RU2465739C2 - Optical illumination system for active 3d camera - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: invention relates to optical systems, specifically systems for generating radiation of diode lasers, particularly in illumination systems of active 3D cameras based on diode lasers. The optical illumination system of an active 3D camera includes an array of primary radiation sources and a forming optical system. The forming optical system consists of intermediate and output forming optical subsystems. The intermediate forming subsystem is configured to form a secondary source and includes a matching optical system and an integrator. The matching optical system includes an array of lenses for initial transformation of radiation of the array of primary sources and a common combiner. The output forming optical subsystem is a variable focus lens.

EFFECT: high uniformity of illumination, minimisation of size and loss of energy.

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Description

The invention relates to the field of optical systems, namely systems for generating radiation of laser diodes, in particular, in the backlight systems of active 3D cameras on laser diodes.

The backlight systems of active 3D cameras on laser diodes have many advantages, among which there is a high speed and a narrow spectral range of radiation sources compared to backlight systems based on LEDs and other non-laser radiation sources.

The main problem that arises when designing illumination systems for active 3D cameras using laser diodes (for example, for modern 3D cameras with infrared illumination) is the task of ensuring uniform illumination of the illumination region at the object while effectively suppressing the speckles of the laser radiation source due to its coherence and monochromaticity, as well as providing a variable angular size of the backlight area on the subject when shooting from various distances while minimizing dimensions and energy losses ov radiation.

The prior art various designs of active 3D camera backlight systems and methods for obtaining uniform illumination and effective speckle suppression. In particular, the following US patents and patent applications may be mentioned: No. 6734450 [1], 7390097 [2], 5850300 [3], 5986807 [4], 6903859 [5], 7443591 [6], 6895149 [7], 2003 / 0174755 [8], 5109465 [9].

The most common solution is to use an array of LED sources located on the outer end of the 3D camera around the main lens. When using LD sources, to suppress speckles and obtain uniform illumination in the illumination region, usually either moving scatterers, or spatial matrix radiation modulators, optical integrators, or multi-lens rasters are used.

The main disadvantage of analog solutions is the use of LED radiation sources without the possibility of changing the angular field of the backlight area at the shooting site.

To achieve high noise immunity and improve the accuracy of the receiving stage of a 3D camera, narrow-band optical radiation filters are usually installed at the input. The use of LED radiation sources leads to a decrease in the signal-to-noise ratio due to a too wide spectrum of their radiation, a decrease in the accuracy of the 3D camera, and large losses of radiation energy.

In addition, LED radiation sources have significantly lower speed compared to laser diodes, which leads to the need for expensive ultra-high-speed shutters to obtain the required backlight strobe duration.

In addition, the inability to change the angular field of the backlight area on the subject sharply limits the functionality of the 3D camera compared to conventional modern photo and movie cameras with a zoom function.

Closest to the claimed solution is the design described in US patent No. 6734450 [1], which was chosen as a prototype.

The problem to which the claimed invention is directed is to develop a design that allows for increased uniformity of illumination in the field of illumination at the object with effective suppression of speckles of the laser radiation source arising due to its coherence and monochromaticity, and also to obtain a variable angular the size of the backlight area on the subject when shooting at various distances, minimizing the size and energy loss in the backlight system of an active 3D camera.

The technical result is achieved due to the fact that laser diodes are used as a radiation source in conjunction with an optical system configured to provide uniform illumination and speckle suppression in a varying illumination region of the object, as well as an optical system configured to provide a variable angular size of the illumination region . In other words, an optical illumination system of an active 3D camera is claimed, including an array of primary radiation sources and forming an optical system,

The essence of the proposed technical solution is that in order to ensure uniform illumination of the illumination region, effectively suppress speckles of the laser radiation source, to provide a variable angular size of the illumination region at the object while minimizing the dimensions and energy losses of radiation sources, the backlight channel circuitry of the active 3D camera includes array of laser multimode radiation sources, matching optical system, optical radiation integrator eniya and zoom.

Figure 1. Circuitry of a backlight system of a known active 3D camera (from US Pat. No. 6,734,450).

Figure 2. Circuitry of the backlight system of an active 3D camera according to the invention.

Figure 3. The intermediate forming subsystem according to the invention.

Figure 4. Wide-angle zoom lens.

Figure 5. The zoom lens is in an intermediate position.

6. Zoom lens in the tele-position.

7. Illumination distribution in a wide-angle position at a distance of 1 m.

Fig. 8. Illumination distribution in an intermediate position at a distance of 1 m.

Fig.9. The distribution of illumination in the body position at a distance of 1 m.

The most promising is the scheme shown in Figure 2. It consists of an array of primary radiation sources 201 and a forming optical system, which, in turn, consists of an intermediate and output forming optical subsystems.

The primary radiation sources 201 are multimode high-power laser diodes with a short coherence length.

The intermediate forming subsystem includes a matching optical system and integrator 205 and is intended to form a secondary source located at the output end face 206 of the integrator 205.

The matching optical system includes an array of lenses 203 of the initial radiation conversion of the array of primary sources 201 and a combiner 204. The lens 203 of the initial radiation conversion of primary sources 201 is a cylindrical lens. Lens 203 reduces the divergence of radiation in a plane perpendicular to the emitter, thereby aligning the angular dimensions of the indicatrix of the primary sources 201 in two mutually perpendicular planes. The combiner 204 is a hexagonal prism of optical glass, the front, rear, and two side faces being refractive, and the upper and lower faces being reflective. A matching optical system combines the rays from the array of primary radiation sources 201 and directs them to the input end face 202 of the integrator 205.

The integrator 205 is a rod of optical glass of constant cross section in the form of a rectangle with the aspect ratio required for a particular embodiment. The integrator 205 performs mixing of the beams, increasing the difference in their path so that it exceeds the coherence length of the laser radiation source 201 for suppressing speckles, and provides a uniform distribution of illumination at the output end 206 (forms a secondary source). In this case, the indicatrixes of the radiation of the secondary source are uniform in its aperture and have angular sizes 2u '= 12.0 ... 16.0 degrees, and their axes are collinear relative to one another.

The output forming optical subsystem is a zoom lens 207, composed of four groups of lenses - 401, 402, 403 and 404 and providing the required difference in the angular dimensions of the backlight area.

The intermediate forming subsystem is illustrated in FIG. 3.

The design parameters of the elements of the optical illumination system of the active 3D camera are related by the relations:

where L is the optical path length from cylindrical lenses to the input end of the integrator, D _int is the diagonal of the integrator cross-section, u 'is the angular size of the radiation indicatrixes at the output of the cylindrical lenses;

where L _int is the length of the integrator, D _int is the diagonal section of the integrator.

The indicated relations for the design parameters of the elements of the optical illumination system of the active 3D camera provide:

- coordination of the indicatrix of the primary sources with the input angular aperture of the integrator;

- coordination of the output indicatrix of the secondary source with the input angular aperture of the zoom lens;

- high uniformity of illumination of the backlight area, speckle suppression and minimization of energy losses.

An example of a preferred implementation of the inventive system

The array of primary radiation sources consists of three powerful wide-emitter multimode laser diodes. Laser diodes: power - 1000 mW; emitter width - 100 microns; radiation wavelength - 850 nm; divergence - 32 ° × 8 ° (at the level of 0.5).

Cylindrical lenses: diameter - 200 microns; length for technological reasons should be more than 200 microns; material - optical glass FPL51.

The distance between the light-emitting area of each LD and its corresponding cylindrical lens is 18 ... 20 microns.

The combiner is a hexagonal prism. The front, rear and two side faces are refracting. The upper and lower faces are reflective. Prism: thickness - 1.0 mm; front face height - 2.5 mm; height of the back face - 0.4 mm; the length of the prism for technological reasons should be more than 0.5 mm; prism material - optical glass S-LAM66 with a refractive index in the range from 1.7 to 1.85.

The integrator is made in the form of a rod, that is, a rectangle with a constant cross section and with an aspect ratio of about 4: 3. Integrator: dimensions: 20.0 × 2.0 × 1.5 mm ³ (L × SH × H); material - optical glass FPL51 with a refractive index in the range from 1.4 to 1.5.

The zoom lens has a focal length difference of the order of 3 times, a fixed object plane, the telecentric course of the main beam and the input aperture angle u = 6.5 ... 8.0 degrees. The zoom lens consists of four lens groups, of which group 401 and group 403 are mobile.

Surface Radius Konik Thickness Light diameter Glass 0 ∞ * 2.5 one 1.777 0.391 3.0 Fpl51 2 1.723 0.280 2.8 S-NPH1 3 1.530 0.020 2.52 four 0.970 -1.227 0.653 2.56 L-NBH54 5 1.821 ** 2.32 6 -6.570 0.275 2.17 S-NPH1 7 -7.815 0.425 2.20 LAH66 8 -2.570 0.02 2.20 9 2.118 0.548 1.90 Fpl51 10 8.160 *** 1.56 eleven -35.16 0.343 2.76 N-PSK57 12 -28.43 0.300 3.00 S-NPH1 13 13.752 1.441 3.10 fourteen -1.621 0.500 3.20 Fpl51 fifteen -20.73 **** 6.50 16 -31.21 1.196 8.00 S-NPH1 17 -7.802 0.864 8.22 L-LAM60 eighteen -5.542 -0.578 - 8.60

Position one 2 3 zoom (Wide angle) (Interim) (Tele) Thickness 0 (*) 0.842 0.835 0.331 Thickness 5 (**) 1.458 1.466 1.969 Thickness 10 (***) 2.784 1.344 0.120 Thickness 15 (****) 0.058 1.498 2.722 Focal length 1.68 2.79 5.83 Output field 60 ° × 45 ° 38 ° × 28.5 ° 20 ° × 15 ° Full length 12.40 12.40 12.40

In the tables - all linear dimensions in mm.

Energy Efficiency:> 90%.

Inhomogeneity in the backlight area of the required angular size: <10%.

Currently, the most effective application is associated with the use of active 3D cameras in backlight systems.

Claims (9)

1. The optical illumination system of the active 3D camera, including an array of primary radiation sources and forming an optical system, characterized in that the forming optical system consists of an intermediate and output forming optical subsystems, and:
the intermediate forming subsystem is configured to form a secondary source and includes a matching optical system and an integrator;
matching optical system includes an array of lenses for the initial conversion of radiation from an array of primary sources and a common combiner;
The output forming optical subsystem is a zoom lens. 2. The optical system according to claim 1, characterized in that the array of primary radiation sources is made in the form of a set of high-power multimode laser diodes with a short coherence length. 3. The optical system according to claim 1, characterized in that the array of lenses of the initial radiation conversion of the array of primary sources consists of cylindrical lenses. 4. The optical system according to claim 1, characterized in that the combiner is made in the form of a hexagonal prism of optical glass with a refractive index in the range from 1.7 to 1.85, the front, rear and two side faces being refractive, and the upper and The bottom faces are reflective. 5. The optical system according to claim 1, characterized in that the integrator is made in the form of a rod of optical glass with a refractive index in the range from 1.4 to 1.5, a constant section in the form of a rectangle with an aspect ratio of about 4: 3. 6. The optical system according to claim 1, characterized in that the secondary radiation source is formed at the output end of the integrator. 7. The optical system according to claim 6, characterized in that the indicatrices of the radiation of the secondary source are uniform in its aperture and have angular sizes 2u '= 12.0 ... 16.0 degrees, and their axes are collinear relative to one another. 8. The optical system according to claim 1, characterized in that the zoom lens has a focal length difference of the order of three times, a fixed object plane, the telecentric course of the main beam and the input aperture angle u = 6.5 ... 8.5 degrees. 9. The optical system according to claim 1, characterized in that the design parameters of the elements of the optical illumination system of the active 3D camera are related by the ratios:

where L is the length of the optical path from the lens to the input end of the integrator;
D _int - diagonal section of the integrator;
u 'is the angular size of the indicatrix of radiation at the output of the lenses;

where L _int - the length of the integrator;
D _int - diagonal section of the integrator.

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