Experimental and theoretical analysis of argon plasma-enhanced quantum-well intermixing

Plasma-enhanced quantum-well intermixing (QWI) has been developed for tuning the bandgap of InGaAs-InP material using an inductively coupled plasma system. The application of inductively coupled plasma enhances the interdiffusion of point defects resulting in a higher degree of intermixing. Based on a semi-empirical model of QW interdiffusion, the bandgap blue-shift with respect to the plasma exposure time and inductively coupled plasma energy has been analyzed. The theoretical results appear to be in good agreement with the experimental data of the intermixed samples. The model serves as a good simulation tool to explain the intermixing mechanism and further to optimize the intermixing process for the fabrication of the photonic integrated circuits.     

High brightness single-mode ridge laser utilizing buried heterostructure defined by quantum-well intermixing

The authors demonstrate a novel high brightness single-lateral mode ridge laser using quantum well intermixing to form a buried heterostructure. Increased discrimination between the fundamental and higher order modes can be achieved using the buried heterostructure to reduce the width of the gain section, enhancing fundamental mode operation. This allows the ridge width to be increased while maintaining fundamental mode operation, hence reducing the optical intensity at the facet and increasing the optical power before mirror degradation. Standard and novel buried heterostructure ridge lasers of 5-/spl mu/m width are compared; far-field beam profiles clearly show improved modal stability for the novel structure.     

Dispersion and modulation of the linear optical properties of GaAs-AlAs superlattice waveguides using quantum-well intermixing

We report on the large modulation of the optical properties of a 14:14 monolayer GaAs-AlAs superlattice waveguide following quantum-well intermixing. Low-temperature photoluminescence measurements illustrate a large 169-meV differential blue-shift obtained between the disordering-suppressed and disordering-enhanced materials. Effective index measurements are presented as a function of polarization, for both the as-grown and disordered material for near-bandedge and half-bandedge wavelengths, which is the wavelength range 775-1550 nm. The largest effective refractive index shift observed was 9/spl times/10/sup -2/ which exceeds that previously reported for disordered AlGaAs ternary multilayer structures, and illustrates the potential of the superlattice for the fabrication of etch-free, planar optical components with large index contrast.     

Theoretical analysis of wavelength tuning in distributed-feedbacklasers by quantum-well intermixing

Wavelength tuning in distributed-feedback (DFB) lasers using quantum-well intermixing is analyzed. A 0.42-nm tuning range is obtained when the bandgap is blue-shifted by 5.9 nm, and this value agrees well with the experimental value of 0.36 nm. The limitation of the tuning range is also discussed, and is because of the increase in carrier density that raises the gain above the threshold after intermixing. The dependence of wavelength shift on bandgap blueshift is not affected by the details of the intermixing process. A maximum tuning range of 3.5 nm is predicted, demonstrating that after device fabrication intermixing process can be used to adjust DFB lasers operating wavelengths to match the predefined wavelength channels of wavelength-division-multiplexing system     

Improvements in mode-locked semiconductor diode lasers using monolithically integrated passive waveguides made by quantum-well intermixing

By using the technique of quantum-well intermixing (QWI), monolithically integrated passive, and active waveguides can be fabricated. It is shown that mode-locked extended cavity semiconductor lasers with integrated low-loss passive waveguides display superior performance to devices in which the entire waveguide is active: the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.2 ps in the all active laser to 3.5 ps in the extended cavity device and there is a decrease in the free-running jitter level from 15 to 6 ps (10 kHz-10 MHz).     

Efficient curvature analysis of buried waveguides

The highly efficient free space radiation mode method is extended, enabling for the first time its use in determining the lossy modes of curved buried semiconductor waveguides. Both the real and imaginary parts of the propagation constant along with the corresponding field profiles, are found with an accuracy comparable to that of more computationally intensive methods     

Modeling of optical gain properties of multiple cationsInGaAs-InAlAs quantum-well intermixing

Multiple cations intermixing in an In_0.53Ga_0.47 As-In_0.52Al_0.48As quantum-well (QW) structure with 60-Å well width is being studied based on the expanded form of Fick's second law. Interdiffusion of the indium sublattice can result in a maximum compressive strain of 0.64% when annealing time reaches 3 h at 812°C. For a small interdiffusion, i.e., 1-1.5 h, the subband separation between the lowest heavy and light hole states is at its greatest. This has a major contribution to the modified band structure and averaged density of states which can result in an enhanced optical gain up to 40%. This initial stage of intermixing provides the best lasing performance. For large interdiffusion, i.e., up to 6 h, a large blue shift of the peak gain from 0.842 eV (λ=1.47 μm) to 1.016 eV (λ=1.22 μm) is obtained, thus giving a high tunability of the lasing wavelength     

Integration of high-gain and high-saturation-power active regions using quantum-well intermixing and offset-quantum-well regrowth

A novel structure and method for fabricating regions of high and low modal gain on the same chip are reported, which enable diode lasers with maximum efficiency to be monolithically integrated with multiple-section semiconductor optical amplifiers having both high gain and high saturation power. This method uses quantum-well intermixing and an offset-quantum-well regrowth to achieve regions with high and low optical confinement. Fabry-Perot broad-area lasers were used to characterise the material in both regions.     

Dual-wavelength laser source monolithically integrated with Y-junction coupler and isolator using quantum-well intermixing

A dual-wavelength laser source monolithically integrated with an isolator and a Y-junction coupler is fabricated by using a new quantum-well intermixing technique. The technique employs a buried Ge layer between the sample surface and the spin-on silica film to control the bandgap tuning in selective areas across a wafer. The integrated isolator can avoid the crosstalk between the two channels of the device. Two distinct lasing wavelengths of 950 and 969 nm are coupled into one single output port through the transparent Y-junction coupler. The two channels have similar threshold current and slope efficiency.     

Modified Airy function method for the analysis of tunnelingproblems in optical waveguides and quantum-well structures

A simple method for the analysis of tunneling through an arbitrary one-dimensional potential barrier, based on the modified Airy function approach, is presented. Truncated step-linear, step-exponential, parabolic, and quartic potential barriers are considered. The results are compared with those obtained by the conventional WKBJ, modified WKBJ, and matrix methods. The effect of the truncation level on the tunneling coefficient is investigated. The tunneling coefficient is sensitive to the truncation level. For the step-linear potential, the tunneling coefficient is a monotonically decreasing function of the truncation level, while for the parabolic potential, it oscillates before saturating to a constant value     

Experimental analysis of metal coated dielectric waveguides

This paper concerns the experimental characteristics of metal coated dielectric waveguides with a rectangular surface corrugation. Waveguide are designed to operate at a second Bragg frequency of 90 GHz. The period, height and the duty cycle of a rectangular grating were calculated using the chosen frequency. A metallic layer of aluminum is sputtered on one side of the slab waveguide. The purpose of the metallic layer is to simulate a layer of high density plasma on the surface of the waveguide similar to that obtained by optical excitation of semiconductor structures. Experiments were performed to examine the far field radiation pattern, attenuation constant and the dispersion relation. Due to the presence of the plasma layer there will be an angular shift in the far field radiation pattern. We have observed angular shifts of about 20? in the radiation pattern of the waveguide before and after coating. Measurements are made in the frequency range of 88–95 GHz. This waveguide structure can be used to design an electronically steerable antenna and an electronic phase shifter operating in the millimeter-wave frequency band.     

Accurate analysis and modeling of laminated multilayered 3-D optical waveguides

The theoretical investigation of waveguides having nonuniform cross-sections is an attractive and challenging problem which deserves serious interest. In this paper, we present a novel analysis of laminated multilayered three-dimensional waveguide, based on two modes: 1) a new coupled transmission line approach that considers the sloping of the layers along the longitudinal direction and 2) a transmission line matrix integral equation (TLMIE) modeling that complete and extends the investigation of the field propagation. In method 1), we neglect radiation modes and their EM coupling. All physical effects instead are accounted for by the full-wave TLMIE method. By using TLMIE, we validate the EM analysis and calculate TE/TM losses, arising from radiation modes.     

Reduction of absorption loss in asymmetric twin waveguide laser tapers using argon plasma-enhanced quantum-well intermixing

Lasers based on asymmetric twin waveguide integration technology are limited by the necessity of pumping the tapers to avoid absorption losses within this section of the active region. Here, we demonstrate that the threshold current is reduced by argon plasma-enhanced quantum-well intermixing in the taper. Intermixing induces a (57/spl plusmn/5) nm wavelength blue shift in the emission peak, accompanied by a <12-nm linewidth broadening of the photoluminescence spectrum, indicating minimal material degradation. The threshold current of a 0.6-mm-long laser is reduced by (18/spl plusmn/1)% to (27/spl plusmn/1) mA using an intermixed taper as compared to a nonintermixed structure.     

Fabrication of multiple wavelength lasers in GaAs-AlGaAs structuresusing a one-step spatially controlled quantum-well intermixing technique

We have applied a new technique, based on impurity-free vacancy diffusion, to control the degree of intermixing across a wafer. Bandgap tuned lasers were fabricated using this technique. Five distinguishable lasing wavelengths were observed from five selected intermixed regions on a single chip. These lasers showed no significant change in transparency current, internal quantum efficiency or internal propagation loss, which indicates that the material quality was not degraded after intermixing     

Measurement of surface roughness in buried channel waveguides

An atomic force microscope is employed in a novel method for measuring the edge roughness of masks used in the fabrication of rectangular-core buried channel waveguides. Light attenuation due to scattering loss from the sides of the core can then be estimated using a simple statistical model of the data.<>     

Demonstration of widely tunable single-chip 10-Gb/s laser-modulators using multiple-bandgap InGaAsP quantum-well intermixing

High-speed wavelength-agile laser-modulators were fabricated for the first time using a quantum-well intermixing processing platform for monolithic integration. Over 19-GHz 3-dB modulator bandwidth was achieved and 10-Gb/s error-free transmission was demonstrated through 75 km of standard fiber.     

Ultrafast, multi-THz-detuning, third-order frequency conversion insemiconductor quantum-well waveguides

The near-band-edge resonance nonlinearity of semiconductor quantum wells has been used to obtain nondegenerate four-wave mixing over a multi-THz frequency detuning range, with large conversion efficiencies. In 1-mm-long, passive AlGaAs/GaAs single-quantum-well waveguides, conversion efficiencies up to -8.5 dB with relatively flat response have been observed over a 7.5-THz range (2.2% of the band gap). The nonlinearity is ultrafast and primarily reactive. The potential application of this technique to wavelength shifting devices is discussed     

Monolithic fabrication of 2 × 2 crosspoint switches inInGaAs-InAlGaAs multiple quantum wells using quantum-well intermixing

In this letter, we report the fabrication of 2 × 2 crosspoint switches, which monolithically integrate passive waveguides, electro-absorption modulators and optical amplifiers onto one chip using sputtered SiO₂ quantum-well intermixing technique. The switches have low insertion loss to be about 4-5 dB and extinction ratios up to 26 dB     

1.55 micrometer ridge DFB laser integrated with a buried-ridge-stripe dual-core spot-size converter by quantum-well intermixing

A ridge distributed feedback laser monolithically integrated with a buried-ridge-stripe spot-size converter operating at 1.55 micrometre wavelength was successfully fabricated by means of low-energy ion implantation quantum-well intermixing and dual-core technologies. The passive waveguide was optically combined with a laterally exponentially tapered active core to control the mode size. The devices emit in a single transverse and single longitudinal mode with a sidemode suppression ratio of 38.0 dB. The threshold current was 25 mA. The beam divergence angles in the horizontal and vertical directions were as small as 8.0 degree X 12.6 degree, respectively, resulting in 3.0-dB coupling loss with a cleaved single-mode optical fiber.     

Electromagnetic modeling of quantum-well photodetectors containingdiffractive elements

An analytical approach for modeling optical fields in quantum-well infrared photodetectors was developed by using a rigorous solution of the corresponding electromagnetic problem. Its application includes structures having a large number of dielectric layers, which may contain gratings having arbitrary profiles and metal-strip arrays acting as electrodes. By representing the fields inside complex photodetector structures in terms of interconnected transmission-line units, this approach helps considerably to clarify the role of each constituent of the photodetector. Examples involving realistic situations reveal that the presence of metal electrodes may affect the photodetection operation in a large class of grating structures. In particular, we show that the sensitivity of specific photodetector configurations can be enhanced by choosing grating parameters that optimize the overall photodetecting performance