Measurement of the group dispersion of the fundamental mode of holey fiber by white-light spectral interferometry

We present a new method for measuring the group dispersion of the fundamental mode of a holey fiber over a wide wavelength range by white-light interferometry employing a low-resolution spectrometer. The method utilizes an unbalanced Mach-Zehnder interferometer with a fiber under test placed in one arm and the other arm with adjustable path length. A series of spectral signals are recorded to measure the equalization wavelength as a function of the path length, or equivalently the group dispersion. We reveal that some of the spectral signals are due to the fundamental mode supported by the fiber and some are due to light guided by the outer cladding of the fiber. Knowing the group dispersion of the cladding made of pure silica, we measure the wavelength dependence of the group effective index of the fundamental mode of the holey fiber. Furthermore, using a full-vector finite element method, we model the group dispersion and demonstrate good agreement between experiment and theory

Plug&Play Fiber‐Coupled 73 kHz Single‐Photon Source Operating in the Telecom O‐Band

A user‐friendly, fiber‐coupled, single‐photon source operating at telecom wavelengths is a key component of photonic quantum networks providing long‐haul, ultra‐secure data exchange. To take full advantage of quantum‐mechanical data protection and to maximize the transmission rate and distance, a true quantum source providing single photons on demand is highly desirable. This great challenge is tackled by developing a ready‐to‐use semiconductor quantum‐dot‐based device that launches single photons at a wavelength of 1.3 µm directly into a single‐mode optical fiber. In the proposed approach, the quantum dot is deterministically integrated into a nanophotonic structure to ensure efficient on‐chip coupling into a fiber. The whole arrangement is integrated into a 19ʺ compatible housing to enable stand‐alone operation by cooling via a compact Stirling cryocooler. The realized source delivers single photons with a multiphoton events probability as low as 0.15 and a single‐photon emission rate of up to 73 kHz into a standard telecom single‐mode fiber.BMBF, 05M20ZBM, Forschungscampus MODAL - Mathematical Optimization and Data Analysis Laboratories - zweite Förderphase (Stabilisierung)TU Berlin, Open-Access-Mittel – 202

Dispersion of the group birefringence of a calcite crystal measured by white-light spectral interferometry

We present a white-light spectral interferometric technique employing a low-resolution spectrometer for a direct measurement of the dispersion of the group birefringence of a calcite crystal over the wavelength range approximately from 490 to 780 nm. The technique utilizes a tandem configuration of a Michelson interferometer and a calcite crystal of known thickness to record a series of spectral interferograms and to measure the equalization wavelength as a function of the optical path difference (OPD) in the Michelson interferometer, or equivalently, the wavelength dependence of the group birefringence of the calcite crystal. We confirm that the measured group birefringence dispersion agrees well with that described by the dispersion equation proposed by Ghosh. Furthermore, we determine precisely the thickness of the calcite crystal from the slope of linear dependence of the measured OPD on the group birefringence given by the dispersion equation

Broad spectral range measurements and modelling of birefringence dispersion in two-mode elliptical-core fibres

We present the results of measurement and modelling of the birefringence dispersion in elliptical-core fibres (ECFs). The measurement is performed over a broad wavelength range (e.g. 450–1450 nm) by two spectral interferometric techniques. First, a technique employing a tandem configuration of a Michelson interferometer and an ECF under test is used for a broad spectral range measurement of the group modal birefringence for two spatial modes supported by the fibre. Second, a method with a lateral point-like force acting on the fibre and based on spectral interferometry is used for measuring the phase modal birefringence at one wavelength for the fundamental mode only. The measured value is combined with the dispersion of the group modal birefringence to obtain the phase modal birefringence over a broad wavelength range. We also modelled the dispersion characteristics taking into account contributions of both the elliptical shape of the core and the residual thermal stress. The dispersion characteristics measured for the three ECFs show very good agreement with the results of numerical modelling

Measurement and modelling of dispersion characteristics of a two-mode birefringent holey fibre

Employing several interferometric methods, we measured in a broad spectral range the wavelength dependences of the phase modal birefringence and the polarization mode dispersion for the LP01 and even LP11 spatial modes supported by a birefringent holey fibre. We also determined the wavelength dependence of the intermodal dispersion between the X- and Y-polarized LP01 and even LP11 spatial modes. Furthermore, using a full-vector finite-element method, we modelled all the measured dispersion characteristics and demonstrated good agreement between experimental and theoretical results

Point-by-point fiber bragg grating inscription in free-standing step-index and photonic crystal fibers using near-ir femtosecond laser

We report what we believe to be the first highly symmetric first-order IR femtosecond laser fiber Bragg gratings within the telecommunications C band in free-standing optical fiber, fabricated with a relatively low NA lens and without use of oil immersion techniques. This grating features the smallest dimensions for a pointby-point fiber grating reported so far (to our knowledge). This achievement paves the way to rapid mass manufacturing of highly efficient and stable Bragg gratings using ultrafast lasers in any type of fiber. Mastering this femtosecond grating inscription technique also allowed the fabrication of the first Bragg gratings with direct near-IR femtosecond inscription in photonic crystal fibers, and without the use of techniques that rely on the compensation of the holey structure