Broadband THz absorption spectrometer based on excitonic nonlinear optical effects

A broadly tunable THz source is realized via difference frequency generation, in which an enhancement to χ (3) that is obtained via resonant excitation of III–V semiconductor quantum well excitons is utilized. The symmetry of the quantum wells (QWs) is broken by utilizing the built-in electric-field across a p–i–n junction to produce effective χ (2) processes, which are derived from the high χ (3) . This χ (2) media exhibits an onset of nonlinear processes at ~4 W cm −2 , thereby enabling area (and, hence, power) scaling of the THz emitter. Phase matching is realized laterally through normal incidence excitation. Using two collimated 130 mW continuous wave (CW) semiconductor lasers with ~1-mm beam diameters, we realize monochromatic THz emission that is tunable from 0.75 to 3 THz and demonstrate the possibility that this may span 0.2–6 THz with linewidths of ~20 GHz and efficiencies of ~1 × 10 –5 , thereby realizing ~800 nW of THz power. Then, transmission spectroscopy of atmospheric features is demonstrated, thereby opening the way for compact, low-cost, swept-wavelength THz spectroscopy

SIMULTANEOUS SELF-SUSTAINED ACTUATION AND PARALLEL READOUT WITH MEMS CANTILEVER SENSOR ARRAY

Parallel readout of a microcantilever array using single magnetic actuator and a single photo detector for concurrent detection is reported. The system includes MEMS cantilever array designed for different resonance frequencies, optical elements for laser beam shaping and focusing, one detector and feedback electronics, and single broadband actuator for parallel excitation. The cantilevers are made using a simple one-mask fabrication process with embedded amplitude gratings at the tips. A line shaped laser beam is used to illuminate the cantilevers. A single readout photodiode is placed at the first order diffraction beam location on the Fourier plane. The amplified photodiode signal is fed back into the magnetic actuation using a preamplifier and a broadband current amplifier. In this paper, we report for the first time parallel monitoring of the thermal resonance peaks of inherently frequency-multiplexed MEMS cantilevers. We demonstrated simultaneous self-sustained oscillations of seven cantilevers by using a single actuator and detector in air environment. The method is suitable for low-cost multiplexed portable biosensors

Monolithically integrated erbium-doped tunable laser on a CMOS-compatible silicon photonics platform.

A tunable laser source is a crucial photonic component for many applications, such as spectroscopic measurements, wavelength division multiplexing (WDM), frequency-modulated light detection and ranging (LIDAR), and optical coherence tomography (OCT). In this article, we demonstrate the first monolithically integrated erbium-doped tunable laser on a complementary-metal-oxide-semiconductor (CMOS)-compatible silicon photonics platform. Erbium-doped Al2O3 sputtered on top is used as a gain medium to achieve lasing. The laser achieves a tunability from 1527 nm to 1573 nm, with a >40 dB side mode suppression ratio (SMSR). The wide tuning range (46 nm) is realized with a Vernier cavity, formed by two Si3N4 microring resonators. With 107 mW on-chip 980 nm pump power, up to 1.6 mW output lasing power is obtained with a 2.2% slope efficiency. The maximum output power is limited by pump power. Fine tuning of the laser wavelength is demonstrated by using the gain cavity phase shifter. Signal response times are measured to be around 200 μs and 35 µs for the heaters used to tune the Vernier rings and gain cavity longitudinal mode, respectively. The linewidth of the laser is 340 kHz, measured via a self-delay heterodyne detection method. Furthermore, the laser signal is stabilized by continuous locking to a mode-locked laser (MLL) over 4900 seconds with a measured peak-to-peak frequency deviation below 10 Hz