Abstract: An optical transmission system of the present invention includes input ports to which laser beams are respectively input, condensing, input optical elements, input reflectors corresponding one-to-one to the input optical elements each, output reflectors, output optical elements, and output ports. Assume that maximum one and minimum one of optical distances between the input optical elements and the output optical elements are DL and DS, respectively. Then, the beam waist position Q of the laser beam output from the input optical element closest to the input port satisfies a relation: 0.9(DL+DS)/4?Q?1.1(DL+DS)/4.

Abstract: A first actuator for controlling positions of all of a plurality of heads within a wide area and a plurality of second actuators for individually controlling the heads within small areas are provided. When two or more of the heads are in write or read state, one or more of the heads, which are not in write or read state, is preliminarily move to a track position to be accessed next.

Abstract: An optical transmission system of the present invention includes input ports to which laser beams are respectively input, condensing, input optical elements, input reflectors corresponding one-to-one to the input optical elements each, output reflectors, output optical elements, and output ports. Assume that maximum one and minimum one of optical distances between the input optical elements and the output optical elements are DL and DS, respectively.

Abstract: A head position signal demodulator that demodulates a position signal indicating the position of the magnetic head in the disk radius direction based on a servo pattern recorded on the magnetic disk includes a waveform shaping circuit which shapes an input signal obtained from the magnetic head according to the servo pattern and a phase comparison circuit which compares a phase of an output signal of the waveform shaping circuit and a phase of a reference signal and outputs a phase difference signal. The head position signal demodulator also includes a position signal generation circuit that generates a position signal of the magnetic head based on the phase difference signal, and a phase shifter which changes the phase of the reference signal during micro jogging, for an amount of the phase which has been set according to the amount of the micro jogging.

Abstract: In a magnetic disk apparatus performing a positioning operation in a sector servo system, an AGC amplification gain measuring circuit measures an amplification gain of an AGC amplifier on the basis of the reproduction of a magnetic pattern in an AGC region within a servo area of a magnetic disk. An AGC amplification gain judgment circuit judges whether the value of the amplification gain measured by the AGC amplification gain measuring circuit is out of a set range, and outputs the judgment result. When receiving from the AGC amplification gain judgment circuit a judgment result indicating that the value of the amplification gain is out of the set range, a recording/reproducing operation control circuit stops the recording operation of a recording circuit.

Abstract: In order to avoid appearance of indifferent zone of positioning signals obtained from a burst pattern recorded on a magnetic disk because of erase bands derived on outer border lines of burst tracks, width of a magnetic gap of the reproducing head of the invention is designed to be not narrower than width of a pitch of the burst tracks added with width of the erased band and not wider than two times of said width of a pitch of the burst tracks reduced of said width of the erased band.