This PDF file contains the front matter associated with SPIE Proceedings Volume 8277, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We report here the photo-pumped lasing operation of GaAs_1-xBi_x with low-temperature-dependent oscillation wavelengths, and show future prospects for the fabrication of Bi-based lasers. The GaAs_0.975Bi_0.025 active layer was grown at 350 °C by molecular beam epitaxy. The lasing oscillation from a GaAs_0.975Bi_0.025/GaAs semiconductor chip with a Fabry-Perot cavity was observed by photo-pumping. The characteristic temperature of the laser was 83 K in the range between 160 and 240 K. The lasing emission peak energy decreased at a constant rate of -0.18 meV/K, which is 40% of the temperature coefficient of the band gap of GaAs in this temperature range. Above 240 K, the lasing threshold pumping power increased sharply, and the lasing emission peak energy started shifting to higher energies. This result is probably due to carrier behaviors at the GaAs_0.975Bi_0.025/GaAs heterointerface, in which a large valence band offset and an almost flat conduction band offset are expected.

Semiconductor quantum dots (QDs) grown using self-assembly techniques in the Stranski- Krastanov (S-K) mode are expected to be useful for high-performance optical devices such as QD lasers. A significant amount of research has been carried out on the development of highperformance QD lasers because they offer the advantages of a low threshold current, temperature stability, high modulation bandwidth, and low chirp. To realize these high-performance devices, the surface QD density should be increased by fabricating a stacked structure. We have developed a growth method based on a strain-compensation technique that enables the fabrication of a high number of stacked InAs QD layers on an InP(311)B substrate. In this study, we employed the proposed method to fabricate QD laser diodes consisting of highly stacked QD layers and investigated the dependence of the diode parameters on the stacking layer number. We fabricated QD laser diodes with 5, 10, 15, and 20 QD layers in the active region. All of the laser diodes operated at around 1.55 μm at room temperature, and their threshold currents showed clear dependence on the stacking layer number. Laser diodes with more than 10 QD layers showed sufficient gain, i.e., the threshold currents decreased with a decrease in the cavity length. On the other hand, for laser diodes with less than 10 QD layers, the threshold currents increased with a decrease in the cavity length.

A fabrication procedure for electrically pumping photonic crystal membrane devices using a lateral p-i-n junction has been developed and is described in this work. The lateral junction is optimized to efficiently inject current into a photonic crystal nanocavity. We have demonstrated electrically pumped lasing by using the lateral junction to pump a quantum dot photonic crystal nanocavity laser. Continuous wave lasing is observed at temperatures up to 150K, and a threshold of 181nA at 50K is demonstrated - the lowest threshold ever demonstrated in an electrically pumped laser. At room temperature we find that our devices do not lase, but behave as single-mode light-emitting diodes (LEDs). When directly modulated, we find that our LEDs have an ultrafast electrical response up to 10 GHz corresponding to less than 1 fJ/bit energy operation. In addition, we have demonstrated electrical pumping of photonic crystal nanobeam LEDs, and have built fiber taper coupled electro-optic modulators in the same lateral junction platform.

The Bragg diffraction condition of surface-emitting lasing action is analyzed and Γ2-1 mode is chosen for lasing. Two types of lateral cavity photonic crystal surface emitting lasers (LC-PCSELs) based on the PhC band edge mode lateral resonance and vertical emission to achieve electrically driven surface emitting laser without distributed Bragg reflectors in the long wavelength optical communication band are designed and fabricated. Deep etching techniques, which rely on the active layer being or not etched through, are adopted to realize the LC-PCSELs on the commercial AlGaInAs/InP multi-quantum-well (MQW) epitaxial wafer. 1553.8 nm with ultralow threshold of 667 A/cm² and 1575 nm with large power of 1.8 mW surface emitting lasing actions are observed at room temperature, providing potential values for mass production with low cost of electrically driven PCSELs.

Red-emitting diode lasers currently do not offer a small spectral linewidth, which is required in a variety of applications like spectroscopy, interferometry and holography. We will present details of our work on diode lasers with internal surface DBR gratings. These DBR lasers exhibit effective operation of the gratings at four different lasing wavelengths from 632.2 nm to 638.1 nm. 30 μm wide DBR lasers obtain a spectrally stabilized optical output power of 250 mW in pulsed operation. We estimate the reflectivity of the rear grating to exceed 60%.

We report an 830nm high power single spatial mode DFB laser design in the AlGaAs/GaAs system that offers performance close to a Fabry-Perot design as well as manufacturing yield compatible with volume production. Single-mode power in excess of 200mW at case temperature up to 60⁰C is consistently obtained for current below 300mA. This performance level is enabled by use of an efficient, partially-corrugated design and a 2nd order grating located on the p-side. Through careful design and an optimized epitaxial re-growth on the grating, promising reliability results compatible with uncooled application are demonstrated.

AlGaInAs-MQW distributed reflector (DR) laser with semi-insulating buried-heterostructure (SI-BH) has been developed as a high speed light source for short reach data transmissions. The DR laser has DBR mirrors on both sides of a DFB active region. Owing to the increased optical feedback with these DBR mirrors, we can obtain short-cavity lasers without increasing threshold gain. The small active region of the DR laser, which comes from the combination of the short cavity structure and the SI-BH waveguide, makes driving current lower. The fabricated DR lasers have shown excellent characteristics such as stable single mode operation, and high values of relaxation oscillation frequencies under low driving current in a wide temperature range. We have achieved 25- and 40-Gbps direct modulation with low driving current. Using four different wavelength DR lasers, whose lasing wavelengths coincide with LAN-WDM grid, 25.8- Gbps direct modulations with sufficient mask margins was obtained. Using 1.55-μm-wavelength DR lasers, we achieved 40-Gbps direct modulation with 5 dB dynamic extinction ratio with the driving current less than 50 mA even at 85°C. 40-Gbps fiber transmission over 10-km single mode fiber under the operation conditions up to 70°C was also confirmed in 1.3-μm wavelength.

High temperature (>125°C) resistant long-wavelength semiconductor lasers are attractive as light sources in a variety of harsh environments. Here, we report extremely high temperature continuous-wave (CW) operation of QD lasers on GaAs substrate emitted at 1300-nm-range by enhancing gain and increasing the quantized-energy separation of the QD active layers. A suppression of the In out-diffusion during MBE from self-assembled InAs QDs significantly reduced inhomogeneous broadening with high QD sheet density maintained. QD-FP laser exhibited record high CW-lasing temperature for long-wavelength laser of 220°C and QD-DFB laser also exhibited high CW-lasing temperature of 150°C by employing high gain QD active media.

The effect of controlled optical feedback has been investigated for InAs/InP laser structures operating in the 1.55 μm fiber window. Mode locked lasers in particular show extremely small phase noise when subjected to optical feedback, implying a very low timing jitter which is of interest for many applications.

Mode-locked diode lasers generate reliably picosecond or even sub-picosecond optical pulses. Especially, colliding pulse mode-locked (CPM) lasers are promising sources for the generation of short optical pulses with a high repetition frequency. We present experimental results for the generation of ps optical pulses with multi-section ridge waveguide CPM lasers. The lasers with a central emission wavelength of 1065nm consist of an odd number of 100μm long electrically separated sections. CPM operation is achieved by reverse DC biasing the central section which acts as a saturable absorber and forward DC biasing the other (gain) sections. For a cavity length of 1.9mm, passive mode-locking is achieved for a reverse bias of -2.0V applied to the saturable absorber. The repetition frequency is about 43GHz and the pulse length is 3.3ps assuming a sech-pulse shape. The frequency comb spans 6nm assuming a dynamical range of 20dB with a frequency spacing of about 21GHz. At a cavity length of 0.9mm a frequency comb with more than 175 single frequencies over 12nm with a spacing of 45GHz is obtained. Detailed investigations of the optical pulse and frequency comb generation in dependence on cavity length, reverse absorber voltage and DC bias current will be presented.

We develop (Al, In)GaN ridge waveguide laser diodes in the violet-blue spectral region. Varying the indium content of the InGaN quantum wells, we tailor the emission wavelength of our devices for specific applications in the range from 390 nm to 425 nm. Using different commercially available free standing GaN substrates, we adjust the epitaxial design and optimize the processing sequence for the different kinds of substrates. In particular we focus on the ridge formation. We compare different fabrication methods to obtain devices with ridge widths around ≤2 μm. So far, we have achieved threshold currents around 60 mA and slope efficiencies exceeding 1 W/A.

The gain characteristics of AlGaN-delta-GaN QWs active region with varying delta-GaN positions and AlGaN compositions are analyzed. From our finding, the use of AlGaN-delta-GaN QW resulted in ~ 7-times increase in material gain, in comparison to that of conventional AlGaN QW, for gain media emitting at 240 nm. By employing asymmetric QW design, with optimized GaN delta layer position and asymmetric AlGaN composition layers, the optimized optical gain can be achievable for AlGaN-delta-GaN QW structure with realistic design applicable for deep and mid UV lasers.

There is a big need on R&D concerning visible lasers for projection applications. The pico-size mobile projection on the one hand awaits the direct green lasers with sufficiently long lifetimes at optical powers above 50mW. In this paper we demonstrate R&D-samples emitting at 519nm with lifetimes up to 10.000 hours. The business projection on the other hand requires high power operation and already uses blue lasers and phosphor conversion, but there is a strong demand for higher power levels. We investigate the power limits of R&D laser structures. In continuous wave operation, the power is limited by thermal roll-over. With an excellent power conversion efficiency of up to 29% the thermal roll-over is as high as 2.5W for a single emitter in TO56 can. We do not observe significant leakage at high currents. Driven in short pulse operation to prevent the laser from self heating, linear laser characteristics of optical power versus electrical current are observed up to almost 8W of optical power.

We demonstrate a dual wavelength mid-infrared Quantum Cascade Laser (QCL) utilizing a single active region to emit at 5-μm and 9-μm. The novelty lies in the large energy difference between the two lasing energies, achieved through simultaneous injection into the top 2 levels of a 4-level cascade employing InGaAs/InAlAs heterostructures latticematched to InP. The gain and losses at both wavelengths were measured by two different methods, Hakki-Paoli and cutback method, and were compared with theoretical predictions. The results for the gain of the 9-μm laser from the two techniques are consistently lower than theoretical predictions. Moreover, the mid-infrared losses are larger than expected at both wavelengths. We are investigating these devices for their potential application of quantum coherence to achieve lasing without inversion. The intense fields generated by the 9-μm laser are expected to partially eliminate the resonant absorption on the transition of interest at an energy corresponding to the difference between the energies of the two lasers. Our results on the dual wavelength QCL provide insights in the detail charge transport and optical properties of this design concept and open up the possibility for future optimization of inversionless lasers.

We demonstrated the room temperature continuous wave (CW) operation of mid-infrared distributed feedback (DFB) quantum cascade lasers (QCLs) made of strain balanced GaInAs/AlInAs material on InP substrates for sensing CO2 isotope and N2O gas for potential applications that need battery powered portable devices in a sensor network. For the former device at 4.35 μm wavelength, we demonstrated a low threshold voltage of less than 8 V for battery operation and a near circular far field pattern with small divergent angles of 33 by 28 degrees full width at half maximum (FWHM) in vertical and horizontal directions, respectively, for easy collimation. For the latter device at 4.5 μm wavelength, we demonstrated a low CW threshold power consumption of 0.7 W at 20 °C. A side mode suppression ratio (SMSR) of 30 dB was achieved within the whole operating current and temperature ranges for both lasers.

A wide wavelength tuning of an external cavity quantum-cascade (QC) laser based on the anticrossed dual-upper-state to multiple-lower-state design is demonstrated in continuous wave (cw) operation at room temperature. The tuning ranges of 321 cm^-1 (Δλ/λ~22%) in pulsed operation and 248 cm^-1 (Δλ/λ~17%) in cw operation are achieved, despite employment of the active region with translational symmetry. The present tuning range in cw operation substantially exceeds the values obtained with the QC lasers based on conventional broadband active region designs. In addition, the continuous, single mode tuning is realized with its widely homogeneous gain spectrum.

A new deep-well (DW) quantum-cascade laser (QCL) design: Tapered Active-Region (TA), for which the barrier layers in each active region are tapered such that their conduction band edges increase in energy from the injection barrier to the exit barrier, causes a significant increase in the energy difference between the upper laser level and the next higher energy level, E₅₄; thus, resulting in further carrier-leakage suppression compared to DW QCLs. High E₅₄ values (80 -100 meV) are primarily obtained because the energy separation between the first excited states of a pair of coupled QWs (CQWs) is larger when the CQWs are asymmetric than when they are symmetric. Then, we reach an optimized TA-QCL design (λ= 4.7 μm) for which E₅₄ values as high as 99 meV are obtained, while insuring good carrier depopulation of the lower laser level (i.e., τ₃ = 0.2 ps) via the double-phonon-resonance scheme. In addition, the upper-laser-level lifetime increases by ~ 15 % compared to that for conventional QCLs. As a result, the relative carrier leakage decreases to values ≤ 1% and the room-temperature (RT) threshold-current density decreases by ~ 25 % compared to that for conventional QCLs. Then, we estimate that single-facet, continuous-wave (CW) RT wallplug-efficiency values as high as 27 % are possible. Preliminary results from TA QCLs include T₀ and T₁ values as high as 231 K and 797 K, respectively, over the 20-60 °C heatsink-temperature range.

We demonstrate lower temperature sensitivity at high temperature in a strained layer InP/AlGaInP self-assembled quantum dot design grown by MOVPE. The lasers emit between 700 - 730 nm, finding application in photodynamic therapies and bio-photonic sensing. We previously achieved a 300 K threshold current density of 150 Acm^-2 in similar structures for 2mm long lasers with as-cleaved facets, however at elevated temperatures J_th increases rapidly with temperature. To address this issue we redesign the layers around the active regions, consisting of five layers of dots, each grown on a lower confining layer of (Al_0.30Ga_0.70)InP lattice matched to GaAs, formed from 3 mono-layers of InP and with a GaxIn(1-x)P upper confining layer. We grew two series of samples, x=0.43-0.58 with (Al_0.70Ga_0.30)_0.51In_0.49P waveguide claddings, and x=0.52-0.58 (AlInP claddings). Dot properties are strongly influenced by the UCL. Properties varied with Ga fraction. Measured absorption and lasing energies increase with Ga percentage, maintaining a constant separation from upper confining layer transition energies. A Ga fraction of x=0.54 (lightly tensile strained with respect to GaAs) gave the strongest and most well defined absorption, the lowest 300K Jth for 2mm long broad area lasers (uncoated facets) of 180 Acm^-2 and lowest rate of J_th increase with temperature.

We demonstrate broadband (THz) cw operation of a modeless external-cavity quantum-dot semiconductor diode laser. The laser cavity design is based on a frequency-shifted-feedback laser design using an intracavity acoustooptic frequency shifter. The rms intensity fluctuations are < 0.5% and the coherence time is 1 μs. The spectral optical power density is (see manuscript) 0.2 μW/MHz.

Laser diodes offer an interesting alternative to commercially available light sources for the generation of ultrashort pulses. They have the unique feature that they can be directly electrically pumped and that the emission wavelength can be controlled over a huge spectral range by changing the composition of the laser material. Hence they have the potential of being a highly flexible, compact and cost effective light source. However there is a considerable chirp of the pulses generated by a diode laser as a consequence of the strong coupling of real and imaginary part of the susceptibility in the semiconductor. This problem is solved by using an external cavity with intracavity dispersion management. By applying this technique we are able to generate pulse durations with less then 200 fs if an additional external pulse compressor is used. By using such a cavity in a master oscillator power amplifier setup the peak power can be increased up to 6.5 kW. This enables a huge field of possible applications like time domain terahertz spectroscopy or material processing. Anyway for some applications like fluorescence lifetime imaging even the repetition rate of an external cavity laser is too high. To solve this problem an ultrafast semiconductor pulse picking element is implemented to reduce the repetition rate into the kHz region. In conclusion we will demonstrate a compact all semiconductor laser system which is capable to generate sub ps pulses with a high peak power and a variable repetition rate at central wavelength of approximately 840 nm.

Red emitting diode lasers with a narrow spectral line-width and continuous tuning are requested as light sources for interferometric measurements with nm-accuracy. Tuning ranges of about 25 GHz together with a spectral line-width smaller than 10 MHz are necessary. A current-tunable miniaturized 633 nm external cavity diode laser (ECDL) will be presented. The resonator is formed without moving parts between the front facet of a semiconductor gain medium and a reflection Bragg grating (RBG). The RBG has a high reflectivity larger than 95% in a small spectral bandwidth, which is approximately equal to the targeted tuning range. Within this bandwidth, the ECDL is tunable by changing the injection current of the gain medium. The length of the resonator is selected so short, that the distance between the laser modes is larger than the tuning range. Herewith, single mode operation should be guaranteed. The device is mounted on an aluminum nitride bench with a footprint of 5 mm x 10 mm. ECDLs using gain media with different front facet reflectivities of 30% and 70% will be compared. Moreover, results for a device encapsulated in a silicon based gel will be presented. For a device with 30% front facet reflectivity in air, a maximal output power of 10 mW was achieved. The tuning range without any mode-hops was 34 pm, i.e. 25 GHz. The line-width was smaller than 10 MHz. The emitted beam was approximately diffraction limited with a M² ≈ 1.1 in both directions.

We present high power, high reliability, single mode ridge waveguide laser diodes operated in an external cavity configuration. The cavity is formed by installing an InGaAsP/InP laser chip into a cavity with a Bragg grating mirror (BGM). The laser has fiber optical output. The devices are characterized by narrow spectral width operation, in pulsed and CW modes. We obtained 1.7 W output power in single mode fiber at 2 - 10 ns pulses, at a 1550 nm wavelength, with an optical line width of 0.15 nm. For CW excitation, the devices emitted 200 mW optical power with a bandwidth of less than 0.01 nm. These devices exhibit high temperature stability of the laser line spectral position. The construction of these devices enables cost-efficient, narrow bandwidth lasers in the wavelength range from 1300 to 1900 nm.

GaSb-based type-I quantum-well lasers, emitting in the spectral range from 2 to 4 μm are promising light sources for various trace gas sensing systems by means of tunable diode laser absorption spectroscopy (TDLAS). Excellent device performance has been achieved so far in the spectral range from 2 to 3 μm, however, room-temperature operation above 3 μm is much more difficult to achieve. In this work we demonstrate the extension of room-temperature operation wavelength of GaSb-based type-I lasers up to 3.73 μm by implementation of high-quality quinternary AlGaInAsSb heterostructures.

A new approach to tunable mid-infrared lasers, an optically pumped, type-II, InGaSb/InAs gain medium with a chirped distributed feedback grating, has been developed. The chirped grating is patterned using an interferometric lithography (IL) technique with spherical wave fronts and etched into the top cladding of the laser slab waveguide structure. Because the period of grating increases gradually laterally, wavelength tuning is implemented by shifting pump stripe to different positions on the device with different grating periods. Fabry-Perot modes from the cleaved facets are successfully suppressed by fabricating the grating 6° tilted with respect to facets and adjusting the pump stripe normal to the grating. Continuous tuning of 30 nm around 3.1 μm with 320 mW single facet output power at 80K and a 1.6 nm FWHM is reported. The present device is designed in the 3- to 4-μm range which matches a low loss atmospheric transmission window, and covers an important region of molecular vibration spectra, in particular, the hydrocarbon C-H stretch at ~ 3.3 μm, making it suitable for atmospheric pressure remote gas sensing of industrially important small molecules such as methane, hydrogen chloride and ammonia.

Our simulations find that the active quantum wells in previous mid-IR interband cascade laser (ICL) designs have invariably contained far more holes than electrons. Further modeling shows that the carrier populations can be rebalanced by heavily doping the electron injector regions to levels more than an order of magnitude higher than in any earlier devices. The experimental implementation of this strategy has dramatically improved nearly all ICL performance characteristics. For devices emitting at wavelengths in the 3.6-3.9 μm range, this includes pulsed room temperature (RT) threshold current density as low as 170 A/cm², maximum cw operating temperature as high as 109 °C, RT cw output power as high as 159 mW, RT cw wallplug efficiency as high as 13.5%, and RT cw input power as low as 29 mW. We also demonstrate RT cw operation to wavelengths as long as 5.7 μm. The extremely low input power to reach threshold, which is more than 25 times lower than the best ever reported for a quantum cascade laser, will strongly impact battery lifetimes and other system requirements in fielded chemical sensing applications.

An interband cascade laser design has been grown by molecular beam epitaxy using uncracked arsenic and antimony sources. Lasers were fabricated into both broad-area and narrow-ridge devices, with cavity lengths ranging between 1 mm and 4 mm. At 300K, under low-duty-cycle pulsed conditions, threshold current densities for lasers with 2-mm cavity lengths are as low as 395 A/cm², with optical emission centered at a wavelength of ~3.82 μm at 300 K. Continuous-wave (cw) performance of the narrow-ridge devices has been achieved for temperatures up to almost 60°C. We present results of both pulsed (broad-area and ridge) and cw (ridge only) measurements on these lasers, including L-I-V, spectral, cavity-length, and Hakki-Paoli analyses.

Three-dimensional (3-D) above-threshold analyses have been performed on laterally antiguided laser structures operated on leaky modes and twin-waveguide structures operated on guided modes for generating watt-range CW powers in a single, stable spatial mode. The 3-D numerical code takes into account carrier diffusion in the quantum well, thermooptic effects as well as edge radiation losses. Additionally, higher-order optical modes on a 'frozen background' provided by the fundamental mode operation are computed by the Arnoldi algorithm. Approaching the threshold for a competing higher-order mode puts a limit on the range for stable, single-mode operation. The modal structure and stability for both device types are studied over a wide range of the active core width and widths of the buried waveguides bordering the low-index device core. The numerical analyses results indicate an essential role of thermal lensing in transformations of optical-modes shapes and in mode stability loss with the drive current increase. The CW operation in a stable, single spatial mode to powers as high as 2 W is predicted for 2-mm length lasers operated on leaky modes. The maximum CW power in single-guided-mode is predicted as high as 2.46 W for 2-mm length and 3.4 W for 3-mm length devices.

Many applications such as pumping of solid state lasers or ignition of explosives require high optical output powers during a short period. Pulsed operated diode lasers meet these requirements. They can be driven at elevated power levels, well above the ones specified for continuous wave (cw) operation. The optical near-field intensity of a diode laser in this operation regime is a key parameter since it determines the beam properties of the device. High power AlGaAs/GaAs quantum well broad area diode lasers are subjected to single pulse step tests carried out up to and beyond their ultimate limits of operation. Laser near-fields are monitored on a picosecond time scale using a streak-camera setup during pulse currents of up to ~50 times the threshold current. A transition from gain guiding to thermally-induced index guiding of the near-field is shown. A further power increase is prevented by catastrophic optical damage (COD). This sudden failure mechanism is studied in conjunction with filamentary properties of the near-field. The defect growth dynamics resolved on the picosecond time scale is used to gather inside into the physics behind COD.

Compared to longer wavelength devices, the development of reliable red-emitting diode lasers is more challenging due to the applicable semiconductors and the limited stability of the laser facets. Reliable operation over 1,000 h is sufficient for the pumping of fs-Cr:LiSAF lasers or in photodynamic therapy, but laser display technology requires material with the potential to operate failure free over more than 10,000 h. Reliability tests for 650 nm broad area (BA) lasers based on a GaInP single quantum well embedded in AlGaInP waveguide layers will be presented. 100 μm stripe width BA lasers with a length of 1.5 mm were fabricated as low mesa structures. The facets were optically coated including a facet passivation procedure. Mounted on diamond heat spreader and standard C-mounts at 15°C the devices had threshold currents of 550 mA, slope efficiencies of 1.2 W/A, and conversion efficiencies up to 0.33. Aging tests of four BA lasers were performed at output powers of 1.1 W and 1.2 W over a total test time of 20,000 h at a heat sink temperature of 15°C. No failure occurred during the lifetime test. The degradation rates for all devices were smaller than 3x10^-6 h-1. A lifetime of 100,000 h at an operational power of 1.2 W can be estimated. These data proof that the material is well suited for the fabrication of high-brightness diode lasers for laser display technology.

Facets of high-power broad area diode lasers are typically coated with one high-reflecting and one partially reflecting layer to improve slope efficiency and maximize output power. The typical cavity lengths of commercial devices have also been progressively increasing, mainly to reduce temperature rise at the active region and improve laser performance and reliability. The asymmetric reflectivities and long cavity length, however, result in a highly inhomogeneous longitudinal profile of the photon density, which induces a spatially non-uniform carrier distribution, so-called longitudinal spatial hole burning (LSHB). A more uniform longitudinal photon and carrier distribution is believed to improve the overall gain of the cavity and reduce gain saturation, although further study is required to understand the impact of LSHB to power efficiency and its implication in laser design optimization to achieve higher peak powers. We present a phenomenological model that incorporates LSHB to describe longitudinal photon and carrier density inhomogeneity, as well as light-current characteristics of a diode laser. The impact of LSHB on the power efficiency is demonstrated through numerical calculation and can be significant under high-power operations. This presents new guidelines for high-power diode laser designs, in which LSHB imposes limits on reducing facet reflectivity and/or increasing cavity length, beyond which performance deteriorates. Alternatively, effects of LSHB can be mitigated through longitudinal patterning of the waveguide or contact to achieve high-power and high-efficiency diode lasers. We propose specially designed longitudinal patterning of electrical contact to mitigate LSHB. Ongoing device implementation will be used to demonstrate performance benefits.

We successfully demonstrated a multi-striped InGaN-based laser diode (LD) array with an optical output power of 6.3 W under continuous wave operation. The LD array was operated on a conventional metal package without any cooling system. The world highest power operation as InGaN LD array is attributed to thermally optimized layout design taking advantage of highly efficient wide-striped emitters.

The wavelength tunable 1060-nm distributed Bragg reflector (DBR) laser chip consists of three sections: a gain section for lasing, and phase and DBR sections for wavelength control. A micro-heater is lithographically integrated on the top of the DBR section to tune the emission wavelength. The phase section is designed with either a top heater or by current injection to provide fine tuning of the wavelength. The wavelength tuning efficiency of our DBR laser is approximately 9 nm/W at the laser heat sink temperature of 25°C. Single-mode output powers of 686 mW and 605 mW were obtained at a CW gain drive current of 1.25 A and heat sink temperatures of 25°C and 60°C, respectively. Gain-switching by applying 1.1 GHz sinusoidal signal mixed with 600 mA DC injection current produced approximately 58 ps long optical pulses with 3.1 W peak power and 228 mW average power. The average power increased to 267 mW and pulse width broadened to 70 ps with DC bias of 700 mA. In CW operation, one of the applications for high-power single-mode DBR lasers is for non-linear frequency conversion. The light emitted from the 1060-nm DBR laser chip was coupled into a single-mode periodically poled lithium niobate (PPLN) crystal waveguide. Up to 350 mW optical power at 530 nm with the wall-plug efficiency of up to 15% was demonstrated.

Semiconductor laser diodes with a tapered gain region provide a beam quality near to the diffraction limit combined with high output power. They can be configured as lasers with a high-reflectivity coating on the rear facet and a high antireflection coating on the front facet. Additionally as amplifier with an antireflection coating on both facets they can be used in MOPA configuration together with a seed laser. Today amplifiers are commercially established with an optical output-power of 1-2W in a wide range of applications such as Raman spectroscopy or frequency doubling. With a new class of tapered lasers and amplifiers based on improved vertical and lateral designs, the output power for both types can be enlarged significantly. Taper design consists of an overall resonator length of 5mm and a taper angle of 4° providing a small lateral far-field angle <12° (95% power included). Tapered lasers emitting at 976nm have demonstrated 16W at 20A operation current with a wall-plug efficiency of 60% at 8.5W and 59% at 10W. Slope efficiency was 1.05W/A. These values are comparable to 100μm wide broad-area lasers with 5mm resonator length. The longterm stability has been tested by lifetime tests at 10W. The dependence of the beam quality on different parameters has been investigated especially for the high-current regime up to 15A. Whereas for lower power levels no changes have been found, slightly changes occurred at 10W after 1000 hours. Best beam quality was M2<1.8 at 8W for tapered lasers as well as for tapered amplifiers.

High power two-section tapered lasers are promising candidates to generate short optical pulses by Q-switching. The main advantage of these devices is that high peak optical power can be generated by using a low excitation current in the ridge-waveguide section. In this work we analyze the Q-switching dynamics of two-section tapered lasers by means of a simplified three-rate-equation model and we compare the results with measurements in 1060 nm DBR multi/section tapered lasers. The experiments and simulations show similar trends with repetition frequency, modulation signal amplitude and bias conditions. The effect of the driving conditions on the peak power and pulse duration is analyzed. 100 ps pulses with 4.2 W peak power are obtained at 900 MHz repetition frequency.

We report on high power wavelength stabilized single-mode lasers operating at ~1060 nm. Due to their capability of fast gain switching (<1 ns) and internal wavelength stabilization, distributed feedback (DFB) lasers are attractive for utilization as an ultrafast seeder for MOPA fiber laser systems. We successfully developed narrow band single mode DFB laser emitting at the wavelength of ~1060 nm and providing >1.5W of peak power in pulse mode. Time response of the DFB lasers was analyzed using both small and large signal modulation techniques. Furthermore, we present the results of integration of DFB lasers into subnanosecond fiber laser system. We obtained spectrally narrow (~50 pm) optical pulses as short as 170 ps with peak power of ~7 kW.

In the last few years there has been significant progress made in the development of high power and high efficiency quantum cascade lasers in the wavelength range of 4 to 5 microns, while QC lasers in the second atmospheric window have been experiencing performance development at a slower pace. Now similar improvements in the QCL design and growth used for the mid-wave IR (MWIR) can be applied to the long-wave IR (LWIR) with some important differences and adaptations to the challenges presented by the operation at longer wavelengths. These include, among others, a smaller optical confinement, larger losses and inter-miniband leakage, stronger sensitivity to background doping, and the need for thicker waveguides. These factors generally result in the degradation of laser characteristics as the emission wavelength increases. Here we present three new designs in the wavelength range of 8.9 to 10.6 μm and compare their performance and design metrics along with two reference designs in the same spectral range. A selective strain design emitting at 10.3 μm achieved threshold currents and slope efficiencies very close to the reference design emitting at 9.9 μm - thus providing longer wavelength emission with no performance deterioration. From the comparison of the designs presented here, after taking into account the differences in performance metrics of devices designed to operate at longer wavelengths, we can point out the contribution to the laser characteristics of the carrier leakage from the upper lasing state to the upper miniband and to the continuum, and of the coupling strength between injector and upper lasing level. We find that designs with similar metrics but larger splitting between ground injector and upper lasing level exhibit superior performance than those with smaller coupling.

We demonstrate a monolithic Quantum Cascade Laser array. We show phase-locking and single-mode emission at λ=8.4μm. It consists of narrow ridges buried into InP:Fe. Phase-locking is provided by evanescent coupling between adjacent ridges. This μ-structuration is simultaneously an answer to the excessive heating and poor beam quality of broad area lasers. First, it increases the surface of exchange between the multi-layer active region and the InP:Fe, which presents a higher thermal conductivity. Secondly, by choosing carefully the width of emitters and the distance between them, we insure phase locking and control of the supermode emission. We have investigated 2μm wide emitters. In order to study the behavior of evanescent coupling, we have chosen spacing from 1 to 8 microns. The number of emitters ranges from 1 to 64. Technological feasibility was demonstrated up to 64 emitters, and lasing operation up to 32 emitters. We have obtained a pure dual-lobe far-field pattern as expected from an anti-symmetrical supermode. The width of each lobes narrows with an increasing array size as expected from the diffraction theory. The beam quality is insensitive to the injective current. The optical power scales linearly with the number of emitters.

An external cavity with a binary phase grating has been developed to achieve the coherent beam addition of five quantum-cascade lasers emitting at 4.65 μm. The combining of these five emitters is achieved by a binary phase grating or Dammann grating able to separate an incident beam into five beams of equal intensities with a 75% efficiency. A CW output power of ~ 0.65 W corresponding to a combining efficiency of 70% with a good beam quality is obtained. More results concerning output power, combining, efficiency stability and beam quality and spectrum are exposed.

We report the operation of quantum cascade lasers (QCLs) as a mid-infrared photodetector as well as a tunable resonant amplifying detector. When biased at low voltage or without bias, QCL works as a photoconductive or photovoltaic detector. When biased near threshold, QCL operates as a tunable resonant amplifying detector. The detected signal reaches its maximum when the QCL bias is close to its threshold. The maximum signal power is over 28 dB higher compared with the case without bias. These interesting mid-IR detection and amplification characteristics of QCL gain material can help with mid-IR optical filtering and photonics integration.

This work shows the modeling process of computing coupling coefficients of first-order distributed feedback (DFB) metal-semiconductor quantum-well lasers. InGaAsP/InP/metal lasers with wavelength 1300 nm and GaAs/AlGaAs/metal lasers with wavelength 850 nm are discussed and compared. The optical waveguide structure for such a laser has semiconductor layers and a built-in metal grating layer. The interface between the metal layer and its neighboring semiconductor layer has sinusoidal corrugation geometry. To compute the coupling coefficient of the metalgrating waveguide, a model is constructed by Floquet-Bloch formalism (FB). Ray optics technique (RO) is also used to calculate the coupling coefficients. These two methods have close results.

We investigate the modulation properties of a three-guide coupled rectangular ring laser having bidirectional lasing characteristics. Two different rectangular lasers having active section lengths of 250 and 350 μm and total cavity lengths of 580 and 780 μm are fabricated. The rectangular laser cavity consists of four low loss total internal reflection mirrors and an output coupler made out of three passive coupled waveguides. For both the clockwise and counterclockwise circulating directions, the lasing threshold currents of around 38 mA are obtained at room temperature under continuous wave operation. A 3-dB modulation bandwidth over 3 GHz is observed in both circulating directions for two different lasers.

We report on spectrally resolved differential carrier lifetime measurements of un-doped and modulation p-doped 1300nm quantum dot laser. We find that the differential carrier lifetime is significantly reduced for p-doped samples compared to essentially identical un-doped samples in line with enhanced Auger recombination. With increasing temperature the results from the un-doped sample are unchanged, whilst an increase in differential carrier lifetime is observed for the pdoped sample. This is in agreement with the Auger rate reducing with increasing temperature. The effect of modulation p-doping on inter-level scattering times and the recombination rate of the excited state are discussed.

Parameters controlling light generation and emission in semiconductor lasers were analyzed. Effects of facet reflectivity on laser emission and the overall power dissipation were studied. It is shown with typical values that, optimized conditions of facet coating can reduce the laser power dissipation by several hundred milliwatts for optical output levels on the order of 10 mw. A mathematical model was developed for external cavity lasing of semiconductor lasers. Effects of threshold shift and changes in slope efficiency for external cavity operation, as reported in the literature, are explained by our model. Our model also explains reported observations of residual Fabry-Pérot modes of oscillation in external cavity operation. It is shown that anti reflection coating plays the most significant role in decreasing the threshold current in external cavity mode compared to that of Fabry Pérot lasing. It is estimated that a coating reflectivity of 10^-5 with an external grating efficiency of 50% can result in a shift of threshold current by more than 50 mA. The effects of grating efficiency and facet reflectivity on increasing the window of feasible external cavity laser operation with reduced competition from residual modes were studied.