Abstract: An optical isolator (10) comprises two similar optical collimators (20), an isolated core (30) and a holder (40). The isolated core comprises a first birefringent crystal (31), an optical nonreciprocal device (33) and a second birefringent crystal (32). The holder has a cylindrical configuration and is formed from metallic material. The holder defines two holes (41) in opposite ends thereof. The collimators are fixed in the two holes, respectively. Three slots (45, 47, 49) are defined in a middle of the holder. The first birefringent crystal, the nonreciprocal device and the second birefringent crystal are respectively fixed into the three slots.