By now, it is still extremely challenging to accurately measure femto-Newton (10-15 N) optical forces. Here, a simple scheme of a suspended tapered nanofiber coupled with a glass substrate is demonstrated to generate and sense the fN optical force, where the ~10 nm deformation of the nanofiber can be resolved by white light interferometry and an ultra-low stiffness of 0.540 fN/nm is obtained for the suspended nanofiber through Brownian motion. Owing to the ultra-low stiffness of the nanofiber, the scheme provides a cost-effective method to sense and measure ultra-weak (5.2 fN) optical force. Moreover, the scheme also provides a simple way to exploit fN optical forces for implementation of micro-Watt all-optical devices.
Optical fibers have long been the backbone of modern communication system. One way of extending the capability of optical fibers is to thin down the core sizes as microfiber which facilitates light-matter interaction through evanescent light. Among different microfiber based structure, the microfiber knot resonator (MKR) is a resonant structure which finds applications in lasing, filtering and optical switching [1-2]. Particularly, when the MKR structure is combined with functional two-dimensional materials, a large panel of devices can be achieved via the investigation of variations in resonance properties.
Here, a layered metal dichalcogenide semiconductor tin disulfide (SnS2), characterized with high intrinsic electron mobility and strong absorption in the visible light regime [3], is chosen to be coated onto MKR. The all-optical control of light functionality is demonstrated in MKR with SnS2 structure where the signal light power is controlled by the external violet pump power via the absorption property of SnS2. The device fabrication, characterization and obtained experimental results will be presented in the talk.
We demonstrated strain sensing of a microfiber with a microarched transition region, which was fabricated by flame heated tapering. Due to multimode interference of different propagation modes of microfiber, two main transmission dips were observed at 1215.0 and 1469.8 nm. Enhanced by the microarched transition region, the depth of the dip was up to 19 dB at 1215.0 nm. The position of the dip red-shifted while the axial strain changed from 0 to 1166.2 μϵ. The axial strain sensitivity was up to 56.6 pm/μϵ, which was one order of magnitude higher than that of the traditional optical strain sensor based on microfiber or fiber Bragg grating. The linear correlation coefficient was 98.21%. This kind of microfiber with a microarched transition region can be widely used in various physical, chemical, and biological sensing and detection fields.
We demonstrated temperature sensing of a side-polished fiber with polymer nanoporous film cladding, which was constructed by dehydrating dichromate gelatin film on the polished surface. Due to intermodal interference of core mode and cladding mode, two main transmission valleys were observed at 1219.2 and 1373.2 nm. The modulation amplitudes are ∼8 and 12 dB, respectively. These two transmission valleys show significant sensitivity to the temperature. At the wavelength of 1373.2 nm, the position of transmission valley blueshifted 114 nm while the temperature changes from 30°C to 90°C, and the sensitivity of temperature was up to 1.92 nm/°C. The linear correlation coefficient was 98.67%. The temperature sensing characteristics of nanoporous cladding fiber was successfully demonstrated, and it shows a high potential in photonics applications.
We established a theoretical model for a single knot-ring resonator and investigated the transmission spectrum by Jones matrix. The numerical results show that two orthogonal polarization modes of knot-ring, which are originally resonated at the same wavelength, will split into two resonant modes with different wavelengths. The mode splitting is due to the coupling between the two orthogonal polarization modes in the knot-ring when the twisted angle of the twist coupler is not exactly equal to 2mπ (m is an integer). It is also found that the separation of the mode splitting is linearly proportional to the deviation angle δθ with a high correlation coefficient of 99.6% and a slope of 3.17 nm/rad. Furthermore, a transparency phenomenon analogous to coupled-resonator-induced transparency was also predicted by the model. These findings may have potential applications in lasers and sensors.
A novel method to measure the remaining cladding thickness of side-polished fiber (SPF) was demonstrated by using the digital holography technology. By using angular spectrum method and accurate least-squares phase unwrapping method, the phase distribution of SPF could be reconstructed. Based on the reconstructed phase distribution, the remaining cladding thickness of SPF could be directly measured. It can reduce the errors due to fiber’s asymmetries and edge diffraction. This method could also be used to measure other special optical fibers such as photonic crystal fiber and nano-fiber.
A method of fabricating three dimensional (3D) microstructured fiber is presented. Polystyrene (PS) microspheres were coated around the surface of a micro-fiber through isothermal heating evaporation induced self-assembly method. Scanning electron microscopy (SEM) image shows that the colloidal crystal has continuous, uniform, and well-ordered face-centered cubic (FCC) structure, with [111] crystallographic direction normal to the surface of micro-fiber. This micro-fiber with three-dimensional photonic crystals structure is very useful in the applications of micro-fiber sensors or filters.
A technique of using phase control method to translate the interference pattern was demonstrated. By using a liquid crystals spatial light modulator (LC-SLM) to regulate the phase of beams, real-time dynamic translations of the patterns were achieved. The translation accuracy is up to 10 nm experimentally. This technique can apply to any kind of multi-beam interference pattern and has no limits in translation accuracy and direction, theoretically.
A one-step introduction of functional defects into a photonic crystal (PC) is demonstrated. By using a multi-beam phasecontrolled
holographic lithography and a diffracting optical element, large area one dimensional (1D) and two
dimensional (2D) PCs with periodic waveguide were fabricated. The uniform area is up to 4 mm2, and tens of waveguide
have been introduced in the one dimension and two dimension PC structure. This technique gives rise to a substantial
reduction of the fabrication complexity and a significant improvement on the accuracy of the functional defects in
photonic crystals. This method can also been used to design and fabricate metamaterials.
A fiber sensor to achieve simultaneous measurement of refractive index and temperature is proposed by using a side
polished fiber Bragg grating. The reflective wavelength of side polished fiber Bragg grating shifts with the ambient
refractive index and local temperature. By overlaying half of the polished surface of fiber Bragg grating with liquid
material, simultaneous discrimination of liquid refractive index and local temperature with dual reflective Bragg
wavelengths is demonstrated. The refractive index sensitivity is from 4.99nm/riu to 252.78nm/riu when refractive index
changes from 1.4098 to 1.4479, and the temperature sensitivity is 0.012nm/°C.
Using full-vector finite element method, transverse optical forces induced by strongly evanescent coupling between
two identical nanofibers is theoretically investigated. It shows that anti-symmetry and symmetry modes can induce
attractive and repulsive force, respectively. When light power of the symmetry (anti-symmetry) mode at 980nm
wavelength is 50mW, the gap between the nanofibers with 400nm diameter nears 392nm, the repulsive force reaches
maximum (11.5 pN/μm), which results in 30nm displacement at the center of 100μm-long free-standing nanofiber.
Based on pump-probe scheme, a novel potential method for optical force measurement is proposed. Using
Euler-Bernoulli beam equation and coupled mode theory for waveguides, the deformation impact on the splitting ratio of
coupling nanofibers is also investigated. It is found that, through the deformation, the repulsive force from 0.9 to 17
pN/μm can change the splitting ratio of coupling nanofibers from 0 to 600 when coupling length of nanofibers is fixed at
100μm, the gap is 400nm and probe light is at 808nm. It shows that measuring the splitting ratio of the strongly coupling
nanofibers can potentially provide a high sensitive method for measuring the optical force.
LCD and edge backlight light guide panel (LGP) are one of the main parts of handset or mobile phone et al. The design
of LGP is vital technique to the design of backlight module. The aim of this paper is to design a handset LGP with LED
as the light source. Three design qualifications are simulated and analyzed with ASAP software. The three qualifications
are rough surface, diffusion-dots and microstructure. The analysis result shows that the factor of diffusion-dots is the
most important ingredient. The surface brightness, the luminance distribution and the light efficiency of LGP are
determined by the density of diffusion dots. The total light loss is also affected by the factor of diffusion-dots to the LGP
whose diffusion dots are printed. A handset LGP is designed according to the research in the paper. The simulation result
is satisfying as good as the practical outcome. The paper is useful to increase the brightness and uniformity of handset
LCD.
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