Phase retarders are vital optical devices used in various optical polarization applications. Phase retarders are constructed using uniaxial birefringent crystals called wave plates. In theory, all birefringent crystals can be used to manufacture wave plates. However, the corresponding thickness of a zero-order 1/4 wave plate in the visible spectrum is only a dozen microns, even if it is constructed from a quartz crystal with low birefringence, making manufacturing difficult. Therefore, the plates are often manufactured with a thickness exceeding 300 μm, called multi-order wave plates. The retardation of a multi-order wave plate is significantly influenced by the temperature of the application environment, which is unfavorable in the natural environment. The design principle and structure of a thick-unit zero-order wave plate that overcome the difficulty in manufacturing zero-order wave plates and the adverse effects of ambient temperature on the retardation of multi-order wave plates are proposed in this study. The design principle and performance parameters of thick-unit zero-order wave plates are analyzed to realize the production of multi-order wave plates, with a retardation accuracy higher than those of the existing zero-order wave plates, whose retardation is less sensitive to temperature than those for multi-order wave plates with the same thickness.

First, the relationship between the optical axis angle and the thickness of the thick-unit zero-order wave plate was determined based on the optical properties of uniaxial birefringent crystals after obtaining the required retardation for the designed wavelength using equations of refraction and the refractive index of the e-ray [Eqs. (9) and (10)]. Second, the effects of the wave plate thickness accuracy and temperature variation on the phase retardation of thick-unit zero-order wave plates were analyzed. The proposed design was compared with a conventional design in an actual design case. Third, experimental samples were fabricated using optical quartz crystals in the proposed design, and their phase retardation was examined using normalized polarization measurements (Fig. 5).

The fundamental design equations [Eqs. (9) and (10)] of a thick-unit zero-order wave plate can be used to design zero-order wave plates with a selectable thickness for any uniaxial birefringent crystal (Fig. 3). Furthermore, the effects of the thickness accuracy and temperature variation on the phase retardation are investigated based on a design case using optical quartz crystals. The results are as follows: 1) A thickness difference of 1 μm has an influence of less than 0.3° on the phase retardation of the thick-unit zero-order wave plate, which is less than 6% of that of the conventionally designed zero-order wave plate or the multi-order wave plate with the same thickness difference (Fig. 4). This indicates that, by using the same manufacturing technology, the thick-unit zero-order wave plate design can achieve higher precision of phase retardation. 2) The effect of temperature variations on the phase retardation of the thick-unit zero-order wave plate is similar to that for the conventional zero-order wave plate and is only 1/30 of that for a conventional multi-order wave plate (Table 1). 3) Tests on the samples verified the feasibility of designing and manufacturing thick-unit zero-order wave plates. When the ambient temperature is varied within a range of ±5 °C, the variation in the phase retardation is within 0.15° (Table 2).

In this study, a design principle and method for thick-unit wave plates are proposed and any uniaxial birefringent crystal can be used to manufacture a zero-order wave plate with a selectable thickness. This overcomes the manufacturing difficulty in conventionally designed zero-order wave plates owing to the minimal thickness and adverse effects of temperature variations on the phase retardation of multi-order wave plates. Given the significant advantages of highly precise retardation, stable temperature, flexible thickness, and ease of manufacturing, the proposed design provides a novel approach for designing and fabricating high-performance zero-order wave plates.