Compensating Method for Splitter in Multi-Channel Off-Axis Three-Mirror Optical System with Large Field and Small F Number

In Optical System such as Multi-Channel off-axis Three-Mirror Optical System with Large Field and Small F Number, beam-split is the most important factor of the optical system design. The traditional compensating method for splitter is using tilt plate and lenses. This compensating method requires long distance between the splitter and the focal plane. On the other hand, too many lenses using in this method will reduce the transmission efficiency of the optical system. The compensating lenses have optical-power, so we must modify the focal length of primary optical system, and then we have to rectify the other channels to make up the changing of the focal length in this channel. In Optical System such as Multi-Channel off-axis Three-Mirror Optical System, the distance between the splitter and the focal plane array is short, usually we don't have enough distance to place the tilted plate and lenses. So in those systems, the enough spatial distance for multi-channel beam-split is the bottleneck for the system design. For the cryogenic optical system, the compensating lenses have difficulty to work in so much different temperature. This paper advanced a new kind of compensating method for splitter, and it is an off-axis spherical lens which has falcate shape (the curvature of the two surface is approximately the same) and with no optical power. It not only can compensate the aberration of the system, and it is rather small in size, so it is propitious to the multichannel beam-split in the Multi-Channel off-axis Three-Mirror Optical System.