A multi-purpose Light-Emitting-Diodes (LED) based lamp is known which contains several light sources, reflector, optical system, battery, and switch, wherein the light source is the LED-containing board having the shape of parabolically bent narrow stripe, equipped with the collimator and light waveguide. Moreover, the light source with LEDs is located inside a solid plastic housing, which has a form of a sector with the convex side bent as a parabola or paraboloid, and equipped with LEDs, and the narrow stripe is truncated and connected with collimator or lens (Russian Federation Patent No. 2194212, published 2002.12. 10). Disadvantage of the abovementioned device is impossibility to control the characteristics of output irradiation in a wide range. Particularly, spatial distribution of the emitted light remains uncontrolled.

An assembly of LEDs is known that includes housing, the lenses for vertical and horizontal light directions from LEDs, the devices for control the LEDs bias current, and power source unit (USA Patent No. 5765940, published 1998.06. 16). Disadvantage of this device is impossibility to control output irradiation characteristics in a wide spectral range because the LEDs spectrum is too narrow and there is no possibility to control their spatial characteristics.

A broadband source of light is a key device needed for carrying out different spectrographic analyses. Such analysis provides, among others, measurements of constitutes of agricultural products and the composition and property of chemical substances. Spectrographic analysis instruments operating in visible range also have important use in analysis and matching of color documents. Efficient broadband source of light for a spectrometer is disclosed in the USA patent No. 5477322 (published 1995.12. 09) comprising multiplicity of light-emitting diodes which transmit light through an entrance slit to irradiate an oscillating diffraction grating. The light is dispersed by the grating toward an exit slit which transmits a narrow bandwidth of light to irradiate a sample. As the grating oscillates, the wavelength of the output light is scanned through a selected spectrum. The main disadvantage of this light source is that it contains movable parts (particularly, oscillating grating) and thus cannot be made compact and portable. In addition, the spatial shape of the power distribution of the output light beam depends on its spectral composition that results in less effective illumination of the object.

Another solution for broadband source of light for a spectrometer is disclosed in USA patent No. 6075595 (published 2000.06. 13). This source comprises a plurality of LEDs arranged in a row with predetermined spacing; said LEDs irradiate a dispersive element. The spacing of light-emitting elements located side by side and the linear wavelength dispersion are so dimensioned that, for each emitting element, the spectrum band of desired wavelength will emerge through the exit slit. However, shortcoming of this device is that the spatial shape of output power distribution of the light beam is independent on the wavelength only in the limited spectral band where the required condition is met. It results in decreasing of the illumination efficiency because an optical system with high numerical aperture must be used for collection of the reflected or scattered light into a photo-receiving subsystem to provide acceptable signal-to-noise ratio.

A spectrometer comprising a broadband light source is known, said light source comprising an array of LEDs where each LED emits a narrow wavelength band but the combination of them emits a desired range of wavelengths, switch means controlling whether the separate LED is on or off in any given time, and multiplexing means for controlling said switch means so as to produce a desired total wavelength range (USA Patent No. 5475221, published 1995.12. 12). Shortcoming of this device is that the output irradiation from different LEDs in the array propagates either in different direction or in separated waveguides causing the spatial characteristics of luminous flux being varied while switching or multiplexing the wavelength. In particular, the arrangement of LEDs in this device does not allow formation of the beam in which the irradiation from all separate LEDs is composed into the common luminous flux. As in the abovementioned devices, it also leads to non-efficient illumination of the object.

It is the object of the present invention to provide a multi-purpose source of polychromatic optical irradiation with spatial shape of output power distribution of the light beam remaining stable in a wide spectral range. Such output beam cross-section leads to more efficient illumination of the object.

It is another object of the invention to provide a source of polychromatic optical irradiation generating the light beam in the form of the line, which shape remains the same in the wide spectral range thus ensuring efficient illumination of reflecting objects.

Summary of the invention The present invention provides the multi-purpose source of polychromatic optical irradiation with spatial shape of output power distribution of the light beam remaining stable in a wide spectral range. The device comprises an array of LEDs operating at different wavelengths which are situated in the

positioning assembly so that their irradiation is incident in a diffraction element under the angle specific for each wavelength in such a way that the diffracted or refracted beams propagate in one common direction composing the total luminous flux in which the directed optical irradiation with characteristics given beforehand, is provided.

According to one aspect of the invention, the multi-purpose source of polychromatic optical irradiation comprises housing, a power source unit, an array of LEDs with respective electronic circuits providing control of the bias current through each LED, and an optical component to control the geometrical characteristics of the beam. The device for LEDs positioning with three degrees of freedom, and the diffraction element are additionally installed into the housing. The light emitting elements are located in the positioning device relatively to the diffraction grating according to the expression of d (sin a, + sin, 8) = mA,, where d is the spacing of the diffraction grating, ai is the angle of incidence measured between the normal to the diffraction grating and the direction of the beam emitted from i-th light emitting element,, is the diffraction angle, m is an integer, and Ai is the wavelength of the light emitted by i-th light emitting element. The array of light emitting elements is mounted inside the housing by means of bonding elements so that to provide adjustment of each light emitting element. The diffraction element, for example, diffraction grating, is mounted inside the housing by means of bonding elements providing possibility of adjustment.

Said diffraction grating provides selection of certain part of the spectrum from each LED as well as formation of output light irradiation according to the given beforehand characteristics. Moreover, said diffraction grating serves to converge n light beams with different Ai, which provides formation of the total light flux and propagation of the deflected irradiation with given beforehand spectral, spatial and temporal characteristics.

In another embodiment of the invention, several chips comprising small-size unpackaged LEDs are arranged in one line in the direction being normal to the diffraction plane of the diffraction element. The plurality of such lines being parallel to each other provides the assembly of line-shaped light emitting elements that operates by the same way as the point-shape light emitting elements in the first embodiment of the invention providing the line- shaped cross section of the output luminous flux.

In yet another embodiment of the invention, the diffraction grating can be substituted by acousto-optic Bragg cell supported with electronics means for excitation and control the diffraction grating running inside said cell. The mirror is located in the light beam path by such a way that the light reflected from this mirror is incident to the diffraction element according to the mentioned above expression. The positioning device provides the necessary adjustment of the LEDs according to the expression mention above in order to obtain the total device spectral characteristic equal to that given beforehand. The presence of the said mirror provides the size minimization of the total device. Said acousto-optic Bragg cell provides not only the total light flux formation but also control of the output light power of any spectral component.

Yet another embodiment of the invention comprises a sequence of the diffraction grating and the acousto-optic Bragg cell arranged in such a way that a part of light-emitting elements is optically connected with said diffraction grating and another part is optically connected with said acousto- optic Bragg cell providing that irradiation emitted by any of light-emitting elements propagates in the same direction as from other elements after said consequence of the diffraction grating and the acousto-optic Bragg cell.

Brief description of the drawings Further features and advantages of the invention will be better understood from the following description of preferred embodiments as illustrated by way of examples in the accompanying drawings in which: Figure 1 illustrates the schematic of the multi-purpose source of polychromatic optical irradiation with stable spatial mode of output light beam in a wide spectral range.

Figure 2 demonstrates the schematic of the multi-purpose source of polychromatic optical irradiation in which an acousto-optic Bragg cell is applied as a diffraction element instead of diffraction grating.

Figure 3 shows the schematic of the multi-purpose source of polychromatic optical irradiation in which both diffraction grating and acousto-optic Bragg cell are used as diffraction elements.

Figure 4 shows the schematic of the source of polychromatic optical irradiation generating the light beam of the line-shaped cross section, which shape remains the same in the wide spectral range.

One should notice that the drawings are only exemplary to illustrate the embodiments of the invention, not for limiting the invention.

Description of the preferred embodiments Figure 1 illustrates schematic of a preferred embodiment according to the invention in which multi-purpose source of polychromatic optical irradiation

comprises housing (10), an array of light-emitting elements (12tr122,... 12n) a micro-optical assembly (13) for formation of spatial characteristics of light beams emitted either by LEDs or by light-emitting crystals, a mirror (15), a diffraction element (16), an optical assembly for formation of the output beam (17), and adjustment elements (11) for adjustment of light-emitting elements, as well as the electronic control device (14). The housing (10) contains small platforms (11) for spatial positioning and fixing of the light- emitting elements (12). These platforms can be fabricated in the housing (10) by mechanical processing or vacuum casting. The angle between the plane of each platform (11) and the plane of the diffraction element (16) is to be calculated before fabrication of the housing (10) with said small platforms. This angle particularly depends on the wavelength of the light emitted by the elements (12). In order to provide an electric insulation of light-emitting elements (12), the thin layer of insulator (for example, Al203) is deposited over all the small platforms. A micro-optical assembly (13) is mounted after the light emitting elements (12) are fixed in the housing (10) and electrical connection is supplied to all light-emitting elements (12).

The device shown in Fig. 1 operates by the following way. The adjustment elements (11) provide the fixation of the light-emitting element (12) to the base of the housing (10) and provide that the angle of incidence (ai) of the light beam emitted by i-th light-emitting element (12d on the diffraction grating (16) is close to the value calculated from the equation of d (sinai + sinß) = _mAi, where d is the spacing of the diffraction element, 8 is the diffraction angle, m is an integer, and Ri is the wavelength of the light emitted by i-th light emitting element. Adjustment elements (11) also provide that the projection of the incident light-beam axis on the plane of the diffraction grating (16) is orthogonal to the grating grooves. Moreover, the adjustment elements (11) provide the spatial coincidence of all the light beams emitted by different light-emitting elements (12) in the plane of the diffraction grating (16).

Light beams from n light-emitting elements (121,... 12n) with known beforehand wavelength of A l... n), the wavelength bandwidth Aj and the solid angle of y ; are directed into the operation aperture of the diffraction grating (16) making the angles of incidence (ai) different for each wavelength Ai and calculated in accordance with the equation of d (sin : xi +sinß) = _mAi. The mirror (15) can be installed in the way of the said light beams propagation to provide compactness of the device. Since the diffraction angle (/ ?) is the same for all wavelengths, n light beams diffracted from the diffraction grating (16) propagate in the same direction forming the output beam. Consequently, the total luminous flux of the output beam consists of light beams emitted by n light-emitting elements. The output light beam is characterized now by any arbitrary combination of the wavelengths emitted from n light-emitting elements because any of these elements can be switched on/off independently. Intensity of total luminous flux as well as any of its spectral components can be controlled by the driving current of the light-emitting elements (12). Note that the spatial distribution of the output power remains the same for all spectral components of the luminous flux.

The solid angle yout of the output irradiation is defined by the spatial parameters of the optical assembly and by the shape of the diffraction grating. Exploitation of a spherical diffraction grating (16) or spherical mirror (15) changes the spatial characteristics of the output beam. Note also that both transmitting and reflecting diffraction grating can be used, and if the diffraction grating operates in the transmission mode, so the configuration shown in Fig. 1 should be changed, for example, by insertion of an additional mirror.

An additional feature of the multi-purpose source of polychromatic irradiation is possibility to introduce a modulation of both the total output power and the power of any spectral component or their arbitrary combination. Such power modulation is achieved due to modulation of the driving current of the light-emitting elements (12).

The driving current of each light emitting element is controlled by means of the control device (14). A programmable microcomputer can be used as the control unit (14). The microcomputer allows control of each light-emitting element irradiation time, the order of switching on/off each light-emitting element or their combination, and the modulation of both the total luminous flux and each spectral component of the output beam.

Either light-emitting diodes or light-emitting crystals can be used as the light- emitting elements (12).

Another preferred embodiment of the invention is shown in Fig. 2 where an acousto-optic Bragg cell serves as the diffraction element (26). The Bragg cell (26) is supported with electronic means (28) for excitation inside the cell an acoustic wave. This wave modulates the refractive index of the Bragg cell (26) providing formation of the running diffraction grating, which operates as a diffraction element. The spacing (A) of the running diffraction grating is defined by the parameters of the acoustic waves and can be controlled by said electronics means. The multi-purpose source of the polychromatic light with the acousto-optic Bragg cell operates in the following way. For producing the output light of desired wavelength Ri, the control device (14) activates irradiation from i-th light emitting element (12i) by applying the driving voltage to this element. Simultaneously, the control device (14) communicates with electronic means (28) so as to provide excitation of the acoustic wave with the spacing Ai such as the equation A ; (sina ; +sin3) =m,, is satisfied. Here ai is the angle of incidence measured between the normal to the Bragg cell (26) and the direction of the beam emitted from i-th light emitting element, 8 is the angle of light diffraction from the Bragg cell, m is an integer, and Ri is the wavelength of the light emitted by i-th light-emitting element. For switching the output wavelength to another value (for example, in) the control device (14) activates another light-emitting element (12n) and simultaneously provides

excitation of another moving grating in the Bragg cell (26) with the spacing An such that the equation An (sin an + sin/3) _ m. n is satisfied.

Schematic of the light source shown in Fig. 3 represents yet another embodiment of the invention. Because of the similarity of light beam diffraction from the diffraction grating and from the acousto-optical Bragg cell, the light beams emitted by a part of light-emitting elements [for example, elements from (121) to (12 » as shown in Fig. 3] are directed to the diffraction grating (16) while the other part [elements from (12i+,) to (12n)] is optically connected with the acousto-optic Bragg cell (26). The diffraction grating and Bragg cell are installed in a consecutive sequence in such a way that any light beam diffracted from the diffraction grating (16) and any light beam diffracted from the acousto-optic Bragg cell (26) propagates in one and the same direction. When the wavelength of the output light is desired to be in the band between i, and Rj, the control device (14) keeps the Bragg cell non-excited and simultaneously activates any or several light-emitting elements of array (121)... (12i). The light beam emitted by these activated elements diffracts from the diffraction grating (16) to propagate at one and the same angle ? and then freely propagates through non-activated Bragg cell (26). Alternatively, when the wavelength of the output beam is desired to be from Aht tpin/the control device (14) activates one of the light- emitting elements from the array (12il)... (12n) and simultaneously the control device (14) communicates with electronic means (28) so as to provide excitation of the acoustic wave with the spacing A corresponding to the desired output wavelength similarly as it was explained in the previous paragraph for embodiment shown in Fig. 2. This configuration allows minimization of the light power losses, and, consequently, it increases the efficiency of the object illumination.

Referring to Fig 3, the diffraction grating can be replaced by another Bragg cell or even by several Bragg cells providing that the diffracted beams from

any Bragg cell propagate in one and the same direction. Synchronization of proper light-emitting element's activation and excitation of the acoustic wave with proper spacing in proper Bragg cell is carried out by the control device (14) through the respective electronic means (28). In this case the sequence of several Bragg cells serves as the diffraction element.

A source of polychromatic optical radiation shown in Fig. 4 operates in the way, which is very similar to that described for the light source described by Fig. 1. The arrays of light emitting elements (421)... (42n) play the same role as the separate light emitting elements (121)... (12n) shown in Fig. 1. Each array (42) consists of a set of unpackaged light-emitted elements arranged in the line. All elements in any array of (42) emit light of almost the same wavelength. However, the wavelength of the light emitted by a line-shaped array (42i) may be different from the wavelength emitted by another array (42n, for example). The line-shaped arrays (42) are preferably situated parallel one to another. The arrays (42) are installed in the support for adjustment (41), which in its turn is fixed to the base of the housing (40).

The light emitted by the line-shaped arrays (42) of light emitting elements is transmitted through the optical means (43), which concentrate the light in the diffraction element (44). The diffraction element (43) is mounted so that the plane of light diffraction is orthogonal to the main direction of the arrays (42) of light emitting elements. The light emitted by each array (42d is incident in the diffraction element (44) under the angle ai, which is different for different arrays and is calculated from the equation d (sinai +sinß) =_mA. Here d is the spacing of the diffraction element, ? is the diffraction angle, m is an integer, and Ai is the wavelength of the light emitted by i-th array of the light emitting elements. After diffraction from the diffraction element (44), the light beams from different arrays (42) propagate in one and the same direction forming the common luminous flux.

The optical means (45) forms the spatial shape of the output luminous flux particularly focusing it in the line at the output plane (46).

The embodiment of the multi-purpose source of polychromatic optical irradiation shown in Fig. 4 is suitable for use as either a component of optical scanners intended for spectral identification of the objects containing color information or an illumination device instead of that containing the incandescent lamp or the xenon lamp.