Electroabsorption modulators (EAM) have attract a lot of interests in high-speed optical communication due to low chirp, high-efficiency operation and the capability to be integrated with other semiconductor devices. Enhancing the operation by overcoming the trade-off between RC-limitation and high-speed performance, traveling-wave types of EAMs (TWEAM) have been documented to be a good candidate. In this thesis, a novel type of TWEAMs, namely undercut-etching-the-active-region type (UEAR), have been characterized and analyzed. There are two topics in this thesis, namely (1) one is to compare the performance of the UEAR and conventional ridge-waveguide (RW) types of TWEAM. The regime of D.C. to 40GHz small-signal modulation and 10 Gbits/sec large-signal data transmission are used to characterize and compare the performance of TWEAMs. In comparison with conventional ridge-waveguide (RW) TWEAM, 3dB lower optical-insertion-loss, at least 6dB higher in RF-link (D.C. to 40GHz) and faster electro-optical response (3dB bandwidth of 25GHz at 50£[-termination for UEAW and 15GHz for RW) are obtained in UEAW-TWEAM. Error-free 10Gbits/sec operation with high sensitivity of ¡V36.2 dBm and low swing voltage of 0.6V have been achieved in UEAW-TWEAM, a 3.2dB enhancement over RW-TWEAM, indicating the trade-off in designing electroabsorption modulators can be greatly released by novel type structure (UEAW). (2) The other topic is the application of TWEAM to all-optical wavelength converters. The generating photocurrent by optical absorption is the effect accompanying with the electrical-to-optical modulation in the EAM. Using the properties of cross-absorption and generating photocurrent, high-speed all-optical modulation can be potentially implemented in the application of EAMs. Long -waveguide high-speed TWEAMs can thus have high-extinction ratio performance in all-optical conversion. The conversion efficiency of -26dB and high extinction ration of >20dB are obtained in this experiment, showing the potential in the application of all-optical conversion.

Abtract Three different microstrip transmission-line layouts between the pads and an optical modulator waveguide have been designed and compared for their circuit response. In the first design, two 50£[ input and output microstrip transmission lines are connected to the center of the 24.58£[ semiconductor waveguide. In the second design, two 78£[ input and output microstrip transmission lines are connected to the center of waveguide. The third design represents a traveling-wave EA modulator. After optimizing the lengths of the transmission lines through our circuit simulation, we find that the traveling-wave optical modulator (the third layout) have the best circuit response of bandwidth ~22.4GHz and voltage reflection coefficient ~40%. The traveling-wave optical modulator not only overcomes the RC constant limit but also makes use of long waveguide to satisfied the high-speed requirement. At the same time, this circuit increases the extinction ratio and optical saturation power. In the fabrication process, we use polyimide to planarize both sides of the ridge waveguide and evaporate the top electrode on the polyimide. In addition, we use a special wet etching to form sloped edges for rasing ground pads up to the same level of the signal pad. This will allow us to use coplanar microwave probes to measure the devices.

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Multiple-quantum-well (M.Q.W.) and quantum-confined-stark-effect (Q.C.S.E.) have been widely used in designing and fabricating electroabsorption modulators. In this paper, material InAlAs/InGaAlAs near 1500nm transition is used to be our target for designing and fabricating EAM due to its high band-offset ratio (electron to hole) and the strong exciton effect. A calculation model for quantum well absorption has been developed to design EAM active region. Asymmetrically inserting a thin-spiked potential barrier into wide Q.W. structure, the Q.W. can have high efficiency of Q.C.S.E. without lowing the electron-hole wave function overlap integral, causing high electroabsorption coefficient and optical modulation. Tuning material composition (~-0.4% tensile strain ) is also used for polarization independence characteristics. Traveling-wave EAM based on InAlAs / InGaAlAs material system is also fabricated and measured. Polarization independence 2~5 dB operation, low voltage swing of 1V for 15 dB extinction ratio, high-speed electrical-to-optical response with ¡V3dB bandwidth of >20GHz at 50£[ termination have been achieved showing high potential in broad band fiber optical communication.

Semiconductor optical amplifiers (SOA) and electroabsorption modulators (EAM) have been become vital elements to obtain high-output-power and high-speed optical signal in the optical fiber communications. In this paper, we propose a novel type cascaded integrated SOAs and EAMs, which are monolithically integrated in the same chip without any regrowth. In the active region, high electron bandgap offset material, InGaAsP/InAlGaAs, is used in order to get high optical gain and also high modulation. Using cascaded SOAs and EAMs, high impedance of microwave stripe lines are the bridges connecting the small EAM elements, bring up higher impedance and thus enhancing the microwave transmission. The optical waveguide is made by selectively undercut etching InGaAsP/InAlGaAs material in order to reduce the optical scattering loss and also the microwave loss due to the low parasitic capacitance. The processing is described by the following steps: (1) ion implantation to get electrical isolation; (2) wet etching to form the optical waveguide ridge; (3) e-gun evaporation to get n- and p- metalization ; (4) spinning PMGI as planarization; (5)Final thick metalizations as for microwave transmission line. The final integrated cascaded SOAs and EAMs has been successfully fabricated and measured. In comparison with single EAM, higher than 10GHz of ¡V3dB electrical transmission has been found, indicating the cascaded integration structure has better impedance matching and also higher electrical transmission. The measured optical gain is higher than 5dB with 11dB/V modulation efficiency at excitation wavelength of 1568nm.

In this thesis various subjects at the crossroads of quantummechanics and device physics are treated, spanning from afundamental study on quantum measurements to fabricationtechniques of controlling gates for nanoelectroniccomponents. Electron waveguide components, i.e. electronic componentswith a size such that the wave nature of the electron dominatesthe device characteristics, are treated both experimentally andtheoretically. On the experimental side, evidence of partialballistic transport at room-temperature has been found anddevices controlled by in-plane Pt/GaAs gates have beenfabricated exhibiting an order of magnitude improvedgate-efficiency as compared to an earlier gate-technology. Onthe theoretical side, a novel numerical method forself-consistent simulations of electron waveguide devices hasbeen developed. The method is unique as it incorporates anenergy resolved charge density calculation allowing for e.g.calculations of electron waveguide devices to which a finitebias is applied. The method has then been used in discussionson the influence of space-charge on gate-control of electronwaveguide Y-branch switches. Electron waveguides were also used in a proposal for a novelscheme of carrierinjection in low-dimensional semiconductorlasers, a scheme which altogether by- passes the problem ofslow carrier relaxation in suchstructures. By studying aquantum mechanical two-level system serving as a model forelectroabsorption modulators, the ultimate limits of possiblemodulation rates of such modulators have been assessed andfound to largely be determined by the adiabatic response of thesystem. The possibility of using a microwave field to controlRabi oscillations in two-level systems such that a large numberof states can be engineered has also been explored. A more fundamental study on quantum mechanical measurementshas been done, in which the transition from a classical to aquantum "interaction free" measurement was studied, making aconnection with quantum non-demolition measurements.

<p>In this thesis various subjects at the crossroads of quantummechanics and device physics are treated, spanning from afundamental study on quantum measurements to fabricationtechniques of controlling gates for nanoelectroniccomponents.</p><p>Electron waveguide components, i.e. electronic componentswith a size such that the wave nature of the electron dominatesthe device characteristics, are treated both experimentally andtheoretically. On the experimental side, evidence of partialballistic transport at room-temperature has been found anddevices controlled by in-plane Pt/GaAs gates have beenfabricated exhibiting an order of magnitude improvedgate-efficiency as compared to an earlier gate-technology. Onthe theoretical side, a novel numerical method forself-consistent simulations of electron waveguide devices hasbeen developed. The method is unique as it incorporates anenergy resolved charge density calculation allowing for e.g.calculations of electron waveguide devices to which a finitebias is applied. The method has then been used in discussionson the influence of space-charge on gate-control of electronwaveguide Y-branch switches.</p><p>Electron waveguides were also used in a proposal for a novelscheme of carrierinjection in low-dimensional semiconductorlasers, a scheme which altogether by- passes the problem ofslow carrier relaxation in suchstructures. By studying aquantum mechanical two-level system serving as a model forelectroabsorption modulators, the ultimate limits of possiblemodulation rates of such modulators have been assessed andfound to largely be determined by the adiabatic response of thesystem. The possibility of using a microwave field to controlRabi oscillations in two-level systems such that a large numberof states can be engineered has also been explored.</p><p>A more fundamental study on quantum mechanical measurementshas been done, in which the transition from a classical to aquantum "interaction free" measurement was studied, making aconnection with quantum non-demolition measurements.</p>

Inter-chip input-output (I/O) communication bandwidth demand, which rapidly scaled with integrated circuit scaling, has leveraged equalization techniques to operate reliably on band-limited channels at additional power and area complexity. High-bandwidth inter-chip optical interconnect architectures have the potential to address this increasing I/O bandwidth. Considering future tera-scale systems, power dissipation of the high-speed I/O link becomes a significant concern. This work presents a design flow for the power optimization and comparison of high-speed electrical and optical links at a given data rate and channel type in 90 nm and 45 nm CMOS technologies. The electrical I/O design framework combines statistical link analysis techniques, which are used to determine the link margins at a given bit-error rate (BER), with circuit power estimates based on normalized transistor parameters extracted with a constant current density methodology to predict the power-optimum equalization architecture, circuit style, and transmit swing at a given data rate and process node for three different channels. The transmitter output swing is scaled to operate the link at optimal power efficiency. Under consideration for optical links are a near-term architecture consisting of discrete vertical-cavity surface-emitting lasers (VCSEL) with p-i-n photodetectors (PD) and three long-term integrated photonic architectures that use waveguide metal-semiconductor-metal (MSM) photodetectors and either electro-absorption modulator (EAM), ring resonator modulator (RRM), or Mach-Zehnder modulator (MZM) sources. The normalized transistor parameters are applied to jointly optimize the transmitter and receiver circuitry to minimize total optical link power dissipation for a specified data rate and process technology at a given BER. Analysis results shows that low loss channel characteristics and minimal circuit complexity, together with scaling of transmitter output swing, allows electrical links to achieve excellent power efficiency at high data rates. While the high-loss channel is primarily limited by severe frequency dependent losses to 12 Gb/s, the critical timing path of the first tap of the decision feedback equalizer (DFE) limits the operation of low-loss channels above 20 Gb/s. Among the optical links, the VCSEL-based link is limited by its bandwidth and maximum power levels to a data rate of 24 Gb/s whereas EAM and RRM are both attractive integrated photonic technologies capable of scaling data rates past 30 Gb/s achieving excellent power efficiency in the 45 nm node and are primarily limited by coupling and device insertion losses. While MZM offers robust operation due to its wide optical bandwidth, significant improvements in power efficiency must be achieved to become applicable for high density applications.