Integrated nonlinear devices are desired for frequency conversion, particularly to generate optical radiation at wavelengths that are not readily generated by presently available laser devices, for example, in mid-IR wavelengths.
Group III-V semiconductors that crystallize in a zinc blende lattice possess a large second-order nonlinear susceptibility, in excess of 100 pm/V. This quality and their wide use in active optoelectronic devices have made III-V materials of interest for integrated nonlinear devices for frequency conversion.
Second-order nonlinear processes require phase matching between the three waves involved. One technique for phase matching involves the optical anisotropy of nonlinear crystals, a technique usually referred to as birefringent phase matching (BPM). However, bulk zinc blende materials are optically isotropic, which makes them not useful for BPM.
Navy scientists have developed a BPM optical semiconductor device from nanomachined type III-V semiconductor materials configured to produce low loss. The appropriate type III-V materials with a large nonlinear susceptibility include AlGaAs, GaAs, GaP, AlAs, or AlGaAsP. Ideal substrates are GaAs, GaSb, or InP. This integrated non-linear device is useful for frequency conversion, particularly for generating optical pulses at wavelengths that are not readily generated by presently available laser devices
The use of a nano slot has the advantage of large index contrast and uniform material properties within the air gap, in contrast to the composite AlAs/Al2O3 layer typically obtained by oxidation. Compared to typical slot waveguides, where the slot is perpendicular to the substrate, this new Navy design utilizes a single slot parallel to the substrate. This creates suspended air-cladding waveguides with tight optical confinement.
In operation, this optical waveguide device is a frequency mixer, difference frequency generator (DFG), sum frequency generator (SFG), or second harmonic generator (SHG), and can be very useful in the mid-IR range. The device can be incorporated as part of a laser system, or external to a laser source.
The suspended nano slot and nano slab waveguide devices have several advantages over quasi-phase matching (QPM) approaches or other BPM devices with nonlinear wavelength conversion including lower loss and larger transparent range.
- Efficient conversion makes this system useful for not only for mid-infrared applications that require a bright, single-mode source, but also for an integrated chip-scale optical parametric oscillator
- Very large difference between indices of AlxGa1-xAs causes giant form birefringence and greatly expands the phase matching region practically throughout the entire IR region
- Tight confinement of radiation in the ridge suspended air-cladding waveguides can enhance the conversion efficiency
- The system can be tuned by varying the air gap distance d between the two waveguides
- Business interests can acquire the technology for commercial development by licensing US patents 8,427,738 and 9,057,891
- License fees are negotiable, contact TechLink for more information