Significance Direct detection—spatially resolving the light of a planet from the light of its parent star—is an important technique for characterizing exoplanets. It allows observations of giant exoplanets in locations like those in our solar system, inaccessible by other methods. The Gemini Planet Imager (GPI) is a new instrument for the Gemini South telescope. Designed and optimized only for high-contrast imaging, it incorporates advanced adaptive optics, diffraction control, a near-infrared spectrograph, and an imaging polarimeter. During first-light scientific observations in November 2013, GPI achieved contrast performance that is an order of magnitude better than conventional adaptive optics imagers. The Gemini Planet Imager is a dedicated facility for directly imaging and spectroscopically characterizing extrasolar planets. It combines a very high-order adaptive optics system, a diffraction-suppressing coronagraph, and an integral field spectrograph with low spectral resolution but high spatial resolution. Every aspect of the Gemini Planet Imager has been tuned for maximum sensitivity to faint planets near bright stars. During first-light observations, we achieved an estimated H band Strehl ratio of 0.89 and a 5-σ contrast of 106 at 0.75 arcseconds and 105 at 0.35 arcseconds. Observations of Beta Pictoris clearly detect the planet, Beta Pictoris b, in a single 60-s exposure with minimal postprocessing. Beta Pictoris b is observed at a separation of 434 ± 6 milliarcseconds (mas) and position angle 211.8 ± 0.5°. Fitting the Keplerian orbit of Beta Pic b using the new position together with previous astrometry gives a factor of 3 improvement in most parameters over previous solutions. The planet orbits at a semimajor axis of 9.0−0.4+0.8 AU near the 3:2 resonance with the previously known 6-AU asteroidal belt and is aligned with the inner warped disk. The observations give a 4% probability of a transit of the planet in late 2017.
Abstract A silicon photonic deep optical neural network integrating convolutional and fully connected layers with on-chip optoelectronic nonlinear activations operates with partially coherent light to achieve high-speed, energy-efficient, end-to-end inference. This demonstration establishes a functional and scalable platform for evaluating complete optical neural processing, representing another step toward specialised, ultrafast photonic architectures beyond electronics.
Abstract Bound states in the continuum (BICs) and exceptional points (EPs), as two distinct physical singularities represented by complex frequencies in non-Hermitian systems, have garnered significant attention and clear definitions in their respective fields in recent years. They share overlapping applications in areas such as high-sensitivity sensing and laser emission. However, the transition between the two, inspired by these intersections, remains largely unexplored. In this work, we reveal the transition process in a non-Hermitian two-mode system, evolving from one bound singularity to a two-dimensional exceptional ring, where the EP is the coalescent state of the quasi-Friedrich-Wintgen (FW)-BIC. This phenomenon is experimentally validated through pored dielectric metasurfaces in terahertz band. Furthermore, external pumping induced photocarriers as the dissipative perturbation, facilitates the breaking of degeneracy in the complex eigenfrequency and enables dynamic EP switching. Finally, we experimentally demonstrate a switchable terahertz beam deflection driven by the phase singularities of the EP. These findings are instrumental in advancing the development of compact devices for sensing and wavefront control within non-Hermitian systems.
Optical whispering gallery modes (WGMs) derive their name from a famous acoustic phenomenon of guiding a wave by a curved boundary observed nearly a century ago. This phenomenon has a rather general nature, equally applicable to sound and all other waves. It enables resonators of unique properties attractive both in science and engineering. Very high quality factors of optical WGM resonators persisting in a wide wavelength range spanning from radio frequencies to ultraviolet light, their small mode volume, and tunable in- and out- coupling make them exceptionally efficient for nonlinear optical applications. Nonlinear optics facilitates interaction of photons with each other and with other physical systems, and is of prime importance in quantum optics. In this paper we review numerous applications of WGM resonators in nonlinear and quantum optics. We outline the current areas of interest, summarize progress, highlight difficulties, and discuss possible future development trends in these areas.
Tien Khee Ng, Alaaeddine Rjeb, Mitchell A. Cox
et al.
A brief account of photonics research activities in the selected countries in the Middle East and Africa is presented in this article. Though not comprehensive, we hope to provide a glimpse of the research landscape in the region, and the collaboration and connection with each other and the international partners.
L.A. Gorodetskaya, A.Y. Denisova, L.M. Kavelenova
et al.
Rare plant species restoration (reintroduction) is one of the main biodiversity conservation activities. Reintroduced plants need constant monitoring in order to study features of their development and control the population state. To reduce the human impact on the natural habitat of plants and simplify the monitoring process, we propose the use of automatic analysis of unmanned aerial vehicles (UAVs) data using the Yolov3 neural network. The article discusses neural network parameters for detecting Paeonia Tenuifolia, reintroduced in the Samara region by ecologists from the Department of Ecology, Botany and Nature Conservation of Samara University. The main issue under research is the possibility of training a neural network from peony images collected in an artificial habitat with a subsequent application to images collected in a natural habitat and the possibilities of using multi-temporal data to improve the network training quality. The experiments have shown that training a neural network exclusively using images collected in the natural habitat makes it possible to achieve a probability of correct detection of peonies of 0.93, while using data obtained at different years allows increasing the probability of correct detection to 0.95.
We demonstrate that by using a cascaded configuration of five solid-core photonic crystal fiber (PCF) samples with progressively decreasing core diameters, ultraviolet light with wavelengths as short as ∼300 nm can be generated in a supercontinuum (SC) set-up. With a nanosecond laser as the pump light, the modulation instability effect leads to the generation of multiple optical solitons in the first PCF sample which has a close-to-zero dispersion value at the pump wavelength (∼1064 nm). The following PCF samples with decreasing core diameters enhance the waveguide nonlinearity, and at the same time provide continuously-shorter phase-matching wavelengths for dispersive-wave emission, thereby pushing the short-wavelength edge of the SC spectrum into the deep ultraviolet spectral region. While the PCF splicing technique ensures the compactness of this SC set-up, the generated SC spectrum, spanning ∼350 nm to ∼2000 nm with a flat spectral profile, may be applied in fluorescence microscopy and biochemical imaging.
Abstract A novel diagnostic method has been used to gain deeper insight into the transverse structure and its evolution of electron pulses generated from a laser-wakefield accelerator.
Thin films of pristine titanium dioxide (TiO2) and doped with different concentrations (0–8) at.% of nickel (Ni) were synthesized onto transparent glass substrates using the spray pyrolysis deposition technique. Field emission scanning electron microscopy revealed the porous and agglomerated surface morphology of the films. X-ray diffractometer demonstrated the anatase crystal structure with a nominal increment of (101) peak. The shifting of peak position revealed the expansion of the unit cell volume from 134.64 to 137.54 (Å)3 whereas crystallite size increased from 34 to 63 nm. Using the Fizeau fringes technique, the thickness of the films was determined between 165 and 190 nm. UV–Vis measurements were employed to examine the optical characteristics of the films. The red shift was observed for 2 at.% Ni content (3.38 eV) while the blue shift was observed for (4–8) at.% Ni content. The wavelength-dependent refractive index and dielectric constant showed anomalous dispersion in the absorption band, representing the transparency of the films. The 4-point probe measurement showed a decreasing trend of resistivity with increasing temperature, whereas the resistivity increased with Ni content. Activation energy indicated a higher amount of adsorbed oxygen in the films due to the high amount of Ni content.
Lucía Castelló-Pedrero, María I. Gómez-Gómez, David Zurita
et al.
Photonic integrated circuits (PICs) fabricated on silicon nitride (SiN) wafers are witnessing a massive implementation because they can provide low-loss waveguides in a broad wavelength range (from the visible to the near infrared) whilst being fabricated in large volumes using standard silicon fabrication processes. One of the most relevant application fields of this technology is biosensing since SiN PICs enable label-free lab-on-a-chip systems for fast and sensitive detection of minute amounts of different biological entities. To this end, resonant structures such as ring resonators (RR) are highly appropriate, but they need suitable interfaces with optical fiber to be tested on-wafer and used in real applications. The interface that satisfies the two previous requirements is the grating coupler (GC). However, experimental evidence of GCs operating at 1310 nm wavelengths for the transverse magnetic (TM) mode, for which RR-based sensors perform better than for the widely employed transverse electric (TE) mode, has not been reported so far. In this work, the operation of fully-etched focusing GCs at 1310 nm wavelengths for the TM mode in a SiN PIC is demonstrated. Experiments show that the fabricated GCs display an ≈40 nm bandwidth and coupling losses around 13 dB per interface. In addition, we show successful biosensing experiments using bovine serum albumin and anti-bovine serum albumin as biological agents in a microfluidic environment. Further engineering for the interface should lead to lower coupling losses, which would pave the way to practical applications of SiN PICs based on RRs operated for the TM mode and at 1310 nm wavelengths.
Andrea Vogliardi, Gianluca Ruffato, Simone Dal Zilio
et al.
Abstract The availability of static tiny optical devices is mandatory to reduce the complexity of optical paths that typically use dynamic optical components and/or many standard elements for the generation of complex states of light, leading to unprecedented levels of miniaturization and compactness of optical systems. In particular, the design of flat and integrated optical elements capable of multiple vector beams generation with high resolution in the visible and infrared range is very attractive in many fields, from life science to information and communication technology. In this regard, we propose dual-functional transmission dielectric metalenses that act simultaneously on the dynamic and geometric phases in order to manipulate independently right-handed and left-handed circularly polarized states of light and generate focused vector beams in a compact and versatile way. In the specific, starting from the mathematical fundamentals for the compact generation of vector beams using dual-functional optical elements, we provide the numerical algorithms for the computation of metaoptics and apply those techniques to the design and fabrication of silicon metalenses which are able to generate and focus different vector beams in the telecom infrared, depending on the linear polarization state in input. This approach provides new integrated optics for applications in the fields of high-resolution microscopy, optical manipulation, and optical communications, both in the classical and single-photon regimes.
While most single‐nanocrystal spectroscopy experiments rely on fluorescent emission, recent years have seen an increasing number of experiments based on absorption and scattering, enabling to correlate those with fluorescence intermittency. Herein, it is shown that nonlinear scattering by second‐harmonic generation can also be measured from single CdSe/CdS core/shell nanoplatelets (NPLs) alongside fluorescence despite the weak scattering signal. It is shown that even under resonant two‐photon conditions the second‐harmonic scattering signal is uncorrelated with fluorescence intermittency and follows Poisson statistics.
A CO sensor based on photoacoustic spectroscopy (PAS) with empirical mode decomposition (EMD) algorithm is investigated and demonstrated in this paper. In the PAS system, the complicated photo-thermal-acoustic conversion is a nonlinear and non-stationary process and contains various noise. In order to compensate the low signal-to-noise ratio (SNR), the EMD is introduced in the PAS system to deal with the photoacoustic signal. The experimental results show that a gain factor of ∼3.0 on the SNR is achieved and the sensor has an excellent linear response to the gas concentration. The minimum detection level (MDL) for CO detection is reduced to 1.14 ppm with a 300 ms integrated time at room temperature and atmospheric pressure.
In this study, the hollow-core photonic crystal fiber (HC-PCF) optical switching effect in liquid nitrogen (LN<sub>2</sub>) environment is demonstrated and experimentally investigated. Turning off the light transmission is realized by the liquefaction of air present in the airholes of the HC-PCF when the fiber is immersed in LN<sub>2</sub>, and turning on the light transmission is realized by the evaporation of air when the fiber is taken out of LN<sub>2</sub>. The extinction ratio of the optical switching effect is found to be ∼50 dB; furthermore, the turn-on and turn-off time of the optical switching effect can reach ∼8 s and ∼3 s, respectively. Thus, optical switching effect in a HC-PCF in LN<sub>2</sub> environment can be easily realized, which is beneficial in building all-fiber in-line low-frequency optical-switching systems that can be potentially applied in areas such as fiber sensors.
Fabio Pavanello, Anton Vasiliev, Muhammad Muneeb
et al.
We demonstrate a broadband digital Fourier Transform (dFT) spectrometer addressing wavelength monitoring applications in the 2.3-<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m wavelength range. The spectrometer is built in a silicon-on-insulator platform and the design allows its fabrication with CMOS-compatible tools. We report an operating bandwidth of 130 nm around 2.3-<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m wavelength using an efficient algorithm for sparse spectra to retrieve the wavelength with an accuracy of 100 pm. The spectrometer can also resolve two laser lines up for dFT spectrometers, which takes advantage of the sparse nature of the spectrum.
A ZBLAN photonic crystal fiber (PCF) with normal dispersion is theoretically designed and investigated. The designed PCF can provide a large normal dispersion coefficient and a low confinement loss in a broad wavelength range of 1.8–3.6 μm. Especially, the PCF exhibits an ultra large normal dispersion value of −351.3 ps/km/nm and a small confinement loss of 0.05 dB/m at 2.9 <italic>μ</italic> m. By using the designed PCF as a dispersion compensator in a mode-locked ZBLAN fiber laser, stretched pulse with compressed pulse duration of 1.56 ps is numerically achieved.
Frequency shifts of light scattered from either a deterministic or random medium have shown great importance in remote sensing imaging applications, however, such scattering system which combines random scatterer with obstacles has not been specifically discussed so far. To solve this problem, we derive analytical expressions for showing the phenomenon that the Young's pinhole wave scattered from a quasi-homogeneous (QH) medium exhibits the red shift of spectral lines, while the first-order Born approximation is applied to treat the weak scattering between the diffractive wave and the medium. The shifted amount of spectrum is strongly dependent of the scattering angle, correlation length of the medium, and Young's pinhole parameter. Furthermore, we also observe that the red shift of the scattered spectrum converts to the blue shift when the correlation length reaches a certain magnitude. Through numerical simulations, analyses are performed on revealing the effects of Young's pinhole parameter and medium's correlation on the spectral shift and spectral switch of the scattered spectrum.