Simulation and Experimental Analysis of Moulding Processes of Glass Diffractive Optical Elements

Driven by the huge market demand, the glass lenses made of various optical glasses are required to be more diversified in sizes/shapes, to have better form accuracy/ surface roughness, to be more environmental durable, and to be more competitive in price. In comparison to conventional refractive lens, diffractive lens (diffractive optical element, DOE) has the advantages of being thinner and lighter, and is widely used in optical systems such as lighting and photovoltaic systems. Glass moulding process(GMP) is regarded as a very promising technique for mass producing high precision optical components such as spherical/ aspheric glass lenses and free-form optics. However, only a handful of materials can sustain the chemical reaction, mechanical stress and temperature involved in the glass moulding process. Besides, almost all of these mould materials are classified as hard-to-machine materials. This makes the machining of these materials to sub-micrometer form accuracy and nanometer surface finish a rather tough and expensive task. As a result, making service life of mould longer has played a critical part in the GMP industry. The excessive stress and/or temperature involved in the moulding process are amongst the main reasons for pre-matured mould failure. This research aimed to analyze the stress/strain conditions and the obtained dimensional accuracy under various molding parameters by simulations. Molding experiments were subsequently carried out to verify the simulated results. A glass DOE of 14.8 mm in diameter and 3.36 mm in thickness are successfully produced in this research and the difference between the simulated and the molded DOE is around 15μm.