The subject matter of the present invention relates generally to light beam deflection apparatus employing an optical fiber which is deflected by a transducer in response to an electrical control signal, and in particular to such an apparatus in which the transducer includes a deflection means attached to the optical fiber and connected to a source of electrical current for deflection of the fiber by movement of such deflection means. The optical fiber deflection device of the present invention is especially useful for scanning optical records of high density data recorded in tracks of data spots representing digital information, as shown in U.S. Pat. No. 3,501,586 of Russell, granted Mar. 17, 1970, or analog information such as the pulse length or frequency modulated data spots of U.S. Pat. No. 3,530,258 of Gregg et al, granted Sept. 22, 1970.
Previously it has been proposed in U.S Pat. No. 3,470,320 of Pike et al, granted Sept. 30, 1969, to provide a light scanner including an optical fiber which is deflected electrostatically or electromagnetically. Electromagnetic deflection apparatus has an advantage over electrostatic deflection apparatus since it is of lower impedance which is more suitable for the transistors used to drive the deflection circuits. However, in the electromagnetic deflection apparatus of Pike, a metal armature of iron or other magnetic material is attached to the glass fiber to enable such fiber to be deflected by electromagnets whose coils are connected to the sources of the deflection signals. This has the disadvantage that the mass which must be moved in order to deflect the fiber is greatly increased, thereby reducing the maximum frequency response and increasing the signal amplitude which must drive the electromagnets. A similar problem is created by the optical fiber deflection apparatus shown in the above-mentioned U.S. Pat. No. 2,530,258 which employs an optical fiber mounted on a strip of magnetic material which greatly increases the mass that is deflected.
The above-mentioned problems are overcome by the optical fiber deflection device of the present invention. In the preferred embodiment of the electromagnetic deflection apparatus of the invention, a romagnetic deflector means formed by a thin wire or conductive layer, is attached to the surface of the fiber and electrical current is caused to flow through such wire or conductive layer to produce a magnetic field around the fiber. The surrounding magnetic field enables the optical fiber to be deflected by an electromagnet or other electromagnetic transducer means in accordance with a control signal applied thereto. As a result of the decrease in mass of the deflected fiber and the conductive element attached thereto, the deflection device of the present invention is capable of operating at a greater frequency and consumes less power than that of the prior art. In addition, other embodiments of the present invention are described using different transducer means for deflecting the optical fiber.
When the optical fiber is employed to scan the light beam along the data track of an optical record, the deflection device of the present invention may be used for tracking purposes to deflect such beam laterally with respect to the center of the track in order to maintain such beam on the track at all times. Such a tracking means is much less expensive and has a faster response than conventional mechanical tracking and those employing rotating mirrors or other moving optical elements. Furthermore, the optical system can be simplified when using an optical fiber of the self-focusing type, such as that described by Uchida et al in "IEEE Journal of Quantam Electronics," Vol. QE-6, No. 10, October 1970, pages 606 to 612. Since the index of refraction of the glass in a self-focusing fiber decreases with increasing distance from its center, such fiber focuses the input light beam to a small focal point at its output. The self-focusing fiber may be provided with a conical input end which focuses the light rays to a narrow beam within the fiber so that a converging lens need not be employed between the input end of the optical fiber and the light source. In addition to the tracking deflection transverse to the data track, a second deflection motion parallel to the data track can be provided by a second transducer for scanning or for correcting errors in the record, such as when the data tracks are not concentric with the scanner wheel carrying the objective lenses used for scanning. It is also possible to provide deflection in a third direction perpendicular to the record for maintaining the light beam in focus on the data track. This can be accomplished by bending the fiber to provide a fiber portion parallel to the record and deflecting such fiber portion with a third transducer.
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