A sensitivity measurement device for an OCT system

Abstract

This application discloses a method for measuring the sensitivity of an OCT system, comprising the following steps: emitting an optical signal from a scanning light source; dividing the optical signal into an initial sampling optical signal and an initial reference optical signal; the initial reference optical signal entering a reference arm; the initial sampling optical signal entering a sampling arm, where the sampling optical signal undergoes 2N+1 attenuations; the output reference optical signal reflected from the reference arm interfering with the output sampling optical signal reflected from the sampling arm to form an interference optical signal; converting the interference optical signal into an electrical signal; converting the electrical signal into an FFT spectrum, obtaining the signal-to-noise ratio (SNR) through the FFT spectrum, and thus calculating the OCT system sensitivity; OCT system sensitivity = attenuation of the sampling optical signal + SNR, where the OCT system sensitivity is S, the attenuation of the sampling optical signal is FA, and the SNR is SNR, i.e., S = FA + SNR; the attenuation of the sampling optical signal = 2N × first attenuation + second attenuation; N ≥ 1. This application also provides an OCT system sensitivity measurement device.

Description

Technical Field

[0001] This case is a divisional application of the application filed on December 25, 2020, entitled "An OCT System Sensitivity Measurement Method and Measuring Device", with application number 2020115643358. Background Technology

[0002] Optical interferometry (OCT) is a biomedical imaging technique similar to ultrasound. It obtains cross-sectional and three-dimensional images of biological tissues by measuring backscattered or reflected light from a sample. It has advantages such as being non-invasive, having high resolution, and being able to perform in vivo imaging, and is currently widely used in clinical diagnosis and research in ophthalmology, dermatology, and cardiology.

[0003] Early OCT systems were primarily time-domain OCT. To improve the imaging speed of OCT systems, researchers proposed frequency-domain OCT systems. Compared to time-domain OCT, frequency-domain OCT has higher sensitivity. Sensitivity reflects the OCT system's ability to detect weak signals. Higher sensitivity means a stronger ability to detect weak signals, resulting in a greater imaging depth of the sample and thus obtaining more information about the sample's structure. Therefore, testing the sensitivity of OCT systems is particularly important.

[0004] The sensitivity of an optical interferometric tomography (OCT) system refers to the maximum allowable attenuation of the light signal by the sample arm of the system. The sensitivity of an OCT system is affected by the intensity of the received light signal and system noise. The intensity of the received light signal depends on the output power of the light source and the optical path attenuation, while system noise originates from the light source, passive optical path, and light reception. General imaging systems primarily rely on the optical structure of the imaging lens, while endoscopic OCT achieves high-sensitivity coherent optical reception by returning the light signal collected by the fiber optic lens to the interferometer for interferometry with the reference light. Balanced detection is used to remove DC signals and improve photoelectric conversion efficiency. After photoelectric conversion, the image is reconstructed. The optical transmission performance directly affects the OCT imaging quality. Similar to optical communication transmission links, the noise in OCT optical transmission links comes from three sources: source noise (quantum noise and mode noise RIN), optical path noise MPI, and detector thermal noise. The swept-frequency OCT source uses an extremely low-noise single-mode laser with negligible mode noise (RIN < 120dBc / Hz), leaving only shot noise (quantum noise). By controlling the optical path connection points to reduce MPI noise, and through high-quality coherent optical reception and balanced detection, the MPI noise and receiver thermal noise can also be reduced to below the source quantum noise, achieving quantum-limited transmission. At a wavelength of 1310nm, the SS-OCT system can achieve a sensitivity close to the theoretical quantum limit of approximately 120dB.

[0005] Since the effective dynamic range of an optical receiver is only 30–40 dB, measuring a sensitivity range of 120 dB requires introducing a fixed attenuation to pre-attenuate the optical signal to the receiver's optimal dynamic range. Then, the signal-to-noise ratio (SNR) of the received signal is measured. The fixed attenuation plus the SNR equals the system's optical sensitivity. However, after introducing a fixed attenuation, there is no consensus in academia and industry on how to accurately measure the SNR and obtain the overall system sensitivity. Currently, the most common method is to use an optical spectrum analyzer (OSA) to measure the SNR of the incoming optical signal, or a beam analyzer to measure the point spread function (PSF) of the received light. The difference between the peak value of the PSF and the noise level is the SNR, and the sensitivity is the fixed attenuation plus the SNR. The drawback of this method is that the photoelectric conversion in the OSA and beam analyzer differs from that in the OCT system's photoelectric receiver; therefore, the obtained SNR does not represent the overall noise performance of the OCT system. Summary of the Invention

[0006] In view of this, this application provides a method for measuring the sensitivity of an OCT system. This method and apparatus can conveniently adjust the attenuation in the sampling arm, ensure the high quality of the sampled optical signal, and directly use the OCT system itself to measure the system noise. It can easily and accurately obtain the sensitivity of the entire OCT system, without the need for expensive beam analyzers and optical spectrum analyzers (OSA), and includes the optical receiver noise of the OCT system itself, making it very suitable for use in actual production.

[0007] To achieve the above objectives, according to one aspect of this application, a method for measuring the sensitivity of an OCT system is provided.

[0008] This application provides the following technical solution.

[0009] 1. A method for measuring the sensitivity of an OCT system, characterized by comprising the following steps:

[0010] The scanning light source emits light signals;

[0011] The optical signal is divided into an initial sampled optical signal and an initial reference optical signal;

[0012] The initial reference optical signal enters the reference arm;

[0013] The initial sampled optical signal undergoes 2N+1 attenuations after entering the sampling arm;

[0014] The output reference light signal reflected from the reference arm and the output sampled light signal reflected from the sampling arm interfere to form an interference light signal;

[0015] The interference optical signal is converted into an electrical signal;

[0016] The electrical signal is converted into an FFT spectrum, and the signal-to-noise ratio is obtained from the FFT spectrum, thereby calculating the sensitivity of the OCT system.

[0017] The OCT system sensitivity = attenuation of the sampled optical signal + signal-to-noise ratio, the OCT system sensitivity is S, the attenuation of the sampled optical signal is FA, and the signal-to-noise ratio is SNR, that is, S = FA + SNR;

[0018] The attenuation of the sampled optical signal = 2N × first attenuation + second attenuation; N≥1.

[0019] 2. The OCT system sensitivity measurement method according to item 1, characterized in that the OCT system includes a scanning light source, a beam splitter, a reference arm, an imaging system interface, an interferometer module, a balanced detector, an FFT transformation module, and a display module, wherein the imaging system interface is connected to the sampling arm, and a sampling object is disposed on one side of the sampling arm.

[0020] 3. The OCT system sensitivity measurement method according to item 2, characterized in that the scanning light source emits a weakly coherent light signal, the beam splitter divides the weakly coherent light signal into an initial sampling light signal and an initial reference light signal, the output reference light signal reflected from the reference arm and the sampling arm interferes with the output sampling light signal in the interference module to form an interference light signal, the interference light signal is converted into an electrical signal by a balanced detector, and the electrical signal is converted into an FFT spectrum by an FFT transformation module and a display module and displayed on the screen of the display module.

[0021] 4. According to the OCT system sensitivity measurement method described in item 3, the sampling arm includes a variable optical attenuator and a fiber optic lens. The initial sampling light signal enters the sampling arm and first passes through the variable optical attenuator and the fiber optic lens in sequence to illuminate the sampling object. After being reflected by the sampling object, the sampling light signal passes through the fiber optic lens and the variable optical attenuator in sequence before being output.

[0022] The attenuation of the initial sampled optical signal is adjusted by the variable optical attenuator, thereby changing the sampled optical signal output by the sampling arm.

[0023] 5. A sensitivity measurement method for an OCT system according to any one of items 1-4, characterized in that the attenuation of the sampling optical signal after passing through the variable optical attenuator 2N times is 2N × a first attenuation; the attenuation of the sampling optical signal after being emitted on the sampling object is a second attenuation;

[0024] The first attenuation is the fixed attenuation of the variable optical attenuator;

[0025] The reflectance of the sample is R;

[0026] The second attenuation is Δx = 10lg(R).

[0027] 6. The OCT system sensitivity measurement method according to item 4, characterized in that the fixed attenuation of the variable optical attenuator is 0 to 50 dB.

[0028] 7. The OCT system sensitivity measurement method according to item 4, characterized in that the sampling object is a plane mirror, the reflectivity of the plane mirror is 30% to 100%, preferably 80% to 100%; the plane of the sampling object and the emitted beam of the fiber optic lens are set perpendicularly.

[0029] 8. The OCT system sensitivity measurement method according to item 1, characterized in that the signal-to-noise ratio = FFT spectrum peak height - noise average value - standard deviation;

[0030] The peak height of the FFT spectrum is the peak height when the peak value of the FFT spectrum reaches its maximum.

[0031] 9. The OCT system sensitivity measurement method according to item 2, characterized in that the wavelength of the weak coherent light signal emitted by the frequency sweep light source is 820nm~1500nm, the bandwidth is 50nm~260nm, and the scanning frequency is 5kHz~10MHz.

[0032] 10. A sensitivity measurement method for an OCT system according to item 2, characterized in that a plane mirror is provided inside the reference arm, the initial reference light signal enters the reference arm, is reflected by the plane mirror and then emitted to form the output reference light signal.

[0033] 11. An OCT system sensitivity measurement device, characterized in that it includes an OCT system and a measurement mechanism, the measurement mechanism includes a sampling arm and a sampling object, the sampling arm includes a variable optical attenuator and a fiber optic lens, and the variable optical attenuator, the fiber optic lens and the sampling object are coaxial, the OCT system is connected to a first end of the variable optical attenuator, and the second end of the variable optical attenuator is connected to the fiber optic lens.

[0034] 12. An OCT system sensitivity measurement device according to item 11, characterized in that the OCT system is provided with an imaging system interface, the first end of the variable optical attenuator is provided with an optical input interface, and the imaging system interface of the OCT system is connected to the optical input interface on the first end of the variable optical attenuator.

[0035] 13. An OCT system sensitivity measurement device according to item 11, characterized in that the second end of the variable optical attenuator is connected to the optical lens via an optical fiber.

[0036] 14. An OCT system sensitivity measurement device according to item 11, characterized in that the sampling object is a plane mirror, and the mirror surface of the plane mirror and the emitted beam of the fiber optic lens are arranged perpendicularly so that the light emitted from the fiber optic lens is perpendicularly incident on the plane mirror.

[0037] The reflectivity of the plane mirror is 30% to 100%, preferably 80% to 100%.

[0038] 15. An OCT system sensitivity measurement device according to item 11, characterized in that the OCT system includes a scanning light source, a beam splitter, a reference arm, an interference module, a balanced detector, an FFT transformation module, and a display module; the scanning light source emits a weakly coherent light signal; the beam splitter divides the weakly coherent light signal into an initial sampling light signal and an initial reference light signal; the output reference light signal reflected from the reference arm and the sampling arm interferes with the output sampling light signal in the interference module to form an interference light signal; the interference light signal is converted into an electrical signal by the balanced detector; and the electrical signal is converted into an FFT spectrum by the FFT transformation module and the display module and displayed on the screen of the display module.

[0039] 16. An OCT system sensitivity measurement device according to item 11, characterized in that the length of the sampling arm is consistent with the length of the reference arm of the OCT system.

[0040] 17. An OCT system sensitivity measurement device according to item 11, characterized in that the distance between the fiber optic lens and the sampled object does not exceed 1.5 mm.

[0041] The OCT system sensitivity measurement method provided in this application involves emitting an optical signal from a scanning light source. This optical signal is divided into an initial sampling optical signal and an initial reference optical signal. An FFT spectrum is obtained by interfering with the output reference optical signal and the output sampling optical signal, performing photoelectric conversion, FFT transformation, and image sampling. By moving the sampled object away from the fiber optic lens, the interference light intensity at the corresponding position of the sampled object can be obtained on the FFT spectrum. This measurement method can be used with OCT systems of different wavelengths and frequencies, and has universal applicability.

[0042] The OCT system sensitivity measurement method or apparatus provided in this application can obtain the signal-to-noise ratio corresponding to the attenuation by gradually increasing the fixed attenuation of the variable optical attenuator, and finally obtain the limiting sensitivity of the OCT system. Therefore, the measurement method of this application is more convenient, effective, low-cost, and easy to operate. The apparatus of this application has a simple structure and can easily and accurately obtain the sensitivity of the entire OCT system. It does not require expensive beam analyzers and optical spectrum analyzers (OSA), and it also includes the optical receiver noise of the OCT system itself, making it very suitable for use in actual production. Attached Figure Description

[0043] The accompanying drawings are provided to better understand this application and do not constitute an undue limitation thereof. Wherein:

[0044] Figure 1 This is a schematic diagram of the OCT system sensitivity measurement device according to this application.

[0045] Figure 2 This is a schematic diagram of the OCT system sensitivity measurement device according to this application.

[0046] List of reference numerals

[0047] 1-OCT system, 2-optical fiber, 3-variable optical attenuator, 4-fiber lens, 5-sample. Detailed Implementation

[0048] The following description provides exemplary embodiments of this application, including various details to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0049] Since the sensitivity of a swept-frequency optical interferometric tomography system depends only on the output optical power and optical path attenuation of the swept-frequency light source, and the system noise comes from the light source and light receiver, it has nothing to do with the mechanical movement or design of the imaging guide tube itself. The sensitivity of the swept-frequency optical interferometric tomography system is 90-120 dB. In order to measure accurately, all interferences such as mechanical movement and guide tube design must be eliminated. Therefore, the optical path was adjusted in the test, and the imaging guide tube was replaced with a fiber optic lens and a plane mirror. This adjustment does not change the sensitivity of the system itself, but is only used to optimize the signal, eliminate interference, and improve measurement accuracy.

[0050] The measurement method described in this application directly obtains the signal-to-noise ratio (SNR) from the OCT system, eliminating the need for expensive beam analyzers and OSA spectrometers, and incorporating the optical receiver noise inherent in the OCT system itself. The OCT system is a point-to-point optical communication transmission link: a laser emitted from a light source illuminates the object being tested through the sample arm; the reflected / scattered light from the object interferes with the reference arm; the interference light signal enters a balanced detector for photoelectric conversion; the resulting electrical signal is then sampled, processed into an FFT image, and the spectrum of the FFT light intensity can be directly displayed on the OCT system's screen. This FFT light intensity spectrum is the SNR of the optical signal received by the system. Unlike the SNR from the beam analyzer and OSA spectrometer, the SNR of this FFT spectrum comes from the system's own photodetector, thus including the system's photodetector noise. Since the OCT reconstructed image is based on this FFT signal, its SNR directly determines the quality of the reconstructed image.

[0051] Because swept-frequency optical interferometry (SFT) tomography systems have extremely high sensitivity, relying solely on direct optical attenuation on the sample arm and observing the system's FFT signal peak drop to a level comparable to noise for detection yields unstable and reliable measurement results. Therefore, a reasonable measurement method should combine optical attenuation and signal-to-noise ratio (SNR): First, attenuate the optical path to a certain extent to achieve the best SNR for the optical receiver. Then, accurately measure the system's SNR (SNR = peak height - average noise level - standard deviation). Attenuation + SNR = sensitivity.

[0052] This application provides a method for measuring the sensitivity of an OCT system, including the following steps:

[0053] Step 1: Scan the light source to emit light signals;

[0054] Step 2: Divide the optical signal into an initial sampled optical signal and an initial reference optical signal;

[0055] Step 3: The initial reference optical signal enters the reference arm;

[0056] Step 4: The initial sampling optical signal undergoes 2N+1 attenuations after entering the sampling arm;

[0057] Step 5: The output reference light signal reflected from the reference arm and the output sampled light signal reflected from the sampling arm interfere to form an interference light signal;

[0058] Step Six: Convert the interference optical signal into an electrical signal;

[0059] Step 7: Convert the electrical signal into an FFT spectrum, obtain the signal-to-noise ratio from the FFT spectrum, and then calculate the sensitivity of the OCT system;

[0060] The OCT system sensitivity is equal to the attenuation of the sampled optical signal plus the signal-to-noise ratio (SNR). The OCT system sensitivity is S, the attenuation of the sampled optical signal is FA, and the signal-to-noise ratio (SNR) is SNR, i.e., S = FA + SNR.

[0061] The attenuation of the sampled optical signal = 2N × first attenuation + second attenuation, where N ≥ 1.

[0062] The OCT system sensitivity measurement method provided in this application involves emitting an optical signal from a scanning light source. This optical signal is divided into an initial sampling optical signal and an initial reference optical signal. The initial sampling optical signal is attenuated after passing through a sampling arm and output as an output sampling optical signal. The initial reference optical signal passes through a reference arm and output as output reference optical information. The output sampling optical signal and the output reference optical signal undergo interference, photoelectric conversion, FFT transformation, and image sampling to obtain an FFT spectrum. The signal-to-noise ratio can be read from the FFT spectrum.

[0063] In this application, the OCT system includes a scanning light source, a beam splitter, a reference arm, an imaging system interface, an interferometer module, a balanced detector, an FFT transformation module, and a display module. The imaging system interface is connected to a measurement mechanism, which includes a sampling arm and a sample. The imaging system interface is connected to a first end of the sampling arm, and the sample is positioned close to a second end of the sampling arm. The sample is coaxial with and spaced apart from the sampling arm.

[0064] The scanning light source is used to provide an optical signal. The beam splitter is used to divide the optical signal into an initial reference optical signal and an initial sampling optical signal. The reference arm is used to output the initial reference optical signal through reflection. The sampling arm is used to attenuate the light intensity of the initial sampling optical signal and reflect it out. The interference module is used to provide conditions for the interference between the output sampling optical signal and the output reference optical signal. The balanced detector is used to convert the interference optical signal into an electrical signal. The FFT transformation module is used to convert the electrical signal into an FFT spectrum. The display module is used to display the FFT spectrum.

[0065] The reference arm and the sampling arm are of the same length, and the output reference optical signal and the output sampling optical signal are output simultaneously and interfere with each other.

[0066] In this application, the scanning light source emits a weakly coherent optical signal, and the beam splitter divides the weakly coherent optical signal into an initial sampling optical signal and an initial reference optical signal. The output reference optical signal reflected by the reference arm and the sampling arm interferes with the output sampling optical signal in the interference module to form an interference optical signal. The interference optical signal is converted into an electrical signal by a balanced detector, and the electrical signal is converted into an FFT spectrum by an FFT transformation module and a display module and displayed on the screen of the display module.

[0067] In this application, the sampling arm includes a variable optical attenuator, a fiber optic lens, and a sampling object. The initial sampling optical signal enters the sampling arm and first passes through the variable optical attenuator and the fiber optic lens in sequence to illuminate the sampling object. After being reflected by the sampling object, the sampling optical signal passes through the fiber optic lens and the variable optical attenuator in sequence before being output.

[0068] The attenuation of the initial sampled optical signal is adjusted by the variable optical attenuator, thereby changing the sampled optical signal output by the sampling arm.

[0069] The variable optical attenuator is an important passive optical device in optical fiber communication, which achieves real-time control of the signal by attenuating the transmitted optical power.

[0070] The initial sampling optical signal undergoes 2N+1 attenuations within the sampling arm, with 2N attenuations occurring after passing through a variable optical attenuator. The attenuation amount is the same for all 2N attenuations, determined by the parameters of the variable optical attenuator. Specifically, the attenuation of the sampling optical signal after passing through the variable optical attenuator twice is 2N × the first attenuation; the attenuation of the sampling optical signal after being emitted onto the sampling object is the second attenuation.

[0071] The first attenuation is the fixed attenuation of the variable optical attenuator;

[0072] The reflectance of the sample is R;

[0073] The second attenuation is Δx = 10lg(R).

[0074] One or more variable optical attenuators can be installed within the sampling arm, depending on the specific circumstances. When there is one variable optical attenuator in the sampling arm, the initial sampled optical signal undergoes three attenuations within the sampling arm, and the number of variable optical attenuators is N.

[0075] In this application, the fixed attenuation of the variable optical attenuator is 0-50dB.

[0076] The fixed attenuation of the variable optical attenuator can be 0, 5dB, 10dB, 15dB, 20dB, 25dB, 30dB, 35dB, 40dB, 45dB, or 50dB.

[0077] In this application, the sampling object is a plane mirror with a reflectivity of 30% to 100%, preferably 80% to 100%; the plane of the sampling object and the emitted beam of the fiber optic lens are arranged perpendicularly to reduce light loss.

[0078] The reflectivity of the plane mirror can be 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.

[0079] In this application, the signal-to-noise ratio = FFT spectrum peak height - noise average value - standard deviation;

[0080] The peak height of the FFT spectrum is the peak height when the FFT spectrum peak reaches its maximum. The peak height, average noise value, and standard deviation of the FFT spectrum can be obtained using an OCT system.

[0081] In this application, the wavelength of the weakly coherent optical signal emitted by the frequency sweep light source is 820nm to 1500nm, the bandwidth is 50nm to 260nm, and the scanning frequency is 5kHz to 10MHz.

[0082] In this application, a plane mirror is provided inside the reference arm. The initial reference light signal enters the reference arm, is reflected by the plane mirror, and is then emitted to form the output reference light signal.

[0083] like Figure 1 and Figure 2 As shown, this application also provides an OCT system sensitivity measurement device, including an OCT system 1 and a measurement mechanism. The measurement mechanism includes a sampling arm and a sampling object 5. The sampling arm includes a variable optical attenuator 3 and a fiber optic lens 4, and the variable optical attenuator 3, the fiber optic lens 4 and the sampling object 5 are coaxial. The OCT system 1 is connected to the first end of the variable optical attenuator, and the second end of the variable optical attenuator is connected to the fiber optic lens 4.

[0084] The initial sampling optical signal is attenuated after entering the variable optical attenuator 3. The attenuated sampling optical signal passes through the fiber optic lens 4 and is not attenuated in the fiber optic lens 4. The sampling optical signal is then reflected on the sampling object 5. The reflected sampling optical signal is then sequentially injected into the fiber optic lens 4 and the variable optical attenuator 3 and enters the OCT system 1.

[0085] The OCT system 1 can be an optical interferometric tomography system.

[0086] The aforementioned OCT system sensitivity measurement method is performed using an OCT system sensitivity measurement device.

[0087] In this application, the OCT system 1 is provided with an imaging system interface, and the first end of the variable optical attenuator 3 is provided with an optical input interface. The imaging system interface of the OCT system 1 is connected to the optical input interface on the first end of the variable optical attenuator 3. The imaging system interface and the optical input interface are connected through an optical fiber 2.

[0088] In this application, the second end of the variable optical attenuator 3 is connected to the optical lens via an optical fiber 2.

[0089] In this application, the sampling object 5 is a plane mirror, and the mirror surface of the plane mirror is positioned directly opposite the fiber optic lens 4 so that the light rays emitted from the fiber optic lens 4 are perpendicularly incident on the plane mirror.

[0090] In this application, the OCT system 1 includes a scanning light source, a beam splitter, a reference arm, an interference module, a balanced detector, an FFT transformation module, and a display module. The scanning light source emits a weakly coherent light signal. The beam splitter divides the weakly coherent light signal into an initial sampling light signal and an initial reference light signal. The output reference light signal reflected from the reference arm and the sampling arm interferes with the output sampling light signal in the interference module to form an interference light signal. The interference light signal is converted into an electrical signal by the balanced detector. The electrical signal is converted into an FFT spectrum by the FFT transformation module and the display module and displayed on the screen of the display module.

[0091] In this application, the length of the sampling arm is the same as the length of the reference arm of the OCT system 1, so that the optical signal reflected from the reference arm and the optical signal output from the sampling arm can interfere.

[0092] In this application, the distance between the fiber optic lens 4 and the sample 5 does not exceed 1.5 mm, so as to reduce the error of the attenuation of the sampled optical signal, thereby improving the measurement accuracy of the detection device and reducing the error.

[0093] Example 1

[0094] A method for measuring the sensitivity of an OCT system includes the following steps:

[0095] Step 1: Scan the light source to emit light signals;

[0096] Step 2: Divide the optical signal into an initial sampled optical signal and an initial reference optical signal;

[0097] Step 3: The initial reference optical signal enters the reference arm;

[0098] Step 4: The initial sampling optical signal enters the sampling arm. The sampling optical signal undergoes two fixed attenuations in the sampling arm (the fixed attenuation amount is the first attenuation amount). The attenuation amount of the two fixed attenuations is 2×35dB, that is, the first attenuation amount is 35dB. At the same time, it passes through the fiber optic lens and reaches the plane mirror, and is reflected back to the fiber optic lens. The emissivity of the plane mirror is 80%.

[0099] Step 5: The output reference light signal reflected from the reference arm and the output sampled light signal reflected from the sampling arm interfere to form an interference light signal;

[0100] Step Six: Convert the interference optical signal into an electrical signal;

[0101] Step 7: Convert the electrical signal into an FFT spectrum, obtain the signal-to-noise ratio from the FFT spectrum, and then calculate the sensitivity of the OCT system.

[0102] Examples 2 and 3 differ from Example 1 in that the first attenuation and the reflectivity of the plane mirror are different in Examples 2 and 3. In Example 2, the first attenuation is 37.5 dB and the plane mirror reflectivity is 90%. In Example 3, the first attenuation is 40 dB and the plane mirror reflectivity is 100%.

[0103] Comparative Example 1

[0104] The method for measuring the sensitivity of an OCT system includes the following steps:

[0105] Step 1: Scan the light source to emit light signals;

[0106] Step 2: Divide the optical signal into an initial sampled optical signal and an initial reference optical signal;

[0107] Step 3: The initial reference optical signal enters the reference arm;

[0108] Step 4: The initial sampling light signal enters the sampling arm. The sampling light signal is attenuated by 2*30dB in the sampling arm and then passes through the connected imaging guide tube to reach the plane mirror and is emitted back to the imaging guide tube. The plane mirror emissivity is 0.1% (due to the limitation of the light output angle of the imaging guide tube and the relative position of the plane mirror, the light signal returned by the reflecting mirror is very weak).

[0109] Step 5: The output reference light signal reflected from the reference arm and the output sampled light signal reflected from the sampling arm interfere to form an interference light signal;

[0110] Step Six: Convert the interference optical signal into an electrical signal;

[0111] Step 7: Convert the electrical signal into an FFT spectrum, observe that the peak value and noise of the system's FFT signal are similar, and then calculate the sensitivity of the OCT system.

[0112] The difference between Comparative Examples 2 and 3 and Comparative Example 1 lies in the different first attenuation and the different reflectivity of the imaging conduit via the plane mirror. In Comparative Example 2, the first attenuation is 35 dB, and the plane mirror reflectivity is 0.2%. In Comparative Example 3, the first attenuation is 40 dB, and the plane mirror reflectivity is 0.4%.

[0113] Table 1 shows the sensitivity and other parameters of the methods used in each embodiment and comparative example.

[0114] Signal-to-noise ratio (dB) plane mirror reflectivity First attenuation / dB Second attenuation / dB Sensitivity / dB Example 1 48.16 80％ 35 0.97 119.13 Example 2 43.81 90％ 37.5 0.46 119.27 Example 3 39.35 100％ 40 0 119.35 Comparative Example 1 0 0.1％ 30 30 90 Comparative Example 2 0 0.2％ 35 26.99 96.99 Comparative Example 3 0 0.4％ 40 23.98 103.98

[0115] Summary: As shown in the table above, the detection sensitivity using the method described in this application is close to the limiting sensitivity (120dB) of the OCT system. In contrast, in Comparative Examples 1-3, due to the limitations of the imaging guide tube's exit angle and the relative position of the plane mirror, the light signal returned by the reflecting mirror is very weak, resulting in a signal-to-noise ratio of 0. The detected sensitivity differs significantly from the limiting sensitivity, and the measurement results fluctuate considerably. Therefore, the method described in this application, by adjusting the attenuation within the sampling arm while minimizing attenuation through the plane mirror, ensures high-quality sampling light signals and avoids the uncertain attenuation introduced by the imaging guide tube. Furthermore, the signal-to-noise ratio can be directly obtained by measuring the noise and interference signals of the OCT system itself, thus enabling a simple and accurate determination of the sensitivity of the entire OCT system.

[0116] Although the embodiments of this application have been described above in conjunction with the specific embodiments described, this application is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the teachings of this specification and without departing from the scope of protection of the claims of this application, and these are all within the scope of protection of this application.

Claims

1. A method for measuring sensitivity using an OCT system sensitivity measuring device, characterized in that, The OCT system sensitivity measurement device includes an OCT system and a measurement mechanism. The measurement mechanism includes a sampling arm and a sampling object. The sampling arm includes a variable optical attenuator and a fiber optic lens. The variable optical attenuator, the fiber optic lens, and the sampling object are coaxial. The OCT system is connected to the first end of the variable optical attenuator, and the second end of the variable optical attenuator is connected to the fiber optic lens. The OCT system includes a scanning light source, a beam splitter, a reference arm, an interferometer module, a balanced detector, an FFT transformation module, and a display module. The method includes: The scanning light source emits a weakly coherent light signal. The beam splitter divides the weakly coherent light signal into an initial sampling light signal and an initial reference light signal. The initial reference light signal enters the reference arm. After entering the sampling arm, the initial sampling light signal undergoes 2N+1 attenuations. The output reference light signal reflected from the reference arm and the sampling arm interferes with the output sampling light signal in the interference module to form an interference light signal. The interference light signal is converted into an electrical signal by a balanced detector. The electrical signal is converted into an FFT spectrum by an FFT transformation module and a display module. The signal-to-noise ratio is obtained from the FFT spectrum and displayed on the screen of the display module. The OCT system sensitivity = attenuation of the sampled optical signal + signal-to-noise ratio, the OCT system sensitivity is S, the attenuation of the sampled optical signal is FA, and the signal-to-noise ratio is SNR, that is, S = FA + SNR; The attenuation of the sampled optical signal = 2N × first attenuation + second attenuation; N≥1; The reflectance of the sample is R; The second attenuation is ∆x = 10lg(R); The first attenuation is the fixed attenuation of the variable optical attenuator; By gradually increasing the fixed attenuation of the variable optical attenuator, the signal-to-noise ratio corresponding to the attenuation is obtained, and finally the limiting sensitivity of the OCT system is obtained.

2. The method according to claim 1, characterized in that, The OCT system is equipped with an imaging system interface, and the first end of the variable optical attenuator is equipped with an optical input interface. The imaging system interface of the OCT system is connected to the optical input interface on the first end of the variable optical attenuator.

3. The method according to claim 1, characterized in that, The second end of the variable optical attenuator is connected to the optical fiber lens via an optical fiber.

4. The method according to claim 1, characterized in that, The sampling object is a plane mirror, and the mirror surface of the plane mirror and the emitted beam of the fiber optic lens are set perpendicularly so that the light emitted from the fiber optic lens is perpendicular to the plane mirror. The reflectivity of the plane mirror is 30% to 100%.

5. The method according to claim 4, characterized in that, The reflectivity of the plane mirror is 80%~100%.

6. The method according to claim 1, characterized in that, The length of the sampling arm is the same as the length of the reference arm of the OCT system.

7. The method according to claim 1, characterized in that, The distance between the fiber optic lens and the sampled object does not exceed 1.5 mm.

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