Terahertz time-domain spectroscopy was used to make experiment and investigation for the characteristics of high quality 0.3BaSrTiO3-0.7NdAlO3 ceramics in the terahertz range, which was made by the solid state reaction method. The frequency resolution of experiment system was 4.5 GHz, and all-solid-state 532nm laser was used as external optical pump, which obliquely incidence on the surface of the sample at the angle of 45°. From the experiment that when the external optical pump’s intensity increased from 0 mW to 300 mW at room temperature, the 0.3BaSrTiO3-0.7NdAlO3 ceramics’ transmission waveform time shifts could be obviously observed, and with the increasing power of pump laser, the absorption coefficient could be modulated, the modulation range varied from 21.38 cm-1 to 13.77 cm-1 and the modulation depth nearly reached up to 36% at 0.55 THz. Further analysis showed that the micro-mechanism of absorption coefficient modulation with the intensity of external optical pump was attributed to the internal space charge field in the 0.3BaSrTiO3-0.7NdAlO3 ceramics caused by the excited free carriers. The experiment and analysis proved that the 0.3BaSrTiO3-0.7NdAlO3 ceramics have higher tunability, lower dielectric loss and good temperature stability in THz range, which will have good reference value and wide application for communication in THz range.
In order to improve manufacture quality and machining efficiency, this paper studies the technology of rectangular flat-topped beam. Flat-topped beam can effectively reduce the region of heat affected zone. Rectangular beam can reduce overlap rate. So, it is very important to convert the circular Gaussian beam to rectangular flat-topped beam. The fiber laser has been widely used to laser manufacture Industry at this present. The fiber has better coupling capability with laser spot. We choose double-cladding fiber to acquire uniform rectangular beam. Laser beam transmission model was created up with RP fiber power soft. We also make the model of the double-cladding fiber. When the Gaussian beam is transmitting along fiber, high-order mode lights appear and mixture with each other. Because the double-cladding fiber has central-dip profile index, the energy transfers from central to edge. The results show that the double-cladding fiber can be used to improve the uniformity of transmitting beam. When the shape of fiber core is rectangular and the chamfer is circle arc work, we can get rectangular uniformity beam.
The box-like optical filter is one of the most important key optical switching components in the dense-wavelength division-multiplexing (DWDM) fiber-optic communication system and the intelligent optical network. The integrated high-order silicon microring resonators (MRRs) are one of the best candidates to achieve the box-like filtering spectrum response. In general, the spectrum response rectangular degree of the single MRR is very low, so that it can not be used in the DWDM system. Using the race-track high order MRRs, the bandwidth of flat-top pass band, the out-of-band rejection degree and the roll-off coefficient of the edge will be improved obviously. In this paper, a box-like optical filter based on the race-track high order MRRs with uniform couplers is presented and demonstrated. Using 15 coupled racetrack MRRs with 10 μm radius, the 3 dB flat-top pass band of 2 nm, the out-of-band rejection ratio of 30 dB and the rising and falling edges of 48 dB/nm are realized successfully.
A novel phase erasure and format conversion of phase-shift keying (PSK) to conventional on-off keying (OOK) is proposed and demonstrated theoretically and experimentally. Using a single-pump nondegenerate phase sensitive amplification process in a highly nonlinear fiber, the 0 and 1-bits of the PSK signal obtain different gains through amplification and de-amplification. As a result, the modulation information is transferred onto the amplitude. With an optimized input power difference between the signal and idler, the signal phase information is erased with wavelength preservation after the PSA. The output constellation and eyediagrams show an effective phase erasure and format conversion of PSK to conventional OOK. The error vector magnitude is utilized to evaluate the scheme performance. The proposed scheme provides the flexibility for future optical communication networks.
Infrared imaging lens is one of the key components of a video security camera. A novel long-wave infrared continuous zoom lens is developed based on the 640×512 high resolution uncooled infrared thermal detector which can substitute the high cost cooled infrared detector. The zoom lens contains five germanium lens and one chalcogenide glass lens, which working in the wavelength range of 8~12 μm. Its F number range is in 1~ 1.1 while the focus length is changing from 20 to 120 mm. Based on the zoom lens design theory, the positive lens mechanical compensation structure is used to calculate the optical parameters and optimize the cam zoom curve, which can have a smooth continuous zoom in the range of all focus lengths. The image analysis show that the system has achieved the modulation transfer function (MTF) value above 0.45 which spatial frequency is 30 lp/mm. The spot diagrams RMS radius is less than 6.3μm which is near the diffraction limit. The real test photos indicate that the lens has the advantages of high resolution, large aperture, smooth zoom and stable image plane. Due to the high image quality and low cost, the continuous zoom lens is easily to be fabricated.
Thermal stress effects on the mode field characteristics of arrayed waveguides are studied precisely by finite element method (FEM) with plain strain model. The amplitudes of Ex and Ey are comparable for the Ex11 mode and the Ey11 mode in a homogeneous and isotropic optical channel waveguide. Considering the elasto-optic effect, the refractive indices are inhomogeneous and anisotropic. It is shown that the amplitude of Ey for the Ex11 mode and that of Ex for the Ey11 mode are much smaller than the other electric field components. The simplest method to apply thermal stress is to place a stress plate on the arrayed waveguides. It is shown that the effective indices of the two modes, especially the Ey11 mode, can be tuned by stress plates with different thickness. The order of magnitude of tune range is 10-4 whereas the material of plate is aluminum. The effective indices can be increased by attaching an aluminum plate with appropriate thickness under arrayed waveguides, and will be decreased whatever the thickness of the plate is set if attached over arrayed waveguides. However, the stress plate has small effect on the optical mode fields.
Analytical solutions are very useful to understand influence factors in the central wavelength temperature sensitivity of
AWGs (arrayed waveguide gratings) and convenient to be used in preliminary design. In this paper, the elastic multilayer
theory and stress concentration effect are combined to estimate thermal stresses in arrayed waveguides. Effective indices
and their temperature coefficients are estimated by use of effective index method. The effects of material properties on
temperature sensitivity in AWGs are completely studied. It is theoretically demonstrated that athermal AWGs can be
obtained by choosing proper material with negative TEC (thermal expansion coefficient) for the substrate. Subsequently,
the theory is extended to study the modified AWGs with a stress plate attached on the bottom, top, or both sides of
arrayed waveguides. It is shown that the temperature sensitivity can be controlled effectively by stress plates with
different TECs. After attaching a plastic plate on the bottom, the temperature sensitivity of central wavelength can be
reduced to -0.003 pm/K for TE mode and 3 pm/K for TM mode, respectively, whereas the thickness is 0.83mm.
According to the tilted incidence characteristics of thin film narrowband interference filter, the stack of four cavities angle-tuned narrowband filter with low polarization dependent loss is designed. Using this kind fo angle-tuned thin film filter, one new structure of three-port tunable filter is developed. The experimental results show that its tunable range is at about 20nm.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.