High power laser diodes at various wavelengths are described. First, performance and reliability of an optimized large transverse mode diode structure at 808 and 941 nm are presented. Next, data are presented on a 9.5 kW peak power array at 900 nm having a narrow emission bandwidth suitable for pumping Yb:S-FAP laser materials. Finally, results on a fiber-coupled laser diode array at approximately 730 nm are presented.

Al-free active-region, 100 micrometers -stripe lasers operating at a wavelength of 0.98 micrometers (0.81 micrometers ), provide high CW powers: 8W (5W) and `wallplug' efficiencies: 66% (45%). At 0.81 micrometers , the devices are potentially twice as reliable as Al-containing active-layer devices.

This paper reviews extensive Raman scattering, reflectance modulation and luminescence microprobe measurements made on GaInP/AlGaInP, GaAs/AlGaAs and InGaAs/AlGaAs ridge quantum well lasers to investigate (1) laser operating temperatures, (2) built-in mechanical stress, (3) atomic disorder in mirror facets, (4) Si recrystallization effects in mirror coatings, and (5) correlations of these parameters with laser performance and reliability data.

We present a near-field optical beam induced current study of aged high power laser diode arrays (LDA). A near-field scanning optical microscope was used as a light source for creating a photocurrent or a photovoltage in the LDA. Mechanisms generating the signal as well as methodical aspects such as resolution limits and application fields of the technique are discussed. The method is demonstrated to provide insight into the microscopic aging properties of LDAs. Both monitoring of the aging status as well as the localization of defects becomes possible.

A new method of producing nearly diffraction limited beam quality from high-power semiconductor lasers is presented. It is shown, both theoretically and experimentally, that well-designed grating curvature in surface-emitting distributed feedback lasers can alleviate the problems of multi-mode operation and filamentation in wide stripe devices. Surface-emitting devices of this type are capable of very high power without the optical damage limitations of edge-emitting lasers. A method for combining arrays of these lasers with series electrical wiring and precision optical alignment has been developed. A 64 element array was demonstrated that produced approximately 160 W of cm power and could be focused into a small spot.

Anti-phase-type complex-coupled, surface-emitting distributed feedback (CC-SE-DFB) diode lasers are analyzed for the first time. For certain design parameters, both loss-coupled as well as gain-coupled structures are shown to select lasing in the symmetric mode (i.e. orthonormal emission in a single-lobe pattern). For loss-coupled structures we analyze a relatively simple configuration: a metallic second-order grating placed atop a diode-laser structure. This type of SE-CC-DFB structure can simply be fabricated by a lift-off and evaporation process; can operate in a single-lobed, orthonormal beam with a rather uniform near-field intensity pattern, and external differential quantum efficiency, (eta) _d, values in excess of 30%. Gain-coupled devices consist of a semiconductor- based 2^nd-order grating placed at the metal- semiconductor p-side interface. By comparison to loss- coupled devices the threshold gain is reduced by a factor of 2 to 3. A design for realizing 2D single-lobe, surface- emitting sources is discussed.

Filament formation is currently a limiting factor in the development of high power, spatially coherent semiconductor amplifiers. An experimental and theoretical investigation has been conducted to examine the filamentation tendencies of tapered amplifier structures. Experimental measurements of the far-field intensity distribution of a tapered amplifier which has been intentionally `seeded' to filament are compared to a perturbative solution of the paraxial wave equation. This model is used to address several design issues which can be optimized to suppress filamentation. The effect of non-uniform carrier injection due to carrier- induced bandgap changes is also investigated numerically.

Tapered structures fabricated in InGaAsP/InP 1.3-micrometers quantum-well material have been evaluated as lasers and as high-gain high-saturation-power amplifiers. The devices, which had a 1-mm-long ridge-waveguide gain section followed by a 2-mm-long tapered gain region, demonstrated > 1 W output power as lasers, with > 85% of the power in a central diffraction-limited lobe. The amplifiers had an unsaturated gain of 26 dB at 2.0 A and about 30 dB at 2.8 A. Saturated output power at 2.8 A was > 750 mW. At 2.0-A drive current and approximately equals 10-mW input power, the relative intensity noise of the amplified signal was <EQ -160 dB/Hz at frequencies >= 2 GHz.

Growth of II-VI and III-V nitrides by MBE and MOCVD is being studied. Using GaAs as a buffer and ZnMgSSe quaternary alloy as a cladding layer together with a ZnSe/ZnTe superlattice for ohmic contact, room temperature CW operation of II-VI lasers has been achieved. Focus topics include the (1) optical properties of ZnSe-based epilayers, (2) the effect of GaAs buffer surface construction and initial growth condition of ZnSe on the defect density and (3) etch-pit configuration of different type of defects in ZnSe-based epilayers. Multilayer p-GaN/MQW GaN-In_0.1GaN/n-GaN were grown on sapphire substrate using MOVPE and plasma-assisted ionized source beam epitaxy. We investigated the (1) growth and properties of III-V nitride films by LP-MOVPE and PAMBE (Plasma Assisted Molecular Beam Epitaxy), (2) etch-pit and wet etching of GaN/(0001)Al₂O₃, (3) ohmic contacts of GaN and (4) GaN etching by CARIBE.

We have demonstrated the feasibility of reading a high density Digital Versatile Disc using a green ZnSe based laser as the light source. In order to achieve this, high quality optical and electrical properties are required from the laser. We fabricated index-guided lasers to produce a single mode gausian optical beam having 7 micrometers of astigmatism. Operating electrical and optical parameters were measured and compare well with currently available semiconductor lasers for optical storage systems. The read- out experiment shows the favorable noise characteristics of ZnSe based lasers.

Data showing the dependence of lasing wavelength on cavity length for CdZnSe single quantum well, buried ridgeguide lasers is presented. The `slope' of the data is opposite in sign to the slope calculated from conventional theory which includes carrier scattering and bandgap renormalization. The calculated slope with Coulomb enhancement included in the model has the correct sign and the correct magnitude to within 30%. Using the Coulomb enhanced model, the key spectral features reported as evidence for an excitonic gain mechanism in room temperature CdZnSe quantum well lasers are reproduced.

The present work is concerned with threshold characteristics of InGaN multi-quantum well laser diodes. The threshold current is analyzed in detail as a function of quantum well parameters and temperature. The laser structure is optimized to improve its threshold characteristics and increase the maximum radiation power.

The various components for red MOPAs (Master Oscillator Power Amplifier) have been demonstrated and exhibit excellent performance. A major impediment has been the regrowth over material with high aluminum concentration, necessary for short wavelength operation. Nevertheless, amplifiers, DFB, and DBR lasers have been demonstrated in discrete form. Single frequency DBR and DFB lasers using a buried diffraction grating emit over 20 mW with efficiencies of up to 0.4 W/A. The DBR can be tuned over 3 nm using current injection in the grating, and preliminary lifetests indicate good reliability. Discrete flared amplifiers exhibited nearly 1.6 W pulsed, and 500 mW CW output power. The performance of the individual devices and integration issues in developing the MOPA will be discussed.

The optical spectroscopic techniques of photoluminescence and photoluminescence excitation are used to determine the electronic band structure of GaAs-lattice matched bulk (Al_xGa_1-x)_0.52In_0.48P and Ga_0.52In_0.48P-(Al_xGa_1-x)_0.52In_0.48P quantum wells. The compositional dependence of both the direct and indirect band gaps is determined for bulk (Al_xGa_1-x)_0.52In_0.48P epitaxial layers. These measurements allow the composition for which the lowest energy band gap becomes indirect to be deduced (x_c equals 0.50 +/- 0.02). Photoluminescence and photoluminescence excitation studies of Ga_0.52In_0.48P-(Al_xGa_1-x)_0.52In_0.48P quantum wells indicate high structural and optical quality and demonstrate that thin (< 40 angstroms) Ga_0.52In_0.48P wells with Al_0.52In_0.48P-(Al_xGa_1-x)_0.52In_0.48P quantum wells to be determined in an accurate and reliable manner. The conduction band offset, (Delta) E_c, expressed as a fraction of the total direct band gap discontinuity, (Delta) E_G, is found to be approximately independent of barrier Al composition ((Delta) E_c approximately equals 0.67 (Delta) E_G).

The dependence of polarization angle to the quantum well structural parameters and measurement conditions is investigated for GaInP/AlGaInP index-guided laser diodes. The laser diodes that have been studied are 635, 650 and 670 nm band laser diodes with strained quantum well active regions. It has been found that the polarization of radiation along (0 1 -1) direction varies by several degrees from ordinary TE/TM mode determined by the growth direction. The polarization tilt varies with respect to the strain and misorientation of the substrates. The polarization tilt seems to result from the birefringence in the asymmetric crystal structure induced by the strain of GaInP quantum well and the substrate misorientation toward [0 1 1].

Al_xGa_yIn_1-x-yAs/AlGaAs quantum well lasers offer the prospect of devices at intermediate wavelengths between about 690 nm and 750 nm with applications in areas such as photodynamic therapy. The larger thermal conductivity of AlGaAs compared to that of AlGaInP could make the Al_xGa_yIn_1-x-yAs system attractive for high power devices. The incorporation of indium in the quantum well also improves material quality and introduces compressive strain which enhances the intrinsic performance beyond that of the phosphide system due to the larger spin orbit splitting and more similar electron and hole density of states in Al_xGa_yIn_1-x-yAs compared with Ga_xIn_1-xP. We have modeled the gain and radiative recombination of Al_xGa_yIn_1-x-yAs wells with Al_0.45Ga_0.55As barriers at a wavelength in the region 720 to 730 nm. This shows that the intrinsic gain-current characteristic is superior to that of an idealized GaInP/AlGaInP laser at the same wavelength. Devices have been fabricated, which operate at 685 nm and 750 nm at room temperature, and the length dependence of the threshold current, measured as a function of temperature between 140 K and 400 K, analyzed. At the shorter wavelength the room temperature threshold current is dominated by thermally activated carrier loss from the well. Although this could be reduced by further optimization, short wavelength operation is severely restricted by the band gap of the AlGaAs barriers and this material system will be of greatest benefit for devices at wavelengths greater than about 710 nm.

An analysis of the second-order nonlinear polarizability of III-V, [112]-oriented heterostructures is presented. This analysis is used as a basis for the discussion of visible second-harmonic light-emitters. It is then shown experimentally that active blue-green light-emitters can be fabricated from (In,Ga)As/GaAs quantum well laser structures.

A low-threshold second-harmonic generation horizontal cavity surface emitting laser (SHG-HCSEL) operating at 0.49 micrometers under electrical pumping is proposed and theoretical design considerations are presented. The strained InGaAs quantum well (QW) laser, implemented on a nearly optimally oriented (311)B-GaAs substrate, incorporates a reduced Al-content, quasi-phase matched (QPM) single guiding GaAs layer (SGL) structure, a novel double-tapered horizontal waveguide with high reflection-coated cleaved facets, and a metallization- free emission window at the center of the device. The horizontal geometry serves to increase the ratio of fundamental power density within the SHG-region to that at the facets, thereby increasing the laser optical power at the onset of catastrophic optical damage (COD) at the facets. Simulations indicate that surface blue emission (on the order of 14 W/cm² peak, corresponding to 50 (mu) W for a 10 micrometers X 100 micrometers emission window) can be obtained from a compact device, with a moderate taper angle of 3 degree(s), operating well below the COD limit. The model also shows that a SGL thickness of 175 nm corresponds with the second QPM-SHG efficiency peak which coincides with peak optical confinement in the QW. Finally, AlGaAs cladding thickness of 113 nm is found to be the optimum etch condition beneath the SHG emission window.

Asymmetric quantum wells which exhibit a blue-shift in their transition energy with increasing optical pump intensity are of interest for use in a variety of optoelectronic devices. The blue-shift is usually achieved by the piezoelectric effect in quantum wells which are grown to be mismatched with respect to a substrate cut on a polar orientation, usually (111) GaAs. The internal piezoelectric field produces a triangular-shaped well which flattens-out as carriers are injected and screen the field. We have overcome a number of difficulties in this approach by generating the internal field in structures grown on (100) substrates by introducing delta-doping layers of opposite type at the well-barrier interface at each side of the well. In this paper we present details of the electro-optical properties of both kinds of structure and we show that the delta-doped structures exhibit similar blue-shifts to their (111) counterparts. We show that both structures produce laser action under injection from a p-n junction.

We present a surface emitting GaAs/AlGaAs laser diode beam steering device based on the surface mode emission (SME) technique. The SME-laser diodes operate in a single-mode and show efficient surface emission into a single beam with a minimum beam divergence of 0.11 degree(s). We demonstrate a large digital beam steering from this device, which is achieved by mode switching. The special SME-structure supports two single-mode emission wavelengths, which are spaced by 8.38 nm. Digital switching between these two modes by a proper current pulse sequence leads to a steering of the surface emitted single-beam by 4.9 degree(s). Presently the beam steering frequency is limited to a maximum value of 0.15 MHz. An optimized device design for a continuous steering of the single, surface emitted beam is proposed.

Recently uncooled complex-coupled (CC) distributed feedback (DFB) lasers, i.e. where the Bragg grating provides both real and imaginary coupling, emerged as potential low-cost single-mode sources. For the imaginary coupling both gain gratings and absorptive gratings have been realized. In the following for the first time cw-operation of 1.55 micrometers CC- DFB lasers with an absorptive grating up to 115 degree(s)C is presented. The optimized grating structure consists of a conventional buried index grating and a thin n-doped InGaAs absorptive grating layer, both embedded in p-InP. The whole laser structure was grown by MOVPE on n-InP substrate, comprising strain-compensation in the active region. From the overgrown DFB structure 2 micrometers wide ridge-waveguide lasers with its simple fabrication technique were processed. For 350 micrometers long devices threshold currents around 15 mA and differential efficiencies up to 0.3 W/A were measured at 25 degree(s)C. The maximum output power at 85 degree(s)C was 20 mW, cw-operation was observed up to 115 degree(s)C. Preliminary small-signal modulation measurements indicate 3 dB- bandwidths around 16 (6) GHz at 25 degree(s)C (85 degree(s)C). All these characteristics are promising for using this 1.55 micrometers DFB type in a coaxial package without active temperature control.

In the past twenty years there has been considerably effort spent in attempting to explain the temperature dependence of the threshold current (I_th) of InGaAsP-InP based semiconductor lasers. These efforts and the mechanisms which have been presumed responsible for this temperature dependence are reviewed. An alternate means of analyzing the threshold current temperature dependence of these lasers, based on a parameter T_max (rather than the conventional T_o) is proposed, and a relationship between the parameter T_max and adjustable device structural and material parameters is presented. Numerous experimental results are analyzed to evaluate the effects of: internal absorption loss; Auger recombination; carrier leakage; and, optical gain on the temperature dependence of InGaAsP-based lasers. It is concluded that the dominant effect on the threshold current temperature sensitivity stems from the temperature dependence of the optical and differential modal gain.

AlGaInAs semiconductor lasers operating at a wavelength of 1.3 micrometers show superior performance compared to InGaAsP lasers. Ridge guide lasers are fabricated from both material systems by the same process. The characteristic temperature T_o for the AlGaInAs lasers (approximately 100 degree(s)K) is about twice that of the InGaAsP lasers (approximately 50 degree(s)K) resulting in substantially lower thresholds (approximately 34 mA compared to approximately 56 mA) at 85 degree(s)C. The 3-dB modulation frequency of AlGaInAs lasers is about 25% higher than that of the InGaAsP lasers.

In this work, we present our recent achievements for the reliability of the Al-free lasers at high temperatures and high powers. Laser operations up to 30,000 hours were achieved without any degradation in the lasers characteristics from 7 randomly selected InGaAsP/GaAs diodes for (lambda) equals 808 nm. The test were performed for lasers without mirror-coating for optical power of 0.5 to 1 W CW at 50 approximately 60 degree(s)C. To the best of our knowledge, this is the first direct demonstration of the extremely high reliability of Al-free diodes operations at high powers and temperatures for periods of time much longer than practical need (approximately 3 years). The characteristics during the tests are discussed in detail.

We propose a novel material: GaInNAs. It can be formed on a GaAs substrate, and has a bandgap energy suitable for long- wavelength-range laser diodes. The band lineup is ideal for preventing electron overflow. Therefore, applying GaInNAs to long-wavelength-range laser diodes is expected to result in excellent high-temperature performance. We have succeeded in demonstrating continuous-wave operation of GaInNAs/GaAs single quantum well laser diodes at room temperature. The threshold current density was about 1.4 kA/cm². The lasing wavelength was about 1.2 micrometers . We have measured some characteristic parameters of the GaInNAs laser diode under pulsed operation. A high characteristic temperature (T₀) of 127 K and a small wavelength shift per ambient temperature change of 0.48 nm/ degree(s)C were obtained. The experimental results indicate the applicability of GaInNAs to long-wavelength-range laser diodes with excellent high- temperature performance.

The high power operation of mid-infrared quantum cascade lasers at temperatures up to T equals 320 K is reported. Gain at high temperature is optimized by a design combining low doping, a funnel injector and a three well vertical transition active region. A molecular beam epitaxy grown InP top cladding layer is also used to optimize heat dissipation. Peak pulsed optical power of 200 mW and average power of 6 mW are obtained at 300 K and at a wavelength (lambda) equals 5.2 micrometers . At (lambda) equals 8.5 micrometers , the pulsed optical power is 10 mW.

It is shown that semiconductor lasers utilizing intersubband transitions in quantum boxes (IQB lasers) can have lower threshold current densities and operating voltages than quantum cascade (QC) lasers provided that a reduction factor of about 10 can be achieved in the LO phonon-assisted electron relaxation rate. The increased gain for the radiative stage in an IQB laser eliminates the need for a multi-radiative-stage structure (typically 25 in QC lasers). This allows the electron injector and Bragg mirror regions on either side of active region to be separately optimized. Due to their inherently lower input power requirements, IQB lasers operating in the mid-IR should be capable of cw operation at room temperature with high wall plug efficiency and higher average output powers than QC lasers.

We have demonstrated room-temperature CW operation of type- II quantum cascade (QC) light emitting diodes at 4.2 micrometers using InAs/InGaSb/InAlSb type-II quantum wells. The type-II QC configuration utilizes sequential multiple photon emissions in a staircase of coupled type-II quantum wells. The device was grown by molecular beam epitaxy on a p-type GaSb substrate and was composed of 20 periods of active regions separated by digitally graded quantum well injection regions. The maximum average output power is about 250 (mu) W at 80 K, and 140 (mu) W at 300 K at a repetition rate of 1 kHz with a duty cycle of 50%.

Electroluminescence in the long-wavelength (6 - 8 micrometers ) spectrum region is observed from Sb-based type-II interband cascade quantum well structures. The device structures were grown by molecular beam epitaxy on GaSb substrates and comprises many (15 for the first sample and 12 for the second sample) repeated periods of active regions separated by digitally graded multilayer injection regions. The devices have been operated at 300 K and 77 K with an output optical power up to 700 nW. The strong blue shift of the electroluminescent peak with the applied bias due to the Stark effect has also been observed.

GaSb-based and InAs-based semiconductor gain media with band-edge wavelengths between 3.3 to 4 micrometers were used in grating-tuned external cavity configuration. Output wavelength was tuned up to approximately 9.5% of the center wavelength; and power from few tens of mW to 0.2-W peak, 20- mW average was achieved at 80 K operation. The tuning range is approximately 2 - 3 times wider than those of near-IR semiconductor lasers, as expected for mid-IR semiconductors which have smaller electron masses. The external cavity laser had a multimode linewidth of 1 - 2 nm, which was approximately 10 to 20 times narrower than that of a free running laser. Analysis of the gain/loss spectral properties indicates that the tuning range is still severely limited by facet anti-reflection coating and non-optimal wafer structure. Model calculation indicates a tuning range a few times larger is possible with more optimal wafer design.

A series of optically-pumped type-II quantum well lasers with emission wavelengths between 3.2 micrometers and 4.5 micrometers have displayed stimulated emission up to ambient operating temperatures. The 4-constituent design combines the advantages of excellent carrier confinement, potential for significant Auger suppression, and a 2D density-of-states for both electrons and holes. For a device emitting at 4.5 micrometers , the characteristic temperature was 41 K and a peak output power exceeding 2 W/facet was observed at 200 K. Auger coefficients extracted from the threshold pump intensity confirm that Auger losses at 300 K were suppressed by at least a factor of two. We also discuss modeling results for a type-II interband cascade laser structure which is predicted to yield much higher output powers and operating temperatures than conventional bipolar diode lasers, as well as lower threshold currents than the intersubband quantum cascade laser.

We demonstrate midwave infrared diode lasers than span the 3 - 4 micrometers range. Laser active regions are multiple quantum well structures with GaInSb/InAs, type-II, broken gap superlattices for the wells and GaInAsSb for the barriers. The superlattice constituents and dimensions were tailored to reduce losses from Auger recombination. AlSb/InAs superlattices are used for both n-type and p-type laser cladding regions. A device with emission at 3.2 micrometers lased up to 255 K. We have achieved 75 mW per facet at 3.0 micrometers at an operating temperature of 140 K with an 85 microsecond(s) ec input current pulse. Device output appears to be limited by resistive heating. A four-layer, strain-balanced superlattice design offers greater laser efficiency.

GaInAsSb/AlGaAsSb multiple-quantum-well diode lasers grown by organometallic vapor phase epitaxy are reported. The laser structure consists of n- and p-doped Al_0.59Ga_0.41As_0.05Sb_0.95 cladding layer, Al_0.28Ga_0.72As_0.02Sb_0.98 confining layers, and four 15-nm- thick Ga_0.87In_0.13As_0.12Sb_0.88 quantum wells with 20-nm-thick Al_0.28Ga_0.72As_0.02Sb_0.98 barrier layers. These lasers, emitting at 2.1 micrometers , have exhibited pulsed threshold current densities as low as 1.2 kA/cm².

Mid-infrared (3 - 5 micrometers ) lasers and LED's are being developed for use in chemical sensor systems. As-rich, InAsSb heterostructures display unique electronic properties that are beneficial to the performance of these midwave infrared emitters. The metal-organic chemical vapor depositions growth of AlAs_1-xSb_x cladding layers and InAsSb/InAsP superlattice active regions are described. A regrowth technique has been used to fabricate gain-guided, injection lasers using undoped (p-type) AlAs_0.16Sb_0.84 for optical confinement. In device studies, we demonstrate lasers and LEDs utilizing the semi-metal properties of a p-GaAsSb/n-InAs heterojunction as a source for injection of electrons into the active region of emitters. This avoids the difficulties associated with n- type doping of AlAsSb cladding layers required for conventional p-n junction lasers and also provides a means for construction of active regions with multiple gain stages. Gain guided injected lasers employing a strained InAsSb/InAs multi-quantum well active region operated up to 210 K in pulsed mode, with an emission wavelength of 3.8 - 3.9 micrometers . A characteristic temperature of 40 K was observed to 140 K and 29 K from 140 K to 210 K. An optically pumped laser with an InAsSb/InAsP superlattice active region is also described. The maximum operating temperature of this 3.7 micrometers laser was 240 K.

In this paper we investigate power and temperature characteristics of continuous-wave InAsSb lasers operating in the 3 - 4 micrometers wavelength range. Basic laser parameters are shown versus direct current and case temperature with special attention to the distribution of optical power between individual laser modes. CW operation temperature as high as 122 K for the InAsSb/InAsSbP double heterostructure lasers grown by liquid phase epitaxy is reported. The influence of temperature on the characteristics is taking into account several non-radiative processes such as Auger processes and carrier leakage due to diffusion effects. Losses and power saturation that observed at a higher temperature (100 K) led to stable single frequency emission at higher temperatures. CW optical power up to 10 mW has been obtained. It is shown that the mode power is limited to about 2 mW both for multi- and for single mode injection lasers in this spectral range.

Comparative study of threshold current temperature dependence, differential quantum efficiency and light polarization was performed for type I and type II InAsSb/InAsSbP heterostructures as well as for tunneling- injection GaInAsSb/InGaAsSb laser based on this type II broken-gap heterojunction. Experimental evidence of non- radiative Auger-recombination suppression in type II InAsSb/InAsSbP heterolasers with high band-offset ratio (Delta) E_v/(Delta) E_c equals 3.4 was obtained. Reduction of temperature dependence of the threshold current was demonstrated for both kinds of type II lasers. Maximum operation temperature and characteristic temperature T equals 203 K with T₀ equals 40 K and T equals 195 K with T₀ equals 47 K were achieved for type II InAsSb/InAsSbP and tunneling- injection p-GaInAsSb/n-InGaAsSb lasers, respectively.

Threshold characteristics of compressively strained InAlAsSb 3 - 4 micrometers MQW lasers have been studied theoretically. The Auger coefficient dependence on the QW composition has been calculated. It is shown that the internal absorption decreases with strain, which results in weaker temperature dependence of the threshold carrier concentration. It is demonstrated that the strain considerably improves threshold characteristics of InAlAsSb QW laser and increases its limiting operation temperature.

Tensile-strained GaInAsP/InP quantum well (QW) lasers emitting at 1.3 micrometers are investigated. By introducing tensile-strained QW as an active region, low threshold current operation with good temperature characteristic are obtained. The lowest threshold current of 1.0 mA was achieved in a triple QW laser. Enhanced differential gain shows the feasibility of high speed operation. We also verified long-term reliability of approximately 10⁵ hours at 85 degree(s)C, 10 mW condition.

The challenge of making a monolithic electrically tunable laser source for wavelength division multiplexing applications covering at least the 30 nm Erbium doped fiber amplifier optical window led to different approaches to extend the limited tuning range (< 15 nm) of common DBR lasers. In the following, we will comment on three types: the vertical coupler filter laser, the sampled-DBR laser or its improved version the super structure grating DBR (SSG- DBR) laser and the grating assisted coupler with sample rear reflector (GCSR) laser. These lasers use carrier induced index change geared up to achieve the wide electrical tuning. Their performance has been continually improved in term of tuning range, wavelength coverage, output power and side mode suppression. Wavelength coverage of 67 nm in a GCSR laser and of 62 nm in SSG-DBR lasers has been demonstrated requiring a three-tuning-current control. Their tuning mechanism and tuning characteristics are discussed as well as linewidth, power and wavelength switching speed. Various switching experiments have been performed that demonstrate switching times between 4 and 20 ns. The latency incurred when switching between wavelengths is due to the spontaneous carrier lifetime.

Spectral characteristics of 1.3 micrometers DFB lasers with different wavelength detunings are investigated at various temperatures ranging from 20 to 80 degree(s)C. DFB lasers have different amounts of detuning at RT: almost no detuning, a positive detuning of 5 nm and a negative detuning of 25 nm. AR-HR coated 300 micrometers long DFB lasers have typical CW threshold currents of 9 mA, slope efficiencies of 0.27 mW/mA, and coupling coefficients (K) of 60 cm^-1. For the DFB LD with a positive detuning, the detuning of +5 nm at 20 degree(s)C is changed to -15 nm at 80 degree(s)C with the SMSR of 38 dB maintained. Whereas, at 80 degree(s)C Fabry-Perot modes appear from the DFB LD with a negative detuning and a smaller SMSR of 35 dB is obtained from the DFB LD with almost no detuning. These results indicate that a DFB LD with a positive detuning shows better spectral characteristics than others.

Strained-layer MQW-DFB lasers at a wavelength of 1.3 micrometers operating from -40 degree(s)C to 85 degree(s)C without any coolers are demonstrated. On the basis of the leakage current analysis, a laser structure including the active layer and the current blocking layer is chosen to achieve low distortion over wide-temperature-range. Extremely low threshold current of 17 mA at 85 degree(s)C and operation current of 37 mA at 5 mW and 85 degree(s)C are obtained. The lasers realize low distortion of less than -50 dBc at 65 degree(s)C in 78-channel CSO measurements. Furthermore, a fabricated laser module with a coaxial package also achieved low CSO values of -55 dBc under 16-channel loading in the temperature range from -40 degree(s)C to 85 degree(s)C. This uncooled DFB laser module is very useful for return path application in CATV systems.

Recent CATV network systems require high power (P_o >= 20 mW), wide band (1 GHz) and low distortion light sources for use in high capacity network schemes. Furthermore, cost effective light sources are also needed for use in narrowing services. We have developed high performance, 1.3-micrometers partially corrugated waveguide laser diodes (PC-LDs) suitable for use in such CATV networks. The production yield of these PC-LDs with respect to low distortion specifications has been improved about three times over that of conventional distributed feedback (DFB) LDs, and this can be attributed to their characteristic of not being sensitive to grating phases as well as their flat electric field profile along the cavities. Excellent low distortion characteristics (a composite second-order distortion <EQ -60 dBc and a composite triple beat <EQ -70 dBc) for an 80-channel CATV specification were also realized for the PC-LDs over the wide power range of 10 approximately 30 mW by reducing junction capacitance of the current blocking layer. Intermodulation distortion in LDs caused by several nonlinear mechanisms was also investigated using a transfer- matrix method and an electric equivalent circuit model of LDs, taking electric field distribution along the cavity and leakage current that flows into the current blocking layer into account. Resonance oscillation and electric field nonuniformity related distortion are predominant in the lower light-output power region, while leakage current related distortion is dominant in the high-power region. Moreover, external optical feedback resistant characteristics of the PC-LDs were theoretically predicted and experimentally demonstrated. Optical feedback resistance of the PC-LDs was about ten times higher than that of conventional DFB-LDs due to their unique electric field profile along the cavity.

Lasing delays on the order of microseconds have been observed in wide-stripe, thin p-clad, InGaAs single quantum well lasers with `thick' p⁺ cap layers. A lasing delay mechanism involving transient, thermally induced refractive index changes due to ohmic loss in the contact resistance is proposed and investigated using computer modeling.

We theoretically demonstrate that a properly placed distributed-feedback grating can provide spatial-mode discrimination in phase-locked antiguided arrays. These novel devices are particularly attractive because both spatial-mode and frequency selection are accomplished in an index-guided structure using a single mechanism that is virtually independent of thermal instabilities and drive level. The analysis includes the effects of facet coatings and accounts for the random nature of the cleave locations relative to the grating phase.