Polarization-independent variable optical attenuator based on rhombic prism

An optical attenuator with special performances, such as wide spectrum, high precision, polarization-independent, and lager dynamic range, is the key device for testing the communication link performance in free-space laser communication systems. We propose a polarization-independent variable optical attenuator based on rhombic prism. Two rhombic prisms are used to balance the polarization aberrations, and the incident surfaces of the rhombic prisms are perpendicular to each other. We control the incident angle of the rays, which incident the reflected surfaces of the rhombic prisms, between the Brewster angle and the critical angle, then the attenuation coefficient of the attenuator can be changed. The results of theoretical analysis and numerical simulation show that the designed attenuator is polarization independent, the wavelength range is from 790nm to 1550nm, the dynamic range of attenuation coefficient is from -40 dB to -3 dB, and the wavefront aberration is less than lambda/20@974nm.