The automatic focusing of a laser photoportraits

 

The automatic focusing of a laser photoportraits consists of optically coupled between a radiation source for auto focus and write, beam splitter, a focusing lens, a recording medium, an additional lens, a position-sensitive photodetector element and electrically connected electronic circuit for sampling signals and actuator element is mechanically connected with the focusing lens. The device also includes svetorasseyanie element made in the form of a diffraction grating with a period greater than T = 21/D, located between the radiation source and the focusing lens. Position-sensitive photodetector element is equipped with at least two separate position-sensitive areas of one quadrant of the photodetector. The technical result - the reduction of the influence of slope and curvature of the surface of the recording medium on the focusing accuracy of the recording radiation. 2 C.p. f-crystals, 4 Il.

The invention relates to optical instruments, namely, devices for automatic focus when printing, photolithography and fabrication photolithography (U.S. patent 5008705, G 03 D 27/52), consisting of optically coupled between a radiation source, a focusing lens, a recording medium, lens and electrically connected photodetecting element, the electronic circuit of the signal processing element.

It is also known a device for determining the focusing plane (U.S. patent 5534687, G 02 B 7/04), consisting of offset from the optical axis of the radiation source, lens and the photodetector element.

The closest technical solution is a system for automatic focusing of a laser photoportraits (ed. mon. The USSR 1605833, G 03 B 3/00) consisting of optically coupled between a source of radiation for auto focus and write beam splitter, a focusing lens, a recording medium, an additional lens, a position-sensitive photodetector element and electrically connected electronic circuits and signal processing element which is mechanically connected with the focusing lens.

A significant disadvantage of the known devices of the automatic focusing is not accurate focusing of the recording radiation, making it impossible to record information on the surface is irowiki recording radiation leads to a change in the size of the recording spots on the surface of the recording medium depending on its longitudinal displacement and tilt. Resize the recording spot leads to a distortion of the recorded data.

In the laser photoportraits, and other recording devices, information focus area of the recording laser radiation and the area of focus of the laser radiation device auto focus usually are posted by some distance. This is done with the purpose of eliminating the influence of recorded information (e.g., topography) on the operation of the automatic focusing. The focusing plane of the recording laser and laser auto focus when recording on a flat surface are the same and the focus error does not occur. In the case of recording on a curved or inclined surface error of focus equal to=d, wherethe angle of inclination of the surface, d is the distance between the areas of focus of the recording laser radiation and auto focus. When the inclination of the surface on=10and d=25 μm, the error rate reaches=4 μm, which is greater than the depth of p is and curved or inclined surface.

In the present invention, the task of creating a device for automatic focusing of a laser photoportraits to maintain the focus point of the radiation recording accurately on the surface of the recording medium regardless of its tilt.

The problem is solved in that the device consisting of optically coupled between a source of radiation for auto focus and write, beam splitter, a focusing lens, a recording medium, an additional lens, a position-sensitive photodetector element and electrically connected electronic circuits and signal processing element which is mechanically connected with the focusing lens is further provided with sitaramaraju element made in the form of a diffraction grating with a period greater than T = 2l/D, wherethe wavelength of the radiation source, l is the distance between the grating and the focusing lens, D is the diameter of the entrance pupil of the focusing lens, and located between the radiation source and the focusing lens, and a position-sensitive photodetector element is further provided with at least two separate region of the photodetector element made in the form of optically coupled quadrant photodetector and installed with a possibility of rotation in the plane of the axis, parallel to the plane surface of the photodetector, two oppositely oriented optical wedges with angles between faces less thanb/l1(n-1), where b is the size of the photosensitive area of the photodetector, l1- the distance between the photodetector and an optical wedge, n is the refractive index of the material of the optical wedge. Optical wedges are made of optical material with the lowest absorption at the wavelength of the radiation source.

The technical result of the invention is to reduce the influence of inclination and curvature of the surface of the recording medium on the focusing accuracy of the recording radiation.

New distinctive features of the invention is that the device is further provided with sitaramaraju element made in the form of a phase grating with a period greater than T = 2l/D, wherethe wavelength of the radiation source, l is the distance between the grating and the focusing lens, D is the diameter of the entrance pupil of the focusing lens, and a position-sensitive photodetector element is further provided with at least two separate position-chuvstvina made in the form of optically coupled quadrant photodetector and installed with a possibility of rotation in the plane of the axis, parallel to the plane surface of the photodetector, two oppositely oriented optical wedges with angles between faces less thanb/l1(n-1), where b is the size of the photosensitive area of the photodetector, l1- the distance between the photodetector and an optical wedge, n is the refractive index of the material of the optical wedge. Optical wedges are made of optical material with the lowest absorption at the wavelength of the radiation source.

The proposed invention is illustrated in the drawings.

In Fig. 1 presents a diagram of the device for automatic focusing of a laser photoportraits.

In Fig.2 presents a diagram of the rays of light when moving the recording medium from the reference position.

In Fig. 3 shows a typical dependence of error signals focus on the value of the inclination of the surface of the recording medium.

In Fig. 4 shows an embodiment of the position-sensitive photodetector element.

The proposed device (Fig.1) consists of a radiation source for auto focus 1 and writing 2, beam splitter 3, a focusing lens 4, the recording medium 5, an additional lens 6, the position-chustvitelinoe the signal processing unit 10, element 11, sitaramayya element 12. Separate position-sensitive areas 8 and 9 photodetector element consists of a 4-quadrant photodetector 13 and two optical wedges 14 and 15 (Fig.4).

The device (Fig.1) works as follows. The luminous flux of the radiation source 1 auto focus goes to sitaramaraju 12 and is divided into two equal intensity of light flux In1and In2extending symmetrically about the optical axis and inclined with respect thereto at an angle. Svetorasseyanie element 12 made in the form of a phase grating with a period of T<2l/D, wherethe wavelength of the light source, l is the distance between svetorasseivateley 12 and the focusing lens 4, D is the diameter of the entrance pupil of the focusing lens 4. When the rectangular profile of the strokes of the grating 81% of the energy of the light source is converted into light fluxes In1and In2equal intensity. The diameters of these light fluxes at the input of the focusing lens 4 are chosen as Db=(0.1-0.5)D. Both light flux focused by the lens 4 to the surface registryroot source 2 radiation record is reflected from the beam splitter 3 and is focused by the lens 4 to the surface of the recording medium 5 in the point O, lying on the optical axis. The recording medium 5 may be flat, concave (curved) or free-form surfaces.

During information recording surface of the recording medium is shifted from the focal plane of the lens 4 due to the uncertainty of the travel drive and the flatness of the surface. In the initial position of the recording medium 5 is placed exactly in the focal plane P of the focusing lens 4. Light streams In1and In2reflected from the recording medium 5, and after passing through the lens 4, is directed (the designation'1and In'2) additional lens 6, which focuses them into a'1and'2(the plane P') on the surface of the position-sensitive photodetection element (PCFA). Output signals PCFA depend on the positions of the points (A'1and'2the camera's viewfinder. When focusing light flux to the point a'1and'2the values of the signals at the output PCFA accepted as precise focusing. The displacement of the recording medium 5 from the initial position of the symmetry of the illumination surface PCFA is broken and its output receive electrical signals functionally related to the magnitude of the defocus l signal processing 10, which computes values of l0(Fig.2) at each time point and correction of the amplitude-frequency characteristics of a closed-loop automatic control system. The output voltage of this circuit goes to the Executive item 11 focus that moves the lens 4 along the optical axis up until the luminous flux of the radiation source 2 will not focus again on the surface of the recording medium 5 at the point O.

In Fig. 2 shows the course of rays of light (for simplicity shown only the Central rays) when the tilt angleand offset by the value of l0the surface P of the recording medium from the reference position. Initially, the light fluxes In the1and In2focused by the lens and then reflected respectively at points a1and A2lying on the surface of R. When the inclination of this surface at an anglelight flows will be reflected in the points With a1and C2and cross the focal plane of the focusing lens at the points D1and D2. As the plane P is optically conjugated with the plane P' PCFA (the magnitude of the transverse magnification is equal to V=f2/f1where f1and f2- focal Reston segments A1D1and a2D2. For light streams In1and In2the values of these signals are determined by the expressions:andwhere is the transmission coefficient PCFA, d = f1tg(- the distance between the focus points of light fluxes In1and In2and the optical axis.

There are two options for performing electronic signal processing unit 10.

Option 1. If the magnitude of the inclination of the surface of the recording medium small (<<1), the expressions (1A) and (1B) are simplified as: S1= 2cV(d+l0)tg() (2a) and S2= 2cV(d-l0)tg(), (2B), the signal processing unit 10 carries out the subtraction of the signals S1and S2. The resulting differential signal is equal to: SS1-S2= 4cVl0tg() (3)
From the expression (3) implies that the differential signal S focusing errors does not depend on the angle of inclination of the surface, while the signals S1and S2individually linearly dependent on the angle at2depends on two variables l0and. The joint solution of these two equations allows to determine the exact values of l0and. Electronic signal processing unit 10 produces the solution of the system of these equations and the calculation of accurate values of defocus l0. The output of the circuit is formed by an electrical signal S proportional to the value of l0. In Fig.3 shows an example of a typical dependency of the signals S, S1and S2the error of focusing on the amount of inclination of the surface of the recording medium with l0=0,= 32(the focusing lens 4 with numerical aperture NA=0.65, d=25 µm, V=c=1 and the signals S' and S2' when defocusing on the l0=0.5 μm (dashed line). It is seen that in the proposed device (option 1) at small angles (<<1) of inclination of the surface of the recording medium 5, the signal S focusing errors varies slightly, while the signals S1and S2linearly increase. The signals S1and S2correspond to the signals of the focusing errors in known devices (prototype). If a valid error focus (globefreddie version of the device permissible bending surface to=5and in the known devices is not more than=0,6.
In option 2, the maximum anglesmaxthe inclination of the surface of the recording medium 4 is only limited by vignetting of the reflected from the surface of the light beams by the aperture D of the focusing lens. If Db<<D
max<max-, (4)
wheremax= arcsin(NA) - maximum aperture angle of the focusing lens. If the device uses a lens with NA=0.65 and= 25then the allowable tilt of the surface aremax<15.
In Fig. 4 shows an embodiment PTFE in the form of optically coupled quadrant of the photodetector 13 and installed with a possibility of rotation in the plane of the axis parallel to the plane surface of the photodetector (O XY), two oppositely oriented optical CL is sub> and'2lying on the axis O X between I, II and III, IV quadrants of the photodetector. The displacement of the recording medium 5 from the initial position of these points will move in opposite directions along the axis O X (in the gap between the quadrants). Located in front of the photodetector of the optical wedges 14 and 15 move the focus point And'1and'2in the new starting position And"1and A"2. Thus the offset of the recording medium 5 will lead to the redistribution of light emission between I and II (luminous flux B'2) and III and IV (luminous flux B'1) quadrants of the photodetector 13 and the emergence of electric signals S1and S2the output of subtractive amplifiers 16 and 17. Optical wedges are made with angles between faces less thanb/l1(n-1), where b is the size of the quadrant photosensitive area of the photodetector, l1- the distance between the photodetector and an optical wedge, n is the refractive index of the material of the optical wedge. To correct the exposure surface of the photodetector radiation records from the source 2 to the optical wedges are made of optical material with the lowest absorption at the wavelength of the radiation source (for example, from a color optical with the other autofocus system with symmetrical with respect to the focus area of the recording radiation position of the probing light flow allows you to greatly reduce the influence of inclination and curvature of the surface of a moving recording medium on the focusing accuracy of the recording radiation. This provides the option of recording information on a curved surface.


Claims

1. The automatic focusing of a laser photoportraits consisting of optically coupled between a source of radiation for auto focus and write, beam splitter, a focusing lens, a recording medium, an additional lens, a position-sensitive photodetector element and electrically connected electronic circuits and signal processing element which is mechanically connected with the focusing lens, wherein it is further provided with sitaramaraju element made in the form of a diffraction grating with a period greater than T = 21/D, wherethe wavelength of the radiation source, l is the distance between the grating and the focusing lens, D is the diameter of the entrance pupil of the focusing lens, and located between the radiation source and the focusing lens, and a position-sensitive photodetector element is equipped with at least two separate position-sensitive areas of one quadrant of the photodetector.

2. The device is in the form of optically coupled quadrant photodetector and installed with a possibility of rotation in the plane of the axis parallel to the plane surface of the photodetector of two oppositely oriented optical wedges with angles between faces less thanb/l1(n-1), where b is the size of the photosensitive area of the photodetector, I1- the distance between the photodetector and an optical wedge, n is the refractive index of the optical wedge.

3. The device under item 1, characterized in that the optical wedges are made of optical material with the lowest absorption at the wavelength of the radiation source.

 

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