CN106840395B - Near-infrared super-continuum spectrum illumination system for active hyperspectral imaging - Google Patents
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Abstract
The invention discloses a near-infrared super-continuum spectrum illumination system for active hyperspectral imaging, and aims to provide a scheme with wide spectrum range, high power level and uniform illumination for the active hyperspectral imaging system. The device consists of a first supercontinuum light source, a second supercontinuum light source, a beacon light source, a wide-spectrum optical fiber beam combiner, an optical fiber end cap, an emission module and a modulation control module; the emission module is an off-axis reflector group, the modulation control module respectively sends two kinds of electric trigger signals to the first super-continuum spectrum light source and the second super-continuum spectrum light source, so that the first super-continuum spectrum light source and the second super-continuum spectrum light source emit super-continuum spectrum pulses with different spectral ranges, the wide-spectrum optical fiber beam combiner combines the super-continuum spectrum pulses, the optical fiber end cap emits the received super-continuum spectrum pulses to the emission module, and the emission module expands and focuses the received super-continuum spectrum and emits the received super-continuum spectrum to a target to achieve uniform illumination. The invention has wide spectrum range, high power level and uniform illumination.
Description
Technical Field
The invention relates to a near-infrared super-continuum spectrum illumination system for active hyperspectral imaging, and belongs to the technical field of laser.
Background
The hyperspectral imaging technology is a novel imaging technology formed by organically combining the traditional two-dimensional imaging technology and the spectral technology. By using the imaging spectrometer, a target object can be continuously imaged in tens of or even hundreds of spectral bands, and the target morphological characteristics are obtained while the spectral information of the target is also obtained. The target is detected and identified through the fingerprint effect of different target reflection spectra. At present, the hyperspectral imaging technology has been applied to the fields of agriculture, vegetation ecology, geological mineral products, marine science and the like.
The traditional hyperspectral imaging system is based on a passive imaging technology, namely, a target is illuminated by natural light such as sunlight, and the target is imaged by an imaging spectrometer, so that the hyperspectral imaging system is easily influenced by factors such as weather and geographical environment of the target in working time, imaging quality and the like. Particularly, under the condition of insufficient illumination at night, cloudy days and the like, the number of target reflected photons is often insufficient, so that the hyperspectral imager is difficult to acquire effective data. In order to break through the limitations of the passive hyperspectral imaging technology in the aspects of working time, imaging quality and the like, the application range of the hyperspectral imaging technology is expanded, and the active hyperspectral imaging technology is developed. The active hyperspectral imaging system replaces a natural light source with an artificial light source to realize active illumination on a target, so that the active hyperspectral imaging system can work all day long. In a laboratory, a lighting system in an active hyperspectral imager system usually adopts a traditional wide-spectrum light source (such as an incandescent lamp, a halogen light source and the like) as a light source, but the light source has poor light beam quality and low brightness, so that the lighting system can only illuminate a target at a short distance and cannot meet the requirement of a hyperspectral imager for long-distance work. The laser light source has good light beam quality and high brightness, and can realize long-distance transmission; however, the output wavelength of a general laser light source is single, and the requirement of a hyperspectral imaging technology on a broad spectrum cannot be met. At present, multispectral illumination light sources are reported, active illumination with a few wavelengths is realized, and the application requirement of a hyperspectral imaging technology on spectral width cannot be met. Therefore, a wide-spectrum, high-power and high-brightness illumination system becomes a bottleneck problem in research and development of a full-time and long-distance active hyperspectral imaging technology. At present, no illumination system for providing an illumination light source for remote hyperspectral imaging exists.
The supercontinuum light source is used as a novel laser light source, has the advantages of wide output spectrum, high brightness, good spatial coherence and the like, can selectively cover the spectrum range from visible light, near infrared to short wave middle infrared according to application requirements, and has the parameters of light beam quality, brightness, spectrum flatness and the like far superior to the traditional wide-spectrum light sources such as halogen light sources and incandescent lamps. The super-continuum spectrum light source has the characteristics of wide spectrum of a common light source and long-distance transmission of a common laser light source, and can solve the problem of a light source of a long-distance active hyperspectral imaging system.
Disclosure of Invention
The technical problem to be solved by the invention is that various traditional wide-spectrum light source-based illumination systems cannot simultaneously meet the requirements of a hyperspectral imaging technology on the spectral range, the beam quality, the power density, the uniform illumination and the like of the illumination system. The invention provides a near-infrared super-continuum spectrum illumination system, and provides a solution of wide spectrum range, high power level and uniform illumination for an active hyperspectral imaging system.
The technical scheme adopted by the invention is as follows:
a near-infrared super-continuum spectrum illumination system for an active hyperspectral imaging technology is composed of a first super-continuum spectrum light source, a second super-continuum spectrum light source, a beacon light source, a wide-spectrum optical fiber beam combiner, an optical fiber end cap, an emission module and a modulation control module.
The emission module is an off-axis reflector group and consists of a collimating mirror, a relay mirror, a secondary emission mirror and a primary emission mirror. The collimating mirror is a concave reflecting mirror, the relay mirror is a plane reflecting mirror, the transmitting secondary mirror is a convex reflecting mirror, and the transmitting primary mirror is a concave reflecting mirror. The off-axis reflector group is placed by the following method: the position of the optical fiber end cap is required to ensure that the emission module can completely receive the light beam emitted by the optical fiber end cap, the output end of the optical fiber end cap is positioned on the focal plane of the collimating mirror, and the collimating mirror can completely receive the light beam emitted by the optical fiber end cap; the reflecting surfaces of the front and rear reflectors are opposite to each other in pairs, and the rear reflector can completely receive the light beam reflected by the front reflector. The divergence angle of the emergent beam and the size of the supercontinuum spot at the target can be changed by changing the distance between the secondary emission mirror and the primary emission mirror. The total reflection type supercontinuum light source collimation and beam expansion emission system adopted by the emission module can avoid chromatic aberration and light energy loss caused by lens materials and obscuration in a transmission type system, thereby obtaining high-efficiency emission. The super-continuum spectrum is firstly expanded by a collimating lens, then is transmitted to a target after being expanded by a secondary emission mirror and a primary emission mirror.
The first super-continuum spectrum light source is connected with a first input fiber of the wide-spectrum optical fiber combiner, the second super-continuum spectrum light source is connected with a second input fiber of the wide-spectrum optical fiber combiner, the beacon light source is connected with a third input fiber of the wide-spectrum optical fiber combiner, and an output fiber of the wide-spectrum optical fiber combiner is connected with an input fiber of the optical fiber end cap. The output end of the fiber end cap is located at the focal plane of the collimating mirror in the emission module.
The first supercontinuum light source and the second supercontinuum light source are both optical fiber amplifier-based supercontinuum light sources. The first supercontinuum light source is required to generate a supercontinuum with a spectral range of 1-2 μm, and the second supercontinuum light source is required to generate a supercontinuum with a spectral range of 2-2.5 μm. The first supercontinuum light source adopts a full-fiber high-power supercontinuum light source structure shown in fig. 1 in academic paper a hundreds of watt all-fiber near-infrared supercontinuum published in Laser Physics Letters, 10 th year 2013, 065402, and the output spectrum of the full-fiber high-power supercontinuum light source structure is shown in fig. 3(a) in the paper, and the spectrum coverage range is 1-2 μm. The second supercontinuum light source adopts a supercontinuum light source structure shown in fig. 4 in academic papers ultra-high-brightness, spectral flat type short-wave infrared supercontinuum light source for long-distance atmospheric application, which is published in Optics Express, volume 24, stage 18, pages 20010 to 20020, and the output spectrum of the supercontinuum light source structure is shown in fig. 5 in the paper, and the spectrum coverage range is 2-2.5 μm.
The beacon light source is a laser output by visible light waveband optical fibers. The working wavelength is any wavelength in the range of 380-780 nm. The beacon light source can be a continuous wave laser or a pulse laser. The beacon light source is used for providing indicating light for debugging of the transmitting module.
The wide-spectrum optical fiber combiner is based on quartz optical fibers, and is required to be capable of performing low-loss beam combination on the super-continuum spectrum with the wave band of 1-2 mu m and the wave band of 2-2.5 mu m, and the insertion loss is less than 0.25 dB. The wide-spectrum fiber combiner adopts a wide-spectrum fiber power combiner structure shown in fig. 1 in academic paper Combined supercontinuum source with >200W power using a 3 × 1 broad-spectrum fiber combiner (based on a 200 watt supercontinuum light source of the 3 × 1 wide-spectrum fiber combiner, which is published in Optics Letters, volume 40, stage 16, pages 3810 to 3813), such as zhonghang, long-nose army, Chengzheng, Chen-zhen, zhang, Chang, Hou-zhen, Hou, Chen jin, Chen-zhen, Hou-ju, Chen-jinbao, and the like. The wide-spectrum optical fiber combiner is obtained by optimizing parameters of an output fiber (namely the diameter of an output fiber core, the numerical aperture of a fiber core, the tapering proportion and the length of a tapering transition region) on the basis of the wide-spectrum optical fiber power combiner shown in figure 1 in the paper. The output fiber of the wide-spectrum optical fiber combiner is a multimode optical fiber, the diameter of the core of the output fiber is any value within the range of 50-100 mu m, and the numerical aperture of the core is any value within the range of 0.08-0.25; the tapering proportion of the optical fiber bundle in the wide-spectrum optical fiber combiner meets the following requirements: after the tapering is finished, the fiber cores of all the signal fibers at the tapered waist of the optical fiber group bundle are all located in the range of the fiber core area of the output fiber; the length range of the tapering transition region is 6-15 mm. The diameter and the numerical aperture of the fiber core of the output fiber of the wide-spectrum optical fiber combiner need to meet the requirement on the number M of independent speckle laser modes of the light spot, and the number M of the independent speckle laser modes of the light spot needs to meet the requirement on the speckle contrast C of the light spot.
The application occasion of active hyperspectral imaging illumination has certain requirements on the uniformity of light intensity. Light intensityThe uniformity is generally measured by the speckle contrast C, which is defined as the ratio of the root mean square value of the fluctuation of the light intensity of the light spot to the average value of the light intensity. The smaller C, the more uniform the light intensity distribution of the light spot. Research shows that for M independent speckle laser modes, the speckle contrast C of a light spot is M-1/2I.e. M ═ C-2. The range of C is more than or equal to 0 and less than or equal to 0.1. The number of modes M output by the wide-spectrum optical fiber combiner can be determined by C, and a certain number of modes M is realized by selecting the appropriate core diameter and numerical aperture of the output fiber. That is, the core diameter is 50-100 μ M, the numerical aperture is 0.08-0.25, and the value satisfying the requirement of the mode number M can be obtained by numerical simulation (e.g. by using software such as Matlab).
The optical fiber end cap is based on quartz glass, and the insertion loss of the wide-spectrum super-continuum spectrum with the wave band of 1-2.5 mu m is required to be less than 0.3 dB. The optical fiber end cap can increase the size of an output light spot, so that the power density of the output end face is reduced, and the damage of the output end face is prevented. The optical fiber end cap adopts an optical fiber end cap structure shown in fig. 1 in an academic paper of Monolithic fiber end cap collimator for high power free-space optical fiber-optical fiber coupling, namely, Applied Optics, 2016 (volume 55, phase 15, pages 4001 to 4004).
The modulation control module is a digital signal generator (i.e., DSP). The modulation control module is connected with the first supercontinuum light source and the second supercontinuum light source and is externally connected with the imaging spectrometer. After being powered on, the modulation control module continuously sends a first electrical trigger signal, a second electrical trigger signal and a third electrical trigger signal to the first supercontinuum light source, the second supercontinuum light source and the external imaging spectrometer respectively. The first electric trigger signal is a pulse cluster comprising a plurality of single pulses, and the width of the pulse cluster is T111Duty ratio of pulse cluster is k1Repetition frequency of f1Wherein 1 mu s is less than or equal to T111≤100ms，0.1％≤k1Less than or equal to 50 percent. Is obviously provided with f1＝k1/T111. First electric trigger signalThe pulse width range of the single pulse is 1ps-10ns, and the duty ratio range is 0.1% -10%. The first supercontinuum light source receives the first electric trigger signal and outputs a supercontinuum pulse cluster which is the same as the first electric trigger signal, namely the pulse cluster has the width of T111Duty ratio of k1. The second electrical trigger signal is also a pulse cluster comprising a plurality of single pulses, the pulse cluster having a width T121Duty ratio of k2Repetition frequency of f2. Requirement T121＝T111，k2＝k1，f2＝f1. The pulse width range of the single pulse of the second electric trigger signal is 1ps-10ns, and the duty ratio range is 0.1% -10%. The second supercontinuum light source receives a second electric trigger signal sent by the modulation control module and outputs a supercontinuum pulse cluster which is the same as the second electric trigger signal, namely the pulse cluster has the width of T121Duty ratio of k2Repetition frequency of f2. The second electric trigger signal and the first electric trigger signal have time delay delta T in time sequence, and the time delay delta T has the function of keeping the pulse cluster output by the first supercontinuum light source and the pulse cluster output by the second supercontinuum light source synchronous in time when being transmitted by the transmitting module. Delta T is more than or equal to 0 and less than or equal to T111/k1. The third electrical trigger signal is a pulse sequence to control the imaging spectrometer to be turned on and off. The pulse width of the third electrical trigger signal is T221Duty ratio of k3Repetition frequency of f3. Requirement T221＜T111And f is3＝2×f1That is, the integrated operating time of the external spectrometer is less than the width of the supercontinuum pulse cluster, and the integrated operating frequency f of the external spectrometer3Repetition frequency f of pulse cluster twice of supercontinuum output1The working mode can reduce the influence of background noise and improve the signal-to-noise ratio of hyperspectral imaging.
The modulation control module respectively sends a first electric trigger signal and a second electric trigger signal to a first super-continuum spectrum light source and a second super-continuum spectrum light source, the first super-continuum spectrum light source and the second super-continuum spectrum light source emit super-continuum spectrum pulses with different spectral ranges, the wide-spectrum optical fiber beam combiner combines the super-continuum spectrum pulses emitted by the first super-continuum spectrum light source and the second super-continuum spectrum light source, the optical fiber end cap emits the super-continuum spectrum pulses output by the wide-spectrum optical fiber beam combiner to the emission module, the emission module expands and focuses the received super-continuum spectrum, and the expanded and focused super-continuum spectrum is emitted to a target, so that uniform illumination of the target is achieved. And the modulation control module sends a third electric trigger signal to the external imaging spectrometer to control the external imaging spectrometer to be switched on and off so as to realize signal receiving.
In order to further reduce the insertion loss of the wide-spectrum optical fiber combiner to the 2-2.5 mu m wave band and further improve the combining efficiency, the wide-spectrum optical fiber combiner can be further optimized, the fiber core diameter and the numerical aperture of an input fiber of the wide-spectrum optical fiber combiner, which is connected with the second supercontinuum laser light source, are increased, the fiber core diameter range of the input fiber is 50-100 mu m, and the numerical aperture range is 0.08-0.25. Under the condition of certain fiber core diameter and numerical aperture, the effective mode field area of the long wavelength laser is larger, so that the fiber core diameter and the numerical aperture of the input fiber of the second super-continuum laser light source connected with the wide-spectrum optical fiber beam combiner are increased, the limitation loss of the wide-spectrum optical fiber power beam combiner on the 2-2.5 mu m waveband super-continuum is favorably reduced, the insertion loss of the wide-spectrum optical fiber power beam combiner on the 2-2.5 mu m waveband super-continuum is reduced, and the beam combining efficiency is improved.
The invention can achieve the following technical effects:
the invention has the advantages of wide spectrum range, high power level, uniform illumination and the like, can meet the requirements of hyperspectral imaging on the aspects of spectral width, working distance, light power density, illumination uniformity and the like of an active illumination light source, has the defects of narrow spectrum and low brightness of common wide-spectrum light sources (such as incandescent lamps, halogen light sources and the like) compared with the traditional single-wavelength laser, and has obvious advantages; in addition, all optical fiber structures are adopted except the transmitting module, so that the high stability of the system can be ensured, and the application and popularization are facilitated.
Drawings
Fig. 1 is a schematic view of the general structure of the present invention.
Fig. 2 is a schematic structural diagram of the transmitting module according to the present invention.
FIG. 3 is a timing diagram of electrical trigger signals sent by the modulation control module to the first supercontinuum light source and the second supercontinuum light source. The I column is a time sequence schematic diagram of a first electrical trigger signal sent by the modulation control module to the first supercontinuum light source, and the II column is a time sequence schematic diagram of a second electrical trigger signal sent by the modulation control module to the second supercontinuum light source.
FIG. 4 is a timing diagram illustrating the operation of the present invention. The ith column is a timing diagram of a first electrical trigger signal sent by the modulation control module to the first supercontinuum light source. Column II is a timing diagram of the cluster of supercontinuum pulses emitted by the first supercontinuum light source. Column III is a timing diagram of a third electrical trigger signal sent by the modulation control module to the external imaging spectrometer. Column IV is the timing diagram for the operation of the external imaging spectrometer.
Detailed description of the preferred embodiments
The operation principle, specific structure and embodiments of the present invention will be further described with reference to the accompanying drawings, but the present invention is not limited to the following examples.
Fig. 1 is a schematic structural view of the present invention. The device consists of a first supercontinuum light source 11, a second supercontinuum light source 12, a beacon light source 13, a wide-spectrum optical fiber beam combiner 14, an optical fiber end cap 15, an emission module 16 and a modulation control module 17. The first super-continuum spectrum light source 11 is connected with a first input fiber of the wide-spectrum optical fiber combiner 14, the second super-continuum spectrum light source 12 is connected with a second input fiber of the wide-spectrum optical fiber combiner 14, the beacon light source 13 is connected with a third input fiber of the wide-spectrum optical fiber combiner 14, and an output fiber of the wide-spectrum optical fiber combiner 14 is connected with an input fiber of the optical fiber end cap 15. The output end of the fiber end cap 15 is located at the focal plane of the collimating mirror 161 in the launch module 16. The modulation control module 17 is connected with the first supercontinuum light source 11 and the second supercontinuum light source 12 and is externally connected with the imaging spectrometer 22. The modulation control module 17 sends a first electrical trigger signal and a second electrical trigger signal to the first supercontinuum light source 11 and the second supercontinuum light source 12 respectively, the first supercontinuum light source 11 and the second supercontinuum light source 12 emit supercontinuum pulses with different wave bands, the wide-spectrum optical fiber beam combiner 14 combines the supercontinuum pulses emitted by the first supercontinuum light source 11 and the second supercontinuum light source 12, the optical fiber end cap 15 emits the supercontinuum pulses output by the wide-spectrum optical fiber beam combiner 14 to the emission module 16, the emission module 16 expands and focuses the received supercontinuum, and emits the expanded and focused supercontinuum to a target, so that uniform illumination of the target is realized. The modulation control module 17 sends a third electrical trigger signal to the external imaging spectrometer 22 to control the external imaging spectrometer 22 to be turned on and off, so as to receive signals.
Fig. 2 is a schematic structural diagram of the transmitting module 16 according to the present invention. The emission module 16 is an off-axis reflector group, and is composed of a collimating mirror 161, a relay mirror 162, a secondary emission mirror 163, and a primary emission mirror 164. The collimating mirror 161 is a concave mirror, the relay mirror 162 is a plane mirror, the emission secondary mirror 163 is a convex mirror, and the emission primary mirror 164 is a concave mirror. The off-axis reflector group is placed by the following method: the output end of the optical fiber end cap 15 is located on the focal plane of the collimating mirror 161, and the collimating mirror 161 can completely receive the light beam emitted from the optical fiber end cap 15; the reflecting surfaces of the front and rear reflectors are opposite to each other in pairs, and the rear reflector can completely receive the light beam reflected by the front reflector. The divergence angle of the outgoing beam and the size of the supercontinuum spot at the target can be varied by varying the distance between the secondary mirror 163 and the primary mirror 164. The transmitting module adopts a total reflection type supercontinuum light source collimation beam expanding and transmitting system, so that chromatic aberration can be avoided, light energy loss caused by lens materials and obscuration in a transmission type system can be avoided, and high-efficiency transmission is obtained. The super-continuum spectrum is firstly expanded by a collimating lens, then is transmitted to a target after being expanded by a secondary emission mirror and a primary emission mirror.
Fig. 3 shows a timing diagram of the first electrical trigger signal and the second electrical trigger signal respectively sent by the modulation control module 17 to the first supercontinuum light source 11 and the second supercontinuum light source 12. In fig. 3, the I-th column is a timing diagram illustrating the first electrical trigger signal sent by the modulation control module 17 to the first supercontinuum light source 11. The first electrical trigger signal sent by the modulation control module 17 to the first supercontinuum light source 11 is a pulse cluster comprising a plurality of pulsesThe width of the punching cluster is T111Duty ratio of k1Repetition frequency of f1. The first supercontinuum light source 11 receives a first electric trigger signal, and the output supercontinuum pulse cluster is the same as the first electric trigger signal, namely the pulse cluster width is T111Duty ratio of k1Repetition frequency of f1. In fig. 3, column II is a timing diagram of the second electrical trigger signal sent by the modulation control module 17 to the second supercontinuum light source 12. The second electrical trigger signal sent by the modulation control module to the second supercontinuum light source 12 is also a pulse cluster comprising a plurality of pulses, the width of the pulse cluster being T121Duty ratio of k2Repetition frequency of f2. The second supercontinuum light source 12 receives a second electric trigger signal sent by the modulation control module 17, and the output supercontinuum pulse cluster is the same as the second electric trigger signal, namely the pulse cluster width is T121Duty ratio of k2Repetition frequency of f2. Wherein, T121＝T111，k2＝k1，f2＝f1. In addition, since the supercontinuum pulse clusters generated by the first supercontinuum light source 11 and the supercontinuum pulse clusters generated by the second supercontinuum light source 12 do not necessarily have the same optical path length from the supercontinuum light source to the emission module, the two pulse clusters are not synchronized in time. Thus, a time delay Δ T is introduced between the first electrical trigger signal sent by the modulation control module 17 to the first supercontinuum light source 11 and the second electrical trigger signal sent by the modulation control module 17 to the second supercontinuum light source 12, the time delay Δ T serving to keep the pulse clusters output by the first supercontinuum light source 11 and the pulse clusters output by the second supercontinuum light source 12 synchronized in time when they are transmitted by the transmission module 16.
The following describes a process of reducing the influence of background noise by modulating the output pulse of the supercontinuum light source and modulating the on and off of the imaging spectrometer according to the present invention, taking fig. 4 as an example, and the operation timing sequence of the first supercontinuum light source 11 and the external imaging spectrometer 22 is taken as an example for explanation. As shown in FIG. 4, column I is a timing diagram of the first electrical trigger signal sent by the modulation control module 17 to the first supercontinuum light source 11. The first electrical trigger signal sent by the modulation control module 17 to the first supercontinuum light source 11 is a pulse cluster comprising a plurality of single pulses, the pulse width range of the single pulses is 1ps-10ns, the duty ratio range is 0.1% -10%, and the width of the pulse cluster is T111Duty ratio of pulse cluster is k1Repetition frequency of f1Obviously, there is f1＝k1/T111. Column II is a timing diagram of the clusters of supercontinuum pulses emitted by the first supercontinuum light source 11. The first supercontinuum light source 11 receives the first electric trigger signal sent by the modulation control module 17, and outputs a supercontinuum pulse cluster which is the same as the first electric trigger signal, namely the pulse cluster has the width of T111Duty ratio of k1. Column III is a timing diagram of a third electrical trigger signal sent by the modulation control module to the external imaging spectrometer. The pulse width of the third electrical trigger signal sent by the modulation control module 17 to the external imaging spectrometer 22 is T221Duty ratio of k3Repetition frequency of f3. Is obviously provided with f3＝k3/T221. Requirement T221＜T111And f is3＝2×f1. Column IV is a schematic timing diagram for operation of the external imaging spectrometer 22. The pulse width and repetition frequency of the integrating operation of the external spectrometer 22 are equal to the pulse width and repetition frequency of the third electrical trigger signal sent by the modulation control module 17 to the external imaging spectrometer 22, i.e. the frequency f of the integrating operation of the external spectrometer 223Repetition frequency f of pulse cluster twice of supercontinuum output1. As in column IV, there are no clusters of supercontinuum pulses in each case during the two adjacent integration operating times of the external spectrometer 22. The working mode can reduce the influence of noise and improve the signal-to-noise ratio of hyperspectral imaging.
The above embodiments are merely examples, and the scope of the present invention is not limited to the above embodiments, and all technical solutions that fall under the spirit of the present invention fall within the scope of the present invention.
Claims (6)
1. A near-infrared supercontinuum illumination system for active hyperspectral imaging is characterized in that the near-infrared supercontinuum illumination system for active hyperspectral imaging is composed of a first supercontinuum light source (11), a second supercontinuum light source (12), a beacon light source (13), a wide-spectrum optical fiber beam combiner (14), an optical fiber end cap (15), an emission module (16) and a modulation control module (17); the first supercontinuum light source (11) and the second supercontinuum light source (12) are both based on a fiber amplifier, the beacon light source (13) is a laser output by visible light band fibers, and the beacon light source (13) provides indicating light for debugging of the transmitting module (16); the wide-spectrum optical fiber combiner (14) is a quartz optical fiber-based wide-spectrum optical fiber combiner; the first supercontinuum light source (11) is connected with a first input fiber of a wide-spectrum optical fiber combiner (14), the second supercontinuum light source (12) is connected with a second input fiber of the wide-spectrum optical fiber combiner (14), the beacon light source (13) is connected with a third input fiber of the wide-spectrum optical fiber combiner (14), and an output fiber of the wide-spectrum optical fiber combiner (14) is connected with an input fiber of an optical fiber end cap (15); the optical fiber end cap (15) is based on quartz glass, and the position of the optical fiber end cap (15) needs to ensure that the emitting module (16) can completely receive the light beam emitted by the optical fiber end cap (15); the modulation control module (17) is a digital signal generator, is connected with the first supercontinuum light source (11) and the second supercontinuum light source (12), and is externally connected with the imaging spectrometer (22); the modulation control module (17) respectively sends a first electric trigger signal and a second electric trigger signal to the first supercontinuum light source (11) and the second supercontinuum light source (12), the first supercontinuum light source (11) receives the first electric trigger signal, an output supercontinuum pulse cluster is the same as the first electric trigger signal, the second supercontinuum light source (12) receives the second electric trigger signal, and the output supercontinuum pulse cluster is the same as the second electric trigger signal; the first supercontinuum light source (11) and the second supercontinuum light source (12) emit supercontinuum pulses with different spectral ranges, the wide-spectrum optical fiber beam combiner (14) combines the supercontinuum pulses emitted by the first supercontinuum light source (11) and the second supercontinuum light source (12), the optical fiber end cap (15) emits the supercontinuum pulses output by the wide-spectrum optical fiber beam combiner (14) to the emitting module (16), the emitting module (16) expands and focuses the received supercontinuum, and the expanded and focused supercontinuum is emitted to a target, so that uniform illumination of the target is realized; the modulation control module (17) sends a third electric trigger signal to the external imaging spectrometer (22) to control the external imaging spectrometer (22) to be switched on and off so as to realize signal receiving;
the first electrical trigger signal and the second electrical trigger signal are both pulse clusters comprising a plurality of single pulses; the pulse cluster width, the duty ratio and the repetition frequency of the first electric trigger signal and the second electric trigger signal are the same; the first electric trigger signal and the second electric trigger signal have time delay in time sequence, so that the pulse cluster output by the first supercontinuum light source and the pulse cluster output by the second supercontinuum light source are synchronous in time when being transmitted by the transmitting module; the pulse cluster width of the third electric trigger signal is less than that of the first electric trigger signal, and the repetition frequency of the third electric trigger signal is twice that of the first electric trigger signal;
the emission module (16) is an off-axis reflector group and consists of a collimating mirror (161), a relay mirror (162), a secondary emission mirror (163) and a primary emission mirror (164); the collimating mirror (161) is a concave reflecting mirror, the relay mirror (162) is a plane reflecting mirror, the emission secondary mirror (163) is a convex reflecting mirror, and the emission primary mirror (164) is a concave reflecting mirror; the output end of the optical fiber end cap (15) is positioned on the focal plane of the collimating mirror (161), and the collimating mirror (161) can completely receive the light beam emitted by the optical fiber end cap (15); the reflecting surfaces of the front and rear reflectors are opposite to each other in pairs, and the rear reflector can completely receive the light beam reflected by the front reflector.
2. The near-infrared supercontinuum illumination system for active hyperspectral imaging according to claim 1, characterized in that the first supercontinuum light source (11) produces a supercontinuum with a spectral range of 1-2 μm and the second supercontinuum light source (12) produces a supercontinuum with a spectral range of 2-2.5 μm.
3. The near-infrared supercontinuum illumination system for active hyperspectral imaging according to claim 1, characterized in that the beacon light source (13) operates at any wavelength within the range of 380-780nm, and the beacon light source (13) is a continuous wave laser or a pulse laser.
4. The near-infrared supercontinuum illumination system for active hyperspectral imaging according to claim 1, characterized in that the wide-spectrum fiber combiner (14) requires low-loss combining of supercontinuum in the 1-2 μm band and 2-2.5 μm band with insertion loss less than 0.25 dB.
5. The near-infrared supercontinuum illumination system for active hyperspectral imaging according to claim 1, characterized in that the fiber end cap (15) requires an insertion loss of less than 0.3dB for a broad spectrum supercontinuum in the 1-2.5 μm band.
6. The near-infrared supercontinuum illumination system for active hyperspectral imaging according to claim 1, characterized in that the divergence angle of the outgoing beam and the size of the supercontinuum spot at the target can be changed by changing the distance between the secondary (163) and primary (164) mirrors.
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| CN111916983B (en) * | 2020-07-24 | 2021-06-04 | 中国人民解放军国防科技大学 | Infrared supercontinuum light source based on multimode chalcogenide glass optical fiber |
| CN117192706B (en) * | 2023-10-23 | 2024-03-19 | 中国人民解放军国防科技大学 | Supercontinuum laser system for realizing hollow beam emission |
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| US5475221A (en) * | 1994-05-11 | 1995-12-12 | Brimrose Corporation Of America | Optical spectrometer using light emitting diode array |
| US7233392B2 (en) * | 2004-03-25 | 2007-06-19 | Opotek, Inc. | Spectral imaging device with tunable light source |
| US8687177B2 (en) * | 2007-01-23 | 2014-04-01 | Chemimage Corporation | System and method for combined Raman and LIBS detection |
| US8120778B2 (en) * | 2009-03-06 | 2012-02-21 | Imra America, Inc. | Optical scanning and imaging systems based on dual pulsed laser systems |
| US7928390B1 (en) * | 2007-09-06 | 2011-04-19 | Kla-Tencor Corporation | Infrared metrology |
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| CN204067843U (en) * | 2014-08-06 | 2014-12-31 | 深圳大学 | A kind of ultra broadband super continuum source based on two waveband fiber laser |
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| CN105068229A (en) * | 2015-08-17 | 2015-11-18 | 哈尔滨工业大学 | Low-temperature collimating optical system |
| CN205138642U (en) * | 2015-10-26 | 2016-04-06 | 苑高强 | Light source with broadband spectrum |
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Application publication date: 20170613 Assignee: BEIJING RAYPOWER LASER TECHNOLOGIES CO.,LTD. Assignor: National University of Defense Technology Contract record no.: X2023980053543 Denomination of invention: Near infrared supercontinuum spectral illumination system for active hyperspectral imaging Granted publication date: 20210115 License type: Common License Record date: 20231228 |
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