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The use of Optical Coherence Tomography in the field of clinical diagnosis is significant. There are different types of swept source lasers available on the market today, however, their design and associated complex fabrication process increase their cost. In the work presented here, an economical six-section slotted tunable laser operating near 850 nm has been designed and fabricated using a UV optical lithography process. The laser is monolithically integrable without a need for any regrowth step. Initial characterization has confirmed the high quality of the slot geometry and stable single mode operation within its tuning range.

Carrier-induced anti-guiding effects emerging at extremely high injection current densities under short-pulse operation necessitate lateral-waveguide design considerations, that differ from those required when continuous-wave operation is desired. Here, we investigate variations of the lateral index-guiding trench design to achieve an excellent brightness value of 27.4 Wmm−1mrad−1 from tapered-ridge-waveguide lasers with more than 18 W output power under 3.3 ns long pulse operation.

In this letter we present new results on high power 970 nm ridge waveguide lasers based on an extreme double asymmetric epitaxial design. Due to an improved lateral-longitudinal design an M2-value below 1.1 and efficiency over 60% could be maintained at power levels slightly above 2 W. The lasers consist of a narrow mode-filter section at the back facet, a relatively broad section at the front facet for high power capability, and a tapered section in between with a very small taper-angle. We achieved the highest reported conversion efficiency for 1 W single lateral mode power to date of 67%, as well as the highest lateral (linear) brightness of 7.5 W/mm $\bullet$ mrad with 55% efficiency at 2.5 W. Results of first life time tests are presented which show the potential for commercial use.

In this letter, the mode hop characteristics of distributed Bragg-reflector ridge waveguide lasers emitting at 1120 nm with different resonator geometries and facet reflectivities are investigated. The emission wavelength is measured systematically for a wide temperature and pump current range in order to find the setup that provides the largest mode hop free tuning range. The measurements are supplemented by calculations based on a phenomenological model, which allows a prediction of the general emission characteristics.

Modulation properties and temperature stability of short cavity ridge waveguide lasers based on high-quality InAs quantum dots exhibiting a total modal gain of ~90 cm -1 are reported. The 338-μm-long lasers show a threshold current of 20 mA at room temperature and an output powers of up to 36 mW. A maximum small signal modulation bandwidth of 15 GHz was obtained at 14 °C, which degrades to 13 GHz at 60 °C and 8 GHz at 80 °C. Digital modulation at 25 Gb/s between 15 °C and 50 °C was obtained with clear open eyes under constant drive conditions (dc and ac). The maximum data rates of 32 and 35 Gb/s were obtained for 338- and 230-μm-long lasers, respectively, at 14 °C.

The lateral brightness achievable with high-power GaAs-based laser diodes having long and broad waveguides is commonly regarded to be limited by the onset of higher-order lateral modes. For the study of the lateral-mode competition two complementary simulation tools are applied, representing different classes of approximations. The first tool bases on a completely incoherent superposition of mode intensities and disregards longitudinal effects like spatial hole burning, whereas the second tool relies on a simplified carrier transport and current flow. Both tools yield agreeing power-current characteristics that fit the data measured for 5–23 µm wide ridges. Also, a similarly good qualitative conformance of the near and far fields is found. However, the threshold of individual modes, the partition of power between them at a given current, and details of the near and far fields show differences. These differences are the consequence of a high sensitivity of the mode competition to details of the models and of the device structure. Nevertheless, it can be concluded concordantly that the brightness rises with increasing ridge width irrespective of the onset of more and more lateral modes. The lateral brightness 2 W mm − 1 mrad − 1 at 10 MW cm−2 power density on the front facet of the investigated laser with widest ridge (23 µm) is comparable with best values known from much wider broad-area lasers. In addition, we show that one of the simulation tools is able to predict beam steering and coherent beam coupling without introducing any phenomenological coupling coefficient or asymmetries.

Semiconductor FP ridge waveguide lasers based on dual-core vertical coupler structure with different ridge height were fabricated. Their modal gain of these devices around the threshold current were extracted and investigated using the Hakki–Paoli (H–P) method. It is observed that the gain spectrum profile and its 3 dB bandwidth vary with the ridge height. The narrower gain bandwidth of 12 nm was achieved when the ridge height was 4.59 μ m, which is smaller than a quarter of that for the laser with the ridge height of 1.6 μ m. This phenomenon is attributed to the narrowed gain spectrum induced by wavelength filtering effect of the dual-core vertical coupler (DCVC) structure induced by their co-directional coupling, which further shrinks its amplified spontaneous emission (ASE) spectrum. In addition, further simulation results show that the coupling length also affects the bandwidth of the DCVC structure. Within a single coupling length, the longer the coupling length, the narrower the bandwidth, and the larger the coupling efficiency. Such narrow-spectrum gain characteristic of DCVC structure will enable one to fabricate single longitudinal mode lasers with no need of fabricating gratings.

Semiconductor ridge waveguide (RWG) laser fabrication process has been optimized. RWG lasers with different ridge height of 0.39 µm, 0.80 µm, 1.23 µm, 1.55 µm and 1.77 µm were fabricated. All the RWG lasers have the same contact ridge width of 50 µm and cavity length of 1100 µm. The dependence of the ridge height on the temperature performance of these lasers has been systematically investigated. It was found that the optimum ridge height is 1.23 µm, corresponding to an etching depth where all the p-doped layers above the active region were removed. The RWG laser with this ridge height worked up to 100 °C successfully, and also showed the highest characteristic temperature (T 0 ) among all the five group lasers. The T 0 became worse when the ridge height extends below the active region. Our study suggests the significance of the optimization of the ridge waveguide to the laser diode performance.

GaSb-based type-I quantum well wide ridge multimode cascade diode lasers generate more than 360 mW near 3.25 μm at room temperature. Double-step narrow ridge waveguide lasers were fabricated to achieve single spatial mode operation with minimal threshold.

We report on the characteristics of our recent room temperature continuous-wave InGaN quantum well laser diodes grown by by molecular beam epitaxy (MBE). Uncoated ridge waveguide lasers fabricated on freestanding GaN substrates have a continuous-wave (cw) threshold current of 110 mA, corresponding to a threshold current density of 5.5 kA cm -2 . We report on our steps taken to reduce threshold voltage to 7 V. Lasers with uncoated facets have a maximum cw output power of 14 mW and a cw characteristic temperature T 0 of 123 K. Cw laser lifetime vs. power dissipation data is presented, with a maximum lifetime of 2.6 hours for the best laser.

We review the significant progress made in the development of nitride laser diodes by molecular beam epitaxy (MBE). We report on our recent result of room temperature continuous-wave operation of InGaN quantum well laser diodes grown by MBE. Ridge waveguide lasers fabricated on freestanding GaN substrates have a continuous-wave threshold current of 125 mA, corresponding to a threshold current density of 5.7 kA cm–2. The lasers have a threshold voltage of 8.6 V and a lifetime of several minutes. We outline the further technical challenges associated with demonstrating lifetimes of several thousand hours and present an assessment of the potential of MBE as a growth method for commercial quality nitride optoelectronic devices. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Quantum-dot gain material fabricated by self-organized epitaxial growth on GaAs substrates is used for the realization of 980-nm and 1.3-/spl mu/m single-mode distributed feedback (DFB) lasers and edge-emitting microlasers. Quantum-dot specific properties such as low-threshold current, broad gain spectrum, and low-temperature sensitivity could be demonstrated on ridge waveguide and DFB lasers in comparison to quantum-well-based devices. 980-nm DFB lasers exhibit stable single-mode behavior from 20/spl deg/C up to 214/spl deg/C with threshold currents 1 mW was obtained for 30-/spl mu/m cavity length. Low-threshold currents of 4.4 mA could be obtained for 1.3-/spl mu/m emitting 400-/spl mu/m-long high-reflection coated ridge waveguide lasers. DFB lasers made from this material by laterally complex coupled feedback gratings show stable CW single-mode emission up to 80/spl deg/C with sidemode suppression ratios exceeding 40 dB.

We report on a ridge waveguide laser diode with laterally tapered waveguides fabricated in a single growing step using a double patterning method. In this structure, nearly constant output power is obtained with the change of the lower tapered waveguide width, and the facet power ratio of 1.4 to 1.5 is observed over the current range. The asymmetric facet power property is also investigated.

Optical feedback effects on the emission properties of 1.3 μm InGaAsP InP ridge waveguide lasers were studied experimentally for both dc pumping and current modulation. The laser diodes used in our experiments showed a current-induced transition from TM to TE polarization without external feedback. At external optical feedback, the current for the onset of TM/TE transition droped by 25 mA and multiple TM/TE switching was observed over a large current interval. The dynamic response of the external-cavity laser to current pulses of various width was found to depend sensitively on the fine tuning of the external cavity length, resulting in TM/TE oscillations of 2 or 10 GHz, respectively, in the case of 2 ns current pulses. The physical mechanism responsible for the observed behaviour is discussed.

The dependence of the ridge height on the performance of the ridge waveguide (RWG) lasers has been systematically studied. It was found that the optimum ridge height corresponds to an etching depth where all the p-doped layers above the active region were removed. InGaAsN triple-quantum-well RWG lasers with optimized ridge height were fabricated with pulsed anodic oxidation. The lowest threshold current density (Jth) of 711A∕cm2 was obtained from a 10×1300μm2 InGaAsN RWG laser. The corresponding transparency current density (Jtr) of the fabricated InGaAsN RWG lasers was 438A∕cm2 (equivalent to 146A∕cm2 per well).

GaInAsSb-AlGaAsSb multiple quantum-well (QW) lasers with an emission wavelength of 2.81 /spl mu/m are reported. The ridge waveguide lasers with highly strained QWs show continuous-wave laser emission up to 25/spl deg/C; in pulsed mode, the lasers operate up to 60/spl deg/C. For pulsed operation, a threshold current density of 360 A/cm/sup 2/ is found for devices with 30-/spl mu/m stripe width and 2-mm cavity length at room temperature. A low threshold current density at infinite length of 248 A/cm/sup 2/ is derived.

Measurement of the strain in the plane of the active region for 1.3 μm InGaAsP ridge waveguide lasers is presented. A strain model is examined and compared with experimental results. The changes in the refractive index and the optical gain owing to the measured strain are estimated. These results are important information for device simulation, modelling, and interpretation of experimental results.

Narrow ridge waveguide (5um) laser diodes were fabricated using type-I InGaAsSb/AlInGaAsSb quantum well active regions on GaSb. The devices operate in continuous-wave mode near 3254nm with a total light output of 7.4mW at 20°C (uncoated facets). © 2012 OSA., 2012 Conference on Lasers and Electro-Optics, CLEO 2012, 6 May 2012 through 11 May 2012, San Jose, CA

We have investigated the etching characteristics of InAlAs for reactive ion etching (RIE) with mixtures of argon (Ar) and chlorine (Cl 2 ). Nearly vertical walls and a smooth surface morphology can be achieved for etch rates of up to 200 nm/min. For an application we have produced dry-etched ridge waveguide lasers in the In(Ga)AlAs/InGaAs material system with threshold currents as low as 12 mA.

A wide optical gain spectrum with full width at half maximum Δλ≈350 nm has been demonstrated in midinfrared (2.2–2.5 μm) room-temperature-operated InGa(As)Sb/GaSb quantum-well (QW) ridge-waveguide diode lasers. A QW width of 200 A ensured a small energy separation between the first and second quantized states in the QW. Transitions from both quantized states contributed equally to the overall gain spectrum when the optical loss was optimized.

High-performance 1.3-/spl mu/m-emitting quantum-dot lasers were fabricated by self-organized growth of InAs dots embedded in GaInAs quantum wells. The influence of the number of quantum-dot layers on the device performance was investigated. Best device results were achieved with six-dot layers. From the length dependence; a maximum ground state gain of 17 cm/sup -1/ for six dot layers could be determined. Ridge waveguide lasers with a cavity length of 400 /spl mu/m and high-reflection coatings show threshold currents of 6 mA and output powers of more than 5 mV. Unmounted devices can be operated in continuous wave mode up to 85/spl deg/C. A maximum operating temperature of 160/spl deg/C was achieved in pulsed operation for an uncoated 2.5-mm-long ridge waveguide laser.

We have developed distributed-feedback ridge waveguide lasers based on AlGa(In)AsSb emitting at 1.72 /spl mu/m. The distributed feedback is obtained by first-order Cr-Bragg gratings defined on both sides of the laser ridge. The threshold current under pulsed operation at room temperature was around 180 mA and an output power of 1.5 mW was obtained. The gratings lead to a side-mode suppression ratio of 27 dB.

Aging tests were carried out on as‐cleaved InGaAs/GaAs strained quantum‐well ridge waveguide lasers. Although the lasers have immunity to sudden failure and have degradation rate as low as 2×10−5 h−1, after over 6000 h of operation, they readily suffered facet oxidation. The measured oxidation rate was comparable to that of GaAs quantum‐well lasers and one order of magnitude higher than that of lattice‐matched InGaAs/InP lasers. This high oxidation rate is considered to be caused by light absorption in the vicinity of the facet where the band gap is reduced because of the stress variation from biaxial to uniaxial.

This letter describes the use of printing and molding techniques to fabricate plastic photopumped laser that use distributed feedback resonators on ridge waveguides. The results indicate (i) potential optoelectronic applications of a set of emerging low cost lithographic techniques that can pattern a range of materials with submicron resolution on nonplanar substrates, (ii) a new type of plastic laser based on molded organic gain materials, and (iii) that thresholds of plastic distributed feedback ridge waveguide lasers are similar to their planar counterparts.

High-temperature characteristics of InAsP-InAlGaAs strained multiquantum-well (MQW) lasers with a large conduction band discontinuity (/spl Delta/E/sub c/) are demonstrated. The InAsP-InAlGaAs MQW ridge waveguide lasers with narrow stripes exhibited a characteristic temperature as high as 143 K in the range from 25/spl deg/C to 85/spl deg/C. This material system is promising for developing a cooling-system-free 1.3-/spl mu/m laser.

Single-mode InGaAsP QW lasers with wavelengths of 700 to 730 nm are demonstrated. These lasers are attractive as light sources for medical and biological applications because biological tissues are relatively transparent in the near-infrared range. The laser has a 2-micrometer-wide ridge-waveguide structure and achieves single-mode 100-mW CW operation at 80°C with an extremely low operating current of 130 mA and a high characteristic temperature of 182 K. These InGaAsP lasers enable innovative solutions in demanding applications by means of a light source with a compact size and low cost.

The paper presents simulation and experimental studies for the optimization of the ridge profile in ridge waveguide edge-emitting lasers emitting at 980 nm. 2D simulations have been performed, both with in-house developed software and with the commercial simulation package LASTIP, for different etching depths and ridge widths. Several ridge geometries have been fabricated in order to verify experimentally the transverse modal behavior dependence on ridge geometry. The simulation and experimental results are used to derive processing guidelines for achieving stable single-transverse-mode operation in 980 nm ridge waveguide lasers.

The lateral farfield characteristics of ridge-waveguide (RW) lasers emitting around 1,064 nm with an output power of 1.3 W at an injection current of 2 A were measured and modeled. Due to trenches with widths between 2.5 and 20 μm defining the narrow RW, radiation leaks out into the outer regions which suppresses higher-order modes, but which can also lead to a double-peaked lateral farfield of the fundamental mode. A simple model taking into account the thermal lensing effect explains well the lateral farfield behavior observed.

We developed an array of ridge waveguide lasers, including an aluminium-free active region. The linear power density exceeds 100 W/cm. The spectrally combined array was successfully applied to EDFA pumping around 980 nm.

GaInNAs triple quantum well (TQW) and single quantum well (SQW) lasers have been fabricated and compared. The TQW GaInNAs lasers showed much higher characteristic temperature than that of SQW GaInNAs lasers with the same dimension.

It was experimentally demonstrated that a record-low threshold current of 4.3 mA was achieved in long-wavelength, 1.29 mum, GaInNAs-TQW RWG lasers. Moreover, high characteristic temperature of 115 K was attained

Direct modulation of 1.3-/spl mu/m InGaAlAs DFB RWG lasers at 40 Gb/s is experimentally demonstrated. This laser achieves a record extinction ratio of 5 dB under 40-Gb/s modulation. Moreover, it can provide 40-Gb/s modulated transmission over 2 km.