Biological measuring instrument based on hollow pyramid delay line and optical path calculation method

Abstract

The invention relates to the technical field of biological optical detection, and discloses a biological measuring instrument based on a hollow pyramid delay line and an optical path calculation method.The biological measuring instrument comprises a low-coherence light source, a 3 * 3 equipartition optical fiber coupler, a reference arm module, a polarization controller, a measuring arm module, a balance detector, an FPGA data acquisition system and a notebook computer; and the measuring arm module comprises a second optical fiber collimator, a plane mirror, a dichroscope, a near-infrared LED target ring, eyes, an imaging lens group and a camera. According to the biological measuring instrument based on the hollow pyramid delay line and the optical path calculation method, the hollow pyramid delay line is adopted as a reference arm scanning device, the hollow pyramid delay line is provided with three reflecting surfaces which are perpendicular to one another, an incident beam can be strictly returned along the original path, the biological measuring instrument is not sensitive to incident angle deviation, and the mechanical stability and vibration interference resistance of a system are effectively improved; and the method is particularly suitable for application scenes with high requirements on stable measurement in a clinical environment.

Description

Technical Field

[0001] This invention relates to the field of bio-optical detection technology, specifically to a bio-measuring instrument and optical path calculation method based on a hollow cone delay line. Background Technology

[0002] Ophthalmic biometry instruments are non-contact optical measurement devices based on the principle of low-coherence interference, and have significant application value in fields such as myopia control and cataract surgery planning. The optical delay line, as the core component of this type of instrument, directly affects the measurement speed and accuracy. While commonly used rotating right-angle reflector delay lines can achieve relatively fast scanning, they have stringent requirements for perpendicular beam incidence and require complex adjustment supports, resulting in limited mechanical stability and anti-interference capabilities.

[0003] Furthermore, existing delay line optical path calculations mostly employ actual geometric optical path tracing methods, which are computationally complex and unsuitable for complex optical structures. In corneal curvature measurement, separate autofocus or ranging devices are often required to determine the distance between the target ring and the cornea. This not only increases system complexity and cost but also affects the integration and real-time performance of the measurement. Summary of the Invention

[0004] To address the problems mentioned in the background art, the present invention provides the following technical solution: a biometer based on a hollow cone delay line, comprising: a low coherence light source, a 3×3 evenly distributed fiber coupler, a reference arm module, a polarization controller, a measurement arm module, a balance detector, an FPGA data acquisition system, and a laptop computer; The reference arm module includes a first fiber collimator, a hollow cone delay line, a turntable, and a plane mirror. The measuring arm module includes a second fiber collimator, a plane mirror, a dichroic mirror, a near-infrared LED target ring, an eye, an imaging lens group, and a camera; The light emitted by the low-coherence light source is split by the 3×3 evenly split fiber coupler. The first light enters the reference arm module, is reflected by the hollow cone delay line and the plane mirror, and then returns. The second light enters the measurement arm module, is reflected by various tissues of the human eye, and then returns. The two lights interfere in the coupler, are received by the balance detector and converted into electrical signals, are processed by the FPGA data acquisition system, and then uploaded to the laptop computer for calculation of axial length, corneal thickness, anterior chamber depth, lens thickness, and vitreous thickness.

[0005] Preferably, the low-coherence light source is an SLD light source with a center wavelength of 840nm and a bandwidth of ±20nm, and the power is set to 6mW.

[0006] Preferably, the hollow cone delay line is composed of three mutually perpendicular plane mirrors, which are fixed on the turntable for rotational scanning. The turntable frequency is not less than 4Hz, the delay line scanning frequency is not less than 12Hz, and the optical path scanning range is not less than 50mm.

[0007] Preferably, the light emitted by the near-infrared LED target ring is reflected by the fundus and then formed into an image on the camera by the dichroic mirror and the imaging lens, which is used to calculate the corneal curvature, pupil diameter, and white-to-white distance.

[0008] Preferably, the formula for calculating the corneal curvature is: In the diagram, β is the camera magnification, r is the radius of the near-infrared LED target ring, d is the distance between the target ring and the cornea, and y0 is the size of the image of the near-infrared LED target ring on the camera.

[0009] Preferably, the distance from the target ring to the cornea is fed back and corrected in real time by the position of the corneal interference peak.

[0010] A method for calculating the equivalent optical path length of a hollow pyramidal delay line, wherein the formula for calculating the equivalent optical path length of the hollow pyramidal delay line is: S = L1 + L2 + L3 = 2L Where L1 is the optical path from the incident surface to the first reflecting surface of the hollow pyramid delay line, L2 is the optical path from the first reflecting surface to the third reflecting surface of the hollow pyramid delay line, L3 is the optical path from the third reflecting surface of the hollow pyramid delay line to the incident surface, and L is the distance from the incident surface to the vertex where the three reflecting surfaces of the hollow pyramid delay line intersect.

[0011] Preferably, the three reflecting surfaces of the hollow cone delay line are perpendicular to each other, and the perpendicularity accuracy of the fit is not less than 30 arcseconds.

[0012] Preferably, the FPGA data acquisition system is used to perform convolution operations, smoothing, interference peak extraction and positioning on the interference signal.

[0013] Preferably, the polarization controller is used to adjust the polarization state of the beam in the reference arm and the measuring arm to optimize the quality of the interference signal.

[0014] Compared with the prior art, the present invention provides a biometer and optical path calculation method based on a hollow cone delay line, which has the following beneficial effects: This biometer and optical path calculation method based on hollow cone delay lines uses a hollow cone delay line as a reference arm scanning device. It has three mutually perpendicular reflective surfaces, which can ensure that the incident beam returns strictly along its original path. It is insensitive to incident angle deviations, effectively improving the mechanical stability and anti-vibration interference capability of the system. It is particularly suitable for clinical applications that require stable measurements.

[0015] This biometer and optical path calculation method based on hollow pyramid delay lines simplifies the complex three-dimensional optical path into a two-dimensional model by proposing an equivalent optical path calculation method. The equivalent formula S=2L is used for calculation, which significantly reduces the complexity of optical path analysis, avoids tedious geometric tracing of each optical path segment, and improves computational efficiency and system design convenience.

[0016] This biometer and optical path calculation method based on hollow cone delay lines, in corneal curvature measurement, uses real-time feedback of the corneal interference peak position to correct the distance d from the target ring to the cornea. This replaces the independent ranging or autofocus module required in traditional systems, simplifying the system structure, significantly reducing hardware costs, and improving the integration and cost-effectiveness of the equipment. This biometric instrument and optical path calculation method based on hollow cone delay lines integrates low-coherence interferometry and imaging measurement functions, enabling the simultaneous acquisition of multi-dimensional parameters such as axial length, corneal thickness, anterior chamber depth, lens thickness, vitreous thickness, corneal curvature, and pupil diameter, thus achieving one-stop, high-efficiency measurement of eye biological parameters.

[0017] This biometric instrument and optical path calculation method based on a hollow cone delay line, through optimized optical path design and signal processing flow, combined with FPGA for real-time data processing, achieves a delay line scanning frequency of no less than 12Hz while ensuring eye safety. The axial length measurement accuracy can reach ±0.01mm, meeting the dual requirements of clinical diagnosis for measurement speed and accuracy. Attached Figure Description

[0018] Figure 1 The diagram shown is a structural diagram of a biometer based on a hollow cone delay line according to the present invention. Figure 2 The diagram shown is a schematic representation of the hollow cone delay line of the present invention. Figure 3 The diagram shown illustrates the calculation of the equivalent optical path length of a hollow cone delay line.

[0019] In the diagram: 1-Low coherence light source, 2-3×3 evenly distributed fiber coupler, 3-Reference arm module, 4-First fiber collimator, 5-Hollow cone delay line, 6-Turntable, 7-Plane mirror, 8-Polarization controller, 10-Measuring arm module, 11-Second fiber collimator, 12-Plane mirror, 13-Dichroic mirror, 14-Near-infrared LED target ring, 15-Eye, 16-Imaging lens group, 17-Camera, 18-Balance detector, 19-FPGA data acquisition system, 20-Laptop; 5-1-First reflecting surface of hollow cone delay line; 5-2-Second reflecting surface of hollow cone delay line; 5-3-Third reflecting surface of hollow cone delay line; 21 - Light incident surface, 22 - Two-dimensional equivalent diagram of hollow cone delay line. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a biometric instrument and optical path calculation method based on a hollow cone delay line. The system achieves highly stable and accurate optical path scanning through the hollow cone delay line, and simplifies optical path analysis by combining equivalent optical path calculation. Simultaneously, it utilizes interference signals and imaging data to achieve rapid measurement of multiple biological parameters of the eye. The system is compact, low-cost, and suitable for clinical ophthalmological testing.

[0022] System overall structure like Figure 1 As shown, the biometer in this embodiment includes a low-coherence light source 1, a 3×3 evenly distributed fiber coupler 2, a reference arm module 3, a polarization controller 8, a measurement arm module 10, a balance detector 18, an FPGA data acquisition system 19, and a laptop computer 20. The reference arm module 3 includes a first fiber collimator 4, a hollow cone delay line 5, a turntable 6, and a plane mirror 7; the measurement arm module 10 includes a second fiber collimator 11, a plane mirror 12, a dichroic mirror 13, a near-infrared LED target ring 14, an eye 15, an imaging lens group 16, and a camera 17.

[0023] The low-coherence light source 1 uses an SLD light source with a center wavelength of 840nm and a bandwidth of ±20nm, and the power is set to 6mW to ensure eye safety. A 3×3 split-beam fiber coupler 2 divides the light emitted from the light source into three paths, two of which enter the reference arm and the measurement arm respectively, and the third path is used for balanced detection. The first fiber collimator 4 and the second fiber collimator 11 both have a focal length of 8.8mm and are used to generate a parallel beam.

[0024] Optical path working process Light from the low-coherence source 1 is split by a 3×3 fiber optic coupler 2, and the first beam enters the reference arm module 3. After being collimated by the first fiber optic collimator 4, it becomes parallel light and is incident on the hollow pyramidal delay line 5. The hollow pyramidal delay line 5 is composed of three mutually perpendicular plane mirrors (e.g., ...). Figure 2As shown in the figure, its vertical alignment accuracy is no less than 30 arcseconds to ensure the beam returns along its original path. The hollow pyramidal delay line 5 is fixed on the turntable 6, which rotates at a frequency of no less than 4Hz, driving the delay line to perform optical path scanning at a frequency of no less than 12Hz, with a scanning range of no less than 50mm. After being reflected by the hollow pyramidal delay line 5, the beam is incident on the plane mirror 7, and after being reflected again, returns to the fiber coupler 2 along its original path.

[0025] The second beam enters the measurement arm module 10, is converted into parallel light by the second fiber collimator 11, and enters the human eye 15 through the 45° plane mirror 12 and the dichroic mirror 13 (highly reflective of 840nm light). After being reflected by the interfaces of the cornea, lens, and fundus of the human eye, the beam returns along its original path to the fiber coupler 2. The beams returning from the reference arm and the measurement arm undergo low-coherence interference in the coupler, and the polarization state of the beams from both arms is adjusted by the polarization controller 8 to optimize the interference signal.

[0026] The balanced detector 18 receives the interference signal and converts it into an electrical signal, which is then transmitted to the FPGA data acquisition system 19. The FPGA system performs convolution operations, smoothing, interference peak extraction and localization on the signal, and finally uploads the data to the laptop computer 20 to calculate parameters such as axial length, corneal thickness, anterior chamber depth, lens thickness and vitreous thickness.

[0027] Imaging and Corneal Curvature Calculation Near-infrared LED target ring 14 emits light to illuminate the human eye 15. After reflection from the fundus, the light passes through a dichroic mirror 13 (transparent to visible light) and an imaging lens group 16, forming an image on a camera 17. The imaging data is uploaded to an FPGA data acquisition system 19, and then a laptop computer 20 calculates the corneal curvature, pupil diameter, and white-to-white distance. The formula for calculating corneal curvature is: Where β is the camera magnification, r is the radius of the near-infrared LED target ring, d is the distance between the target ring and the cornea, and y0 is the size of the near-infrared LED target ring image on the camera. The distance between the target ring and the cornea is fed back in real time through the position of the corneal interference peak: the FPGA system detects the corneal interference peak and adjusts the position of the target ring through motor control to achieve automatic correction without the need for an additional ranging device, thus simplifying the system structure.

[0028] Calculation of equivalent optical path length of hollow pyramid delay line like Figure 3As shown, the equivalent optical path of the hollow pyramidal delay line 5 is calculated using a simplified method. Light enters the delay line from the incident surface 21, and returns after being reflected by the first reflecting surface 5-1, the second reflecting surface 5-2, and the third reflecting surface 5-3. The formula for calculating the equivalent optical path is: S = L1 + L2 + L3 = 2L, where L1 is the optical path from the incident surface to the first reflecting surface of the hollow pyramidal delay line, L2 is the optical path from the first reflecting surface to the third reflecting surface, and L3 is the optical path from the third reflecting surface back to the incident surface; L is the distance from the incident surface to the intersection vertex of the three reflecting surfaces of the hollow pyramidal delay line. This method simplifies the complex three-dimensional optical path into a two-dimensional equivalent model, significantly reducing the computational complexity. Specific Implementation

[0029] In a preferred embodiment, the system parameters are set as follows: Low coherence light source: SLD light source, center wavelength 840nm, bandwidth ±20nm, power 6mW.

[0030] Fiber collimator: focal length 8.8mm, numerical aperture 0.25.

[0031] Hollow cone delay line: optical path scanning range 50mm, turntable frequency 4Hz, delay line scanning frequency 12Hz.

[0032] Camera: CCD or CMOS sensor, magnification, target ring radius.

[0033] Data processing: The FPGA uses the Xilinx Artix-7 series to achieve real-time signal processing; the laptop runs customized software, and the parameter calculation time is less than 1 second.

[0034] This invention achieves beam return along its original path using a hollow cone delay line, making it insensitive to the incident angle and improving system stability and anti-interference capabilities. The equivalent optical path calculation method simplifies optical path analysis and avoids complex geometric modeling. Combined with interference peak feedback for real-time correction of the target ring distance, it eliminates the need for additional ranging devices and reduces costs. Experiments show that the system achieves an axial length measurement accuracy of ±0.01mm and a corneal curvature measurement accuracy of ±0.1D, making it suitable for large-scale ophthalmic screening and clinical diagnosis.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A biometric instrument based on a hollow cone delay line, characterized in that, include: Low coherence light source (1), 3×3 evenly split fiber coupler (2), reference arm module (3), polarization controller (8), measurement arm module (10), balance detector (18), FPGA data acquisition system (19) and laptop (20); The reference arm module (3) includes a first fiber collimator (4), a hollow cone delay line (5), a turntable (6), and a plane mirror (7). The measuring arm module (10) includes a second fiber collimator (11), a plane mirror (12), a dichroic mirror (13), a near-infrared LED target ring (14), an eye (15), an imaging lens group (16), and a camera (17). The light emitted by the low coherence light source (1) is split by the 3×3 evenly split fiber coupler (2), and the first light enters the reference arm module (3), and returns after being reflected by the hollow pyramid delay line (5) and the plane mirror (7); The second beam enters the measuring arm module (10), is reflected by various tissues of the human eye, and returns; the two beams interfere in the coupler, are received by the balance detector (18) and converted into electrical signals, are processed by the FPGA data acquisition system (19) and uploaded to the laptop (20) for calculation of axial length, corneal thickness, anterior chamber depth, lens thickness and vitreous thickness.

2. The biometer according to claim 1, characterized in that, The low coherence light source (1) is an SLD light source with a center wavelength of 840nm and a bandwidth of ±20nm, and the power is set to 6mW.

3. The biometer according to claim 1, characterized in that, The hollow cone delay line (5) is composed of three mutually perpendicular plane mirrors, which are fixed on the turntable (6) for rotational scanning. The turntable frequency is not less than 4Hz, the delay line scanning frequency is not less than 12Hz, and the optical path scanning range is not less than 50mm.

4. The biometer according to claim 1, characterized in that, The light emitted by the near-infrared LED target ring (14) is reflected by the fundus and then imaged onto the camera (17) by the dichroic mirror (13) and the imaging lens group (16) to calculate the corneal curvature, pupil diameter and white-to-white distance.

5. The biometer according to claim 4, characterized in that, The formula for calculating the corneal curvature is: In the middle, β is the magnification of the camera (17), r is the radius of the near-infrared LED target ring (14), d is the distance between the target ring and the cornea, and y0 is the size of the image of the near-infrared LED target ring (14) on the camera (17).

6. The biometer according to claim 5, characterized in that, The distance from the target ring to the cornea is fed back and corrected in real time by the position of the corneal interference peak.

7. A method for calculating the equivalent optical path length of a hollow pyramidal delay line, characterized in that, The equivalent optical path length of the hollow pyramid delay line (5) is calculated as follows: S = L1 + L2 + L3 = 2L Where L1 is the optical path from the incident surface to the first reflecting surface of the hollow pyramid delay line, L2 is the optical path from the first reflecting surface to the third reflecting surface of the hollow pyramid delay line, L3 is the optical path from the third reflecting surface of the hollow pyramid delay line to the incident surface, and L is the distance from the incident surface to the vertex where the three reflecting surfaces of the hollow pyramid delay line intersect.

8. The optical path calculation method according to claim 7, characterized in that, The three reflecting surfaces of the hollow cone delay line (5) are perpendicular to each other, and the perpendicularity accuracy of the fit is not less than 30 arcseconds.

9. The biometer according to claim 1, characterized in that, The FPGA data acquisition system (19) is used to perform convolution operations, smoothing, interference peak extraction and positioning on the interference signal.

10. The biometer according to claim 1, characterized in that, The polarization controller (8) is used to adjust the polarization state of the beam in the reference arm and the measuring arm to optimize the quality of the interference signal.

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