JPS5956239A - Optical head - Google Patents

Abstract

PURPOSE:To form a reading part which is small-sized and lightweight and can be moved at a high speed, by transmitting a reflected luminous flux to a detecting means by a polarization plane preserving optical fiber. CONSTITUTION:The luminous flux from a laser light source 1 is led to an optical fiber 12 by a condenser lens 22. This optical fiber is so-called a polarization plane preserving optical fiber; and when linearly polarized light having an oscillating plane in a proper direction is made incident to one end of this optical fiber, the polarized light is transmitted to the other end while keeping the oscillating plane as it is. A condenser lens 4 condenses the luminous flux onto a photomagnetic recording medium 6 through a substrate 5, and the reflected luminous flux is reflected by a beam splitter 3 and is condensed by a condenser lens 13 and is led to an optical fiber 14. This optical fiber 14 is a polarization plane preserving optical fiber to transmit a pair of beams of linearly polarized light orthogonal to each other independently of each other, and photomagnetic recording information is read out by photodetectors 10 and 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical head that optically reads information magnetically recorded on an information medium.

Magneto-optical recording materials and the like are known as information carriers such as those described above, and the 74'ff button for recording information has the effect that when a linear deflection is reflected by a magnetic film, its vibration plane rotates ( Magneto-optical corrosion (effect) is widely used. An example of a conventional optical head used for reading such information is shown in FIG. In FIG. 1, the collimation lens 2 converts the light beam radiated from the laser light source 1 into a 3V-row beam by the collimation lens 2.

The light passes through the tin litter 6 and is focused by the L lens 4 (therefore, the light is focused on the substrate 5 to form a small spot on the recording medium 6. Magneto-optical recording medium 6
The 70 beams, whose vibration planes have been rotated by a small angle, pass through the condenser lens 4 and become parallel beams, and are sent to the beam splitter 6.
After being reflected by the polarizing beam splitter 7, which is used for differential amplification,
reactor. One of the divided light beams is condensed onto a photodetector 10 by a condensing lens 8, and the light beam on the fLIJ side is condensed onto a photodetector 11 by a YJ lens 9. The difference between the optical outputs detected by each photodetector is taken by an amplifier with a difference σ (not shown), and a signal with a high signal-to-noise ratio is read.

The principle of signal +j detection performed by a polarizing beam splitter is shown in Fig. 2 (a), (1)).
Figure (al) is a diagram showing the relationship between the vibration plane of the incident linearly polarized light and the vibration plane of the reflected light beam. In the figure, 100 is the vibration direction of the incident light beam, 101 is the information *t: 117F even 11 Vibration direction of the light beam reflected from the dark part, 10
2 indicates the vibration direction of the reflected light beam from the information recording portion. Here, the IH signal is recorded by changing the magnetization direction of the recording medium, and the luminous flux changes as shown in Fig. 2(a). ij! □ Corresponding to the ratio direction, the vibration surface is rotated in the opposite direction due to the magneto-optical Kerr effect and reflected. Usually, this rotation angle (Kerr rotation angle) is a minute angle of 1° or less. FIG. 2(b) shows reflected light from areas where no information is recorded. By setting the transmission vibration plane of the polarizing beam splitter 7 in FIG. 1 at 45° Jj with respect to the direction 101, the amount of light detected by the photodetector 10 in FIG. 1 corresponds to the arrow 106. The amount of light detected by the photodetector 11 is indicated by arrow 1.
The light corresponding to 04 is 8. As a result, the difference between the two becomes zero, and on the other hand, in the light beam 102 from the information recording portion, the two amounts of dust are equal, so a signal is output, making it possible to read the information. The advantage of such differential sensing is that
This not only increases the apparent degree of signal modulation, but also cancels to a considerable extent the effects of reflectance fluctuations in the recording section, dust, light source intensity changes, etc., and the effect is very large.

However, in the conventional optical head as described above, the reading section has become large, and the reading section that irradiates the recording medium with 1. There was a drawback that tlt also increased. When such an optical head is used in a magneto-optical disk device, etc., the above-mentioned Wf
It is necessary to do X'+, as mentioned above! A 1° increase results in a significant amount of ThIrt. Furthermore, when an avalanche photodiode is used as the photodetector and a temperature control means such as a heat pipe is provided, the aforementioned problems of increased size and increased weight become more serious.

In view of the above facts, the present invention makes it possible to construct a compact, 1ll-1';) reading section capable of high-speed daytime operation.
To provide the 7th grade head to j27 (-1 target).

In the present invention, a luminous flux having polarization characteristics is projected onto an arsenic nail medium.
7. A change in the polarized Y state of the reflected light beam is detected by the Sugimi output means, and the magnetic recording #l/! Body K Hi',
, fJ information, the above object is achieved by transmitting the reflected )0 beam to the detection means through a polarization preserving optical fiber.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 6 is a schematic diagram showing a first embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. Here, the light beam from the laser light source 1 is guided to the optical fiber 12 by a condenser lens 22. The optical fiber used here is a so-called polarization preserving (C) fiber, and when linearly polarized light with a plane of vibration Φb in an appropriate direction is incident on one end of the fiber, the polarized light is transferred to the other end with the plane of vibration unchanged. The light beam emitted from the other end of the optical fiber becomes a parallel light beam by the collimation lens 2 and passes through the polarizing beam splitter 6. This beam splitter 3 converts the magneto-optical recording signal. It is desirable to have polarization characteristics that are optimal for readout; for example, for the incident light beam, it has a transmittance of 70q6 and a reflectance of 30%, and for linearly polarized light orthogonal to this, it has a transmittance of 70q6 and a reflectance of 100%. A lens having a reflectance is used.The condenser lens 4 condenses the light beam onto the magneto-optical recording medium 6-t through the substrate 5, and the reflected light beam passes through this lens 4 again. It becomes a parallel light beam.The reflected light beam is reflected by the beam splitter 6, and then condensed by the condenser lens 13 and sent to the optical fiber 14.
guided by. This original fiber 14 is a polarization maintaining optical fiber, and has vibration planes in the directions shown at 103° and 104 in FIG. 2, respectively. A set of mutually orthogonal linearly polarized lights is transmitted independently. At the other end of the optical fiber, a collimation lens 15.degree. polarizing beam splitter 16 and photodetectors 10 and 11 are placed, and the magneto-optical recording is read out in the same manner as the optical head shown in FIG.

By adopting such a configuration, when the present invention is used in a magneto-optical disk device, etc., the reading section shown by A in FIG. Only a minimum number of optical components are disposed, and the detection section, which avoids heavy-duty photodetectors, amplifiers (not shown), etc., can be fixed to the main body of the apparatus. The glaring section detection section is connected with an optical fiber that can be bent freely, so the ila section can move freely at high speed. In addition, the mutual position adjustment of the polarizing beam splitter 9 condensing lens and the B0 detector, which required a delicate H+, 1 degree angle, can now be adjusted to the correct position 1f,
7. Since you only need to run the optical fiber 1R in the correct rotation direction, the number of parts is reduced and it becomes f#I JrI.

4(a) and (1)) show a second embodiment of the present invention, and FIG. 4(b) is a schematic diagram of Il: (al is a plane), and FIG. 4(b) is a schematic side view. Here, the same parts as in FIG. 6 are given the same reference numerals. The light flux guided from the C source through the optical fiber 12, collimation lens 42, and beam splitter 6 is diffracted by the hologram lens 62 formed in the prism 31-1, and passes through the substrate 5 to the magneto-optical recording medium 6. The reflected light beam is again diffracted by the hologram lens 62 and becomes a parallel light beam, which is reflected by the beam splitter 6 and condensed by the lens 13. A beam splitter 23 having almost no polarization property is placed near the point, and polarization maintaining optical fibers 14 and 1 are arranged on the exit surface of the beam splitter 23.
4' are joined.

The beam splitter 26 has an emission angle of 9 NA rrii of 1 to . 1. By detecting the difference or ratio of the nine signals transmitted by the zero fiber 14 and the C fiber 14/, the defocus direction and hill can be obtained. [On the other hand, -W; ++:<Record signal reading takes 21 seconds.
2 As in the actual M1j example shown in Section 1, the outputs of photodetectors 10 and 11 and) Y, and detectors 10' and 11' are
By detecting TIIJ, it is possible to do so.

In accordance with J-C explained above, the present invention is applied to a conventional optical head as follows: 1) Small size, light Lll, (i; 11', 41゜ slot!)
Can be done 2) Take h no ") 11th evening Vt1: j・J Kero part's place i1? 1. ji? 4 ? + ij becomes t〆11 simply. , 4. The drawings are schematic diagrams illustrating an embodiment of the present invention, respectively.

1--e laser light source 2.15--Collimation lens 3.16...Polarizing beam splitter-4,1
22...Condensing lens 5...Substrate 6...ji
', magnetic l'i1 recording medium 10.11... photodetector 12.14... polarization preservation) °0 fiber origin [1
People Canon Co., Ltd.

Claims (1)

[Claims] (1) Polarized light/l'? In the optical head for reading information recorded on the magnetic recording medium, a change in the polarization state of the reflected light beam is detected by a detection means, and a change in the polarization state of the reflected light beam is projected onto a magnetic recording medium. An optical head characterized in that a light beam is transmitted to the detection means by a polarization preserving optical fiber.