We show that large modulation of the amplitude and phase of mid-infrared light can be achieved by dynamically shifting the resonance of graphene-metal plasmonic antennas via electrical tuning of the optical conductivity of graphene. Intensity modulation with on-off extinction ratio exceeding 100 and phase modulation over a range of 240° are demonstrated by simulations of scattered light from arrays of such antennas. The modulation rate is estimated to be on the order of a few GHz. These properties are promising for creating reconfigurable flat optical components such as spatial light modulators in the mid-infrared spectral range.

Modulation of mid-infrared light using graphene-metal plasmonic antennas

In the last few years Mid InfraRed (MIR) photonics has received renewed interest for a variety of commercial, scientific and military applications. This paper reports the design, the fabrication and the characterization of SiGe/Si based graded index waveguides and photonics integrated devices. The thickness and the Ge concentration of the core layer were optimized to cover the full [3 - 8 µm] band. The developed SiGe/Si stack has been used to fabricate straight waveguides and basic optical functions such as Y-junction, crossings and couplers. Straight waveguides showed losses as low as 1 dB/cm at λ = 4.5 µm and 2 dB/cm at 7.4 µm. Likewise straight waveguides, basic functions exhibit nearly theoretical behavior with losses compatible with the implementation of more complex functions in integrated photonics circuits. To the best of our knowledge, the performances of those Mid-IR waveguides significantly exceed the state of the art, confirming the feasibility of using graded SiGe/Si devices in a wide range of wavelengths. These results represent a capital breakthrough to develop a photonic platform working in the Mid-IR range.

Low loss SiGe graded index waveguides for mid-IR applications

Exemplary embodiment can utilize the properties of tunable thin-film, material (e.g., graphene) to efficiently modulate the intensity, phase, and/or polarization of transmitted and/or reflected radiation, including mid-infrared (“mid-IR”) radiation. Exemplary embodiments include planar antennas comprising tunable thin-film material sections and metallic sections disposed in contact with the tunable thin-film material sections, each metallic section having a gap with at least one dimension related to a wavelength of the radiation, which in some embodiments may be less than the wavelength. The metallic layer may comprise rods arrange in one or more shapes, or one or more apertures of one or more shapes. Embodiments of the antenna may also comprise a substrate, which may be a semiconductor or conductor in various embodiments. Embodiments also include systems, computer-implemented methods, devices, and computer-readable media for effectuating desired modulation of incident radiation by, e.g., varying the doping level of the tunable thin-film material.

System, method and computer-accessible medium for depth of field imaging for three-dimensional sensing utilizing a spatial light modulator microscope arrangement

Synchrotron radiation photoemission spectroscopy and optical transmission spectrum measurements have been performed on an HfO2 thin film grown on a Si(100) substrate to determine the band structure of the HfO2/Si stack. The result shows a valence-band offset of 2.5 eV and a conduction-band offset of 2.2 eV for the HfO2/Si interface. The Schottky barrier height between Au and HfO2 is obtained from current density–voltage measurement. The characterization reveals that the dominant conduction mechanism in the region of low field under gate injection is Schottky emission. The energy-band diagram of an Au–HfO2–Si MOS stack was obtained from these results.

Band structure and valence-band offset of HfO2 thin film on Si substrate from photoemission spectroscopy

8.4 μm-emitting quantum cascade lasers (QCLs) have been designed to have, right from threshold, both carrier-leakage suppression and miniband-like carrier extraction. The slope-efficiency characteristic temperature T1, the signature of carrier-leakage suppression, is found to be 665 K. Resonant-tunneling carrier extraction from both the lower laser level (ll) and the level below it, coupled with highly effective ll-depopulation provide a very short ll lifetime (~0.12 ps). As a result the laser-transition differential efficiency reaches 89%, and the internal differential efficiency ηid, derived from a variable mirror-loss study, is found to be 86%, in good agreement with theory. A study of 8.8 μm-emitting QCLs also provides an ηid value of 86%. A corrected equation for the external differential efficiency is derived which leads to a fundamental limit of ~90% for the ηid values of mid-infrared QCLs. In turn, the fundamental wallplug-efficiency limits become ~34% higher than previously predicted.

86% internal differential efficiency from 8 to 9 µm-emitting, step-taper active-region quantum cascade lasers.

We propose a technique based on Fabry-Perot fringes to analyze, in a broad wavelength range, the waveguide properties of semiconductor lasers in the midinfrared spectrum. This technique has been applied to strain-balanced Ga0.32In0.68As∕Al0.64In0.36As quantum cascade lasers, with a double phonon active region, in order to determine propagation losses and the effective index between 2.5 and 8μm wavelength. These results are in good agreement with the values obtained using another method.

Measurement of semiconductor waveguide optical properties in the midinfrared wavelength range

We demonstrated an integrated three terminal device able to modulate the cavity losses of quantum cascade lasers. By growing asymmetric doped quantum wells coupled to the laser’s mode an absorption peak can be electrically shifted in and out the laser transition. The use of three terminals allows one to drive the laser independently from the wells and therefore to modulate the laser’s amplitude with an electrical power of only a few milliwatts. This is far less than the power needed for a direct modulation of the laser light.

Integrated quantum cascade laser-modulator using vertically coupled cavities

We developed a three terminal mid-infrared quantum cascade laser. The third terminal allows one to electrically modulate the optical losses and thus the laser output - independently of the laser's driving current.

Amplitude modulation of quantum cascade laser with vertically coupled cavities

We present an optimized technique for the measurement of gain and losses of semiconductor lasers. We optically inject the beam of a distributed feedback laser (DFB) inside the cavity of the lasers under study. The DFB laser operates in a pulsed mode and shifts its emission wavelength as a function of time. This frequency chirp creates the Fabry–Perot fringes of the transmitted intensity that contains all the information on the cavity losses. The setup has been validated by a quantitative study of the losses as a function of the injected current, for a quantum cascade laser emitting at 7.6 μm.

Measurement of gain and losses of a midinfrared quantum cascade laser by wavelength chirping spectroscopy

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Papers

Measurement of semiconductor waveguide optical properties in the midinfrared wavelength range

Integrated quantum cascade laser-modulator using vertically coupled cavities

Amplitude modulation of quantum cascade laser with vertically coupled cavities

Measurement of gain and losses of a midinfrared quantum cascade laser by wavelength chirping spectroscopy