Abstract: An optical pickup apparatus having first and second light sources emitting first and second light fluxes having wavelength of ?1 and ?2, respectively, an light-converging optical system including first and second objective optical elements, and a lens holder to hold the first and second objective optical elements. When the optical pickup apparatus converges the first or the second light flux onto first or second information recording surface of first or second information recording medium through one protective substrate, which has a thickness of t1 or t2 and is provided on the first or second information recording surface, with utilizing the first or second objective optical element for conducting information recording and/or information reproducing of the first or second information recording medium, a variation of each of a coma aberration and an astigmatism is not more than 0.02 ?1 rms or 0.02 ?2 rms, respectively.

Abstract: An objective optical system according to the present invention is provided for use in an optical pickup apparatus for recording or reproducing information on an information recording surface of a first optical information recording medium using a first light flux emitted from a first light source. The objective optical system is provided with: a first lens with a positive refractive power including plastic; a second lens with a positive refractive power including plastic; and a first phase structure. A wavefront aberration change amount of the objective optical system when a wavelength of the first light flux changes, and a wavefront aberration change amount of the objective optical system when an ambient temperature of the objective optical system satisfy the predefined condition.

Abstract: An objective optical system according to the present invention is provided for use in an optical pickup apparatus for recording or reproducing information on an information recording surface of a first optical information recording medium using a first light flux emitted from a first light source, and the objective system includes: a first lens with a positive reflective power including plastic; and a second lens with a positive refractive power including plastic. Opposite optical surfaces of the first lens are convex surfaces, and a refractive power of the first lens and a power of a whole system of the objective optical system satisfy the predefined condition.

Abstract: A vehicle includes a sensor sensing external temperature, a 2WD/4WD switch operated to input an instruction to switch a two-wheel drive state and a four-wheel drive state, a transfer switching mechanical power transfer for the two-wheel drive state and that for the four-wheel drive state, an actuator actuating the transfer, and an ECU controlling the actuator. The ECU determines from a value detected by the sensor a current supplied to the actuator. Preferably, the transfer includes a synchronizer mechanism driven by power generated by the actuator to transfer a drive shaft's rotation to a driven shaft and engage the shafts together when they achieve synchronous rotation.

Abstract: A vehicle includes a wheel speed sensor sensing a vehicle speed V, a 2WD/4WD switch operative to input an instruction to switch between a two-wheel driving state and a four-wheel driving state, a transfer and an actuator switching the two-wheel driving state and the four-wheel driving state, and an ECU driving the actuator. The ECU instructs the actuator to switch from the four-wheel driving state to the two-wheel driving state regardless of the switching instruction from the 2WD/4WD switch if the vehicle tows a trailer and runs in the four-wheel driving state when the vehicle speed exceeds a predetermined value. Consequently, it is possible to provide a four-wheel drive vehicle capable of running while towing an object and also avoiding an increase in the size of the peripheral parts of driving wheels.

Abstract: An optical system for use in an optical pickup apparatus has a chromatic aberration correcting element having plural ring-shaped zones divided with a stepped section in such a way that one of the neighboring ring-shaped zones located apart from the optical axis has a longer optical path than the other one located closer to the optical axis, and an objective lens having plural ring-shaped zones divided with a stepped section shaped in the optical axis direction in such a way that the stepped section causes a optical path difference between light fluxes having passed through the neighboring ring-shaped zones. The ring-shaped zonal structure of the chromatic aberration correcting element corrects a deviation of a focal point caused by the objective lens due to a wavelength fluctuation of an incident light flux coming into the optical system.

Abstract: The present invention provides an objective lens for optical pick-up devices in which the amount of change in the astigmatic aberration is small when there is a temperature distribution that is not circularly symmetric with respect to the optical axis within an objective lens constructed with at least two optical elements and which permits stable and high-speed information recording and reproduction with high-density optical disks, and to provide further an optical pick-up device provided with such an objective lens, and an optical information recording and/or reproducing apparatus employing such an optical pick-up device.

Abstract: An objective optical system for use in an optical pickup apparatus, comprises an aberration correcting element having at least two phase structures of a first and second phase structures; and a light converging element to converge the first light flux emitted from the aberration correcting element onto an information recording plane of the first optical disk and to converge the second light flux emitted from the aberration correcting element onto an information recording plane of the second optical disk; wherein the second phase structure refrains at least one of a change in the light converging characteristic of the objective optical system due to a change in the wavelength of the first light flux and a change in the light converging characteristic of the objective optical system due to a change in environmental temperature.

Abstract: An optical pick-up system comprising: a first light source for projecting a first light flux having a wavelength of not more than 450 nm; a second light source for projecting a second light flux having a wavelength within a range of 630 nm to 680 nm; an objective optical system for converging the first light flux on a first optical disk, and for converging a second light flux on a second optical disk, and having at least a plastic lens having a positive refractive power, and wherein a ratio ?SA/?T of a change of a spherical aberration to a temperature change satisfies the following expression (1); and an aberration correction optical system arranged in an optical path between the first light source and the objective optical system, and having a plastic lens having a positive refractive power and a glass lens.

Abstract: An optical pickup device comprises a light source to emit a light flux having wavelength &lgr;; an objective lens including at least two plastic lenses of a first plastic lens having positive refractive power and a second plastic lens having positive refractive power, wherein the first plastic lens and the second plastic lens are arranged in this order from the light source side; and an actuator to drive the objective lens; wherein the objective lens satisfies the following expression (1-1):

Abstract: An optical system for use in an optical pickup apparatus has a chromatic aberration correcting element having plural ring-shaped zones divided with a stepped section in such a way that one of the neighboring ring-shaped zones located apart from the optical axis has a longer optical path than the other one located closer to the optical axis, and an objective lens having plural ring-shaped zones divided with a stepped section shaped in the optical axis direction in such a way that the stepped section causes a optical path difference between light fluxes having passed through the neighboring ring-shaped zones. The ring-shaped zonal structure of the chromatic aberration correcting element corrects a deviation of a focal point caused by the objective lens due to a wavelength fluctuation of an incident light flux coming into the optical system.