Abstract: A marking method for a sintered product of the invention includes forming a concave portion on the sintered product by irradiating the sintered product with laser light thereby to write identification information on the sintered product. The depth of the concave portion is adjusted in a range between 0.1 &mgr;m and 5 &mgr;m, inclusive.

Abstract: A marking method for a sintered product of the invention includes forming a concave portion on the sintered product by irradiating the sintered product with laser light thereby to write identification information on the sintered product. The depth of the concave portion is adjusted in a range between 0.1 &mgr;m and 5 &mgr;m, inclusive.

Abstract: A radio communication analyzer tests the signal characteristics of a carrier, as a target signal to be tested, which has undergone quadrature modulation using a digital data signal output from a radio unit to be tested. A quadrature demodulation section performs quadrature demodulation of the target signal and outputs a baseband signal. A storage section stores the waveform data of the baseband signal. A clock synchronous detection section detects clock synchronization information contained in the target signal based on the waveform data. A demodulation section sequentially reads out the waveform data and obtains demodulated digital data in accordance with the clock synchronization information. A burst synchronous detection section generates burst synchronization information representing a burst start position of the target signal on the basis of the demodulated digital data or the waveform data.

Abstract: The present invention provides a method of manufacturing a porous preform for an optical fiber, including the steps of removing impure particles from silica powder while being stirred in an alkaline liquid phase, and obtaining the porous preform for an optical fiber by applying the powder forming method to the silica powder used as a main raw material. The present invention further has a method of manufacturing a porous preform for an optical fiber, including the step of preparing a forming material by adding fine particles having a particle diameter satisfying the following formula (I) to the silica powder, and obtaining the porous preform by applying the powder forming method to the forming material: ##EQU1## wherein d: diameter of fine particles, and D: diameter of silica powder.

Abstract: A process for the production of an optical fiber a core which is elliptical in cross-section at one end and circular at the other end and which has little transmission loss and less of a reduction in the difference in indexes of refraction between the core and cladding, which consists of heating an optical fiber (1) having a core (c) having a uniform cross-sectional area in the longitudinal direction and a cladding (2) formed with at least one through hole (4A) along the longitudinal direction of the core while successively changing the heating temperature along the longitudinal direction of the optical fiber so as to continuously change the shape of the through hole, continuously change the cross-sectional shape of the core along the longitudinal direction of the optical fiber, and thereby make the cross-sectional shape of the core at one end of the optical fiber and the cross-sectional shape of the core at the other end different.

Abstract: The present invention provides a method of manufacturing an optical fiber preform having the steps of disposing a rod member made of a silica-based material within a cavity of a mold, followed by loading a molding material within the mold cavity, and applying pressure to the mold from the outside to form a porous layer on the surface of the rod member and, thus, to obtain a porous preform, wherein at least one end portion of the rod member extends outside the mold cavity in the step of applying pressure to the mold. The particular method permits manufacturing a high quality porous preform free from splits or cracks, making it possible to obtain a high quality optical fiber preform free from residual bubbles.

Abstract: The method of manufacturing a silica glass preform comprises the steps of inserting a rod-like member mainly containing a ductile material, into a forming space of a mold, charging the remaining space of the forming space with a forming material containing silica glass powder or doped silica glass powder, compressing the mold charged with the forming material from outside such as to form a porous glass body of the forming material around the rod-like member, removing the rod-like member from the porous glass body, inserting a glass rod into the hole formed after removal of the rod-like member, purifying said porous glass body in which the glass rod is inserted, and consolidating said porous glass body purified in the above purifying step.

Abstract: A silica-based glass rod is inserted into a space portion of a mold. Then, a slurry, which is obtained by dispersing a silica glass powder material in pure water, is poured into a molding space between the glass rod and the inner surface of the mold, whereby a porous glass shaped body is formed around the glass rod. Drying this shaped body results in a silica glass base material which includes the glass rod and the porous glass shaped body surrounding the same.

Abstract: An extruding apparatus having at least two independent inlet ports, one outlet port communicating with the inlet ports, and at least two passages connecting the inlet ports with the outlet port, in which a section of a joint portion of the passages has a central portion and an outer peripheral portion which are concentrically arranged, is prepared. A core material is supplied to one of the passages communicating with the central portion of the joint portion from a corresponding inlet port, and a cladding material is supplied to the other passage communicating with the outer peripheral portion from a corresponding inlet port, thereby causing the two materials to join each other at the joint portion. An integral shaped body having a portion corresponding to a core at its central portion and a portion corresponding to a cladding around the central portion is extruded from the outlet port. Water and a binder and other impurities are removed from the shaped body, and the resultant body is consolidated.