Papers by Keyword: Grating

Abstract: A novel leaky waveguide grating (LWG) biosensor is reported where a continuous waveguide film of chitosan was photo patterned, resulting in a periodic modulation of the concentration of recognition elements (streptavidin in this case). This resulted in a periodic variation in the refractive index of the waveguide film, forming a phase grating at resonance angles of the LWG. Thus, a diffraction pattern was observed at resonance angles, but not at other angles. The position of resonance angles and hence diffraction pattern was a function of the refractive index of chitosan waveguide strips, forming the basis of biosensing and quantitative measurements.

Abstract: Two kinds of high absorber were designed based on sub-wavelength grating structure for aluminum substrate. The absorption and electric field distribution of these two structures were calculated by using the finite difference time domain method. One absorber was obtained by using Al₂O₃/SiO₂ double layers and Al rectangular sub-wavelength layer which has high absorption peaks both in TE polarization and TM polarization in infrared spectrum. Another absorber was a single layer structure with a triangular sub-wavelength grating structure which had a broadband absorption in TE polarization at spectral range of 300-1000nm.Simulation results showed that the absorption of this absorber increase and then decreases with the increasing of the height of sub-wavelength grating. The average absorption reached the maximum when the height of grating was 800nm.

Abstract: Cylindrical grating angle sensor is a common angle measuring device with high precision. Due to the reflecting arc surface of the cylindrical grating the effects of relative displacement of graduation line and gap variation will interact. Significant residual errors still exist even with high precision cylindrical grating and multiple reading heads around the scale disc .In this paper, based on the principle of circumference closure, the principle of self-calibration is deduced and analyzed in detail. The calibration curve is obtained by obtaining the deviation between the certain position and an ideal position of the graduation line position in real time. A simple self-calibration method of cylindrical grating is acquired. It can calibrate random errors and system errors with time and improve the angle measurement accuracy. The method has the advantages of simple structure and strong maneuverability, and provides technical means for the miniaturization and high precision of cylindrical grating.

Abstract: In the paper, interference measurement method for end surface parallel measurement of transparent materials is described. Firstly, basic principles of optical plane template equilibrium point detection are analyzed, measurement algorithms and formulas for calculating optical parallelism are proposed, then possible error of algorithm is analyzed in details, concrete plan for correcting the error is proposed, overall method for testing parallelism is proposed on the basis, and finally related experiment is designed for testing and analyzing the method. Test results show that the method can prominently improve precision of testing parallelism with excellent testing effect.

Abstract: We present the fabrication and optical testing of a fine grating on a ZnS substrate to be used as a wideband infrared spectral disperser and for which the primary application is measurement of the composition of the atmospheres of transiting exoplanets using space-borne infrared astronomical telescopes. A grating with a blaze angle of 2.1 deg. and pitch of 166.667 μm was constructed on a roughly flat 10 mm × 10 mm substrate with a maximum thickness of 1 mm. To obtain high accuracy, the sample was fabricated on a ZnS monocrystal using a high performance processing machine at Canon Inc. The surface roughness measured with a microscope interferometer was 2.6 nm rms. The shape of the fabricated grating edges was examined with a scanning electron microscope. The diffraction efficiency was evaluated by optical experiments at λ = 633 nm, 980 nm, and 1550 nm, and compared with the efficiencies calculated using a Fourier Modal Method. The results showed that the differences between the diffraction efficiencies obtained from experiment and by calculation were between just 0.9 % and 2.4 %. We concluded that the quality of the fabricated ZnS grating was sufficiently high to provide excellent diffraction efficiency for use in the infrared wavelength region. We also present the design of a spectral disperser in CdTe for future more advanced performance.

Abstract: The study of the mechanical ruling process of aluminum grating needs a new test device. And a program controlled test device for mechanical ruling was analyzed, designed, manufactured and tested in this paper. The developed mechanical ruling techniques of this device to fabricate micropatterns are introduced with the characteristics of multiple degrees of freedom, openness, visualization, and operability. After some primary tests, assessment of microgrooves was performed with mini video microscopy, which confirmed the validity of the new device for mechanical ruling process investigation.

Abstract: Optical encoders have been used for decades as displacement measuring devices. As far as image measurement is concerned, CCD and CMOS are gradually used in metrology fields. In practice, performance of image ultraprecise optical encoders are related to environmental temperature, humidity, data processor speed, and vibration, thus measurement precision of encoders will be affected, and these factors limit their usage scale. Among these factors, the vibration is the largest effect factor. Here, a new experiment system was built to study vibration effect of measurement. Experiments indicated that the effects of vibration mainly exist in two aspects. Firstly, vibration induced deformation of glass grating, so distance of adjacent grating lines got uncertain. Secondly, random vibration affected CMOS image sharpness, and it reduced accuracy of encoding and decoding. Finally, some methods are provided to reduce the vibration of the grating encoder.

Abstract: The effect of liquid crystal (LC) vertical alignment on phase separation dynamics of liquid crystal optical devices with different cell gaps is investigated in this paper. As the cell gap increases, the surface effect on the bulk LC droplets is reduced due to the longer distance. It is found in this experiment that the vertical alignment film can influence the LC droplets in the middle of the gap, and in the meanwhile the surface effect is not too strong to disturb phase separate. In that case, the LC droplets separate at a fixed position during phase separation and also can flow to form good morphology. The surface vertical alignment has a significant effect on the morphology of liquid crystal optical devices.

Abstract: A novel optical communication device is investigated in this paper. The device is a kind of optical switch. The intensity of emergent light is tunable continuously by introducing liquid crystal technique. Holographic technique is used to fabricate this optical device. According to optical theories and through many experiments, the ideal optical switching device can be obtained when the photosensitive monomers are mixed together with liquid crystal with certain weight ratio. The emergent light intensity of liquid crystal grating can be modulated by electric field because of the electric control characteristics of liquid crystal. The output light is only 5% of the incident light when the electric field is more than 15V. Besides, the liquid crystal also has the advantages of large electro-optic coefficient, fast response speed and so on. Consequently, the liquid crystal grating has immense potential productivity in passive optical communication device such as optical switching and variable optical attenuator.

Abstract: Surface plasmon polariton (SPP) waves exhibit local characteristics that can break diffraction limits; for this reason, the production of subwavelength optoelectronic device has been the focus of current studies. To determine the importance of surface plasmon wave applications, we aim to investigate whether or not the theoretical dispersion obtained in the plasma and metal (Drude model) exhibits the same expression, satisfy the relationship of SPPs by controlling the electron density of the plasma and the frequency of the incident electromagnetic wave, and derive the system performance parameters and plasma density parameters by changing the grating geometry and dielectric constant of the surrounding medium by using the grating structure based on surface plasmon propagation characteristics associated with sensor research. The simulation results of then design structure showed that transmission bandwidth rapidly decreases and transmission peak gradually decreases as metal dielectric thickness decreases. An SPP sensor can effectively eliminate light instability in the two wavelengths of light intensity difference to obtain anti-interference and improve the range of the measuring instrument by using two fiber-grating structure filters. Therefore, studies on surface plasmon devices for integrated application are of promotional importance.