Patent SE-529915-C2 (SE)
Title: Controlling intensity and polarization of light beam propagated using non linear Bragg lattice, by altering strength of applied magnetic field, directing beam into lattice and shifting narrow transmission bands
Inventor: JONSSON KARL FREDRIK
IPC: G02F1/01
Filed: 2005-12-22
Abstract: The method comprises the following steps: (1) applying a magnetic field in the direction for refraction index modulation in the Bragg lattice, in order to increase polarization state degeneration in the narrow transmission band by means of the Faraday effect, such that the band is shifted for the respective orthogonal circular polarized state in opposite directions in the spectrum, creating a first and second narrow transmission band each corresponding to an orthogonal circular polarized transmitting state; (2) altering the strength of the magnetic field so that the first and second bands become distinctly separated from each other; (3) directing the beam into the lattice so that is oriented along the magnetic field and has an optical frequency which at a weak optical intensity corresponds to the optical frequency at which the first band has a maximum, allowing the lattice to transmit only one of the circular polarized components of the beam at a weak optical intensity; and (4) shifting the first and second bands in a spectral direction by an intensity-dependent refraction index during exposure to an intense optical field, so that the lattice can alternate between transmission and reflection of the orthogonal circular polarized state of the beam. For controlling the intensity and polarization state of an optical signalling beam of light propagated via a non-linear magneto-optical Bragg lattice in which at least one defect layer opens up a narrow transmission band spectrum within the remaining high reflectance spectral regions defined by the Bragg resonance conditions for the lattice. Independent claims are also included for the following: (A) Optical component for controlling intensity transmission and transmitted polarization state, comprising a stack of non-linear magneto-optical layers with alternating refraction index values and/or magneto-optical gyration coefficients, at least one layer being a defective one having a different optical thickness than the other layers in the rest of the periodic structure, the optical thickness being defined as the geometric thickness multiplied by the layer refraction index; a means for applying a magnetic field through the stack; with the exception of the defective layer, the stack is designed to provide high reflectance at a predetermined optical design wavelength, the optical thickness of the layer varying by not more than 10% of one quarter of this wavelength; the defective layer opens at least one narrow transmission band for each circular polarized state for the light, within the rest of the high reflectance spectral region defined by the periodic structure of the stack; the applied field is strong enough to separate the narrow band for the orthogonal circular polarization state of the light by at least half the width of the widest narrow transmission bands; the field is applied in the normal direction towards the plane of the magneto-optical layer; the signal beam and intense light beam are both directed into the double cone formed at 30 deg. to the direction normal to the plane of the magneto-optical layer; and at least one of the defective layers has an intensity-dependent refraction index (optical Kerr effect) large enough to cause a spectral shift of the narrow transmission band by at least half the width of the widest of the narrow transmission bands, allowing changes in the orthogonal transmitted circular polarization states; (B) Optical system comprising an optical circulator transmitting a beam entering via a first port and exiting via a second port at the same time as light entering the second port is transmitted further via a third port without it reaching the first port; the above optical component; an optical two-to-one connector which adds light entering via a first port to light entering via a second port and transmits the superposed light as an optical signal exiting via a third port, so that the light from the second and third ports of the optical circulator is combined to form a common output signal; and a means for directing and combining the optical beams via the system components; (C) Method for controlling the polarization state of light using the optical system, by directing the signal beam into the first port of the circulator; transmitting the beam from the second port of the circulator; directing the transmitted beam into the optical component so that it becomes divided into a reflected and transmitted beams; directing the reflected beam into the second port of the circulator, extracting it via the third port of the circulator, and directing it into the first port of the connector; directing the transmitted beam into the second port of the connector; and extracting the beams superposed using the connector to form an optical beam.; and (D) Information transmission system comprising the optical system; a light source for generating an optical carrier wave for the signal beam, including a polarizing optical component; a pulsing light source for optically modulating the system, including a polarizing optical component; a control unit for the pulsing light source; a component for generating a magnetic field; a power source for the magnetic field generating component; an optical detector; and an optical signal analyzer with a feedback connection to the control unit.