Waveguide doublers

Although a large variety of nonlinear materials have been used in prototype harmonic doublers (15-17), only waveguide doublers in LiNb03 have been of usable quality. A list of previous waveguide doublers can be found in references 15-17. The key figure of merit is... 

Schottky barrier varactors do not store charge at all. When driven into forward conduction the Schottky diode absorbs energy and the multiplier efficiency is increased, as long as it is not overdriven to a point where rectification occurs, that is when the MMW power is converted into DC. For a discussion of these devices and their application the text by Maas is recommended. The Schottky barrier varactor multiplier is thus the preferred choice for doublers and triplers at MMW frequencies. Like the other devices they would normally be bought in their waveguide structures with the tuning stubs to match the device impedance to the source and load. 

Potassium niobiate (KN) KNbOj 712 30-137 Waveguide device, frequency doublers. 

When the chromophores (dipoles) of a polymer are oriented electrically (electric field poling) and mobility is frozen below the glass transition temperature of the polymer, these materials can be used as frequency doublers (second harmonic generation (SHG)), and materials for waveguides and electro-optical devices. ... 

---