Non-reciprocal photonic devices, including optical isolators and circulators, are indispensible components in optical communication systems. However, the integration of such devices on semiconductor platforms has been challenging because of material incompatibilities between semiconductors and magneto-optical materials that necessitate wafer bonding, and because of the large footprint of isolator designs. Here, we report the first monolithically integrated magneto-optical isolator on silicon. Using a non-reciprocal optical resonator on an silicon-on-insulator substrate, we demonstrate unidirectional optical transmission with an isolation ratio up to 19.5 dB near the 1,550 nm telecommunication wavelength in a homogeneous external magnetic field. Our device has a small footprint that is 290 mm in length, significantly smaller than a conventional integrated optical isolator on a single crystal garnet substrate. This monolithically integrated non-reciprocal optical resonator may serve as a fundamental building block in a variety of ultracompact silicon photonic devices including optical isolators and circulators, enabling future low-cost, large-scale integration.Non-reciprocal photonic devices that break the time-reversal symmetry of light propagation provide critical functionalities such as optical isolation and circulation in photonic systems. Although widely used in optical communications, such devices are still lacking in semiconductor integrated photonic systems 1,2 because of challenges in both materials integration and device design. On the materials side, magneto-optical garnets used in discrete nonreciprocal photonic devices show large lattice and thermal mismatch with semiconductor substrates, making it difficult to achieve monolithic integration of garnets with phase purity, high Faraday rotation and low transmission loss 3,4 , and requiring wafer bonding to incorporate them on a semiconductor platform. On the device side, non-reciprocal mode conversion (NRMC) and non-reciprocal phase shift (NRPS) integrated optical isolators have large footprints with length scales from millimetres to centimetres 5,6 , which severely limits the feasibility of large-scale and low-cost integration. Efforts have been pursued both in the monolithic integration of iron garnet and the exploration of other magneto-optical materials with better semiconductor compatibility. Polycrystalline Y 3 Fe 5 O 12 (YIG) films 3 , epitaxial Sr(Fe-doped InP films 9 have been demonstrated to have promising magneto-optical performance at a wavelength of 1,550 nm. In relation to device design, several monolithic non-reciprocal photonic devices capitalizing on optical resonance effects (for example, magneto-optical photonic crystals 10 , garnet thin-film based optical resonators 11 , silicon ring resonators with magneto-optical polymer cladding 12 and modulated ring resonators using non-reciprocal photonic transitions 1 ) have been theoretically analysed with a view to reducing the device footprint. However, the experimental realization of monolit...

The development and current status of microwave ferrite technology is reviewed in this paper. An introduction to the physics and fundamentals of key ferrite devices is provided, followed by a historical account of the development of ferrimagnetic spinel and garnet (YIG) materials. Key ferrite components, i.e., circulators and isolators, phase shifters, tunable filters, and nonlinear devices are also discussed separately.

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BiFeO 3 and Bi 2 FeMnO 6 films were epitaxially grown on SrTiO 3 ͑001͒ substrates by pulsed-laser deposition, and their structural, magnetic, magneto-optical and optical properties were measured. In Bi 2 FeMnO 6 , Fe is mainly present in the 3+ valence state, while Mn shows multivalence states. Bi 2 FeMnO 6 exhibits low magnetization at room temperature and at 5 K indicating there is no significant B-site ordering. The BiFeO 3 film shows high optical transparency, while Bi 2 FeMnO 6 shows high absorption loss in the infrared. Densityfunctional theory modeling of BiFeO 3 , BiMnO 3 and Bi 2 FeMnO 6 was carried out by applying the generalized gradient approximation ͑GGA͒ and GGA+ U methods. The formation enthalpy of ordered Bi 2 FeMnO 6 is positive for several crystal symmetries and for ferromagnetic ͑FM͒ or antiferromagnetic ͑AFM͒ spin structures at 0 K temperature, indicating B-site ordering is not favored. The electronic structure calculations are consistent with the electronic and optical properties of these films.

From an analysis of the one-dimensional constant-loss theory of secondary electron emission, maximum yield (δm), primary electron energy at maximum yield (Eom), and both crossover energies EIoc and EIIoc are shown to depend on the surface and bulk properties of the emitting material through simple relations. In particular, the results strongly suggest that the first crossover energy can be very dependent on surface properties, whereas the energy at maximum yield is entirely controlled by bulk properties. Refinement of the low-energy part of the reduced yield curve by means of the results of the more realistic three-dimensional theory leads to the development of the expression EIoc=0.51Eomδm−1.32. Comparison between theory and experiment for several secondary-emitting materials is presented to demonstrate the accuracy of this useful relation. Finally, the implications of these results for different classes of materials are discussed in terms of basic physical properties, such as density, electrical conductivity, work function, and band gap.