US20110188120A1 - Broadband optics for manipulating light beams and images - Google Patents

Abstract

The objective of the present invention is providing optical systems for controlling with propagation of light beams in lateral and angular space, and through optical apertures. Said light beams include laser beams as well as beams with wide spectrum of wavelengths and large divergence angles. Said optical systems are based on combination of diffractive waveplates with diffractive properties that can be controlled with the aid of external stimuli such as electrical fields, temperature, optical beams and mechanical means.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
• This invention was made with Government support under Contract No. W911QY-07-C-0032.
CROSS REFERENCES
• [1] S. R. Nersisyan, N. V. Tabiryan, D. M. Steeves, B. R. Kimball, “Optical Axis Gratings in Liquid Crystals and their use for Polarization insensitive optical switching,” J. Nonlinear Opt. Phys. & Mat., 18, 1-47 (2009).
• [2] P. F. McManamon, P. J. Bos, M. J. Escuti, J. Heikenfeld, S. Serati, H. Xie, E. A. Watson, A Review of Phased Array Steering for Narrow-Band Electrooptical Systems, Proceedings of the IEEE, 97, pp. 1078-1096, 2009.
• [3] S. R. Nersisyan, N. V. Tabiryan, L. Hoke, D. M. Steeves, B. Kimball, Polarization insensitive imaging through polarization gratings, Optics Express, 17 (3), 1817-1830, 2009.
• [4] C. Oh, J. Kim, J. F. Muth, M. Escuti, A new beam steering concept: Riesley gratings, Proc. SPIE, vol. 7466, pp. 74660J1-J8, 2009.
• [5] J. C. Wyant, Rotating diffraction grating laser beam scanner, Applied Optics, 14, 1057-1058, 1975.

• U.S. Patent Documents

  	7,319,566	January 2008	Prince et al.
  	7,324,286	January 2008	Glebov et al.
  	6,792,028	September 2004	Cook et al.
  	3,721,486	March 1973	Bramley

RIGHTS OF THE GOVERNMENT
• The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
FIELD OF THE INVENTION
• This invention relates to optical beam control and, in particular, to methods, systems, apparatus and devices for manipulating with light beams, including laser beams and beams with wide spectra and divergence angles, by translating them in the lateral direction and varying their propagation direction over large angles for optical switching, beam scanning, spectral modulation, optical tweezers, thermal seeker, imaging, information displays, and other photonics applications.
BACKGROUND OF THE INVENTION
• The present invention relates to optical systems for controlling with propagation of light beams. Pointing and positioning systems are enabling components for most laser applications. Conventionally, this is accomplished using mirrors, scan wheels, optical wedges, and other two-axis gimbal arrangements as exemplified, for example, in the U.S. Pat. No. 7,319,566 to Prince et al. These opto-mechanical systems are complex, bulky and heavy for large area beams. For example, the prism apex angle, hence its thickness is increased to achieve larger deflection angles. The electromechanical systems for rotation, translation or oscillation of such mirrors, prisms, and other optical components require high electrical power for their operation. They are relatively slow and have limited range of angles that could be covered within given time period.
• Thus, there is a need for thin, light-weight, fast, and inexpensive pointing, positioning, and switching systems for light beams, particularly, for laser beams. The state-of-the-art developments include all-electronics systems and rotating diffraction gratings. The all-electronics systems with no moving parts, as reviewed in P. F. McManamon, P. J. Bos, M. J. Escuti, J. Heikenfeld, S. Serati, H. Xie, E. A. Watson, A Review of Phased Array Steering for Narrow-Band Electrooptical Systems, Proceedings of the IEEE, Vol. 97, pages 1078-1096 (2009), require a large number of high efficiency diffraction gratings and spatial light modulators and/or electrically controlled waveplates. As a result, the overall transmission of these systems is reduced along with their radiation damage threshold, and their speed is limited by the liquid crystal spatial light modulators and variable retarders.
• Rotating diffraction gratings as described in J. C. Wyant, “Rotating diffraction grating laser beam scanner,” Applied Optics, 14, pages 1057-1058 (1975), and in the U.S. Pat. No. 3,721,486 to Bramley, partially solves the problem of obtaining larger diffraction angle in thinner optical system, compared, for example to the system of Risley prisms. The light beam diffracted by the first grating in the path of the beam is further diffracted by the second grating. Depending on orientation of those gratings with respect to each other, the deflection angle of the beam can thus be varied between nearly 0 to double of the diffraction angle exhibited by a single grating. The problem with such systems is that phase gratings typically diffract light into multiple orders that need to be blocked along with the order beam. High efficiency Bragg type gratings have narrow spectral and angular range as described in the U.S. Pat. No. 7,324,286 to Glebov et al., and can be used practically for laser beams only, expanded and collimated to minimize divergence. Blazed gratings such as proposed in the U.S. Pat. No. 6,792,028 to Cook et al., still exhibit a multitude of diffraction orders due to their discontinuous structure and do not improve considerably on angular selectivity and efficiency.
• The cycloidal diffractive waveplates (DWs), essentially, anisotropic plates meeting half-wave condition but with optical axis orientation rotating in the plane of the waveplate in a cycloidal manner, as described in the review S. R. Nersisyan, N. V. Tabiryan, D. M. Steeves, B. R. Kimball, “Optical Axis Gratings in Liquid Crystals and their use for Polarization insensitive optical switching,” J. Nonlinear Opt. Phys. & Mat., 18, 1-47 (2009), do not have the disadvantages of conventional phase gratings. Moreover, DWs, referred to also as optical axis gratings and polarization gratings, can provide nearly 100% diffraction efficiency in micrometer thin layers. Furthermore, due to their waveplate nature, their diffraction spectrum is broadband, and can even be made practically achromatic. Due to their thinness and high transparency, they can be used in high power laser systems.
• Thus, replacing Risley prisms, wedges, mirrors and/or phase gratings with DWs, provides many advantages for manipulating with light beams and imaging. As shown in S. R. Nersisyan, N. V. Tabiryan, L. Hoke, D. M. Steeves, B. Kimball, Polarization insensitive imaging through polarization gratings, Optics Express, 17, 1817-1830 (2009), not only laser beams, but complex images can be steered over large angles without light attenuation or image deformation. That paper further showed that utilizing a pair of closely spaced DWs, one of them with switchable characteristics, it is possible to manipulate with transmission of unpolarized beams and images. This concept suggested and demonstrated in S. R. Nersisyan, N. V. Tabiryan, L. Hoke, D. M. Steeves, B. Kimball, “Polarization insensitive imaging through polarization gratings,” Optics Express, 17, 1817-1830 (2009) was subsequently cited and tested in C. Oh, J. Kim, J. F. Muth, M. Escuti, “A new beam steering concept: Riesley gratings,” Proc. SPIE, vol. 7466, pp. 74660J1-J8 (2009).
BRIEF SUMMARY OF THE INVENTION
• Thus, the objective of the present invention is providing means for switching and manipulating with light beams and images in lateral and angular space using a set of DWs capable of deflecting nearly 100% of light using thin material layers for a broad band of wavelengths and divergence angles.
• The second objective of the present invention is incorporating in said set DWs with controlled characteristics of their optical properties for further enhancing optical manipulation capabilities of said systems.
• A further objective of the present invention is providing optical systems, incorporating said DW set, wherein manipulation of light and images with the DW set is transformed into transmission modulation of at the output of the optical system.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• FIG. 1A schematically shows deflection of a circularly polarized light beam with a pair of diffractive waveplates.
• FIG. 1B schematically shows the structure of diffractive waveplates at different rotational positions.
• FIG. 2A shows sample dependence of the propagation angle of a light beam at the output of a pair of diffractive waveplates as a function of the rotational position between the waveplates.
• FIG. 2B demonstrates the capability of a pair of diffractive waveplates to steer with no distortions complex images carried by an unpolarized light.
• FIG. 3A schematically shows the displacement of a light beam by a pair of diffractive waveplates with parallel orientation of their optical axis modulation directions.
• FIG. 3B schematically shows the increase in the resultant deflection angle of a light beam by a pair of diffractive waveplates with anti-parallel orientation of their optical axis modulation directions.
• FIG. 3C shows the optical axis orientation pattern in diffractive waveplates with anti-parallel orientation of their optical axis modulation directions.
• FIG. 4A schematically shows increasing of the deflection angle of a light beam by a set of four diffractive waveplates each arranged anti-parallel with respect to the previous one.
• FIG. 4B demonstrates increasing deflection angle of a light beam by increasing the number of diffractive waveplates from one to four, and comparing them to the original propagation direction of the beam.
• FIG. 5 shows increasing deflection angle of a light beam by a system of diffractive waveplates tilted with respect to each other.
• FIGS. 6A and B schematically show switching between transmittive and deflective states of a pair of diffractive waveplates when switching one of the diffractive waveplates into an optically homogeneous non-diffractive state shown in C.
• FIG. 7 shows a schematic of a beam combining function of a pair of diffractive waveplates.
• FIGS. 8A, B and C show a schematic of a system for controlling the spectrum of a light beam with the aid of a set of diffractive waveplates.
DETAILED DESCRIPTION OF THE INVENTION
• Before explaining the disclosed embodiment of the present invention in detail it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not limitation.
• The preferred embodiment of the present invention includes two DWs, marked withnumerals103 and105 inFIG. 1A, arranged parallel to each other in close proximity. At the output of the system ofDWs103 and105, the pointing direction of thelight beam108, circularly polarized as shown byspirals102 and107, is, in general, different from that of the propagation direction of thelight beam101 incident on the system, controlled with relative rotational positions of the DWs as schematically shown byarrows104 and106. The optical axis orientation pattern corresponding to different rotational positions of said DWs is shown inFIG. 1B wherein the axes ofelongated ellipses109 correspond to local optical axis orientation direction. In the preferred embodiment, DWs are made of liquid crystal polymers though other optically anisotropic materials and material structures such as subwavelength gratings can be used as well. In general, the layer of DW, typically only a few micrometer thick, is coated on asubstrate110 for stability and robustness. The substrate can be made of a material adequate for the particular application. As an example, a fused silica can be used when controlling UV light beams, and highly transparent glass materials with low absorption can be used for controlling high power laser beams.
• The plot of output angles measured for a sample system as a function of angular position between the DWs in S. R. Nersisyan, N. V. Tabiryan, L. Hoke, D. M. Steeves, B. Kimball, “Polarization insensitive imaging through polarization gratings,” Optics Express, 17 (3), 1817-1830 (2009) is shown inFIG. 2A for normal incidence of the beam on the first DW. In the setup shown inFIG. 1A, the polarization of the incident beam is assumed circular, as schematically shown by thespiral102. Theoutput beam108 in this case maintains thecircular polarization state107. In case of incident unpolarized or linearly polarized beam, two beams of orthogonal circular polarization are generated at the output of the system of two DWs, and the angle between them changes from nearly 0 to nearly double of the diffraction angle depending on relative rotational positions between the DWs as shown inFIG. 2B for light beam carrying a complex image. No image distortions occurs in this process.
• Increasing the distance Δz between twoidentical DWs302 and304,FIG. 3, introduces transverse shift Δx of thebeam305 emerging from the system with respect to the position of theinput beam301 as a result of deflection of the beam by thefirst DW302. Said emergingbeam305 propagates parallel to theinput beam301 in case the optical axis modulation directions ofDWs302 and304 are parallel,FIG. 3A, and it also changes in propagation direction when theDW304 is rotated with respect toDW302 into anew position306,FIG. 3B. The overall deflection angle of the beam can be maximized positioning theoutput DW306 anti-parallel with respect to theinput DW302. The optical axis alignment patterns foranti-parallel DWs302 and306 are schematically shown inFIG. 3C. The beam can be steered over arbitrarily large angles by adding DWs into the system. Four DWs,406-409, are shown inFIG. 4A as an example. Theinput light401 undergoes four deflections,402-405. In order for each subsequent deflection to further increase the resultant deflection angle, theDWs407 and409 have to be arranged anti-parallel toDWs406 and408. A demonstration of light deflection by such a system of four DWs is shown inFIG. 4B. In general, DWs can be tilted with respect to each other such as each of the subsequent DWs is nearly perpendicular to the beam deflected by the previous DW. TheDWs507 and509 are anti-parallel to theDWs506 and508, and all four deflected beam502-505 of theinput beam501 result in increasing total deflection angle.
• In another embodiment, one or more DWs in a system can be switched between diffractive and non-diffractive states, optically, thermally, electrically, mechanically, or by any other means, due the effect of external stimuli on optical anisotropy and optical axis orientation modulation pattern. For example, the DW can be made of azobenzene liquid crystal polymer that can be transformed into isotropic state or realigned by light beams as discussed in S. R. Nersisyan, N. V. Tabiryan, D. M. Steeves, B. R. Kimball, “Optical Axis Gratings in Liquid Crystals and their use for Polarization insensitive optical switching,” J. Nonlinear Opt. Phys. & Mat., 18, 1-47 (2009). Alternatively, DWs can be transformed into homogeneous orientation state by electrical fields if they are made of liquid crystals or liquid crystal polymer network materials.
• Particularly important is the case shown inFIG. 6 when aDW603 with a fixed diffractive property is paired with acontrollable DW602 in configuration when their optical axis modulation directions are parallel. As noted in S. R. Nersisyan, N. V. Tabiryan, L. Hoke, D. M. Steeves, B. Kimball, “Polarization insensitive imaging through polarization gratings,” Optics Express, 17 (3), 1817-1830 (2009), this state corresponds to total cancellation of diffraction, and such a pair allows transmitting thelight beam601 through the system as shown schematically inFIG. 6A. Animage sensor604 furnished with anaperture605 large enough not to block the transmitted beam would not register any distortions to the beam. In case theDW602 is transformed into anon-diffractive state606, the diffraction of, generally, an unpolarized light on the remainingDW603 redirects theinput beam601 into diffractedbeams607 and608 as shown inFIG. 6B, diffracting it into orthogonal circular polarized components in case of unpolarized or linearly polarized incident beam. No beam is acting on animage sensor604 in this case provided the deflected beams propagate beyond the receiving aperture of the image sensor. Thus, the system described inFIG. 6 undergoes switching from high transmission to no or low-transmission state as a result of switching the structure of one of the DWs in the system fromdiffractive state603 into anon-diffractive state606,FIG. 6C. Indeed, such change in transmission through particular aperture can be obtained also by mechanically changing the rotational position of the DWs or the distance between them.
• Paired DWs and their systems can have many applications in photonics. A setup for beam combining is shown inFIG. 7. Two parallel propagating light beams of orthogonalcircular polarizations701 and704, after being deflected by thefirst DW707 are further deflected intobeams702 and705, emerging as overlapping beams of thesame propagation direction703 and706 by thesecond DW707 inFIG. 7.
• Given the thinness of individual DW layers, a multilayer system can be designed for spectrally selective switching without compromising the high throughput and the small size of the system. In the embodiment shown inFIG. 8, a set of DW pairs is used for controlling with the spectral content of the transmitted light by allowing light at different portions of the spectrum at least partially be deflected out of the system. Thebeams801 and804 inFIG. 8 are assumed to possess with different, non-overlapping, spectral content. The individual DWs in thefirst pair807 are optimized for diffracting thelight beam801 while having diffraction spectrum out of the spectral range of thebeam804. The individual DWs in thesecond pair808 are optimized for diffracting thelight beam804 while having diffraction spectrum out of the spectral range of thebeam801. Thus, when DWs in both pairs are parallel aligned with respect to their optical axis modulation direction, all the light is transmitted, and the spectral content of the output light is the same as in the input light. In this case shown inFIG. 8A, theinput light801 propagates through the first DW pair into thebeam802 without changing its propagation direction due to diffraction on both DWs constituting thepair807. Thebeam802 further propagates through thesecond DW pair808 into thebeam803 without deflection since its spectrum is out of the diffraction spectrum of thesecond DW pair808. Similarly, theinput light804 propagates through the first DW pair into thebeam805 without changing its propagation direction since its spectrum is out of the diffraction spectrum of thefirst DW pair807. Thebeam805 further propagates through thesecond DW pair808 into thebeam806 due to the diffraction on both DWs constituting thepair808.
• In case one of the DWs constituting thefirst pair807 is switched intonon-diffractive state809, or is rotated to double the diffraction angle of thebeam801 by the first DW in thepair807, thebeam801 is diffracted out of the optical system into abeam810. Propagation of thebeam804 is not affected by that. Thus the light spectrum obtained at the output of the optical system coincides with that of thebeam804,FIG. 8B.
• In case one of the DWs constituting thesecond pair808 is switched intonon-diffractive state811, or is rotated to double the diffraction angle of thebeam805 by the first DW in thepair808, thebeam805 is diffracted out of the optical system into abeam812. Propagation of thebeam802 is not affected by that. Thus the light spectrum obtained at the output of the optical system coincides with that of thebeam801,FIG. 8C.
• Although the present invention has been described above by way of a preferred embodiment, this embodiment can be modified at will, within the scope of the appended claims, without departing from the spirit and nature of the subject invention.

Claims (11)

1. A system for positioning light beams comprising:

(a) a light source;

(b) a plurality of diffractive waveplates;

(c) means for independently controlling the diffractive properties of individual diffractive waveplates.

2. The system ofclaim 1 wherein the light source includes means for shaping the light beam it irradiates by controlling one or a combination of its characteristics: divergence, spectral content, polarization, profile.

3. The system ofclaim 1 wherein the plurality of diffractive waveplates comprises at least one pair of optically identical diffractive waveplates.

4. The system as inclaim 1 wherein the material properties of at least one in the plurality of diffractive waveplates, including optical anisotropy, optical axis orientation, and layer thickness, can be controlled with one or a combination of the following stimuli: electric field, magnetic field, optical radiation, temperature, mechanical stress.

5. The system ofclaim 4 wherein the plurality of diffractive waveplates is deposited sequentially on the same substrate.

6. The system ofclaim 1 wherein the means for independently controlling the diffractive properties of individual diffractive waveplates include one or the combination of the following: electric field, magnetic field, optical radiation, temperature, mechanical rotation assembly, mechanical displacement assembly.

7. The system ofclaim 1 wherein the light beam is produced by a laser source with quasi-monochromatic spectrum.

8. The system ofclaim 1 wherein the light beam is produced by a source with broadband angular spectrum.

9. The system ofclaim 1 wherein the diffractive waveplates deflect light with nearly 100% efficiency in a broad spectrum of wavelengths.

10. The system ofclaim 7 wherein the light beam is produced by a source with broadband wavelength spectrum.

11. The system ofclaim 1 further comprising an optical setup for receiving and controlling the light at the output of the plurality of diffractive waveplates, said optical setup including one or a combination of the following: spatial filters, spectral filters, polarizers, diffraction gratings.

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