A theoretical model of the fiber Bragg grating Fabry–Perot（FBG-FP） transmission spectrum considering loss of FBG and intra-cavity fiber is presented. Several types of FBG-FPs are inscribed experimentally, and their...A theoretical model of the fiber Bragg grating Fabry–Perot（FBG-FP） transmission spectrum considering loss of FBG and intra-cavity fiber is presented. Several types of FBG-FPs are inscribed experimentally, and their spectra are measured.The results confirm that weak intra-cavity loss is enhanced at the resonance transmission peak, that is, loss of transmission peaks is observably larger than other wavelengths. For FBG-FPs with multi resonance peaks, when the resonance peak wavelength is closer to the Bragg wavelength, the more significant loss effect of resonance transmission peak is exhibited.The measured spectra are fitted with the presented theoretical model. The fitted coefficient of determinations are near 1,which proves the validity of the theoretical model. This study can be applied to measure FBG loss more accurately, without a reference light. It can play an important role in FBG and FBG-FP writing process optimization and application parameter optimization.展开更多
The generation of study state hisher-Order squeezing in the sense of Hons andMandel [Phys. Rey. Lett. 54, 323 (1985) ; phys. Rev. A32,974 ( 1985 )] andalso of Hillery [Phys. Rev. A36 , 3796 (1987) ] in a multiphoton m...The generation of study state hisher-Order squeezing in the sense of Hons andMandel [Phys. Rey. Lett. 54, 323 (1985) ; phys. Rev. A32,974 ( 1985 )] andalso of Hillery [Phys. Rev. A36 , 3796 (1987) ] in a multiphoton micromaser isstudied. The results show that the cotangent state which is generated by thecoherent trapping scheme in a niultiphoton microniaser can exhibit not onlysecond-order squeezing but alaso fourth-order and squared field aniplitudesqueezing. The influence of the cavity loss on the squeezings is investigated.展开更多
In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity th...In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity through the rim seal interacts with the main flow, producing additional aerodynamic loss due to the mixing process which plays a significant role in the formation, development and evolution of downstream secondary flow. In this paper, a set of cascade representative of low aspect ratio turbine is selected to numerically investigate the influence of upstream cavity purge flow on the hub secondary flow structure and aerodynamic loss. Cascade with/without upstream cavity and four different purge mass flow rates are all taken into account in this simulation. Then, a deep insight into the loss mechanism of interaction between purge flow and main flow is gained. The results show that the presence of cavity and purge flow has a significant impact on the main flow which not only changes the vortex structure in both the passage and upstream cavity, but also alters the cascade exit flow angle distribution along the spanwise. Moreover, aerodynamic loss in the cascade rises with the increase of purge flow rate while the sealing effect is also enhanced. Therefore, the effect of upstream cavity purge flow must be considered in the process of turbine aerodynamic design. What is more, it is necessary to minimize the purge flow rate in order to reduce aerodynamic loss on the premise of satisfying cooling requirements.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61405212,61377062,61405218,and 61775225)Scientific Innovation Fund of Chinese Academy of Sciences(Grant No.CXJJ-17S010)
文摘A theoretical model of the fiber Bragg grating Fabry–Perot（FBG-FP） transmission spectrum considering loss of FBG and intra-cavity fiber is presented. Several types of FBG-FPs are inscribed experimentally, and their spectra are measured.The results confirm that weak intra-cavity loss is enhanced at the resonance transmission peak, that is, loss of transmission peaks is observably larger than other wavelengths. For FBG-FPs with multi resonance peaks, when the resonance peak wavelength is closer to the Bragg wavelength, the more significant loss effect of resonance transmission peak is exhibited.The measured spectra are fitted with the presented theoretical model. The fitted coefficient of determinations are near 1,which proves the validity of the theoretical model. This study can be applied to measure FBG loss more accurately, without a reference light. It can play an important role in FBG and FBG-FP writing process optimization and application parameter optimization.
文摘The generation of study state hisher-Order squeezing in the sense of Hons andMandel [Phys. Rey. Lett. 54, 323 (1985) ; phys. Rev. A32,974 ( 1985 )] andalso of Hillery [Phys. Rev. A36 , 3796 (1987) ] in a multiphoton micromaser isstudied. The results show that the cotangent state which is generated by thecoherent trapping scheme in a niultiphoton microniaser can exhibit not onlysecond-order squeezing but alaso fourth-order and squared field aniplitudesqueezing. The influence of the cavity loss on the squeezings is investigated.
基金Key Laboratory Foundation (9140C4103091003C) for funding this work
文摘In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity through the rim seal interacts with the main flow, producing additional aerodynamic loss due to the mixing process which plays a significant role in the formation, development and evolution of downstream secondary flow. In this paper, a set of cascade representative of low aspect ratio turbine is selected to numerically investigate the influence of upstream cavity purge flow on the hub secondary flow structure and aerodynamic loss. Cascade with/without upstream cavity and four different purge mass flow rates are all taken into account in this simulation. Then, a deep insight into the loss mechanism of interaction between purge flow and main flow is gained. The results show that the presence of cavity and purge flow has a significant impact on the main flow which not only changes the vortex structure in both the passage and upstream cavity, but also alters the cascade exit flow angle distribution along the spanwise. Moreover, aerodynamic loss in the cascade rises with the increase of purge flow rate while the sealing effect is also enhanced. Therefore, the effect of upstream cavity purge flow must be considered in the process of turbine aerodynamic design. What is more, it is necessary to minimize the purge flow rate in order to reduce aerodynamic loss on the premise of satisfying cooling requirements.
