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Several approaches to fabricate micro optical elements by use of half tone masks are studied and compared.It is shown that haft tone masks employed in filtering image systems can obtain gray patterns with considerably high precision,but it is hard to operate from the viewpoint of operation.The method using contacting lithography technology or laser ablation can be easily operated with the cost of reducing fabrication precision and the trouble of choosing appropriate materials.For all of these methods,the coding of half tone masks with corrections for the nonlinear characteristics of coding,imaging and photoresist is recommended.