US 12,066,698 B2
Optical isolator
Akira Yahagi, Takasaki (JP); Masanori Ikari, Takasaki (JP); and Takuto Matsumoto, Annaka (JP)
Assigned to SHIN-ETSU CHEMICAL CO., LTD., Tokyo (JP)
Appl. No. 17/285,051
Filed by SHIN-ETSU CHEMICAL CO., LTD., Tokyo (JP)
PCT Filed Oct. 2, 2019, PCT No. PCT/JP2019/038848
§ 371(c)(1), (2) Date Apr. 13, 2021,
PCT Pub. No. WO2020/085017, PCT Pub. Date Apr. 30, 2020.
Claims priority of application No. 2018-198964 (JP), filed on Oct. 23, 2018.
Prior Publication US 2022/0146866 A1, May 12, 2022
Int. Cl. G02F 1/09 (2006.01); C04B 35/50 (2006.01); G02F 1/01 (2006.01); G02F 1/055 (2006.01)
CPC G02F 1/093 (2013.01) [C04B 35/50 (2013.01); G02F 1/0136 (2013.01); G02F 1/055 (2013.01)] 7 Claims
OG exemplary drawing
 
1. An optical isolator comprising:
a Faraday rotator comprising a trivalent ion exchange TAG (terbium-aluminum garnet), and
arranged around the Faraday rotator, (i) a central hollow magnet and (ii) a first hollow magnet unit and a second hollow magnet unit each arranged to sandwich the central hollow magnet in an optical axis direction,
wherein:
a magnetic flux density B [T] in the Faraday rotator and an optical path length L [mm] where the Faraday rotator is arranged satisfy:
0<B  (1) and
14.0≤L≤24.0  (2),
the central hollow magnet and the first and second hollow magnets are neodymium-iron-boron (NdFeB) type magnets, and
the Faraday rotator has, at an optical path length of L≤24.0 mm, optical characteristics comprising:
an absorption coefficient of 0.001 cm−1 or less,
an extinction ratio of 25 dB or more, and
a lower insertion loss of 0.04 dB or less.