An external cavity quantum cascade laser （QCL） array with a wide tuning range and high output power is pre- sented. The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow ...An external cavity quantum cascade laser （QCL） array with a wide tuning range and high output power is pre- sented. The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration. Taking advantage of the single-lobed fundamental supermode far-field pattern, the tuning capa- bility of 30.6cm-1 is achieved with a fixed injected current of 3.5 A at room temperature. Single-mode emission can be observed in the entire process. The maximum single-mode output power of the external cavity setup is as high as 25mW and is essential in real applications.展开更多
External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backseattering in fiber distributed feedback （DFB） fiber laser sensor system have been investigated. If the feedback...External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backseattering in fiber distributed feedback （DFB） fiber laser sensor system have been investigated. If the feedback intensity exceeds critical amount, excess noise would be induced in the demodulator. The maximum tolerable intensity back-reflection coefficient Rc and backscattering coefficient Sc into a fiber DFB laser with lead fiber length from I m to 37.5 km before the onset of instabilities are shown. Rc is found to decrease with increasing lead fiber length while Sc was relatively invariable with varying fiber length. The coherent Rayleigh backscattering （CRBS） would induce neglectable noise with a lead fiber exceeding 13.5 kin. To eliminate these noises, one or two isolators should be incorporated in the system.展开更多
The objective of this study is to demonstrate that tensile stress resulting due to applied force on cornea can be accurately measured by using a time-domain common-path optical coherence tomography （OCT） system with...The objective of this study is to demonstrate that tensile stress resulting due to applied force on cornea can be accurately measured by using a time-domain common-path optical coherence tomography （OCT） system with an external contact reference. The unique design of the common-path OCT is utilized to set up an imaging system in which a chicken eye is placed adjacent to a glass plate serving as the external reference plane for the imaging system. As the force is applied to the chicken eye, it presses against the reference glass plate. The modified OCT image obtained is used to calculate the size of contact area, which is then used to derive the tensile stress on the cornea. The drop in signal levels upon contact of reference glass plate with the tissue are extremely sharp because of the sharp decline in reference power levels itself, thus providing us with an accurate measurement of contact area. The experimental results were in good agreement with the numerical predictions. The results of this study might be useful in providing new insights and ideas to improve the precision and safety of currently used ophthalmic surgical techniques. This research outlines a method which could be used to provide high resolution OCT images and a precise feedback of the forces applied to the cornea simultaneously.展开更多
基金Supported by the National Basic Research Program of China under Grant No 2013CB632801the National Key Research and Development Program of China under Grant No 2016YFB0402303+2 种基金the National Natural Science Foundation of China under Grant Nos 61435014,61627822,61574136,61306058 and 61404131the Key Projects of Chinese Academy of Sciences under Grant No ZDRW-XH-2016-4the Beijing Natural Science Foundation under Grant No 4162060
文摘An external cavity quantum cascade laser （QCL） array with a wide tuning range and high output power is pre- sented. The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration. Taking advantage of the single-lobed fundamental supermode far-field pattern, the tuning capa- bility of 30.6cm-1 is achieved with a fixed injected current of 3.5 A at room temperature. Single-mode emission can be observed in the entire process. The maximum single-mode output power of the external cavity setup is as high as 25mW and is essential in real applications.
基金supported by the National 863 Program under Grant No. 2007AA03Z415.
文摘External optical feedback effects due to reflection, Rayleigh backscattering and coherent Rayleigh backseattering in fiber distributed feedback （DFB） fiber laser sensor system have been investigated. If the feedback intensity exceeds critical amount, excess noise would be induced in the demodulator. The maximum tolerable intensity back-reflection coefficient Rc and backscattering coefficient Sc into a fiber DFB laser with lead fiber length from I m to 37.5 km before the onset of instabilities are shown. Rc is found to decrease with increasing lead fiber length while Sc was relatively invariable with varying fiber length. The coherent Rayleigh backscattering （CRBS） would induce neglectable noise with a lead fiber exceeding 13.5 kin. To eliminate these noises, one or two isolators should be incorporated in the system.
文摘The objective of this study is to demonstrate that tensile stress resulting due to applied force on cornea can be accurately measured by using a time-domain common-path optical coherence tomography （OCT） system with an external contact reference. The unique design of the common-path OCT is utilized to set up an imaging system in which a chicken eye is placed adjacent to a glass plate serving as the external reference plane for the imaging system. As the force is applied to the chicken eye, it presses against the reference glass plate. The modified OCT image obtained is used to calculate the size of contact area, which is then used to derive the tensile stress on the cornea. The drop in signal levels upon contact of reference glass plate with the tissue are extremely sharp because of the sharp decline in reference power levels itself, thus providing us with an accurate measurement of contact area. The experimental results were in good agreement with the numerical predictions. The results of this study might be useful in providing new insights and ideas to improve the precision and safety of currently used ophthalmic surgical techniques. This research outlines a method which could be used to provide high resolution OCT images and a precise feedback of the forces applied to the cornea simultaneously.
