Erasable thin-film optical diode based on a photoresponsive liquid crystal polymer.

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DOI: 10.1039/C3NR06623A

Erasable thin-film optical diode based photoresponsive liquid crystal polymer

on

a

Xinping Zhang,*a Jian Zhang,a Yujian Sun,bc Huai Yang,*d and Haifeng Yu*d a

Institute of Information Photonics Technology and College of Applied Sciences, Beijing University of Technology, Beijing 100124, P. R. China Anshan Normal University, Anshan 114005, Liaoning, China

c

School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 10083, China d

Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, P. R. China *Emails: [email protected], [email protected], [email protected]

Abstract We report a thin film optical diode written into thin films of one liquid-crystalline polymer (LCP), which is based on the photoinduced LC-to-isotropic phase transition of LCPs. The interference pattern between a collimated and a focused UV laser beam is imprinted as chirped volume-phase gratings in photoresponsive LCP films and no further processing steps like development or liftoff are required for the fabrication. The resultant thin-film device not only possesses fundamental functions of an optical lens for laser beam focusing, but also shows diode effects with the focusing/defocusing function dependent on the direction of light incidence and orientation of the device. Furthermore, this photonic thin-film lens exhibits spatially tunable spectroscopic response, revealing unique physics of secondary excitations of resonance modes of the single-layer LCP waveguide grating structures. This reveals mechanisms for the focusing/defocusing of laser beams by chirped grating structures. Erasability and reconstructibility of the photoresponsive LCPs guarantee rewritability of the thin-film diode lens. 1


Published on 20 January 2014. Downloaded by Aston University on 23/01/2014 09:41:24.

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1. Introduction Photoresponsive liquid-crystalline polymers (LCPs) are a kind of rewritable materials that can be applied extensively in optical storage, optical switching, photodriven

applications are based on the unique features of LCPs, where the rod-like mesogens with a strong birefringence can be well aligned on the surface of mechanically rubbed polyimide film and destroyed or erased by laser illuminations within their absorption spectra.4-6,13,14 However, the erased ordering of liquid crystal (LC) orientation may be reconstructed in the polymer film by further mechanical rubbing process or photoalignment treatment.4-6 In this work, we make use of these functions of the LCP thin films to holographically record the functions of an optical lens, where the thin film lens possesses both the functions of a single optical lens and new functions of photonic optical diodes unavailable in conventional devices due to its composition of chirped nanostructures. Holography is a conventional technique for three-dimensional (3D) recording and image-reconstructing of objects, where the interference pattern with sub-wavelength periods is written into the recording medium. The corresponding hologram is in fact a photonic device and the incident light is diffracted to reproduce the object light beams in the image-reconstruction process. This is actually how the photonic crystals work,12-15 which involve complicate interactions between light and the diffractive micro- or nano-structures.16-22 Thus, light beams can be modulated in their propagation,23-26 colors,27-29 polarizations,29-32 and even group velocity of ultrashort 2



device, photomechanical elastomers, and photocontrollable nanofabrication.1-12 These

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pulses. Meanwhile, the micro- and nano-structured hologram may produce further effects or functions that cannot be realized by the original object. Accordingly, this kind of holographic imprinting of optical functional devices extends the concept and

photoresponsive LCPs and holographic imprinting enables unique fabrication of multi-functional thin-film devices with further tunable parameters.

2. Holographic recording of an optical lens into polymeric liquid crystals 2.1 Polymeric liquid crystals The LCP of PM6ABOC2,2 as shown in Fig. 1(a), was synthesized via free radical polymerization of one azobenzene-containing monomer 6-(4-(4-ethoxyphenylazo) phenoxy)-hexyl methacrylate with 2,2-azobisisobutyronitrile (AIBN) as the initiator. The PM6ABOC2 appearing as yellow powder showed a number-average of 25, 000 and a molecular-weight distribution of 1.6. A typical nematic LC characteristic of Schlieren texture was observed on heating. To prepare alignment films for the LCP, clean glass substrates were spin-coated with 3 wt% poly (amic acid) solutions in N,N-dimethylformamide (DMF) at 500 rpm for 5 s and 3000 rpm for 30 s. Then, the surface-treated glass substrates were soft-baked at 100 °C for 1 hour and hard-baked at 250 °C for 2 hours to remove the solvent and thermally-induced imidization. Then, the obtained polyimide film was mechanically rubbed in a unidirectional way with a rubbing machine. Finally, a transparent PM6ABOC2 solution in

3



applications of both holography and photonic crystals. In particular, combination of

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tetrahydrofuran (THF) with a concentration of 2 wt% was spin-coated on the glass surfaces coated with rubbed polyimide films above-mentioned to obtain orientated LCP films. After the solvent was removed at room temperature, the LCP film heated

vacuum oven for 4 hours. The rubbing-induced alignment of LCPs was confirmed upon observation with a polarizing optical microscope. When the sample film was tilted by 45° with respect to the rubbing direction and the polarizer, a bright image was clearly observed in the rubbed area, whereas, a dark image appeared when the sample film was tilted by 0° or 90°. Such alternating bright and dark sphere images appeared with a periodicity of 90°. Fig. 1(b) shows the scheme of LCP alignment on the rubbed polyimide film. The alignment of LCs was further characterized with polarized UV-vis absorption spectra shown in Fig. 1(c). According to the differential scanning calorimetry (DSC) measurements shown in the supporting information (Fig. S1), PM6ABOC2 has a glass-transition temperature of about 82 oC and a clearing point at about 139 oC. The most important feature of this LCP utilized here is the trans-to-cis photoisomerization of azobenzene mesogens under UV irradiation. Fig. 1(d) shows the polarization optical microscopic image of the LCP film, where the right half of the studied field was irradiated by UV light. Clearly, transitions from LC to isotropic phases have been triggered by UV-irradiation, so that a high-contrast boundary is observed between the UV-irradiated isotropic phase and the non-irradiated LCP phase. Furthermore, it should be noted that although cis-to-trans back isomerization easily occurs at room 4



up to 170 °C and then cooled down to 150 °C and annealed at this temperature in a

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light, it is really difficult for the recovery of the LC phase at room temperature because of the high viscosity of the materials at the temperature below its glass transition temperature. This ensures the stability of the LCP-based optical diode lens

2.2 Direct holographic interference patterning Fig. 2(a) shows the optical scheme for holographic transferring of an optical lens into the LCP film, where the “reference” is a collimated beam with a diameter of about 7 mm and the “object” is an optical lens with its functions carried by a focused laser beam. A He-Cd laser at 325 nm supplies the UV light that produces the “reference” and “object” beams, which are managed to have the same size on the overlap. The “object” lens has a focal length of 20 cm and is placed about 5 cm before the LCP thin-film recording medium. The beam size and the power of the laser in the reference and object paths have been controlled to be identical on the overlap area, where each arm has an average power of about 10 mW over the circular area with 7-mm diameter. Fig. 2(b) shows the basic principle how the volume phase grating was record in the aligned LCP film with an interference pattern of two coherent laser beams at 325 nm. Upon irradiation, trans-to-cis photoisomerization of azobenzene mesogens is triggered in the bright area of the interference pattern, while the trans-azobenzene remains in the dark area (lower panel of Fig. 2(b)). This means that photoinduced LC-to-isotropic phase transition occurred in the bright area and aligned LC phase kept unchangeable in the dark area.1,2 Thus, the phase-type grating was obtained upon periodical photomodulation of refractive index in the oriented LCP films. It should be noted that 5



described in this work.

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there exists a threshold for the light intensity for the trans-to-cis photoisomerization, which is denoted by It in the upper panel of Fig. 2(b). This implies a clearly defined transition from the isotropic to the LC phases, which enhances the diffraction

The exposure process is controlled by an electronic shutter with a time resolution of 0.1 second. A red laser beam at 633 nm from a He-Ne laser is used to monitor the generation dynamics of hologram by measuring the peak spectral intensity of the diffracted laser beam using a USB 4000 spectrometer from Ocean Optics as a function of the exposure time, which is plotted in Fig. 2(c). The exposure process is stopped as soon as the diffracted beam intensity starts to decline, which means saturated exposure. According to Fig. 2(c), it took about 70 seconds for the exposure to reach its saturation, which finalizes the fabrication process. The inset on the top-left corner of Fig. 2(c) shows the geometry for the detection of the diffracted laser beam and that on the bottom-right shows the evolution dynamics of the spectrum of the diffracted laser beam at 633 nm. The broad bandwidth of the measured spectrum of the He-Ne laser results from the low-resolution (~7 nm) configuration of the spectrometer. Fig. 3(a) shows photographs of the thin-film lens written into the LCP, which have been taken at different observation angles (A-C) so that the thin-film lens exhibits different colors within the exposed area. The thin-film lens also has a diameter of about 7 mm, which is exactly coincident with the diameter of the recording laser beams on the overlap. For comparison, a photoresist device is shown as sample D in 6



efficiency of the resultant volume-phase grating.

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Fig. 3(a), which has been produced by interference lithography through exposing S1805 photoresist thin film to the same holographic pattern. Clearly, the photoresist grating has stronger diffraction due to its relief-hologram feature and shows more

across the effective area. In fact, the photoresist grating may reveal the true spatial details of the relief hologram by microscopic measurements. Fig. 3(b) shows the atomic force microscopic (AFM) images of the thin-film lens at 2 different sites measured on sample D in Fig. 3(a). Clearly, the chirped grating consists of large-period gratings interlaced with smaller-period ones. The small period is determined by Λ=λ/2sinα(X), which determines the diffraction and the diode lens properties of the chirped grating structures. It should be noted here that the separation angle (2α) between the two UV laser beams in interference lithography is a spatial function and varies with the spatial coordinates X, as depicted in Fig. 2(b). Furthermore, each grating line is found to extend in a spiral style, as can be recognized in Fig. 3(c), which confirms a three-dimensional configuration of the planar chirped grating structures.

3. Optical diode: directional focusing/defocusing and spatially dispersed spectroscopic response The function of the thin-film lens is realized by reconstructing the “object” beam using the incident “reference” beam. This is in essence the interaction between a laser beam and chirped gratings recorded as a volume-phase hologram in the LCP thin film. The spatial chirp in the LCP gratings can be characterized either by the microscopic images or by the spatially resolved extinction spectroscopy. 7



obvious chirping in the grating period by different colors of the diffraction pattern

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3.1 Diode lens with directional focusing and defocusing by chirped gratings Fig. 4 illustrates the basic principles how a chirped grating achieves focusing and defocusing of a laser beam. A negatively chirped grating is defined such that the

to the fabricated structures shown in Fig. 3. According to the classic diffraction equation: Λ(sinθi+sinθ)=λ, when a collimated light beam at λ with a diameter of D0 is incident at an angle of θi onto the chirped grating and diffracted into θ, smaller grating periods (Λ) at larger X induces diffraction into larger angles of θ, whereas, a smaller value of X corresponds to a larger Λ and consequently a smaller θ. This explains focusing of a light beam by a chirped grating with Λ2θ1, as illustrated in Fig. 4(a). On the basis of the geometry in Fig. 4(a), the thin-film lens functions differently as the laser beam is incident in different directions, which defines the diode effect of such a photonic device. The configuration that focuses the diffracted beam is defined as forward biasing, whereas, that defocuses the diffracted beam is defined as backward biasing. If the laser is incident in an opposite direction to that in Fig. 4(a), the diffraction by the chirped grating produces a divergent beam, as shown in Fig. 4(b). Furthermore, if the incident laser beam is symmetric with that shown in Fig. 4(a) about the normal of the substrate, a divergent beam is again produced in the diffraction path, as shown in Fig. 4(c). However, the diffracted beam becomes converged again if the incident beam is in an opposite direction to that in Fig. 4(c), as shown in Fig. 4(d). Comparing the geometries in Fig. 4, the mirror imaging about the

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grating period decreases with increasing the coordinate X, which corresponds exactly

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substrate produces similar functions, whereas, that about the normal of the substrate produces opposite functions. In Fig. 4, we have defined positive incident angles (θi) for clockwise directions with respect to the normal of the thin-film lens and negative

Fig. 4 presents two pairs of the diode lens effects, where the direction of the incident beam is changed with respect to the orientation of the thin-film lens device. In fact, more derivatives may be possible if the orientation of the device is changed with respect to a fixed direction of the incident laser beam. Thus, another four configurations of the diode lens may be achieved by turning the device upside-down or the front side to the back. For an incident angle of θi, a beam diameter of D0, a center grating period of Λ0, and grating periods of Λ1 and Λ2 for the left and right edges of the beam, respectively, the focal

length

may

be

expressed

as:

f=D0/[(tgθ2-tgθ1)cosθicosθ0],

where

θ0=sin-1(λ/Λ0-sinθi), θ1=sin-1(λ/Λ1-sinθi), and θ2=sin-1(λ/Λ2-sinθi). Therefore, f is a function of wavelength (λ) and it is measured in the direction of θ0. Fig. 5 plots the focal length (f) and diffraction angle (θ) as a function of wavelength (λ) at three different angles of θi=0, 20, and 40 degrees. According to Fig. 5, longer wavelengths are focused into larger angles of θ and shorter focal lengths of f, whereas, shorter wavelengths are focused with smaller θ and larger f. Furthermore, with increasing the angle of incidence, the operation or acceptance bandwidth of such a diode lens for forward biasing becomes larger. The calculation results in Fig. 5 have been based on a photoresist relief grating. Nevertheless, clear dispersion of the focal length and the 9



incident angles (-θi) for anti-clockwise directions.

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diffraction angle with wavelength applies well to the LCP device. Fig. 6 shows experimental demonstration of the diode lens effect by focusing and defocusing a red laser beam at 655 nm from a laser diode and a green laser beam at

diode effects with the device orientation fixed while the red laser beam incident at opposite directions. The left panel of Fig. 6(a) shows forward biasing configuration of the diode lens, where the beam incident at about 50o is focused into a diffraction angle of about 45o with a focal length of about 75 mm. In the right panel of Fig. 6(a), the laser beam is incident in an opposite direction, thus, the diode lens becomes backward biased so that the incident beam is diverged after passing through the diode lens. This not only demonstrates the function of a lens of the thin-film photonic device, but also verifies the diode effects based on the chirped gratings. Fig. 6(b) shows another example of focusing/defocusing of a green laser beam at 532 nm by the thin-film diode lens, where the incident direction of the laser beam is fixed while the device is oriented oppositely. The left panel of Fig. 6(b) illustrates a forward-biasing configuration, where the green laser beam is focused into a diffraction angle of about 30o with a focal length of about 100 mm for an incident angle of 50o. In the right panel of Fig. 6(b), the thin-film lens is rotated about a vertical axis by 180 degrees or the front side is turned to the back, thus, the configuration is changed to backward biasing, so that the incident beam becomes divergent.

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532 nm from a solid-state laser in (a) and (b), respectively. Fig. 6(a) demonstrates the

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It should be noted that the LCP can be rewritten by light within its absorption band.1,2 Therefore, the diode lens using LCP is not applicable for light beams in the blue and UV spectral band. According to Fig. 1(c), the wavelength should be longer than 500

green according to Fig. 1(c). Therefore, long-term illumination by the green laser beam may also destroy the holographic grating structures, which can be identified by a black “hole” on the diffraction pattern of the grating structures, as marked by a dotted circle in Fig. 3(a). This also verifies the erasability of the diode lens device. 3.2 Spatially chirped spectroscopic response of the thin-film lens The volume phase hologram can be taken as waveguide grating structures (WGS),33 where the LCP layer contains both the grating and the waveguide. The propagation waveguide modes may be diffracted further to excite higher orders of resonance modes. As shown in Fig. 7(a), the normally incident beam (the downward red arrow) is diffracted into +1 and -1 orders (the red arrows in the LCP film), which excite the fundamental waveguide resonant modes at a degenerate wavelength and can be described by: Λnsinφ=λ, where Λ is the grating period, n is the refractive index of LCP, and φ is the angle of diffraction at a wavelength λ. Since the waveguide layer is composed of volume phase holographic gratings, the propagation of the fundamental waveguide modes excite further diffractions, where the diffracted beams at +1 and -1 orders can be taken as “virtual incidence” from air (the blue and green dashed arrows) at a larger angle (β) with sinβ=nsinφ. Therefore, the second-order diffractions (+2 and -2 orders) can be considered as diffractions of the beams “incident” at β, as shown in

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nm for the lens device. Nevertheless, the LCP film still has some absorption in the

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Fig. 7(a). Since these beams result from the +1 and -1 orders of diffraction, we define these processes as secondary excitations of diffraction and subsequent resonance modes. The +2 and -2 orders of diffraction induce resonance modes at different

resonance mode related to +1 and -1 orders of diffraction. Thus, three resonance modes can be observed in the extinction spectrum, as shown in Fig. 7(b). For example, narrow extinction peaks may be observed at 644, 696, and 755 nm on the red curve in Fig. 7(b). However, with increasing the angle of incidence, the degenerate fundamental resonance modes become split into two branches extending in opposite spectral directions.33 Because of the breaking of the degeneracy of the fundamental resonance mode, the two virtual incidence for second-order diffractions are not symmetric about the normal of the substrate anymore. On this basis, the second-order diffractions also get split and more resonance modes will be observed. As shown in Fig. 7(c), a white light beam is incident at θi and is diffracted into angles of γ and φ for the +1 and -1 orders of diffraction with Λ(sinθi+nsinγ)=λ1 and Λ(sinθi-nsinφ)=−λ2, respectively. These diffractions into γ and φ can be taken as refractions from “virtual incidence” at

α and β with sinα=nsinγ and sinβ=nsinφ, respectively. The “incidence” at α is diffracted into beams +2a and -2a at two non-degenerate wavelengths, whereas, the “incidence” at β is diffracted into +2b and -2b beams at two other non-degenerate wavelengths, as shown in Fig. 7(c). All of above diffractions may excite waveguide resonance mode in the LCP layer and more optical extinction peaks may be observed. 12



spectral positions due to the non-zero incident angle of β in addition to the degenerate

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Fig. 7(d) show the measurements on the shorter-wavelength branches of the above resonance modes when the light beam is incident at θi=22o. At least four pronounced peaks may be observed at 501, 536, 582, and 627 nm on the red extinction spectrum

acceptable bandwidth of the spectrometer, resonance modes at wavelengths shorter than 450 nm are not observable. The spatial chirping is the most important feature of the diode lens device, which also determines the spatial tuning of the spectroscopic response of the WGS, where multifold waveguide resonant modes shift with changing the spatial position. The optical extinction spectra in Fig. 7(b) and (d) have been measured as a function of the position (X) across the horizontal diameter of the chirped grating in a range from -2.4 to 2.4 mm with the “0” set to the center of the structures. The detection head of the fiber-coupled spectrometer has been mounted behind the device and is translated across the horizontal diameter of the white-light beam transmitted through the LCP gratings. The spectra were taken at steps of 200 µm, which is as large as the diameter of the detection fiber of the spectrometer. Fig. 7(b) and (d) both show obvious chirping in the multifold resonance modes, where a “s”-like trace may be observed for the evolution of the extinction peak intensity of the waveguide resonance modes. As marked by the upward red arrows, the resonance mode shifts between 580 and 598 nm in Fig. 7(b) and that between 568 and 585 nm in Fig. 7(d). Fig. 7 not only verifies the chirped-grating nature of the diode lens, but also demonstrates the special spectroscopic response of the volume phase hologram with spatial chirping features. 13



in Fig. 7(d). However, limited by the spectral range of the white-light source and the

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4. Conclusions One photoresponsive LCP has been applied successfully in holographic transferring of an optical lens into thin-film optical diode, where visible laser beams may be

orientation. The single-step fabrication technique has been based on the photoinduced LC-to-isotropic phase transition of the LCP within the bright fringes as the LCP film is exposed to the interference pattern of UV laser beams. The photocontrollable erasability and mechanical-rubbing-aided reconstructability of the LCP materials enable erasing and rewriting of the diode lens device. This kind of diode lens is essentially a diffractive device consisting of spatially chirped volume-phase gratings, which exhibits unique physics of multifold photonic resonance modes excited by primary and secondary diffractions. Furthermore, this kind of thin-film optical diode is potentially important for integrated optics and optical communication systems.

Acknowledgement We acknowledge the 973 program (2013CB922404) and the National Natural Science Foundation of China (Grant no. 11274031, 51322301, 51025313) for the support.

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Figure captions: Fig. 1 (a) The molecular structures of PM6ABOC2. (b) Schematic illustration for the fabrication of the liquid crystal film through mechanical rubbing. (c) Polarized

polarizations parallel (A//) and perpendicular (A⊥) to the mechanical rubbing or the alignment direction of the liquid crystals. Fig. 2 (a) The optical design for recording the diode lens in LCP film through exposing to the holographic interference pattern of UV laser beams. (b) Principles for writing the interference pattern into the LCP film: spatial distribution of the light intensity over the interference pattern with a top view of the exposed LCP film, where It denotes the threshold laser intensity that induces transition from LC to isotropic phases. (c) Variation of the diffraction intensity of the incident red laser at 633 nm by the hologram recorded in the LCP film with exposure time, showing dynamics of the holographic recording process. Insets: optical geometry showing the relationship between the holographic recording and (right-top) and variation of the diffraction spectrum with exposure time (left-bottom). Fig. 3 (a) Photographs of the LCP thin-film diode lens at different observation angles (A-C) under white-light illumination and that recorded as chirped grating in photoresist for comparison (D). (b) AFM images of the chirped holographic gratings on two different sites on the thin-film lens (sample D), showing interlaced configuration between small- and large-period gratings. (c) Enlarged 17



UV-vis absorption spectra of the PM6ABOC2 liquid-crystal film for

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DOI: 10.1039/C3NR06623A

AFM images showing the spiral features of each photoresist grating line. The blue arrows indicate the spiral surface facing the observation direction. Fig. 4 Different biasing configurations of the diode lens: (a) forward biasing with an

opposite to (a); (c) backward biasing with negative incident angle (-θi); (d) forward biasing with an incident direction opposite to (c). Fig. 5 Calculated focal lengths (f) and diffraction angles (θ) for different wavelengths (λ) at different angles of incidence (θi=0, 20, 40 degrees). Fig. 6 Experimental demonstration of the diode lens effect: (a) the orientation of the device is fixed and a red laser beam at 655 nm is incident in opposite directions; (b) the incident direction of the green laser beam at 532 nm is fixed and the device is rotated about a vertical axis by 180 degrees. Fig. 7 Spectroscopic characterization of the LCP diode lens as waveguide chirped grating structures. (a) Multi-mode resonance: the LCP layer functions both as a waveguide and a grating, and the propagation mode is diffracted further to excite higher orders of resonance modes. (b) and (c): Optical extinction spectrum measurement as a function of spatial position X (from -2.4 to +2.4 mm) for normal incidence (θi=0) and for an incident angle of 22 degrees (θi=22o), respectively.

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positive incident angle (θi); (b) negative biasing with an incident direction



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Nanoscale


DOI: 10.1039/C3NR06623A

Manuscript ID: NR-ART-12-2013-006623.R1 based

on

a

Table of Contents entry Color graphic:

Text: A thin-film lens consisting of chirped photonic structures is produced by holographic interference patterning into a liquid crystal polymer.



Title: Erasable thin-film optical diode photoresponsive liquid crystal polymer

All-optical transistor- and diode-action and logic gates based on anisotropic nonlinear responsive liquid crystal.

Optical switch based on the electrically controlled liquid crystal interface.

Meso- and microscopic motions in photoresponsive liquid crystalline polymer films.

Multi-stable variable optical attenuator based on a liquid crystal gel-filled photonic crystal fiber.

Photoresponsive ionic liquid crystals based on azobenzene guanidinium salts.

Electrically tunable microlens arrays based on polarization-independent optical phase of nano liquid crystal droplets dispersed in polymer matrix.

Photoresponsive liquid crystals based on halogen bonding of azopyridines.

Polymer-dispersed liquid crystal elastomers.

Enhanced Nonlinear Optical Effect in Hybrid Liquid Crystal Cells Based on Photonic Crystal.

Ultra-compact broadband mode converter and optical diode based on linear rod-type photonic crystal waveguide.

drop multiplexer for orbital-angular-momentum-multiplexed optical links.

Optical mechanotransduction with carbazole-based luminescent liquid single-crystal elastomers.

Liquid crystal assisted optical fibres.

Polymer Fibers.

Spiral phase plate based on polymer dispersed liquid crystal for wide visible band applications.

Electro-optical characteristics of holographic polymer dispersed liquid crystal gratings doped with nanosilver.

Highly-sensitive liquid crystal biosensor based on DNA dendrimers-mediated optical reorientation.

Modal liquid crystal array of optical elements.

A 3D Optical Surface Profilometer Using a Dual-Frequency Liquid Crystal-Based Dynamic Fringe Pattern Generator.

Photoresponsive polymer nanocarriers with multifunctional cargo.

All-optical diode based on dipole modes of Kerr microcavity in asymmetric L-shaped photonic crystal waveguide.

Ultrafast all-optical response of a nematic liquid crystal.

Lasing and waveguiding in smectic A liquid crystal optical fibers.

All-optical, polarization-insensitive light tuning properties in silver nanorod arrays covered with photoresponsive liquid crystals.