An achromatic waveplate is composed of two birefringent crystals of different materials. Due to the distinct dispersive properties of the two materials, it can achieve relatively uniform phase retardation over a wide wavelength range. Thanks to its uniform wavelength response and the broadest wavelength coverage (310 to 1100 nm or 600 to 2700 nm), the achromatic waveplate is suitable for use in tunable lasers, multi-wavelength laser systems, and other broadband light source products.