Single-Chip Parametric Frequency Up/Down Converter Using Parallel PPLN Waveguides

We propose a novel structure for a monolithically integrated parametric frequency up and down converter using two parallel periodically poled lithium niobate (PPLN) waveguides combined with a reflective wavelength-division multiplexer (WDM) to realize second-harmonic-pumped parametric mixing on one chip. The parallel configuration of the PPLN waveguides provides a long interaction length for efficient conversion. The reflective WDM used for (de)multiplexing 0.78- and 1.56-μm light consisted of two multimode interference (MMI) (de)multiplexers and a dichroic mirror. The utilization of the wavelength selectivity of both the MMI (de)multiplexers and the dichroic mirror enabled us to achieve high isolation of the fundamental light for generating a second-harmonic pump. We fabricated the integrated device using a direct-bonded LiNbO3 ridge waveguide. Frequency conversion achieved with two-stage second-harmonic generation and difference frequency generation processes was successfully demonstrated with a high isolation of the fundamental and a parametric gain of the signal in the integrated device.