High performance mid-infrared optical isolators based on Y3Fe5O12 magneto-optic ceramics

As one of the essential optical components, optical isolators and their core magneto-optic (MO) materials have been widely researched in the visible to near infrared (NIR) wavelength range. However, there is relatively a limited selection of MO materials reported for mid-infrared wavelength optical isolators, and their performance is not satisfactory. In this study, the Faraday effects of Y3Fe5O12 (YIG) MO materials in the form of commercial single crystals, films, and recently emerging ceramics were tested and compared at mid-infrared wavelengths. The results showed that YIG ceramics have Faraday rotation angles as high as 114 deg/cm and 60 deg/cm at 2.1 µm and 3.8 µm, respectively. Combined with their size advantages, the mid-infrared optical isolators based on YIG ceramics exhibited an extinction ratio of 25.26 dB and an insertion loss of 1.01 dB at a wavelength of 2.1 µm, and an extinction ratio of 28.3 dB and an insertion loss of 1.17 dB at a wavelength of 3.8 µm. The further improvement of YIG ceramic optical quality is expected to provide an important and feasible approach for mid-infrared optical isolators.