In our previous study, we demonstrated that a surface supported rapid evaporation crystallization (SSREC) method can be utilized to effectively prepare single nanometer nanocrystals (NCs) of 4-N, N-dimethylamino-4’-N’-methylstilbazolium tosylate (DAST), a bench mark of organic nonlinear optical (NLO) crystal. In this study, first, we extend the SSREC method to DAST single crystal nanowires (NWs) preparation by using a polymer-type surfactant. With one-drop of DAST-methanol solution, millimeter-scale the DAST NWs can be attained within one minute. We presume that this highly efficient driving forces of the fast self-assembling process originate from Coulombic interactions of the DAST nanocrystals. In order to further increase the crystal quality of the NWs, we propose a one-drop self-assembly process which separates the SSREC self-assembling process into two steps: SSREC process for NCs preparation and static cultivation process for NWs self-assembly. By this method, we successfully attain 4-N, N-dimethylamino-4'-N'-methylstilbazolium 2-naphthalenesulfonate (DSNS-2) NWs. The obtained DSNS-2 NWs have very high surface quality with surface roughness <150 pm, which is highly beneficial for fabricating integrated optical devices. Furthermore, the onedrop self-assembly method only requires reagents in microgram quantities, and thus this method is extremely environment-friendly.
In this paper, several organic-inorganic composites were prepared for Terahertz (THz) devices fabrication. First, a two-layer structure was designed for femtosecond (fs) laser/THz radiation separation. The top layer was made by sintered 20-40 nm hollow quartz particles which can diffuse the incident fs laser thus decrease the power intensity. The bottom layer comprised of silicon 100 nm particles and cycle-olefine polymer (COP), by which the fs laser light can be greatly scattered and absorbed but THz radiation can propagate insusceptibly. With this two-layer structure a high efficient fs-laser/THz filter was fabricated successfully. Second, titania–polymer composites with a very high refractiveindex tunability and high transparency in the THz region were prepared. By controlling the blending ratio of the titania particle, a broad refractive-index tuning range from 1.5 to 3.1 was realized. Then, the composites were used to fabricate antireflective (AR) layers on a high-resistivity silicon (HR-Si) substrate. By utilizing the thermoplasticity of the titania– polymer composite, a graded-index structure was fabricated via a hot-embossing method. Because of the good refractive-index matching between the composite and the HR-Si substrate, a broadband AR layer was fabricated.
We fabricated a terahertz anti-reflective structure on a polystylene by using a hot-embossing method. Polystylene was spin-coated onto a silicon substrate and then transformed by using a metallic mould comprising a bunch of Chinese acupuncture needles. The transformation layer yielded gradient refractive index profiles on the substrate which can reduce the surface reflection effectively. The samples were evaluated by a terahertz time-domain spectroscope. Compared with a bare silicon substrate, we observed an increase of ~30% in the transmittance. We also observed broader bandwidth properties compared with a single-layer antireflective structure. The process imposes no substrate limiting; i.e., it has great potential to be applied onto various THz devices.
The influence of the waveguide spacing on transmission response for parallel-plate waveguide with single deep groove has been experimentally studied. The results indicate that the decrease of spacing can efficiently excite the higher order cavity modes in very deep groove. The relationship between the spacing and the channel number presents the possibility of a notch filter to mechanically select the channel number. Experimental data and simulations results verify this channel number tunibility, which may be of great interest for communication applications.
Based on transformation optics and complementary media (folded geometry), levitative carpet cloak and overlapping effects (anti-mirror effects) can be realized. In common case, the levitative carpet cloak is limited by the shape of the hidden object, and the early folded geometry method can just make two objects with different shapes appear as only one. Here, based on transformation optics and finite element simulations, we propose an anisotropic but homogeneous shifting media that can shift an arbitrary-shaped object from original place to another place in terahertz (THz) region. As a result, an arbitrary shaped object levitated on a flat perfect electric conductor ground and covered with the shifting media cannot be detected, leading to the levitative and shape-independent carpet cloak. Furthermore, optical overlapping effects such as making two separated objects with the same shape appear as only one, can be also realized by using this kind of shifting media.
Size- and concentration-dependent of Rayleigh scattering properties of transparent TiO2 nanohybrid polymer have been
systematically investigated. By utilizing the Rayleigh scattering technique, we can obtain the Rayleigh ratio of TiO2
nanohybrid polymer prepared with different concentrations of TiO2. We observed that these Rayleigh ratios are strongly
dependent on the size and concentration of the nanoparticles. The larger the size and concentration of nanoparticles is,
the larger the Rayleigh scattering is. Furthermore, this technique can be used to examine the saturation effect of Rayleigh
scattering observed at high input power, and evaluate the size uniformity of nanoparticles in nanohybrid polymer.
Polymer optical waveguide devices are getting popular for optical printed circuit board and/or home-network applications. In order to accelerate the development of polymer optical waveguide devices, evaluation of waveguide characteristics should be reliable and speeded up. Polymer optical chip containing a combination of 45°-angled cut waveguide, Y-splitter and S-bend structures was designed and fabricated for simple evaluation of multimode waveguides. Input launching conditions such as mode scrambler was investigated for reliable measurement for standardization.
We have fabricated and characterized polymeric slab asymmetric waveguides doped with a near-infrared-emitting dye, 2-(6-(p-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl)-3-ethylbenzothiazolium perchlorate. Upon nanosecond photopumping, the waveguides have shown a small-signal gain coefficient of 37.2 ± 2.1 cm-1 at 820 nm for a pump fluence of 1.57 mJ/cm2 (314 kW/cm2). The loss coefficient and transparency fluence have been found to be 7.3 ± 1.0 cm-1 at 820 nm and 0.14 mJ/cm2 (28 kW/cm2), respectively. It is shown that a small-signal gain of 19.7 ± 2.3 dB is achievable in a 1.2-mm-long waveguide. Furthermore, near-infrared laser emission from self-assembled luminescent polymer microcavities has been demonstrated. The microrings are formed around silica optical fibers of varying diameters (80, 125, and 200 μm) and the larger microresonators have an overall quality factor of ~2 × 103, which is limited by surface roughness and scattering. We illustrate how the laser threshold varies inversely with both the quality factor and the inner diameter of the microrings. The free spectral range and the intensity variation of the laser output are also presented.
We developed a novel waveguide fabrication technology, i.e., femtosecond (fs) pulse laser assisted self-writing
waveguide technology, to overcome problems of standard technologies, such as time consuming and high cost. Based on
a light induced self-written (LISW) waveguide fabrication technology, a 488nm cw laser was launched through an
optical fiber into UV curable resin. At the same time a 800nm fs laser was additionally used as a 3D position selective
assistant beam. As the UV resin was cured by the 488nm laser and 800nm fs laser irradiation, a fiber/waveguide
connecting 2D/3D waveguide was easily fabricated.
A ridge waveguide of an organic salt, 4-N,N-methyl- stilbazorium tosylate, DAST, which has the largest second- order optical nonlinearities among organic materials, was fabricated for the first time to our knowledge. DAST crystal was covered by poly (methyl methacrylate) as a protect layer for a photo-resist solution, then standard photolithography and oxygen reactive ion etching (RIE) processes were applied. DAST ridge waveguide, 34x20 micrometers and 6x6 micrometers channel s with 2mm in length were successfully fabricated by this process. To reduce the refractive index of the crystal, photo bleaching was effectively applied for DAST crystal. So, photobleaching can be applied to fabricate a cladding layer for the ridge waveguide.