Novel In-Plane Semiconductor Lasers XXI

To realize a high-speed high-reliability wavelength switching at a future WDM networks, we proposed the injection current/temperature cooperative control method of the tunable-distributed-feedback (DFB) laser array (TLA) for reducing the large injection current which is the primary cause of laser degradation. We successfully demonstrated a full-c-band wavelength switching within a short time of 124 ms and following injection current reduction from 420 to 63 mA. Compared to the conventional control method, the mean time to failure of the TLA in the proposed method is estimated to be extended by 44 times.

We demonstrated a 2-μm wavelength InGaAs-InGaAs superstructure grating (SSG-) distributed Bragg reflector (DBR) laser with stable single-mode operations across a 53-nm tuning range. We adjusted the wavelength detuning to make the lasing performance uniform across the tuning range. As a result, side-mode suppression ratios (SMSRs) exceeding 30 dB were achieved for all 40 consecutive wavelength channels with 100 GHz spacing from 1978.4 to 2031.0 nm. The fluctuation of the light intensity during wavelength tuning was also suppressed to less than 6.5 dB, which is much lower than that in the previous report (>15 dB).

An electrically wavelength tunable DBR ridge-waveguide laser suitable for multi-wavelength excitation Raman spectroscopy near 785 nm is presented. The 3 mm long device consists of a 2.2 µm wide ridge waveguide and a 10th order DBR surface grating. Resistors implemented near the grating enable flexible wavelength tuning by Joule heating. At 25°C heat sink temperature, laser emission with 100 mW optical output power and a spectral width of 20 pm is obtained. A current of 0.6 A applied to the resistors results in 2.2 nm wavelength tuning. Single emission wavelengths can be adjusted with time constants of about 500 ms.

A low index layer between the boundary of a first-order grating combined with a high index cover layer provides significantly higher reflected power per unit length and reduces losses at the waveguide-grating interface compared to conventional gratings in III-V waveguides. The dependence of the peak and spectral width of the reflected power for Enhanced Coupling Strength (ECS) gratings is analyzed for two different ECS grating geometries. These properties of ECS gratings allow integration of optical components such as high-speed modulators with short horizontal cavity lasers that can operate without temperature control over wide temperature and wavelength ranges.

In this paper we present for the first-time high-speed modulation results for Photonic crystal surface emitting lasers (PCSELs) emitting at 940 nm, a 3dB bandwidth of 4.2 GHz was measured at a drive current of 2.2 x Ith for a device not optimised for high-speed operation. Extracting the ‘K factor’ from the measurements yields a damping limit to device operation of approximately 25GHz. We go on to show that careful optimization of device design, namely increasing differential gain and decreasing mode volume, can yield PCSEL devices with direct modulation bandwidths of 50-100 GHz.

A slotted Y-branch laser providing two-color emission in the 1550 nm region with an optical beat frequency of 1 THz is characterized and used as a photonic source for thickness measurements of high resistive silicon wafers with continuous wave Terahertz radiation. Frequency tuning is obtained through segment current tuning of the individual branches. Determination of the refractive index and thickness is obtained by MSE fitting of the theoretical etalon transmission to the experimental measurements without additional knowledge.

InP-based quantum dot (QD) laser devices emitting at 1.3 µm were realized by incorporating a GaAs nucleation layer underneath the InAs QD layers. A good carrier confinement while retaining the waveguiding properties is achieved by embedding the QDs in In0.528Al0.371Ga0.101As. Length dependent P-I characteristics yielded static parameters, which were comparable to static parameters obtained for InP-based lasers emitting at 1.55 µm. Additionally, temperature dependent measurements were conducted and evaluated. The lasers show ground mode lasing up to high operation temperatures with good temperature stability of the threshold current density and external quantum efficiency.

The parasitic electron-hole recombination outside of a quantum-confined active region still presents a challenge in conventional injection lasers. The use of asymmetric barrier layers (ABLs) (one on each side of the active region) should efficiently suppress this recombination. However, even in lasers with ABLs, excited states may be present in the active region in addition to the ground state. Excited states may strongly affect delivery of charge carriers to the lasing ground state. In this work, dynamic properties of quantum dot (QD) lasers with ABLs are studied in the presence of excited states in QDs. The situation is considered when the carrier capture into the lasing ground state in QDs is excited-state-mediated. It is shown that the modulation bandwidth of the ABL QD laser can be considerably impacted by excited-to-ground state relaxation delay in QDs. Hence a strict control of the intradot relaxation time will be required to enhance the modulation bandwidth in ABL QD lasers.

The performance of O-band InAs/GaAs quantum-dot (QD) lasers grown by molecular beam epitaxy with three different doping strategies are investigated in a temperature range 17 °C – 97 °C. We demonstrate lasers with a reduced threshold current using direct n-doping (during the dot formation) in the active region compared lasers with a nominally undoped active region. We explain results using calculations of the dot and wetting layer potentials and the electron and hole energy levels.

In this paper we analyze the deep levels within bandgap in n-type GaAsBi Schottky Barrier Diodes by means of capacitive deep level transient spectroscopy. We proved that in the probed semiconductor region are present four majority and two minority traps with concentration below 10^14 cm^-3. Moreover, the carrier capture kinetic of the defects indicate that the dominant electron trap and hole traps are associated respectively to a dislocation and a point defect with capture barrier. By comparing our results with other literature reports, we also found that only one trap may be associated with the presence of bismuth.

Optically pumped waveguide coherent laser arrays are demonstrated in an 1-micron-thick-semiconductor-membrane-InGaAs-quantum-well laser transferred on a silicon carbide heat spreader emitting at 1010 nm. We employ a real and Fourier space imaging setup to study the emission of single and arrays of laser cavities. We are able to create waveguide laser arrays with modal widths of approximately 5-10 μm separated by 5-10 μm which maintain their mutual coherence while operating on either single or multiple longitudinal modes. This laser geometry can be accurately controlled by the laser pump and they offer a new high gain laser platform that permits integration with photonic structures.

Quantum cascade laser combs enable the generation of high average power coherent optical frequency combs. Combination of RF injection in specially designed devices enable the recompression of the emission into high peak power pulses for non-linear optics applications. A combination of techniques are used to analyse the temporal profile of the emission.

Frequency combs are ideal candidates to realize miniaturized spectrometers without moving parts and hence are of great interest for integrated photonics. Most comb research is focused on the generation of pulses. However, frequency combs can also exhibit a very different behavior that is characterized by a continuous output intensity – the frequency modulated (FM) combs. The two states are characterized by in-phase or anti-phase couplings. Here, an overview on our experimental investigations on semiconductor frequency combs to identify the key roles of parameters such as the linewidth enhancement factor and how the bandwidth of such combs can be optimized is given.

The recent generalised theory of frequency comb generation in externally pumped cavities with and without population inversion suggested an intimate link between quantum cascade lasers (QCLs) and Kerr resonators. In this talk we overview recent experimental developments in chip-scale ring cavity QCLs with and without output coupling ports, that allow operation in self-pumped and externally pumped configurations, and their ability to support cavity solitons.

We report on self-organization phenomena in a coherently driven unidirectional ring Quantum Cascade Laser. In particular our simulations based on a generalized Lugiato-Lefever equation show the existence in the intracavity field profile of Cavity Solitons (CSs) and Turing patterns previously identified in Kerr micro-resonators. In the perspective of applications in e.g. information processing, high precision spectroscopy and wireless communications, we demonstrate the external addressing of one or more CS and we investigate the possibility to exploit their universal properties as dissipative localized structures to manipulate the spectral content of the associated optical frequency combs.

Optical frequency combs are perfectly periodic waveforms of light. These waveforms can be formed due to optical nonlinearities, which provide coherent coupling of the amplitude and phase of the light. We show that Bloch gain serves as the physical origin of the linewidth enhancement factor and yields a giant Kerr nonlinearity, which plays an essential role in the formation of quantum cascade laser combs. We develop a laser master equation to self-consistently include the Bloch gain. Our results explain the generation of self-starting combs in Fabry-Perot QCLs, and the emission of localized structures in ring resonators, akin to dissipative Kerr solitons.

We propose and design a high-brightness, ultra-compact electrically pumped GaSb-based laser source of polarization-entangled photons generated by intracavity parametric down-conversion of lasing modes. We develop a nonperturbative quantum theory of parametric down-conversion of waveguide modes which takes into account the effects of modal dispersion, group and phase mismatch, propagation, dissipation, and coupling to noisy reservoirs. We provide convenient analytic expressions for interpreting experimental results and predicting the performance of monolithic quantum photonic devices based on nonlinear wave mixing of laser modes.

This work investigates on the impact of temperature and of diffusion processes on the optical degradation of 1.3 um InAs quantum-dot lasers epitaxially grown on silicon. By means of a series of constant-current stress experiments carried out at different temperatures we were able to ascribe the peculiar temperature activation of the detected threshold current degradation process to a recombination-enhanced diffusion process, driven by the escape of carriers from the InAs QDs. The comparison of the experimentally-determined diffusion coefficient with the literature ultimately allowed us to relate the Ith degradation to the p-dopant Be, or to defects determining its diffusivity.

We study the stability of a hybrid laser source consisting of a III-V RSOA edge-coupled to a SiN Mach-Zehnder interferometric mirror, loaded by two high-Q microring resonators, providing a narrow band effective reflectivity. We simulate the laser dynamics through a model of time-delayed algebraic equations accounting for the frequency-selective mirror reflectivity and identify the best regions of CW operation in terms of bias current, mirror bandwidth, and laser detuning with respect to the reflectivity peak. Finally, we test the CW laser stability with respect to optical feedback, mimicking the effect of spurious back-reflections from the passive parts of the circuit.

In this work we present results of different control strategies with the aim to achieve single mode lasing wavelengths with 10 GHz spacing (90 pm) between 1480 and 1570 nm, on an InP monolithically integrated widely tunable laser system for optical coherence tomography (OCT) applications. To tune the laser, we apply 8 reversely bias voltage control settings on electro-refractive modulators which are responsible for the laser wavelength selection, with low thermal dissipation. The OCT requirements of a 1 GHz resolution and stable calibration are addressed, and two different strategies to select the lasing wavelengths, over its tuning range, are discussed.

We report a type-II interband cascade laser grown on an on-axis silicon substrate. We demonstrate continuous-wave lasing operation at temperatures up to 50°C at 3.5µm with a threshold current of 45 mA at room temperature and 20 mW/facet output power. We extrapolate a mean time to failure of at least 300,000 h, which we attribute to the design of the active region eliminating the non-radiative recombination process.

In this work present high performance QCL-based THz combs operating on fundamental and harmonic comb states operating up to 110 K in the spectral region from 2 to 4 THz . We employ double-metal, Copper- based laser resonators planarized with a polymer allowing high performance with CW operation up to 118 K . Such waveguide layout allows as well optimized RF coupling facilitating injection of high RF power. We analyze the laser emission by means of SWIFTS technique employing an Hot-Electron-Bolometer based on NbN. Different regimes are observed as the RF injection power is increased, going from FM emission to a pure AM. Spectral bandwidths as large as 700 GHz are observed corresponding to a fully coherent laser operation. For specific waveguide geometries and injection conditions pulses as short as 4 ps are observed. We present as well SWIFTS measurements for THz QCL combs operating on harmonic states under RF injection at the harmonic frequency of 17.6 GHz.

Millimeter wave (mmWave) generation using photonic techniques has so far been limited to the use of near-infrared lasers that are down-converted to the mmWave region. However, such methodologies do not currently benefit from a monolithic architecture and suffer from the quantum defect. Here we show how miniaturized terahertz (THz) quantum cascade lasers (QCLs) can open up the possibility of ntegrating both laser action and mmWave generation in a single device. We demonstrate intracavity mmWave generation within THz QCLs over the unprecedented range of 25 GHz to 500 GHz using their inherent giant nonlinearities.

INVITED TALK This talk will review our recent developments in engineering and devising novel highly efficient broadband QCL resonators, behaving as frequency combs at THz frequencies, with > 100 μW optical powers per mode and a record dynamic range. Novel architectures, exploiting exotic device technologies, advanced materials and/or physical phenomena will be discussed, highlighting the promising role of THz frequency combs in quantum science, hyper-spectral imaging and dual-comb spectroscopy.

The study of high Al containing barriers in Terahertz Quantum Cascade lasers has led to the improvement of operation temperature and of the quantum efficiency. This is mainly caused by the reduction of transport channels through higher states. In consequence, the electron transport in these new devices is dominated by photon assisted tunneling. The originating non-linearity provides a huge potential for different operation modes. We try to further study this by coupling distributed QCL devices on a chip which has led to the observation of bi-stable operation and THz switching. We use the non-linear behavior for the control of the emission spectra of surface emitting random laser structures. Furthermore, ring structures can be realized which can be tuned from single mode to frequency comb operation.

Different phase-locking schemes are developed for surface-emitting terahertz quantum-cascade lasers (QCLs) with watt-level output power and radiating in symmetric single-lobed beams. In the first-scheme, multiple metallic microcavities are coupled through surface-plasmon-polaritons traveling in surrounding medium of cavities, that leads to peak-power output of 2.03W for a single-mode 3.3THz QCL with a slope-efficiency of 1.57W/A. In the second-scheme, a phase-locking scheme with hybrid second- and fourth-order Bragg gratings is demonstrated to realize a multi-mode surface-emitting THz QCL with 2.13W output power. Both QCLs operate at ~60K. Preliminary data for a scheme to achieve electrical tunability of such lasers is also reported.

The THz region of the electromagnetic spectrum has been underutilized due to the lack of proper sources. The quantum cascade laser pumped molecular laser uses QCLs to pump a molecular gain medium in order to obtain laser emission at discrete THz frequencies separated by twice the rotational constant of the molecule. Following an initial proof of concept of a quantum cascade laser pumped molecular laser,in 2019, we now report significantly improved power levels while maintaining multi-line lasing spanning from 250 GHz up to 5 THz depending on the chosen gain medium.

A terahertz quantum-cascade VECSEL is demonstrated to exhibit multi-mode operation, despite the fact that spatial-hole burning is nominally suppressed within the amplifying metasurface. A specially designed output coupler mirror is used such that large numbers of modes have nearly identical lasing thresholds. Up to nine lasing modes with a FSR of approximately 21 GHz are demonstrated – a significant increase from previous QC-VECSELs in which only 2 or 3 modes have been observed to lase at once. This work is an intermediate step towards eventually demonstrating THz QC-VECSELs as broadband incoherent emitters or frequency combs.

Photonic crystal surface emitting lasers emitting up to 2.6 µm have been designed and fabricated. A high-index-contrast photonic crystal layer was incorporated into the laser heterostructure by air-hole-retaining epitaxial regrowth. Transmission electron microscopy studies demonstrated uniform and continuous regrowth of the nano-patterned GaSb surface with AlGaAsSb alloy until air-pockets start being formed. The photonic crystal surface emitting lasers based on diode laser and cascade diode laser heterostructures generated narrow spectrum low divergence beams with mW-level output power. The angle-resolved electroluminescence analysis demonstrated well resolved photonic subbands corresponding to Γ2 point of square lattice and photonic gaps of several meV.

We report wide tuning of external cavity interband cascade lasers (EC-ICLs) in continuous-wave operation at room temperature. The antireflection coated ICL gain chips were tuned with a diffraction grating in the Littrow configuration. A tuning of range of 313 cm-1 (360 nm) from 2789 cm-1 to 3102 cm-1 (3.22 to 3.58 μm) in continuous wave at 20oC was demonstrated with a 5 μm-wide, 1.5 mm-long gain chip. A maximum output power of 13 mW and a minimum threshold current of 62 mA were measured at the peak gain. The heat dissipation of the chip was 0.2 W at threshold and 0.8 W at the maximum current of 200 mA.

We present our recent results on the impact of intersubband absorption in the valence band on the performance of interband cascade lasers (ICLs). We observe a clear performance dependence on the thickness and composition of the Ga_(1-x) In_x Sb hole-quantum well (QW), reflecting in the characteristic temperature T_0 and the threshold current density J_(th). By carefully adjusting the design of the active W-QW the intersubband absorption in the valence band can be tailored and even completely avoided, allowing us to enhance ICL performance outside of the sweet spot 3-4 μm region, paving the way towards higher cw operating temperatures and output powers.

The integration on silicon of light sources emitting in the 2-5 µm wavelength range for sensing applications is currently under the focus of attention. In this work we have studied the influence of the quantum well number (from 1 to 4 QWs) on the performances of GaSb-based laser diodes grown on silicon and emitting at 2.3 µm. We have observed that – somewhat counterintuitively – the best performances in terms of threshold current and internal losses are achieved with 1 QW. The results will be discussed in comparison with similar laser diodes grown on native GaSb substrates.

We present a novel InGaAs/InAlAs/InP quantum cascade detector (QCD) operating in the long wave infrared (LWIR) range, crucial for the exploitation of new free-space optical telecommunication channels at wavelengths between 8-12 µm. The comparison of differently sized detector ridges, processed on substrates with a 15-period as well as a single-period design, allows a characterization of the spectral photocurrent and a comparison of their performance in terms of sensitivity, spectral responsivity, detector noise etc. The goal is to distinguish design guidelines for the best candidate to establish a monolithic-integrated heterodyne detection system, able to secure high-speed and low-noise free-space data transmission.

Surface emitting quantum cascade lasers (QCLs) are the attractive mid-infrared light source candidates for many laser-based applications. The vertical cavity surface-emitting laser structure cannot be applied to QCLs in principle, therefore using photonic crystals (PCs) is the remarkable solution to enable precise control of light behavior, such as wavelength selection and light extraction angle. Since the PCs are formed by lithography and dry etching, there is a difference between the design value and the finished dimensions. We observed the finished dimensions of InGaAs PCs after InP buried process, and evaluated the deviation from the design value.

Enhanced Coupling Strength (ECS) outcoupler gratings theoretically provide an order of magnitude reduction of grating length compared with conventional outcoupler gratings in III-V photonic waveguides. The dependence of the magnitude and spectral width of the outcoupled power of ECS outcoupling gratings is analyzed using a Floquet-Bloch space-harmonic approach for two different ECS grating geometries. ECS outcoupler gratings allow near-surface normal emission of integrated optical devices such as laser transmitters consisting of short horizontal cavity lasers combined with high-speed modulators that can operate without temperature control over a wide temperature and wavelength ranges.

High-power diode lasers use long resonators and asymmetric facet reflectivities, leading to longitudinally varying photon density (recombination rate) and early power saturation due to spatial-hole-burning. We summarize recent experimental studies into the relation between device geometry and local current and carrier densities to high powers (10W per 90µm stripe) and compare these to simulation. We use custom devices with segmented contacts (local current density) or back-side window (carrier density and temperature). Strong non-uniformity is observed that increases with bias, above prediction. Local heating at the front facet induces non-saturating carrier accumulation at the stripe edges, a key source of non-uniformity.

Photonic-crystal surface-emitting lasers (PCSELs) are an unprecedented type of semiconductor laser that have the potential of operating in a single longitudinal and lateral mode over a broad area. Recently, we achieved 10-W continuous wave (CW), high-beam-quality (M2~2) operation using a single-chip PCSEL with a circular resonator diameter of 1 mm. Very recently, we have succeeded in further increase of the output power to ~30W under CW condition by constructing a single chip PCSEL with a circular resonator diameter of 2 mm. In this conference, we will review such rapid progress of PCSELs.

Tapered diode amplifiers feature an intrinsic astigmatism for vertical and horizontal beam axis. Additionally, the magnitude of astigmatism changes for different device working points. This work investigates the optical behaviour of tapered diode structures at different states of operation by means of an advanced theoretical model. It focuses on devices at an emission wavelength of 980 nm and a tapered section length of 4 mm. The theoretical model is based on a beam propagation method which is coupled to a thermal and an electrical model. The simulation outcomes are necessary for an advanced understanding of experimental outcomes.

4 mm long DBR tapered diode lasers at 785 nm with three different lateral layouts will be presented. The devices consist of an unpumped DBR section, a ridge waveguide section, and a tapered section with a full taper angle of 6°. The impact of different lengths of the 10th order surface DBR gratings on the spectral behavior and the beam parameters at different RW currents will presented. With the best layout, the devices reach up to 7 W of optical output power together with a narrow spectral width smaller than 19 pm and a beam parameter M2 below 3 (1/e2 level).

We present a quantum-mechanical model for photon-driven transport in QCLs that is computationally inexpensive, requires no phenomenological parameters, and is conducive to intuition building. The model stems from a rigorous theoretical framework with a positivity-preserving Markovian master equation of motion for the density matrix. The equation of motion is solved self-consistently and nonperturbatively, and used to compute the steady-state and frequency response of a previously published midinfrared QCL. Our results show how PA tunneling alters electron transport around and above lasing threshold, and explain why the changes are pronounced in diagonal QCLs. With the inclusion of PA tunneling, the calculated curves for current density versus field and output power versus current density are in close agreement with experiment.

Accurate simulation of V-I characteristics for mid-IR quantum cascade lasers (QCLs) with photon-induced carrier transport (PICT) is achieved by using the non-equilibrium Green’s function method coupled with the interface-roughness scattering formalism taking into account graded interfaces and axial correlation lengths. Analysis of 4.9 µm- and 8.3 µm-emitting, buried-heterostructure (BH) QCLs reveals that PICT action reduces the differential resistance by a factor of 2.5 and increases the maximum-current density by ~ 30 % compared to conventional BH QCLs, which explains their record-high, single-facet wall-plug efficiency values (i.e., 27 % and 17 %). Interface grading allows obtaining emission wavelengths close to experiment.

We report on the surface emitting quantum cascade lasers (QCL) using a two-dimensional photonic crystal (PC) at 4μm. The quantum well of the light-emitting layer was a strain-compensated system, and the crystal regrowth for buried PC was achieved while maintaining the crystal quality under thermal budgets of high-temperature regrowth. PC-QCLs lasing was realized on the single-mode vertical-emission at 77K under pulse operation. The threshold current density is 760 A/cm2. The far-field radiation pattern showed a very small divergence angle of less than 2°

Quantum-cascade lasers (QCL) enable emission in a broad range of infrared radiation unavailable for convectional quantum well bipolar lasers. However in-plane geometry of QCLs hinders achieving properties required in numerous applications which are inherently possessed by vertical-cavity surface-emitting lasers (VCSELs). In proposed design of QC-VCSEL the role of top mirror and element inducing component of electric field necessary to stimulated emission in quantum cascades is served by subwavelength monolithic high-refractive-index contrast grating (MHCG) in which quantum cascade active region is embedded. This paper based on numerical analysis presents influence of QC-VCSELs configuration details on threshold currents and mode distributions.

Quantum Cascade Lasers (QCLs) are an ideal light source for many mid-infrared applications due their high power, small size and the ability to customize the output wavelength through quantum engineering, rather than material composition. For most applications, high output power and high efficiency should be achieved without compromising other key characteristics, such as beam quality, spectral brightness or reliability. These goals are often in conflict and this presentation will emphasize the production process control as well as engineering design choices that enable us to demonstrate reliable watt-level output powers across the mid-infrared.

In this work we monolithically integrate a quantum cascade laser (QCL) and detector (QCD) addressing the same wavelengths lambda=1550-1650 cm-1 for liquid spectroscopy. QCL and QCD are combined using a 50-100 µm-long dielectric-loaded surface-plasmon-polariton (DLSPP) waveguide, which typically guides >>90% of the mode outside of the cavity. We show the analysis of the protein bovine serum albumin (BSA) and its denaturation process between 25°C-90°C in real time in a microfluidic cell (60 µl) for 20-60 mg/ml BSA-concentrations. To further test the sensor-robustness, we directly submerge it into a beaker and detect H2O up to 35%-40%, solved in isopropyl alcohol.

Long-wave infrared communication systems are poised to become one of the key wireless technologies in order to extend the current communication network, especially in areas where fiber deployment is rather difficult and expensive or when the emitter and receiver need to be mobile. We demonstrate a high-speed data transmission with a room-temperature quantum cascade laser emitting at 8.1 µm. The maximum data rate we can achieve is above 1 Gbits/s and allows broadcasting an uncompressed high-definition video on a remote screen. This proof-of-concept experiment is promising for long-distance free-space transmission because long-wave infrared wavelengths are almost immune to weather perturbations.

Here we report on the multi-gas detection of carbon monoxide (CO), nitrous oxide (N2O), carbon dioxide (CO2), and water vapor (H2O) by using a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor exploiting a Vernier-effect distributed-feedback quantum cascade laser as excitation source. This innovative laser behaves as a switchable, multi-color, electrically tunable light source with an extended tuning range, ranging from 2100 cm-1 to 2220 cm-1. The achieved detection limits were 4 ppb, 7 ppb, and 71.8 ppm for CO, N2O, and CO2, respectively, at 100 ms of integration time. Finally, QEPAS sensor was tested with laboratory air samples for two days.

Semiconductor-loaded plasmonic (SLSPP)-waveguides are a very efficient link for optoelectronic devices, facilitating miniaturized photonic integrated circuits. However, for long-wave infrared applications (8-12 µm), the material selection is challenging as most commonly used mid-IR materials absorb in this region. Therefore, we selected and investigated the properties of germanium in a hybrid semiconductor-metal-configuration to overcome these limitations. The experimental characterization of Si(substrate)-Au-Ge fabricated SLSPP-waveguides show very good agreement with FEM-simulations. Moreover, the realized devices offer low losses between 8.8 and 22 dB/mm (single device) and even within 8.8-15 dB/mm (multiple devices), respectively, for the entire investigated octave-spanning 5.6 – 11.2 µm range.