Abstract: A core part of a multimode optical fiber including the core part and a cladding part has a structure composed of a plurality of concentric layers in which a refractive index is decreased stepwise from a first core layer as an innermost layer to a third core layer as an outermost layer. The structure having the plurality of layers is formed by adjusting a quantity of addition of fluorine to silica glass. Fluorine is added to the cladding part so that a refractive index is lower than that of the third core layer as the outermost layer of the core part.

Abstract: An optical fiber is formed for use in optical communications systems capable of transmitting and receiving a large volume of information. The optical fiber has a chromatic dispersion of at least 4 ps/nm/km and at most 15 ps/nm/km at a wavelength of 1,550 nm, a transmission loss of at most 0.190 dB/km at a wavelength of 1,530 to 1,570 nm, and an effective cutoff wavelength measured by the 2-meter method of 1610 nm or more. An optical transmission line and an optical communications system are structured by using the foregoing optical fiber.

Abstract: A core part of a multimode optical fiber including the core part and a cladding part has a structure composed of a plurality of concentric layers in which a refractive index is decreased stepwise from a first core layer as an innermost layer to a third core layer as an outermost layer. The structure having the plurality of layers is formed by adjusting a quantity of addition of fluorine to silica glass. Fluorine is added to the cladding part so that a refractive index is lower than that of the third core layer as the outermost layer of the core part.

Abstract: An optical fiber suitable for use in optical communications systems capable of transmitting and receiving a large volume of information. The optical fiber has a chromatic dispersion of at least 4 ps/nm/km and at most 15 ps/nm/km at a wavelength of 1,550 nm and a transmission loss of at most 0.190 dB/km at a wavelength of 1,530 to 1,570 nm. The optical fiber comprises an inner core (refractive index: n1) including the optical central axis, an outer core (refractive index: n2) encircling the inner core, and a cladding (refractive index: n3) encircling the outer core. The relationship between the refractive indexes is expressed as n1>n2>n3. The inner core is made of practically pure silica glass undoped with GeO2. The outer core and the cladding are doped with a refractive-index-reducing dopant such as fluorine. An optical transmission line and an optical communications system are structured by using the foregoing optical fiber.

Abstract: In a method of manufacturing a porous glass preform for an optical fiber which preform is formed as a deposit of fine glass particles by using a burner, a method to prevent the contamination of any glass particles having failed to be properly deposited so that the generation of voids may be minimized in a transparent glass preform which is produced by heating the porous glass preform. An inert gas is caused to flow through the burner at a rate of at least 25 m/s before fine glass particles are formed by the hydrolysis and/or oxidation of a glass material in a flame produced by the burner supplied with a mixture of a gas of the glass material and a gas for combustion and are deposited on a rotating starting member. It is desirable to elevate the pressure of the inert gas above the atmospheric pressure by a device connected to the burner by a pipeline, and cause it to flow rapidly through the burner.

Abstract: In a method of manufacturing a porous glass preform for an optical fiber which preform is formed as a deposit of fine glass particles by using a burner, a method to prevent the contamination of any glass particles having failed to be properly deposited so that the generation of voids may be minimized in a transparent glass preform which is produced by heating the porous glass preform. An inert gas is caused to flow through the burner at a rate of at least 25 m/s before fine glass particles are formed by the hydrolysis and/or oxidation of a glass material in a flame produced by the burner supplied with a mixture of a gas of the glass material and a gas for combustion and are deposited on a rotating starting member. It is desirable to elevate the pressure of the inert gas above the atmospheric pressure by a device connected to the burner by a pipeline, and cause it to flow rapidly through the burner.

Abstract: The present invention relates to a tape cassette suitable for VTRs which allows mounting of two kinds of tape cassettes whose outer dimensions are different from each other. The tape cassette has a front cover for covering a magnetic tape stretched in the front of a cassette body and a rear cover for covering the rear side of the magnetic tape, and the front edge of the upper surface of the rear cover is arranged to be normal to the upper surface of the cassette body so as to prevent error-insertion and to allow simple and sure insertion into a VTR and provide an excellent air-tightness, resulting in the prevention of image deterioration due to increase of drop out caused by entering of dust and so on.

Abstract: The present invention relates to a magnetic recording and reproducing system of a rotary head type in which a video signal of a predetermined unit and audio signals corresponding to the video signal of the predetermined unit are sequentially recorded on and reproduced from a magnetic tape as a single record locus which is slanted with respect to the longitudinal direction of the magnetic tape by rotary heads. Two pairs of rotary heads are used as the rotary heads and the video signal and the audio signals to be processed are recorded by one pair of preceding heads among those two pairs of heads, while upon reproduction, the audio signals are reproduced by one pair of preceding heads and the video signal is reproduced by one pair of delayed heads. The reproduced audio signals and the video signal are processed to thereby obtain the video and audio signals in which the timings are coincident.

Abstract: A tape cassette for use in a video tape recorder or the like, which includes a cassette main body having an upper case and a lower case fitted to each other to define the main body, and a front cover movably mounted on the cassette main body for covering a magnetic tape stretched along a front face of the cassette main body, and is characterized in that there are provided a protrusion formed at the lower portion of the front cover so as to extend in a direction toward the lower case, and a corresponding protruding portion formed on the lower case so as to extend in a direction toward the magnetic tape, and thus, upon closure of the front cover, the protrusion of the front cover is adapted to be located at a position below the protruding portion of the lower case.

Abstract: An improved standard size video cassette has a top shell and a bottom shell held together so as to define a rectangular casing for storing therein a magnetic tape wound on reels. The bottom shell is formed with a groove having a width sufficiently wide to receive the projection therein with hardly any contact during cassette insertion into or ejection from the holder. An improved reduced size video cassette has a top shell and a bottom shell held together so as to define a rectangular casing for storing therein a magnetic tape wound on reels. The bottom shell is formed with the groove which is located such that a distance between the center of the groove and one end of the rectangular casing is slightly smaller than the distance between a center of the projection and one of the opposite side plates.