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.
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.
The laser beam shaping system which can convert Gaussian beam to flat-top beam has been widely applied in laser illuminating, laser materials processing and laser medical treatment, etc. For the application of laser illuminating, a laser beam shaping system with simple structure and high efficiency was developed, which used two aspherical lenses to convert the 2 mm waist diameter Gaussian beam to a flat-top beam. To achieve a long-distance illuminating for different object positions, the shaped laser beam divergence angle is required variable. Therefore, a continuous zoom lens which had the zoom ratio of 18.4:1.04 was added to the front of the aspherical lenses. By moving the axial positions of the zoom lens, the continuous change of the beam divergence angle can be achieved. With the aid of ZEMAX software, this laser beam shaping system was simulated and optimized. The simulation results showed that the beam divergence angle can be continuously changed in 1°~18°, while the laser facular area energy distribution keeping uniform of 5m, 45m and 65m illuminating distances, which can satisfy the different long-distances laser illuminating requirements.
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.
Due to the biological multi mode identification technology, a novel fingerprint and finger vein multiple images acquisition optical system is developed and described. The fingerprint and finger vein imaging systems contain respectively 3 and 12 spherical lenses, which work at 650nm and 850nm wavelength with a 640×480 CCD and a 640×512 uncooled IR detector as the imaging devices. With the aid of ZEMAX software, the optical systems were designed and optimized to cause a good imaging quality. The MTF value of the fingerprint imaging lens is above 0.6 at 67lp/mm, while the finger vein imaging lens is above 0.8 at 30lp/mm. The spot diagrams’ RMS radiuses of the two lenses are all much smaller than the detectors’ pixel size, which are close to the diffraction limit. Both the two lenses have distortions less than 0.5%. The experiments proved that this optical system has the merits of fine image quality and high resolution with compact structures and low cost.
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.
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