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This tutorial describes the basic principles and performance analysis of optical intensity modulators using electrooptic and electroabsorption effects, for use in analog and digital communication systems. These include lithium niobate modulators, semiconductor electroabsorption modulators, semiconductor Mach-Zehnder modulators, and polymer modulators.

We describe how the material properties of III–V semiconductors, including bandgap, band structure, band offset, refractive index, absorption, and ionization coefficient, are exploited for lasers and photodetectors for fiber-optic communications. The material systems discussed for 1.3 μm and 1.55 μm light emission include the more traditional GaInAsP and AlGaInAs on InP, the more recently investigated GaInAs quantum dots and low-bandgap GaInNAs on GaAs as well as GaAsSb/GaAs Type II structures, and the potentially viable GaN/AlGaN from intersubband transitions (i.e., between quantized conduction-band energy levels). As an example of photodetector applications, GaInAsP/InP and wafer-fused GaInAs/Si are discussed in terms of gain and noise factor for use in avalanche photodiodes with separate absorption and multiplication regions.

Semiconductor quantum well (QW) light-emitting diodes (LEDs) have limited temporal modulation bandwidth of a few hundred MHz due to the long carrier recombination lifetime. Material doping and structure engineering typically leads to incremental change in the carrier recombination rate, whereas the plasmonic-based Purcell effect enables dramatic improvement for modulation frequency beyond the GHz limit. By stacking Ag-Si multilayers, the resulting hyperbolic metamaterials (HMMs) have shown tunability in the plasmonic density of states for enhancing light emission at various wavelengths. Here, nanopatterned Ag-Si multilayer HMMs are utilized for enhancing spontaneous carrier recombination rates in InGaN/GaN QWs. An enhancement of close to 160-fold is achieved in the spontaneous recombination rate across a broadband of working wavelengths accompanied by over tenfold enhancement in the QW peak emission intensity, thanks to the outcoupling of dominating HMM modes. The integration of nanopatterned HMMs with InGaN QWs will lead to ultrafast and bright QW LEDs with a 3 dB modulation bandwidth beyond 100 GHz for applications in high-speed optoelectronic devices, optical wireless communications, and light-fidelity networks.

This paper proposes the integration of an antenna with a photodetector for high capacity wireless communications. A waveguide photodetector (WGPD), illuminated on the side, is used to convert the RF-modulated optical power into a microwave signal. That microwave signal is used to feed an antenna built on the same plane as the photodetector. The WGPD is a standard p-i-n device grown on a semi-insulating InP. The performance of this RF/photonic antenna in the frequency range 17–20 GHz is studied theoretically and experimentally. An equivalent circuit model for the WGPD is developed to predict the photodetector impedance as a function of frequency. The photodetector is matched to the input impedance of the antenna. The agreement between measurement and the circuit model results for the WGPD impedance is very good. It is envisioned that a large number of such RF/Photonic antenna elements could be networked together into a star configuration, feeding in and out of a radio hub. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 179–184, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10550

Integrated metrology in the lithography cluster is a promising solution to tighten process control. It is shown that optical CD metrology using YieldStar, an angular resolved scatterometer, meets all requirements in terms of precision, process robustness, throughput and matching to CD-SEM, the current tool-of-reference. The same metrology tool supports also diffraction-based overlay metrology. Using an appropriate sampling plan and the full scanner correction capabilities, overlay control can be improved. The throughput of the integrated tool is sufficient to support high volume sampling plans for combined CD and overlay monitoring and control, with 100% lot coverage.

In this letter, we demonstrate a design of GaN-based Schottky diodes for microwave varactor applications. Using suitable InGaN surface layer structures, the Schottky diodes exhibit an enhanced high-voltage handling capability. The breakdown voltage is increased by ~40 V, and the reverse leakage current is significantly suppressed under high reverse voltages. The breakdown-voltage enhancement and leakage-current suppression are attributed to a reduction in the surface electric field and an increase in the electron tunneling distance due to polarization-induced charges at the InGaN/GaN interface.

Polarized neutron and X-ray reflectivity methods have been used to study the permalloy epitaxial thin films on sapphire with Cr as a buffer layer. The reflectivity result indicates that the magnetic interface is smoother than the chemical interface. It is possible that the magnetic moment of the intrusive Ni or Fe atoms across the interface can be assimilated by the near-by Cr atoms or the other way around.

Theoretical analysis and numerical calculations are presented for ultrahigh-speed (>50 GHz) traveling-wave electroabsorption modulators (TW-EAM's), including effects of velocity mismatch, impedance mismatch, and microwave attenuation. A quasi-static equivalent circuit model is used to examine the TW-EAM microwave properties, including the effect of photocurrent. Due to the optical propagation loss of the waveguide, the TW-EAM waveguide length for maximum RF link gain is currently limited to 200-300 /spl mu/m. The discussion indicates that the carrier transit time in the intrinsic layer may not severely limit the TW-EAM bandwidth. Three TW-EAM design approaches are discussed: low-impedance matching; reducing the waveguide capacitance; and distributing the modulation region.

Using the method of projection operators based on plane wave expansion, we theoretically investigate photonic band structures in two-dimensional metallodielectric photonic crystals, especially, square arrays of dielectric and perfectly conducting cylinders. Existence of photonic band gaps in metallodielectric photonic crystals and validity of the proposed numerical method are demonstrated.

A novel approach to the design of electroabsorption waveguide modulators for use in broadband, analog radio frequency (RF) links is presented. The approach utilizes a linear combination of two electroabsorption effects (the Franz-Keldysh effect and the quantum-confined Stark effect) to improve the spurious-free dynamic range of the waveguide modulator. Measured transfer curves verify simultaneous improvement in linearity and modulation efficiency for an exemplary combination structure. Residual absorption is modeled to determine the impact on modulation efficiency.

The phase of an optical signal can be linearly converted to voltage by using a receiver incorporating an electrooptic feedback loop. We demonstrate such a receiver in an externally modulated analog link, showing 12-dB improvement in input third-order intercept point with no second-order distortion. Feedback loop gain is achieved without electronic amplification, using only electrooptic and passive components.

Planar separate-confinement, double-heterostructure, single-quantum-well photoelastic GaAs/AlGaAs lasers have been fabricated using a novel yet practical processing technique involving thin-film surface WNi stressors for waveguiding and ion implantation for isolation. A p++-GaAs contact layer regrown by chemical beam epitaxy has been used to improve the WNi ohmic contacts to the lasers. Even without bonding on heat sinks, these planar photoelastic lasers operate at continuous wave at room temperature. The lowest threshold is 29 mA for a cavity length of 178 μm and a stressor width of 5 μm. The internal quantum efficiency above threshold is 75%. The characteristic temperature is 114 K. The main waveguiding mechanism of the photoelastic lasers is determined to be weak index guiding with the beam waist in the junction plane measured 10 μm behind the end facet.

We introduce the method of projection operators based on plane-wave expansion to compute photonic band structures in periodic media containing perfectly conducting elements. Eigenfunctions of a unit configuration potential generate suitable projection operators in the form of a set of eigenvectors in the Fourier domain. By simply applying a projection operator onto a proper subspace, a quadratic or cubic eigensystem for finitely conducting media can be transformed into an ordinary symmetric eigensystem in the limit of perfect conductors. The procedure is equivalent to finding solutions of wave equations under the condition that the electromagnetic fields are entirely zero inside periodic perfect conductors. The methodology developed here, in fact, can be viewed as a generalization of the conventional metal waveguide or cavity theory. The method is numerically handy, fast, and readily extendible to general metallodielectric photonic crystals. As examples, we present photonic band structures in two-dimensional metal and metallodielectric cylinder structures.

Propagation of elastic waves can be completely inhibited, irrespective of propagation directions, if oscillation frequencies of elastic waves fall inside elastic wave band gaps—three-dimensional frequency stop bands of elastic waves generated in three-dimensional periodic elastic materials. The three-dimensional linear vector equation of motion is transformed into a matrix eigensystem and solved numerically by the plane wave expansion method. Existence of elastic wave band gaps is theoretically demonstrated for the face centered cubic lattice structure based on isotropie materials. The example structure is spherical tungsten scatterers embedded in a polyethylene matrix. Complex elastic wave band structures were also computed for tunneling evanescent waves at symmetric points at X and L points.

Analog optical links using electroabsorption modulators have a gain limit caused by the photocurrent in the modulator. The gain limit results in a minimum link noise figure as well. The gain limit is due to the voltage-dependent absorption causing a voltage-dependent component to the photocurrent; the gain limit applies to a modulator that has this relationship

Bandwidth requirements continue to drive the need for low-power, high speed interconnects. Harnessing the mature CMOS technology for high volume manufacturing, Silicon Photonics is a top candidate for providing a viable solution for high bandwidth, low cost, low power, and high packing density, optical interconnects. The major drawback of silicon, however, is that it is an indirect bandgap material, and thus cannot produce coherent light. Consequently, different integration schemes of III/V materials on silicon are being explored. An integrated CMOS tunable laser is demonstrated as part of a composite-CMOS integration platform that enables high bandwidth optical interconnects. The integration platform embeds III-V into silicon chips using a metal bonding technique that provides low thermal resistance and avoids lattice mismatch problems. The performance of the laser including side mode suppression ratio, relative intensity noise, and linewidth is summarized.

An integrated tunable CMOS laser for silicon photonics, operating at the C-band, and fabricated in a commercial CMOS foundry is presented. The III-V gain medium section is embedded in the silicon chip, and is hermetically sealed. The gain section is metal bonded to the silicon substrate creating low thermal resistance into the substrate and avoiding lattice mismatch problems. Optical characterization shows high performance in terms of side mode suppression ratio, relative intensity noise, and linewidth that is narrow enough for coherent communications.

We report an ultrathin NiOx catalyzed Si np(+) junction photoanode for a stable and efficient solar driven oxygen evolution reaction (OER) in water. A stable semi-transparent ITO/Au/ITO hole conducting oxide layer, sandwiched between the OER catalyst and the Si photoanode, is used to protect the Si from corrosion in an alkaline working environment, enhance the hole transportation, and provide a pre-activation contact to the NiOx catalyst. The NiOx catalyzed Si photoanode generates a photocurrent of 1.98 mA cm(-2) at the equilibrium water oxidation potential (EOER = 0.415 V vs. NHE in 1 M NaOH solution). A thermodynamic solar-to-oxygen conversion efficiency (SOCE) of 0.07% under 0.51-sun illumination is observed. The successful development of a low cost, highly efficient, and stable photoelectrochemical electrode based on earth abundant elements is essential for the realization of a large-scale practical solar fuel conversion.

Fabrication tolerances for control of the Bragg wavelength of gratings in waveguides are studied. Techniques are demonstrated to hold the period of the grating constant to /spl plusmn/0.04 nm over the majority of the exposed wafer area, and ridge waveguides fabricated with standard thin film process equipment are found to have Bragg wavelengths constant to within /spl plusmn/0.2 nm. Additionally, adjacent ridges with differing widths are written in a single photomask/etch process step and found to controllably shift the Bragg wavelength over a 10-20-nm band suitable for a distributed Bragg reflector (DBR) laser array or a monolithic comb filter for wavelength division multiplexing (WDM) filtering/routing arrays.

We have used cross-sectional scanning tunneling microscopy (STM) to study interface structure in arsenide/phosphide heterostructures grown by gas-source molecular beam epitaxy (GSMBE) and by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). High-resolution images of GSMBE samples consisting of GaAs interrupted at 200A intervals with a 40 s P2 flux reveal substantial, growth-temperature-dependent incorporation of phosphorus with nanometer-scale lateral variations in interface structure. STM images of InGaAs/InP multiple quantum well structures grown by LP-MOVPE show evidence of interface asymmetry and extensive atomic cross-incorporation at the interfaces. Data obtained by STM have been corroborated by high-resolution x-ray diffraction and reflection high-energy electron diffraction. Together, these studies provide direct information about nanometer-scale grading and lateral nonuniformity of arsenide/phosphide interfaces that can occur under these growth conditions.

We have constructed an optically transparent, memoryless 2:1 statistical TDM packet multiplexor for constant packet-length input. This multiplexor is the fundamental building block in a class of Cascaded Optical Delay (COD) multiplexors intended for wide-area terabit networks. The multiplexor does not require slot-aligned traffic. This multiplexor can be cascaded to build multiplexors with improved packet loss rate. In this article we present the experimental packet loss rate of the memoryless multiplexor as well as the calculated packet loss rate of larger, buffered COD multiplexors. Furthermore, we outline an optical loss compensation scheme for buffered COD multiplexors.

The radio-over fiber (RoF) transmission is a promising method for broadband signal transmission over long distances. For intensity modulated broadband signals, the fiber dispersion accumulated over long fiber can lead to power fading of the signal. The power fading drawback can be largely alleviated when optical single-side-band (OSSB) modulation approach is adopted, which had been demonstrated via different optical filter schemes [1][2]. However, the majority of these past filtering approaches also introduce additional distortions due to the filter response. We have recently proposed and demonstrated a novel yet practical approach of cascading four identical off-the-shelf 100 GHz optical bandpass Fabry-Perot filters into a fiber link, which not only minimizes the power fading effect, but also increases Carrier-to-Noise ratio and maintains the distortions at a low level [3]. In this paper the distortions are further characterized and compared between links using single filter and cascaded filter respectively, which provides insight on how the cascaded filter maintains the linearity while mitigates the power fading.

In this paper, we propose and experimentally verify that optical filters with fast linear roll-off property, when incorporated in an optical transmitter, can minimize not only the fading effect commonly observed in high bit rate, long distance fiber links, but also improve the link Carrier-to-Noise ratio, and at the same time can maintain the 3rd order inter-modulation distortions at a relatively low level.

We show that propagation of elastic waves can be completely inhibited, irrespective of propagation directions, if oscillation frequencies of elastic waves fall inside elastic wave band gaps—three‐dimensional frequency stop bands of elastic waves generated in three‐dimensional periodic elastic materials. We also develop a classical theory for the calculation of radiated fields and energy from a point source load located in three‐dimensional periodic elastic media by incorporating the plane wave method, dyadic Green’s function, Poynting theorem, and tetrahedron k‐space integration. The fcc structure of tungsten spheres in polyethylene background is studied as an example. The resulting frequency spectra indicate the total inhibition of energy transmission in the elastic wave band gaps and unusual enhancement near the band edges. In addition, the computed data suggest the strong dependency of radiation spectra on the source position in the periodic elastic materials.

Peripheral coupled waveguide (PCW) design has been deployed in InGaAsP multiple quantum-well (MQW) electroabsorption modulator (EAM) at 1.55-/spl mu/m wavelength. PCW enhances the optical saturation power and reduces the optical insertion loss and the equivalent V/sub /spl pi// simultaneously. A radio-frequency link using a 1.3-mm-long lumped-element PCW EAM has achieved experimentally a link gain of -3 dB, at 500 MHz and at input optical power of 80 mW. The corresponding two-tone multioctave spurious-free dynamic range (SFDR) at the same bias is measured at 118 dB/spl middot/Hz/sup 2/3/. The single-octave SFDR at the third-order null bias is 132 dB/spl middot/Hz/sup 4/5/.

A novel electroabsorption modulator (EAM) using intrastep quantum wells (IQWs) and a single-sided large optical cavity waveguide is demonstrated to operate at up to 100 mW of input optical power. When the IQW EAM with uncoated facets is tested in an analog fiber link, the radio-frequency link gain reaches -16.1 dB at 100-mW optical power. We have measured a single-octave spurious-free dynamic range (SFDR) of 121 dB/spl middot/Hz/sup 4/5/ and multioctave SFDR of 110 dB/spl middot/Hz/sup 2/3/ for this EAM.

Severe acute pancreatitis (SAP) is a serious systemic disease with a sustained high mortality rate. Extensive evidence has shown that gut barrier dysfunction plays a critical role in the pathophysiology of SAP.Investigating the role of intestinal mucosa oxidative stress in gut barrier dysfunction of SAP.Twenty-four BALB/c mice were randomly divided into two groups with twelve mice each group. The SAP group mice received six intraperitoneal injections of cerulein (50 µg/kg) at 1-hour intervals, then given one intraperitoneal injection of 10 mg/kg lipopolysaccharide (LPS from E. coli) for inducing SAP. Normal saline was given to the mice of control group. The animals of each group were averaged to two batches. Four and eight hours after the final injection, respectively, mice were anesthetized and blood and tissue samples were harvested for examination. The pathological changes of pancreas and gut were observed and scored. The serum levels of diamine oxidase (DAO), amylase and tumor necrosis factor-alpha (TNF-α) were measured. The contents of malondialdehyde (MDA) and reduced glutathione (GSH) and activity of superoxide dismutase (SOD) and xanthine oxidase (XO) in gut mucosa were detected. In gut mucosa, the caspase-3 activity was measured and the cell apoptosis and apoptosis index (AI) were determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. The data were analyzed by ANOVA and t-test.At four and eight hours after SAP induction, the SAP group mice had significantly higher pancreatic and gut pathological scores (p0.01) and increased serum levels of amylase (p0.05), DAO and TNF-α (p0.01) and increased MDA contents and XO activity of gut mucosa (p0.01) compared with those of control mice. There were significantly lower GSH contents (p0.05) and SOD activity (p0.01) of gut mucosa in the SAP mice. It was also observed that the gut mucosa cells of SAP mice had significantly higher caspase-3 activity and apoptosis index (p0.01).In SAP, waterfall-style release of inflammatory factors such as TNF-α led to ischemia-reperfusion injury of gut mucosa which resulted in serious oxidative stress and activation of caspase-3 pathway and severe apoptosis of gut mucosa. Therefore, intestinal mucosal oxidative stress may play an important role in the mechanism of gut barrier dysfunction.

An integrated tunable C band laser fabricated in a commercial CMOS foundry is discussed. The laser is embedded in the silicon chip, and is hermetically sealed. Preliminary optical characterization results are presented.

The conduction band alignment of compressively strained In1−xGaxP relative to lattice matched InGaP/GaAs has been determined by capacitance-voltage profil-ing. A modified version of Kroemer’s capacitance-voltage profiling method is developed wherein a quantum well is profiled instead of a single heterojunction. A one-dimensional Poisson-Schrodinger solver was used to fit the reconstructed carrier profiles corresponding to a value of ΔEc at varying temperatures. Schottky barrier diode structures containing a single strained InGaP quantum well were grown by low pressure metalorganic chemical vapor deposition. The two strained compositions studied contained 35 and 31% gallium. Conduction band offsets of 101 and 131 meV were found for the 35 and 31% samples, respectively, with an estimated accuracy of ±5 meV. These results agreed closely with values predicted by empirical calculations.

We have investigated the use of thin film technology to introduce controllable and thermally stable stress into semiconductor heterostructures. Two simple schemes are used. The first scheme is to use interfacial reactions between a metal and the substrate, such as Ni, Co, Pd, and Pt on GaAs/AlGaAs. The induced stress in the structure is reproducible and controllable because the volumetric change for a given reaction is fixed, as long as the deposited film is fully reacted to form a compound. The stability of the stress depends on the stability of the compound. In the case of Ni and Co on GaAs/AlGaAs, the induced stress is thermally stable up to 600 °C. Evaporated films and reacted films are usually under tension. The second scheme is to use rf sputtered W or WNi alloy films where W or WNi is sputtered onto a negative dc biased substrate. This scheme effectively provides highly compressed films. The thermal stability depends on the concentration of Ni in the WNi alloy. Using the two schemes above, we have ...

We demonstrate a digitally tunable microwave-photonic notch filter based on a differential group-delay module which produces a relative delay between two orthogonal polarizations. A maximum rejection level greater than 60 dB is obtained. The tunability of the filter is achieved through real-time electronic control of the relative delay time.

The paper presents a quasi-TEM equivalent circuit model for two optically driven coplanar waveguide (CPW)-fed slot antennas. This model takes into account both the electromagnetic fields in the CPW structure as well as the effects of the discontinuities of the antenna design. The results are compared with simulations taken from IE3d using the method of moments.

In this paper, we demonstrate the critical design considerations for GaN-based microwave power varactors for the purpose of achieving high breakdown voltage, high Q-factor and high linearity. The extraction of these parameters from a real GaN-based power varactor diode is also presented. High values of these parameters are obtained, which is critical for the applications in the wireless base-station communications.

Efficient 1.3 and 1.55 μm InP‐based electroabsorption waveguide modulators with planar device structures have been demonstrated. Elevated temperature oxygen ion implantation and/or the photoelastic effect induced by W metal stressor stripes deposited on the semiconductor surface have been used to produce these self‐aligned planar guided‐wave devices. The oxygen ion mixing process has been used to simultaneously achieve compositional disordering and electrical isolation of superlattice material while the photoelastic effect has been used to improve the lateral mode confinement. A 1.3 μm Franz–Keldysh modulator with a ≳10 dB extinction ratio at 2 V and a 1.55 μm device with a ≳10 dB extinction ratio at 7 V are reported. These single growth step planar processing techniques have also been used to fabricate relatively low‐loss (

A fused InGaAs-Si avalanche photodiode (APD) with a low excess noise factor of 2.3 at a gain of 20 is reported. This corresponds to a k factor of 0.02 for the silicon avalanche region. Dark current density as low as 0.04 mA/cm/sup 2/ at -5 V and 0.6 mA/cm/sup 2/ at a gain of 10 are measured; a small thermal coefficient, 0.09%//spl deg/C, of the breakdown voltage is observed for this APD.

Semiconductor varactors are receiving increasing attention because of their potential to provide adaptive and tunable characteristics for the front-end of wireless communication systems, enabling efficient multi-band and software-defined radios. For base-station applications, Q > 100, breakdown voltage > 100 V and OIP3 > 65 dBm are required. The combination of high Q and high-breakdown voltage requires semiconductors with high mobility and high-breakdown electric field [1]; GaN with a mobility of >∼ 500 cm2/Vsec and a breakdown electric field of 2.5 MV/cm is a promising candidate. SiC-based varactors have also been recently reported [2]. We have previously demonstrated GaN large-area varactors that achieve high-breakdown voltage. The addition of a thin InGaN surface layer was shown to increase the diode breakdown voltage and reduce the leakage current under high reverse bias [3]. In this work, InGaN/GaN Schottky-diode microwave varactors with Q > 100 at 1 GHz, breakdown voltage > 120 V and OIP3 > 71 dBm are reported. To the best of our knowledge, the combination of Q, voltage handling capability and OIP3 represents advancement from any other reported varactors.

The objective of this project was to exploit a variety of semiconductor nanostructures, specifically semiconductor quantum wells, quantum dots, and nanowires, to achieve high power conversion efficiency in photovoltaic devices. In a thin-film device geometry, the objectives were to design, fabricate, and characterize quantum-well and quantum-dot solar cells in which scattering from metallic and/or dielectric nanostructures was employed to direct incident photons into lateral, optically confined paths within a thin (~1-3um or less) device structure. Fundamental issues concerning nonequilibrium carrier escape from quantum-confined structures, removal of thin-film devices from an epitaxial growth substrate, and coherent light trapping in thin-film photovoltaic devices were investigated. In a nanowire device geometry, the initial objectives were to engineer vertical nanowire arrays to optimize optical confinement within the nanowires, and to extend this approach to core-shell heterostructures to achieve broadspectrum absorption while maintaining high opencircuit voltages. Subsequent work extended this approach to include fabrication of nanowire photovoltaic structures on low-cost substrates.

Careful measurements of the OIP3 in high power photodetectors show a resonance peak at a particular bias voltage and photocurrent combination. In fact, for a given photocurrent, there exists an optimum bias voltage that maximizes the OIP3. One can envision a DC control circuit that would be able to maintain the optimum OIP3 performance from the photodiode. By optimizing the bias voltage for a given photocurrent, a peak OIP3 of +65dBm was measured which is believed to be the highest reported value to date.

The small size, light weight and low cost are main advantages of analog fiber links over coax links. In particular, analog fiber link is examined for photonic antenna (see Fig. 1) operating at high center frequencies in which a high power photodiode is deployed close to the antenna for downlink broadcasting [1]. High power and high output third order intercept point (OIP3) are among critical photodiode requirements in such application.

We have described a high optical power transmitter suitable for applications in harsh environments that require data modulation rates of up to 10 Gbps and modulated optical output power up to 25 mW. The compact package format enables size reductions for free space laser communications and antenna remoting terminals. High efficiency operation at lower optical power will provide DC power savings for digital transmission.

HPM systems fall into two general categories. The first uses moderately high power, quasi CW sources in the MW range with pulse duration around a millisecond and are generally of narrow bandwidth but with large average power. In the second category we have very high Peak power - in the GW range, but of very short pulse duration, typically in the 100ns range, and are of a large bandwidth. These sources, due to their pulse power technology are limited in average power and pulse repetition frequency. Some HPM applications require beam steering either by mechanical means or by phasing an array. Some applications, such as counter electronics, require the continuous sweeping of the beam over a large forward area. Sweeping arrays require phase shifters that are costly and difficult if they are required to accommodate a large bandwidth and Power.

The spatial distribution of strain in organometallic vapor phase epitaxy grown InGaAs/InP superlattice structures has been studied by varying the thicknesses of the InGaAs well and the InP barrier layers and measuring the strain. High resolution x-ray diffraction rocking curves were used to measure the strain from angular separation between the zeroth-order superlattice peak and the substrate (004) peak. The results are consistent with a compressive strain resulting from arsenic carryover into the InP following InGaAs growth. The strain is not localized at the interfaces but extends into the InP barrier layer. The amount of arsenic carryover increases with the growth time of the InGaAs well.

High-saturation power traveling-wave electroabsorption modulators (TW-EAMs) with modulation bandwidth greater than 40 GHz have been demonstrated. Microwave properties of the TW-EAM waveguide are extracted from the measured S-parameters using an equivalent circuit model. Excellent agreement is obtained between the predicted and the measured frequency responses.

Using high temperature fusion of InGaAs/InP on Si, we demonstrated an InGaAs/Si p-i-n photodiode with a photomultiplication gain of 11 at relatively low bias of −15 V. The photodiode exhibited a dark current of 30 nA at −5 V, and a responsivity of 0.3 A/W at 1.32 μm wavelength without antireflection coating. The measured device behavior were consistent with that predicted by a model of charged interface states resulting from the fusion.

We propose an efficient high-optical-saturation-power electroabsorption modulator (EAM) using intra-step-barrier quantum wells (IQWs) incorporating a step-barrier inside the well for both the conduction and the valence bands. From the simulation, we show that in the IQW (a) the onset of the redshift of the quantum-confined Stark effect is delayed to a higher electric field; and after the onset, (b) the transition energy and the oscillator strength respond sharply to the electric field. As the screening effect by the photogenerated carriers is reduced at the higher electric field, the optical saturation effect in the IQWs can be significantly reduced. Due to the higher optical power handling capability and better modulation efficiency, the EAM with IQWs is expected to substantially improve the fiber link performance.

Voltage-dependent responsivity nonlinearities are characterized experimentally and analytically for uni-traveling carrier directional coupled photodiodes (DCPD) with two types of design variations. OIP3 data follows the voltage-dependent responsivity predictions for both MMI width and PD width variations of the baseline DCPD. A maximum OIP3 of 39dBm was achieved for a device with a 3µm wide PD at 20mA and 4V.

A novel photodiode is presented using a directional coupler incorporated with a UTC style photodiode with 0.88 A/W responsivity and 35 dBm OIP3 at 25 mA. The device responsivity is characterized at various photocurrents up to 10 mA and the OIP3 is measured up to 25 mA and 10 GHz. Additionally, the device capacitance is measured and used to model the capacitance limited OIP3 of the device. The failure of the device was compared to a traditional waveguide photodiode showing burnout no longer occurs at the front of the device and demonstrated the potential of the new design to control the photocurrent density profile for a waveguide style photodiode.

The phenomenon of simultaneous compositional disordering and the formation of electrical resistive layers induced by oxygen implantation in InGaAs/InP superlattices has been investigated. The disordering characteristics have been studied as a function of implantation temperature and ion dose. It was found that implantation at elevated temperatures (referred to as the IM or ion mixing process) usually leads to much more efficient disordering compared to implantation at room temperature followed by annealing at the same elevated temperature (referred to as the implantation plus annealing process). Of particular interest is the observation that ion mixing at 550 °C with 1×1013 O+/cm2 leads to significantly more disordering than implantation with the same dose at room temperature followed by annealing at 550 °C for the same period of ion mixing time. In addition, the electrical resistance of the ion‐mixed layer at 550 °C increases 2600 times for the p‐type InGaAs/InP superlattice structure, whereas the sample...

Compositional disordering of III‐V compound superlattice structures has received considerable attention recently due to its potential application for photonic devices. The conventional method to induce compositional disorder in a layered structure is to implant a moderate dose of impurity ions (∼1015/cm2) into the structure at room temperature, followed by a high‐temperature annealing step (this process is referred to as IA here). Ion irradiation at room temperature alone does not cause any significant intermixing of layers. The subsequent high‐temperature annealing step tends to restrict device processing flexibility. Ion mixing (IM) is capable of enhancing compositional disordering of layers at a rate which increases exponentially with the ion irradiation temperature. As a processing technique to planarize devices, ion mixing appears to be an attractive technology. In this work, we investigate compositional disordering in the AlGaAs/GaAs and the InGaAs/InP systems using ion mixing. We found that the ion mixing behavior of these two systems shows a thermally activated regime as well as an athermal regime, similar to that observed for metal‐metal and metal‐semiconductor systems. Ion mixing is observed to induce compositional disordering at significantly lower temperatures than that for the IA process. We have compared the two processes in terms of five parameters: (1) irradiation temperature, (2) dose dependence, (3) dose rate dependence, (4) annealing, and (5) ion dependence (including electrical effects and mass dependence). We found that the IM process is more efficient in utilizing the defects generated by ion irradiation to cause disordering. Both the physical mechanism of ion mixing and possible device implications will be discussed.