Thin-film ferrites for microwave and millimeter-wave applications

The Faraday effect in the thick epitaxial films of magnetic garnets of the type used in magneto‐optic isolators can be used as the basis for a fiber‐optic magnetic field sensor. These films have uniaxial anisotropy perpendicular to the surface and they contain bismuth to enhance the Faraday rotation. The typical magnetic domain pattern of meandering stripes changes in response to an applied field perpendicular to the film and this changes the polarization of infrared light propagating perpendicular to the film. Theory and experiment show that the speed of operation is limited by relaxation or resonance effects to upper frequencies between 106 and 109 Hz. Maximum sensitivity requires low magnetic moment and large thickness, in conflict with the requirements for high speed.

High frequency magnetic field sensors based on the Faraday effect in garnet thick films

We developed a free-space monolithically integrated semi-isolator based on a new type of wire-grid polarizer, nanowire-grid polarizer. The nanowire-grid polarizer, which has an active structure with a total thickness of about 1 /spl mu/m, was fabricated directly onto a Faraday magnetooptic rotator by nanofabrication processes. Full free-space isolators based on the integrated semi-isolators were assembled which achieved very low insertion loss (/spl sim/0.2 dB) and high isolation (/spl sim/35 dB). The integrated semi-isolator enables fabrication of the full isolator more efficient and, furthermore, it allows a smaller footprint which is crucial for applications requiring a compact footprint.

Monolithically integrated isolators based on nanowire-grid polarizers

A novel type of polarization-independent optical isolator is described which utilizes the polarization walkoff provided by birefringent crystals. Isolation of 44 dB is measured at a wavelength of 1.3 mu m with single-mode fiber insertion loss of 1.5 dB. A temperature-independent scheme is also described that provides at least 39 dB of isolation over the temperature range of 25-75 degrees C. >

Polarization independent isolator using spatial walkoff polarizers

The design and performance of polarization-independent isolators that are substantially insensitive to variations of temperature and wavelength are presented. Three single-mode fiber isolators have been designed, constructed, and tested. The first isolator is a 1.3-microm two-stage isolator that has more than 40 dB of isolation and less than 2.0 dB of insertion loss over the temperature range of 15-70 degrees C. The second isolator is a two-stage dual-wavelength isolator with an insertion loss of less than 4 dB and an isolation of better than 35 dB at 1.3 and 1.52 microm over the temperature range of 15-75 degrees C. The third isolator is a three-stage isolator with an insertion loss of less than 2.5 dB and an isolation of better than 63 dB over the wavelength range 1275-1355 nm.

High-performance single-mode fiber polarization-independent isolators.

Bi-substituted rare-earth iron garnet thick films have been grown epitaxially as a material for optical isolators. Films with thicknesses in the range of 300-500 microns were obtained without apparent defects using CaMgZr-GGG substrates. In the course of obtaining thick films of good quality, possible mechanisms for crystal defects, lattice mismatch, and bending behavior of the thick film at the growth temperature have been studied. The temperature dependence of Faraday rotation has also been studied with various combinations of rare-earth ions on the c-site. Films of (YbTbBi) 3Fe5O12 show excellent characteristics of the Faraday rotation at the wavelength of 1.3 micron. The rotation is -1800 deg/cm; insertion loss is 0.3 dB; isolation is 42 dB; and the temperature dependence of Faraday rotation is as small as 0.060 deg/K at room temperature. These materials also show good qualities for isolators at the wavelength of 1.55 micron. This technology will lead to the efficient production of the optical isolator used in optical systems.

K. Machida

Papers

GROWTH OF Bi-SUBSTITUTED GARNET THICK EPITAXIAL FILMS FOR OPTICAL ISOLATORS