On-chip microwave photonic beamformer circuits operating with phase modulation and direct detection

Microwave Enthrakometric Labs-On-A-Chip and On-Chip Enthrakometric Catalymetry: From Non-Conventional Chemotronics Towards Microwave-Assisted Chemosensors

A unique chemical analytical approach is proposed based on the integration of chemical radiophysics with electrochemistry at the catalytically-active surface. This approach includes integration of: radiofrequency modulation polarography with platinum electrodes, applied as film enthrakometers for microwave measurements; microwave thermal analysis performed on enthrakometers as bolometric sensors; catalytic measurements, including registration of chemical self-oscillations on the surface of a platinum enthrakometer as the chemosensor; measurements on the Pt chemosensor implemented as an electrochemical chip with the enthrakometer walls acting as the chip walls; chemotron measurements and data processing in real time on the surface of the enthrakometric chip; microwave electron paramagnetic resonance (EPR) measurements using an enthrakometer both as a substrate and a microwave power meter; microwave acceleration of chemical reactions and microwave catalysis оn the Pt surface; chemical generation of radio- and microwaves, and microwave spin catalysis; and magnetic isotope measurements on the enthrakometric chip. The above approach allows one to perform multiparametric physical and electrochemical sensing on a single active enthrakometric surface, combining the properties of the selective electrochemical sensor and an additive physical detector.

Surface acoustic waves for acousto-optic modulation in buried silicon nitride waveguides

We theoretically investigate the use of Rayleigh surface acoustic waves (SAWs) for refractive index modulation in optical waveguides consisting of amorphous dielectrics. Considering low-loss Si₃N₄ waveguides with a standard core cross-section of 4.4×0.03 μm² size, buried 8-μm deep in a SiO₂ cladding, we compare surface acoustic wave generation in various different geometries via a piezo-active, lead zirconate titanate film placed on top of the surface and driven via an interdigitized transducer (IDT). Using numerical solutions of the acoustic and optical wave equations, we determine the strain distribution of the SAW under resonant excitation. From the overlap of the acoustic strain field with the optical mode field, we calculate and maximize the attainable amplitude of index modulation in the waveguide. For the example of a near-infrared wavelength of 840 nm, a maximum shift in relative effective refractive index of 0.7x10^-3 was obtained for TE polarized light, using an IDT period of 30-35 μm, a film thickness of 2.5-3.5 μm, and an IDT voltage of 10 V. For these parameters, the resonant frequency is in the range of 70-85 MHz. The maximum shift increases to 1.2x10^-3, with a corresponding resonant frequency of 87 MHz, when the height of the cladding above the core is reduced to 3 μm. The relative index change is about 300 times higher than in previous work based on non-resonant proximity piezo-actuation, and the modulation frequency is about 200 times higher. Exploiting the maximum relative index change of 1.2×10^-3 in a low-loss, balanced Mach-Zehnder modulator should allow full-contrast modulation in devices as short as 120 μm (half-wave voltage length product = 0.24 Vcm).

Low-loss, broadband and high fabrication tolerant vertically tapered optical couplers for monolithic integration of Si3N4 and polymer waveguides

A low-loss, broadband and high fabrication tolerant optical coupler for the monolithic integration of Si₃N₄ and polymer waveguides is designed and experimentally demonstrated. The coupler is based on the adiabatic vertical tapering of the Si₃N₄ waveguides. Low-loss operation is experimentally verified at both 976 and 1460-1635 nm wavelengths. Measured losses per coupler are as low as 0.12 and 0.14 dB at 976 and 1550 nm, respectively, and below 0.2 dB at both wavelengths for lateral misalignments between the Si₃N₄ and polymer waveguides up to 1.0 μm.

Simultaneous even- and third-order distortion suppression in a microwave photonic link based on orthogonal polarization modulation, balanced detection, and optical sideband filtering

A microwave photonic link (MPL) with simultaneous suppression of the even-order and third-order distortions using a polarization modulator (PolM), an optical bandpass filter (OBPF), and a balanced photodetector (BPD) is proposed and experimentally demonstrated. The even-order distortions are suppressed by utilizing orthogonal polarization modulation based on the PolM and balanced differential detection based on the BPD. The third-order distortions (IMD3) are suppressed by optimizing the spectral response of the OBPF with an optimal power ratio between the optical carrier and the sidebands of the phase-modulated signals from the PolM. Since the suppression of the IMD3 is achieved when the MPL is optimized for even-order distortion suppression, the proposed MPL can operate with simultaneous suppression of the even-order and third-order distortions. The proposed MPL is analyzed theoretically and is verified by an experiment. For a two-tone RF signal of f₁ = 10 GHz and f₂ = 19.95 GHz, the spurious-free dynamic range (SFDR2) is enhanced by 23.4 dB for the second harmonic (2f₁), and 29.1 and 27.6 dB for the second intermodulation (f₂-f₁ and f₁ + f₂), as compared with a conventional MPL. For a two-tone RF signal of f₁ = 9.95 GHz and f₂ = 10 GHz, the SFDR3 is increased by 13.1 dB as compared with a conventional MPL.