Narrow-band Mirrors Research Articles

First-order type A waveguide Bragg gratings with under-diffraction-limited periodicities and sub-millimeter length for NIR applications

Since its demonstration in 2017, laser-induced Type A modifications in silver-containing glasses have been exploited for fabricating waveguides, couplers, volume Bragg Gratings and, more recently, waveguides Bragg Gratings. Laser-induced silver-supported structures exhibit sub-diffraction characteristics being always associated with a positive refractive index change resulting from multi-photon energy deposition under multiple-pulse femtosecond laser irradiation. These properties have been exploited in this work for the fabrication of efficient first-order helicoidal Type A waveguides Bragg gratings in the near-infrared (NIR) range, with periodicities well below the diffraction limit and with typical length L = 500 μm, showing narrowband mirror behaviours. Moreover, this work demonstrates that such helicoidal Type A waveguides Bragg gratings allow for modulating the refractive index of the waveguide at half the periodicity of the helix. Such a peculiarity has been exploited to fabricate efficient first-order Type A waveguides Bragg gratings in the NIR range, as well as in the far red range of the visible spectrum, showing a remarkably strong coupling coefficient, up to one order of magnitude higher than what is reported in the literature.

Far UV narrowband mirrors tuned at H Lyman α.

Imaging at H Ly-α (121.6 nm), among other spectral lines in the short far UV (FUV), is of high interest for astrophysics, solar, and atmosphere physics, since this spectral line is ubiquitously present in space observations. However, the lack of efficient narrowband coatings has mostly prevented such observations. Present and future space observatories like GLIDE and the IR/O/UV NASA concept, among other applications, can benefit from the development of efficient narrowband coatings at Ly-α. The current state of the art of narrowband FUV coatings lacks performance and stability for coatings that peak at wavelengths shorter than ∼135 nm. We report highly reflective AlF3/LaF3 narrowband mirrors at Ly-α prepared by thermal evaporation, with, to our knowledge, the highest reflectance (over 80%) of a narrowband multilayer at such a short wavelength obtained so far. We also report a remarkable reflectance after several months of storage in different environments, including relative humidity levels above 50%. For astrophysics targets in which Ly-α may mask a close spectral line, such as in the search for biomarkers, we present the first coating in the short FUV for imaging at the OI doublet (130.4 and 135.6 nm), with the additional requirement of rejecting the intense Ly-α, which might mask the OI observations. Additionally, we present coatings with the symmetric design, aimed to observe at Ly-α, and reject the strong OI geocoronal emission, that could be of interest for atmosphere observations.

CW Emission and Self-Pulsing in a III-V/SiN Hybrid Laser With Narrow Band Mirror

We report on how external cavity III-V/SiN hybrid lasers operate in regimes of ultra-damped relaxation oscillations or in CW unstable dynamical regimes (self-pulsing or approaching turbulence) as a consequence of mirror dispersion, non-zero linewidth enhancement factor, and four-wave mixing in the gain medium. The impact of the dispersive mirror bandwidth and different mirror effective lengths on the laser tolerance to external optical feedback is also discussed.

Damping of relaxation oscillations, photon-photon resonance, and tolerance to external optical feedback of III-V/SiN hybrid lasers with a dispersive narrow band mirror.

We address the stability of a tunable hybrid laser based on a III-V Reflective Semiconductor Optical Amplifier (RSOA) edge-coupled with a Silicon Photonic (SiPh) dispersive mirror through a model of time-delayed algebraic differential equations that accounts for the narrow band mirror. Our results allow to (i) analyze the stability of single mode lasing, (ii) quantify the impact of the mirror bandwidth on the damping of the laser relaxation oscillations and the emergence of photon-photon resonance, and (iii) study the tolerance of the laser to the external optical feedback. Thanks to this analysis, we find a mirror design that gives ultra-high stability up to an external feedback level of -10 dB. The aim of the work is providing a tool for understanding and interpreting the dynamics of these lasers and design configurations for isolator-free operation.

Photonic crystal lasers: from photonic crystal surface emitting lasers (PCSELs) to hybrid external cavity lasers (HECLs) and topological PhC lasers [Invited

Photonic crystals (PhC) represent an important class of silicon photonics components employed as wavelength selective resonators to act as narrow-band mirrors in integrated lasers due to their small footprint, high surface area, and Q-factor/volume ratio that enables efficient confinement of light, required for improved performances of the laser. These properties of PhCs are key for the potential deployment of PhC based high power, energy efficient and versatile semiconductor lasers for telecom, datacom, optical sensing and biomedical applications. In this paper, we report the main advances on PhC based lasers from photonic crystal surface-emitting lasers (PCSELs) to the new hybrid external cavity laser (HECLs) configurations.

Application of optical narrow-band mirrors in sensor of concentration of dust in coal mines

The article presents a new design of the sensor for measuring dust, which is based on the effect of absorption of optical radiation passing through the dust layer. Fundamentally new is the use of a powerful low-cost LED, the spectral part of the radiation range required for measurement of which is formed by the structure of auxiliary reflective optical interference filters. A technique based on the introduced stability criterion of the synthesized interference coating is developed, which makes it possible to study the transformation of the spectra with real errors in the film thicknesses.

Reflection Spectra of Composite Photonic Crystals Based on Anodic Alumina Filled with Ferroelectric Sodium Nitrite

Reflection spectra of a composite one-dimensional photonic crystal (PC) based on porous anodic alumina filled with ferroelectric sodium nitrite have been recorded in the wavelength range of 400 to 1200 nm. Significant spectral shifts of the first and second stopbands are revealed for the composite PC. The stopband spectral half-width is found to decrease by a factor of four to five. The possibility of applying composite alumina-based photonic crystals as selective narrowband mirrors is discussed.

Semiconductor Fano Lasers

In this paper, a new type of semiconductor laser based on Fano interference is described. One of the laser mirrors relies on the interference between the continuum of waveguide modes and a side-coupled nanocavity, leading to a narrow-band mirror that provides the Fano laser with unique characteristics. In addition to being truly single-mode, the laser can be modulated through the mirror at frequencies far exceeding the relaxation oscillation resonance. Furthermore, nonlinearities in the nanocavity can be used to implement a saturable mirror, leading to passive pulse generation with repetition frequencies in the gigahertz range. This paper reviews the theory of Fano lasers and the current experimental status. Experimentally, the Fano laser concept is demonstrated using a photonic crystal platform with quantum dot active material. Both continuous wave operation and self-pulsing is observed for optically pumped lasers operating at room temperature.

Reflection spectra of 1D photonic crystals based on aluminum oxide

Optical properties (transmission and reflection) of 1D photonic crystals (PCs) based on mesoporous anodic aluminum oxide with the lattice periods of 188 and 194nm are investigated. The experimentally measured reflection spectrum is compared in its first bandgap region with the theoretical dependence obtained from the dispersion relation for the 1D PC. Angular dependence is established for spectral positions of bandgaps in the 1D PC. A possibility of using mesoporous aluminum-oxide-based 1D PCs as narrow-band filters, narrow-band mirrors, and refractive sensors of molecular compounds is analyzed.

Multilayer dielectric narrow band mangin mirror

The design of multilayer stack of dielectric films for narrow band mirror is developed using thin film coating software. The proposed design is materialized by employing thin film coating (PVD) method and reflectance in narrow band spectrum range is achieved. Thickness of high and low refractive index material is taken precisely up to nanometer level. The curved coated substrate is cemented with another K9 matching substrate that forms a Mangin mirror for wavelength 650nm. Narrow band mirrors with reflectivity more than 90% has been produced by properly stacking of 21 layers and advantage of the use of this type of mirror as an interference filter is discussed.

SU‐F‐BRE‐12: Optical Resonator Water Calorimeter

Purpose:Water calorimetry based on resistance thermometry has matured as a primary standard. Developing an optical technique hold the promise to push the boundaries of what is currently achievable with dosimetry. We will present a feasibility study and the current progress of construction of a Fabry‐Perot resonator for dose to water measurement. Additionally, estimations of the theoretical limits resonator sensitivity and potential sources of noise for the system are described.Methods:A temperature change from the dose to water would be measured by the change in the index of refraction from the water in the cavity. Calculations are presented of the expected signal from the resonator for dose to water. The Fabry‐Perot resonator constructed from optical quality narrowband mirrors is described. A water cell will be inserted into the cavity gap to provide the medium swept cavity length technique is explored as a specific implementation of this technique.Results:Calculations indicate that a dose to water on the order of a Gray is measureable with a reasonably implementable system. A resonator is currently under construction and progress towards a proof of principle measurement will be presented. The primary sources of noise, in order of importance, are expected to be; optical absorption by the medium, mechanical perturbations of the cavity length and thermal expansion of the optical mounts. Estimations of these noise sources and mitigation techniques will be discussed.Conclusion:A Fabry‐Perot resonator is a promising technique for measuring the absorbed dose to water from a radiotherapy beam. This technique has the potential to serve as a check on the current primary standard for dose to water measurements. As well, i0074 may be the foundation for a new class of optical property based dosimetry measurement.

A detection of atmospheric relative humidity profile by UV Raman lidar

A new spectroscopic filter constructed with a high-spectral-resolution grating and two narrow-band mirrors is designed to separate the elastic scattering and the vibrational Raman scattering spectra in an ultraviolet (UV) Raman lidar system. The density of humidity and water vapor mixing ratio are calculated from the vibrational Raman scattering signals of N 2 and H 2O. Water vapor mixing ratio is retrieved from this development. With this measured water vapor mixing ratio, the relative humidity is calculated with atmospheric temperature profile obtained by another Raman temperature lidar. Preliminary experiments and comparison results between lidar and radiosonde showed that the UV Raman lidar system has the capability for profiling the water vapor mixing ratio up to a height of 2 km with less than 10% of the uncertainty under the conditions of laser energy of 300 mJ and signal-averaging time of 10 min.

Measurements of reflection spectra of soft X-ray multilayer mirrors using a broadband laser-plasma radiation source

The reflection spectra of several concave (spherical and parabolic) periodic Mo/Si, Mg/Si, and Al/Zr multilayer mirrors intended for cosmic experiments were studied with the help of a laser-plasma soft X-ray radiation source. An investigation was made of the reflection spectra of a laboratory aperiodic Mo/Si multilayer mirror optimised for maximum uniform reflectivity in the 125–250-Å range. 'Satellites' were observed in the neighbourhood of the principal peak in the spectrum of the periodic 132-Å multilayer mirror. High-intensity second-order interference reflection peaks at wavelengths of about 160 Å were experimentally revealed in the reflection spectra of the periodic Mo/Si 304-Å mirrors. By contrast, the second-order reflection peak is substantially depressed in the spectra of the narrow-band mirrors based on the Mg/Si multilayer structure. The experimental data are compared with theoretical calculations. Manifestations of the NEXAFS structure of the L2,3 absorption edges of Al and Al2O3 were observed in the spectra recorded.

紫外域拉曼激光雷达精细探测气溶胶消光系数

An ultraviolet (UV) Raman lidar system at 354.7 nm has been developed for accurately measuring the aerosol extinction profiles. A spectroscopic filter combining a high-spectral-resolution grating with two narrowband mirrors is used to separate the vibrational Raman scattering signal of N2 at a central wavelength of 386.7 nm and the elastic scattering signal at 354.7 nm. The aerosol extinction is derived from the Raman scattering of N2 and the elastic scattering by the use of Raman method and Klett method, respectively. The derived results of aerosol extinction are used to compare the difference of two retrieval methods, and the preliminary experiment shows that the Raman lidar system operated in analog detection mode has the capability of measuring aerosol profiles up to a height of 3 km with a laser energy of 250 mJ and an integration time of 8 min.

Stable and widely tunable all-fiber Pr^3+-doped cw laser system using fiber Bragg gratings

A simple and strictly all-fiber 1300-nm cw laser is presented. It is tunable over 16 nm with 0.5-nm linewidth and several milliwatts of output power in the whole tuning range from 1292 to 1308 nm. The setup uses a fiber Bragg grating as a combined tuning element and narrow-band output mirror. The simplicity and stability of this system are due to the following two characteristics: First, polarization control is not necessary anywhere in the system, and second, a wavelength-selective system and a narrow-band mirror are combined into one novel fiber-optic element.

The Casimir force for passive mirrors

We show that the Casimir force between mirrors with arbitrary frequency dependent reflectivities obeys bounds due to causality and passivity properties. The force is always smaller than the Casimir force between two perfectly reflecting mirrors. For narrow-band mirrors in particular, the force is found to decrease with the mirrors' bandwidth.