This PDF file contains the front matter associated with SPIE Proceedings Volume 12905, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In recent years, red laser diodes (LDs) have been considered for automotive applications. The limitation of high temperature performance of AlGaInP-based red LDs has been one of the technological bottlenecks. Since the most important challenge was electron leakage from the active layer to the p-cladding layer, the p-cladding layer was applied AlInP with the highest band gap material and applied higher doping to minimize electron leakage. We fabricated two types of LDs, single-mode for high temperature operations and multi-mode for high power operations. Single-mode 642 nm 200 mW CW LDs were demonstrated. Optical output power at 350 mA reached 110 mW at 85°C and 90 mW at 90°C. Life test results showed stable operation in 2,000 hours at 85°C, 50 mW CW, and at -40°C, 200 mW CW. This red LD meets the high reliability requirements for automotive components. Also, Multi-mode 638 nm 4.2 W pulsed LDs were demonstrated. Optical output power at 6.0 A reached 4.6 W at 45°C and 3.5 W at 55°C. The estimated life time exceeding MTTF 20,000 hours at 45°C, 4.2 W pulse, frequency 240 Hz, duty 40%. In addition, 4.2 W at 45°C and WPE 45.6% at 25°C under pulsed operation are the world highest optical output power and WPE to the best of our knowledge. We believe that these excellent red LDs will be utilized for automotive applications in the future.

We have investigated the kinetics of photoluminescence (PL) of so-called “wide” 25-nm In_0.17Ga_0.83N quantum wells (QW), where the studied 450 nm emission comes from excited states of the QW. These states are very closely separated and are therefore considered as a quasi-continuum of "bulklike" states. The recombination kinetics shows clear exponential behavior with time constants of 1...2 and 7...9 ns at 5 and 300 K, respectively, a behavior which indicates the dominance of radiative recombination. However, if the decay curves are resolved spectrally, a variety of kinetics is revealed, the appearance of which is likely determined by a slower energy relaxation of the photoexcited carriers in the "wide" QW. The results point to a route to improved polar optoelectronic device architectures based on “wide” QWs.

The limits to the continuous-wave (CW) output power of the GaAs-based high-power diode lasers with an asymmetric photon density along the resonator are experimentally investigated. Spontaneous emission measurement in CW mode and electro-optical characterization both in CW and short pulse mode have been performed to clarify the impact of temperature, bias, and photon density profile on CW output power. Diode lasers with a 90 µm stripe and 6 mm resonator have been fabricated with a backside metallization window along the resonator to measure spontaneous emission intensity (and hence relative carrier density) profile and wavelength to infer temperature. Also, the longitudinal photon density profile has been varied using 98% rear facet reflectivity and 0.8% and 20% front facet reflectivities. Spontaneous emission data demonstrates that asymmetric photon density leads to non-uniform carrier density with higher carrier density at the back facet and increasing temperature at the front compared to the back facet, due to the longitudinal spatial hole burning (LSHB) effect, which becomes more severe with bias. Spontaneous emission data also shows that carriers accumulate at the front facet stripe edges, which can be attributed to the higher temperature at the front facet and lateral spatial hole burning. Further, light-current characteristics in pulse mode show that non-uniform carrier density triggers losses at high temperatures, increasing threshold and reducing internal efficiency. The reduction in internal efficiency becomes much larger in CW operation, due to the large lateral and longitudinal local temperature variations, which lead to strong carrier accumulation at the front stripe edges.

We report on the continuous wave (CW) room temperature operation of epitaxially regrown monolithic GaSb-based photonic crystal surface emitting diode lasers (PCSEL) with λ ≈ 2 μm. The devices are based on laser heterostructure containing carrier stopper layer designed to inhibit electron leakage into buried photonic-crystal section. Atomic hydrogen cleaning of the nanopatterned surface followed by optimized epitaxial step resulted in highly uniform airpocket-retaining regrowth. The increase of the number of air-pockets in unit cells of the buried photonic crystal layer led to enhancement of the PCSEL output power and improvement of the far field pattern The PCSELs with buried high-index-contrast photonic crystal utilizing four air-pockets per unit cell generated 30 mW of continuous wave power from 200 μm diameter aperture.

We compare the spontaneous formation of Optical Frequency Combs (OFCs) in ring and Fabry-Perot (FP) Quantum Cascade Lasers (QCLs), adopting a reduced model derived from the Effective Semiconductor MaxwellBloch Equations near threshold and in the hypothesis of fast medium polarization and carriers. This model consists of a single spatiotemporal equation for an order parameter represented by the electric field. While in the ring configuration it reduces to a single complex Ginzburg-Landau equation (CGLE), in agreement with recent studies, in the FP configuration a non local integral term accounts for the coupling between forward and backward fields and the corresponding equation is equivalent to two coupled CGLEs. We first demonstrate how this approach allows us to reproduce the main features of OFCs in the two considered configurations. Then, we leverage its reduced mathematical complexity and universality to gain more physical insight into not fully understood phenomena, such as the self-starting emergence of harmonic OFCs.

Mid-infrared optical solitons may be a powerful tool for applications in on-chip integrated photonics and spectroscopy, as they provide broadband, phase-locked frequency combs. Quantum cascade lasers (QCLs) embedded in a ring cavity have been found to enable self-starting optical soliton generation. In order to study these phenomena numerically, we use a model based on coupled Maxwell-density matrix equations. The introduction of backscattering in our model stabilizes self-assembled soliton field solutions, which is in very good agreement with experimental data. In this contribution, we present our model and discuss the mechanisms that lead to soliton operation in ring QCLs.

We demonstrate the generation of harmonic comb states in mid-infrared quantum cascade laser frequency combs by optical feedback injection from an external cavity. A Vernier-like method is presented to control the order of generated harmonic states up to the 6th order. In addition to increased repetition rates, such external cavity induced harmonic states also offer increased optical bandwidth and higher comb coherence. This scheme is easy to implement in spectroscopic systems based on quantum cascade laser frequency combs that can take advantage of these improved parameters.

We demonstrate the full frequency stabilization of a Quantum Cascade Laser Frequency Comb by using radio-frequency injection for locking the mode spacing and frequency locking to a crystalline microresonator for stabilizing the offset frequency. A final mode linewidth of 30 kHz over 2 ms is achieved.

Lasers are a key enabling technology in the field of quantum computing, quantum sensing and quantum metrology. These applications require technically challenging properties from the lasers in use, such as stable and precisely controlled wavelength, up to watt level output power, and a narrow linewidth. Semiconductor diode lasers offer a very compact size, low power consumption, as well as scalability of cost and manufacturing volume due to their wafer scale manufacturing process. The monolithic integration of frequency selection on-chip in Distributed Bragg reflector (DBR) lasers offers advantages such as higher robustness, reduced system complexity and smaller size compared to external cavity frequency selection configurations. Thus, DBR lasers provide an optimal solution for a compact narrow linewidth laser source for selected quantum applications. Bandgap engineering of semiconductor gain media enables emission across the spectrum from UV to mid-IR. Wavelengths matching atomic transitions in the 7xx nm wavelength region include 760 nm and 770 nm for Yb, and 780 nm and 795 nm for Rb. In this work we describe the design, manufacturing, and performance of DBR lasers in the 7xx nm wavelength regime. The effects of key device design parameters are investigated to optimize the device performance. These include emitter width, gain and grating length, grating duty cycle, and residual layer thickness. To further scale the laser output power, tapered amplifiers are manufactured and characterized. The lasers are integrated into a laser system platform containing optical isolation, fiber coupling, low-noise laser drivers and temperature controllers. The system includes features such as compact footprint, controlled environment, cloud-connectivity and predictive maintenance.

We introduce a diode-based laser with a fast frequency noise of 30 Hz²/Hz, corresponding to a Lorentzian linewidth of 100 Hz. We examine its characteristics in detail. Our focus is on exploring the variations and similarities in frequency noise and linewidth reduction. Additionally, we present the locking capability of these systems when applied to medium finesse cavities. The results provide insights into the unique operational characteristics of these ultra-low noise lasers and their potential applications in quantum technology.

Diode laser-based dual-wavelength light sources are experimentally compared in individual and common operation. First, a Y-branch distributed Bragg reflector diode laser is presented. It consists of two laser cavities with a single output waveguide. The device provides 180 mW and dual-wavelength laser emission around 785 nm. The measured spectral widths and spectral distance are 20 pm and 0.6 nm, respectively. Resistors implemented next to the gratings allow changing the wavelength spacing within a range of 0.0 nm - 1.7 nm. Lateral far field profiles show a strong modulation and a lateral shift of 1° between both far fields indicates beam steering. Second, a multimode interference coupler-based master oscillator power amplifier is presented. It provides 500 mW dual-wavelength laser emission. Within the available power range, spectral widths of 20 pm and nearly constant peak emission wavelengths are measured. In comparison to quasicontinuous wavelength tuning obtained for the Y-branch laser, the MMI MOPA enables non-continuous wavelength tuning. As an example, selected spectral distances of 0.0 nm, 0.5 nm, 1.0 nm, 1.5 nm, and 2.0 nm are demonstrated in individual operation. Beam steering is successfully eliminated. Near field widths of 5 μm and far field angles of 15° result in beam propagation ratios of M² = 1.2 at the 1/e² level in all operation modes. This enables easy beam shaping or efficient single-mode fiber coupling. Both devices are suitable for spectroscopic applications such as Raman spectroscopy and shifted excitation Raman difference spectroscopy as well as for the generation of THz radiation by photomixing.

Laser systems with ultra-stable and narrow linewidth operation are a crucial part for many quantum computing and quantum sensing technologies, such as trapped ion and neutral ion approaches. The particular interest in this work is the fabrication of a 935 nm Distributed Bragg reflector (DBR) laser which can be used to repump Yb ions permitting Doppler cooling. DBR’s can provide output powers in the range of hundreds of milliwatts with stable narrow linewidth operation, with small system size and without the complexity of the external cavity configuration, thus providing an excellent solution for quantum technologies. Furthermore, the development in laser technologies is enabling the scalability and commercial use of quantum technologies where single frequency DBR lasers can be used as a part of a multiwavelength laser platform. In this work we have demonstrated high-power and narrow linewidth operation at 935 nm. The in-house epitaxial design is based on AlGaAs structure including an AlGaInAs active area. The position of the active region is optimized with asymmetric waveguides to enhance the device performance. The lasers are fabricated using metalorganic vapor phase deposition (MOCVD) after which the surface gratings are defined by electron beam lithography (EBL). The high-aspect ratio gratings are etched by inductively coupled plasma reactive ion etching (ICP-RIE). For device optimization purposes the gain medium section lengths, grating periods and cavity lengths were varied to find the optimal performance.

A narrow-linewidth semiconductor laser chip with highly linear frequency modulation response is presented and validated in two coherent sensing test experiments. This distributed feedback laser monolithic chip has an intrinsic linewidth of less than 10 kHz and an output power over 60 mW. When its injection current is modulated by a triangular function, the laser optical frequency can be modulated by more than 7 GHz at rates up to 100 kHz. The laser frequency modulation response is extremely flat up to 100 MHz, which allows correcting the residual sweep nonlinearities by a proper pre-distortion of the modulation signal. In a first test experiment, the laser was used into a monostatic FMCW lidar system. A point cloud was acquired with a field of view of 20°(H) × 10°(V) and an angular resolution of 0.05° along both axes. The acquisition was performed without averaging using a 7 mm diameter output beam of 100 mW. A high-quality point cloud including several objects of varying reflectivity was measured. In a second test experiment, the laser was used into an OFDR system for a distributed acoustic sensing (DAS) experiment. A short portion of a 50 m long SMF-28 fiber was exposed to a 2 kHz acoustic signal. Processed data clearly shows a strong 2 kHz tone at the location of the acoustic perturbation. In both test experiments, the laser was successfully linearized using modulation signal pre-distortion based on interferograms obtained with a Mach-Zehnder interferometer.

Laser diodes operating in the 2.3-μm band are attractive for detecting trace carbon oxide (CO) gas because of the strong absorption lines of CO and weak interference from H₂O in this band. As a light source for CO-gas detection, we previously developed a 2.3-μm-band distributed feedback (DFB) laser with InAs/InGaAs multiple quantum wells (MQWs) grown on InP. To construct a high-speed with high-accuracy measurement system for CO, the light source must be capable of fast wavelength tuning over a wide range. In this study, we developed InAs/InGaAs distributed Bragg reflector (DBR) laser operating in the 2.3-μm band that uses current injection and has wider and faster wavelength tuning compared with DFB lasers using chip-temperature control. The laser cavity consists of an active region with InAs/InGaAs MQWs, front/rear DBR regions, and phase-control region. The DBR and phase-control regions are monolithically integrated with the active region by using the butt-joint technique. The measured lasing wavelength was 2348.1 nm with an injection current for the active region of 100 mA at room temperature and under continuous wave operation. When the DBR current (front + rear) increased from 0 to 100 mA, the lasing wavelength shifted by -12.0 nm. The estimated refractive index change was 0.51%, which is comparable to that of conventional devices operating in the telecommunication band. Furthermore, by sweeping the currents for the DBRs and phase-control region, the lasing wavelength could be continuously tuned over a range of 4.2 nm, which covers multiple CO absorption lines in the 2.3-μm band.

We fabricate directly modulated membrane distributed-reflector lasers on a Si platform using a micro-transfer printing method. Single-mode lasing with a low threshold current of 1.2 mA and 50-Gbaud-class direct modulation are demonstrated.

We address the dynamics of a III-V/SiN external cavity hybrid laser with a frequency-selective mirror. Simulations through a set of time-delayed algebraic equations accounting for the narrowband SiN mirror reflectivity demonstrate that CW instability occurs when relaxation oscillations become resonant with the beating between longitudinal modes. In the CW unstable regime, we observe the emergence of frequency combs due to four wave mixing, characterized by a modulation of amplitude and frequency. We then characterize the resulting combs in terms of achievable bandwidth. These results are also confirmed through a more accurate time-domain traveling wave model.

Multi-wavelength laser sources on silicon photonics can enable large spectral coverage for DWDM optical I/O links and leverage the scalability of a CMOS compatible process simultaneously. In this work, we report a laser array of four four-wavelength distributed feedback lasers that produce in total sixteen wavelength channels simultaneously with a wavelength spacing of 200 GHz and output power of 17 dBm per laser. We show integrated III-V/Si hybrid lasers on the same die with wafer-level bonded epitaxial III-V layer that spans a spectral coverage of 17 nm through the 16 wavelength channels. We also measured the relative intensity noise (RIN) of all sixteen wavelength channels to be under -135 dB/Hz and the Lorentzian linewidth to be less than 300 kHz.

Our mid-infrared integration platform allows for seamless monolithic integration of low-loss InGaAs passive waveguides with high power InGaAs/AlInAs quantum cascade laser (QCLs) active regions. Efficient light coupling between the active region and passive waveguide is achieved by using an adiabatic taper. We present a single monolithic waveguide-coupled device producing 1.2 W output power under pulse mode operation at room temperature, and a wavelength-tunable photonic integrated circuit (PIC) with tuning range of 7.5 cm^-1 at 4.6 μm. Our PIC exhibits excellent output power stability over its entire tuning range, a feature unachievable with conventional QCL devices.

We report the fabrication of a monolithic closed-loop wavelength beam combined quantum cascade laser (QCL) source. The chip comprises five QCL gain sections connected to 5 × 1 arrayed waveguide gratings (AWG) via active/passive tapered couplers and a router. The chip is fabricated on a MOCVD-grown III-V semiconductor substrate. The entire passive section of the chip undergoes ion implantation to reduce the propagation losses due to free carrier absorption. The peak power for all the QCL array elements reached 600 mW per facet with a 2 kA/cm² threshold current density under pulsed operation. Furthermore, our WBC approach is compatible with buried heterostructure processing, which allows continuous wave operation with high output power. Our results hold promise in manufacturing compact and multiwavelength mid-infrared sources with good beam quality.

In this paper we presents a gas sensing setup based on interband cascade laser (ICL) and quantum cascade laser (QCL) combined with a negative-curvature hollow core fiber (HCF). We demonstrate simultaneous detection of water vapor, methane, nitrous oxide and carbon monoxide using wavelength modulation spectroscopy technique. With a 1m-long HCF we were able to record WMS signals with high signal/noise ratio for ambient concentrations of nitrous oxide and methane. Presented setup marks the first instance of a HCF-based sensor combining two mid-infrared semiconductor lasers (ICL near 3.3 μm and QCL near 4.5 μm) into a hollow-core fiber, giving good perspective for the development of portable, compact mid-infrared systems that enable multi-species detection with high sensitivity and selectivity.

In many precision sensing applications, the final detection sensitivity is tightly related to the intensity noise of the laser source, which might represent the ultimate limit to the sensor performance. In this framework, we present here the intensity noise characterization of three different mid-infrared semiconductor devices (two quantum cascade lasers and one interband cascade laser). A fast homemade balanced detection system is used to measure the intensity noise of the emitted radiation over a broad Fourier-frequency range, facilitating the observation of shot-noise-limited radiation under specific measurement conditions and detection efficiency. This study allows for a direct performance comparison of the most widespread laser sources in mid-infrared sensing systems.

Interband Cascade Lasers are becoming more and more attractive sources for sensing applications due to their direct mid-IR emission and low power consumption. In many demanding applications of precision spectroscopy and imaging, the laser frequency and intensity noise represent the ultimate limiting factor for the final sensitivity. Here, we first characterize the response of a DFB ICL to a frequency modulation and measure its tuning coefficients. A frequency noise analysis of the ICL is then provided, through experimental investigation of the frequency noise power spectral density, with a particular attention to the technical noise contribution. A possible scheme for frequency stabilization and linewidth narrowing is presented through frequency locking to a high-Q factor microresonator.

Conventional diode lasers suffer from electron-hole recombination outside of their active region [primarily in the optical confinement layer (OCL) but also in the wetting layer in the case of quantum dot (QD) lasers]. This parasitic recombination negatively impacts the laser’s operating characteristics by raising the threshold current, making it more temperaturesensitive (decreasing the characteristic temperature), and leading to sublinear light-current characteristics. One proposed solution to this problem is the addition of asymmetric barrier layers (ABLs) in the OCL – one on each side of the active region. Ideally, if the ABLs are properly tuned, parasitic recombination outside of the active region (i.e., in the entire OCL) should be entirely suppressed. However, due to material constraints, it may be desirable to first manufacture a laser with only a single ABL suppressing parasitic recombination only on one side of the OCL. Here we study the effect of a single ABL on the steady-state operation of QD lasers. Our theoretical model is based on the set of rate equations for charge carriers in the multilayer structure and photons. We show that, despite the limited improvement to output optical power, the addition of a single ABL significantly improves the temperature stability of the laser – its characteristic temperature is much higher than that of the conventional QD laser. Our study thus justifies the concept of using even a single ABL in injections lasers for improving their operating characteristics.

The 2 μm spectral window is a host of a variety of applications in communication and sensing. However, the development of nanoscale emitters for this window has largely stagnated. Here, we present our growth, fabrication, and testing of InAs quantum dash (Qdash) lasers on InP for 2 μm photonics. The samples were grown by molecular beam epitaxy. Ridge waveguide lasers emitted at 1.97 μm, coinciding with the ground-state emission from the Qdash ensemble. A low threshold current density of 131 A/cm² per Qdash layer was calculated under pulsed mode conditions. Good thermal stability was observed up to 50 °C, with a characteristic temperature of 44 K. InAs Qdash on InP is promising 0D laser gain materials for 2 μm communication and sensing.

In this study, we conduct a comparative analysis of an InAs/InP quantum dot diode laser and an InGaAsP/InP quantum well laser. Both lasers are monolithic, 840 μm long devices. They have a two-part buried heterostructure with 10%/90% reflection coated facets and emit at 1550 nm (quantum dot laser) respectively 1570 nm (quantum well laser). In passive mode-locking operational mode, the larger section of both devices is continuously pumped with forward current, while the second, smaller section (50 μm) is operated with reverse absorber voltage. In self mode-locking operation both sections of the laser are connected and pumped with forward current. Femtosecond pulses have been detected in both operational modes.

Results of novel broad area QCL waveguides fabricated at Air Force Research Laboratory are discussed. An “ultrawide” Fabry-Perot waveguide design is modified to bring the waveguide mode closer to the electrical contact and splitting said contact into a Dual Contact Strip. The mode quality in the fabricated ultrawide device is rectified to fundamental-like behavior. Overlapped angled cavity waveguides with a low tilt angle, interrupted with “notches” etched out of areas far from the internal beam path of the fundamental mode, are designed and fabricated. The beam quality of the overlapped angled cavity array demonstrates coherence between outputs.