Terahertz waveguide emitters in photonic crystal fiber form

The phase-matching condition for broadband terahertz (THz) wave generation based on optical rectification re-quires that the group velocity of the optical pump beam be equal to the phase velocity of the THz wave. The design of GaP THz waveguide emitters in the form of photonic crystal fibers (PCFs) for a pump source of wavelength 1040 nm is reported. By analogy with a circular waveguide emitter, we show how the phase-matched THz wave frequency can be tuned widely by the air hole pitch and finely tuned by the air hole size. In addition, a single THz wave mode can be guided in the endlessly single-mode regime of the fiber waveguide. The layers of air holes in the PCF design not only allow tunability of the generated THz radiation but also make small emitters easy t