CN108009533A - Optical fingerprint identification system - Google Patents

Abstract

The present invention discloses an optical fingerprint recognition system, which uses a light guide panel surface as a fingerprint sensing area for finger pressing, provides a collimated optical signal, and introduces the optical signal into the light guide panel to be transmitted through the total internal reflection effect. The finger pressing will cause the total internal reflection of the optical signal in the light guide panel to be destroyed, and the photosensitive element can detect the waveform change of the optical signal and process it into a fingerprint image. Therefore, when the present invention integrates the optical fingerprint recognition system into the display panel, the photosensitive element can be hidden on the back of the display panel, and it does not need to receive the reflected light of the fingerprint, and there is no problem of penetration. The fingerprint sensing area can be implemented in the entire or partial area of the light guide panel, which can not only provide more flexible use, but also meet the aesthetic needs of consumers for the appearance of the product.

Description

Optical Fingerprint Recognition System

technical field

The invention relates to a fingerprint identification technology, in particular to an optical fingerprint identification system which utilizes the internal total reflection effect of light for sensing and identification.

Background technique

Fingerprint identification is a kind of biometric identification technology, which uses the unique fingerprint information on human fingers for identification, and is widely used for its advantages in safety and convenience; for example, almost all smart phones today The fingerprint recognition function has been added, which can provide fingerprint encryption and fingerprint unlocking.

An optical fingerprint identification system 10, please refer to FIG. 1, a pressing plate 12, a light diffusion plate 13 and a photosensitive element 11 are arranged in sequence from top to bottom, and a plurality of light sources 14 are arranged around the photosensitive element 11. Wherein, the pressing plate 12 has a plate surface 121 that can be pressed by fingers. The light diffusion plate 13 guides the incident light emitted by the light source 14 to the pressure plate 12 and has a through hole 131 through which the reflected light passes. When the incident light is projected to the finger A by the light diffusion plate 13 , it will be reflected to the photosensitive element 11 below through the through hole 131 . Since the crests of the fingerprint reflect light and the troughs absorb light, the reflected light will form light and dark contrast stripes, allowing the photosensitive element 11 to achieve the effect of fingerprint identification.

Currently, combining the fingerprint recognition function with the display function of the display panel is a hot topic that the industry is actively researching. In the method of integrating or combining the fingerprint identification system into the display panel, if the related components of fingerprint identification are placed above the display panel, since the silicon wafer-based photosensitive element is opaque, it will be exposed outside the display panel , and there is a problem of penetration when placed under the display panel, it may not be able to receive the reflected light of the fingerprint well, thereby affecting the accuracy of fingerprint recognition. Therefore, there are certain limitations in combining the fingerprint identification system with the display panel, and it is difficult not to interfere with the appearance design of the product.

Therefore, there is a need to develop an optical fingerprint recognition system that can be well integrated into the display panel so that the photosensitive element will not be exposed to meet the appearance requirements of the product. It is not only different from the structure of the prior art, but also can effectively overcome the Its various deficiencies; its specific structure and implementation will be described in detail below.

Contents of the invention

In view of the above problems, the main purpose of the present invention is to provide an optical fingerprint identification system, which allows optical signals to be transmitted in the light guide panel through the total internal reflection effect, so that the optical signal can be completely reflected in the light guide panel by pressing with a finger The destruction, in order to achieve the role of fingerprint identification.

Another object of the present invention is to provide an optical fingerprint identification system, which can hide the photosensitive element on the back of the display panel without being exposed to the outside. At the same time, the fingerprint sensing area can be set on the whole or partial area of the light guide panel, preferably It satisfies the various needs of consumers for product appearance and flexibility of use.

Therefore, in order to achieve the above object, the present invention provides an optical fingerprint identification system, which mainly includes a light guide panel, a light source, a signal amplifier and a photosensitive element. Wherein, the surface of the light guide panel has a fingerprint sensing area for finger pressing, and the light guide panel is respectively provided with a first light guide part and a second light guide part at a light incident end and a light output end . The light source is adjacent to the first light guide part and provides at least one optical signal. The optical signal is guided into the light guide panel through the first light guide part and transmitted in the light guide panel through the internal total reflection effect, and then passes through the second light guide panel. The light part is exported. The signal amplifier is adjacent to the second light guiding part, it receives the optical signal derived from the second light guiding part, amplifies the optical signal and then leads it out. The photosensitive element is adjacent to the signal amplifier, which receives the optical signal derived from the signal amplifier, and processes the optical signal into a fingerprint image, so as to achieve the purpose of fingerprint identification.

According to an embodiment of the present invention, the fingerprint sensing area may be the entire or partial area of the surface of the light guide panel.

According to an embodiment of the present invention, the light guide panel is disposed above a display panel.

According to an embodiment of the present invention, the light guide panel is attached to the display panel by coating optical glue or dispensing glue.

According to an embodiment of the present invention, the light source may be a collimated light source or a non-collimated light source.

According to an embodiment of the present invention, the light source may be a laser (Laser), a vertical cavity surface emitting laser (VCSEL), or a combination of a non-collimated light source and a secondary optical element.

According to an embodiment of the present invention, the secondary optical element may be selected from a parabolic surface condenser, a compound parabolic condenser (CPC), a lens, a prism, a Fresnel lens (Fresnellens) and combinations thereof.

According to an embodiment of the present invention, the wavelength of the optical signal is between 380-1400 nanometers (nm).

According to an embodiment of the present invention, when the optical signal travels in the light guide panel, the angle between the optical signal and the normal to the surface or bottom surface of the light guide panel needs to be larger than arcsin( n ₀ /n ₂ ) and arcsin(n ₁ /n ₂ );

Wherein, n ₀ is the refractive index of the surface of the light guide panel;

n ₁ is the refractive index of the bottom surface of the light guide panel; and

n ₂ is the refractive index of the light guide panel.

According to an embodiment of the present invention, the first light guide part, the second light guide part and the light guide panel may be an integrated structure.

According to an embodiment of the present invention, the first light guide part and the second light guide part may be disposed separately from the light guide panel.

According to an embodiment of the present invention, a coating film is formed on the surface of the light guide panel, the coating film can pass through visible light, and reflect light of other wavelength bands.

According to an embodiment of the present invention, the first light guide part and the second light guide part may be in the form of a mirror or an optical fiber.

According to an embodiment of the present invention, the signal amplifier may be in the form of a mirror.

According to an embodiment of the present invention, a lens, a prism film (Prismfilm), an angle filter (Angular filter), a polarization beam splitter prism (PBS), and a beam splitter ( BS) or a combination thereof.

According to an embodiment of the present invention, the angle filter may be a vertical or inclined grating filter.

According to an embodiment of the present invention, the grating filter is a single-layer structure composed of multiple layers of first material thin films arranged at intervals.

According to an embodiment of the present invention, the grating filter is a single-layer structure composed of multiple layers of first material films and multiple layers of second material films arranged at intervals.

According to an embodiment of the present invention, wherein the grating filter is a multi-layer structure composed of multiple layers of first material thin films and multiple layers of second material thin films spaced apart, and the different layers of the multi-layer structure The first material films are aligned or staggered.

According to an embodiment of the present invention, the photosensitive element is arranged in parallel or obliquely with respect to the light guide panel.

According to an embodiment of the present invention, at least one prism (Prism) is further included between the first light guide part and the light source and/or between the second light guide part and the signal amplifier, and the prism Available as fixed or rotatable prisms.

According to the optical fingerprint identification system provided by the present invention, the internal total reflection effect of the optical signal in the light guide panel can be used to obtain the fingerprint image by detecting the waveform change of the optical signal. When the optical fingerprint identification system and the display When the panel is integrated, the photosensitive element can be concealed on the back of the display panel, and the problem of insufficient penetration will not affect the recognition rate, which is beneficial to the design of the product appearance. At the same time, regional or comprehensive fingerprint sensor can be designed The detection area allows users to use the fingerprint recognition function more flexibly and conveniently.

The following will be described in detail through specific examples, when it is easier to understand the purpose, technical content, characteristics and effects of the present invention. Through the detailed description of the specific embodiments and the accompanying drawings, it will be easier to understand the purpose, technical content, characteristics and effects of the present invention.

Description of drawings

FIG. 1 is a cross-sectional view of an optical fingerprint identification system provided by the prior art.

FIG. 2 is a cross-sectional view of an optical fingerprint identification system provided by an embodiment of the present invention.

3A to 3C are schematic diagrams of combinations of different secondary optical elements and non-collimated light sources used in the optical fingerprint identification system provided by the embodiment of the present invention.

3D is a schematic diagram of a combination of a prism and a non-collimated light source used in the optical fingerprint identification system provided by an embodiment of the present invention.

4A-4D are schematic diagrams of the optical fingerprint recognition system provided by the embodiment of the present invention using a lens, a prism film, an angle filter, and a combination of a prism film and an angle filter in a photosensitive element.

5A to 5C are schematic diagrams of using filters with different angles on the photosensitive element in the optical fingerprint identification system provided by the embodiment of the present invention.

5D to 5F are schematic diagrams of the optical fingerprint recognition system provided by the embodiment of the present invention using different combinations of angular wave filters and prism films on the photosensitive element.

FIG. 6A and FIG. 6B are schematic diagrams of different arrangements of photosensitive elements used in the optical fingerprint identification system provided by the embodiment of the present invention, respectively.

FIG. 7 is a schematic diagram of the combination of the optical fingerprint identification system and the display panel provided by the embodiment of the present invention.

FIG. 8 is a schematic diagram of the combination of the optical fingerprint identification system provided by the embodiment of the present invention and the camera lens of the mobile phone.

Explanation of reference signs: 10-optical fingerprint identification system; 11-photosensitive element; 12-press plate; 121-plate surface; 13-light diffusion plate; 131-through hole; Light guide panel; 211-fingerprint sensing area; 212-light input end; 213-light output end; 214-first light guide part; 215-second light guide part; 216-optical glue; 22-collimated light source; 221 -parabolic condenser or CPC; 222-non-collimated light source; 223-Fresnel lens; 224-lens; 225-prism; 23-signal amplifier; 24-photosensitive element; 251-lens; 252-prism film; Filter; 254-first material film; 255-second material film; 30-display panel; 40-lens module; 41-polarization beam splitter prism or beam splitter; A-finger;

Detailed ways

Please refer to FIG. 2 , which shows a cross-sectional view of an optical fingerprint identification system 20 provided by an embodiment of the present invention. The optical fingerprint identification system 20 is mainly composed of a light guide panel 21 , a collimated light source 22 , a signal amplifier 23 and a photosensitive element 24 .

In this embodiment, the surface of the light guide panel 21 has a fingerprint sensing area 211 that can be pressed by the finger A; in practice, the fingerprint sensing area 211 can be designed on the entire area or a partial area of the surface of the light guide panel 21 . In this embodiment, the light guide panel 21 has a light-incoming end 212 and a light-outgoing end 213 on both sides respectively, and a first light-guiding portion 214 and a second light-guiding portion 215 are respectively provided on the light-incoming end 212 and the light-outgoing end 213, Specifically, the first light guide part 214 and the second light guide part 215 can be reflectors to adjust the transmission angle of the optical signal; The middle cutout end of the light panel 21. The material of the light guide panel 21 can be glass, the first light guide part 214 and the second light guide part 215 can be in the form of a mirror or an optical fiber, and the first light guide part 214 and the second light guide part 215 are relatively light guide parts. The panel 21 can be provided separately, of course, the first light guide part 214 and the second light guide part 215 can also be designed as an integrated structure with the light guide panel 21 .

In this embodiment, the collimated light source 22 is adjacent to the first light guide portion 214 for providing at least one collimated optical signal. Furthermore, the collimated light source 22 generates a collimated optical signal, and projects the optical signal to the first light guide part 214, and the first light guide part 214 will reflect or transmit the optical signal, and then enter the guide through the light incident end 212. In the optical panel 21 , the optical signal can be transmitted in the light guide panel 21 through Total Internal Reflection (TIR) effect, and then transmitted to the light output end 213 , and then reflected or transmitted through the second light guide portion 215 .

Furthermore, in order to allow the optical signal to be totally internally reflected in the light guide panel 21, the included angle between the optical signal and the normal line of the surface or bottom surface of the light guide panel 21 (herein for the convenience of the following description, referred to as Incidence angle θ), the minimum angles are respectively arcsin(n ₀ /n ₂ ) and arcsin(n ₁ /n ₂ ) to achieve total internal reflection. Therefore, when the optical signal travels in the light guide panel 21, its incident angle θ must be greater than the minimum angle required by the above two items of total internal reflection at the same time, that is, the incident angle θ must be greater than arcsin(n ₀ /n ₂ ) and arcsin(n ₁ /n ₂ );

Wherein, n ₀ is the refractive index of the surface of the light guide panel 21;

n ₁ is the refractive index of the bottom surface of the light guide panel 21; and

n ₂ is the refractive index of the light guide panel 21 .

In this embodiment, the refractive index of the light guide panel 21 is 1.5. When the surface and the bottom surface of the light guide panel 21 are adjacent to the air, the angle between the traveling direction of the optical signal in the light guide panel 21 and the surface or the bottom surface is That is, the incident angle θ is greater than 43 degrees; when only one of the surface and the bottom surface of the light guide panel 21 is adjacent to air, and the other side is adjacent to a material with a refractive index of 1.4, the optical signal travels in the light guide panel 21 The angle between the direction and its surface or bottom surface, that is, the angle of incidence θ is greater than 70 degrees.

In this embodiment, the collimated light source 22 can be a laser (Laser), a vertical cavity surface emitting laser (VCSEL) or a combination of a non-collimated light source and a secondary optical element; specifically, the secondary optical element can be selected Parabolic surface condenser, compound parabolic condenser (CPC), lens, prism, Fresnel lens (Fresnellens) and combinations thereof. As shown in FIG. 3A , it shows that an embodiment of the present invention uses a parabolic condenser or CPC221 in combination with a non-collimated light source 222 to provide collimated optical signals; as shown in FIG. 3B , it shows that an embodiment of the present invention uses a Fresnel The lens 223 cooperates with the non-collimated light source 222 to provide a collimated optical signal; as shown in FIG. straight optical signal. As also shown in FIG. 3D , it shows that the embodiment of the present invention uses one (or more) prisms (Prism) 225 to cooperate with a non-collimated light source 222 to provide collimated optical signals through the prism 225; in the present invention, the prism 225 It can be arranged only between the first light guide part 214 and the collimated light source 22 or the non-collimated light source 222, or between the second light guide part 215 and the signal amplifier 23, or even both of them. setting, and the prism 225 can be a fixed or rotatable prism.

In addition, the wavelength of the optical signal can be between 380-1400 nanometers (nm); in practical applications, it can be divided into a visible light segment (380-780 nm) and a near-infrared segment (780-1400 nm). To further explain, when using the wavelength of visible light, it is visible to the naked eye, and different wavelengths can be used to mark the effective or invalid area to help users understand the available area; when using the near-infrared wavelength, it is invisible to the naked eye and is suitable for use Under the display panel (underdisplay) or in an environment where the requirement is not noticed by the user. In addition, a coating film (not shown in the figure) can be formed on the surface of the light guide panel 21 to allow visible light to pass through, and light in other wavelength bands is reflected in the light guide panel 21 .

In this embodiment, the signal amplifier 23 is adjacent to the second light guide part 215, and is used for receiving the optical signal derived from the second light guide part 215, amplifying the optical signal and then exporting it; the signal amplifier 23 may be in the form of a mirror.

In this embodiment, the photosensitive element 24 is adjacent to the signal amplifier 23 for receiving the optical signal derived from the signal amplifier 23 and processing the optical signal into a fingerprint image, so as to achieve the purpose of fingerprint identification. When the user presses the fingerprint sensing area 211 on the surface of the light guide panel 21 with the finger A, it will cause the destruction of the total internal reflection of the optical signal in the light guide panel 21, and the photosensitive element 24 can detect the waveform change of the optical signal, and It is processed into a fingerprint image to achieve the purpose of fingerprint identification.

In this embodiment, a lens, a prism film (Prism film), an angle filter (Angular filter) or a combination thereof may be further included between the photosensitive element 24 and the signal amplifier 23 . Please refer to FIG. 4A to FIG. 4D , which respectively illustrate the use of the lens 251 , the prism film 252 , the angle filter 253 and the combination of the prism film 252 and the angle filter 253 on the photosensitive element 24 in the embodiment of the present invention.

Wherein, the angle filter 253 shown in Figure 4C is a vertical grating filter, as shown in Figure 5A, the angle filter 253 can also be a sloped grating filter, and as shown in Figure 4C and Figure 5A, The angle filter 253 is a single-layer structure formed by a multi-layer first material film 254 arranged at intervals, or the angle filter 253 may also be formed by an interval arrangement of a multi-layer first material film 254 and a multi-layer second material film 255 single layer structure. In addition, as shown in FIG. 5B , the angle filter 253 can be a multi-layer structure composed of multiple layers of first material films 254 and multiple layers of second material films 255 arranged at intervals, and the first layers of different layers in the multi-layer structure The material films 254 are aligned, or, as shown in FIG. 5C , the first material films 254 of different layers in the multilayer structure are staggered. In addition, as shown in FIG. 5D to FIG. 5F , respectively depict implementations of combining the angle filter 253 and the prism film 252 on the photosensitive element 24 corresponding to FIG. 5A to FIG. 5C .

In the above embodiment, the collimated optical signal is provided for total internal reflection in the light guide panel 21. In practical applications, the non-collimated light source 222 can also be used directly to provide an uncollimated optical signal in the light guide panel 21. , and then arrange a high-order angle filter 253 on the side of the photosensitive element 24, which can also achieve the purpose of fingerprint imaging.

In addition, as shown in FIG. 6A, the photosensitive element 24 in the optical fingerprint identification system 20 provided by the embodiment of the present invention can be placed parallel to the light guide panel 21; as shown in FIG. 6B, the optical fingerprint recognition system 20 provided by the embodiment of the present invention The photosensitive element 24 in the fingerprint recognition system 20 can also be placed obliquely relative to the light guide panel 21 , and the inclination angle α can be, for example, 10 degrees, 45 degrees or 90 degrees.

The present invention is applied to a product in which the optical fingerprint recognition system 20 is integrated with a display panel. As shown in FIG. In practical applications, the light guide panel 21 is attached to the display panel 30 by coating optical glue 216 or dispensing according to the design requirements. In order to easily achieve fingerprint recognition on the entire surface, the light guide panel 21 is better. It is the method of coating optical glue on the entire bottom surface. Since the photosensitive element 24 of the present invention does not detect by receiving the reflected light of the fingerprint, it does not cause the problem of insufficient penetration, which makes it more widely used.

In addition, the present invention can also combine the optical fingerprint identification system 20 with the camera lens of the mobile phone. As shown in FIG. The mirror (BS) 41, on the one hand, can provide the optical signal derived by the signal amplifier 23 to the photosensitive element 24 to sense imaging, and on the other hand, can also provide the optical signal transmitted by the lens module 40 to the photosensitive element 24 to sense imaging, That is to say, the present invention can be shared with the camera lens of the mobile phone up to the photosensitive element 24, so that the optical fingerprint identification system 20 does not need to occupy too much structural space, and the volume of the final product can be simplified.

In the above-mentioned embodiment, the type, shape, quantity, and relative relationship between the light guide panel 21 and its first light guide part 214 and second light guide part 215, collimated light source 22 or non-collimated light source 222, signal amplifier 23 and photosensitive element 24 The relationship such as position is only an example, and is not limited thereto, and any equivalent to the spirit of the present case does not depart from the scope of the present invention.

To sum up, the optical fingerprint identification system provided by the present invention uses the light guide panel as the fingerprint sensing area for finger pressing, and provides collimated optical signals at the same time, and is designed with the first light guide part and the second light guide The part enables the optical signal to be transmitted in the light guide panel through the effect of total internal reflection, and then the signal is amplified, and finally the wave form change is detected by the photosensitive element, so as to obtain the fingerprint image. Compared with the existing optical fingerprint recognition system, the photosensitive element is detected by receiving the light reflected by the finger, and there is a problem of penetration above the photosensitive element, which makes the configuration of fingerprint recognition related components limited; The optical fingerprint identification system provided by the invention is relatively easy to configure, especially when the optical fingerprint identification system is integrated with the display panel, the photosensitive element can be concealed on the back of the display panel, and there is no need to worry about the lack of penetration that will affect the identification rate. It is beneficial to the appearance design of the product to meet the aesthetic needs of consumers for the appearance of the product. The present invention can also integrate the optical fingerprint identification system with the lens module, and only need to add a polarizing beam splitter (PBS) or beam splitter (BS) to share the photosensitive element and simplify the product structure. Furthermore, regional or comprehensive fingerprint sensing areas can also be designed, allowing users to use the fingerprint recognition function more flexibly and conveniently.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the implementation scope of the present invention. Therefore, all equivalent changes or modifications based on the features and spirit described in the claims of the present invention shall be included in the protection scope of the present invention.

Claims (21)

1. An optical fingerprint identification system, characterized in that, comprising: A light guide panel, the surface of which has a fingerprint sensing area for finger pressing, and the light guide panel is respectively provided with a first light guide part and a second light guide part at a light incident end and a light output end; A light source, adjacent to the first light guide part, and providing at least one optical signal, the optical signal is guided into the light guide panel through the first light guide part and transmitted in the light guide panel through internal total reflection effect, and then passes through the light guide panel The second light guide is exported; A signal amplifier, adjacent to the second light guiding part, receives the optical signal derived from the second light guiding part, amplifies the optical signal and then leads it out; and A photosensitive element, adjacent to the signal amplifier, receives the optical signal derived from the signal amplifier, and processes the optical signal into a fingerprint image. 2. The optical fingerprint identification system according to claim 1, wherein the fingerprint sensing area is the entire or partial area of the surface of the light guide panel. 3. The optical fingerprint identification system according to claim 1, wherein the light guide panel is disposed above a display panel. 4. The optical fingerprint identification system according to claim 3, wherein the light guide panel is bonded to the display panel by coating optical glue or dispensing glue. 5. The optical fingerprint identification system according to claim 1, wherein the light source is a collimated light source or a non-collimated light source. 6. The optical fingerprint identification system according to claim 5, wherein the collimated light source is a laser, a vertical resonant cavity surface-emitting laser, or a combination of a non-collimated light source and a secondary optical element. 7. The optical fingerprint identification system according to claim 6, wherein the secondary optical element is selected from the group consisting of parabolic concentrating mirrors, compound parabolic concentrating mirrors, lenses, prisms, Fresnel lenses and combinations thereof. 8. The optical fingerprint identification system according to claim 1, wherein the wavelength of the optical signal is between 380-1400 nanometers. 9. The optical fingerprint identification system according to claim 1, wherein when the optical signal travels in the light guide panel, the distance between the optical signal and the normal of the surface or a bottom surface of the light guide panel is The included angle must be greater than arcsin(n ₀ /n ₂ ) and arcsin(n ₁ /n ₂ ); Wherein, n ₀ is the refractive index of the surface of the light guide panel; n1 is the refractive index of the bottom surface _of the light guide panel; and n ₂ is the refractive index of the light guide panel. 10 . The optical fingerprint identification system according to claim 1 , wherein the first light guide part, the second light guide part and the light guide panel are an integrated structure. 11 . 11 . The optical fingerprint identification system according to claim 1 , wherein the first light guide part and the second light guide part are disposed separately from the light guide panel. 12 . The optical fingerprint identification system according to claim 1 , wherein a coating film is formed on the surface of the light guide panel, and the coating film allows a visible light to pass through, and the light of other wavelength bands is reflected. 13 . 13. The optical fingerprint identification system according to claim 1, wherein the first light guide part and the second light guide part are in the form of mirrors or optical fibers. 14. The optical fingerprint identification system according to claim 1, wherein the signal amplifier is in the form of a mirror. 15. The optical fingerprint identification system according to claim 1, wherein a lens, a prism film, an angle filter, a polarizing beam splitting prism, a beam splitting mirror or the like are further included between the photosensitive element and the signal amplifier. combination. 16. The optical fingerprint identification system according to claim 15, wherein the angle filter is a vertical or inclined grating filter. 17. The optical fingerprint identification system according to claim 16, wherein the grating filter is a single-layer structure composed of multiple layers of first material thin films arranged at intervals. 18. The optical fingerprint identification system according to claim 16, wherein the grating filter is a single-layer structure composed of multiple layers of first material films and multiple layers of second material films arranged at intervals. 19. The optical fingerprint identification system according to claim 16, characterized in that the grating filter is a multi-layer structure composed of multiple layers of first material thin films and multi-layer second material thin films arranged at intervals, and the multi-layer The films of the first material in different layers in the structure are aligned or staggered. 20. The optical fingerprint identification system according to claim 1, wherein the photosensitive element is placed parallel or obliquely relative to the light guide panel. 21. The optical fingerprint identification system according to claim 1, wherein at least one prism is further included between the first light guide part and the light source and/or between the second light guide part and the signal amplifier, And the prism is a fixed or rotatable prism.