CN117647878A - Dense optical path folding device - Google Patents
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Abstract
The application relates to the field of optical sensing and provides a dense optical path folding device, which adopts a plane reflector and a main concave reflector with aberration to form a reflecting cavity, introduces a sub-concave reflector, and sets the sub-concave reflector on the plane reflector, so that at least one of a reflecting surface of the plane reflector and a light of the sub-concave reflector is not on a focal plane of the main concave reflector, and the position and the angle are not coincident when an optical signal reflected by the sub-concave reflector returns to the sub-concave reflector after being reflected for multiple times in the reflecting cavity due to the aberration of the main concave reflector; and because the normal directions of different positions of the sub-concave reflecting mirror are different, after the optical signal returns to the sub-concave reflecting mirror again, the reflecting direction is different from the previous time and deviates from the original track direction, a semi-closed track is formed in the reflecting cavity, and after the optical signal is output from the output end, the total optical path in the reflecting cavity is improved by more than 10 times compared with the traditional optical path folding device, and the optical path volume ratio is higher.
Description
Technical Field
The application relates to the field of optical sensing, in particular to a dense optical path folding device.
Background
In a limited volume, multiple reflections of the optical signal are realized, so that the optical signal passes through a relatively long optical path, and the optical device has important application in the field of optical sensing, in particular to the field of sensing and analysis of special gases.
Currently, semiconductor tunable laser absorption spectroscopy (Tunable Diode Laser Absorption Spectroscopy, TDLAS) technology and fourier transform infrared spectroscopy (Fourier Transform Infra-Red, FTIR) technology are two main technological routes, the former mainly based on tunable laser light source for spectral analysis in near infrared band, and the latter adopts broad spectrum light source for spectral analysis in mid-far infrared band by fourier transform.
To achieve adequate detection accuracy, both TDLAS and FTIR techniques require the use of a long path gas cell to transmit the optical signal in the gas to be analyzed for sufficient optical path to enhance the absorption spectrum of the gas, and to bring the volume of the detection instrument within acceptable limits, the long path gas cell typically requires the use of an optical path folding device to reflect the optical signal as many times as possible within a limited volume to achieve sufficient optical path.
For TDLAS applications, since the divergence angle of the laser signal is small, the industry commonly adopts a herriot chamber structure, as shown in fig. 1, the herriot chamber 100 adopts two concave mirrors 103 and 104 with the same focal length f to form a reflective cavity, when the input direction and position of the optical signal input by the input end 101 and the distance d between the two concave mirrors along the z direction meet certain conditions (generally taking an out-of-focus configuration of 0< d <2f or 2f < d <4 f), the optical signal will be reflected back and forth between the two concave mirrors for multiple times, and finally output from the output end 102. Fig. 2 shows that on two concave mirrors 203, 204 the reflection points form a circular spot track 201 in the x-y plane.
For FTIR applications, since the light source needs to use an incoherent broad spectrum thermal light source, the divergence angle of the optical signal is large, the performance of the herriott cell cannot meet the requirements, and this is caused by the defocusing configuration characteristic necessary for the herriott cell, the divergence angle cannot converge after the incoherent optical signal is reflected multiple times in the defocusing system, therefore, the industry generally adopts a conventional white cell structure, as shown in fig. 3, the white cell 300 is composed of three concave mirrors with the same radius of curvature and focal length f, the primary mirror 301 is located at one side, the two secondary mirrors 302 and 303 are located at opposite sides of the primary mirror, the input optical signal 304 and the output optical signal 305 are located at both sides of the primary mirror, the two secondary mirrors 302 and 303 have a certain inclination angle, the distance between the primary mirror 301 and the two secondary mirrors 302 and 303 is set to be 2f, so that the optical signal is reflected multiple times between the primary mirror 301 and the two secondary mirrors 302 and 303, and finally is output from the primary mirror 301 side. The locus of the light spot on the primary mirror 301 is shown in fig. 4, and typically the position 404 of the input optical signal is offset from the axis 402 of the primary mirror 401 so that the light spot is distributed over two rows of loci 403, 406 to obtain the maximum number of reflections. The location 405 of the output optical signal is typically on the other side of the track 406 in line with the input optical signal.
With the improvement of the gas detection precision requirement in the industry, the requirement on a long-optical-path gas chamber is further improved, a longer optical path (more than 20 meters and even more than 100 meters) needs to be realized in a limited volume, and the Herriott chamber and the white chamber are difficult to realize more reflections in a certain volume. Based on the Herriott room and the white room, there are many improved designs, such as the use of an astigmatic lens proposed by the Herriott, but there is a problem that the astigmatic lens is difficult to process, and although the requirement of reducing the processing precision by rotating the astigmatic lens is still met, the problem of high processing cost of the astigmatic lens is still not solved; joel. A. Silver et al propose to achieve dense spot distribution, i.e. more reflection times, with a double cylindrical mirror, but due to the non-rotationally symmetric nature of the double cylindrical mirror, the optical signal no longer has the same optical signal characteristics as the input optical signal after multiple reflections, and cannot be applied in application scenarios where maintenance of optical signal characteristics (optical signal radius, divergence half angle, etc.) is required.
Other improved designs, such as the optical path folding device 500 shown in fig. 5, include an input end 501, an output end 502, a concave mirror 503, a main plane mirror 504, and an inclined mirror 505, where the distance 507 from the focal plane 506 of the concave mirror 503 to the concave mirror 503 is the focal length of the concave mirror 503; an origin 509 of the focal plane 506 is an intersection point of an optical axis 508 of the optical system formed by the main plane mirror 504 and the concave mirror 503 on the focal plane 506, and an inclination angle between a normal line of the first inclined sub-mirror 505 and a normal line of the main plane mirror 504 is not zero; the light beam is input from the input terminal 501, reflected multiple times by the concave mirror 503, the main plane mirror 504, and the inclined mirror 505, and then output from the output terminal 502. The optical path folding device 500 can achieve a longer optical path with a larger number of reflections and a higher optical path volume ratio than the herriott cell 100 and the white cell 300, but the improvement ratio of the optical path to the optical path volume ratio is still limited, and the requirements of the industry on the longer optical path and the larger optical path volume ratio cannot be met.
Disclosure of Invention
One of the purposes of the embodiments of the present application is: a compact optical path folding device is provided which can achieve a longer optical path and a larger optical path volume ratio than existing optical path folding devices.
The embodiment of the application provides a dense optical path folding device, which comprises:
an input terminal for inputting an optical signal;
the output end is used for outputting an optical signal;
a main concave reflector with focal length f, curvature radius R and aberration;
a plane mirror, the distance from the reflecting surface of the plane mirror to the optical center of the main concave mirror is L 1 ＝(1+x 1 )f，-1＜x 1 ＜1；
Concave reflecting mirror with focal length f 0 Radius of curvature R 0 And is arranged in the saidThe orthographic projection area of the reflecting surface of the sub-concave reflecting mirror on the reflecting surface of the plane reflecting mirror is smaller than the area of the reflecting surface of the plane reflecting mirror, and the distance from the optical center of the sub-concave reflecting mirror to the optical center of the main concave reflecting mirror is L 2 ＝(1+x 2 )f，R 0 ＝mR，-1＜x 2 ＜1，x 1 And x 2 Not simultaneously 0, m > 0;
the input end is arranged on the main concave reflector or the plane reflector, the output end is arranged on the main concave reflector, the plane reflector or the sub-concave reflector, and the reflecting surface of the main concave reflector is opposite to the reflecting surface of the plane reflector and the reflecting surface of the sub-concave reflector;
the optical signal is input from the input end, and is output from the output end after being reflected for a plurality of times by the main concave reflector, the plane reflector and the sub concave reflector.
In one embodiment, the dense optical path folding device comprises:
the optical centers of the two sub-concave reflectors are symmetrically arranged about the optical axis, and the orthographic projections of the reflecting surfaces of the two sub-concave reflectors on the reflecting surfaces of the plane reflectors are not overlapped;
wherein the optical axis is perpendicular to the reflecting surface of the plane reflecting mirror and passes through the optical center and the focal point 0< x of the main concave reflecting mirror 2 (1+2mx 1 -x 1 x 2 )＜2m；
The optical signals are input from the input end, and are output from the output end after being reflected for a plurality of times by the main concave reflector, the plane reflector and the two sub concave reflectors.
In one embodiment, the orthographic projection of the optical center of the sub-concave reflector on the reflecting surface of the plane reflector is located at the origin of the optical axis;
wherein the optical axis is perpendicular to the reflecting surface of the plane reflecting mirror and passes through the optical center and the focus of the main concave reflecting mirror, and the origin is the optical axisIntersection point with reflecting surface of said plane reflector, 0< x 2 (1+2mx 1 -x 1 x 2 )＜2m。
In one embodiment, x 2 ＞0；
And/or, m is more than or equal to 1 and less than or equal to 10, and x is more than or equal to 0.05 and less than or equal to 10 1 ≤0.5。
In one embodiment, the orthographic projection of the reflecting surface of the sub-concave reflecting mirror on the reflecting surface of the plane reflecting mirror deviates from the origin of the optical axis;
wherein the optical axis is perpendicular to the reflecting surface of the plane reflecting mirror and passes through the optical center and the focal point of the main concave reflecting mirror, and the origin is the intersection point of the optical axis and the reflecting surface of the plane reflecting mirror, x 1 ＝x 2 ＝x，0＜x(4x+1/m)＜1。
In one embodiment, x > 0.
In one embodiment, 0< x < 0.1.
In one embodiment, the primary concave mirror is a spherical mirror with aberrations, or the primary concave mirror is an aspherical mirror with aberrations designed.
In one embodiment, the input end, the output end and the sub-concave reflecting mirror are separately arranged, and the input end and the output end are both arranged on the plane reflecting mirror;
or the input end and the output end are overlapped to form an input end and an output end, and the input end and the sub-concave reflector are arranged separately and are arranged on the plane reflector;
or the input end and the output end are arranged separately, the input end is arranged on the plane reflector, and the output end is the main concave reflector; the optical signals are input from the input end, output to the first converging lens from the output end after being reflected for multiple times by the main concave reflector, the plane reflector and the sub concave reflector, and are converged to the receiving end by the first converging lens;
or the input end and the output end are arranged separately, the input end is arranged on the plane reflector, and the output end is the sub-concave reflector; the optical signals are input from the input end, and are output from the output end to the receiving end after being reflected for multiple times by the main concave reflector, the plane reflector and the sub concave reflector.
In one embodiment, the input end, the output end and the two sub-concave reflectors are separately arranged, and the input end and the output end are both arranged on the plane reflector.
The dense optical path folding device provided by the embodiment of the application adopts the plane reflector and the main concave reflector with aberration to form a reflecting cavity, the sub-concave reflector is introduced, the sub-concave reflector is arranged on the plane reflector, at least one of the reflecting surface of the plane reflector and the light of the sub-concave reflector is not arranged on the focal plane of the main concave reflector, and the main concave reflector has aberration, so that the position and the angle are not overlapped when the light signal reflected by the sub-concave reflector returns to the sub-concave reflector after being reflected for multiple times in the reflecting cavity; and because the normal directions of different positions of the sub-concave reflecting mirror are different, after the optical signal returns to the sub-concave reflecting mirror again, the reflecting direction is different from the previous time and deviates from the original track direction, so that a semi-closed track is formed in the reflecting cavity, and finally, after the optical signal is output from the output end, the total optical path in the reflecting cavity can be improved by more than 10 times compared with the existing optical path folding device, and further, the optical path volume ratio is higher.
Drawings
For a clearer description of the technical application in the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a schematic diagram of a prior art Herriott cell;
FIG. 2 is a graph of the spot light trace of a prior art Herriott cell;
FIG. 3 is a schematic diagram of a prior art white room;
FIG. 4 is a graph of the light signal reflection point light spot trace of a prior art bosom;
FIG. 5 is a schematic diagram of a prior art optical path folding device;
FIG. 6 is a schematic diagram of a first dense optical path folding device provided in an embodiment of the present application;
fig. 7 shows an embodiment of the present application providing m=6.37, n=45, x 1 ＝x 2 When x, x and B N Schematic diagrams of the corresponding relation between the two;
FIG. 8 is a schematic diagram of a second dense optical path folding device provided in an embodiment of the present application;
FIG. 9 is a schematic diagram of a third dense optical path folding device provided in an embodiment of the present application;
FIG. 10 is a schematic diagram of a fourth dense optical path folding device provided in an embodiment of the present application;
FIG. 11 is a schematic diagram of a fifth dense optical path folding device provided in an embodiment of the present application;
FIG. 12 is a schematic diagram of a sixth dense optical path folding device provided in an embodiment of the present application;
fig. 13 is a schematic diagram of a seventh dense optical path folding device provided in an embodiment of the present application.
Detailed Description
In order for those skilled in the art to better understand the present application, a technical application of embodiments of the present application will be clearly described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, shall fall within the scope of the present application.
The term "comprising" in the description of the present application and the claims and in the above figures, as well as any variants thereof, is intended to cover a non-exclusive inclusion. Furthermore, the terms "first" and "second," etc. are used for distinguishing between different objects and not for describing a particular sequential order.
As shown in fig. 6, the present application provides a dense optical path folding device 600 comprising:
an input 601 for inputting an optical signal;
an output 602 for outputting an optical signal;
a main concave mirror 603 having a focal length f, a radius of curvature R, and an aberration;
a plane mirror 604, the distance from the reflecting surface of the plane mirror 604 to the optical center of the main concave mirror 603 is L 1 ＝(1+x 1 )f；
Concave mirror 605 with focal length f 0 Radius of curvature R 0 And is arranged on the plane mirror 604, the orthographic projection area of the reflecting surface of the sub-concave mirror 605 on the reflecting surface of the plane mirror 604 is smaller than the area of the reflecting surface of the plane mirror 604, and the distance from the optical center of the sub-concave mirror 605 to the optical center of the main concave mirror 603 is L 2 ＝(1+x 2 )f，R 0 ＝mR；
Wherein, the optical axis 608 of the optical system formed by the plane mirror 604 and the main concave mirror 603 is perpendicular to the reflecting surface of the plane mirror 604 and passes through the optical center and the focal point of the main concave mirror 603, the optical axis 608 has an origin 609, and the origin 609 is the intersection point of the optical axis 608 and the reflecting surface of the plane mirror 604;
the input end 601 is disposed on the main concave mirror 603 or the plane mirror 604, the output end 602 may be disposed on the main concave mirror 603, the plane mirror 604 or the sub-concave mirror 605, the orthographic projection of the optical center of the sub-concave mirror 605 on the reflecting surface of the plane mirror 604 is located at the origin 609, or the orthographic projection of the reflecting surface of the sub-concave mirror 605 on the reflecting surface of the plane mirror 604 is offset from the origin 609, the input end 601 and the output end 602 are illustrated in fig. 6 to be disposed separately and all disposed on the plane mirror 604, the orthographic projection of the optical center of the sub-concave mirror 605 on the reflecting surface of the plane mirror 604 is located at the origin 609;
the reflecting surface of the main concave reflecting mirror 603 is arranged opposite to the reflecting surface of the plane reflecting mirror 604 and the reflecting surface of the sub concave reflecting mirror 605;
the optical signal is input from the input terminal 601, reflected multiple times by the main concave mirror 603, the plane mirror 604, and the sub concave mirror 605, and output from the output terminal 602.
In application, x 1 The offset of the reflecting surface of the plane reflecting mirror relative to the focal plane of the main concave reflecting mirror is defined as a first defocus amount, x 1 When=0, L 1 F, the reflecting surface of the plane mirror is located at the focal plane of the primary concave mirror; x is x 2 The deviation of the optical center of the sub-concave reflector relative to the focal plane of the main concave reflector is defined as a second defocus amount, x 2 When=0, L 2 The optical center of the concave sub-mirror is located at the focal plane of the concave main mirror. X is x 1 And x 2 Is dimensionless, at least one of the reflecting surface of the planar mirror and the optical center of the sub-concave mirror is not located at the focal plane of the main concave mirror, i.e. x 1 And x 2 And not 0 at the same time.
In application, due to R 0 =mr, f 0 Let f=1 without loss of generality, then there are:
L 1 ＝1+x 1 the method comprises the steps of carrying out a first treatment on the surface of the (equation 1)
L 2 ＝1+x 2 The method comprises the steps of carrying out a first treatment on the surface of the (equation 2)
f 1 =m; (equation 3)
Wherein, -1 < x 1 ＜1，-1＜x 2 ＜1，m＞0。
In one embodiment, the planar mirror includes a plurality of reflective regions, at least one of all reflective regions of the planar mirror being the input end, the input end having a reflectivity less than or equal to a reflectivity of the other reflective regions of the planar mirror;
or the main concave surface reflector comprises a plurality of reflection areas, at least one of all reflection areas of the main concave surface reflector is the input end, and the reflectivity of the input end is smaller than or equal to that of other reflection areas of the main concave surface reflector;
or the input end is a light passing hole or an open angle formed in the plane reflector.
In one embodiment, the primary concave reflector includes a plurality of reflective regions, at least one of all reflective regions of the primary concave reflector being an output, the output having a reflectivity less than or equal to the reflectivity of the other reflective regions of the primary concave reflector;
or the plane reflector comprises a plurality of reflection areas, at least one of all the reflection areas of the plane reflector is an output end, and the reflectivity of the output end is smaller than or equal to that of other reflection areas of the plane reflector;
or the sub-concave reflector comprises a plurality of reflecting areas, at least one of all the reflecting areas of the sub-concave reflector is an output end, and the reflectivity of the output end is smaller than or equal to that of other reflecting areas of the sub-concave reflector;
or the output end is a main concave reflector or a sub concave reflector;
or the output end is a light-passing hole or an open angle formed in the plane reflector.
In application, the reflective area is the position on the reflective surface of the reflector for reflecting the optical signal, and due to the limitation of the modern coating technology, the reflectivity Rmax of the reflective surface of the reflector can reach 0.99999, the difficulty and cost of increasing the reflectivity upwards are greatly increased, and the transmissivity Tmin of the reflective surface of the corresponding reflector (namely 1-R) can reach 0.00001, namely Tmin can reach 10 -5 Magnitude. For reflection areas as input or output having a reflectivity less than or equal to the reflectivity of other reflection areas, i.e. for reflection areas as input or output having a transmissivity greater than or equal to the transmissivity of other reflection areas, T for reflection areas as input or output 0 Can be of a size of 10 -5 -10 -3 Magnitude, e.g., between 0.0009 and 0.005. The positions, sizes and numbers of the reflecting areas used as the input end or the output end can be set according to actual needs, so long as the input end is ensured to be arranged on the main concave reflector or the plane reflector, and the output end is arranged on the main concaveA plane mirror, a plane mirror or a sub-concave mirror. When the number of reflection areas for use as input terminals is at least two, the transmittance of these input terminals may be the same or different; similarly, when the number of reflection areas for the output ends is at least two, the transmittance of the output ends may be the same or different; when both the input and output are reflective regions, the transmissivity of the input and output may be the same or different.
In application, the reflective areas with different transmittance in the main concave reflector, the plane reflector and the sub-concave reflector can be coated based on an integrated coating method or a split coating method. In the integrated coating process, a mask is used to create different layers in different areas of the reflective surface of the mirror. In the split type coating process, the reflecting surface of the reflecting mirror is separated into mutually independent areas, and the different areas are coated separately.
In application, by making the reflectivity of the input end or the output end smaller than that of the rest reflective area, the average reflectivity of all reflective areas is slightly reduced, so that the effective optical path of the reflective cavity is slightly reduced, which has a negative effect on the signal to noise ratio, but the technical means also greatly increases the light energy of the light signal output by the output end, when the optical signal processing device is applied to a gas optical sensing device (such as a gas absorption spectrum detection device), the light energy of the reflective cavity coupled to the receiving end (such as a photoelectric detector or a spectrum analyzer) can be improved, the signal to noise ratio of the gas absorption spectrum detection device is positively influenced, and the signal to noise ratio is greatly improved due to the positive influence being far larger than the negative influence, and the improvement multiple of the signal to noise ratio is positively correlated with the reflection times of the light signal in the reflective cavity.
In application, when the input end or the output end is a light-passing hole or an open angle, the device is suitable for inputting or outputting incoherent light signals with larger divergence angles, and the light signals enter the input end from free space and are output from the output end to free space.
In one embodiment, the input end and the output end are overlapped to form an input end and an output end, and the input end and the output end are arranged on the plane reflector or the main concave reflector;
or the input end and the output end are arranged separately and are both arranged on the plane reflecting mirror;
or the input end and the output end are arranged separately, the input end is arranged on the plane reflecting mirror, and the output end is arranged on the main concave reflecting mirror or the output end is the main concave reflecting mirror;
or the input end and the output end are arranged separately, the input end is arranged on the plane reflecting mirror, and the output end is arranged on the sub-concave reflecting mirror or the output end is the sub-concave reflecting mirror.
In application, the positions of the input end and the output end can be coincident or separated. When the positions of the input end and the output end are coincident, the two are the same, and the input end and the output end are defined as the input end and the output end, and the input end and the output end can be arranged on the plane reflector or the main concave reflector. When the positions of the input end and the output end are separated, the input end and the output end can be arranged on the same reflecting mirror (for example, a plane reflecting mirror) or can be arranged on different reflecting mirrors (for example, the input end is arranged on the plane reflecting mirror, the output end is arranged on the main concave reflecting mirror or the output end is the main concave reflecting mirror, the input end is arranged on the plane reflecting mirror, and the output end is arranged on the sub-concave reflecting mirror or the output end is the sub-concave reflecting mirror). When the output end is the main concave reflector or the sub-concave reflector, the output end comprises all reflection areas of the main concave reflector or the sub-concave reflector.
In one embodiment, the primary concave mirror is a spherical mirror with aberrations, or the primary concave mirror is an aspherical mirror designed with aberrations.
In application, the main concave reflecting mirror can adopt a spherical reflecting mirror, and the spherical reflecting mirror has aberration and is easy to process. The main concave surface reflecting mirror can also adopt an aspherical reflecting mirror, and the aspherical reflecting mirror usually has no aberration, so that a special aspherical reflecting mirror with aberration can be designed according to actual needs, and the design flexibility is certain.
In one embodiment, a dense optical path folding device comprises:
the optical centers of the two sub-concave reflectors are symmetrically arranged about the optical axis, and the orthographic projections of the reflecting surfaces of the two sub-concave reflectors on the reflecting surfaces of the plane reflectors are not coincident;
the optical signal is input from the input end, and is output from the output end after being reflected for multiple times by the main concave reflector, the plane reflector and the two sub concave reflectors.
In applications, the sub-concave mirror may be disposed concavely or convexly with respect to the reflective surface of the planar mirror, for example, the sub-concave mirror may be disposed embedded in the planar mirror, or may be adhered to the reflective surface of the planar mirror. When the dense optical path folding device includes two sub-concave mirrors, the reflective surfaces of the two sub-concave mirrors may be the same or different in size, that is, the forward projection areas of the reflective surfaces of the two sub-concave mirrors on the reflective surfaces of the planar mirrors may be the same or different. The fact that the orthographic projections of the two sub-concave reflectors on the reflecting surface of the plane reflector are not coincident and deviate from the origin means that the two sub-concave reflectors can be adjacently (i.e. contacted) or intermittently (i.e. not contacted) arranged on the plane reflector without shielding the origin.
In one embodiment, for the first case where the orthographic projection of the optical center of the sub-concave mirror onto the reflecting surface of the planar mirror is located at the origin of the optical axis, or the dense optical path folding device includes two sub-concave mirrors, to stabilize the reflecting cavity of the optical system, the optical system needs to satisfy a first stabilizing condition: x is 0< x 2 (1+2mx 1 -x 1 x 2 )＜2m；
For the second case that the orthographic projection of the reflecting surface of the sub-concave reflecting mirror on the reflecting surface of the planar reflecting mirror deviates from the origin of the optical axis, in order to stabilize the reflecting cavity of the optical system, the optical system needs to satisfy a second stabilizing condition: 0< x (4x+1/m) < 1.
In application, the derivation of the stable conditions of the optical system is as follows:
let the transmission matrix of the optical signal in the single circulation reflection in the reflection cavity beIt can be demonstrated that det (T) =1, i.e. AD-BC＝1；
Let the transmission matrix of the optical signal when the N times of cyclic reflections in the reflecting cavity be:
where θ=acos [ (a+d)/2 ].
So that the optical signal does not spill out of the cavity after N cycles of reflection in the reflective cavity, A N 、B N 、C N 、D N Real numbers are required and convergence is required, so-1 < (A+D)/2 < 1 (formula 4) is required to be satisfied;
for the first case, the transmission process of the optical signal circularly reflected once in the emission cavity is defined as: the optical signal is transmitted to the reflecting surface of the main concave reflecting mirror from the reflecting surface of the plane reflecting mirror, is transmitted to the reflecting surface of the sub concave reflecting mirror after being reflected by the reflecting surface of the main concave reflecting mirror, is transmitted to the reflecting surface of the main concave reflecting mirror again after being reflected by the reflecting surface of the sub concave reflecting mirror, is transmitted to the reflecting surface of the plane reflecting mirror again after being reflected by the reflecting surface of the main concave reflecting mirror, and is reflected by the reflecting surface of the plane reflecting mirror (definition 1);
according to definition 1, equations 1 through 3 and the matrix optics principle, the transmission matrix corresponding to definition 1 is expressed as:
wherein a=d= - (m-x) 2 +x 1 x 2 2 -2mx 1 x 2 )/m，B＝(x 1 x 2 -1)(2mx 1 -x 1 x 2 +1)/m，C＝x 2 (2m-x 2 )/m；
And->Representing a transmission matrix of the optical signal as it is transmitted in free space;
representing a transmission matrix when the light signal is reflected by the main concave mirror;
representing a transmission matrix when the sub-concave mirror reflects the optical signal;
according to equation 4, the first stabilization condition is:
-1＜-(m-x 2 +x 1 x 2 2 -2mx 1 x 2 ) M is less than 1; (equation 5)
Simplifying equation 5, a first stabilizing condition may be obtained as:
0＜x 2 (1+2mx 1 -x 1 x 2 )＜2m；
for the second case, the transmission process of the optical signal circularly reflected once in the emission cavity is defined as:
the optical signal is transmitted to the reflecting surface of the main concave reflecting mirror from the reflecting surface of the plane reflecting mirror, is transmitted to the reflecting surface of the plane reflecting mirror after being reflected by the reflecting surface of the main concave reflecting mirror, is transmitted to the reflecting surface of the main concave reflecting mirror again after being reflected by the reflecting surface of the plane reflecting mirror, is transmitted to the reflecting surface of the plane reflecting mirror again after being reflected by the reflecting surface of the main concave reflecting mirror, and is reflected by the reflecting surface of the plane reflecting mirror;
the optical signal is transmitted to the reflecting surface of the main concave reflecting mirror after being reflected by the reflecting surface of the plane reflecting mirror, is transmitted to the reflecting surface of the sub concave reflecting mirror after being reflected by the reflecting surface of the sub concave reflecting mirror, is transmitted to the reflecting surface of the main concave reflecting mirror again after being reflected by the reflecting surface of the main concave reflecting mirror, is transmitted to the reflecting surface of the plane reflecting mirror again after being reflected by the reflecting surface of the main concave reflecting mirror, and is reflected by the reflecting surface of the plane reflecting mirror (definition 2);
let x 1 ＝x 2 The transmission matrix corresponding to definition 2 is expressed as:
wherein a= - (4 x) 5 +8mx 4 +5x 3 -8mx 2 -x+m)/m，B＝-(x 2 -1)(4x 2 -8m 3 -5x 2 +4mx+1)/m，C＝-x(4x 3 -8mx 2 -3x+4m)/m，D＝(-4x 5 +8mx 4 +7x 3 -8mx 2 -3x+m)/m；
The 3 rd matrix on the right side of the equation is equal to the product of the 8 th matrix and the 9 th matrix, i.e
The 4 th matrix on the right side of the equation may be omitted;
the decimal term above third order (i.e. containing x 3 、x 4 、x 5 According to equation 4), the second stabilization condition is:
0＜x(4x+1/m)＜1。
in one embodiment, for the first case, x is in the case that the optical system satisfies a first stable condition 2 ＞0。
In one embodiment, for the first case, 1.ltoreq.m.ltoreq.10, 0.05.ltoreq.x, with the optical system satisfying the first stable condition 1 ≤0.5。
In the application, for the first case, when x, in the case where the optical system satisfies the first stable condition 2 At negative values, to ensure x 2 (1+2mx 1 -x 1 x 2 )＞0，x 1 Also has to be negative and has an absolute value greater than 1/2m, m has a value ranging from 1 to 10, x 1 The value of (2) is in the range of 0.05 to 0.5, which isIn the case of the optical system, the far focus distance configuration is unfavorable for the distribution of light spots, and therefore, x 2 The distance between the optical center of the sub-concave mirror and the reflecting surface of the main concave mirror may be set to be a positive value, i.e., greater than the focal length of the main concave mirror.
In one embodiment, for the second case, x > 0 where the optical system satisfies the second stable condition.
In the application, in the case that the optical system satisfies the second stable condition, when x is a negative value, in order to ensure that x (4x+1/m) > 0, the absolute value of x is larger, and in this case, the optical system is configured with a far focal distance, which is unfavorable for the distribution of the light spots, so x may be set to a positive value, that is, the distance between the optical center of the sub-concave mirror and the reflecting surface of the plane mirror to the reflecting surface of the main concave mirror is greater than the focal length of the main concave mirror.
In application, further analysis shows that, in case the optical system satisfies a stable condition, after N times of cyclical reflections of the optical signal in the reflective cavity, the transmission matrix T N B in (B) N When the angle relation between the position of the output light spot and the input light is equal to or close to 0, the dependence of the angle relation between the position of the output light spot and the input light is minimum, and the optical system is most stable.
In one embodiment, for the second case, 0< x < 0.1 in the case where the optical system satisfies the second stable condition.
In application, for the second case, as shown in fig. 7, m=6.37, n=45, x are exemplarily shown 1 ＝x 2 When x, x and B N The correspondence between the x values and the B values is represented by the horizontal axis coordinates N Is a value of (2). As can be seen in FIG. 7, when x is less than 0, the reflective cavity is unstable, B as x changes from 0 to 1 N Oscillating between-2 and 2 (for different optical system configurations, B N Fig. 7 is merely one example) and has a plurality of zero crossings, the value range of x may be set to 0 to 0.1, for example, x may take any value of the plurality of zero crossings in fig. 7, since the excessive defocus optical system is unfavorable for the spot distribution.
As shown in fig. 8, in one embodiment, the input end 601, the output end 602, and the sub-concave mirror 605 are separately disposed, and both the input end 601 and the output end 602 are disposed on the plane mirror 604;
the orthographic projection of the optical center of the sub-concave mirror 605 onto the reflecting surface of the planar mirror 604 is located at the origin.
As shown in fig. 9, in one embodiment, the input end 601, the output end 602 (not shown in the figure), and the sub-concave mirror 605 are separately disposed, and both the input end 601 and the output end 602 are disposed on the plane mirror 604;
the forward projection of the optical center of the sub-concave mirror 605 onto the reflecting surface of the planar mirror 604 is offset from the origin.
In application, the structure of the dense optical path folding device shown in fig. 8 and fig. 9 is different in that the orthographic projection positions of the optical centers of the sub-concave reflectors on the reflecting surfaces of the plane reflectors are different, so that the light spot tracks formed by the optical signals in the reflecting cavities are different, and the design flexibility is improved. Fig. 9 shows less variation in spot size on the planar mirror than fig. 8.
As shown in fig. 10, in one embodiment, the input end 601 and the output end 602 overlap to form an input/output end, and the input/output end and the concave sub-mirror 605 are separately disposed and disposed on the plane mirror 604;
the orthographic projection of the optical center of the sub-concave mirror 605 onto the reflecting surface of the planar mirror 604 is located at the origin.
As shown in fig. 11, in one embodiment, the input end 601 and the output end 602 are separately disposed, the input end 601 is disposed on the plane mirror 604, and the output end 602 is the primary concave mirror 603 itself;
the orthographic projection of the optical center of the sub-concave mirror 605 on the reflecting surface of the planar mirror 604 is located at the origin;
the optical signal is input from the input end 601, is output from the output end 602 to the first converging lens 610 after being reflected multiple times by the main concave mirror 603, the plane mirror 604 and the sub concave mirror 605, and is converged to the receiving end 611 by the first converging lens 610.
In application, the structure of the dense optical path folding device shown in fig. 11 is an application example based on the off-axis integrating cavity technology, and since the entire main concave mirror is used as the output end, the cross-sectional areas of the first converging lens and the main concave mirror in the direction perpendicular to the optical axis are required to be equivalent (for example, the cross-sectional area of the first converging lens in the direction perpendicular to the optical axis is greater than or equal to the cross-sectional area of the main concave mirror in the direction perpendicular to the optical axis), so that the optical signal output via the output end can be completely collected by the first converging lens and converged on the receiving surface of the receiving end.
As shown in fig. 12, in one embodiment, the input end 601 and the output end 602 are separately disposed, the input end 601 is disposed on the plane mirror 604, and the output end 602 is a sub-concave mirror 605;
the orthographic projection of the optical center of the sub-concave mirror 605 on the reflecting surface of the planar mirror 604 is located at the origin;
the optical signal is input from the input end 601, reflected multiple times by the main concave mirror 603, the plane mirror 604, and the sub concave mirror 605, and output from the output end 602 to the receiving end 611.
In application, the structure of the dense optical path folding device shown in fig. 12 is also an application example based on the off-axis integrating cavity technology, and since the cross-sectional area of the sub-concave mirror in the direction perpendicular to the optical axis is small, in the case where the area of the receiving surface of the receiving end is sufficiently large (for example, the cross-sectional area of the sub-concave mirror in the direction perpendicular to the optical axis is smaller than or equal to the area of the receiving surface of the receiving end), the optical signal output via the output end can be completely received by the receiving surface of the receiving end.
As shown in fig. 12, in one embodiment, a second converging lens 612 is disposed between the output end 602 and the receiving end 611;
the optical signal is input from the input end 601, is output from the output end 602 to the second converging lens 612 after being reflected multiple times by the main concave mirror 603, the plane mirror 604, and the sub concave mirror 605, and is converged to the receiving end 611 by the second converging lens 612.
In application, by providing the second converging lens between the output end and the receiving end of the dense optical path folding device shown in fig. 12, only the second converging lens and the sub-concave mirror are required to have the same cross-sectional area perpendicular to the optical axis (for example, the cross-sectional area of the second converging lens perpendicular to the optical axis is greater than or equal to the cross-sectional area of the sub-concave mirror perpendicular to the optical axis), the optical signal output via the output end can be completely collected and converged by the second converging lens on the receiving surface of the receiving end, so that the area of the receiving surface of the receiving end can be smaller, and the volume of the receiving end can be reduced, thereby reducing the overall volume of the optical system. In the dense optical path folding device shown in fig. 12, since the entire sub-concave mirror is adopted as the output end, and the cross-sectional area of the sub-concave mirror in the direction perpendicular to the optical axis is smaller than that of the main concave mirror in the direction perpendicular to the optical axis, the required cross-sectional area of the second converging lens in the direction perpendicular to the optical axis is smaller than that of the first converging lens in the dense optical path folding device shown in fig. 11, so that the overall volume of the optical system can be smaller.
In one embodiment, the dense path folding device shown in fig. 12 may be applied to a Yu Laman spectral detection system, where the input is used to input the excitation light signal;
the output end is used for outputting a Raman optical signal;
the reflecting surface of the sub-concave reflecting mirror is plated with a film layer for reflecting the excitation light signal and transmitting the Raman light signal;
the excitation light signal is input from the input end, photons of the excitation light signal and molecules of a sample to be detected are in inelastic collision in the repeated reflection process through repeated reflection among the main concave reflector, the plane reflector and the sub concave reflectors, so that an enhanced Raman light signal is generated, and the enhanced Raman light signal is output from the output end to the receiving end.
In application, a sample to be detected in the Raman spectrum detection system can be nitrogen, hydrogen or oxygen and other gases with Raman characteristic spectrums, and the receiving end can be a spectrum analyzer.
As shown in fig. 13, in one embodiment, an input end 601 (not shown), an output end 602, and two sub-concave mirrors 605 are separately disposed, and both the input end 601 and the output end 602 are disposed on a plane mirror 604;
the front projections of the two sub-concave mirrors 605 on the reflecting surface of the planar mirror 604 are spaced apart and offset from the origin.
In application, the dense optical path folding device shown in fig. 13, by providing two sub-concave mirrors that are symmetrical with respect to the optical axis and offset from the origin, increases design flexibility compared to a structure employing a single sub-concave mirror (e.g., the dense optical path folding device shown in fig. 9) such that the optical signal forms a different spot track within the reflective cavity.
According to the dense optical path folding device provided by the embodiment of the application, the plane reflector and the main concave reflector with aberration are adopted to form the reflecting cavity, the sub-concave reflector is introduced, the sub-concave reflector is arranged on the plane reflector, at least one of the reflecting surface of the plane reflector and the light of the sub-concave reflector is not arranged on the focal plane of the main concave reflector, and the main concave reflector has aberration, so that the position and the angle are not overlapped when the light signal reflected by the sub-concave reflector returns to the sub-concave reflector after being reflected for multiple times in the reflecting cavity; and because the normal directions of different positions of the sub-concave reflecting mirror are different, after the optical signal returns to the sub-concave reflecting mirror again, the reflection direction is different from the previous time and deviates from the original track direction, so that a semi-closed track is formed in the reflecting cavity, finally, after the optical signal is output from the output end, the total optical path in the reflecting cavity can be improved by more than 10 times compared with the existing optical path folding device, further, the optical path volume ratio is higher, the optical path track formed by the optical signal in the reflecting cavity is different according to actual requirements, the design is flexible and high, and the optical path measuring device can be applied to various gas optical sensing devices, such as gas absorption spectrum detecting devices, raman spectrum detecting systems and the like.
The foregoing description of the preferred embodiment of the present invention is not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Claims (10)
1. A dense optical path folding device, comprising:
an input terminal for inputting an optical signal;
the output end is used for outputting an optical signal;
a main concave reflector with focal length f, curvature radius R and aberration;
a plane mirror, the distance from the reflecting surface of the plane mirror to the optical center of the main concave mirror is L 1 ＝(1+x 1 )f，-1＜x 1 ＜1；
Concave reflecting mirror with focal length f 0 Radius of curvature R 0 The orthographic projection area of the reflecting surface of the sub-concave reflecting mirror on the reflecting surface of the plane reflecting mirror is smaller than the area of the reflecting surface of the plane reflecting mirror, and the distance from the optical center of the sub-concave reflecting mirror to the optical center of the main concave reflecting mirror is L 2 ＝(1+x 2 )f，R 0 ＝mR，-1＜x 2 ＜1，x 1 And x 2 Not simultaneously 0, m > 0;
the input end is arranged on the main concave reflector or the plane reflector, the output end is arranged on the main concave reflector, the plane reflector or the sub-concave reflector, and the reflecting surface of the main concave reflector is opposite to the reflecting surface of the plane reflector and the reflecting surface of the sub-concave reflector;
the optical signal is input from the input end, and is output from the output end after being reflected for a plurality of times by the main concave reflector, the plane reflector and the sub concave reflector.
2. The dense optical path folding device of claim 1 comprising:
the optical centers of the two sub-concave reflectors are symmetrically arranged about the optical axis, and the orthographic projections of the reflecting surfaces of the two sub-concave reflectors on the reflecting surfaces of the plane reflectors are not overlapped;
wherein the optical axis is perpendicular to the reflecting surface of the plane reflecting mirror and passes through the optical center and the focal point of the main concave reflecting mirror, and x is more than 0 2 (1+2mx 1 -x 1 x 2 )＜2m；
The optical signals are input from the input end, and are output from the output end after being reflected for a plurality of times by the main concave reflector, the plane reflector and the two sub concave reflectors.
3. The dense optical path folding device of claim 1 wherein an orthographic projection of an optical center of the sub-concave mirror onto a reflecting surface of the planar mirror is located at an origin of an optical axis;
wherein the optical axis is perpendicular to the reflecting surface of the plane reflecting mirror and passes through the optical center and the focal point of the main concave reflecting mirror, and the origin is the intersection point of the optical axis and the reflecting surface of the plane reflecting mirror, and 0< x 2 (1+2mx 1 -x 1 x 2 )＜2m。
4. The dense optical path folding device of claim 1 wherein an orthographic projection of the reflecting surface of the sub-concave mirror onto the reflecting surface of the planar mirror is offset from an origin of the optical axis;
wherein the optical axis is perpendicular to the reflecting surface of the plane reflecting mirror and passes through the optical center and the focal point of the main concave reflecting mirror, and the origin is the intersection point of the optical axis and the reflecting surface of the plane reflecting mirror, x 1 ＝x 2 ＝x，0＜x(4x+1/m)＜1。
5. The dense optical path folding device of claim 4 wherein x > 0.
6. The dense optical path folding device of claim 5 wherein 0< x < 0.1.
7. A dense path folding device according to claim 2 or 3 wherein x 2 ＞0；
And/or, m is more than or equal to 1 and less than or equal to 10, and x is more than or equal to 0.05 and less than or equal to 10 1 ≤0.5。
8. A dense optical path folding device according to any one of claims 1 to 6 wherein the primary concave mirror is a spherical mirror with aberrations, or is an aspherical mirror with aberrations designed.
9. A dense optical path folding device according to claim 3 wherein said input end, said output end and said sub-concave mirror are separately disposed, said input end and said output end being disposed on said planar mirror;
or the input end and the output end are overlapped to form an input end and an output end, and the input end and the sub-concave reflector are arranged separately and are arranged on the plane reflector;
or the input end and the output end are arranged separately, the input end is arranged on the plane reflector, and the output end is the main concave reflector; the optical signals are input from the input end, output to the first converging lens from the output end after being reflected for multiple times by the main concave reflector, the plane reflector and the sub concave reflector, and are converged to the receiving end by the first converging lens;
or the input end and the output end are arranged separately, the input end is arranged on the plane reflector, and the output end is the sub-concave reflector; the optical signals are input from the input end, and are output from the output end to the receiving end after being reflected for multiple times by the main concave reflector, the plane reflector and the sub concave reflector.
10. A dense path folding device according to claim 2 wherein said input end, said output end and two of said sub-concave mirrors are disposed separately, said input end and said output end being disposed on said planar mirror.
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