Mid-infrared Ring Interband Cascade Laser: Operation at the Standard Quantum Limit.

Many precision applications in the mid-infrared spectral range have strong constraints based on quantum effects that are expressed in particular noise characteristics. They limit, e.g., sensitivity and resolution of mid-infrared imaging and spectroscopic systems as well as the bit-error rate in optical free-space communication. Interband cascade lasers (ICLs) are a class of mid-infrared lasers exploiting interband transitions in type-II band alignment geometry. They are currently gaining significant importance for mid-infrared applications from < 3 to > 6 µm wavelength, enabled by novel types of high-performance ICLs such as ring-cavity devices. Their noise behavior is an important feature that still needs to be thoroughly analyzed, including its potential reduction with respect to the shot-noise limit. In this work, we provide a comprehensive characterization of λ = 3.8 µm-emitting, continuous-wave ring ICLs operating at room temperature. It is based on an in-depth study of their main physical intensity noise features such as their bias-dependent intensity noise power spectral density and relative intensity noise. We obtained shot-noise-limited statistics for Fourier frequencies above 100 kHz. This is an important result for precision applications, e.g., interferometry or advanced spectroscopy, which benefit from exploiting the advantage of using such a shot-noise-limited source, enhancing the setup sensitivity. Moreover, it is an important feature for novel quantum optics schemes, including testing specific light states below the shot-noise level, such as squeezed states.

High-speed quantum cascade detector characterized with a mid-infrared femtosecond oscillator.

Quantum cascade detectors (QCD) are photovoltaic mid-infrared detectors based on intersubband transitions. Owing to the sub-picosecond carrier transport between subbands and the absence of a bias voltage, QCDs are ideally suited for high-speed and room temperature operation. Here, we demonstrate the design, fabrication, and characterization of 4.3 µm wavelength QCDs optimized for large electrical bandwidth. The detector signal is extracted via a tapered coplanar waveguide (CPW), which was impedance-matched to 50 Ω. Using femtosecond pulses generated by a mid-infrared optical parametric oscillator (OPO), we show that the impulse response of the fully packaged QCDs has a full-width at half-maximum of only 13.4 ps corresponding to a 3-dB bandwidth of more than 20 GHz. Considerable detection capability beyond the 3-dB bandwidth is reported up to at least 50 GHz, which allows us to measure more than 600 harmonics of the OPO repetition frequency reaching 38 dB signal-to-noise ratio without the need of electronic amplification.