Recent Progresses on the Development of an Yttrium Orthoferrite Based Optical Switch

In our department we investigate applications of yttrium orthoferrite single-crystals for sensors and actuators. In this paper we report from the development of a magneto-optical switch where this orthoferrite crystal acts as faraday rotator. Using the extremely fast domain wall motion unsurpassed switching times down below 50 ns were achieved. We demonstrate and discuss an experimental set-up for a repetition rate of up to 100 kHz. This high-speed performance is obtained with a switch prototype where a short magnetic field pulse for each switching operation is needed. This pulse is produced in a coil concentric with the optical axis and with very low inductance. The disadvantage of this arrangement is a comparatively high amount of stray field which could cause interactions of adjacent components and thus, obstruct further miniaturization. In order to improve the electromagnetic compatibility a new optical switch set-up is now under investigation. In this arrangement the magnetic field is concentrated in a torus shaped ferrite yoke allowing to decrease the switching current down to 20%. However, since this change is connected to an increase of inductance of the magnetic circuit, the switching speed is also reduced. The optimization procedure on the base of an estimation of the circuit inductance and magnetic field measurements are discussed in detail. The fabrication of our first magneto-optical switch prototypes is demonstrated. The effect of stray fields produced during one switching cycle in one switch on the magnetic state in a crystal of a neighbored switch is also discussed. The optical switching behavior at a wavelength of 1300 nm and 1550 nm is determined experimentally by measuring the switching time at both, single switch cycles and at a high repetition rate.