Gain and noise figure analysis of Er<Superscript>3+</Superscript>-doped YAG transparent ceramic microchip amplifier

The rate equations and the power evolution equations based on excited state absorption (ESA) and cooperative upconversion (CUC) of high concentration erbium-doped yttrium aluminum garnet (YAG) transparent ceramic waveguide amplifier are set up to analyze the effects of the pump power, active ion concentration and waveguide length on the amplifier gain and noise figure (NF). The numerical analysis predicts that with a pump power of 100mW, an active ion concentration of 1.0×10²⁶ ion/m³ and a waveguide length of 3 cm, a small-signal gain of 30 dB and an NF of 5 dB can be achieved in the micro-chip amplifier.     

Theoretical analysis of Er<Superscript>3+</Superscript>-doped telluride glass fiber amplifier for 2.700 μm laser amplification

The rate equations and power evolution equations of erbium-doped telluride glass fiber amplifier for both 1.530 and 2.700 μm lasers are solved numerically, the dependences of gain spectra on fiber length, dopant concentration and pump power are analyzed, and the gain of 2.700 μm laser is calculated and compared with the experimental result from reference. The numerical analysis shows that with 8 × 10²⁴ ion/m³ erbium ion concentration, 5m fiber length and 600mW pump power, the gains at 1.530 and 2.700 μm may achieve 23dB or so. With larger power pump and higher dopant concentration, a net gain of 17 dB is obtained from the Er³⁺-doped telluride glass fiber amplifier for 110mW input signal. This fiber amplifier is promising for both 1.530 μm signal amplification and 2.700 μm laser amplification.     

脉冲来流和激波作用下的涡轮流场

船用柴油机的工作特点使得废气涡轮增压器的进口气流出现周期性脉动特征，在脉冲来流和激波作用下涡轮的流场呈现复杂的非定常性。采用数值计算方法研究涡轮内激波的发展过程以及脉冲振幅和频率对涡轮性能的影响，结果表明：在脉冲振幅增大时，涡轮转静交界面附近的流动损失经历了尾迹、附面层、激波依次占主导的变化过程；当脉冲系数增大为0.7时，涡轮效率相比均匀来流降低了13.2%；在脉冲频率增大到15Hz时，叶轮叶片50%叶高处的时均载荷分布趋近于均匀来流，涡轮效率下降了7.4%。可见，脉冲振幅和频率的增大加剧了流动损失，进而导致涡轮效率降低。