Optical and Quantum Electronics

We investigate the ultra-short pulse propagation through the 3D photonic crystal in the optical region. We made pulse-shape measurements using the femtosecond pulses for the first time and compared the result with the calculation result

The inverted slot line (ISL) structure which has been proposed for millimeter wave LiNbO₃ optical modulator is found to be very simple in structure, and also is capable of achieving perfect velocity matching between carrier and modulating waves. This paper describes the development of a Mach-Zehnder Ti-diffused LiNbO₃ optical intensity modulator using the ISL at 60 GHz. To launch millimeter waves into the ISL structure two types of transitions have been developed successfully. In one type, a balun which is made from semirigid coaxial cable is used to feed millimeter waves into the ISL. In another type, nonradiative dielectric (NRD) waveguide, which can provide the total integration of the modulator with millimeter wave integrated circuits, is used to excite the ISL structure ensuring minimum transition losses. Optical response of 0.17 W^-1 could be obtained at 60 GHz using a Mach-Zehnder interferometer with a rather poor extinction ratio of 5 dB at an optical wavelength of 0.633 μm

A small footprint integrated optical amplifier on Silicon-on-insulator is proposed in this article. By choosing to use optical pumping to drive the device, electrical contacting is avoided and the active waveguide can be made as thin as 100 nm, maximizing the optical confinement in the quantum well layers. Furthermore, the optical pumping is done through the silicon waveguide layer to optimally use the pump light. This leads to a compact device with high gain. We show 8 dB gain in pulsed regime in a 100 μm long device using a peak pump power of only 4.5 mW, while a comparable gain using an electrically pumped device would require an order of magnitude higher power consumption. This is an important step towards a CMOS-compatible optical amplifier for intra-chip optical interconnects.

The effect of inelastic scattering on the electron reflection in multi-quantum barriers has been examined for the first time by using the damped resonant tunneling model. The electron reflectivity deteriorates below unity most significantly at discrete energies in the virtual barrier. The largest dip in reflectivity is about 15% for intraband relaxation time of 0.16 ps. It is also shown that this deterioration can be reduced by utilizing strain-compensated superlattice in the multi-quantum barriers

Scattering of the light beam propagating through a dielectric-slab optical waveguide occurs due to refractive index inhomogeneities of the thin film region and due to boundary irregularities of the filmsubstrate and the film-air interfaces. The quantity and direction of the scattered light are evaluated by means of a perturbation method together with the use of a stationary phase method, for a variety of correlation lengths and variances and the thin film thicknesses. The results show that for a slab waveguide of t/λ=10.0, t and λ being the thickness of thin film and the wavelength of light, the effect of refractive index inhomogeneities is pronounced in comparison with that of waveguide wall irregularities. In this case, therefore, the scattering pattern is determined mainly by the correlation length of refractive index inhomogeneities.

Soliton propagation in a directional fiber coupler is investigated. By using Fourier series analysis technique (FSAT), the effects of radii ratio and intermodal dispersion on soliton switching have been investigated

Computer-aided design tools based on various finite element and beam propagation methods which are indispensable to modeling of microwave photonic devices are briefly reviewed. Some of them are utilized to simulate a traveling-wave Ti:LiNbO₃ optical modulator with a ridge structure

We report successful simulation of current-injection photonic crystal laser showing the spatial-temporal evolution of the electromagnetic field as well as carrier distribution using our dynamical semiconductor medium (DSM) FDTD model, showing its capability in dealing with complex electromagnetic structures and semiconductor carrier dynamics.

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We review here nanophotonic devices based on stacked semiconductor NMs on Si, glass and flexible PET substrates. Photonic crystal Fano resonance-based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Flexible photodetectors and solar cells have also been developed based on the NM stacking processes. Such NM stacking process can lead to a paradigm shift on silicon photonic integration and hybrid organic/inorganic flexible photonics.

We propose a novel type Mach-Zehnder interferometric optical switching device using micro-electro mechanical systems (MEMS) as a phase shifter. As the analytical result, the amount of stretch length is 70 nm at the applied voltage of 60 V per one phase shifter. The pi-shift is achieved using cascade connections of 4-7 shifters.

Spatial solitons are self-trapped optical beams that propagate without changing their spatial shape, since the diffraction and the nonlinear refraction balance each other in a self-focusing medium. In this paper we study the behavior of a soliton beam in a second order material and in a waveguide which, in the plane between the cladding and the substrate, has a distribution of refractive index that follows a Gaussian curve, where the initial position of the maximum of the intensity of the soliton is shifted with respect to the maximum of the index profile. In this situation the beam is attracted towards the center of the index profile, acquiring a certain velocity that allows it to pass this point and to continue to move forward to the other side of the index profile, decreasing its velocity

The expression for inversion density in a gas laser includes an additional term if one allows elastic and/or resonant collisions among the active atoms. This term is a function of the line parameters 1, and 2 and describes the effect of homogeneous broadening on the saturated gain profile. Measurements of these parameters show that the homogeneous broadening in a 0.63 m He-Ne laser plays an important role.

Pulse-code modulation of a 0.6328m He-Ne laser by simultaneous mode-locking and coupling modulation is achieved at a bit-rate of 150 Mbits–1 using a single modulation element. Both modelocking techniques, loss modulation and phase modulation are used and compared. The phase of the output signal is stabilized by means of a phase-locked loop. The influence of the coupling modulation on the resonator energy causes a time-dependent decrease of the output signal amplitude. This effect can be compensated by controlling the coupling voltage. A calculation of the maximum available bitrate for a 2 mm bore He-Ne laser tube is given.

Effect of the carrier shape in the ultra high dense wavelength division multiplexing (WDM) return to zero differential phase shift keying (RZ-DPSK) transmission has been examined through numerical optimization of the pulse form, duty cycle and narrow multiplex/de-multiplex (MUX/DEMUX) filtering parameters.

A new approach to epitaxial GaN growth utilizing radiofrequency plasma-assisted ionized source beam epitaxy (PAISBE) is described. To facilitate the reaction between Ga and atomic nitrogen, the Ga beam was partially ionized and accelerated. The reactive atomic nitrogen flux was obtained from an RF discharge nitrogen plasma with controllable power and frequency. A grid was placed at the exit end of the plasma tube to prevent N inf2 up+ from hitting the substrate. The growth parameters were chosen to systematically investigate the effects of Ga-beam ionization and grid bias. The crystal quality of the PAISBE-grown GaN was analysed by RHEED and x-ray diffraction. The FWHM of a 0.4-m-thick GaN epilayer grown with ionized Ga beam and RF nitrogen plasma with 140W power was measured to be 25 min at (0002) diffraction peak. This and other preliminary data from the present study indicate that PAISBE is a promising technique for GaN growth.

Optical transmission systems, using extremely low-loss fibres in the 1.0–1.4m wavelength region are proposed. Possibilities and expected performances are reviewed for optical components in the low-loss band, such as optical oscillators, modulators, detectors, isolators and fibre connectors. Basic considerations for the systems are described. These systems will have advantages such as a reduction in the number of repeaters and in the system costs by expanding the repeater spacing up to several tens of kilometers. Reliability requirements for repeaters, power supply and maintenance problems will be relaxed by accommodating repeaters in stations instead of manholes.

We report a comparative numerical study of the performances of different linear configurations of a third order cascaded Raman laser CW pumped at the wavelength of 1.064 m by a Nd-doped double clad fibre laser. We compare the maximum conversion efficiencies, slope efficiencies and thresholds of various configurations characterized by different parameters of the fibre, different fibre lengths and third Stokes output couplings to give indications towards Raman laser system optimization.

Data are presented on InGaAsP/InP planar buried heterostructure (PBH) distributed feedback (DFB) lasers operating at 1.3 µm. A four-step MOVPE process and holographic lithography are employed to fabricate these lasers. The CW laser threshold and the slope efficiency from these lasers are 9 mA and 0.23 mW/mA per facet at room temperature. Single-longitudinal-mode operation with side-mode suppression of more than 35 dB is obtained at 5 mW.

In this work, we perform a multi-parameter design study to improve the performance of an uncooled directly modulated 1.3μm GaInNAs ridge waveguide laser for high speed operation especially at high temperature. The static and dynamic performance of the improved design is analyzed using an accurate in-house 2D electro-opto-thermal laser simulator. The improved structure is shown to have a lower threshold current, higher thermal roll-over limit and higher modulation bandwidth—especially under high temperature operation. The improved structure also has a lower vertical beam divergence compared to a reference structure with a conventional design.

Active mode-locking of uncoated InGaAsP diode lasers having an external diffraction grating cavity was investigated experimentally. A high frequency r.f. signal and short-duration electrical pulses were used to drive the lasers. The pulse duration was measured by an ultrafast streak camera. Pulses as short as 13 ps at 1.3m and 29 ps at 1.55m were generated at a repetition rate of 1 GHz. The reason for obtaining broader pulses from the 1.55m laser which had the same structure as the 1.3m diode laser is explained.

A new tensile strained InGaAs/InGaAlAs quantum well structure in the 1.3μm wavelength region is proposed for high temperature characteristics via quantum well band structure and optical gain calculations. To obtain such features, a tensile-strained InGaAs/InGaAlAs quantum well structure, which emits light dominated by TM polarization, is considered. This proposed structure has very high temperature characteristics (T 0>130K) due to its high density of state at the first transition edge. This results clearly show the potential of tensile strained quantum well structure usage for the high temperature operation of quantum well semiconductor lasers.

In(Ga)As/GaAs quantum-dot (QD) lasers with emission wavelength at 1295 nm at room temperature are fabricated. The laser active region contains a threefold stack of QD layers with surface dot density of 4.56 1010 cm–2. The laser structure is aluminum-free with InGaP as cladding layers. Threshold current density of a narrow stripe laser of 8 m wide and 3.5 mm long is 152.5 A/cm2. The highest relaxation oscillation frequency measured at room temperature is 1.8 GHz, corresponding to a modulation bandwidth of 2.8 GHz due to the small damping factor. From the above measurement, the differential gain and gain compression factor were extracted to be 4.3 10–16 cm2 and 3.4 10 –17 cm 3, respectively. Using these parameters, the maximum modulation bandwidth f 3 dB max is estimated as 7.9 GHz.

In the paper, the self-consistent optical–electrical–thermal-gain model of the oxide-confined long-wavelength 1.3-m quantum-dot (InGa)As/GaAs diode laser is demonstrated. The model has been applied to analyse room-temperature (RT) threshold-operation characteristics of the advanced laser of this kind. It may be used to describe physics of the above arsenide-based diode lasers to better understand their threshold performance and finally to optimize their structures.

The effect of In-segregation on optical properties in 7.5-nm GaInNAs/GaAs single quantum well (QW) is studied theoretically. The nominal (In, N) contents in the QW are chosen to be (0.35, 0.015) and (0.39, 0.03) for the emission wavelengths around 1.3 and 1.55μm, respectively. Muraki’s model is used to model the composition profiles in the QWs. In-plane strain, confinement potential, and subband energy levels of the QW are calculated using multi-band effective mass theory. We show a space-indirect transition between light holes localized in indium deficient region and electrons localized in indium rich region of the quantum well. Our results show that the optical transition energies are approximately constant for the segregation efficiencies smaller than 0.7 in both QWs.

In the paper, a comprehensive fully self-consistent three-dimensional simulation of an operation of the GaAs-based oxide-confined long-wavelength 1.3-m quantum-dot (QD)(InGa)As/GaAs vertical-cavity surface-emitting diode lasers is demonstrated. The model has been intentionally prepared for the PC-class microcomputers to enable its easy application in designing optimal structures of the above devices with desired performance characteristics. An impact of some structure parameters on QD VCSEL room-temperature (RT) continuous-wave (CW) lasing thresholds is discussed. A stable RT CW operation on a single fundamental mode has been found to be possible in modern QD VCSELs with active regions containing more uniform and more dense QDs in stacks of QD layers. The desired single fundamental-transverse-mode operation is possible for smaller active regions of diameters not exceeding 8 m. In the case of larger active regions, on the other hand, higher-order transverse modes of an increasing order are excited first because of increasingly more non-uniform optical-gain distributions.

We have investigated the temperature dependencies of the slope efficiency and the threshold current for strained multiquantum well (MQW) lasers as a parameter of the well number. Smaller well numbers mean larger temperature dependencies of the slope efficiency and the threshold current, while larger well numbers mean larger internal loss and broadening of the photoluminescence linewidth of the MQW structure. Furthermore, the change in the slope efficiency with temperature change is related to the change in internal loss. In this work, the 1.3-m strained MQW laser with a compressive strain of 1.0% and 7 wells shows the highest output power of 6.8 mW for an injection current of 50 mA and the lowest threshold current of 5.5 mA at 85C, and the lowest variation in output power of 2.0 dB from 25–85C at injection current of 50 mA.

We present a comprehensive study of spectral photoluminescence (PL), photoconductivity and Hall mobility in undoped, n and p-type modulation-doped quantum wells of Ga1-x Inx Ny As1-y /GaAs with varying nitrogen concentration. We show that the increasing nitrogen composition red shifts the energy gap and this red shift is accompanied with a reduction of the 2D electron mobility in the quantum wells. True temperature dependence of the band gap, free from errors associated with nitrogen induced exciton trapping effects, is observed because in the modulation doped QW samples PL emission is dominated by band-to-band recombination and the S-shape temperature dependence is eliminated. Excellent fit to semi-experimental Varshni equation is obtained and the temperature dependence of the band gap in the linear regime (dE/dT) is tabulated as a function of nitrogen concentration and the type of dopant.

We report mode missing and modal instability of uncooled Fabry–Perot (FP) lasers for the temperature range from –45 to 85C and their effect on transmission performance. Using the time domain laser model (TDLM), mode missing has been modeled in FP lasers with structural defects in the active layer. Using this model, we have estimated eye opening penalty (EOP) due to missing modes up to 2.5 Gbps data rate. These simulation results suggest that FP lasers should have less than two missing modes for stable operation and high performance for optical data links.

The work presents a comparison between results of optical simulations based on the scalar and vectorial models applied to both stripe – geometry Fabry-Perot (FPL) as well as vertical-cavity surface-emitting (VCSEL) diode lasers designed for the 1.3-μm optical–fibre communication. As compared to vectorial optical approaches, scalar ones are known to be less exact but simultaneously they need as many as approximately 100 times shorter computation time, which favours those models in many applications. Therefore, vectorial models should be applied only in cases of confirmed faulty performance of scalar ones. While the Effective Index Method and the Effective Frequency Method have been chosen as scalar approaches to FPLs and VCSELs, respectively, simulations, the Method of Lines has been used in both cases as a vectorial one. Scalar models have been found to be quite exact in the case of a determination of the effective refractive index and wavelength of emitted radiation, whereas their exactness in the lasing threshold analysis is much worse, especially in the case of higher-order modes. Our analysis is concluded with the determination of the regions where both models give satisfactorily close results.

This paper describes the growth and device performance of electroabsorption modulators on GaAs substrates operating near 1.3 m, the dispersion minimum for silica fibres. The key to the successful molecular beam epitaxial (MBE) growth of these devices was the incorporation of a linearly-graded buffer layer beneath the InGaAs/AlGaAs multi-quantum-well active layer. Both transmission and reflection modulators are produced. For transmission devices, larger modulation is achieved when the buffer is graded more slowly: The maximum modulation reported was 22% for T/T O corresponding to a 0.86 dB contrast ratio with an insertion loss of roughly 5 dB at 1.34 m. Antireflection coating a transmission modulator yields a reasonable reflection modulator. However, improved performance is reported for a reflection modulator using a novel technique of integrating the bottom quarter-wave mirror into a buffer with linearly-graded In composition. At 1.33 m, a normally-off reflection modulator with an integrated mirror exhibited a R/R O of 73%, a constrast ratio of 2.38 dB, and an insertion loss of 4 dB.

Physical aspects of an operation of the GaAs-based InGaAs/GaAs quantum-well (QW) VCSELs with the intentionally detuned optical cavities have been considered in the present paper using the comprehensive three-dimensional self-consistent optical–electrical–thermal-gain simulation. In GaAs-based structures, very good DBR resonator mirrors and a very efficient methods to confine radially both the current spreading and the electromagnetic field with the aid of oxide apertures may be applied. It has been found using the above simulation that even currently available immature technology enables manufacturing the above devices emitting radiation of wavelengths over 1.20μm. In particular, while the room-temperature 1.30-μm lasing emission is still beyond possibilities of the InGaAs/GaAs QW VCSELs, these structures may offer analogous 1.25-μm emission, especially for the high-power and/or high-temperature operation.

A diode-pumped 1.34 m Nd:GdVO4 laser operating in cw and active Q-switching modes has been demonstrated. 4.15 W of cw output power was obtained at the highest attainable pump power of 12.3 W, resulting in an optical conversion efficiency of 33.7%, the slope efficiency was determined to be 37.6%. In Q-switching operation, a maximum average output power of 2.7 W was generated at pulse repetition frequency (PRF) of 50 kHz, with an optical conversion efficiency of 22% and a slope efficiency of 29.2%. The laser pulses with shortest duration, highest energy and peak power were achieved at PRF of 10 kHz, the parameters being 15 ns, 160 J, and 10.7 kW, respectively. By intracavity frequency-doubling with a type II phased-matched KTP crystal, 0.62 W average power at 0.67 m was produced at a PRF of 15 kHz, the resulting pulse energy, peak power, and pulse width being 41.3 J, 2.2 kW, and 19 ns, respectively. A group of analytical formulae, based on rate equations, are presented to evaluate the operational parameters of an actively Q-switched laser. Calculated results were found to be in close consistency with the experimental data.

High power polarization-insensitive InGaAsP-InP multiple quantum well (MQW) superluminescent diodes (SLD's) emitting at 1.3μm were investigated. A combination of tensile strained and compressively strained quantum wells called complex strained MQW were used in a single active layer in order to obtain polarization insensitivity. Low-pressure metalorganic chemical vapor phase epitaxy was used for crystal growth. High resolution X-ray diffraction and photoluminescence spectra showed excellent crystal quality. The SLD's were fabricated to ridge waveguide structure with 7° tilted cavity, the two facets were coated with two layers anti-reflection TiO2/SiO2 films, residual facet reflectivity was found to be less than 0.04%. The SLD's exhibited a up to 18.8 mW optical output power and less than 1 dB polarization dependence of output power with a less than 0.5 dB optical spectra modulation at 250 mA.

A new quantum structure, the type 1.5 quantum well, is proposed and modelled. The type 1.5 quantum well has a greater absorption modulation depth with low applied fields (30 kV cm–1) than standard type I quantum wells. In addition, the type 1.5 quantum well has better insertion loss and attenuation characteristics under negative alpha parameter (blue chirped) conditions than standard type I quantum well materials.

Structure optimisation of the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode lasers (VCSELs) has been carried out using the comprehensive three-dimensional self-consistent physical model of their room-temperature (RT) continuous-wave (CW) threshold operation. The model has been applied to investigate a possibility to use these devices as carrier-wave lasing sources in the third-generation optical-fibre communication. In this simulation, all physical (optical, electrical, thermal and gain) phenomena crucial for a laser operation including all important interactions between them are taken into consideration. As expected, the 1.5λ-cavity VCSEL has been found to demonstrate the lowest RT CW threshold. However, for many VCSEL applications, the analogous VCSEL equipped with a longer 3λ-cavity should be recommended because it exhibits only slightly higher threshold but manifest much better mode selectivity – the desired single-fundamental-mode operation has been preserved in these devices up to at least 380 K. The Auger recombination has been found to be decidedly the main reason of the threshold current increase at higher temperatures. A proper initial red detuning of the resonator wavelength with respect to the gain spectrum may drastically decrease CW lasing thresholds, especially at higher temperatures.

Pulsed laser diodes with flared waveguides operating int he 1.5-m eye-safe wavelength band are fabricated for the first time. High-power (9.6-W) operation with narrow lateral far-field divergence (4) has been obtained. These devices will be applicable for free-space optical measurement systems as eye-safe light sources.

In order to further suppress the F–P lasing and increase the superluminescent power, the tilted ridge waveguide was introduced to the integrated superluminescent device [monolithic integration of the superluminescent diode (SLD) with semiconductor optical amplifier (SOA)[. By this means, high power 1.5 m integrated superluminescent light source has been fabricated without anti-reflection (AR) coating. The F–P oscillations between the two cleaved facets were suppressed successfully compared with the device without ridge waveguide. More than 200 mW peak pulsed power was obtained under quasi-CW condition (0.1 ms pulse width, 10% duty cycle) by co-operation of the two integrated sections. The spectral FWHM is 25 nm.

The small-signal modulation characteristics of 1.5 m lattice-matched InGaNAs/GaAs and InGaAs/InP quantum well lasers and their temperature dependence have been calculated. It is found that the maximum bandwidth of the InGaNAs/GaAs quantum well lasers is about 2.3 times larger than that of the InGaAs/InP quantum well lasers due to the high differential gain which results from the large electron effective mass in the dilute nitride system. The slope efficiency for the 3 dB bandwidth as a function of optical density is twice as large for InGaNAs/GaAs as for InGaAs/InP quantum well lasers.

Robust single-frequency operation of an erbium–ytterbium glass waveguide laser based on the twisted-mode technique is demonstrated. A single-mode output power of 0.7 mW with relative-intensity-noise peak value of –90 dB/Hz has been obtained.

Molecular absorption lines due to vibrational-rotational transitions in14NH3 are observed near 1.5 m. An InGaAsP DFB laser is frequency stabilized to a linear absorption line within 500 MHz at 1543.08 nm. Such an absolute frequency-stabilized DFB laser is useful for coherent optical system applications owing to its long-term frequency stability and for residual gas detectors.

A 1.55-m fiber grating laser (FGL) was fabricated by optically packaging a non-anti-reflection (AR) coated Fabry–Perot (FP) laser to a lensed fiber grating. The FGL demonstrates a single-longitudinal mode operation with a side-mode suppression ratio (SMSR) of up to 40 dB. The SMSR oscillates and diminishes to 5 away from the facet normal of the FP laser. We have performed numerical simulations on the single-longitudinal mode operation for the FGL. The SMSR for the FGL increases over 40 dB as the increase of the fiber grating reflectivity (R g) above 0.7 with non-AR-coated FP laser facet. Our calculations also show that the strong current-dependent SMSR oscillation is from the mode selection by the fiber grating external cavity and the heating effect in the FP laser.

We report on the design, fabrication, and characterization of InP-based 1.55 μm wavelength large diameter (50 μm) electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs). The hybrid device consists of a half vertical cavity surface emitting laser (1/2-VCSEL) structure assembled with a concave dielectric external mirror. The 1/2-VCSEL is monolithically grown on InP substrate and includes a semiconductor Bragg mirror and a tunnel junction for electrical injection. Buried (BTJ) and ion implanted (ITJ) tunnel junction electrical confinement schemes are compared in terms of their thermal and electrical characteristics. Lower thermal resistance values are measured for BJT, but reduced current crowding effects and uniform current injection are evidenced for ITJ. Using the ITJ technique, we demonstrate Room-Temperature (RT) continuous-wave (CW) single transverse mode laser operation from 50-μm diameter EP-VECSEL devices. We show that the experimental laser optical output versus injected current (L–I) curves are well-reproduced by a simple analytical thermal model, consistent with the thermal resistance measurements performed on the 1/2-VCSEL structure. Our results indicate that thermal heating is the main mechanism limiting the maximum CW output power of 50-μm diameter VECSELs, rather than current injection inhomogeneity.

A novel polarization independent InGaAs/InGaAlAs quantum well (QW) structure in the 1.55 m wavelength region is proposed. A coupled QW structure with tensile strain in the QW and/or barrier region is considered for the reduction of the optical gain difference between TE and TM modes in the wide spectral range. A triple-coupled QW structure with alternative strain (tensile/compressive/tensile) is found to be the most effective in reducing the polarization gain difference. This is because the transition strength difference of each polarization is reduced by energy states coupling. The optimized triple-coupled QW structure shows polarization independence for wide carrier density and wavelength range, which is suitable for polarization independent operation of QW based semiconductor devices, such as semiconductor optical amplifiers.

The design of an electrically pumped InGaAs quantum well based vertical cavity surface emitting laser (VCSEL) on InP substrate is presented. Such optically pumped VCSELs have already been demonstrated. To design electrically pumped VCSEL, three simulations steps are needed: optical simulation gives access to the standing-wave electric field distribution, to design the active region and the Bragg mirrors. Thermal simulation is helpful to design metallic contacts while the energy band diagram is obtained by electrical simulation to design the buried tunnel junction useful for carrier injection. All these simulations are compared to experiment.

Polarization-insensitive AlGaInAs'InP semiconductor optical amplifier is realized at wavelength of 1.55 . The active layer consists of three tensile strained wells with strain of 0.40%. The amplifier is fabricated to ridge waveguide structure. The testing result shows the amplifiers have excellent polarization insensitivity (less than 0.8dB). The 1540 nm wavelength optical gain is 20 dB at the bias current of 200 mA.

We report low threshold and high speed 1.55 m complex-coupled distributed feedback (CCDFB) lasers with gain coupling induced by a current blocking grating. Excellent device performance has been demonstrated with a record-low threshold of 5.6 mA, a large modulation bandwidth of 11 GHz and useful high temperature operation up to 95C.

We present a theoretical study of the optical properties of GaInNAs quantum dot (QD) structures, emitting at 1.55 µm wavelength. The theoretical model is based on a 10 ×10 k · p band-anti-crossing Hamiltonian, incorporating valence, conduction and nitrogen-induced bands. We have investigated the influence of the nitrogen to the conduction band mixing, and piezoelectric field on the ground state optical matrix element. For QDs grown on GaAs substrate with a reduced amount of indium and an increased amount of nitrogen in the QD the e x polarized optical matrix element becomes on the average larger and less sensitive to the variation of both the QD shape and size than is the case of an InNAs QD. For the QD grown on InP substrate the dominant optical dipole matrix element is of the e z light polarization. Our results identify the specific In and N content in the QDs required for optimal long-wavelength emission on both substrates.

In this paper, a theoretical model is used to investigate the lasing spectrum properties of InAs/InP (113)B quantum dot (QD) lasers emitting at 1.55μm. The numerical model used is based on a multi-population rate equation (MPRE) analysis. It takes into account the effect of the competition between the inhomogeneous broadening (due to the QD size dispersion) and the homogenous broadening as well as a nonlinear gain variation associated to a multimode laser emission. The double laser emission and the temperature dependence of lasing spectra of self-assembled InAs/InP quantum dot lasers is studied both experimentally and theoretically.