We point out that the equation can be approximated by a set of linear ones and the exciton polarization wave can be regarded as a Bose field only in the limit of low excitation.
我们指出只有在激发比较弱时，这组方程才可近似为一组线性方程，电子空穴极化波才可以看作玻色场。
2
It must be set up suitable quiescent point in order to works in linear region. This decides that the analysis of amplifier includes direct current analysis and alternating current analysis.