Device for acquiring fingerprint image

Abstract

The present invention relates to biometric feature recognition technology, and in particular to a device for acquiring fingerprint images. According to one aspect of the present invention, the device for acquiring fingerprint images comprises: a first optical waveguide; a light source unit disposed below the first optical waveguide, configured to provide a parallel light beam incident on the first optical waveguide at a certain angle, wherein the angle is set such that when the upper surface of the first optical waveguide is not covered by an object, the parallel light beam does not satisfy the total reflection condition in the first optical waveguide; a first light coupling output unit disposed on the surface of the first optical waveguide, configured to guide the light beam that is totally reflected in the first optical waveguide to the outside of the first optical waveguide and perform imaging when the upper surface of the first optical waveguide is covered by an object; and an image receiving unit disposed at the imaging position of the first light coupling output unit.

Description

Technical Field

[0001] The present invention relates to biometrics recognition technology, and in particular to a device for acquiring fingerprint images. Background Art

[0002] Biometric recognition technology uses the physiological or behavioral characteristics inherent in the human body to identify individuals. Available biometric recognition technologies include fingerprints, faces, voiceprints, irises, etc., and fingerprints are the most widely used. In recent years, fingerprint recognition technology has been gradually applied to mobile terminals such as smartphones and tablets, becoming an important basic technology to support functions such as unlocking and online payment. The principle of fingerprint recognition is that when a finger contacts the detection plane, it will cause changes in certain physical states. This change is measured by the sensor and converted into a corresponding fingerprint image, which is then compared and identified based on the image. According to the different image acquisition methods, fingerprint acquisition is divided into three types: optical, capacitive and radio frequency.

[0003] The optical fingerprint collection method has the advantages of long service life, not easy to damage, low price and good image quality. Figure 1 FIG. 1 is a schematic diagram of an optical fingerprint collection device in the prior art. Figure 1 As shown, the light beam emitted by the light source enters the prism P through the first surface S1 of the prism, and the second surface S2 of the prism is the detection surface. When no finger is placed on the second surface S2, the light beam is totally reflected by the second surface S2 and then emitted from the third surface S3 of the prism. On the other hand, when a finger is placed on the second surface S2, the light beam is scattered at the ridge of the fingerprint and only part of the light beam is totally reflected. The totally reflected light beam is imaged by the focusing lens L to obtain a fingerprint image with ridge / valley contrast. Limited by the volume of the prism and the long focal length of the focusing lens (in order to eliminate the scattered component), the above device is difficult to be miniaturized, thus hindering its application in mobile terminals, especially under the trend of thin and light terminals. Summary of the invention

[0004] An object of the present invention is to provide a device for acquiring a fingerprint image, which has the advantages of compact structure and good integration with a mobile terminal.

[0005] The device for acquiring a fingerprint image according to one aspect of the present invention comprises:

[0006] a first optical waveguide;

[0007] a light source unit disposed below the first optical waveguide, configured to provide a parallel light beam incident on the first optical waveguide at a certain angle, wherein the angle is set such that when the upper surface of the first optical waveguide is not covered by an object, the parallel light beam does not satisfy a total reflection condition in the first optical waveguide;

[0008] a first light coupling output unit disposed on the surface of the first light waveguide, configured to guide the light beam totally reflected in the first light waveguide to the outside of the first light waveguide for imaging when an object covers the upper surface of the first light waveguide; and

[0009] An image receiving unit is arranged at the imaging position of the first light coupling output unit.

[0010] Preferably, in the above device, an illumination area of ​​the parallel light beam on the first optical waveguide corresponds to a fingerprint detection area on the first optical waveguide.

[0011] Preferably, in the above device, the first optical waveguide has a micro-prism structure in a region illuminated by the parallel light beam.

[0012] Preferably, in the above device, a coating layer is provided on the surface of the first optical waveguide in a region close to the first light coupling-out unit.

[0013] Preferably, in the above device, the light source unit comprises:

[0014] Point light source;

[0015] A collimating lens disposed before the point light source, configured to convert light emitted from the point light source into a parallel light beam;

[0016] A second optical waveguide is arranged on the path of the output light beam of the collimating lens, and has a coated inclined surface at the end facing the collimating lens so that the parallel light beam from the collimating lens is totally reflected in the second optical waveguide; and

[0017] A second light coupling output unit is arranged on the surface of the second light waveguide, which is configured to guide the parallel light beam that is totally reflected in the second light waveguide to the outside of the second light waveguide, and the size of the second light coupling output unit is set to be equivalent to the irradiation area of ​​the parallel light beam on the first light waveguide.

[0018] Preferably, in the above device, the light source unit comprises:

[0019] Point light source;

[0020] A collimating lens disposed before the point light source, configured to convert light emitted from the point light source into a parallel light beam;

[0021] A second optical waveguide disposed on the path of the outgoing light beam of the collimating lens;

[0022] a light coupling input unit disposed on a first surface of the second optical waveguide, configured to cause the parallel light beam from the collimating lens to be totally reflected within the second optical waveguide, the first surface facing the collimating lens; and

[0023] A second light coupling output unit is arranged on the surface of the second light waveguide, which is configured to guide the parallel light beam that is totally reflected in the second light waveguide to the outside of the second light waveguide, and the size of the second light coupling output unit is set to be equivalent to the irradiation area of ​​the parallel light beam on the first light waveguide.

[0024] Preferably, in the above device, the light source unit comprises:

[0025] Point light source;

[0026] A collimating lens disposed before the point light source, configured to convert light emitted from the point light source into a parallel light beam;

[0027] A second optical waveguide disposed on the path of the outgoing light beam of the collimating lens;

[0028] a light coupling input unit disposed on a second surface of the second optical waveguide, configured to cause the parallel light beam from the collimating lens to be totally reflected within the second optical waveguide, the second surface being opposite to a surface of the second optical waveguide facing the collimating lens; and

[0029] A second light coupling output unit is arranged on the surface of the second light waveguide, which is configured to guide the parallel light beam that is totally reflected in the second light waveguide to the outside of the second light waveguide, and the size of the second light coupling output unit is set to be equivalent to the irradiation area of ​​the parallel light beam on the first light waveguide.

[0030] Preferably, in the above device, the light coupling input unit is one of a tilted grating, a wedge-shaped reflection surface and a reflection prism.

[0031] Preferably, in the above device, the first light coupling output unit is one of a nano-grating pixel array, a Fresnel lens, a super lens, a microlens array and a short-focus lens.

[0032] Preferably, in the above device, the second light coupling output unit is a grating. Each of the submodules comprises: BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The figure is a schematic diagram of a device for acquiring a fingerprint image according to an embodiment of the present invention.

[0034] Figure 2 The figure is a schematic diagram of a device for acquiring a fingerprint image according to an embodiment of the present invention.

[0035] Figure 3 for Figure 2 A schematic diagram of a light source unit in a device for acquiring a fingerprint image is shown.

[0036] Figure 4 For application Figure 2 A schematic diagram of a light source unit in a device for acquiring a fingerprint image is shown.

[0037] Figure 5 For application Figure 2 A schematic diagram of another light source unit in a device for acquiring a fingerprint image is shown.

[0038] Figure 6 For use in Figure 2 Schematic diagram of a nanograting pixel array in a device for acquiring fingerprints. DETAILED DESCRIPTION

[0039] The device for acquiring fingerprint images of the present invention will be described in more detail below with reference to the accompanying drawings.

[0040] Figure 2 The figure is a schematic diagram of a device for acquiring a fingerprint image according to an embodiment of the present invention.

[0041] Figure 2 The device 20 for acquiring a fingerprint image includes a first optical waveguide 210 , a light source unit 220 , a first light coupling-out unit 230 , and an image receiving unit 240 .

[0042] like Figure 2 As shown, the light source unit 220 is disposed below the first optical waveguide 210 and is configured to provide a parallel light beam to the first optical waveguide 210. By setting an incident angle for the parallel light beam to enter the first optical waveguide 210, when the upper surface of the first optical waveguide 210 is not covered by an object, the parallel light beam does not meet the total reflection condition in the first optical waveguide 210.

[0043] See also Figure 2When an object (such as a finger in the figure) covers the upper surface of the first optical waveguide 210, the parallel light beam at the position corresponding to the ridge of the finger undergoes diffuse reflection, and the angle of part of the light beam after diffuse reflection satisfies the total reflection condition and thus continues to propagate in the optical waveguide 210; on the other hand, at the position corresponding to the valley of the fingerprint, the light does not meet the total reflection condition and thus cannot propagate in the optical waveguide 210. When the part of the parallel light beam that undergoes total reflection and continues to propagate reaches the first light coupling output unit 230 disposed on the surface of the first optical waveguide 210, the total reflection condition is no longer satisfied, and at this time the light beam will be guided by the first light coupling output unit 230 to the outside of the first optical waveguide 210 and imaged. Thus, a fingerprint image can be obtained on the image receiving unit 240 disposed at the imaging position of the first light coupling output unit 230.

[0044] exist Figure 2 In the illustrated embodiment, preferably, the irradiation area of ​​the parallel light beam on the first optical waveguide 210 corresponds to the fingerprint detection area on the first optical waveguide 210, that is, the size of the irradiation area is substantially the same as the fingerprint detection area and is substantially aligned in a direction perpendicular to the surface normal of the first optical waveguide 210. In addition, in order to increase the incident angle of the parallel light beam from the light source unit 220 to improve the light energy utilization rate, preferably, the area of ​​the first optical waveguide 210 irradiated by the parallel light beam (e.g. Figure 2 The lower left surface in the figure) forms a micro-prismatic structure.

[0045] See also Figure 2 Preferably, coating layers 251 and 252 are respectively disposed on the upper surface and the lower surface of the first optical waveguide 210 in the region close to the first light coupling output unit 230 to further improve the light energy utilization rate.

[0046] exist Figure 2 In the embodiment shown, if the total reflection angle is too small, the light irradiated on the fingerprint will still be in the fingerprint detection area after experiencing a total reflection ( Figure 2 In order to prevent this situation, preferably, the total reflection angle can satisfy the following relationship:

[0047] tanα≥L2 / 2L1(1)

[0048] Wherein α is the total reflection angle, L1 and L2 are the thickness of the first optical waveguide 210 and the length of the detection area respectively.

[0049] The refractive index of the coating layers 251 and 252 satisfies the following relationship:

[0050]

[0051] Where n2 and n3 are the refractive indices of the first optical waveguide and the coating layer respectively.

[0052] Therefore, the refractive index of the coating layer should satisfy the above equations (1) and (2).

[0053] In addition, Figure 2 In the embodiment shown, preferably, the length of the coating layer satisfies the following relationship:

[0054] L2+L3≤L0(3)

[0055] L4=L3+L5(4)

[0056] Wherein L0 is the length of the first optical waveguide, L2 is the length of the fingerprint detection area, L3 and L4 are the lengths of the coating layers 251 and 252 respectively, and L5 is the length of the first light coupling output unit or grating.

[0057] Figure 3 for Figure 2 A schematic diagram of a light source unit in a device for acquiring a fingerprint image is shown.

[0058] like Figure 3 As shown, the light source unit 220 includes a point light source 221, a collimating lens 222, a second optical waveguide 223 and a second light coupling output unit 224. The point light source 221 can be a monochromatic light source or a non-monochromatic light source, which is arranged near the focus or on the focal plane of the collimating lens 222. The second optical waveguide 223 is arranged on the path of the outgoing light beam of the collimating lens 222. Preferably, the collimating lens 222 can be a refractive lens, a diffractive lens or a super lens, and its shape can be square, circular, etc., and the lens material can be selected from a resin material (such as PMMA material) with good transmittance in the visible light band.

[0059] See also Figure 3 The light emitted from the point light source 221 is converted into a parallel light beam by the collimating lens 222 and then incident on the second optical waveguide 223. Figure 3 As shown, the left end of the second optical waveguide 223 has a coated inclined surface, so that the parallel light beam from the collimating lens 222 is totally reflected after entering the second optical waveguide 223. Figure 3 In the light source unit 220 shown in the figure, the second light coupling output unit 224 is arranged on the surface of the second light waveguide 223, and is configured to guide the parallel light beam totally reflected in the second light waveguide to the outside of the second light waveguide, so as to illuminate the Figure 2 The parallel light beams on the lower surface of the first optical waveguide 210 are shown.

[0060] Preferably, the second light coupling-out unit 224 is implemented in the form of a grating, and the size of the grating is set to be equivalent to the illumination area of ​​the parallel light beam on the first optical waveguide 210. More preferably, the back side of the grating is blackened to maximize the utilization of light energy.

[0061] The grating 224 used as the second light coupling-out unit satisfies the following grating equation:

[0062] n1T sinθ1+n2T sinθ2=λ(5)

[0063] Where T is the grating period, n1 is the refractive index of the incident medium, n2 is the refractive index of the exiting medium, θ1 is the incident angle of the light entering the grating, θ2 is the diffraction angle of the grating, and λ is the wavelength of the light.

[0064] It can be seen from equation (5) that the incident angle θ1 and the grating period T can be determined based on the required diffraction angle θ2.

[0065] It should be pointed out that the above Figure 3 The light source unit described is merely exemplary, and the present invention may also adopt light source units with other structures.

[0066] Figure 4 For application Figure 2 A schematic diagram of a light source unit in a device for acquiring a fingerprint image is shown, wherein Figure 3 The same or similar components in the light source unit are denoted by the same reference numerals.

[0067] and Figure 3 Compared to the light source unit shown, Figure 4 The main difference of the light source unit shown is that the parallel light beam from the collimating lens 222 is introduced into the second optical waveguide 223 by using the light coupling input unit 225, and the introduced light beam is totally reflected in the second optical waveguide 223 by setting a suitable incident angle.

[0068] See also Figure 4 The light coupling input unit 225 is arranged on the first surface of the second optical waveguide 223 (ie Figure 4 The light emitted from the point light source 221 is converted into a parallel light beam by the collimating lens 222 and then incident on the light coupling input unit 225. Under the action of the light coupling input unit 225, the parallel light beam enters the second optical waveguide 223 at a suitable angle, so that the parallel light beam is totally reflected inside the second optical waveguide 223. Figure 4 In the light source unit 220 shown in the figure, the second light coupling output unit 224 is arranged on the surface of the second light waveguide 223, and is configured to guide the parallel light beam totally reflected in the second light waveguide to the outside of the second light waveguide, so as to illuminate the Figure 2 The parallel light beams on the lower surface of the first optical waveguide 210 are shown.

[0069] exist Figure 4In the light source unit shown, the light coupling input unit 225 can be, for example, an element that changes the direction of the light beam, such as a grating, a wedge-shaped reflecting surface or a reflecting prism. In order to improve the coupling-input efficiency, the light coupling input unit is preferably a tilted grating. Preferably, the groove shape of the tilted grating can be one of a triangular, sinusoidal or straight groove shape. Preferably, the groove shape is asymmetric relative to the normal line of the second optical waveguide surface to suppress the diffraction efficiency of the -1 order diffracted light, thereby improving the light utilization rate of the +1 order illumination light.

[0070] Figure 5 For application Figure 2 A schematic diagram of another light source unit in a device for acquiring a fingerprint image is shown, wherein Figure 3 and 4 The same or similar components in the light source unit are denoted by the same reference numerals.

[0071] and Figure 4 Compared to the light source unit shown, Figure 5 The main difference of the light source unit shown is that the light coupling input unit 225 is arranged on the second surface of the second light waveguide 223 (ie Figure 5 The surface opposite to the surface facing the collimating lens 222). Figure 4 , the light emitted from the point light source 221 is converted into a parallel light beam by the collimating lens 222 and enters the second optical waveguide 223, and then enters the optical coupling input unit 225. Under the action of the optical coupling input unit 225, the parallel light beam returns to the second optical waveguide 223 at a suitable angle, so that when there is no object covering the upper surface of the second optical waveguide 223, the parallel light beam is totally reflected. Figure 5 In the light source unit 220 shown in the figure, the second light coupling output unit 224 is arranged on the surface of the second light waveguide 223, and is configured to guide the parallel light beam totally reflected in the second light waveguide to the outside of the second light waveguide, so as to illuminate the Figure 2 The parallel light beams on the lower surface of the first optical waveguide 210 are shown.

[0072] exist Figure 3-5 In the light source unit shown, when the light coupling input unit 225 and the second light coupling output unit 224 adopt a grating structure, the size of the fingerprint collection device, especially the thickness of the fingerprint collection device, can be greatly reduced.

[0073] exist Figure 2 In the illustrated embodiment, preferably, the first light coupling output unit 230 is one of a nano-grating pixel array, a Fresnel lens, a super lens, a micro lens array, and a short-focus lens. When the nano-grating pixel array is used to realize image focusing and imaging functions, the size of the fingerprint collection device, especially the thickness of the fingerprint collection device, can be greatly reduced.

[0074] Figure 6 For use in Figure 2 Schematic diagram of a nanograting pixel array in a device for acquiring fingerprints.

[0075] like Figure 6 As shown, the nano-grating pixel array is a stacked structure of multi-layer gratings with different grating periods and orientation angles, which is essentially a diffraction grating (or diffraction grating pixel) with a structural size at the nanometer level processed on a phase plate.

[0076] According to the grating equation, the period and orientation angle of the diffraction grating pixel satisfy the following relationship:

[0077] tanφ1=sinφ / (cosφ-nsinθ(Λ / λ))(6)

[0078] sin 2 (θ1)=(λ / Λ) 2 +(nsinθ) 2 -2nsinθcosφ(λ / Λ)(7)

[0079] Assuming that the light is incident on the XY plane at a certain angle, θ1 and φ1 represent the diffraction angle (the angle between the diffracted light and the negative direction of the z-axis) and azimuth (the angle between the diffracted light and the positive direction of the y-axis) of the diffracted light, θ and λ represent the incident angle (the angle between the incident light and the negative direction of the z-axis) and wavelength of the light incident on the diffraction grating, Λ and φ represent the period and orientation angle (the angle between the groove direction and the positive direction of the x-axis) of the diffraction grating, and n represents the refractive index of the light in the medium.

[0080] It can be seen from the above equations (6) and (7) that after setting the wavelength and incident angle of the incident light and the diffraction angle and diffraction azimuth of the diffracted light, the required grating period and orientation angle can be determined.

[0081] See again Figure 2 The image receiving unit 240 is located at an imaging position or image distance below the first light coupling output unit 230, and may be, for example, a CMOS device or a CCD device, and is configured to collect fingerprint images.

[0082] exist Figure 2 In the device shown, the object distance of the first light coupling output unit 230 satisfies the following relationship:

[0083] L=3*L1tanα(8)

[0084] Wherein L is the object distance of the first light coupling output unit 230 , L1 is the thickness of the first optical waveguide 210 , and α is the total reflection angle of the light in the first optical waveguide 210 .

[0085] Accordingly, the image distance of the first light coupling output unit 230 satisfies the following relationship:

[0086]

[0087] Wherein L6 is the image distance of the first light coupling output unit 230, L f is the focal length of the first light coupling output unit 230 , and L is the object distance of the first light coupling output unit 230 .

[0088] Compared with the prior art, the present invention has many advantages. For example, due to the use of ultra-thin directional light guide illumination, the thickness of the light source unit is greatly reduced, which is conducive to the miniaturization of the optical imaging system. For another example, since the overall thickness of the device can be reduced by using ultra-thin waveguides to transmit signal light, the device of the present invention can be well integrated into mobile devices such as mobile phones, keys and payment cards. Furthermore, secondary total reflection imaging through waveguide surface coating can effectively filter out stray light, thereby enhancing the resolution and recognition of image acquisition.

[0089] The above describes the principles and preferred embodiments of the present invention. However, the present invention should not be construed as being limited to the specific embodiments discussed. The preferred embodiments described above should be considered illustrative rather than restrictive, and it should be understood that those skilled in the art may make changes in these embodiments without departing from the scope of the present invention as defined in the following claims.

Claims

1. A device for acquiring a fingerprint image, characterized in that: Include: a first optical waveguide; a light source unit disposed below the first optical waveguide, configured to provide a parallel light beam incident on the first optical waveguide at a certain angle, wherein the angle is set such that when the upper surface of the first optical waveguide is not covered by an object, the parallel light beam does not satisfy a total reflection condition in the first optical waveguide; a first light coupling output unit disposed on the surface of the first light waveguide, configured to guide the light beam totally reflected in the first light waveguide to the outside of the first light waveguide for imaging when an object covers the upper surface of the first light waveguide; and An image receiving unit is arranged at the imaging position of the first light coupling output unit.

2. The device according to claim 1, wherein: The irradiation area of ​​the parallel light beam on the first optical waveguide corresponds to the fingerprint detection area on the first optical waveguide.

3. The device according to claim 1, wherein: The first optical waveguide has a micro-prism structure in a region illuminated by the parallel light beam.

4. The device according to claim 1, wherein: A coating layer is disposed on the surface of the first optical waveguide in a region close to the first light coupling output unit.

5. The device according to claim 1, wherein: The light source unit comprises: Point light source; A collimating lens disposed before the point light source, configured to convert light emitted from the point light source into a parallel light beam; A second optical waveguide is arranged on the path of the output light beam of the collimating lens, and has a coated inclined surface at the end facing the collimating lens so that the parallel light beam from the collimating lens is totally reflected in the second optical waveguide; and A second light coupling output unit is arranged on the surface of the second light waveguide, which is configured to guide the parallel light beam that is totally reflected in the second light waveguide to the outside of the second light waveguide, and the size of the second light coupling output unit is set to be equivalent to the irradiation area of ​​the parallel light beam on the first light waveguide.

6. The device according to claim 1, wherein: The light source unit comprises: Point light source; A collimating lens disposed before the point light source, configured to convert light emitted from the point light source into a parallel light beam; A second optical waveguide disposed on the path of the outgoing light beam of the collimating lens; a light coupling input unit disposed on a first surface of the second optical waveguide, configured to cause the parallel light beam from the collimating lens to be totally reflected within the second optical waveguide, the first surface facing the collimating lens; and A second light coupling output unit is arranged on the surface of the second light waveguide, which is configured to guide the parallel light beam that is totally reflected in the second light waveguide to the outside of the second light waveguide, and the size of the second light coupling output unit is set to be equivalent to the irradiation area of ​​the parallel light beam on the first light waveguide.

7. The device of claim 1, wherein: The light source unit comprises: Point light source; A collimating lens disposed before the point light source, configured to convert light emitted from the point light source into a parallel light beam; A second optical waveguide disposed on the path of the outgoing light beam of the collimating lens; a light coupling input unit disposed on a second surface of the second optical waveguide, configured to cause the parallel light beam from the collimating lens to be totally reflected within the second optical waveguide, the second surface being opposite to a surface of the second optical waveguide facing the collimating lens; and A second light coupling output unit is arranged on the surface of the second light waveguide, which is configured to guide the parallel light beam that is totally reflected in the second light waveguide to the outside of the second light waveguide, and the size of the second light coupling output unit is set to be equivalent to the irradiation area of ​​the parallel light beam on the first light waveguide.

8. The device according to claim 6 or 7, wherein: The light coupling input unit is one of a tilted grating, a wedge-shaped reflection surface and a reflection prism.

9. The device of claim 1, wherein: The first light coupling output unit is one of a nano-grating pixel array, a Fresnel lens, a super lens, a micro-lens array and a short-focus lens.

10. The device according to any one of claims 5 to 7, wherein: The second light coupling-out unit is a grating.

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