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The intensity noise of a laser source represents one of the key factors limiting the ultimate sensitivity in laser-based systems for sensing and telecommunication. For advanced applications based on interferometry, the availability of a shot-noise-limited local oscillator is even more important for the effective feasibility of high-precision measurements. This is particularly crucial in quantum optics applications based on homodyne detection schemes to measure non-classical light states, such as squeezed states. This work deeply investigates and analyzes the intensity noise features of the most widely used mid-infrared semiconductor heterostructured lasers: quantum cascade and interband cascade lasers. For this purpose, a comprehensive comparison of three different continuous-wave lasers operating at room temperature around 4.5 {\mu}m wavelength is presented. First, a thorough electro-optical characterization is given, highlighting the differences and the shared common characteristics of the tested devices. Then, a detailed intensity noise analysis is reported, identifying their different noise operations with a particular reference to shot-noise-limited operations. Finally, some perspectives towards advanced applications are discussed., Comment: 17 pages, 5 figures

Interband Cascade Lasers (ICL) have matured into a versatile technological platform in the mid-infrared spectral domain. To broaden their applicability even further, ongoing research pursues the emission of ultrashort pulses. The most promising approach is passive mode-locking with a fast saturable absorber. However, despite vast attempts no passive mode-locked ICL has been demonstrated up to date. In this study we perform pump-probe measurements on the ICL gain and show that its dynamics are mainly ($\sim$70%) governed by a fast recovery time of 2 ps. Our findings explain why passive mode-locking has not succeeded so far, shedding a new light on ICL dynamics as we propose strategies to overcome the current limitations.

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 laser exploiting interband transitions in type-II band alignment geometry. They are currently gaining significant importance for mid-infrared applications from <3 {\mu}m to >6 {\mu}m 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 {\lambda} = 3.8 {\mu}m-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 (INPSD) and relative intensity noise (RIN). We obtain 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.

We present GaSb-based interband cascade lasers emitting at a center wavelength of 6.12 $\mu$m at 20$^\circ$C in continuous-wave operation up to a maximum operating temperature of 40$^\circ$C. Pulsed measurements based on broad area devices show improved performance by applying the recently published approach of adjusting the GaInSb layer thickness in the active region to reduce the valence intersubband absorption. The W-quantum well design adjustment and the optimization of the electron injector, to rebalance the electron and hole concentrations in the active quantum wells, improved the device performance, yielding room temperature current densities as low as 0.5 kA/cm$^2$ for broad area devices under pulsed operation. As a direct result of this improvement the long wavelength limit for GaSb-based ICLs in continuous wave operation could be extended. For an epi-side down mounted 23 $\mu$m wide and 2 mm long device with 9 active stages and high-reflectivity back facet the threshold power is below 1 W and the optical output power is over 25 mW at 20$^\circ$C in continuous-wave mode. Such low-threshold and low-power consumption interband cascade lasers are especially attractive for mobile and compact sensing systems.

The generation of mid-infrared pulses in monolithic and electrically pumped devices is of great interest for mobile spectroscopic instruments. The gain dynamics of interband cascade lasers (ICL) are promising for mode-locked operation at low threshold currents. Here, we present conclusive evidence for the generation of picosecond pulses in ICLs via active mode-locking. At small modulation power, the ICL operates in a linearly chirped frequency comb regime characterized by strong frequency modulation. Upon increasing the modulation amplitude, the chirp decreases until broad pulses are formed. Careful tuning of the modulation frequency minimizes the remaining chirp and leads to the generation of 3.2 ps pulses.

Optical frequency combs enable all-solid-state spectrometers that will trigger a breakthrough in miniaturization and on-chip integration of mid-infrared sensing technology. Interband cascade lasers (ICLs) are an ideal candidate for practical implementations due to their low power consumption and zero-bias detection functionality. Here, we demonstrate the generation of self-starting ICL frequency combs. We show that the gain is fast enough to respond to beating of the intracavity field, which hinders the formation of short pulses. Instead, the ICL operates in a comb state, where the phases of the fundamental intermode beatings are splayed over a range of $2\pi$. This state appears to be general to self-starting combs based on the inherent gain nonlinearity and minimizes oscillations of the population inversion. Using the same epi-layer material, we demonstrate efficient detector operation at room temperature up to several GHz bandwidth and thereby provide a complete and unmatched platform for monolithic and battery driven dual-comb spectroscopy.