Giant electron-mediated phononic nonlinearity in semiconductor-piezoelectric heterostructures.

Efficient and deterministic nonlinear phononic interactions could revolutionize classical and quantum information processing at radio frequencies in much the same way that nonlinear photonic interactions have at optical frequencies. Here we show that in the important class of phononic materials that are piezoelectric, deterministic nonlinear phononic interactions can be enhanced by orders of magnitude via the heterogeneous integration of high-mobility semiconductor materials. To this end, a lithium niobate and indium gallium arsenide heterostructure is utilized to produce the most efficient three- and four-wave phononic mixing to date, to the best of our knowledge. We then show that the conversion efficiency can be further enhanced by applying semiconductor bias fields that amplify the phonons. We present a theoretical model that accurately predicts the three-wave mixing efficiencies in this work and extrapolate that these nonlinearities can be enhanced far beyond what is demonstrated here by confining phonons to smaller dimensions in waveguides and optimizing the semiconductor material properties.

110 GHz, 110 mW hybrid silicon-lithium niobate Mach-Zehnder modulator.

High bandwidth, low voltage electro-optic modulators with high optical power handling capability are important for improving the performance of analog optical communications and RF photonic links. Here we designed and fabricated a thin-film lithium niobate (LN) Mach-Zehnder modulator (MZM) which can handle high optical power of 110 mW, while having 3-dB bandwidth greater than 110 GHz at 1550 nm. The design does not require etching of thin-film LN, and uses hybrid optical modes formed by bonding LN to planarized silicon photonic waveguide circuits. A high optical power handling capability in the MZM was achieved by carefully tapering the underlying Si waveguide to reduce the impact of optically-generated carriers, while retaining a high modulation efficiency. The MZM has a [Formula: see text] product of 3.1 V.cm and an on-chip optical insertion loss of 1.8 dB.

Towards single-chip radiofrequency signal processing via acoustoelectric electron-phonon interactions.

The addition of active, nonlinear, and nonreciprocal functionalities to passive piezoelectric acoustic wave technologies could enable all-acoustic and therefore ultra-compact radiofrequency signal processors. Toward this goal, we present a heterogeneously integrated acoustoelectric material platform consisting of a 50 nm indium gallium arsenide epitaxial semiconductor film in direct contact with a 41° YX lithium niobate piezoelectric substrate. We then demonstrate three of the main components of an all-acoustic radiofrequency signal processor: passive delay line filters, amplifiers, and circulators. Heterogeneous integration allows for simultaneous, independent optimization of the piezoelectric-acoustic and electronic properties, leading to the highest performing surface acoustic wave amplifiers ever developed in terms of gain per unit length and DC power dissipation, as well as the first-ever demonstrated acoustoelectric circulator with an isolation of 46 dB with a pulsed DC bias. Finally, we describe how the remaining components of an all-acoustic radiofrequency signal processor are an extension of this work.

Investigation of a Solid-State Tuning Behavior in Lithium Niobate.

Electric field-based frequency tuning of acoustic resonators at the material level may provide an enabling technology for building complex tunable filters. Tunable acoustic resonators were fabricated in thin plates (h/ λ  âˆ¼  0.05 ) of X-cut lithium niobate (LiNbO3) (90°, 90°, ψ = 170° ). LiNbO3 is known for its large electromechanical coupling ( K 2 ) for the shear and symmetric Lamb modes (SH0: K 2 = 40 %, S0: K 2 = 30 %) in thin plates and, thus, applicability for low-insertion loss and wideband filter applications. We demonstrate the effect of a dc bias in X-cut LiNbO3 to shift the resonant frequency by ~0.4% through direct tuning of the resonator material. A nonlinear acoustic computation predicted 0.36% tuning, which was in excellent agreement with the tuning measurement. For X-cut, we predicted electrical tuning of the S0 mode up to 1.6% and for Y-cut the electrical tuning of the SH0 and S0 modes was up to 7.0% with K 2 = 27.1 %. The mechanism is based on the nonlinearities that exist in the piezoelectric properties of LiNbO3. The X-cut SH0 mode resonators were centered near 335 MHz and achieved a frequency tuning of 6 kHz/V through the application of a dc bias.

In vivo evaluation of tetrahedral amorphous carbon.

The in vivo behavior and tissue reaction to tetrahedral amorphous carbon (ta-C) has been evaluated for periods of up to 6 months in SV129 mice. Two sample types were tested--silicon die coated with ta-C (n = 53) and micromachined particles (n = 40). The coated samples were compared to uncoated silicon die (n = 22). Die samples were implanted subcutaneously, and tissue reaction and capsule formation were evaluated at various time points. Micromachined particles of 1, 3, 10, and 30 microm were injected adjacent to the sciatic nerve, and tissue samples were examined histologically at various time points (4 days-6 months). Tissue reaction to ta-C was mild and was localized to the area of the injection or implantation. Samples with a higher ratio of 3-fold bonding appeared to shed material during the experiments; this was not observed on samples with a higher level of 4-fold bonding, nor on uncoated silicon die. The results strongly suggest that films with greater 4-fold bonding character (more diamond-like) are more resistant to in vivo fragmentation than films with higher 3-fold character (more graphitic).

Experimental demonstration of a laterally deformable optical nanoelectromechanical system grating transducer.

We experimentally demonstrate operation of a laterally deformable optical nanoelectromechanical system grating transducer. The device is fabricated in amorphous diamond with standard lithographic techniques. For small changes in the spacing of the subwavelength grating elements, lossy propagating resonant modes in the plane of the grating cause a large change in the optical reflection amplitude. An in-plane motion detection sensitivity of 160 fm/square root(Hz) was measured, exceeding that of any other optical microelectromechanical system transducer to our knowledge. Calculations predict that this sensitivity could be improved to better than 40 fm/square root(Hz) in future designs. In addition to having applications in the field of inertial sensors, this device could also be used as an optical modulator.