Olympus Optical Company, Ltd.

Shozi Yoshikawa

Kunio Yamamiya

Hiroshi Kodama

Masaharu Sakamoto

Kiichi Kato

Ken Ohsima

Mitsugu Sakai

Masanori Doi

Haruhiko Takemura

Seizi Kitagawa

There is provided an optical information recording and reproducing system which comprises a light source, a light beam power compensation circuit which can compensate a fluctuation of an emitted light beam power from the light source in response to a detected monitor signal corresponding to a light flux from the light source, a light beam control circuit composed of at least one control loop which controls the light beam emitted from the light source and irradiates the same onto a data storing medium, and a light beam inhibit circuit which can inhibit irradiation of the light beam onto the data storing medium.

Optical information recording reproducing memory system with both power

A magneto-optical information system writes and erases information on and from a magneto-optical information recording medium under application of a bias-magnetic-field to the recording medium according to writing and erasing command signals. A differential amplifying circuit differentially processes the writing and erasing command signals to produce a differential output signal, and a constant current power amplifying circuit produces a stable drive current according to the differential output signal. A bias-magnetic-field generating coil is driven by the stable drive current so that a stable bias-magnetic-field is applied to the information recording medium according to the differential output signal.

Bias-magnetic-field generating apparatus in magneto-optical information

A plurality of supply voltages are supplied form a power supply to a semiconductor laser drive device. One of these supply voltages is applied to a discrimination circuit. The discrimination circuit includes a first zener diode, to which one of the supply voltages is applied, and which has a zener breakdown voltage corresponding to the lower limit of a threshold voltage range, and a second zener diode, to which the same supply voltage is applied, and which has a zener breakdown voltage corresponding to the upper limit of the threshold voltage range. First and second light-emitting diodes are connected in series with the respective first and second zener diodes. Light emitted from the first and second light-emitting diodes is received by respective first and second phototransistors connected in series between a voltage supply terminal and a ground terminal. A resistor is connected in parallel with the second phototransistor connected to the ground terminal. Voltage at the connection point between the first and second phototransistors is applied to the gate of a junction field-effect transistor, which has its drain grounded and its source connected to a control terminal of a switch in parallel with and for shunting the semiconductor laser.

Semiconductor laser drive device with an abnormal voltage protection

A stabilized laser device has a semiconductor laser, an optical detector for performing photoelectrical conversion of laser light from the laser and producing a detection signal, and a variable voltage power source for outputting an analog voltage signal as a preset value for the laser output light. A differential amplifier produces a differential signal representing the difference between the detection signal and the preset analog voltage signal, and a gate circuit supplies a clock pulse from a clock pulse generator to one of the up and down terminals of an up/down counter in accordance with the output signal from the differential amplifier. A D/A converter converts the output digital signal from the counter to an analog signal and supplies it to a driver circuit for the laser. The D/A converter generates an analog signal which corresponds to the product of the output digital signal from the counter and the preset analog voltage signal from the variable voltage power source.

Stabilized laser device

An apparatus for controlling the tracking of an optical disk by moving an objective lens and a carriage supporting the objective lens. The apparatus comprises a lens tracking mechanism comprising an actuator and a lens tracking circuit, and an equivalent circuit having the same response characteristic as the lens tracking mechanism. The lens tracking mechanism moves the lens in real time in the radial direction of the disk in accordance with a tracking error signal representing the distance between a laser beam spot and a target track. The carriage is moved also in the radial direction of the disk in accordance with a sine-wave signal approximating the eccentricity of the disk. The eccentricity has been detected from the distance over which the lens is moved when the carriage is not moved. This distance is not detected by measuring, but obtained from the output signal which the equivalent circuit generates in response to the tracking error signal.

Tracking control apparatus

A stabilized laser apparatus includes a semiconductor laser, a photodetector for detecting an output laser beam from the semiconductor laser, a differential amplifier for comparing the laser detection signal with a first or second reference signal, a window comparator for comparing a threshold range with an output from the differential amplifier, an up/down counter operated in response to an output from the window comparator, and a driving circuit for supplying a drive current to the semiconductor laser in accordance with a count of the up/down counter. A servo loop from the photodetector to the up/down counter is operated in response to an operation instruction signal or an adjustment instruction signal. The drive current is adjusted to coincide with a reference value before operation, and the adjusted drive current is stored in the up/down counter.

Stabilized laser apparatus

A light source degradation detecting apparatus for a laser device monitors drive currents and output laser beams. The degradation detecting apparatus includes drivers for supplying three drive signals to the laser, a photodiode for detecting laser outputs produced in response to the drive signals, a memory for storing measured values and the drive signals, and a discriminator for calculating ratio P from storage data (laser outputs W.sub.n, W.sub.n+1, and W.sub.n+2 produced in response to drive currents I.sub.n, I.sub.n+1, and I.sub.n+2) as follows:

Light source degeradation detecting apparatus for laser device

In a stabilized laser device of an optical recording/reproduction apparatus, in the reproduction mode, a laser beam of reproduction level is radiated on an optical disk, and data is read from the disk in the form of the light reflected from the disk. In the recording mode, a laser beam of the recording level (several times higher than the reproduction level) is radiated on the disk to form pits in the disk surface. The device has a semiconductor laser, a reference voltage generation source for generating reference values of the reproduction and recording levels, and a photodiode for photoelectrically converting laser light from the semiconductor laser so as to generate a detection signal a source of drive signals is provided for generating a first drive signal corresponding to the difference between the reference value of the recording level and the detection signal from the photodiode, and a second drive signal corresponding to the difference between the sum of reference values of the recording and reproduction levels and the detection signal from the photodiode. A switch supplies, in the reproduction mode, the first drive signal to the semiconductor laser and, in the recording mode, supplies one of the first drive signal and the sum of first and second drive signals in accordance with recording data.

Stabilized laser device of optical information recording/reproduction

A laser beam emitted from a semiconductor laser is detected by a PIN type photodiode. A forward bias source or a reverse bias source is coupled to the photodiode through a switch. When a power source is turned on, the switch is switched to connect the forward bias source to the photodiode. A forward bias current is applied to the photodiode. At this time, a driver circuit has not yet been supplying a drive current to the semiconductor laser. With a forward bias current applied, a forward voltage drop is generated across the photodiode. A discrimination circuit compares the forward voltage drop to a reference voltage range. When the forward voltage drop is outside the range, it is determined that the photodiode is abnormal, and the driver circuit is controlled such that no drive current is supplied to the semiconductor laser. When the forward voltage drop is in the reference voltage range, the operation of the driver circuit is started, and the switch is switched to connect the reverse bias source to the photodiode. Therefore, the semiconductor laser is caused to effect intensity modulation oscillation according to an externally supplied modulation signal. The photodiode supplies a photoelectric conversion signal corresponding to the quantity of received light to an APC circuit, so that the output of the semiconductor laser is controlled for stabilization.

Semiconductor laser driver

An input signal containing a base line which fluctuates to a great extent is detected or restored by comparing the input signal with reference levels which are shifted in accordance with the fluctuation of base line. The input signal is sampled at a variable sampling rate and an average of sampled values for a predetermined period is derived to produce a profile signal which resembles accurately the fluctuation of the base line. The profile signal thus obtained is added to upper and lower threshold voltages to produce the reference levels which have been corrected in accordance with the fluctuation of the base line of input signal.

Apparatus for detecting input signal

In order to read out information recorded on a disc rotating at a constant angular velocity by means of a pick-up head movably arranged in a disc radius direction, a head position on the disc is detected to obtain a position signal representing a distance from a disc center to the pick-up head, and then a pulse signal having a frequency corresponding to the position signal thus obtained is generated. A detection signal supplied from the pick-up head and the pulse signal are supplied to an AND gate and pulses of the gated out pulse signal are counted by a counter. The number of the counted pulses represents correctly a length of the information recorded on the disc irrespective of position of the information on the disc.

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Tokyo, Japan

Shozi Yoshikawa