Optical head with GRIN lens

1. An optical head comprising:

a slider adapted to fly a predetermined distance above a recording layer for data recording;

a graded index (GRIN) lens mounted on the slider for focusing an incident beam of light to form an exit light spot of a predetermined size on an exit surface of the GRIN lens; and

a light-emitting unit for emitting the incident beam of light to the GRIN lens;

wherein the exit surface is not covered by a layer that limits light emission through the GRIN lens from the incident beam of light; and

wherein the GRIN lens forms the exit light spot of the predetermined size on the exit surface by multistage focusing.

2. The optical head of claim 1 , wherein the exit surface of the GRIN lens is coplanar with a bottom surface of the slider adjacent to the recording layer.

3. The optical head of claim 1 , wherein the GRIN lens is a single GRIN lens including a first region and a second region respectively having gradient-index parameters that radially vary and satisfy the following condition:

ω 1 <ω 2

where ω1 is the gradient-index parameter of the first region, which is located toward the light-emitting unit, and where ω 2 is the gradient-index parameter of the second region, which is located toward the recording layer.

4. The optical head of claim 3 , wherein the second region protrudes from the first region, such that the second region is coplanar with the bottom surface of the slider.

5. The optical head of claim 4 , wherein the second region one of (1) has a shape that tapers toward the recording layer, and (2) has a cylindrical shape with a constant diameter.

6. The optical head of claim 5 , wherein the first region has a predetermined length to form a first light spot of the incident beam on a boundary surface between the first region and the second region.

7. The optical head of claim 6 , wherein the second region has a predetermined length to form the exit light spot of the incident beam, which is smaller than the first light spot.

8. The optical head of claim 7 , wherein the light-emitting unit is a semiconductor laser diode separated a predetermined distance from the first region.

9. The optical head of claim 7 , wherein the light-emitting unit is a semiconductor laser diode arranged on an entry surface of the first region.

10. The optical head of claim 9 , further comprising:

a heat sink interposed between the semiconductor laser diode and the entry surface of the first region, the heat sink being operative cool the semiconductor laser diode and the first region by absorbing heat generated during laser oscillation.

11. The optical head of claim 1 , wherein the GRIN lens comprises a first GRIN lens and a second GRIN lens respectively having gradient-index parameters that radially vary and satisfy the following condition:

ω 1 <ω 2

where ω 1 is the gradient-index parameter of the first GRIN lens, and where ω 2 is the gradient-index parameter of the second GRIN lens.

12. The optical head of claim 11 , wherein the first GRIN lens is fixed in a hole of the slider, and wherein the second GRIN lens protrudes from a bottom center region of the first GRIN lens, such that the second GRIN lens is coplanar with the bottom surface of the slider.

13. The optical head of claim 12 , wherein the second GRIN lens one of (1) has a shape that tapers toward the recording layer, and (2) has a cylindrical shape with a constant diameter.

14. The optical head of claim 13 , wherein the first GRIN lens has a predetermined length to form a first light spot of the incident beam on an exit surface of the first GRIN lens, which is in contact with the an entry surface of the second GRIN lens.

15. The optical head of claim 14 , wherein the second GRIN lens has a predetermined length to form the exit light spot of the incident beam, which is smaller than the first light spot.

16. The optical head of claim 15 , wherein the light-emitting unit is a semiconductor laser diode separated a predetermined distance from the first GRIN lens.

17. The optical head of claim 15 , wherein the light-emitting unit is a semiconductor laser diode arranged on an entry surface of the first GRIN lens.

18. The optical head of claim 17 , further comprising:

a heat sink interposed between the semiconductor laser diode and the entry surface of the first GRIN lens, the heat sink operative to cool the semiconductor laser diode and the first GRIN lens by absorbing heat generated during laser oscillation.

19. An optical head, comprising:

a slider, adapted to fly a predetermined distance above a recording layer, for data recording;

a graded index (GRIN) lens mounted on the slider for focusing an incident beam of light to form an exit light spot of a predetermined size on an exit surface of the GRIN lens, the GRIN lens comprising:

a first GRIN lens, fixed in a hole of the slider and having a gradient-index parameter ω 1 that radially varies, and

a second GRIN lens, protruding from a bottom center region of the first GRIN lens, such that the second GRIN lens is coplanar with the bottom surface of the slider and having a gradient-index parameter ω 2 that varies radially,

where ω 1 <ω 2 ;

a light-emitting unit for emitting the incident beam of light to the GRIN lens;

wherein the exit surface of is not covered by a layer that limits light emission through the GRIN lens from the incident light;

wherein the second GRIN lens has one of a shape that tapers toward the recording layer and a cylindrical shape with a constant diameter; and

wherein the second GRIN lens includes a plurality of stacked GRIN lenses respectively having (1) diameters that decrease toward the recording layer and (2) gradient-index parameters that increase toward the recording layer.

20. The optical head of claim 19 , wherein each of the plurality of GRIN lenses forming the second GRIN lens has a predetermined length to form a light spot on a respective exit surface that is smaller than a light spot formed on the exit surface of the preceding GRIN lens.