Systems and methods for shaping wavefronts in polychromatic light using phase shifting elements

ES 2 330 656 T3

DESCRIPTION

Systems and procedures for modeling wave fronts in polychromatic light using phase shift elements.

Field of the invention

The present invention relates generally to systems and methods for wavefront modeling. More particularly, the present invention relates to systems and methods for modeling wavefronts that may include light having several different wavelengths. The present invention is particularly, but not exclusively, useful for creating a polychromatic wavefront exhibiting a selected wavefront shape.

Background of the invention

The term "wavefront" can be defined as an imaginary surface joining points of constant phase in a wave propagating through a medium. For light waves, a wavefront can be thought of as an imaginary three-dimensional surface of constant optical path length, orthogonal to a family of rays emanating from a radiation surface. In terms of shape, a wavefront can be spherical, flat, or arbitrarily patterned. In fact, for a monochromatic wave propagating from a point source through a medium with a constant refractive index, a spherical-shaped wavefront will be emitted from the surface. However, at long distances from the surface, the wavefront can be considered roughly flat. On the other hand, imperfect optical systems, natural phenomena (for example, atmospheric turbulence) and many other factors can give rise to non-uniform irregular wave fronts. For example, a component of an optical system, such as a lens that is not well polished, can create an aberration that distorts an otherwise uniform (eg, flat) wavefront.

To date, with regard to monochromatic light, various types of apparatus have been developed to measure the shape of wave fronts. For example, methods for measuring phase deviations have been disclosed in conjunction with devices such as the so-called "Hartmann-Shack sensor" and in publications such as US Patent No. 5,062,702 issued to Bille for an invention entitled "Device for Mapping Corneal Topography." . An interferometer is another common type of device that can be used to measure the shape of a wavefront.

In addition to measuring wave fronts, devices and procedures for wave front reshaping have been disclosed. For example, US Patent No. 6,220,707 (hereinafter the '707 patent) issued to Bille for an invention entitled "Method for Programming an Active Mirror to Mimic a Wavefront" discloses the use of a faceted mirror to reshape a wavefront. . Specific applications disclosed in the '707 patent include reshaping a distorted wavefront into a substantially flat wavefront, and vice versa. Furthermore, this reshaping can be carried out for distorted wavefronts in which the depth of the three-dimensional wav efront, measured in the direction of light propagation, exceeds one wavelength.

The '707 patent discloses in greater detail a phase-wrapping technique in which the outputs of a Hartmann-Shack wavefront analyzer are processed to determine a total offset in phase shift for each of a plurality of contiguous subbeams of a wavefront. These offsets can be measured with respect to the phase of corresponding subbeams of a reference wavefront, such as a planar wavefront. For a light that exhibits a wavelength λ, each measured "total deviation" includes a modular phase shift component "n, l" (also called a modular phase phase component "n2n") and a modular phase phase component "λ" (also called the 2π modular phase shift component). After measuring the total offset deviation, the particular modular offset for each sub-beam is compensated for by subtracting nλ, (n + 1), lo (n-1), l, etc., as appropriate, from the total offset for each sub-beam. Each element of the faceted mirror is then adjusted to minimize the modular phase shift deviation λ of each respective sub-beam to efficiently transform a beam of light between a distorted wavefront and a flat wavefront.

Although the advancements described above have been successful in measuring and modifying the wavefronts of monochromatic light, many applications require the use of polychromatic light. For these applications it may be desirable to control and modify wave fronts of a polychromatic light flux. One such application, by way of example, is the correction of aberrations created by an optical system during imaging of a multi-colored object. Another exemplary application includes creating a flux of polychromatic light that exhibits controlled wavefront shapes that are used to test the influence of optical aberrations on human vision.

Document EP-A-1 199 026, on which the preamble of claim 1 is based, discloses a system for active wavefront modeling comprising a source for sequentially generating a first beam of light presenting a first wavelength λ1, and a second light beam having a second wavelength λ2, each beam presenting a plurality of contiguous sub-beams, said sub-beams establishing a wavefront λ1 and a wavefront λ2, and an active mirror.

Accordingly, in view of the foregoing, it is an object of the present invention to provide a system and method for reshaping the wave fronts of a light stream containing light of several different wavelengths. Another object of the present invention is to provide systems and methods for remodeling fronts of

ES 2 330 656 T3 polychromatic light waves having a three-dimensional wavefront depth, measured in the direction of light propagation, exceeding one wavelength. Yet another object of the present invention is to provide systems and methods for modeling polychromatic wavefronts using offset elements that are easy to use, relatively easy to manufacture, and comparatively inexpensive.

Summary of the invention

The present invention is directed to systems and methods for actively reshaping wave fronts of an input light source having at least two wavelengths (di, λ₂) different. For the purposes of this description, the input light can be described in terms of one or more light beams, each beam being formed by a plurality of contiguous sub beams. These subbeams establish a wavefront for light λ₁ (that is, a wavefront λ₁) and a wavefront for light λ₂ (that is, a wavefront λ₂).

The input light is received by an optical offset device that may include one or more arrays, each array presenting a plurality of elements. Functionally, in a particular array, each element can be independently adjusted to selectively alter the optical path length of a corresponding sub-beam. Therefore, clustering can be programmed to selectively reshape a wavefront. More specifically, once programmed into a selected configuration, the array of elements functions to receive an incoming beam that exhibits a first initial wavefront, and to process the beam to create an output beam that exhibits a modified second wavefront.

For the present invention, the array of elements may be, but is not necessarily limited to, a faceted active mirror, an array of liquid crystals, or a sheet metal mirror featuring an array of actuators that can be independently operated to deform. selectively the surface of the foil mirror. In a typical embodiment an active mirror is used having approximately forty thousand individual facets, each facet being able to move independently along a respective substantially parallel path.

For a source light that has two wavelengths (λ₁, λ₂), a first clustering configuration is used to reshape the waveform of wavelength λ₁ initial and a second cluster configuration is used to reshape the waveform of wavelength λ₂ initial. As will be described in greater detail later, for the present invention, the first and second array configuration can be obtained using a single array of elements or two different arrays. In any case, once the wave fronts have been reshaped, both light of wavelength λ1 and light of wavelength λ2 are directed on a common beam path. Once on the common beam path, the light can be seen, imaged, or further processed.

In a particular embodiment of the present invention, the input light includes alternating pulses of the light of wavelength λ₁ and of the light of wavelength λ₂. For this embodiment, a single common array of elements can be used to reshape multi-wavelength light. Specifically, the movements of the individual grouping elements can be synchronized with the alternating input light source to sequentially and selectively reshape the wavefronts λ.₁ and λ₂ pressed.

In another embodiment of the present invention, the input light simultaneously includes light of wavelength λ₁ and light of wavelength λ₂. For this embodiment, the input light is divided (spatially) to direct the light of wavelength λ₁ on a first beam path and to direct the light of wavelength λ₂ on a second beam path. Once separated, a first grouping of elements is used to reshape the wavefront of wavelength λ₁ and a second grouping of elements is used to reshape the wavefront of wavelength λ₂. After wavefront reshaping, the output beams from the clusters recombine on a common beam path.

For some system applications, a wavefront sensor, such as a Hartmann-Shack sensor, may be provided to measure the wavefront λ₁, the wavefront λ₂, or both. This measurement can be carried out in light propagating toward a cluster, in light propagating away from a cluster, or both. The sensor output is then used to program the cluster to perform selected wavefront reshaping.

In one implementation of the system, the sensor is used to measure a total deviation in phase shift for each of the wavefront subgroups. These offsets are measured with respect to the phase of corresponding individual subbeams of a reference wavefront, such as a planar wavefront. Each measured "total deviation" includes a modular phase shift component "nd" and a modular phase phase component "λ" for light having a wavelength λ.

Once the total phase shift has been determined for each sub-beam of the measured wavefront, the grouping of elements is divided into regions. Specifically, a region is identified with an integer "n" where all the sub-beams that affect elements of the region "n" have the same modular phase shift. Next, boundary facets are detected so that all boundary facets have a modular phase shift (n + 1) d with a modular phase shift deviation λ of zero. A region "n + 1" is then identified that is adjacent to the bordering facets, but outside the region "n". Similarly, other bordering facets with a modular phase shift can be detected.

ES 2 330 656 T3 (n-1) d with a modular phase shift deviation d of zero. If this is so, an "n-1" region is identified. Similarly, "n + 2" and "n + 3" regions, etc., as well as "n-2" and "n-3" regions, etc. can be identified.

The particular modular offset for each region is compensated for by subtracting nd, (n + 1) d or (n-1) d, etc., as appropriate, from the total offset for each sub-beam within the region. In this way, the modular phase shift deviations d are determined for each wavefront sub-beam. Therefore, if determined by the application, each element can be adjusted to minimize the modular offset deviation λ of each respective sub-beam. Collectively, when this compensation is done for all elements, active grouping can effectively transform a beam of light between a distorted wavefront and a flat wavefront.

Brief description of the drawings

The novel characteristics of this invention, as well as the invention itself, as regards both its structure and its operation, will be better understood from the attached drawings, taken together with the attached description, in which the characters of Similar references refer to similar parts, and in which:

fig. 1 is a schematic view of the main components of a system for reshaping wavefronts of polychromatic light;

fig. 2 is a detailed schematic view of the system shown in FIG. 1;

fig. 3 is a front view of an array viewed in the direction of arrow 3-3 of FIG. 2;

fig. 4 is a schematic view showing reshaping of a wavefront having a wavefront depth, measured in the direction of light propagation, that exceeds one wavelength;

fig. 5 is a schematic view of the main components of another embodiment of a system for reshaping wavefronts of polychromatic light;

fig. 6 is a detailed schematic view of the system shown in FIG. 5;

fig. 7 is a front view of a light source having a filter wheel that is used in the embodiment shown in FIGS. 5 and 6;

fig. 8 is a cross-sectional view of a filter wheel viewed along line 8-8 of FIG. 7.

Description of the preferred embodiments

Referring to fig. 1 shows a wavefront reshaping system generically designated 20. As generically shown in FIG. 1, system 20 includes a source 22 for generating a beam 24 of light having three wavelengths (d₁, d₂, d₃) different. Although three wavelengths are shown and described, it should be appreciated that system 20 can reshape light having more than three and at least two wavelengths. Furthermore, system 20 is not limited to light within the visible spectrum. Fig. 1 further illustrates that bundle 24 may be conveniently described as consisting of a plurality of contiguous sub-beams, of which sub-beams 26a through 26d are shown and labeled by way of example. These sub-beams simultaneously establish wave fronts 28 d₁, d₂, d₃ initials in beam 24.

From source 22, beam 24 of light is impinged on an optical offset device 30. For system 20, optical phase shift device 30 can be programmed to independently reshape wave fronts 28 d₁, d₂, d₃ to generate wavefronts 32 d₁, d₂, d₃ modified. Once modified, the wavefronts 32 d₁, d₂, d₃ they exit the optical offset device 30 along a common beam path 34. Fig. 1 further shows that a detector 36 can be positioned in beam path 34 to allow modified wavefronts 32 exiting device 30 to be viewed, imaged, or further processed.

Figure 2 shows the system 20 in greater detail, including the individual components of the optical phase shifting device 30. As shown, a source 22 generates a continuous beam 24 of light that simultaneously includes three wavelengths (d₁, d₂, d₃) different. Although different rays are used to illustrate the three different wavelengths coming out of source 22 in FIG. 2, it should be appreciated that the entire continuous beam 24, when it leaves source 22, includes three wavelengths (d₁, d₂, d₃) different. By way of example, source 22 may be a multicolored object illuminated with natural light to include white light, artificial light, or light that has been specially generated or filtered to include only the three wavelengths (d₁, d₂, d₃) desired. In one implementation, the three wavelengths (d₁, d₂, d₃) desired correspond to a set of three primary colors. As used herein, the term "primary colors" refers to any set of three or more colors that when added in an appropriate combination will give white. For example, d₁ can be blue light in the wavelength range of 435 to 480 nm, d₂ can be red light in the wavelength range of 605 to 750 nm, and d₃ it can be green light in the wavelength range of 500 to 560 nm. In some applications of the system 20, light from the "traditional" RGB space is used, (ie, red at 700 nm, green at 546.1 nm, and blue at 435.8 nm). For other applications, it may be preferable to use eye-sensitive wavelengths. Specifically, the receptors (cones) of the human eye

ES 2 330 656 T3 that are responsible for color vision are most sensitive in the following wavelength regions: 550 to 580 nm (yellow-green), 520 to 540 nm (green), and 415 to 450 nm (blue ).

Fig. 2 shows that from source 22, beam 24 first strikes a spacer 38a which directs light of wavelength di over a beam path 40a and into an array 42a. As shown, the remainder of the light from separator 38a, including light having wavelengths λ₂ and d₃, is directed along a path 44 toward the spacer 38b. In the separator 38b, the light having a wavelength λ₂ it is directed on a beam path 40b towards an array 42b. The remainder of the light from separator 38b, including light having a wavelength λ₃, is directed along a path 46 toward the spacer 38c. In the separator 38c, the light having a wavelength λ₃ it is directed on a beam path 4c towards an array 42c.

It can also be seen in fig. 2 that a part of the light of wavelength λ₁ moving toward cluster 42a on path 40a is directed toward wavefront sensor 48a. More or less similarly, a part of the light of wavelength λ₂ moving toward cluster 42b on path 40b is directed toward a wavefront sensor 48b and a portion of the light of wavelength λ₃ moving toward cluster 42c on path 40c is directed toward wavefront sensor 48c. Each wavefront sensor 48a to 48c may be, for example, a Hartmann-Shack sensor or some other suitable device known in the relevant art for measuring a wavefront.

Figure 2 further shows that system 20 includes a processor 50 that is connected in electronic communication with a control unit 52 via cable 54. For system 20, each wavefront sensor 48a to 48c is connected to the processor. 50 through a cable 56. It can further be seen that the control unit 52 is connected to each cluster 42a to 42c via cables 58a to 58c, respectively. With this structural cooperation, the output of a sensor 48a through 48c can be used to program a respective cluster 42a through 42c to individually perform selected wavefront reshaping for light on each of respective paths 40a through 40c of you do.

In greater detail and as can best be appreciated by cross reference to Figs. 2 and 3, each cluster 42a to 42c includes a plurality of items 60 of which items 60a to 60c have been labeled by way of example. Functionally, in a particular array 42a to 42c, each element 60 can be independently adjusted to selectively alter the optical path length of a corresponding sub-beam 26 (see FIG. 1). Thus, each cluster 42a to 42c can be programmed to selectively reshape one wavefront. For system 20, each array 42 may be, but is not necessarily limited to, a faceted active mirror, a sheet metal mirror featuring an array of actuator elements that can be independently operated to selectively deform the surface of the sheet metal mirror, or a grouping of liquid crystals. Thus, each cluster 42, depending on its particular configuration, can function by reflection or transmission to reshape a wavefront.

In a typical embodiment an active mirror is used having approximately forty thousand individual facet elements 60, with each facet element 60 being independently movable along a respective substantially parallel path. A more detailed description of an active faceted mirror can be found in US Patent No. 6,220,707. Functionally, as shown in fig. 2, once programmed into a selected configuration, each cluster 42a to 42c functions to receive a respective incoming beam that presents a first initial wavefront 62a to 62c, and processes the beam to create a respective output beam that exhibits a second front. wave 64a to 64c modified. Fig. 2 shows that after reshaping, the modified wavefronts 64a to 64c are directed onto a common beam path 34 by respective mirrors 66a to 66c for reception by a detector 36, which in this case is a human eye.

The applications of the particular embodiment shown in fig. 2 may include, but are not limited to, improving the optical characteristics and quality of binoculars, microscopes, endoscopes, and other imaging equipment. Alternatively, the system 20 shown in FIG. 2 can be used to generate polychromatic light having previously selected wavefront characteristics. In this case, instead of an illuminated object a source 22 consisting of one or more high quality light emitters (which can be monochromatic or polychromatic) is normally used. With respect to the embodiment shown in FIG. 2, it should be appreciated that wavefront sensors 48a to 48c can be selectively positioned to measure initial wavefronts 62a to 62c, modified wavefronts 64a to 64c, or both. In all of these cases, the sensor outputs can be used to program clusters 42a through 42c to obtain modified wavefronts 64a through 64c having preselected shapes. In some applications of the system 20, the shape of the wavefronts of the source may be known, or it may be predicted or calculated. In these applications, it may not be necessary to use a wavefront measuring device (eg, a Hartmann-Shack sensor) to modify and generate a preselected wavefront shape.

For system 20, clusters 42a to 42c can be used to reshape the initial monochromatic wavefronts 62a to 62c in which the depth of the three-dimensional wavefront, measured in the direction of light propagation, exceeds one wavelength . This technique that is used with monochromatic light is fully described and claimed in jointly owned US Patent No. 6,220,707. In particular, the '707 patent shows and describes a computer operation for processing the outputs of a Hartmann-Shack wavefront analyzer to determine a total offset in phase shift for each of a plurality of continuous subbeams.

ES 2 330 656 T3 guides of a wave front. In one instance, these total offsets can be measured with respect to the corresponding subbeam phase of a reference wavefront, such as a planar wavefront.

Fig. 4 illustrates a phase wrapping technique that is used in conjunction with an active mirror 68 having a plurality of facets 70 of which facets 70a through 70c have been labeled by way of example. Specifically, fig. 4 shows a convergent monochromatic wavefront 72 having a wavelength λ incident on the facets 70 of the active mirror 68. As shown, each facet 70 can independently move through a distance λ / 2 along a respective substantially parallel path. It can further be seen that the converging wavefront 72 has a wavefront depth, measured in the direction of light propagation, that exceeds a wavelength λ. It can also be seen that upon interaction with facets 70 of mirror 68 a substantially flat wavefront 74 is generated and propagates away from active mirror 68.

To obtain the remodeling shown in fig. 4, a computer processes the outputs of a Hartmann-Shack wavefront analyzer to determine a total offset in phase shift for each of a plurality of contiguous sub-beams of a wavefront. For this purpose, the desired wavefront shape, after reshaping, can be used as a reference wavefront to measure "total drift". For light having a wavelength λ, each measured "total deviation" includes a modular phase shift component "nd" and a modular phase shift component "λ". After measuring the total offset deviation, the particular modular offset for each sub-beam is compensated for by subtracting nd, (n + 1) d or (n-1) d, etc., as appropriate, from the total offset for each sub-beam. Each element in the active array can be adjusted to minimize the modular phase shift deviation λ of each respective sub-beam to efficiently transform a beam of light, such as the converging wavefront 72 to a flat wavefront, such as the wavefront. wave 74 remodeled.

Referring now to FIG. 5, another embodiment of a wavefront reshaping system generically designated 20 'is shown. For system 20 ', source 22' is configured to sequentially emit pulses of light that alternate in wavelength from pulse to pulse (e.g. λ_Β λ₂, λ₃, λ_Β λ₂, λ₃ ... λ₁, λ₂, λ₃ ...) as shown. For convenience, each pulse can be described as consisting of a plurality of contiguous sub-beams of which sub-beams 26a 'and 26b' are shown and labeled by way of example. These subgroups establish a periodic train of wave fronts λ_Β λ₂, λ₃ initials that are impinged on an optical phase shift device 30 '.

For system 20 ', the optical offset device 30' is synchronized with the source 22 'and can be programmed to sequentially and independently reshape the wavefronts λ₁, λ₂, λ₃ initials. As further shown in FIG. 5, the pulses exit the optical offset device 30 'along a common beam path 34' and have wavefronts λ₁, λ₂, λ₃ modified. Fig. 5 also shows that a detector 36 'can be positioned in beam path 34' to allow the modified wavefronts exiting device 30 'to be viewed, imaged, or further processed.

Fig. 6 shows the system 20 'in greater detail, including the individual components of the source 22' and the optical offset device 30 '. As shown, a source 22 'includes an object 76 (which may or may not have multiple colors) that is illuminated by three light emitters 78a to 78c (i.e., bulbs), each emitter 78a to 78c generating a length of wave ^ i, λ₂, λ₃) of different light. In one implementation, the three wavelengths (λ_Β λ₂, λ₃) desired correspond to a set of three primary colors. For example, λ₁ can be blue light in the wavelength range of 435 to 480 nm, λ2 can be red light in the wavelength range of 605 to 750 nm, and λ3 can be green light in the wavelength range of 500 at 560 nm. In some applications of system 20 ', "traditional" RGB space light is used, (ie, red at 700 nm, green at 546.1 nm, and blue at 435.8 nm). For other applications, it may be preferable to use eye-sensitive wavelengths. Specifically, the receptors (cones) of the human eye that are responsible for color vision are most sensitive in the following wavelength regions: 550 to 580 nm (yellow-green), 520 to 540 nm (green), and 415 at 450 nm (blue). The intensities of the emitters 78a through 78c can be independently adjusted, if desired, to generate light that exhibits a preselected composite color. As shown, each emitter 78a through 78c is connected to control unit 52 'which is programmed to sequentially drive the three emitters 78a through 78c to generate the time varying beam of light described above.

Figs. 7 and 8 show an alternative arrangement of a font (designated as font 22 ") for use in system 20 '. As shown, a polychromatic (eg, white light) emitter 80 directs a beam of polychromatic light through a filter wheel 82 and onto a beam path 34 ". Filter wheel 82 includes filters 84a through 84c that are azimuthly distributed as shown in FIG. 8. For the 22 ”source, a wavelength λ passes through each filter 84a to 84c₁, λ₂, λ₃ respective light. A motor 86 is coupled to filter wheel 82 to rotate filter wheel 82 in the direction of arrow 88. With this structural cooperation, the concerted interaction of emitter 80 and rotating filter wheel 82 generates a sequence of light pulses alternating in wavelength (λ₁, λ₂, λ₃ ... λ₁, λ₂, λ₃ ...).

Referring again to FIG. 6, it can be seen that a part of each pulse that propagates away from source 22 '(or alternatively from source 22 ") is directed towards a wavefront sensor 48' which can be, for example, a Hartmann sensor -Shack or some other suitable device known in the relevant art for measuring a wavefront. Fig. 6 further shows that the system 20 'includes a processor 50' that is connected in electronic communication with a control unit 52 'and the wavefront sensor 48'. Can be seen

ES 2 330 656 T3 furthermore that the control unit 52 'is connected to the cluster 42'. Processor 50 'and control unit 52' are synchronized with alternating emitters 78a through 78c (or with filter wheel 82 when source 20 "is used). With this cooperative structure, the output of sensor 48 'can be used to program array 42' to sequentially effect selected wavefront reshaping, pulse by pulse, for a pulse pattern generated by source 22 'or 22 ". After reshaping, the modified wavefronts are directed toward a detector 36 ', which in this case is a human eye. For some types of detectors 36 'a minimum pulse repetition frequency must be maintained. For example, for human eye vision, each wavelength must be pulsed at greater than fifty hertz and preferably greater than sixty hertz. For three wavelengths, the state of cluster 42 'would then change with a wavelength of one hundred and eighty hertz or greater.

Applications of the particular embodiment shown in fig. 2 may include, but are not limited to, improving the optical characteristics and quality of binoculars, microscopes, endoscopes, and other imaging equipment. Alternatively, the system 20 shown in FIG. 2 can be used to generate polychromatic light having preselected wavefront characteristics. With respect to the embodiment shown in FIG. 6, it should be appreciated that the wavefront sensor 48 'can be selectively positioned to measure a wavefront before cluster 42', after cluster 42 ', or both. In all of these cases, the sensor outputs can be used to program the clusters 42 'to obtain modified wavefronts having preselected shapes. In some applications of the system 20 'the shape of the source wavefronts may be known, or it may be predicted or calculated. In these applications, it may not be necessary to use a wavefront measuring device (eg, a Hartmann-Shack sensor) to modify and generate a preselected wavefront waveform. Like system 20 described above, array 42 'for system 20' can be used to reshape initial wavefronts where the depth of the three-dimensional wavefront, measured in the direction of light propagation, exceeds a wavelength.

Although the particular systems and procedures for modeling wavefronts in polychromatic light shown and described in detail in this document are fully capable of achieving the objects and providing the advantages outlined earlier in this document, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitation applies to the details of construction or design shown herein other than those described in the appended claims.