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Diffractive waveplates enable stackable ultrathin light-weight large area optics fast-switchable with low-voltage/low power fields. State-of-the-art systems and low-cost manufacturing opportunities will be presented aimed at next generation augmented, virtual reality, flexible, polarizer-free displays, LiDARs, etc.

Circularly polarized light is employed to write information into cholesteric liquid crystal (CLC) cells that initially exhibit homogeneous planar alignment and are fabricated with a photoaligning boundary layer. Overlap of the writing beam with light reflected from the CLC phase disrupts the reflective Grandjean texture, resulting in a localized region that strongly scatters light. These scattering areas can be geometrically patterned using circularly polarized light and a mask, erased and brought back to the original reflective condition by exposure to linearly polarized light, and then repatterned with a different mask using circularly polarized light. The light-induced scattering is localized to the side of the cell being exposed. Within the scattering region a microscopic texture is formed, which exhibits an average feature, or “domain”, size related to cell thickness and helical pitch. The behavior occurs only when the CLC and incoming writing radiation exhibit the same handedness and when the reflection bandwidth of the CLC is commensurate with the wavelength of the incoming radiation. This new phenomena provides the ability to reconfigure reflectivity from a CLC cell and is expected to be useful for systems where all optical control of dynamic information is needed.

We study the opportunity of using electrohydrodynamic instabilities in a nematic liquid crystal mixture with negative dielectric anisotropy for controlling laser beams. Switching between naturally transparent and diffuse light scattering states is achieved by application of low frequency, low amplitude voltages. The specifics of diffuse light scattering state depending on the orientation and thickness of the liquid crystal layer are revealed. The switching occurs on a milliseconds time scale. Combination of thin, flexible liquid crystal cells allows polarization independent, high contrast, fast switching in a broad band of visible wavelengths.

We report on lenses that operate over the visible wavelength band from 450 nm to beyond 700 nm, and other lenses that operate over a wide region in the near-infrared from 650 nm to beyond 1000 nm. Lenses were recorded in liquid crystal polymer layers only a few micrometers thick, using laser-based photoalignment and UV photopolymerization. Waveplate lenses allowed focusing and defocusing laser beams depending on the sign of the circularity of laser beam polarization. Diffraction efficiency of recorded waveplate lenses was up to 90% and contrast ratio was up to 500:1.

Photosensitive liquid crystals (PLCs) are promising materials that can combine a high-refractive-index modulation, typical of LCs, with high photosensitivity, due to the presence of photochromic molecules such as azobenzene and derivates. [1] These can undergo a reversible isomerization from a thermodynamically stable trans to a cis conformation when acted on by UV or visible light; a reverse transition can be obtained upon heating or irradiation with a different (longer wavelength) visible light. Thanks to these materials andprocesses, thepossibility toconfine and stabilize photosensitive materials has been considered in the past [2] and the perspective of producing fast photonic devices of scientific and technological interest looks highly realistic. There is, however, a serious problem represented by instability far from room temperature. [2] One way to reduce this effect has been found in using composite polymeric materials: [3] Holographic diffraction gratings, which exploit LC composite materials (HPDLCs), [4] are low-cost components with a wide range of possible photonic and optoelectronics applications. Therefore, the possibility of fabricating an optically controllable photonic device has been investigated by combining the photosensitivity of azobenzene materials with the optical properties of HPDLCs. [5] Devices of this kind can exhibit, however, an intrinsic drawback when the droplet size of the LC component inside the polymeric matrix is comparable with the wavelength of the diffracted light, thus yielding a strong light scattering. [6] Recently, a good improvement has been obtained by using a new kind of holographic diffraction grating with better optical qualities, which consists of polymer slices alternated to films of regularly aligned nematic LC (NLC). Depending on the particular procedure utilized for its fabrication, this structure is called POLIPHEM [7] orPOLICRYPS [8] andisobtainedby UV-curingofa mixture of monomer and NLC. In a recent attempt [9] to fabricate

We report on the laser and sunlight driven, fast and large oscillation of cantilevers composed of photoresponsive liquid crystal polymer materials. The oscillation frequency, driven with a focused 100 mW laser of multiple wavelengths (457, 488, 514 nm), is as high as 270 Hz and is shown to be strongly correlated to the physical dimensions of the cantilever. The experimental frequency response is accurately described by the calculated natural resonant frequency for a non-damped cantilever. To further understand the conversion efficiency of light energy to mechanical work in the system, the oscillatory behavior of a 2.7 mm × 0.7 mm × 0.04 mm cantilever was examined at pressures ranging from 1 atm to 0.03 atm. A large increase in amplitude from 110° at STP to 250° at low pressure was observed. A first approximation of the system efficiency was calculated at 0.1%. The large increase in amplitude at low pressure indicates strong hydrodynamic loss and thus, the material efficiency is potentially much greater. Using a simple optical setup, oscillatory behavior was also demonstrated using sunlight. This work indicates the potential for remotely triggered photoactuation of photoresponsive polymer cantilevers from long distances with lasers or focused sunlight.

We report on the fast and optically controlled angular bending of cantilevers made from liquid crystal polymer networks functionalized with azobenzene moieties (azo-LCN). For potential applications such as adaptive optics, photoresponsive cantilevers should rapidly deform to controlled angles while maintaining a modulus that can accomplish appreciable mechanical work. This work demonstrates cantilevers made of monodomain azo-LCN containing pendant (side chain) azobenzene mesogens with a storage modulus of 1.4 GPa bend 85° in less than 300 ms upon exposure to 442 nm irradiation. Moreover, the bending angle of these monodomain azo-LCN cantilevers can be controlled by the polarization angle of the source relative to the long-axis of the cantilever. The bending performance (deformation angle and speed) of this monodomain system is compared to a polydomain analogue. The impact of azobenzene concentration, laser intensity, and thickness on these parameters is also presented.

Phototuning of Bragg reflection bandgap from green to blue and from red to green wavelengths was induced with a green (λ = 532 nm) laser beam in a cholesteric liquid crystal based on highly sensitive azobenzene nematic BEAM 1005 (BEAM Co.) and UV transparent non-photoisomerizable optically active dopant ZLI-6248 (R-2011) (Merck Ltd.). Optical switching between reflected and transmitted beams, as well as nonlinear transmission and reflection due to Bragg reflection band shift are studied in detail.

Cholesteric liquid crystals (CLCs) which possess a periodicity in the visible portion of the spectra, exhibit selective reflection of circularly polarized light. The ability to modulate this color through a variety of means has been explored, including work which incorporated azobenzene LCs. Two types of systems have recently been explored utilizing wavelength-specific cis-trans isomerization processes, which enable unprecedented photosensitivity. The first system exhibits large blue or red-shifted changes in reflection wavelength upon visible irradiation. The second system exploits the metastable, long-lived photoinduced isotropic state, whose return to the reflective Grandjean texture can be induced by wavelength-specific radiation. We demonstrate nonlinear transmission from both types of systems, starting with submicrowatt power levels and spanning over four orders of magnitude dynamic range. The power dependence and temporal evolution of this effect (10–100 ms) is documented here for red or green laser wavelengths. The effect for the former case is due to bandgap auto-tuning, when the laser beam is tuning the CLC Bragg reflection band to its own wavelength. For the latter case, autonomous, optical feedback due to bandgap restoration is the cause of the nonlinear transmission properties.

Mixtures of cholesteric liquid crystals doped with high clearing temperature azobenzene nematic liquid crystals are shown to possess large, fast, and reversible dynamic photosensitive features. Selective wavelength shifts approaching 400 nm are reported, and depending on the host cholesteric liquid crystal, both red-shifted and blue-shifted wavelength changes can be induced. The photoinduced states of these material systems are shown to be stable for long periods of time upon removal of the radiation source, completely reversible, and dynamically fast. These phototunable features are demonstrated using both continuous wave (CW) and nanosecond laser beams. The latter is used to change the selective reflection wavelength from blue to green with a single nanosecond pulse and the ability to write information into these films using these processes are demonstrated.

We present new lenses - waveplate lenses created in liquid crystal and liquid crystal polymer materials. Using an electrically-switchable liquid-crystal half-wave retarder we realized switching between focused and defocused beams by the waveplate lens. A combination of two such lenses allowed the collimation of a laser beam as well as the change of focal length of optical system.

We show that photovoltaic fields generated internally in LiNbO3:Fe substrates are capable of efficiently reorienting liquid crystal molecules leading to new concepts of optically addressable light modulators. Using an arrangement consisting of a liquid crystal layer in contact with one or more LiNbO3:Fe photovoltaic substrates, we observe spatial filtering due to self-phase modulation in a planar oriented cell. The LiNbO3:Fe substrates are arranged such that light propagates along the +c axis, allowing a secondary process of power transfer to occur through photorefractive contra-directional two-beam coupling.

A nonlinear extinction of transmitted light is observed in liquid crystal cells with large concentrations of anthraquinone dye. Two distinct mechanisms are responsible for this effect when exposed to low and high intensity light, respectively. At low intensities, critical opalescence, micro-scatter, and an increase in linear absorption occur; whereas high intensities result in scattering from photo-induced micro-bubbles.

The isothermal formation of concentric colour domains has been observed in a cholesteric mixture doped with 10 wt % of a photochromic nematic material. The host cholesteric mixture included the Merck materials BL131a and BL130, while the photochromic dopant was a mixture of 4-n-butyl-4′-n-alkoxyazobenzenes (BAAB). The helical pitch of the host cholesteric mixture was increased, as expected, on addition of the photochromic nematic material prior to irradiation with the molecules in the purely trans-configuration. On irradiation with low power (0.6 mW) argon ion laser light, cis-isomers formed within the interaction region and concentric colour domains appeared. Selective reflection from the colour domains occurred in the 400–560 nm spectral range. The coloured domains persisted in the time period following irradiation and extended beyond the interaction region because of diffusion of the cis-isomers. Using the diffusion equation, an expression has been obtained for the average concentration of cis-isomers ...

Diffractive waveplate technology presents an opportunity for designing arrays of all types of optical components. We present here different architectures of arrays of waveplate lenses and vector vortex waveplates. Due to the continuous nature of diffractive waveplate coatings and the high spatial resolution of the technology, the sizes of array elements can span from micrometers to tens of millimeters. Both fixed and electrically switchable arrays are discussed. Arrays of diffractive waveplates present new challenges and opportunities for digital light polarization holography for applications in polarizer-free displays, smart windows, optical communications, beam shaping, and other photonics technologies.

The process of optical switching of a modulator based on nonlinear variation of the reflection coefficient at the “glass–dye-doped liquid-crystalline layer” interface near the critical angle of total internal reflection that occurs as the layer is heated with a pulsed solid-state laser radiation has been studied. Various switching modes based on reflection of the s- and p-polarized waves from either thin ( d ∼ λ ) or thick ( d ≫ λ ) absorbing LC layer have been investigated. Q-switching of a ruby laser by means of the LC modulator has been realized, and giant pulses of 1 J energy and 60 ns duration have been obtained. Changing the LC layer orientation director by a DC field enables to control laser operation mode and giant pulse parameters.

The effect of trans-cis photoisomerisation of azofragments of a polymer film on the molecular reorientation of a liquid crystal is studied. It is shown that, using nanosecond laser pulses, one can perform both the reversible and static data recording in liquid-crystal cells with an azo-modified surface. The rise time of the reorientation is measured by the methods of dynamic holography to be about ~ 30 μs, and the grating efficiency achieves 15 %.

The director reorientation in the liquid crystals (LCs) cells initiated by the trans‐cis isomerization of azo-dyes was studied with the aid of pump‐probe‐beam experiments. Two diAerent types of the samples were used, namely, a planar aligned LC layer, doped with an azo-dye, placed between substrates coated with rubbed poly(vinyl alcohol) (PVA) films, and an undoped LC layer placed between substrates, one of which (input) was coated with an untreated azopolymer film and other one was coated with rubbed PVA film. The cells were excited with nanosecond pulses of the second harmonic of an Nd:YAG laser. By comparing the reorientation dynamics with the help of dynamic holography method in both samples it was established that the values of development times of the orientational eAects were the same. The reorientation develops within 15‐17 ls and the eAciency of the orientational gratings is 13‐15%. In both kinds of samples the director orientation on the output surface with the rubbed PVA coating was not changed after irradiation. Contrary, the orientation of the director on the input substrate was changed in both cases. In case of a LC cell with azo-modified surface the reorientation is due to the photoisomerization of the azo-polymer film. In case of the cell with azo-dye-doped LC layer the photoisomerization of dye in the bulk of LC together with PVA film rearrangement on input substrate exert an influence on the director reorientation. ” 2000 Elsevier Science B.V. All rights reserved.

The stable and high quality wave front conjugation (WFC) of short laser pulses in azo-dye doped LC was obtained. The effect is based on the conformational nonlinearity and implies that the refractive index changes arise due to the dependence of the LC order parameter on the concentration of photoinduced dye-isomers. It was found that increasing of the pulse energy density in the range (7.5…12.5)×10 −2 J/cm 2 leads to the saturation of the conjugation coefficient. This effect was explained as a consequence of the light-induced changes of the absorption coefficient due to the saturation of the trans–cis transition. A phenomenological description of the nonlinear absorption was made on the base of the rate equations for the number of isomers. The nonlinear constant, which defines the WFC reflection coefficient, was estimated. It equals 0.25 cm 3 /J, that is ten times higher then the corresponding constant of the thermal nonlinearity.

Photoelectric phenomena and orientational nonlinearity have been studied which are induced in planar liquid crystal layers oriented by SiO and doped with polymethyne dyes (0.1 wt.%) under irradiation with nanosecond laser pulses. It was demonstrated that illumination of LC cells with Q-switched ruby laser pulses results in a drastic molecular reorientation which develops during 20 ms. This phenomenon is caused by photo-generation of surface and space charges in the LC cell and spatial distribution of space charges along the grating vector and beam propagation direction both with and without a DC field applied. A model is discussed which explains the orientational mechanism of photo-excitation by emergence of electrohydrodynamic instability at presence of both unipolar injection and anisotropy of conductivity and dielectric permittivity.

The photoelectric phenomena and orientational nonlinearity induced by nanosecond laser pulses in planar layers of liquid crystals oriented by silicon oxide (SiO) and activated with polymethine dyes were investigated. These phenomena are due to the photogeneration of surface and bulk charges in the liquid crystal cell, their spatial distribution between the grating vector and the beam propagation directions, and the electrohydrodynamic instability.

Two mechanisms of optical response in liquid crystals (LC) of homologous series 4-n-butyl-4′-n-alkoxyazobenzenes (BAAB), namely the photochemical phase transition and reorientation in bulk of LC are considered. The temporal parameters of writing (Ar+ laser) and erasing (He-Ne laser) of information on BAAB on the basis of photoinduced phase transition are presented. The phenomenon of reorientation of BAAB molecules in planar oriented layer induced with second of Nd:YAG laser in directions orthogonal to initial alignment was revealed.

The effect of flow-reorientation coupling on to the relaxation process of refractive index grating in nematic liquid crystals has been theoretically investigated. It is shown that in case of oblique incidence of the two beams onto the homeotropic cell the shear flow induced by the electromagnetic field can enhance the amplitude of the director reorientation to about ten times.

Wave-front conjugation (WFC) in four-wave interaction (FWI) of monopulse radiation of ruby laser in dye-doped liquid crystals (DDLC) was obtained. The amplification of conjugation wave was observed. The amplitude gratings and the phase gratings on thermal nonlinearity give the contribution in wave front conjugation.

High power laser (P∼106W/cm2) induced “domain”-like reorientation in homogeneously oriented by silicon monoxide dye doped liquid crystals (DDLC) has been observed. Reorientation can be accompanied with writing of static gratings that are induced by a radiation on monoxide layer surface.

We demonstrate some basic all-optical (electrically unbiased) logic gates in azobenzene liquid crystalline cells, exploiting their large nonlinearity for light localization and the trans-cis photoisomerization for all-optical external control. Spatial solitons were excited at microwatt power levels at 632.8 nm, whereas gating and switching were achieved with milliwatt beams at 409 nm

Orientation effect induced in bleachable dye doped planar nematic layer has been observed. It is believed that the effect is caused by dye-induced torque and hydrodynamic reorientation of the layer.

Peculiarities have been studied of modulation of nonpolarized light in reflection from glass-plane parallel ferroelectric smectic C boundary in the vicinity of total-internal-reflection angle under the action of electric field. LC materials with optical inclination angle of the local director of the smectic layer with respect to normal to the layer 45° are discussed. Optical characteristics are studied of modulated light beam for the cases of one- and two-fold reflection from the boundary. The results of investigations makes it possible to contruct an LC-valve characterized byhigh transmission (≈ 90%) of nonpolarized light in a wide spectrum range in the open state.

Pairs of cycloidal diffractive waveplates can be used to doubly diffract or collinearly propagate laser radiation of the appropriate wavelength. The use of a dynamic phase retarder placed in between the pair can be utilized to switch between the two optical states. We present results from the implementation of an azo-based retarder whose optical properties can be modulated using light itself. We show fast and efficient switching between the two states for both CW and single nanosecond laser pulses of green radiation. Contrasts greater than 100:1 were achieved. The temporal response as a function of light intensity is presented and the optical switching is shown to be polarization independent.

We report our recent efforts on the fabrication and characterization of light responsive devices realized in soft composite materials. Periodic microstructures obtained by means of a photolithographic technique and a chemical etching process have been used to micro confine a light responsive liquid crystal stabilized through a self-organization processes. The high quality, light responsive, periodic microstructures have been exploited for realizing different all-optical, fast and low power applications. An overview of the realized photonic devices is presented.

We review our comprehensive investigation of light self-localization phenomena in planarly configured azobenzene liquid crystals. Cis-trans isomerization of azobenzene molecules and related changes in the order parameter of the liquid crystals support a high nonlinear response and the formation of optical spatial solitons at microwatt excitations. We describe bright soliton angular steering, deflection, interleaving and merging, as well as dark solitons.

We report on fabrication and characterization of two different kinds of optically controlled diffraction gratings realized in soft composite materials. The periodic microstructures have been obtained by combining a photolithographic technique and a chemical etching process. The samples have been infiltrated with two classes of photosensitive materials, and then characterized. The first material is a common azo-dye dissolved in a liquid crystal (LC), while the second one is an azobenzene LC (azo-LC). The response and relaxation times, lifetimes and spectral absorption range of the LC mixtures confined in the microstructures were measured. Detailed comparison of investigated characteristics reveals a better overall performance of the azo-LC based sample.

Reversible, fast, all-optical switching of the reflection of a cholesteric liquid crystal (CLC) is demonstrated in a formulation doped with push-pull azobenzene dyes. The reflection of the photosensitive CLC compositions is optically switched by exposure to 488 and 532 nm CW lasers as well as ns pulsed 532 nm irradiation. Laser-directed optical switching of the reflection of the CLC compositions occurs rapidly, within a few hundred milliseconds for the CW laser lines examined here. Also observed is optical switching on the order of tens of nanoseconds when the CLC is exposed to a single nanosecond pulse with 0.2 J/cm(2) energy density. The rapid cis-trans isomerization typical of push-pull azobenzene dye is used for the first time to rapidly restore the reflection of the CLC from a photoinduced isotropic state within seconds after cessation of light exposure.

We report on the characterization of an all optical switching effect that takes place when a UV light beam irradiates an azo-POLICRYPS diffraction grating. This high quality polymeric structure is utilized to confine and stabilize a well aligned nematic liquid crystal (NLC) film doped with a small percentage of azo-NLC molecules. The optical control of the grating diffraction efficiency is obtained by exploiting the photochemical phase transition between the nematic and the isotropic phases of the liquid crystal, based on the photoisomerization of the azobenzene guest molecules. The switch ON-OFF of the grating diffraction efficiency is triggered by a UV pump laser and is investigated by means of a low power red probe beam.

Optically deformable membranes and cantilevers based on azobenzene liquid crystal polymer networks (azo-LCN) are demonstrated in the context of dynamic optical systems. Large modulations in laser beam propagation direction or amplitude directed by laser-induced changes in material shape are demonstrated. These macroscopic shape changes are induced by local changes to the liquid crystalline order induced by photoisomerization processes. We demonstrate herein a number of concepts including the focusing and defocusing action of an azo-LCN membrane, laser beam steering from a bimorph azo-LCN/metal cantilever, and surface initiated bending and blocking of a parallel propagating laser beam. High speed and large angle deformations of an incident or reference beam is demonstrated when coupled into suitable optical architectures. The concepts under discussion appear to be highly practical for a number of applications due to the significant nonlinearity and photosensitivity of azo-LCN materials.

We study optical switching properties of novel azobenzene liquid crystal (azo LC) material systems based on mesogenic azo dyes distinguished by enhanced absorption in the visible spectrum and a short lifetime of the photoexcited state. Due to their mesogenic nature these azo dyes can be doped at high concentrations in room temperature LCs. This permits one to obtain results using low energy density values required for observation of strong nonlinear optical processes and short spontaneous restoration times of their original state. A photoinduced nematic-isotropic phase transition could be induced with a single nanosecond pulse. Thin material layers of the order of radiation wavelength were used in the study.

A low power laser beam is used to induce large and fast variations in the shape of a polymer film due to photoinduced contraction and expansion of the polymer film surface subject to the beam. The direction of the photoinduced bend or twist of the polymer can be reversed by changing the polarization of the beam. Thus the film orientation could be varied within +/-70 masculine. The phenomenon is a result of optically induced reorientation of azobenzene moieties in the polymer network.

Different types of liquid crystal (LC) Q-switches and means for controlling radiation parameters of solid-state lasers by using the Q-switches are discussed.

Temperature dependences of the extraordinary wave refractive index and the absorption of light by dichroic dyes in oriented nematic layers have been studied. It is shown that there are such directions of the light wave relative to the nematic layer director for which the above-mentioned parameters are independent of temperature.

Stabilization of thermodynamic relaxation of photoinduced cis isomers of azobenzene liquid-crystal molecules is observed in nanoparticulate networks. The phenomenon permits bistability of the phase state (anisotropic and isotropic) of the material and reversible all-optical switching between those states, resulting in strong changes in the light-scattering properties of the material. Recording of complex optical structures with high spatial resolution with the aid of laser beams of different wavelengths is demonstrated.

We report on the photoactuation of high modulus liquid crystalline polymers with side chain azobenzene mesogens (azo-LCP). Photomechanical deformation is actuated with the 442 nm line of a He-Cd laser. Early results show that this system achieves displacement of up to 85° towards the actinic source when the He-Cd polarization is parallel to the nematic director and approximately 30-40° when the polarization is orthogonal to the nematic director. A wide range of materials have been synthesized by the photopolymerization of a liquid crystal diacrylate monomer (RM257) and an azobenzene-containing monoacrylate liquid crystalline monomer. Interestingly, azo-LCP formed with holographic photopolymerization have faster bending rates than polymers formed with flood-lit illumination of equivalent intensity.

We demonstrate an optical axis grating (OAG) recorded in a nematic liquid crystal that yields a higher than 80% diffraction efficiency and over 800:1 switching contrast between diffraction orders for a laser beam of a red wavelength in a material layer only 1.5 microm thick. The grating was used for combining two laser beams with high efficiency. These observations prove the feasibility of new generation high-efficiency diffractive optical components, which are most promising for infrared and high-power applications owing to their enhanced transparency and reduced thermal effects in thin material layers.

We study the phenomena of laser beam propagation in azobenzene liquid crystals (azo LCs) in waveguiding configuration. We found that spatial solitons can be formed at microwatt power levels of a He-Ne laser beam. We have observed several well-known processes of nonlinear propagation such as undulation of solitons, their interaction and merging. In addition, we have shown that due to the memory of the nonlinear waveguide in azo NLC, the solitons are steered following mechanical displacement of the LC cell, a phenomenon that can be used for stabilized coupling of radiation into optical fibers. Cis-trans isomerization of azobenzene molecules and related change in the LC order parameter is the underlying mechanism of optical nonlinearity that makes possible formation of solitons. This mechanism is present in the mesophase as well as in the photoinduced isotropic phase of the material. We have shown that the photoinduced isotropic phase may be locally induced to form a waveguide that steers the solitons to large angles without noticeable attenuation of the beam at distances ~ 1 cm. We have presented a simple 3-level theory for describing the complexity of the effects of laser beams on azo LCs.

We show that photovoltaic fields are capable of efficiently reorienting liquid crystals, leading to new concepts of optically addressable light modulators. Using an arrangement consisting of a liquid-crystal layer between LiNbO3:Fe photovoltaic substrates, we observed spatial filtering due to self-phase modulation in a planar-oriented cell and nonlinear transmission between crossed polarizers in a twist-oriented cell. These processes do not require an external electric field. The substrates are arranged such that light propagates along the +c axis in each substrate, allowing a secondary process of power transfer to occur through contradirectional photorefractive two-beam coupling.

Cycloidal nematic liquid crystal cells are capable of high diffraction efficiency in thin layers of materials comparable to the radiation wavelength. We demonstrate switching between diffraction orders of such grating using phase retarder.