Optical recording and pickup head for digital versatile disc compatible with read-writable compact disc by adopting flat plate lens having staircase type diffraction grating structure
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| Title: | Optical recording and pickup head for digital versatile disc compatible with read-writable compact disc by adopting flat plate lens having staircase type diffraction grating structure |
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| Patent Number: | 7,016,291 |
| Publication Date: | March 21, 2006 |
| Appl. No: | 10/869096 |
| Application Filed: | June 17, 2004 |
| Abstract: | An optical recording and pickup head having a flat plate lens of a staircase type diffraction grating structure is compatible with a DVD and a CD-RW. The optical recording and pickup head includes a first optical source for emitting first light having a relatively short wavelength, a second optical source for emitting second light having a relatively long wavelength, a photo detector, an objective lens for focusing the light emitted from the first and second optical sources on the information recording surfaces of the optical discs, respectively, an optical path altering unit for transferring the light emitted from the first and second optical sources to the objective lens and transferring the first and second light reflected from the information recording surfaces of the plurality of discs to the photo detector, respectively, and a flat plate lens for substantially totally transmitting the first light proceeding from the optical path altering unit to the objective lens and diffracting the second light proceeding from the optical path altering unit to the optical axis of the objective lens. |
| Inventors: | Yoo, Jang-Hoon (Seoul, KR); Lee, Chul-Woo (Kyungki-do, KR); Cho, Kun-Ho (Kyungki-do, KR); Seong, Pyong-Yong (Seoul, KR) |
| Assignees: | Samsung Electronics Co., Ltd. (Suwon-Si, KR) |
| Claim: | 1. A lens for receiving light having respectively different wavelengths, the lens comprising: a first area; a second area, wherein said first area comprises an optical center of the light receiving plane, said second area is located outside of said first area, and wherein said first area substantially totally transmits first and second light having respectively different wavelengths, and said second area totally transmits the first light and diffracts most of the second light toward optical axis of lens. |
| Claim: | 2. The lens according to claim 1 , wherein said second area is formed in annular form. |
| Claim: | 3. The lens according to claim 2 , wherein said second area comprises diffraction grooves. |
| Claim: | 4. The lens according to claim 3 , wherein said diffraction grooves are formed on the receiving plane receiving the first and second light. |
| Claim: | 5. The lens according to claim 4 , wherein said diffraction grooves are etched shallow as they become farther from the optical center of said lens. |
| Claim: | 6. The lens according to claim 3 , wherein said diffraction grooves have a staircase or saw-tooth pattern structure which is periodically repeated. |
| Claim: | 7. The lens according to claim 6 , wherein said diffraction grooves have the saw-tooth structure repeating twice. |
| Claim: | 8. The lens according to claim 6 , wherein said diffraction grooves are configured in the number satisfying the following equation in a staircase pattern structure, N=λ 1 /(λ 2 −λ 1) where N denotes the integer number of diffraction grooves, λ 1 denotes the wavelength of the first light, and λ 2 denotes the wavelength of the second light. |
| Claim: | 9. The lens according to claim 8 , wherein said diffraction grooves have transmission efficiency coefficients satisfying the following equation with respect to the incident second light, [mathematical expression included] where T m denotes the transmission efficiency coefficient of m-th diffraction order, T denotes the width of the staircase type diffraction groove structure corresponding to one cycle, m denotes the diffraction order number, π denotes the ratio of the circumference of a circle to its diameter, i denotes the imaginary unit, X denotes the distance from the optical center of the lens, and T j (X) denotes the transmission efficiency coefficient at X. |
| Claim: | 10. The lens according to claim 9 , wherein in said staircase type diffraction structure of one cycle, each diffraction groove which is located on the j-th position from the optical center of the lens has a transmission efficiency coefficient T j (X) satisfying the following equation, [mathematical expression included] where λ denotes the wavelength of the incident light, d denotes the depth of the diffraction groove which is etched in the deepest in one cycle of the staircase type diffraction groove structure, n denotes the refractive index of the flat plate lens, n 0 denotes the refractive index of air, and N is the number of stairs. |
| Claim: | 11. The lens according to claim 10 , wherein said diffraction grooves generate phase differences satisfying the following equation, [mathematical expression included] where δ j denotes the optical phase difference generated by the j-th step difference from the optical center of the flat plate lens, π denotes the ratio of the circumference of a circle to its diameter, n denotes the refractive index of the flat plate lens, n 0 denotes the refractive index of air, and d j denotes the step difference of the j-th diffraction groove. |
| Claim: | 12. The lens according to claim 10 , wherein said first area is an area of the numerical aperture of 0.3 or less, and said second area is an area of the numerical aperture of from 0.3 to 0.5. |
| Claim: | 13. The lens according to claim 12 , wherein said second area has a staircase type structure which is repeated two times, and one of the staircase type structure is formed over the area from about 1000 μm to about 1500 μm in radial direction from the optical center of the flat plate lens and the other is formed over the area from about 1500 μm to about 1700 μm. |
| Claim: | 14. The lens according to claim 1 , wherein said second area diffracts about 70% or more of the photo quantity of the incident second light in the convergence direction with reference to the optical axis. |
| Current U.S. Class: | 36911/213 |
| Patent References Cited: | 5446565 August 1995 Komma et al. 5809000 September 1998 Choi 5838496 November 1998 Maruyama et al. 6181668 January 2001 Kajiyama et al. 0747893 December 1996 0859356 August 1998 0831469 September 1998 0932145 July 1999 0936604 August 1999 0936604 August 1999 98/13826 April 1998 98/19303 May 1998 |
| Primary Examiner: | Huber, Paul W. |
| Attorney, Agent or Firm: | Buchanan Ingersoll PC |
| Accession Number: | edspgr.07016291 |
| Database: | USPTO Patent Grants |
| Abstract: | An optical recording and pickup head having a flat plate lens of a staircase type diffraction grating structure is compatible with a DVD and a CD-RW. The optical recording and pickup head includes a first optical source for emitting first light having a relatively short wavelength, a second optical source for emitting second light having a relatively long wavelength, a photo detector, an objective lens for focusing the light emitted from the first and second optical sources on the information recording surfaces of the optical discs, respectively, an optical path altering unit for transferring the light emitted from the first and second optical sources to the objective lens and transferring the first and second light reflected from the information recording surfaces of the plurality of discs to the photo detector, respectively, and a flat plate lens for substantially totally transmitting the first light proceeding from the optical path altering unit to the objective lens and diffracting the second light proceeding from the optical path altering unit to the optical axis of the objective lens. |
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