A proposed device for combining or switching electromagnetic beams would have three ports, would not contain any moving parts, and would be switchable among three operating states:
- Two of the ports would be for input; the remaining port would be for output.
- In one operating state, the signals at both input ports would be coupled through to the output port.
- In each of the other two operating states, the signal at only one input port would be coupled to the output port. The input port would be selected through choice of the operating state.
In one potential application, the device would be used to switch or combine microwave signals in a quasi-optical transmission-line assembly that would be part of a millimeter-wave radar or telecommunication system. In another potential application, a modified version of the device would be used to switch or combine light signals in a fiber-optic telecommunication link.
The two input ports would be configured to accommodate signals having mutually orthogonal linear polarizations. A polarizer would be positioned to bisect the right angle formed by the longitudinal axes of the input ports, and its polarization would be oriented to so that it would allow one input signal to pass through and would reflect the other input signal. The orientations of the aforementioned components would be such that after impinging on the polarizer, both input signals would propagate toward a three-state Faraday rotator. The components of the Faraday rotator would be a ferrite disk, a solenoidal electromagnet coil for applying magnetic bias, and two impedance-matching plates — one on each side of the ferrite disk. The output port would be positioned on the side opposite the input side of the Faraday rotator and would be oriented to support polarization at an angle of 45° relative to both of the input polarizations.
The operating state would be selected by adjusting the magnetic bias to select one of three states of the Faraday rotator. In one state, the magnetic bias would be set to cause the polarization of a propagating signal to rotate through an angle of +45° so as to allow one of the input signals to propagate to the output port. In another state, the direction of the magnetic bias would be set at the reverse of that of the first-mentioned state to obtain a polarization rotation of 45°, thereby allowing the other input signal to propagate to the output port.
The third state would be used for combining the powers of two mutually coherent input signals that, in an ideal case, would be of equal magnitude and would differ in phase by 90°. In this state, the magnetic bias (and thus, the Faraday rotation) would be set to zero and the super-position of the input signals would result in a 45°-polarized sum signal that would propagate to the output port. In practice, because of magnetic hysteresis, this state could not be obtained by simply abruptly turning off the current in the electromagnet: It would be necessary to apply a damped sinusoidal excitation to the electromagnet coil to effect degaussing.
This work was done by Raul Perez of Caltech for NASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Refer to NPO-44316, volume and number of this NASA Tech Briefs issue, and the page number.