Basic methods of broad-band phase transformers calculation are well-known. However, they are not suitable for the case if measuring system has high resolution. So we have modified the methods to take into account interference effect. Broad-band phase transformers consist of several specially oriented crystal quartz plates. The plates are stacked together and fixed into a holder. According to Jones formalism system of several retardation plates is optically equal to system containing only two elements: so called “retarder” and “rotator” (please see Fig.1). Retarder provides required phase shift (usually π or π/2). Rotator turns the polarization plane at angle ω.

There are two types of broad-band phase transformers:

1) ω is not 0º and it depends on the wavelength. We call it “achromatic polarization converter” (APC). Example of ω behavior is below.

2) ω is about 0º and it is constant within the operating wavelength range. In this case it is usual “achromatic waveplate” (AWP) and its operating principle is the same as of monochromatic waveplate.