RU2164668C1 - Spectrum analyzer - Google Patents

Abstract

FIELD: study of spectra of sources of optical radiation. SUBSTANCE: spectrum analyzer has family of optical fibers whose inputs are inputs of analyzer. Outputs of optical fibers are optically coupled via color division prism to inputs of photoelectron converters whose outputs are connected via commutator to input of analog-to-digital converter, output of the latter being connected to inputs of personal computer. Information outputs of personal computer are information outputs of analyzer. Controlling output of personal computer is connected to controlling input of commutator. Outputs of optical fibers are arranged in one line for change of angle of incidence and displacement along boundary of color division prism. EFFECT: enhanced precision and authenticity of measurement thanks to exclusion of possibility of superimposition of spectra of different points of light spot, simplified process of adjustment and re-adjustment of analyzer. 1 cl, 4 dwg

Description

 The invention relates to spectral analysis and can be used in various fields of technology to determine the spectra of optical radiation sources, as well as to classify (recognize) radiation sources based on the analysis of their spectra.

 The prior art device for measuring emission spectra containing optically coupled radiation source, a mirror with a selective reflective coating, spherical mirrors, a capacitor and a spectrometer (ed. Certificate of the USSR N 1117460, G 01 J 3/28).

 There is also a known method of recording spectral lines and a device for its implementation, containing a series-connected tuning element, a tunable laser, an absorbing element, a detector, a smoothing filter, an analog-to-digital converter and a recording unit (ed. Certificate of the USSR N 1562718, G 01 J 3 / 12, 1988).

 Closest to the invention is an automated device for diagnostics in oncology, which includes a structurally integrated illumination channel with an eyepiece and lens and an endoscope instrument channel, the input of the illumination channel through a switch is optically connected to the outputs of the visible radiation source and the ultraviolet radiation source, a multi-channel analog-to-digital converter, controlled light sources, a personal computer and two groups of optical fibers, optical fiber inputs of the second group are the optical inputs of the device, the outputs of the multi-channel analog-to-digital converter are connected to the information inputs of the personal computer, the information output of which is the information output of the device, and the control outputs of the personal computer are connected respectively to the inputs of the group of controlled light sources, the outputs of which are optically connected to the inputs of the corresponding optical fibers of the second group, the outputs of which are the optical outputs of the device, color separation ISM and a group of photoelectronic converters, the outputs of which are connected respectively to the inputs of a multi-channel analog-to-digital converter, the input of the color separation prism being optically connected to the outputs of the optical fibers of the first group, and the outputs of the color separating prism being optically connected to the inputs of the group of corresponding photoelectric converters (decision to grant a patent on application Russia N 98116617/14, A 61 B 14/00, 1998).

In the known device, the range of the analyzed spectrum is divided into n subbands (i = 1, n), in each of which the average value of the signal amplitude A _i at the output of the photoelectric converter of the corresponding subband λ _{i is} determined from the measurement results. Since the number of subbands must be sufficiently large to increase the accuracy of the analysis, the distance between the centers of the subbands is comparable and even smaller than the photoelectronic converters installed on one of the faces of the color separation prism. The inability to set the required number of subbands (photoelectronic converters) leads to a decrease in the accuracy and reliability of the analysis results.

 In addition, for existing spectrum analyzers, there is no general methodology for choosing the location of radiation photodetectors depending on the angle of incidence of the analyzed radiation and the characteristics of the color separation prism.

 In addition, in the known device, the magnitude of the light spot is comparable with the exit diameter of the beam of optical fibers of the second group. The presence at the input of the color separation prism not of a slit radiation source, but of a light spot of certain linear dimensions leads to superposition of spectra from different points of the light spot and, as a result, to a decrease in the accuracy and reliability of the analysis results.

 The technical result from the use of the invention is to increase the accuracy and reliability of measurements by eliminating the imposition of spectra from various points of the light spot.

 In addition, the technical result consists in simplifying the process of tuning and rebuilding the analyzer by providing the ability to select the number of spectrum analysis ranges and the location of the optical radiation receivers depending on the angle of incidence of the radiation and the characteristics of the prism.

 This technical result is achieved in that the spectrum analyzer, consisting of a group of optical fibers, the inputs of which are the optical inputs of the analyzer, and the outputs of the optical fibers of the group through a color separation prism are optically connected to the inputs of the photoelectric converters, analog-to-digital converter, the outputs of which are connected respectively to the information inputs personal electronic computer, information outputs of which are information outputs of the analyzer, additional о contains a switch, the information inputs of which are connected respectively to the outputs of the photoelectronic converters, the output of the switch is connected to the input of an analog-to-digital converter, and the control input of the switch is connected to the control output of a personal electronic computer, and the outputs of the optical fibers of the group are located in one line relative to each other forming a radiation source equivalent to a slit radiation source, and a plane passing through the centers of linearly located optical their fibers, perpendicular to the plane of the prism in which color separation is carried out.

 An additional technical result is ensured by the fact that the outputs of the optical fibers of the group are installed with the possibility of changing the angle of incidence of the light flux on the color separation prism and with the possibility of their linear movement along the edge of the color separation prism.

 In FIG. 1 is a diagram of an analyzer; FIG. 2 is a diagram explaining the path of rays in a color separation prism; FIG. 3 is a layout diagram of the outputs of the optical fibers (line output of the fiber optic bundle), FIG. 4 - graphs explaining the principle of the analyzer.

 The spectrum analyzer contains a group 1 of optical fibers with inputs 2 and 3, color separation prism 4 and photoelectric converters 5, the inputs of which are optically connected through color separation prism 4 with the outputs 3 of optical fibers of group 1, the outputs of the photoelectronic converters are connected respectively to the information inputs of switch 6, output which is connected to the input of the analog-to-digital Converter 7, the outputs of which are connected respectively to the information inputs of a personal electronic computer ins 8, which are data outputs data outputs of the analyzer, and a control output coupled to a control input of the switch. R stands for the face of the prism in which color separation is performed.

 In FIG. 3, P denotes a plane passing through the centers of linearly located optical fibers. As a personal computer can be used IBM compatible PC domestic or foreign production.

 The color separation prism and each of the photoelectric converters connected to it are designed to convert the radiation power level at the corresponding spectral component of the measured input optical signals in the spectrum band to the corresponding level of the analog electrical signal at the output of the photoelectric converter.

 The analyzer can operate in several modes: measurements, calibration and classification (recognition) of radiation sources.

Для получения относительных δ значений спектра измеряемого оптического излучения (нормированного по максимуму) после окончания измерения и получения всей совокупности значений A_i, ЭВМ также по известному алгоритму
A_max= sup A_i (2)
определяет максимальное значение амплитуды сигнала и нормирует все результаты измерений спектральных составляющих по соотношению
A _{i отн}= A_i/A_max. (3)
В результате получают совокупность относительных значений амплитуд сигналов
A_{1 отн} = A₁/А_max
...................................In the measurement mode, the inputs of 2 fibers 1 are installed at the source of optical radiation. The optical signal through the fibers 1 enters the color separation prism 4, which decomposes the broadband optical signal into spectral components. Photoelectric converters 5 located in the corresponding sections of the output surface of the prism (color separation areas) convert the amplitudes of the corresponding spectral component of the signals into the equivalent value of the electrical signal. From the output of each photoelectronic converter, electrical signals are fed to the corresponding input of the switch 6, which, under the influence of control commands from the personal computer 8, periodically connects the output of each of the photoelectric converters 5 to the input of the analog-to-digital converter 7. To increase the reliability of the measurement results, connect each converter 5 to the analog one by one -digital converter 7 is produced N times. After conversion by an analog-to-digital converter 7 to a digital code, A _{ik is} transmitted to a PC 8, where the mathematical expectation of the amplitude of the spectral component of the signal is determined according to a known algorithm

To obtain the relative δ values of the spectrum of the measured optical radiation (normalized to the maximum) after the end of the measurement and to obtain the entire set of values of A _i , the computer also according to the known algorithm
A _max = sup A _i (2)
determines the maximum value of the signal amplitude and normalizes all the results of measurements of spectral components by the ratio
A _{i rel} = A _i / A _max . (3)
The result is a set of relative signal amplitudes
A _{1 rel} = A ₁ / A _max
...................................

A _{i rel} = A _i / A _max , (4)
....................................

A _{n rel} = A _n / A _max
which characterize the distribution of radiation levels over the entire measured spectrum (λ ₁ ≅ λ _i ≅ λ _n ).
The transition to the relative values of the signal amplitudes eliminates the influence of the following factors on the measurement results:
a random change in the distance between the ends of the optical fibers 8 and the investigated source of optical radiation;
accidental changes in radiation intensity or interference.

 In FIG. Figure 4 shows an example of a curve constructed by relation (3). Characteristic for it is that at least in one of the subranges its value is 1. Actual distributions can be of arbitrary shape and depend on the type of spectrum of the studied optical radiation source.

For the subsequent use of the claimed analyzer in the classification mode of objects that are sources of primary or secondary radiation, an auxiliary calibration mode of the device is provided. In the calibration mode, criterial spectra (spectral images) of various source samples taken as reference are obtained. As a result of measuring set (4) of the relative values of the amplitudes of the spectral components A _i , for each reference sample we obtain a characteristic of the distribution of the spectrum (spectral image), which can be used as a classification criterion (for example, as a diagnostic criterion in the technical diagnosis of materials in medical diagnostics, etc.).

For preliminary obtaining the classification criteria for radiation sources, a calibration mode is provided. The essence of these criteria is that the set (4) of the relative values of the signal amplitudes A _{i rel} (for all wavelength subbands λ _i of the secondary emission spectrum is an objective characteristic of the radiation source. When analyzing the analyzer, samples of radiation sources with a known spectrum.

где A_{ij отн} (λ_i) - относительные значения амплитуд сигналов спектральных составляющих;
K_j - классификационный признак, означающий, что конкретное полученное устойчивое сочетание А_ij (λ_i) является признаком конкретного эталонного источника излучения с известным спектром.As a result of repeated measurements of reference sources, stable combinations of relative signal amplitudes for each reference radiation source are obtained

where A _{ij rel} (λ _i ) are the relative values of the amplitudes of the signals of the spectral components;
K _j is a classification feature, which means that the particular stable combination A _ij (λ _i ) obtained is a feature of a specific reference radiation source with a known spectrum.

 The operation algorithm of a computer in this mode is characterized by ratios 1–4. The difference is that the reference sources of radiation with characteristic spectrum distributions are used as samples.

In FIG. 4c, an example is given characterizing the principle of obtaining classification features, where numbers 1–4 indicate: spectra of reference radiation sources with characteristic spectrum distributions. For each type of reference source, the maxima can be located in different subbands, and the shape of the spectral distribution curves is different. For the subsequent classification of sources, it is necessary to correctly identify the relative spectral distributions obtained from the radiation source under study with one of the curves characterizing the spectrum of the reference source (Fig. 4c). After calibrating the device and obtaining classification criteria K _j for each type of reference radiation source, the device is suitable for recognizing radiation sources. As a result of measuring the spectrum of the examined source of an unknown class, a set of (4) samples of the relative values of the amplitudes of the signals of the spectral components of the input optical radiation is obtained. The resulting set of samples is compared in turn with the spectral distributions (5) obtained from the reference ones. Moreover, calibration spectral images (5) are used as criteria for assessing the type of radiation source. Comparison of the spectral distribution obtained during measurements of the examined source with the criteria (5) obtained during measurements of the reference sources is carried out according to the principle of greatest likelihood. Among the classification criteria (reference spectral images) (5), one determines the criterion in which the combination of samples A _{i rel} (λ _i ) is closest to the spectral distribution (4) obtained by measuring the source under study. Based on the selected closest criterion, a conclusion is drawn on the classification of the studied radiation source as the corresponding type (or corresponding state).

 The computer operation algorithm in this mode can, for example, be presented in the following form.

где j = 1,2,..., n - число эталонных источников излучений;
i - номер частотного поддиапазона;
а после определяется номер (тип) эталонного источника, соответствующий минимальному квадрату отклонения
j=min E_j. (7)
Основной задачей, решаемой в режиме предварительной настройки анализатора, является выбор числа поддиапазонов измерений спектральных составляющих n, мест x_i их расположения на выходной грани призмы в зависимости от угла ω падения и коэффициента преломления материала призмы, характеризующегося углом преломления α призмы, расстояния А от края входной грани призмы до места подсоединения линейчатого выхода жгута и коэффициента преломления материала призмы n (λ_i) для излучения с длиной волны λ_i фиг. 2).The square of the deviation of the relative values of the amplitudes for the studied source A _{i rel} from the values of A _{ij rel from the} spectrum of the reference source is calculated by the ratio

where j = 1,2, ..., n is the number of reference radiation sources;
i is the number of the frequency subband;
and then the number (type) of the reference source is determined, corresponding to the minimum squared deviation
j = min E _j . (7)
The main task to be solved in the analyzer preset mode is the choice of the number of measurement sub-ranges of spectral components n, places x _{i of} their location on the output face of the prism depending on the angle of incidence ω and the refractive index of the prism material, characterized by the angle of refraction of the prism, distance A from the edge the input face of the prism to the point where the line output of the bundle and the refractive index of the prism material n (λ _i ) are connected for radiation with a wavelength λ _{i of} FIG. 2).

.From the known relation for a refractive prism
φ _i = n (λ _i ) 2-ω, (8)
where φ _i is the beam exit angle with wavelength λ _i from the output face of the prism from FIG. 2, we can obtain the relations

.

Then the distance between adjacent photoelectric converters will be equal
Δx _i = x _i -x _i-1 , (11)
for the chosen values of α and n (λ _i ), i.e. for the selected material of the refractive prism and the magnitude of its refractive angle, relations (9-11) are functions of only the quantities A and ω, i.e., by changing the angle of incidence ω and the value of A, we can choose the location of the photoconverters for each color component of the spectrum so as to ensure the required number of sub-ranges of measurements and to provide linear placement of photoconverters along the output face of the prism. Moreover, the plane P (Fig. 3) is always perpendicular to the face R.

 The output location of the optical fiber bundle in the form of a line of optical fibers of FIG. 3 allows you to achieve several technical results.

 First, a clearer separation of the spectral color components of the signal is obtained in the form of color lines on the output face of the prism, which eliminates the overlap of adjacent color components and provides the necessary measurement accuracy and color separation of the spectrum.

 Secondly, the energy of each color spectral component supplied to the input face is maximally supplied to the input of the corresponding photoelectric converter.

 Thirdly, the linear arrangement of the output of the bundle creates additional conveniences for more precise control of the location of the bundle A on the input face and the incidence angle ω of the input light flux relative to the input face of the prism.

Claims (2)

 1. The spectrum analyzer, consisting of a group of optical fibers, the inputs of which are the optical inputs of the analyzer, and the outputs of the optical fibers of the group through a color separation prism are optically connected to the inputs of the photoelectronic converters, analog-to-digital converter, the outputs of which are connected respectively to the information inputs of a personal electronic computer , the information inputs of which are the information outputs of the analyzer, characterized in that it further comprises a switch, the information inputs of which are connected respectively to the outputs of the photoelectronic converters, the output of the switch is connected to the input of an analog-to-digital converter, and the control input of the switch is connected to the control output of a personal electronic computer, and the outputs of the optical fibers of the group are located in one line relative to each other, forming a radiation source equivalent to a slit radiation source, and the plane passing through the centers of linearly located optical fibers is perpendicular The plane of the prism in which the color separation is carried out is bright.  2. The spectrum analyzer according to claim 1, characterized in that the outputs of the optical fibers of the group are installed with the possibility of changing the angle of incidence of the light flux on the color separation prism and with the possibility of their linear movement along the edge of the color separation prism.

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