photonic silicon structures

ABSTRACTWe have recently reported the fabrication of Si based subnanometer linewidth microcavities and omnidirectionnal mirrors. The structures were made of microporous silicon by electrochemical anodization. The structure high quality and the observation of omnidirectionnal stop bands have been made possible by the optimisation of the starting material, the etching conditions, and the structure design. In this paper we discuss more specifically the choice of these parameters considering the material intrinsic limitations.

Optical microcavities with subnanometer linewidths based on porous silicon

We have fabricated a number of high-quality porous silicon optical microcavities operating in the near infrared that exhibit cavity resonances with subnanometer linewidths. This was achieved through the low temperature anodic oxidation of highly doped p-type silicon wafers. We have investigated the optical properties of these microcavities using reflectivity and photoluminescence measurements and compared our results with theoretical predictions. From our analysis, we conclude that, for the low temperature fabrication process, the refractive index difference between adjacent layers of the multilayered structure is maximized while optical losses in the cavity are minimized. Furthermore, by considering the origin of optical losses in these microcavities, we demonstrate that fluctuations in the position of the resonance wavelength and optical absorption play an important role in the realization of high-quality interferometric structures.