Abstract: A fiber type light wave-length converting apparatus having a fiber type light wave-length converting element and an axicon lens. The fiber type light wave-length converting element is arranged to a position relative to the axicon lens satisyfing a predetermined condition, whereby an SH wave of a parallel light having a circular intensity distribution is obtained.

Abstract: A fiber wavelength modulator device which emits a secondary harmonic component by Cerenkov radiation, including a core being a single crystal of a non-linear optical material and a cladding being composed of glass, wherein the relative difference between the core and the cladding has a refraction index with respect to an incident beam, of at lesat 0.015.

Abstract: A fibre-type light wavelength conversion device for converting the wavelength of an incident light beam and issuing the incident light beam as a light beam having a predetermined wavelength, having a core and a cladding layer around the core. The device is characterized by the provision of a transparent cylindrical layer provided around the cladding layer, having a refractive index substantially equal to the refractive index of the cladding layer and having a predetermined wall thickness. According to a feature of the invention the wall thickness is determined so that the condition d>l tan .theta. is satisfied, where d represents a diameter of said cylindrical layer, l represents an operating length of the device, and .theta. represents Cerenkov angle.

Abstract: A fibre-type light conversion device comprises a fibre-type light conversion element for converting the wavelength of an incident light and an optical system which introduces a light beam from a light source to the light conversion device as the incident light. The optical system is provided with a phase-shifting device which rotates the plane of polarization of the incident light. With this provision it is possible to set the efficiency of light conversion at a maximum level without necessity of rotating the light conversion element.

Abstract: A fibre-type light wavelength conversion device comprises a fibre-type wavelength conversion element for changing the wavelength of an incident light and a prismatic means for transforming said incident light, whose wavelength has been changed by said wavelength conversion element, into a parallel light, wherein said prismatic means is a Fresnel lens comprised of a plurality of concentric conical ring zones whose cross-section including its optical axis has a saw-tooth shape or comprised of a same pitch circular grating. Furthermore, a vertical angle of a surface of emergence of said conical ring zones is determined so as to satisfy the following equations of:sin x=n.sing yy+z=(.pi./2)-.alpha.cos .alpha.=n.

Abstract: A fibre-type light conversion device comprises a fibre-type conversion element for changing the wavelength of an incident light and a converging lens for converging said incident light whose wavelength is changed by the conversion element. The device is characterized in that the converging lens is a single lens having an aspherical surface configured such that a distance Zi from a plane perpendicular to an optical axis of the lens and passing an extremity of the lens to a point on the aspherical surface having a height Y from the optical axis is expressed by the following equation ##EQU1## where Ci is an inverse number of the radius of curvature of the "i"th surface at an intersecting point between the "i"th surface and the optical axis, Ki, A.sub.1 (i).about.A.sub.10 (i) are constants, and Y is the height from the optical axis to the refracting surface.