Effect of Phase Noise on the Frequency Calibration of a Tunable Laser by Heterodyne Signal Filtering

Using a frequency comb as frequency reference to calibrate the instantaneous frequency of a tuning laser allows high spectral resolution and a wide calibration range. To obtain the instantaneous frequency of the laser under test, a classical method consists in filtering the heterodyne signal between the frequency comb and the tunable laser with a narrow bandpass filter. For free-running femtosecond lasers, the phase noise of the comb lines affects the instantaneous frequency of the heterodyne signal and the envelope of the filtered calibration signal. In this paper, the characteristics of the frequency calibration signal envelope is analyzed by modeling. Three different filters are used to determine the envelope characteristics. Simulation results show that the probability density function (pdf) of the envelope amplitude tend to be a uniform distribution at higher phase noise level. At low tuning speed, the pdf distributions are the same at symmetric frequency positions of the passband of the filter. At high tuning speed, their distributions become different. The standard deviation of the center of mass becomes larger at higher phase noise level and higher tuning speed

Ultra-narrow photonic nanojets through a glass cuboid embedded in a dielectric cylinder

A glass cuboid, embedded inside a dielectric cylinder is studied when illuminated with a monochromatic plane wave. A photonic nanojet (PNJ) with a full-width at half-maximum (FWHM) waist of around 0.25λ0 is obtained outside the external surface of the cuboid. The influence of the parameters of a square section cuboid is studied. Three particular phenomena can be obtained and are discussed: an ultra-narrow PNJ on the external surface of the cuboid, a long photonic jet and the excitation of whispering gallery modes (WGMs). A parametric study, over the width and the height of a rectangular section cuboid, shows that these parameters can be used to control the photonic jet properties. We also study several other geometries of the insert, which shows that the key parameter is the refractive index of the inserted material. Finally, we show that by changing the incident angle we can obtain a curved photonic jet

Roadmap on Label-Free Super-resolution Imaging

Label-free super-resolution (LFSR) imaging relies on light-scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super-resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state-of-the-art in this field, and to discuss the resolution boundaries and hurdles that need to be overcome to break the classical diffraction limit of the label-free imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction-limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super-resolution capability that are based on understanding resolution as an information science problem, on using novel structured illumination, near-field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere-assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field.Peer reviewe