This PDF file contains the front matter associated with SPIE Proceedings Volume 6485, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We have used pulsed operation, wide area InGaN laser diodes in conjunction with Littrow type external cavity to build a tunable, single mode laser operating around 398 nm. Special coatings had been applied to the device - antireflection coating on the output mirror and high - reflector on the back facet. The tuning range of this device was 5.5 nm, the maximum output power reached 40mW in a single mode operation. This value compares well with the output power of an uncoupled laser diode -170mW. The coupling between the external cavity and the internal resonator is estimated to be around 2.5% for a waveguide dimensions of 20 x 0.3 x 500&mgr;m³.

High-power pure blue laser diodes (LDs) are expected to be adopted to the light sources for full color laser display systems. We have succeeded in fabricating high-power blue (445nm) LDs with an output power of 500mW. The typical operating current, voltage and wall-plug efficiency of these LDs were 480mW, 4.8V and 21.7%, respectively. The lifetime of these LDs was estimated to be over 10,000 hours under continuous-wave operation. Moreover, we succeeded in fabricating the high-luminance white light source by combining the high-power blue LD, optical fiber, and phosphor. In this paper, we report recent progress and future prospects of the high-power GaN-based blue LDs and the new concept of high-luminance white light source.

In this work we present the reliability study of InGaN violet laser diodes fabricated by metaloorganic vapor phase epitaxy on high pressure grown bulk GaN crystals. Our devices were tested both in cw and a pulse regime. We found out that the degradation rate of the laser diodes does not depend on the photon density (at least up to around 50 mW of an output optical power). We show also that the main factor influencing the degradation rate is an operation current density on which the degradation rate depends exponentially. Additionally, we reconfirm that the degradation follows the square root dependence between threshold current and time suggesting that the diffusion may be a main mechanism causing damage of diodes.

We review our recent progress in novel planar blue-violet laser diodes (BV-LDs). The planar BV-LDs are characterized by an inner-stripe waveguide formed with a buried AlN current-blocking layer and a wide regrown cladding layer that also acts as a current and heat spreader. These features enable high-power operation for BV-LDs thanks to their low electrical and low thermal resistance even with a narrow-stripe waveguide. In this paper, we report successful demonstration of the planar inner-stripe BV-LDs by utilizing low-temperature-grown AlN and the regrown cladding layer. Low electrical resistance of the regrown cladding layer was confirmed by scanning spread resistance microscopy. Heat spreading characteristics were also investigated by 2-dimensional thermal simulation. The fabricated BV-LDs with a 1.4-&mgr;m-wide stripe achieved a low threshold current of 32 mA, a low threshold voltage of 4.1 V and greater than 200- mW kink-free output power under CW operation. Moreover, the kink-free output level surpassed 1,000 mW for the 1.0- &mgr;m stripe BV-LDs under 0.03%-duty-pulsed operation. The BV-LDs operated stably for more than 1,000 hours at a high output power of 200 mW at 80oC under a 50%-duty-pulsed condition. After the reliability test, transmission electron microscopy revealed no defect near the regrown interface of the tested LDs.

We measure gain spectra for commercial (Al,In)GaN laser diodes with peak gain wavelengths of 470 nm, 440 nm, 405 nm, and 375 nm, covering the spectral range accessible with electrical pumping. For this systematic study we employ the Hakki-Paoli method, i.e. the laser diodes are electrically driven and gain is measured below threshold current densities. The measured gain spectra are reasonable for a 2D carrier system and understandable when we take into account homogeneous and inhomogeneous broadening. While inhomogeneous broadening is almost negligible for the near UV laser diode, it becomes the dominant broadening mechanism for the longer wavelength laser diodes. We compare the gain spectra with two models describing the inhomogeneous broadening. The first model assumes a constant carrier density, while the second model assumes a constant quasi Fermi level. Both are in agreement with the experimental gain spectra, but predict very different carrier densities. We see our measurements as providing a set of standard gain spectra for similar laser diodes covering a wide spectral range which can be used to develop and calibrate theoretical manybody gain simulations.

We present the status of quantum-cascade lasers without injector regions, based on a four- and five-level staircase, respectively. First lasers were realized at a wavelength of ~ 10 &mgr;m. By applying an optimized design, we achieved high performance injectorless quantum-cascade lasers emitting at ~ 6.7 &mgr;m. On the basis of this design, we investigated the influence of doping density and the number of periods of active sections. A sample with a doping sheet density of 2.5x10¹⁰ cm^-2 and 60 periods of active sections shows record low threshold current densities of 0.75 kA/cm² at 300 K. Recently, we have further extended the wavelength range even down to ~ 4.2 &mgr;m.

We report on the experimental study of the electronic and thermal properties in state of art Sb-based quantum-cascade lasers (QCLs) operating in the range 4.3-4.9 &mgr;m. This information has been obtained by investigating the band-to-band photoluminescence signals, detected by means of an InGaAs-array detector. This technique allowed to probe the spatial distribution of conduction electrons as a function of the applied voltage and to correlate the quantum design of devices with their thermal performance. We demonstrate that electron transport in these structures may be insufficient, thus affecting the tunneling of electrons and the electronic recycling and cascading scheme. Finally, we present the first measurement of the electronic and lattice temperatures and of the electron-lattice coupling in Sb-based QCLs based on a quaternary-alloy. We extracted the thermal resistance (R_L = 9.6 K/W) and the electrical power dependence of the electronic temperature (R_e = 12.5 K/W) of Ga_0.47In_0.53As/Al_0.62Ga_0.38As_1-xSb_x structures operating at 4.9 &mgr;m, in the lattice temperature range 60 K - 90 K. The corresponding electron-lattice coupling &agr;= 9.5 Kcm²/kA) reflects the efficient electronic cooling via optical phonon emission. The experimental normalized thermal resistance R_L^* = 3.9 Kxcm/W demonstrates the beneficial use of quaternary thicker barriers in terms of device thermal management.

Quantum Cascade (QC) lasers are used in many ways such as external cavity mode in the mid-infrared regime. They require at least one of the facets to have very low reflectivity in order to suppress the formation of coupled cavities and also enhance the output power. Although conventional thin film antireflection (AR) coatings have been used to reduce facet reflectivity, they tend to degrade under thermal cycling of the QC lasers. In order to alleviate this problem, we demonstrate the use of sub-wavelength gratings acting as antireflective structures. These gratings have two advantages, (i) they are etched into the QC laser facet and thus avoid adhesion problems (ii) they can, in theory, reduce the facet reflectivity to 0%. Because the sub-wavelength grating period is much smaller than the incident wavelength, it acts as a homogeneous medium. This allows us to combine the thin film theory with the effective medium approach to compute the grating parameters, such as the fill factor and the depth, that result in minimum reflectivity. These gratings were fabricated on &lgr; = 4.9 &mgr;m and &lgr; = 9.8 &mgr;m QC lasers using focused ion beam milling. The lasers were characterized before and after milling the gratings by measuring the light-current-voltage characteristics. A facet reflectivity of about 1-3% was determined from the theory fitted to data. Although this reflectivity is comparable to AR coatings on QCL facets, further optimization is possible.

We have made quantum wells laser diodes by Molecular Beam Epitaxy with emission wavelengths from 2.3 &mgr;m to 3.1 &mgr;m. With growing wavelength, threshold current densities increase almost exponentially. We obtained threshold values as low as 65 A/cm² at 2.3 &mgr;m and 156 A/cm² at 2.62 &mgr;m. At the same time, the valence-band offset decrease from 132 meV (at 2.3 &mgr;m) to 78 meV (at 2.6 &mgr;m). A threshold current density study shows that Auger effect is not the only responsible for the augmentation of J_th. The reduction of internal efficiency η_i has a greater impact on the increase of Jth. The diminution of the holes confinement is incriminated for the degradation of η_i with growing wavelength. Therefore, to improve Jth at higher wavelengths another kind of barrier has to be utilized (for example, thanks to the use of the quinary material AlGaInAsSb).

Single frequency and single spatial mode diode lasers emitting at 852nm are strategic components for systems such as atomic clocks (positioning systems for navigation, in space atomic clock like Galileo or Pharao (cold atom), measurement of fundamental constants), or interferometry applications. We have developed the technological foundations of lasers at 852nm to address these different applications. These include an Al free active region, a single spatial mode ridge waveguide and a DFB (distributed feedback) structure. The device is a separate confinement heterostructure with a GaInP large optical cavity and a single compressive strained GaInAsP quantum well. For an AR-HR coated ridge Fabry Perot laser, we obtain a power of 230mW with M²=1.3. An optical power of 150mW was obtained at 854nm, 20°C for AR-HR coated devices. We obtain a single spatial mode emission and a SMSR over 50dB, both at 150mW. DFB Lasers at 852.12nm, corresponding to the D2 caesium transition, were then realised with a power of 40mW per facet, 37°C for uncoated devices. At 40mW, we determine a M² value of 1.3. We measure a SMSR value around 50dB between 10°C and 80°C. On this last laser run, we obtain very homogeneous spectral linewidth values for five different lasers, measured with a Fabry Perot interferometer. We obtain at 20°C a low average linewidth value of 1.40MHz and 1.10MHz at respectively 40mW and 20mW, together with a low standard deviation of 0.1MHz. At 852.12nm (37°C, 40mW), a low linewidth value of 1MHz was measured, for one laser preliminary tested.

Tapered lasers offer both high-power, together with good beam quality. They contain a ridge waveguide, which acts as a modal filter, and a tapered section of increasing width, which provides high power. Our lasers are based on Al-free active region and the material structure, which was grown by Metallorganic Chemical Vapor Deposition, has very low internal losses of 0.5 cm^-1, a very low transparency current density of 86 A/cm², a high internal quantum efficiency of 86%, and a high characteristic temperature T0 of 171 K. Based on these good results, we have realised fully index-guided single emitters (IG1) with a narrow output width of a few tens of microns, a narrow taper angle of less than 1°, which deliver a maximum power of 1 W CW, together with a good beam quality parameter M²_&sgr;&sgr; =3 at &lgr;=915nm. In order to obtain higher power, we have realized an array of N=6 fully index-guided tapered diode lasers. They deliver a maximum output power of 4W CW. The emitters of the free-running array are not optically coupled to each other, as a consequence, the array has a highly beam quality parameter M² which is at least equal to N times the single emitter one. In order to improve beam quality of diode arrays, several approaches have been investigated to combine them coherently such as evanescent coupling [1], intracavity spatial filtering [2, 3, 4], or a combining technique using a binary phase grating [5] and also the Talbot effect. For the Talbot effect, both monolithic [6] as well as external Talbot cavity [7] configurations have been demonstrated. The Talbot effect refers to a diffraction phenomenon and consists of a reproduction of the field of an illuminated periodic object at certain distances away from the object plane. These distances are multiples of the Talbot distance Z_T=2d²/&lgr;, where d is the spatial periodicity of the object and &lgr; the wavelength. It was studied for many kinds of lasers such as CO₂ lasers [8] or semiconductor lasers [9]. Particular interest was placed on semiconductor lasers because of their small size and high efficiency. Here, we demonstrate for the first time the coherent operation of an array of tapered diode lasers placed in an external Talbot cavity. The in phase supermode is selected by tilting the reflecting mirror. The divergence of the central peak is 0.4° FWHM.

We have been developing a high power, high brightness semiconductor diode laser concept, the Slab-Coupled Optical Waveguide Laser (SCOWL). This laser concept is based upon slab coupling, in which a large, multimode waveguide is converted to a large, single mode waveguide by means of slab coupling of the higher order waveguide modes. SCOWL devices feature large, nearly circular mode sizes (≈4 x 4 &mgr;m and larger) and low modal loss, leading to low gain per unit length, allowing for the construction of long (≈1 cm cavity length) devices. These characteristics allow for high single mode output power. For 980-nm AlGaAs/InGaAs/GaAs-based SCOWL devices, we have demonstrated > 1 W CW output power in a single spatial mode, with brightness levels of > 100 MW/cm²-str. We have constructed high power arrays of SCOWL devices with bar widths of 1 cm and cavity lengths of 3 mm, and have demonstrated > 90 W under CW operation. By using the technique of wavelength beam combining (WBC), which is analogous to wavelength division multiplexing in optical communications, we have been able to combine the outputs from the elements of a SCOWL array to obtain 50 W peak power (30 W CW) with nearly diffraction-limited beam quality. These SCOWL arrays combined by WBC have demonstrated record single bar brightness levels, 3.6 GW/cm²- str. The WBC SCOWL approach is inherently scalable, and offers a route to obtaining kW-class, nearly diffraction limited output from an all-diode laser source. We have also recently extended single SCOWL devices to the multi-Watt regime, demonstrating 2.8 W CW output power from a 980-nm SCOWL with a novel design.

High power single mode InGaAsP/InP DFB laser diodes with narrow linewidth and emitting near 1310nm are key devices for Analog transmission and Sensor applications since they can be rugged and compact sources more suited to harsh environment than solid-state or fiber-based lasers. Typically, the useful output power of DFB sources is limited to about 100mW when sub-MHz linewidth is required Ref [1] by the so-called "re-broadening effect" which causes the spectral linewidth to increase due to spatial-hole burning and other effects. We report here sub-MHz linewidth at output power levels exceeding 500mW resulting from cavity design that successfully addresses the concerns of linewidth re-broadening. Single-frequency operation can be maintained from threshold to the high power operating point without mode hops.

We have calculated recombination rates of an inhomogeneous ensemble of 10⁶ dots by summing localized recombination rates at individual dots, with occupation of dot states in the inhomogeneous distribution specified by Fermi Dirac statistics. We assign the same single dot recombination lifetime (1 ns) to all recombination processes to reveal the effect of localization on the overall rates. For the simplest system of the ground states alone deep state, radiative and Auger recombination processes depend in a similar manner upon the population of electrons in the ground states Consequently the light-current curves for the ground state are approximately linear and are not sensitive to the dominant non-radiative process. When excited states are included Auger recombination becomes dominant at high ensemble populations due to the higher degeneracy assigned to the excited states. While the form of the light-current curves of the total dot system do depend upon the dominant recombination process, an analysis based on power law relations with respect to the ensemble electron population are not appropriate.

We have measured I-V, L-I curves and electroluminescence spectra from InAs/InGaAsP quantum dot (QD) laser diodes (LDs) to investigate how to optimize QD LDs for high output power. The slope of an L-I curve, which is proportional to the differential quantum efficiency, decreased rapidly after lasing due to heat in cw mode. Since the heat problem is not significant in pulse mode, the efficiency is constant up to a rather high current level. In spite of the heat problem, the maximum output power is over 79 mW from a single facet in cw mode at 20 °C. At the same temperature, the lowest threshold current is 132 mA with cavity length, width and QD layers of 500 um, 5 um and 7 stacks, respectively. The characteristic temperatures of QD LD are 188 K and 111 K under pulse and cw mode, respectively. Typical lasing wavelength is around 1.55 um. The slope efficiency, internal loss and gain are 0.368 W/A, 5.2 cm-1 and 15 cm-1, respectively.

Mode-locked semiconductor lasers have great promise for many emerging applications if they can be made sufficiently robust. Typical performance requirements are 1-10 ps pulses with timing jitter ~1 ps and 1-10 GHz repetition rates with peak powers 10-100 mW. Here we consider pulse width and timing jitter in passively mode-locked two-section InAs quantum-dot lasers emitting at 1310 nm. We have identified two distinct, extensive mode-locked regions with robust short pulses and low timing jitter. A record combination of 2 ps pulses and 20 fs/cycle timing jitter (500 fs, from 1-100 MHz), with 100 mW peak power per facet is demonstrated. The implications for practical systems design are discussed.

We summarize recent results in the development of terahertz quantum cascade lasers (QCLs) based on resonant-phonon active region designs. First, we describe attempts to improve high-temperature operation of terahertz QCLs by the use of double-phonon depopulation in order to prevent thermal backfilling of the lower radiative state. While the best of the three tested devices displayed a threshold current density of J_th=170 A/cm² at 5 K and lased up to 138 K in pulsed mode, no temperature advantage was observed compared to single-phonon designs. Also, we describe high power operation of two different THz QCLs that emit up to 248 mW (pulsed) and 135 mW (continuous-wave) at 4.3-4.5 THz, and 75 mW (pulsed) at 4.8-5.0 THz.

MOCVD grown quantum cascade lasers (QCLs) have demonstrated about the same level performance as MBE grown QCLs. With the regrowth capability to fabricate buried heterostructure (BH) waveguides, the QCL output power has been dramatically increased and that opens the door to many mid-IR (and THz) applications. With the stable and high growth rate to produce high performance and reliable BH lasers, commercialization of QCLs with reasonable qualification and affordable price becomes possible. Furthermore with a good gain material and the etching and regrowth capability, optoelectronic integration can be realized using MOCVD growth techniques. We compare the MBE and MOCVD growth techniques and discuss important issues on growth rate stabilization and the control of growth quality at the hetero-interface. We also go over a few growth and integration examples we are working on that are preferentially done by MOCVD. Finally we describe a detailed QCL BH regrowth study and discussed how that can be done right.

Room temperature, continuous wave (CW) operation of distributed feedback (DFB) quantum cascade lasers with widely spaced operation frequencies is reported. The relatively small temperature tuning range of a single device, smaller or equal to approximately 1 % of the wavelength, usually limits their efficiency for spectroscopic investigations. By using a bound-to-continuum active region to create a broad gain spectrum and monolithic integration of different DFB gratings, we achieved high-performance devices with single-mode emission between 7.7 and 8.3 &mgr;m at a temperature of +30 °C. This frequency span corresponds to 8 % of the center frequency. The maximum CW operation temperature achieved was 63 °C at the gain center and as much as 35 °C and 45 °C, respectively, at the limits of the explored wavelength range.

A nonselective wet thermal oxidation technique for AlGaAs-containing heterostructures has been shown to enable the fabrication of a variety of novel high-efficiency, high-power GaAs-based in-plane laser devices. Applied in conjunction with a deep anisotropic dry etch, nonselective oxidation yields a simple, self-aligned high-index-contrast (HIC) ridge waveguide (RWG) structure. The native oxide grown directly on the waveguide ridge simultaneously provides excellent electrical insulation, passivation of the etch-exposed bipolar active region, and a low refractive index cladding, leading to numerous laser performance benefits. The resulting strong lateral optical confinement at the semiconductor/oxide interface (with refractive index contrast &Dgr;n~1.7) enables half-racetrack ring resonator lasers with a record small 6 &mgr;m bend radius. A nearly circularly-symmetric output beam is demonstrated on narrow w=1.4 &mgr;m aperture width straight stripe-geometry lasers with single spatial and longitudinal mode total power output of ~180 mW at 228 mA (9x threshold). With the complete structural elimination of lateral current spreading, the excellent overlap of the optical field with the gain region provides high slope efficiency performance (ranging from >1.0 W/A at w=1.4 &mgr;m to 1.3 W/A for w=150 &mgr;m broad area stripes) for 300 K cw operation of unbonded, p-side up 808 nm InAlGaAs graded-index separate confinement heterostructure (GRINSCH) active region lasers. Using the direct thermal oxidation of a dilute nitride GaAsP/InGaAsN MQW active region, 1.3 &mgr;m emission GaAs-based HIC RWG lasers exhibit a >2X threshold reduction and kink-free operation relative to conventional low-confinement devices. Other recent progress on the application of nonselective oxidation to GaAs-based semiconductor lasers will be reported.

The room-temperature 1.55 &mgr;m continuous-wave (CW) operation of single-lateral mode GaInNAsSb ridge waveguide lasers grown on GaAs is reported. Detailed measurements of the light output power and spectral properties were used to assess the device characteristics as a function of applied current and temperature in both CW and pulsed operation. An exemplary, 3&mgr;×750&mgr;m, device with a 92% high-reflectivity back facet coating exhibited a record low CW threshold current of 63~mA, with a peak output power of 15~mW. High-resolution modal gain spectra were extracted from amplified spontaneous emission measurements yielding the internal loss (8.0~cm^-1, transparency current (50~mA) and the wavelength dependence of the differential gain. The latter was used with careful measurements of the Fabry-Perot mode shift with injection current to determine the linewidth enhancement factor of 2.8 at the transparency current. The first measurement of intrinsic modulation frequency in 1.55 &mgr;m GaInNAsSb lasers is reported, based on the observed relative intensity noise (RIN). The RIN measurements indicate a maximum modulation frequency of 7.2~GHz, which is a promising result for future telecommunications applications.

We present an evaluation of new terahertz sources for biomedical imaging based upon quantum cascade lasers (QCL) and orientation patterned gallium arsenide (OP-GaAs) optical parametric oscillator (OPO). The recently developed terahertz quantum cascade laser emits a peak output power of up to 40mW at 3.7 THz (&lgr;=81&mgr;m). Utilizing coherent terahertz radiation greatly improves the signal to noise ratio of the detection, where it provides a relatively large dynamic range and high spatial resolution. We demonstrated biomedical imaging of malignant tissue contrast in an image of a mouse liver with developed tumors with a THz imaging system based on a QCL. In addition, images of various tissues, such as lung, liver, and brain sections from the laboratory mouse were also obtained. We also explored distinct images from fat, muscle and tendon and measured the absorption coefficient and compared this with FTIR measurements. Another recent technological advance in THz source is based on cascaded optical down-conversion in an OP-GaAs OPO, which provides a tunable THz source over a broad wavelength range with an average power of 1mW at room temperature (RT). The tunability of the OPO source provides additional imaging modes through the ability to excite molecular vibrations and obtain biochemical and structural information in addition to normal absorption or reflectivity contrast.

We discuss peculiarities of the nonlinear optical processes utilizing intersubband nonlinearities in high band offset heterostructures formed by three nearly lattice matched binaries, InAs, GaSb, AlSb, and their alloys. We show that these materials offer unique benefits for nonlinear optics due to great flexibility in designing optical interaction schemes in a wide frequency range and very large values of the nonlinear susceptibilities even involving short-wavelength transitions. The resulting nonlinear conversion efficiency for the second-harmonic or sum-frequency generation is in the mW/W² range even for very short coherence lengths of the order of several &mgr;m.

Recent results on GaAs-based high-speed mode-locked quantum dot (QD) lasers and optical amplifiers with an operation wavelength centered at 1290 nm are reviewed and their complex dependence on device and operating parameters is discussed on the basis of experimental data obtained with integrated fiber-based QD device modules. Hybrid and passive mode-locking of QD lasers with repetition frequencies between 5 and 80 GHz, sub-ps pulse widths, ultra-low timing jitter down to 190 fs, high output peak power beyond 1 W and suppression of Q-switching are reported, showing the large potential of this class of devices for O-band optical fiber applications. Results on cw and dynamical characterization of quantum dot semiconductor optical amplifiers are presented. QD amplifiers exhibit a close-to-ideal noise figure of 4 dB and demonstrate multi-wavelength amplification of three CWDM wavelengths simultaneously. Modelling of QD polarization dependence shows that it should be possible to achieve polarization insensitive SOAs using vertically coupled QD stacks. Amplification of ultra-fast 80 GHz optical combs and bit-error-free data signal amplification at 40 Gb/s with QD SOAs show the potential for their application in future 100 Gb Ethernet networks.

We developed high-power and long-lived AlGaInN-based pure-blue semiconductor lasers emitting in the 440-450 nm wavelength range. The half lifetime (the time for the output power to degrade to half its initial value in constant current mode) was estimated to be more than 10000 hours at a power of 0.75 W under continuous-wave operation at 35°C. Reducing the density of structural defects newly originating from the multiple quantum well active layer and reducing the operating current density were shown to be important for producing high-performance pure-blue lasers.

The use of a silicon-germanium platform for the development of optically active devices will be discussed in this paper, from the perspective of Raman and Brillouin scattering phenomena. Silicon-Germanium is becoming a prevalent technology for the development of high speed CMOS transistors, with advances in several key parameters as high carrier mobility, low cost, and reduced manufacturing logistics. Traditionally, Si-Ge structures have been used in the optoelectronics arena as photodetectors, due to the enhanced absorption of Ge in the telecommunications band. Recent developments in Raman-based nonlinearities for devices based on a silicon-on-insulator platform have shed light on the possibility of using these effects in Si-Ge architectures. Lasing and amplification have been demonstrated using a SiGe alloy structure, and Brillouin/Raman activity from acoustic phonon modes in SiGe superlattices has been predicted. Moreover, new Raman-active branches and inhomogeneously broadened spectra result from optical phonon modes, offering new perspectives for optical device applications. The possibilities for an electrically-pumped Raman laser will be outlined, and the potential for design and development of silicon-based, Tera-Hertz wave emitters and/or receivers.

We present a chip-scale ring resonator Raman silicon laser and amplifier based on a silicon-on-insulator rib waveguide with an integrated p-i-n diode structure. The laser cavity consists of a race-track shaped ring resonator connected to a straight bus waveguide via a directional coupler which couples both pump and signal laser light into and out of the cavity. The optical propagation loss of the ring resonator is reduced to <0.3 dB/cm on average and the effective free carrier lifetime in the waveguide can be shortened to <1 ns under reverse biasing, which efficiently reduces the nonlinear loss due to two-photon absorption induced free carrier absorption. We achieve continuous-wave, single-mode lasing with threshold of <20 mW and slope efficiency of >23%. Based on the same ring resonator architecture, we build a compact, chip-scale Raman amplifier that takes advantage of the cavity enhancement effect to lower the pump power and reduce the device size. We achieve over 3 dB amplification with 3 times less pump power in a 3 cm ring resonator compared to a straight waveguide of the same length. Our experimental results agree with simulations. The ring resonator based laser and amplifier can be integrated on chip with other silicon photonics components to provide a monolithic integrated photonic device.

The current status of the development of the novel dilute nitride Ga(NAsP)/GaP for the monolithic integration of optoelectronic functionality to Si is summarized from the concept, design and epitaxial optimization to the verification of direct energy gap and the realization of electrical injection laser devices at room temperature.

We have studied the growth and characteristics of self-organized InGaAs/GaAs quantum dot lasers and their monolithic integration with waveguides and quantum well electroabsorption modulators on Si. Utilizing multiple layers of InAs quantum dots as effective dislocation filters near the GaAs-Si interface, we have demonstrated high performance quantum dot lasers grown directly on Si that exhibit, for the first time, relatively low threshold current (J_th = 900 A/cm²), large characteristic temperature (T₀ = 278 K), and output slope efficiency ( ⩾0.3 W/A). Focused-ion-beam milling has been used to form high-quality facets for the cavity mirror and coupling groove of an integrated laser/waveguide system on Si. We have also achieved a groove-coupled laser/modulator system on Si that exhibits a coupling coefficient greater than 20% and a modulation depth of ~ 100% at 5 V reverse bias.

We present an electrically pumped silicon evanescent laser that utilizes a silicon waveguide and offset AlGaInAs quantum wells. The silicon waveguide is fabricated on a Silicon-On-Insulator (SOI) wafer and is bonded with the AlGaInAs quantum well structure using low temperature O₂ plasma-assisted wafer bonding. The optical mode in the hybrid waveguide is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V active region providing optical gain via electrical current injection. The device lases continuous wave at 1577 nm with a threshold of 65 mA at 15 °C. The maximum single-sided fiber-coupled cw output power is 1.8 mW. The maximum operating temperature is 40 °C mainly limited by a high series resistance of the device. Operation up to 60 °C should be achievable by lowering the series resistance and thermal impedance.

A master oscillator power amplifier system operating around 670 nm is presented. For the master laser an external cavity diode laser is used with an output power of 25 mW at tunable wavelength and with narrow line width. A tapered amplifier boosts the power up to 970 mW while maintaining the spectral characteristics and keeping the beam quality close to the diffraction limit. The performance of the laser system is presented and a Lithium spectrum depicting the suitability of the system for Lithium spectroscopy, cooling and trapping.

High-brightness tapered lasers and amplifiers at 670 nm with output powers up to 1 W and nearly diffraction limited beam quality were realised. The devices consist of a 750 &mgr;m long straight section and a 1250 &mgr;m long tapered section. Devices with a taper angle of 2°, 3° and 4° were manufactured. The material quality was studied in a long-term test for ridge-waveguide lasers. Devices with 7.5 &mgr;m ridge width show reliable operation at 100 mW output power over more than 10000 h. At a temperature of 15°C a tapered lasers with an angle of 4° reached an output power of 1 W at a current of 2.1 A. The highest conversion efficiency for this device was 24%, the peak wavelength of the emission was 668 nm and the spectral width was smaller than 0.2 nm. The beam propagation factor was M² = 1.7 (1/e²) and M² = 3.0 (second moments). At 500 mW output power, master-oscillator power-amplifier (MOPA) devices showed also a nearly diffraction limited beam quality with M² < 1.5 and reliable operation with degradation rates as low as 7x10^-6 h^-1 over 1200 h. The spectral line-width in this arrangement is determined by the master oscillator and is suitable for high-resolution spectroscopy.

Recently, GaAs-based long wavelength lasers have attracted much attention owing to their advantages such as low substrate cost, mature AlGaAs/GaAs DBR and the high conduction band offset. Among the GaAs-based material system, highly compressive strained InGaAs would be a suitable candidate for the 1300nm VCSEL application while combined with the large gain-cavity detuning technique. In this work, we have successfully fabricated the highly compressivestrained InGaAs broad-area lasers grown by MOVPE. After optimized the epitaxial parameters, these lasers were operating at 1219.56nm with narrow line width of 0.08nm. The InGaAs laser could be operated under continuously waving (CW) situation at 20°C, while its threshold current density Jth was 140A/cm². To our knowledge, the demonstrated InGaAs QW laser has the lowest Jth/QW =46.7 A/cm². The fitted characteristic temperature (T₀) was 146.2K indicating the good electron confinement ability. In addition, by lowering the growth temperature to 475°C, we have also obtained the InGaAs/GaAs double quantum wells whose PL peak was at 1244.5nm and FWHM was 43meV. These good characteristics indicate the possibility of fabricating InGaAs VCSELs lasing at 1300nm.

Regression models are developed for lifetime prediction of diode lasers with increasing or decreasing operating current in the gradual degradation stage of their lifetime. Programmable expressions for laser lifetime extrapolation are presented. Analytical results are explicated by case examples based on measured data from reliability tests of commercially available 10mW and 650nm wavelength InGaAlP lasers conducted under accelerated ageing conditions.