Abstract: An optical transmission apparatus including a port for connection to an optical fiber for releasing non-visible laser light for transmission through the optical fiber. The optical transmission apparatus includes a visible light generator optically connected to the port for releasing at the port a visible light tracer for propagation in the optical fiber with the non-visible laser light.

Abstract: The effects of dispersion of light on a link having an optical transmission fibre characterised by positive dispersion and large positive relative dispersion slope can be reduced by employing a sufficient length of dispersion compensating fibre (“DCF”) so that dispersion slope on the link is substantially nulled and the net dispersion of the link is made negative. Optical signals launched on the link with a positive chirp will be compensated for by the net negative dispersion.

Abstract: Some optical transmission fibers, such as LEAF and EFEAF, have a positive dispersion slope too great to be fully compensated for by a dispersion compensation fiber (DCF). To achieve improved dispersion compensation for such transmission fibers, the signals may be passed through a non-dispersion shifted fiber (NDSF) as well as through a DCF.

Abstract: The problems of maintaining proper alignment of the mirrors of an excimer laser in the face of thermal and pressure distortions of the ends of the laser vessel and when replacing the mirrors after removal for cleaning are overcome by mounting the mirrors on a separate, fixed supporting frame that is not influenced by movement of the vessel ends. The mounts nevertheless serve to connect the mirrors to the respective vessel ends so as to seal the pressurized gases in the vessel interior from the exterior. This sealing connection is a yielding one that permits relative movement between the vessel ends and the mirrors and hence avoids affecting the alignment of the mirrors. The mounts also include provision for ensuring that, after removal and replacement, wedge shaped mirrors are correctly realigned in respect of rotation about the axis of the laser beam, and that the mirrors can be replaced with their reference surfaces in exactly the original plane.

Abstract: Purification of the gas mixture used in an excimer laser is carried out by cooling such mixture in a cryogenic trap to a temperature that is low enough that the lasting gas or gases (e.g. krypton, xenon, fluorine, hydrogen chloride) and the impurities are all substantially fully condensed. This temperature is nevertheless sufficiently high that the buffer gas (neon or helium or a mixture thereof) remains substantially all in gaseous form. The trap is then isolated from the laser vessel and the condensed gases therein are treated to remove at least the condensed impurities from the system. In a xenon chloride laser the condensed impurities can be effectively separated from the condensed laser gases by heating, i.e. differential distillation. After this has been done, the laser gases are returned to the laser vessel. In those instances in which such separation by differential distillation is not practicable, e.g.