Abstract: The invention relates to an optical system for converting the frequency, and thereby the wavelength, of a single photon and a method for converting the frequency of a single photon by difference-frequency generation (DFG). Further, the invention relates to a frequency converter. A single photon with a first wavelength (?p) and a laser irradiation with a second wavelength (?i) are arranged for combining in a multiplexer and transmitted to a nonlinear waveguide. The multiplexer comprises two input waveguides for receiving the single photon and the laser irradiation and is combining them in one of the waveguides from where it is transmitted to the nonlinear waveguide. In the nonlinear waveguide, the single photon interacts with the laser irradiation and the material of the nonlinear waveguide, so as to frequency convert the single photon from the first wavelength (?p) to a third wavelength (?s).

Abstract: A laser source device including a pump laser system, a combinator, and nonlinear frequency generation module. The pump laser system is made of one of more laser diodes, each of which generates one or more light beams whose wavelengths are in the visible spectral range having a wavelength in the range 380 nm to 740 nm. The combinator allows passing of the light beams from the pump laser system and combines them and couples them to the next module. The nonlinear frequency generation module allows passing of the light beams and, while passing through, employs nonlinear optical phenomenon of sum-frequency generation for providing a UVC light beam.

Abstract: A method or apparatus for narrowing the linewidth of a single mode laser is provided. The linewidth of a single mode laser is narrowed by injecting an optical feedback simultaneously into the first laser cavity mirror and the second laser cavity mirror of the single mode laser.

Abstract: An electromagnetic radiation frequency, or equivalent wavelength, converter, the converter including a nonlinear optical component or part having or consisting of a predetermined nonlinear optical material, and a guiding module. The guiding module has a predetermined geometry defining or controlling an effective refractive index of the guiding module, and is configured to receive and guide pump light resulting in a guided pump beam. The nonlinear component or part is bonded with or joined to the guiding module. The bonding is configured to allow at least a part of the guided pump beam to overlap and/or evanescently couple into the nonlinear optical material, and the nonlinear optical component or part is configured to convert the guided pump beam in the nonlinear optical material to an un-guided signal mode radiated as an output light signal at a different frequency or an equivalent wavelength.

Abstract: A method or apparatus for narrowing the linewidth of a single mode laser is provided. The linewidth of a single mode laser is narrowed by injecting an optical feedback simultaneously into the first laser cavity mirror and the second laser cavity mirror of the single mode laser.