Optical structure for acquiring fingerprint image
An optical structure for acquiring a fingerprint image with high resolution and minimum distortion is provided. The optical structure includes a prism configured to comprise an input surface to which light is irradiated, a contact surface formed horizontally to be in contact with a finger, and an output surface through which the light that has been irradiated to the input surface and reflected from the finger in contact with the contact surface passes; a lighting unit configured to emit a beam to the input surface of the prism; a reflector unit configured to reflect a fingerprint image passing through the output surface of the prism; a lens unit configured to comprise two or more lenses, each being configured to receive the fingerprint image reflected from the reflector unit; and an image sensor on which the fingerprint image passing through the lens unit is formed.
1. An optical structure for fingerprint acquisition, comprising:
a prism configured to comprise an input surface to which light is irradiated, a contact surface formed horizontally to be in contact with a finger that reflects the light that has been irradiated to the input surface, and an output surface through which the light that has been irradiated to the input surface and reflected from the finger in contact with the contact surface passes;
a lighting unit configured to irradiate a beam of light to the input surface of the prism;
a reflector unit configured to reflect a fingerprint image passing through the output surface of the prism;
a lens unit configured to comprise two or more lenses, each being configured to receive the fingerprint image reflected from the reflector unit,
wherein the lens unit comprises a first lens configured to receive the fingerprint image reflected from the reflector unit and a second lens configured to receive the fingerprint image from the first lens; the first lens and the second lens are aligned to each other in such a manner that the principal axis of the second lens is eccentric with respect to the principal axis of the first lens such that a light ray of the fingerprint image corresponding to a point of the fingerprint image that passes through the center of the first lens is received on a periphery of the second lens outside the center of the second lens and an outer edge of the fingerprint image passing through the first lens is received at the center of a surface of the second lens facing the first lens and passes along the principal axis of the second lens; and
an image sensor on which the fingerprint image passing through the second lens is formed, wherein the image sensor is tilted and, the reflector unit is positioned between the prism and the lens unit so as to directly reflect the fingerprint image to the lens unit.
2. The optical structure of claim 1 , further comprising:
an image adjusting unit configured to adjust the fingerprint image formed on the image sensor to have the same aspect ratio or size as the contact surface.
3. The optical structure of claim 1 , wherein the input surface of the prism is further configured to comprise a first input surface that adjoins the contact surface and is tilted with respect to the contact surface, and the lighting unit is further configured to comprise a first lighting unit to irradiate a beam of light to the first input surface.
4. The optical structure of claim 3 , wherein the input surface of the prism is further configured to comprise a second input surface formed facing in parallel to the contact surface, and the lighting unit is further configured to comprise a second lighting unit to irradiate a beam of light to the second input surface.
5. The optical structure of claim 1 , wherein the input surface of the prism is further configured to comprise a second input surface formed facing in parallel to the contact surface, and the lighting unit is further configured to comprise a second lighting unit to irradiate a beam of light to the second input surface.
6. The optical structure of claim 1 , wherein the reflector unit comprises a concave mirror to reflect and focus the received fingerprint image to the lens unit.
7. An optical structure for fingerprint acquisition, comprising:
a prism configured to comprise an input surface to which light is irradiated, a contact surface formed horizontally to be in contact with a finger that reflects the light that has been irradiated to the input surface, and an output surface through which the light that has been irradiated to the input surface and reflected from the finger in contact with the contact surface passes;
a lighting unit configured to irradiate a beam of light to the input surface of the prism;
a reflector unit configured to reflect a fingerprint image passing through the output surface of the prism;
a lens unit configured to comprise two or more lenses, each being configured to receive the fingerprint image reflected from the reflector unit; and
wherein the input surface of the prism comprises a first input surface that adjoins the contact surface and is tilted with respect to the contact surface, and a second input surface formed facing in parallel to the contact surface;
the lighting unit is further configured to irradiate a beam of light to the first input surface and the second input surface;
the lens unit comprises a first lens configured to receive the fingerprint image reflected from the reflector unit and a second lens configured to receive the fingerprint image from the first lens;
the first lens and the second lens are aligned to each other in such a manner that the principal axis of the second lens is eccentric with respect to the principal axis of the first lens such that a light ray of the fingerprint image corresponding to a point of the fingerprint image that passes through the center of the first lens is received on a periphery of the second lens outside the center of the second lens and an outer edge of the fingerprint image passing through the first lens is received at the center of a surface of the second lens facing the first lens and passes along the principal axis of the second lens; and
an image sensor on which the fingerprint image passing through the second lens is formed, wherein the image sensor is tilted.
8. An optical structure for fingerprint acquisition, comprising:
a prism configured to comprise an input surface to which light is irradiated, a contact surface formed horizontally to be in contact with a finger that reflects the light that has been irradiated to the input surface, and an output surface through which the light that has been irradiated to the input surface and reflected from the finger in contact with the contact surface passes;
a lighting unit configured to irradiate a beam of light to the input surface of the prism;
a reflector unit configured to reflect a fingerprint image passing through the output surface of the prism;
a lens unit configured to comprise a first lens and a second lens, the first lens being configured to receive the fingerprint image reflected from the reflector unit and the second lens being configured to receive the fingerprint image from the first lens;
the first lens and the second lens being aligned to each other in such a manner that the principal axis of the second lens is eccentric with respect to the principal axis of the first lens such that a light ray of the fingerprint image corresponding to a point of the fingerprint image that passes through the center of the first lens is received on a periphery of the second lens outside the center of the second lens and an outer edge of the fingerprint image passing through the first lens is received at the center of a surface of the second lens facing the first lens and passes along the principal axis of the second lens; and
an image sensor on which the fingerprint image passing through the second lens is formed, wherein the image sensor is tilted,
wherein the reflector unit is positioned between the prism and the lens unit so as to directly reflect the fingerprint image to the lens unit.