Optical fiber-photomultiplier tube detector and dynamic range expansion method and device thereof

Abstract

The present application relates to fiber-optic photomultiplier tube detector, specifically to fiber-optic photomultiplier tube detector and its dynamic range expansion method and device, used to solve the problem of insufficient dynamic range of fiber-optic photomultiplier tube detector. The dynamic range expansion method of the fiber-optic photomultiplier tube detector, the original dynamic range of the measured light signal is controlled and modulated, and the dynamic range is reduced, so that the photoelectric conversion is carried out by using the limited dynamic range of the photomultiplier. The present application improves the upper limit of the dynamic range of the photomultiplier detector, and meets the fine measurement requirement of the intensity of the pulse light signal in a larger intensity range.

Description

Technical Field

[0001] This invention relates to fiber optic photomultiplier tube detectors, and more specifically to fiber optic photomultiplier tube detectors and their dynamic range extension methods and devices. Background Technology

[0002] Photomultiplier tubes (PMTs) are among the most widely used photodetectors in scientific research. They mainly consist of a photocathode, a dynode, and an anode, and possess advantages such as high sensitivity and fast time response. However, due to their high sensitivity, they are easily affected by background light radiation, electromagnetic fields, and high-energy rays in practical applications, often requiring rigorous shielding. Using optical fibers to guide the light pulse signal to be measured to the photocathode of the PMT, thereby achieving rigorous shielding of the PMT, is a widely used practice in pulsed light radiation measurements under complex electromagnetic environments. This type of detector, which uses optical fibers to collect and transmit the light to be measured and then uses a photomultiplier tube for photoelectric conversion, is called a fiber-optic photomultiplier tube detector.

[0003] During the operation of a photomultiplier tube, a weak light signal generates photoelectrons at the photocathode. These photoelectrons are multiplied by a series of electrodes and eventually converted into an electrical signal at the anode. The number of electrons reaching the anode is typically 10 times greater than the number of photoelectrons generated at the photocathode. 4 -10 6 The electron gain. Under normal circumstances, the amplitude of the anode electrical signal is proportional to the intensity of the incident light. However, if the input light signal is strong, more photoelectrons are generated by the photocathode. After multiplication, the large number of electrons changes the electric field distribution between the last few stages of the photocathode and the anode, causing the electron beam to fail to be effectively multiplied as designed. This results in the anode electrical signal no longer being proportional to the intensity of the incident light. This is the nonlinear effect of the photomultiplier tube.

[0004] The nonlinear effect of photomultiplier tubes determines the upper limit of the dynamic range of photomultiplier tube detectors. The linear dynamic range of commonly used photomultiplier tubes is usually only two orders of magnitude, which cannot meet the requirements for fine measurement of pulse light signal intensity over a wider range of intensity. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of insufficient dynamic range of fiber optic photomultiplier tube detectors, and to provide a fiber optic photomultiplier tube detector and its dynamic range extension method and device.

[0006] To address the shortcomings of the existing technology, the present invention provides the following technical solution:

[0007] A method for extending the dynamic range of a fiber optic photomultiplier tube detector, characterized by the following steps:

[0008] Step 1: arranging a dynamic range expansion device between an optical fiber and a photomultiplier tube in an optical fiber-photomultiplier tube detector, for adjusting light intensity;

[0009] Step 2: judging in real time the intensity I0(t) of a light signal to be measured input to the dynamic range expansion device; t represents time;

[0010] if I0(t)<A, performing step 3;

[0011] if I0(t)≥A, performing step 4;

[0012] A is a critical light intensity value for dynamic range expansion;

[0013] Step 3: the dynamic range expansion device is in an unmodulated state, directly outputting the light signal to be measured to the photomultiplier tube through the dynamic range expansion device, and then outputting the signal through the photomultiplier tube;

[0014] the output light intensity of the dynamic range expansion device is I1(t)=T0I0(t), wherein T0 is the intrinsic light transmittance of the dynamic range expansion device;

[0015] the output signal V(t) of the photomultiplier tube is V(t)=s1×I1(t), wherein s1 is the operating coefficient of the photomultiplier tube;

[0016] Step 4: modulating the light signal to be measured by the dynamic range expansion device, then outputting the modulated signal to the photomultiplier tube, and outputting the signal through the photomultiplier tube, so as to realize expansion of the dynamic range of the optical fiber-photomultiplier tube detector;

[0017] the output light intensity of the dynamic range expansion device is I1(t)=I0(t)×T(t), wherein T(t) is the light transmittance of the dynamic range expansion device, T(t)=f(S(t-τ)), and τ is the delay of the light transmittance T(t) relative to a control signal S(t) of the dynamic range expansion device;

[0018] the output signal V(t) of the photomultiplier tube is V(t)=s1×I1(t)=I0(t)×f(S(t-τ)), wherein s1 is the operating coefficient of the photomultiplier tube.

[0019] Further, the dynamic range expansion device adopts one of an electro-optic modulator, an acousto-optic modulator, an electroabsorption optical modulator and a photoinduced refractive index change modulator.

[0020] Meanwhile, the present invention provides a dynamic range expansion device for an optical fiber-photomultiplier tube detector, which is located between an optical fiber and a photomultiplier tube detector and is configured to implement the above dynamic range expansion method for an optical fiber-photomultiplier tube detector, and is characterized in that: the device comprises a pulse generator, a beam shaping optical path, a polarizer, an electro-optic crystal and an analyzer which are sequentially arranged along an optical path;

[0021] The beam shaping optical path is used to shape the outgoing light from the optical fiber into a quasi-parallel beam.

[0022] The polarizer is used to adjust the quasi-parallel beam into quasi-parallel linearly polarized light.

[0023] The electro-optic crystal is used to modulate quasi-parallel linearly polarized light;

[0024] The pulse generator is used to apply a pulse voltage U to the electrodes at both ends of the electro-optic crystal to control the polarization state of the light transmitted by the electro-optic crystal; the pulse voltage U is the amplitude of the output signal S(t) of the pulse generator;

[0025] The analyzer is used to selectively transmit and output the modulated quasi-parallel linearly polarized light.

[0026] The present invention also provides a fiber-photomultiplier tube detector, comprising a fiber and a photomultiplier tube detector arranged sequentially along the optical path, wherein the present invention is characterized by further comprising the aforementioned dynamic range extension device.

[0027] The dynamic range extension device is located between the optical fiber and the photomultiplier tube.

[0028] The optical fiber is used for collecting and transmitting the optical signal to be tested.

[0029] The dynamic range extension device is used to modulate the optical signal under test and reduce the dynamic range of the optical signal under test.

[0030] The photomultiplier tube is used to perform photoelectric conversion on the modulated optical signal to be measured and output it.

[0031] Furthermore, the core diameter of the optical fiber is less than or equal to 50 μm;

[0032] The polarizer and analyzer of the dynamic range extension device are parallel, and the light transmittance T(t) of the dynamic range extension device and the phase difference between the o-ray and e-ray in the light signal under test are... The relationship is as follows:

[0033]

[0034] The modulation factor B is defined as follows:

[0035]

[0036] T1 is the maximum value of light transmittance T(t), T2 is the minimum value of light transmittance T(t), and Δ is the increase in light transmittance when the non-ideal parallel monochromatic beam in the light signal under test passes through the dynamic range extension device when the light transmittance T(t) = T2.

[0037] Furthermore, the core diameter of the optical fiber is greater than 50 μm and less than or equal to 500 μm;

[0038] The polarizer and analyzer of the dynamic range extension device are perpendicular to each other. The light transmittance T(t) of the dynamic range extension device and the phase difference between the o-ray and e-ray in the light signal under test are also considered. The relationship is as follows:

[0039]

[0040] The modulation factor B is defined as follows:

[0041]

[0042] T1 is the maximum value of light transmittance T(t), T2 is the minimum value of light transmittance T(t), and Δ is the increase in light transmittance when the non-ideal parallel monochromatic beam in the light signal under test passes through the dynamic range extension device when the light transmittance T(t) = T2.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] (1) The present invention provides a method for extending the dynamic range of an optical fiber-photomultiplier tube detector, which controls the modulation of the optical signal to be measured, which originally has a large dynamic range, to reduce its dynamic range so as to utilize the photomultiplier tube with a limited dynamic range for photoelectric conversion; the present invention increases the upper limit of the dynamic range of multiplier tube detectors, and meets the need for fine measurement of pulse light signal intensity over a larger intensity range.

[0045] (2) The present invention provides a dynamic range extension method for fiber-optic photomultiplier tube detectors. In order to improve the modulation factor of dynamic range extension devices with large core diameter (50-500μm), the present invention, through optimization analysis, designed a high modulation factor technology of "modulation high pass, natural low pass" under the condition of certain beam shaping capability. Even if the intensity modulator has the lowest transmittance when no voltage is applied, it has the highest transmittance when the strongest modulation state is applied, thus realizing >100 times intensity modulation of the light emitted from large core diameter optical fibers.

[0046] (3) The present invention provides a method for extending the dynamic range of a fiber optic photomultiplier tube detector, which can be used not only for fiber optic photomultiplier tube detectors, but also for extending the dynamic range of vacuum phototubes and semiconductor photodetectors. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of a method for extending the dynamic range of a fiber optic photomultiplier tube detector according to the present invention.

[0048] Figure 2 This is a schematic diagram of the structure of a fiber optic photomultiplier tube detector according to the present invention.

[0049] Description of the reference numerals is as follows: 1-beam shaping optical path; 2-polarizer; 3-electro-optic crystal; 4-analyzer; 5-pulse generator; 6-optical fiber; 7-photomultiplier tube. DETAILED DESCRIPTION OF EMBODIMENTS

[0050] The present invention will be further described below with reference to the accompanying drawings and exemplary embodiments.

[0051] Referring to Figure 1 , Figure 2 , a method for expanding the dynamic range of an optical fiber-photomultiplier tube detector comprises the following steps:

[0052] Step 1: arranging a dynamic range expansion device between the optical fiber 6 and the photomultiplier tube 7 in the optical fiber-photomultiplier tube detector, for adjusting light intensity;

[0053] Step 2: judging the intensity I0(t) of the light signal to be measured input to the dynamic range expansion device in real time; wherein t is time;

[0054] if I0(t)<A, executing step 3;

[0055] if I0(t)≥A, executing step 4;

[0056] A is a critical light intensity value for dynamic range expansion, which is 10 2 ;

[0057] Step 3: directly outputting the light signal to be measured to the photomultiplier tube 7 through the dynamic range expansion device, and then outputting the signal through the photomultiplier tube 7;

[0058] said dynamic range expansion device is in a non-modulation state, the output light intensity of the dynamic range expansion device is I1(t)=T0I0(t), and T0 is the intrinsic light transmittance of the dynamic range expansion device;

[0059] the output signal V(t) of said photomultiplier tube 7 is V(t)=s1×I1(t), and s1 is the working coefficient of the photomultiplier tube 7;

[0060] Step 4: modulating the light signal to be measured by the dynamic range expansion device, then outputting the modulated signal to the photomultiplier tube 7, and outputting the signal through the photomultiplier tube 7, thereby realizing expansion of the dynamic range of the optical fiber-photomultiplier tube detector;

[0061] Referring to Figure 1 , the output light intensity of the dynamic range expansion device I1(t)=I0(t)×T(t), T(t) is the light transmittance of the dynamic range expansion device, T(t)=f(S(t-τ)), that is, T(t) is a function of S(t-τ), and τ is the delay of the light transmittance T(t) relative to the control signal S(t) of the dynamic range expansion device;

[0062] I0(t) increases first and then decreases as t increases. At t1, I0(t) ≥ A, so T(t) decreases from 1 to 0.01, resulting in I1(t) = 1. From t1 to t2, T(t) remains constant, and I1(t) changes linearly with I0(t).

[0063] The output signal of the photomultiplier tube 7 is V(t) = s1 × I1(t) = I0(t) × f(S(t-τ)), where s1 is the operating coefficient of the photomultiplier tube 7.

[0064] like Figure 2 As shown, the present invention also discloses a dynamic range extension device for an optical fiber-photomultiplier tube detector, located between the optical fiber 6 and the photomultiplier tube detector 6, for implementing the above-mentioned dynamic range extension method for the optical fiber-photomultiplier tube detector.

[0065] The dynamic range extension device includes a pulse generator 5, and a beam shaping optical path 1, a polarizer 2, an electro-optic crystal 3, and an analyzer 4 arranged sequentially along the optical path.

[0066] The beam shaping optical path 1 is used to shape the light emitted from the fiber 6 into a quasi-parallel beam.

[0067] Polarizer 2 is used to adjust the quasi-parallel beam into quasi-parallel linearly polarized light.

[0068] Electro-optic crystal 3 is used to modulate quasi-parallel linearly polarized light; pulse generator 5 is used to apply pulse voltage U to the electrodes at both ends of electro-optic crystal 3 to control the polarization state of the light transmitted by electro-optic crystal 3; pulse voltage U is the amplitude of the output signal S(t) of pulse generator 5.

[0069] The analyzer 4 is used to selectively transmit the light emitted from the electro-optic crystal 3, thereby achieving intensity control of the light signal to be measured.

[0070] The present invention also discloses an optical fiber-photomultiplier tube detector, comprising an optical fiber 6, the aforementioned dynamic range extension device, and a photomultiplier tube detector 6 arranged sequentially along the optical path.

[0071] In this embodiment, the core diameter of optical fiber 6 is greater than 50μm and less than or equal to 500μm;

[0072] The polarizer 2 and analyzer 4 of the dynamic range extender are perpendicular to each other. The light transmittance T(t) of the dynamic range extender and the phase difference between the o-ray and e-ray in the light signal under test are also considered. The relationship is as follows:

[0073]

[0074] Phase difference The amplitude of the output signal S(t) from the pulse generator 5 is controlled by the pulse voltage U applied across the electro-optic crystal. For a typical electro-optic crystal, the following applies:

[0075]

[0076] The light transmittance T(t) can be controlled by controlling the timing, amplitude, and pulse width of the output signal of the pulse generator 5.

[0077] The extension factor of the dynamic range of the fiber-optic photomultiplier tube detector in this invention is simultaneously limited by the modulation factor B of the dynamic range extension device and the linear dynamic range of the photomultiplier tube.

[0078] The modulation factor B is defined as follows:

[0079]

[0080] T1 is the maximum value of light transmittance T(t), T2 is the minimum value of light transmittance T(t), and Δ is the increase in light transmittance when a non-ideal parallel monochromatic beam passes through the dynamic range extension device when light transmittance T(t) = T2.

[0081] As can be seen from the modulation factor B, B ~ 500. Even considering the influence of factors such as the wavelength of the optical signal under test, it is still easy to achieve a modulation factor B > 100, thus achieving dynamic range matching with the photomultiplier tube 7.

[0082] In other embodiments, the core diameter of optical fiber 6 is less than or equal to 50 μm;

[0083] The polarizer 2 and analyzer 4 of the dynamic range extender are parallel to each other. The light transmittance T(t) of the dynamic range extender and the phase difference between the o-ray and e-ray in the light signal under test are also considered. The relationship is as follows:

[0084]

[0085] The modulation factor B is defined as follows:

[0086]

[0087] T1 is the maximum value of light transmittance T(t), T2 is the minimum value of light transmittance T(t), and Δ is the increase in light transmittance when a non-ideal parallel monochromatic beam passes through the dynamic range extension device when light transmittance T(t) = T2.

Claims

1. A method for extending the dynamic range of a fiber optic photomultiplier tube detector, characterized in that, Includes the following steps: Step 1: A dynamic range extension device is set between the optical fiber (6) and the photomultiplier tube (7) in the fiber-photomultiplier tube detector to adjust the light intensity. The dynamic range extension device includes a pulse generator (5) and a beam shaping optical path (1), a polarizer (2), an electro-optic crystal (3), and an analyzer (4) arranged sequentially along the optical path. The beam shaping optical path (1) is used to shape the light emitted from the optical fiber (6) into a quasi-parallel beam. The polarizer (2) is used to adjust the quasi-parallel beam into quasi-parallel linearly polarized light. The electro-optic crystal (3) is used to modulate the quasi-parallel linearly polarized light. The pulse generator (5) is used to apply a pulse voltage to the electrodes at both ends of the electro-optic crystal (3). The pulse voltage controls the polarization state of the transmitted light by the electro-optic crystal (3). Output signal for pulse generator (5) The amplitude; the analyzer (4) is used to selectively transmit and output the modulated quasi-parallel linearly polarized light; Step 2: Real-time determination of the intensity of the optical signal to be measured input to the dynamic range extension device. ; For time; like Then proceed to step 3; like Then proceed to step 4; To extend the dynamic range to the critical light intensity value; Step 3: The dynamic range extension device is in a non-modulated state. The light signal to be measured is directly output to the photomultiplier tube (7) through the dynamic range extension device, and then output through the photomultiplier tube (7). The output light intensity of the dynamic range extension device is , The intrinsic light transmittance of the dynamic range extension device; The output signal of the photomultiplier tube (7) , The operating coefficient of the photomultiplier tube (7); Step 4: After the optical signal to be measured is modulated by the dynamic range extension device, it is output to the photomultiplier tube (7) and then output through the photomultiplier tube (7) to realize the extension of the dynamic range of the fiber-optic photomultiplier tube detector. Output light intensity of dynamic range extension device , For the light transmittance of the dynamic range extension device, , Light transmittance Control signals relative to dynamic range extension devices The delay; The output signal of the photomultiplier tube (7) , is the operating coefficient of the photomultiplier tube (7).

2. A fiber-optic photomultiplier tube detector, comprising an optical fiber (6), a dynamic range extension device, and a photomultiplier tube (7) arranged sequentially along an optical path, wherein the dynamic range of the fiber-optic photomultiplier tube detector is extended using the dynamic range extension method of claim 1; characterized in that: The optical fiber (6) is used for collecting and transmitting the optical signal to be tested; The dynamic range extension device is used to modulate the optical signal under test and reduce the dynamic range of the optical signal under test. The photomultiplier tube (7) is used to perform photoelectric conversion on the modulated optical signal to be measured and output it.

3. The fiber-optic photomultiplier tube detector according to claim 2, characterized in that: The core diameter of the optical fiber (6) is less than or equal to 50 μm; The polarizer (2) and analyzer (4) of the dynamic range extension device are parallel in direction, and the light transmittance of the dynamic range extension device is... The phase difference between the o-ray and e-ray in the optical signal to be measured The following relationship must be satisfied: ； Define modulation factor as follows: ； Light transmittance The maximum value, Light transmittance The minimum value, Light transmittance When the non-ideal parallel monochromatic beam in the light signal under test passes through the dynamic range extension device, the light transmittance increases.

4. The fiber-optic photomultiplier tube detector according to claim 2, characterized in that: The core diameter of the optical fiber (6) is greater than 50 μm and less than or equal to 500 μm; The polarizer (2) and analyzer (4) of the dynamic range extension device are perpendicular to each other, and the light transmittance of the dynamic range extension device is... The phase difference between the o-ray and e-ray in the optical signal to be measured The following relationship must be satisfied: ； Define modulation factor as follows: ； Light transmittance The maximum value, Light transmittance The minimum value, Light transmittance When the non-ideal parallel monochromatic beam in the light signal under test passes through the dynamic range extension device, the light transmittance increases.

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