飞秒脉冲同步泵浦光学参量振荡器(SPOPO)可以产生非经典光学频率梳,在时域多模量子光场基础上,引入光场的空间自由度,可以获得具有时空多模特性的新型压缩态光场。这种多模压缩态可以同时实现波分复用和空分复用,是扩充量子信道容量、实现量子计算的重要工具。由于SPOPO中凹面镜的入射(出射)光线与法线通常具有一定的折叠角,其引入的像散导致某些同阶数高阶模式(例如厄米高斯01和10模)在腔内产生的Gouy相位不同,无法在腔内共振,从而限制了空间多横模压缩态的产生。本文在理论上计算了SPOPO中子午面和弧矢面产生的光束腰斑大小、位置及Gouy相位差,提出了一种补偿像散的方案,实验上实现了SPOPO内的厄米高斯01与10模的同时共振。

Femtosecond pulse synchronously pumped optical parametric oscillator (SPOPO) can generate nonclassical optical frequency comb. Based on this time-domain multimode quantum field, by introducing spatial degrees of freedom,we can exhibit both temporal and spatial characteristics of the multimode squeezed state light field. This multimode squeezed state can realize both wavelength division multiplexing and space division multiplexing. It is an important tool to expand the capacity of quantum channel and realize quantum computation. Usually, there is a non-zero angle between the input (output) beam and normal line of the concave mirror in the SPOPO. The astigmatism due to this angle introduces different Gouy phase makes the spatial mode with identical order (e.g. HG01 and HG10 mode) nonresonant in the cavity, hence limiting the generation of spatial multimode squeezed state. In this paper, we theoretically calculated the waist size, waist position and Gouy phase difference in the tangential and sagittal plane of SPOPO, and proposed an experimental scheme for compensation of astigmatism, realized simultaneous resonance of HG01 and HG10 mode in the SPOPO.