This PDF file contains the front matter associated with SPIE Proceedings Volume 9767, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in spectral region from 3.1 to 3.3 μm. The experiment showed that the increase of the number of cascades from two (previously used in record cascade 3 μm emitters) to three led to critical enhancement of the differential gain and reduction of the threshold current density of λ > 3 μm lasers. Light p-doping of the AlGaAsSb graded section did not introduce extra optical loss but aided hole transport as required for realization of the efficient multi-stage cascade pumping scheme. Corresponding coated three-stage devices with ~100-μm-wide aperture and 3-mm-long cavity demonstrated CW output power of 500 mW near 3.18 μm at 17 °C – more than twofold increase as compared to previous state-of-the-art diode lasers emitting only 200 mW. Three-stage lasers with quantum wells designed to emit in the middle of methane absorption band near 3.25 μm demonstrated record output power levels above 350 mW – nearly threefold improvement over previous non-cascade state-of-the-art diodes. Utilization of the different quantum wells in cascade laser heterostructure was demonstrated to yield wide gain lasers as often desired for tunable laser spectroscopy. Two step etching was applied in effort of simultaneous minimization of both internal optical loss and the lateral current spreading in narrow ridge lasers.

The aim of this paper is to present detailed experimental and theoretical investigations of the behavior of ridge-waveguide (RW) lasers emitting at 670 nm under injection of sub-ns current pulses with high amplitudes. The RW lasers are based on strained GaInP double quantum wells embedded in an asymmetric AlGaInP/AlInP waveguide structure. The width of the ridge is 15 μm and the cavity length 3 mm. The laser diode is mounted on an in-house developed laser driver with a final stage based on GaN transistors, which generates nearly rectangular shaped current pulses with amplitudes up to 30 A and widths down to 300 ps. The pulse width can be varied electronically between 300 ps and 1.2 ns with a repetition frequency up to 1 MHz, which results in a variation of the pulse width of the emitted optical pulses between 200 ps and 1.2 ns. The maximum pulse power depends on the electrical pulse width and reaches 7.2 W for a ridge width of 15 μm. At high pulse current amplitudes the pulse power saturates. Time-dependent simulations with the drift-diffusion simulator WIAS-TeSCA reveal that accumulation of excess electrons under the ridge is the root cause for the power saturation, limiting the maximum achievable output power.

We demonstrate GaAs-based superluminescent diodes (SLDs) incorporating a window-like back facet in a self-aligned stripe. SLDs are realised with low spectral modulation depth (SMD) at high power spectral density, without application of anti-reflection coatings. Such application of a window-like facet reduces effective facet reflectivity in a broadband manner. We demonstrate 30mW output power in a narrow bandwidth with only 5% SMD, outline the design criteria for high power and low SMD, and describe the deviation from a linear dependence of SMD on output power as a result of Joule heating in SLDs under continuous wave current injection. Furthermore, SLDs processed normal to the facet demonstrate output powers as high as 20mW, offering improvements in beam quality, ease of packaging and use of real estate.

Fully microscopic many-body models are used to determine important material characteristics of GaAsBi and InAsBi based devices. Calculations based on the band anti-crossing (BAC) model are compared to first principle density functional theory (DFT) results. Good agreement between BAC-based results and experimental data is found for properties that are dominated by states close to the bandgap, like absorption/gain and photo luminescence. Using the BAC model for properties that involve states in the energetic region of the BAC defect level, like Auger losses and free carrier absorption results in a sharp resonance in the dependence of these quantities for Bismuth concentrations for which the bandgap becomes resonant with the spin-orbit splitting or the BAC-splitting of the light and heavy hole bands. DFT calculations show that the BAC model strongly over-simplifies the influence of the bismuth atoms on the bandstructure. Taking into account the more realistic results of DFT calculations should lead to a reduction of the sharp resonance and lead to enhancements or suppressions for other Bismuth concentrations and spectral regions.

In this paper, a novel strain-induced quantum well intermixing (QWI) technique is employed on InGaP/InAlGaP material system to promote interdiffusion via application of a thick-dielectric encapsulant layer, in conjunction with cycle annealing at elevated temperature. Broad area devices fabricated from this novel cost-effective QWI technique lased at room-temperature at a wavelength as short as 608nm with a total output power of ~46mW. This is the shortest- wavelength electrically pumped visible semiconductor laser, and the first report of lasing action yet reported from post- growth interdiffused process. Furthermore, we also demonstrate the first yellow superluminescent diode (SLD) at a wavelength of 583nm with a total two-facet output power of ~4.5mW - the highest optical power ever reported at this wavelength in this material system. The demonstration of the yellow SLD without complicated multiquantum barriers to suppress the carrier overflow will have a great impact in realizing the yellow laser diode.

Low threshold current BeZnCdSe single quantum-well (SQW) laser diodes (LDs) have been developed. The waveguide was formed of a ridge structure with etching away the top p-type BeMgZnSe/ZnSe:N short-period superlattice cladding layer, and then covered with a thick SiO₂ layer and planarized with chemical-mechanical polishing and reactive ion etching process. Three type LDs with different SQW thickness and Cd content were developed and compared at varying waveguide width and length. Lasing wavelength of 535, 563, and 567 nm were realized respectively, at room-temperature continuous-wave condition with the laser cavity formed by the cleaved waveguide facets coated with high-reflectivity dielectric films. Compared with our previously developed gain-guided diode structure for a 5-μm-wide, 800- μm-long gain-guided green laser with a threshold current and voltage of 68 mA and 10.4 V, a 535-nm green laser with 7- nm-thick SQW can realize a threshold current and voltage of 7.07 mA and 7.89 V, respectively, for a cavity width of 4 μm and length of 300 μm. A 563-nm yellow LD with 4-nm-thick SQW was also developed with 7.4-mA and 8.48-V threshold current and voltage for a 3-μm-wide, 300-μm-long cavity. A 567-nm yellow LD with 7-nm-thick SQW can achieve a threshold current and voltage of 10.8 mA and 8.4 V, respectively, for a cavity length of 300 μm and width of 7 μm. The threshold current and voltage were decreased due to the reinforced confinement of carriers in cavities. The device performance can be significantly improved with much lower power consumption. The threshold current and power consumption is also sufficiently low compared with that of InGaN/GaN green LDs, which will benefit the potential application for ZnSe-based LDs as light sources in full-color display as well as some biomedical devices.

Spectroscopy applications of free-running laser diodes (LD) are greatly restricted as its broad band spectral emission. And the power of a single blue-violet LD is around several hundred milliwatts by far, it is of great importance to obtain stable and narrow line-width laser diodes with high efficiency. In this paper, a high efficiency external cavity diode laser (ECDL) with high output power and narrow band emission at 405 nm is presented. The ECDL is based on a commercially available LD with nominal output power of 110 mW at an injection current of 100 mA. The spectral width of the free-running LD is about 1 nm (FWHM). A reflective holographic grating which is installed on a home-made compact adjustable stage is utilized for optical feedback in Littrow configuration. In this configuration, narrow line-width operation is realized and the effects of grating groove density as well as the groove direction related to the beam polarization on the performances of the ECDL are experimentally investigated. In the case of grating with groove density of 3600 g/mm, the threshold is reduced from 21 mA to 18.3 mA or 15.6 mA and the tuning range is 3.95 nm or 6.01 nm respectively when the grating is orientated in TE or TM polarization. In addition, an output beam with a line-width of 30 pm and output power of 92.7 mW is achieved in TE polarization. With these narrow line-width and high efficiency, the ECDL is capable to serve as a light source for spectroscopy application such as Raman scattering and laser induced fluorescence.

Ultraviolet (UV) lasers with wavelength (λ) < 300 nm have important applications in free-space communication, water/air purification, and biochemical agent detection. Conventionally, AlGaN quantum wells (QWs) are widely used as active region for UV lasers. However, high-efficiency electrically injected mid-UV lasers with λ ~ 250-300 nm are still very challenging as the corresponding AlGaN QWs suffer from severe band-mixing effect due to the presence of the valence sub-band crossover between the heavy-hole (HH) and crystal-field split off (CH) sub-bands, which would result in very low optical gain in such wavelength regime.

Therefore, in this work, we propose and investigate the use of AlInN material system as an alternative for mid-UV lasers. Nanostructure engineering by the use of AlInN-delta-GaN QW has been performed to enable dominant conduction band – HH sub-band transition as well as optimized electron-hole wave function overlap. The insertion of the ultra-thin delta-GaN layer, which is lattice-matched to Al^0.82In_0.18N layer, would localize the wave functions strongly toward the center of the active region, leading to large transverse electric (TE) polarized optical gain (g_TE) for λ~ 250- 300 nm. From our finding, the use of AlInN-delta-GaN QW resulted in ~ 3-times enhancement in TE-polarized optical gain, in comparison to that of conventional AlGaN QW, for gain media emitting at ~ 255 nm. The peak emission wavelength can be tuned by varying the delta layer thickness while maintaining large TE gain. Specifically, gTE ~ 3700 cm^-1 was obtained for λ ~ 280-300 nm, which are very challenging for conventional AlGaN QW active region.

Self-organized InAs quantum dot (QD) lasers based on InP substrate were grown by means of solid source molecular beam epitaxy (SSMBE). Six InAs QD layers with high dot density and highly uniform dot sizes were used as active medium. Broad area (BA) and ridge waveguide (RWG) lasers with different cavity lengths were processed and characterized. Also the influence of a post-growth rapid thermal annealing (RTA) process on the laser characteristics was investigated. The lasers showed a high modal gain of 12 - 14.5 cm^-1 per dot layer and a threshold current density for infinite cavity length of 120 A/cm² per dot layer. In pulsed operation, as-cleaved BA lasers with a cavity length of 292 μm can be operated up to 120 °C. High characteristic temperature values were obtained with T₀ = 125 K (20 °C to 45 °C) and T0 = 100 K up to 120 °C. The slope efficiency of about 0.28 W/A can be kept constant over a wide operating temperature range of up to 100 °C. Mounted RWG lasers with 388 μm cavity length and operated in pulsed mode showed a maximum output power of 120 mW a slope efficiency of 0.42 W/A at 15 °C. The lasers can be operated at 150 °C with 25 mW output power. These results demonstrate very well the temperature insensitive lasing performance expected in nearly ideal QD lasers due to the high density of states localized at the transition energy, which allow a very robust ground state lasing.

In this work, electrically-injected microdisk lasers with diameter varied from 15 to 31μm based on an InAs/InGaAs QD active region have been fabricated and tested in continuous wave regime. At room temperature, lasing is achieved at wavelength around 1.26…1.27 μm with threshold current density about 900 A/cm². Specific series resistance is estimated to be about 10^-4 Ohm•cm². The lasers were tested at elevated temperatures. Lasing is achieved up to 100°C with threshold current of 13.8mA and lasing wavelength of 1304nm in device with 31μm diameter. To the best of our knowledge, this is the highest CW lasing temperature and the longest lasing wavelength ever reported for injection QD microdisk/microring lasers on GaAs substrates. Emission spectrum demonstrates single-mode lasing with side mode suppression ration of 24dB and dominant mode linewidth of 35pm. The far field radiation pattern demonstrates two narrow maxima off the disk plane. A combination of device characteristics achieved (low threshold, long wavelength, operation at elevated temperatures) makes them suitable for application in future optoelectronic circuits for optical interconnect systems.

Due to the discrete density of states distribution and spatial localization of carriers in quantum dot (QD) material, the dynamics should be strongly enhanced in comparison to quantum well material. Based on improved 1.5 μm InAs/InGaAlAs/InP QD gain material short cavity ridge waveguide lasers were fabricated. Devices with cavity, lengths of 230 to 338 μm with high reflection coatings on the backside exhibit record value for any QD laser in small and large signal modulation performance with up to 15 GHz and 36 GBit/s, respectively, obtained at 14 °C. Due to the high temperature stability of threshold current and external differential efficiency, the lasers exhibit also nearly constant modulation bandwidth between 14-60 °C.

Mode-locked semiconductor lasers are a promising source for applications such as ultrafast optical sampling. For such an application, the reduction of timing jitter of the pulse source in a cost-effective manner is a key challenge. While monolithic devices have been the source of much recent interest, external cavity lasers have been less well studied. In this work, the noise of an external cavity laser under passively mode-locked operation is evaluated. A ridge-waveguide super-large optical cavity material system is used.

Ultrashort pulse generation with semiconductor lasers poses a promising alternative to currently available femtosecond laser sources like solid state and fiber lasers. Semiconductor devices can be produced inexpensively, are energy efficient and their wavelength can be designed by band gap engineering. Furthermore they feature a tunable repetition rate. Yet pulse duration and peak power of those devices limit their potential for applications so far. However, recent research demonstrated a reduction of the pulse width from 534 fs (full width half maximum) to 216 fs by shaping the spectrally resolved spectral phase and amplitude inside the cavity. The utilized system consisted of a mode-locked edge emitting semiconductor laser diode, a spatial light modulator inside the external cavity to carry out the pulse shaping and an evolutionary algorithm to optimize the phase and amplitude. Here we present the results of separate phase and amplitude shaping as well as their interaction if optimized together at the same time. Furthermore we demonstrate the flexibility of the phase and amplitude shaping with respect to each other. Thus we expect of our system to enable adaptation to a resonator external dispersion.

The ever-growing need for higher data rates is a driving force for the implementation of higher order coherent communication formats. A key element in coherent detection is the local oscillator (LO) of the decoding unit. This device has to provide coherent light with a narrow linewidth in order to distinguish between different phase and amplitude states of the incoming signal. As predicted by theory, a drastic linewidth reduction is expected from quantum dot (QD) laser materials by the quasi zero-dimensional nature of the gain function. The impact of different gain materials consisting of different numbers of QD layers on the linewidth of distributed feedback (DFB) lasers was investigated and shows an unambiguous dependence on the layer design. Intrinsic linewidths as low as 110 kHz could be determined.

A master oscillator power amplifier system emitting alternatingly at two neighbored wavelengths around 965 nm is presented. As master oscillator (MO) a Y-branch DFB-laser is used. The two branches, which can be individually controlled, deliver the two wavelengths needed for a differential absorption measurement of water vapor. Adjusting the current through the DFB sections, the wavelength can be adjusted with respect to the targeted either “on” or “off” resonance, respectively wavelength λ_on or wavelength λ_off. The emission of this laser is amplified in a tapered amplifier (TA). The ridge waveguide section of the TA acts as optical gate to generate short pulses with duration of 8 ns at a repetition rate of 25 kHz, the flared section is used for further amplification to reach peak powers up to 16 W suitable for micro-LIDAR (Light Detection and Ranging). The necessary pulse current supply user a GaN-transistor based driver electronics placed close to the power amplifier (PA). The spectral properties of the emission of the MO are preserved by the PA. A spectral line width smaller than 10 pm and a side mode suppression ratio (SMSR) of 37 dB are measured. These values meet the demands for water vapor absorption measurements under atmospheric conditions.

Dual-mode multi-section quantum-well distributed feedback lasers with surface gratings have been fabricated, without regrowth, at 1310 and 1550 nm using UV nano-imprint lithography. Several laser and grating sections have been employed to control and stabilize the dual-mode emission and to reduce mode competition. Frequency differences between 15 GHz and 1 THz were achieved for different longitudinal structures. Frequency difference variations of several GHz have been measured under bias modulation with rates up to a few GHz. Higher frequency difference modulation rates are expected from improved measurement setups and from employing quantum dot active regions for further reduction of mode competition.

Monolithic wavelength stabilized diode lasers, e.g. distributed Bragg reflector (DBR) ridge waveguide (RW) lasers, are well-suited light sources for compact and portable Raman spectroscopic systems. In the case of in situ and outdoor investigations, the weak Raman lines are often superimposed by daylight, artificial light sources or fluorescence signals from the samples under study. Among others, shifted excitation Raman difference spectroscopy (SERDS) has been demonstrated as a powerful and easy-to-use technique to separate the Raman lines from disturbing background signals. SERDS is based on subsequential excitation of the sample with two slightly shifted wavelengths. The Raman lines follow the change in the excitation wavelength whereas the non-Raman signals remain unchanged. For SERDS dual-wavelength light sources, e.g., mini-arrays containing two DBR-RW lasers, are requested. Moreover, for portable Raman instruments such as handheld devices robust and reliable excitation light sources with lifetimes > 1,000 h are preferred. In this work, reliability investigations of dual-wavelength DBR-RW mini-arrays over a total test time of 5,000 h are presented. Wavelength stabilization and narrowing of the spectral emission is realized by 10th-order DBR surface gratings defined by i-line wafer stepper technology. The DBR-section has a length of 500 μm, the devices a total length of 3 mm. The ridge waveguide has a stripe width of 2.2 μm. Maximum output powers up to 215 mW per emitter were measured. Over the whole power range, 95 % of the emitted power is within a spectral width of 0.15 nm (2.5 cm⁻¹), which is smaller than the spectral width needed to resolve most Raman lines of solid and liquid samples. In a step-stress test, the devices were tested at 50 mW, followed by 75 mW and finally at 100 mW per emitter. Electro-optical and spectral measurements were performed before, during and after the test. All emitters under study did not show any deterioration of their electro-optical and spectral properties demonstrating their applicability for portable Raman systems.

We demonstrate GaSb-based laterally-coupled distributed-feedback type-I cascade diode lasers emitting near 2.9 μm as potential sources for OH measurements. The laser heterostructures consist of two GaInAsSb quantum well stages in series separated by GaSb/AlSb/InAs tunnel junction and InAs/AlSb electron injectors. Single-mode emission is generated using second order lateral Bragg grating etched alongside narrow ridge waveguides. The lasers were fabricated into 2-mm-long devices, solder-mounted epi-up on copper submounts, and operate at room temperature. With an anti-reflection coating at the emission facet, the lasers exhibit a typical current threshold of 110 mA at 20 °C and emit more than 14 mW of output power. The Bragg wavelength temperature tuning rate was 0.29 nm/°C.

Here we report the demonstration of a Si/InAlGaAs/InP PIN cavity enhanced LED around 1.5 um by using membrane transfer method. The silicon layer is acting not only as the optical guiding layer but also the hole injection layer. The new hybrid integrated LED could be further developed as laser source for silicon photonics.

Optical interconnects are expected to reduce the power consumption of ICT instruments. To realize chip-to-chip or chip-scale optical interconnects, it is essential to fabricate semiconductor lasers with a smaller energy cost. In this context, we are developing lambda-scale embedded active-region photonic-crystal (LEAP) lasers as light sources for chip-scale optical interconnects. We demonstrated the first continuous-wave (CW) operation of LEAP lasers in 2012 and reported a record low threshold current and energy cost of 4.8 μA and 4.4 fJ/bit at 10 Gbit/s in 2013. We have also integrated photonic crystal photodetectors on the same InP chip and demonstrated waveform transfer along 500-μm-long waveguides. Although LEAP lasers exhibit excellent performance, they have to be integrated on Si wafers for use as light sources for chip-scale optical interconnects. In this paper, we give a brief overview of our LEAP lasers on InP and report our recent progress in fabricating them on Si. We bonded the InP wafers with quantum-well gain layers directly on thermally oxidized Si wafers and performed all process steps on the Si wafer, including high-temperature regrowth. After this process modification, we again achieved CW operation and obtained a threshold current of 57 μA with a maximum output power of more than 3.5 μW at the output waveguides. An output light was successfully guided through 500 × 250-nm InP waveguides.

Tunable Laser Absorption Spectroscopy (TLAS) has proven to be a versatile tool for gas sensing applications with significant advantages compared to other techniques. These advantages include real time measurement, standoff detection and ruggedness of the sensor. Especially the Mid-Infrared (MIR) wavelength region from 3 to 6 microns is of great interest for industrial process control and the reduction of pollutants. In this contribution we present novel ICL devices developed to address the crucial air pollutant sulfur dioxide SO₂ at its transition around 4 μm. In general, interband cascade lasers (ICLs) have evolved into important laser sources for the MIR spectral range. Compared to quantum cascade lasers, they offer significant advantages with respect to threshold power density as well as overall power consumption. In contrast to conventional diode lasers, ICLs are able to cover the entire MIR wavelength range of interest. For application in TLAS, single-mode devices are required. In this work application-grade distributed feedback (DFB) ICL devices for addressing SO₂ at the wavelength range around 4 μm are presented. A lateral metal grating, defined by electron beam lithography, is used to achieve DFB operation and hence spectrally single-mode emission. Continuous wave laser operation with threshold power consumption below 100 mW at room temperature, side mode suppression ratio of > 30 dB and wavelength tuning range up to 28 nm are demonstrated.

By stepwise tapering both the barrier heights and quantum-well depths in the active regions of 8.7 μm- and 8.4 μm-emitting quantum cascade lasers (QCLs) virtually complete carrier-leakage suppression is achieved, as evidenced by high values for both the threshold-current characteristic temperature coefficient T₀ (283 K and 242 K) and the slope-efficiency characteristic temperature coefficient T₁ (561 K and 279 K), over the 20–60 °C heatsink-temperature range, for low- and high-doped devices, respectively. Such high values are obtained while the threshold-current density is kept relatively low for 35-period, low- and high-doped devices: 1.58 kA/cm² and 1.88 kA/cm², respectively. In addition, due to resonant extraction from the lower laser level, high differential-transition-efficiency values (89-90%) are obtained. In turn, the slope-efficiency for 3 mm-long, 35-period high-reflectivity (HR)-coated devices are: 1.15-1.23 W/A; that is, 30- 40 % higher than for same-geometry and similar-doping conventional 8-9 μm-emitting QCLs. As a result of both efficient carrier-leakage suppression as well as fast and efficient carrier extraction, the values for the internal differential efficiency are found to be ≈ 86%, by comparison to typical values in the 58-67 % range for conventional QCLs emitting in the 7-11 μm wavelength range.

Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) are demonstrated with high-power, single-lobe surface emission. A 2nd-order Au-semiconductor distributed-feedback (DFB)/ distributed-Bragg-reflector (DBR) grating is used for feedback and out-coupling. The DFB and DBR grating regions are 2.55 mm- and 1.28 mm-long, respectively, for a total grating length of 5.1 mm. The lasers are designed to operate in a symmetric longitudinal mode by causing resonant coupling of the guided optical mode to the antisymmetric surface-plasmon modes of the 2nd-order metal/semiconductor grating. In turn, the antisymmetric longitudinal modes are strongly absorbed by the metal in the grating, causing the symmetric longitudinal mode to be favored to lase, which produces a single lobe beam over a grating duty-cycle range of 36-41 %. Simulations indicate that the symmetric mode is always favored to lase, independent of the random phase of residual reflections from the device’s cleaved ends. Peak pulsed output powers of ~ 0.4 W were measured with single-lobe, single-mode operation near 4.75 μm.

We investigated the multi-mode operation of long-cavity terahertz quantum-cascade lasers (l ≥ 7.5 mm). For QCLs based on an active region design with longitudinal optical (LO) phonon transitions, emission with 30–40 strong modes in a range of more than 270 GHz (9 cm^-1) is observed. For certain operating conditions, we found evidence for stable frequency comb operation, which has been further proven by a self-mixing technique. In general, the multimode dynamics is characterized by a complex alternation of broad- and narrow-beat note regimes for these devices. In contrast, only a single narrow-beat note regime was observed for a different long-cavity device based on a bound-to-continuum active region, for which the emission comb spans only 33 GHz (1.1 cm^-1). We further report a technique based on a tunable bandpass filter to confirm the presence of weak emission modes in the periphery of THz combs, which allowed for the unambiguous detection of modes within a dynamic range of 35 dB. We found that the 35-dB width of the comb can exceed the 20-dB width by a factor of two.

We review a microscopic laser theory for quantum dots as active material for quantum cascade lasers, in which carrier collisions are treated at the level of quantum kinetic equations. The computed characteristics of such a quantum-dot active material are compared to a state-of-the-art quantum-well quantum cascade laser. We find that the current requirement to achieve a comparable gain-length product is reduced compared to that of the quantum-well quantum cascade laser.

Nearly diffraction-limited emission from a distributed Bragg reflector (DBR) tapered diode laser is presented. Intrinsic wavelength stabilization is achieved with a 3rd order DBR grating manufactured by electron beam lithography. At a heatsink temperature of 15°C an optical output power of 12.7 W with an electro-optical efficiency > 40% is obtained. The corresponding emission wavelength is 1030.57 nm and spectral bandwidths of 0.02 nm are measured over the whole power range. At 10.5 W of optical power 8.1 W are contained in the central lobe. The measured beam propagation ratio and brightness are 1.1 (1/e²) and 700 MWcm^-2 sr^-1, respectively. With these parameters, the laser is suitable for applications such as non-linear frequency conversion.

Mode-locked semiconductor laser technology is a promising technology candidate considered by European Space Agency (ESA) for optical metrology systems and other space applications in the context of high-precision optical metrology, in particular for High Accuracy Absolute Long Distance Measurement. For these applications, we have realised a multi-section monolithic-cavity tapered laser diode with a record cavity length of 13.5 mm. The laser operates at 975 nm wavelength. It is designed for the emission of ultra-short optical pulses (<1 ps) at a repetition rate of 3 GHz with an average optical power of 600 mW. It is based on a MOVPE grown laser structure with Aluminium free active region enabling high optical gain, low internal losses and low series resistance. The first results obtained under CW pumping of such centimetre-long laser at 20 °C heatsink temperature show the lasing threshold current as low as 1.27 A and the differential external efficiency as high as 0.55 W/A.

We present experimental results on a three-section master oscillator power amplifier at 1.57 μm to be applied in an integrated path differential absorption LIDAR system for column-averaged atmospheric CO₂ measurements. The application requires high power and good beam quality together with spectral purity and modulation capacity to be used in a random modulation CW LIDAR system. The device consists of a distributed feedback laser acting as master oscillator, a bent modulator section and a tapered optical amplifier section with a tilted front facet to avoid coupled cavity effects. The modulator section acts as an absorber or amplifier when driven at zero or positive bias. Devices with different geometries and epitaxial structures were fabricated and characterized, presenting CW output powers higher than 350 mW and stable single mode emission. At the frequency required by the application (12.5 MHz) a high optical modulation amplitude and extinction ratio were achieved.

Progress in studies to increase the lateral brightness B_lat of broad area lasers is reviewed. B_lat=P_out/BPP_lat is maximized by developing designs and technology for lowest lateral beam parameter product, BPP_lat, at highest optical output power P_out. This can be achieved by limiting the number of guided lateral modes and by improving the beam quality of low-order lateral modes. Important effects to address include process and packaging induced wave-guiding, lateral carrier accumulation and the thermal lens profile. A careful selection of vertical design is also shown to be important, as are advanced techniques to filter out higher order modes.

In the mid-infrared (Mid-IR), arrays of distributed feedback Quantum Cascade Lasers (QCL) have been developed as a serious alternative to obtain extended wavelength operation range of laser-based gas sensing systems. Narrow-linewidth, single mode operation and wide tunability are then gathered together on a single chip with high compactness and intrinsic stability. In order to benefit from this extended wavelength range in a single output beam we have developed a platform for InP-based photonics. After the validation of all required building blocks such as straight waveguides, adiabatic couplers between active and passive waveguides, and echelle grating multiplexers, we are tackling the integration into a single monolithic device. We present the design, fabrication and performances of a tunable source, fully monolithic based on the echelle grating approach. Advantages are design flexibility, relatively simple processing and the need for one single epitaxial growth for the entire structure. The evanescent coupler has been designed to transfer all light adiabatically from the active region to a low loss passive waveguide, while taking advantage of the high gain available in the quantum wells. The multiplexer is based on an etched diffraction grating, covering the whole range of the 30 lasers of the array while keeping a very compact size. These results show the first realization of a monolithic widely tunable source in the Mid-IR and would therefore benefit to the development of fully integrated spectroscopic sensor systems.

We report on room-temperature, continuous-wave operation of single-mode quantum cascade lasers designed for minimal threshold power consumption in the 4 to 10 μm spectral range. Narrow-ridge distributed feedback lasers were developed with plasma-etched sidewall corrugations and infrared-transparent dielectric cladding, enabling fabrication without any epitaxial steps beyond the initial growth of the planar laser wafer. The devices exhibit single-mode emission with stable, mode-hop-free tuning and side-mode suppression greater than 25 dB. We demonstrate packaged single-mode devices with continuous-wave threshold power consumption near 1 W above room temperature.

Quantitative laser spectroscopic measurements of complex molecules that have a broad absorption spectra require broadly tunable laser sources operating preferably in the mid-infrared molecular fingerprint region. In this paper a novel broadband mid-infrared laser source comprising of an array of single-mode distributed feedback quantum cascade lasers was used to target a broadband absorption feature of benzene (C₆H₆), a toxic and carcinogenic atmospheric pollutant. The DFB-QCL array is a monolithic semiconductor device with no opto-mechanical components, which eliminates issues with mechanical vibrations. The DFB-QCLs array used in this work provides spectral coverage from 1022.5 cm^-1 to 1053.3 cm^-1, which is sufficient to access the absorption feature of benzene at 1038 cm^-1 (9.64 μm). A sensor prototype based on a 76 m multipass cell (AMAC-76LW, Aerodyne Research) and a dispersive DFB-QCL array beam combiner was developed and tested. The Allan deviation analysis of the retrieved benzene concentration data yields a short-term precision of 100 ppbv/Hz^1/2 and a minimum detectable concentration of 12 ppbv for 200 s averaging time. The system was also tested by sampling atmospheric air as well as vapors of different chemical products that contained traces of benzene.

When analyses need rapid measurements, cost effective monitoring and miniaturization, tunable semiconductor lasers can be very good sources. Indeed, applications like on-field environmental gas analysis or in-line industrial process control are becoming available thanks to the advantage of tunable semiconductor lasers. Advances in cascade lasers (CL) are revolutionizing Mid-IR spectroscopy with two alternatives: interband cascade lasers (ICL) in the 3-6μm spectrum and quantum cascade lasers (QCL), with more power from 3 to 300μm. The market is getting mature with strong players for driving applications like industry, environment, life science or transports. CL are not the only Mid-IR laser source. In fact, a strong competition is now taking place with other technologies like: OPO, VCSEL, Solid State lasers, Gas, SC Infrared or fiber lasers. In other words, CL have to conquer a share of the Mid-IR application market. Our study is a market analysis of CL technologies and their applications. It shows that improvements of components performance, along with the progress of infrared laser spectroscopy will drive the CL market growth. We compare CL technologies with other Mid-IR sources and estimate their share in each application market.

This paper reports on numerical analysis of longitudinal mode discrimination in coupled-cavity AlInAs/InGaAs/InP quantum cascade lasers. Using a three dimensional, self-consistent model of physical phenomena in edge emitting laser we performed exhaustive analysis of geometrical parameters of CC QCL on spectral characteristics. We discuss the enhancement of the single mode operation in multi-section designs concerning variable dimensions of sections and air gaps between sections and provide designing guidelines assuring single-mode operation. We also show impact of independent current tuning of laser sections inducing Stark effect and heating as additional elements enhancing single mode operation.

The simulation of broad spectral bandwidth light sources (semiconductor optical amplifiers (SOA) and superluminescent diodes (SLD)) for application in ophthalmic optical coherence tomography is reported. The device requirements and origin of key device parameters are outlined, and a range of single and double InGaAs/GaAs quantum well (QW) active elements are simulated with a view to application in different OCT embodiments. We confirm that utilising higher order optical transitions is beneficial for single QW SOAs, but may introduce deleterious spectral modulation in SLDs. We show how an addition QW may be introduced to eliminate this spectral modulation, but that this results in a reduction of the gain spectrum width. We go on to explore double QW structures where the roles of the two QWs are reversed, with the narrow QW providing long wavelength emission and gain. We show how this modification in the density of states results in a significant increase in gain-spectrum width for a given current.

We investigate the beam divergence in far-field region, diffraction loss and optical confinement factors of all-semiconductor and void-semiconductor photonic-crystal surface-emitting lasers (PCSELs), containing either InGaP/GaAs or InGaP/air photonic crystals using a three-dimensional FDTD model. We explore the impact of changing the PC hole shape, size, and lattice structure in addition to the choice of all-semiconductor or void-semiconductor designs. We discuss the determination of the threshold gain from the diffraction losses, and explore limitations to direct modulation of the PCSEL.