The dependence of thickness and concentration product (TCP) of single-wall carbon nanotubes saturable absorber (SWCNTs SA) on stabilizing and shortening pulse width in passively mode-locked erbium-doped fiber ring laser (MLEDFL) was investigated and measured. The TCP represented the amounts of SWCNTs, which the optical beam encountered when passing through the SWCNTs SA. If the TCP was smaller than 8.25 (£gm x wt%), the spectral bandwidth was below 2 nm. The pulse shaping was dominated by its own self amplitude modulation (SAM) of SWCNTs SA. With further increasing TCP, the soliton-like ML operation was achieved and the spectral bandwidth was expanded to 6 nm. For soliton-like mode locking (ML) operation, the area theorem dominated the pulse shaping. Through area theorem analysis, the estimation of SPM increased as the TCP increased. The adequate enhanced SPM for balancing the slight negative GVD was provided to generate soliton-like ML pulses shorten the pulse width. However, as the TCP increased, the soliton pulse energy decreased. The decreasing soliton pulse energy restricted the further pulse shortening. The results showed that the dependence of the pulse energy and nonlinear self phase modulation (SPM) on TCP enabled to determine the shortest pulse width in MLEDFL based on the area theorem. At optimized TCP of 70.93 (£gm x wt%), it was found that the shortest pulse width of 418 fs. In addition, based on the estimated SPM from area theorem, the nonlinear refractive index n2 was calculated at the level of 0.4 - 1 x 10^-15 m^2/W that was close to the literature values of 10^-15 - 10^-16 m2/W. It provides another way to estimate the nonlinear refractive index except for the Z-scan measurement. We could also estimate the SPM if an active Z-scan measurement was taken to obtain the nonlinear refractive index of the sample. We realized the trend of pulse energy through few samples in MLEDFL, the behavior of pulse width could be theoretically simulated based on area theorem. Hence, with the area theorem analysis, the optimized TCP of SWCNTs SA could be simulated and estimated to generate the shortest pulse width from the trends of pulse energy and estimated SPM. The significant effect of TCP on pulse energy, SPM, pulse width, and spectral bandwidth of MLFLs suggests that the TCP represents the total amount of SWCNTs in SA, which can be used as one of key parameters for characterizing the passive MLFL pulse width. Through the study of the dependence of TCP on ML pulses in MLEDFL, it may provide a guideline to fabricate an effective SWCNTs SA to generate the shortest pulse width of the MLEDFL.

In the current transmission systems, the transmission capacity is still not enough. The information bandwidth of the optical fiber communication system is limited by the optical amplifier bandwidth, and more efficient use of the bandwidth is a very important issue. Therefore, the amplitude and phase shift keying (APSK) is one attractive method of multi-bit per symbol modulation scheme to improve the spectral efficiency, and it can effectively increase the transmission capacity. To improve the capacity and the spectral efficiency, the advanced modulation format is effective, and the coherent detection scheme is also effective. However, an optical phase-locked loop (PLL) to lock the local oscillator (LO) phase and the signal phase required for the homodyne detection is still difficult to realize and it makes the receiver circuit complicated. Using the digital coherent receiver, the optical carrier phase information can be recovered by means of the digital signal processing (DSP), and this scheme enables to eliminate the optical PLL circuit by the phase estimation algorithm through the DSP. The stored data can be offline processed by using the MATLAB program. This master thesis is focusing on studying the transmission performance of the APSK format using the DSP in the digital coherent receiver. 497km transmission experiment has been conducted. Subsequently, the stored data are offline processed by the algorithms of the DSP. Then, the APSK performances between back-to-back and 497km transmission are compared.

The grid voltage is normally required to avoid transient current of the inverter due to asynchronously grid-paralleling connection. This paper presents a seamless transition method to allow the inverter to connect to the grid at any time with no requirement of the grid voltage. The control of the inverter consists of the droop control and the riding-through control. In the droop-controlled mode, the inverter can connect to the utility and supply power according to its rated capacity. On the other hand, the riding-through mode is proposed to suppress the transient current due to asynchronous paralleling. In this mode, the zero-current control is realized to reduce transient current and a phase-locked loop is designed to correct the angle of the inverter output voltage. In addition, the virtual inductance is implemented to improve transient current resulting from the mode transition back to the droop control mode. Design considerations of the seamless transition method are provided and test results are conducted to verify its effectiveness.

Coherent nonlinear effects such as Electromagnetically Induced Transparency (EIT), Coherent Population Trapping (CPT), and Slow light are studied in thermal Rb vapor by both continuous and pulsed laser fields. This work primarily includes three parts: (I) mode-locked rubidium laser and its applications (II) enhanced coupling between optical and sound waves in the forward direction via ultra-slow light (III) optical steering via ultra-slow light in rubidium vapor. In part(I), I describe the construction and study of a mode-locked rubidium laser operating at the Rb D1 line using an active mode-locking technique inside the laser cavity. The mode-locked laser field is used to observe coherent effects in a dense rubidium gas. In part(II), I experimentally demonstrate enhanced acoustic-optic coupling that occurs when the velocity of sound is close to the group velocity of light. Dragging of the light by effective motion of the gas in a Rb cell is the origin of enhanced coupling. Good agreement between theory and experiment is found. In part(III), I experimentally demonstrate optical beam deflection in coherently driven rubidium vapor due to the steep refraction index profile in the region of EIT.

Circuit optimization is extremely important in order to design today's high performance integrated circuits. As systems become more and more complex, traditional optimization techniques are no longer viable due to the complex and simulation intensive nature of the optimization problem. Two examples of such problems include clock mesh skew reduction and optimization of large analog systems, for example Phase locked loops. Mesh-based clock distribution has been employed in many high-performance microprocessor designs due to its favorable properties such as low clock skew and robustness. However, such clock distributions can become quite complex and may consist of hundreds of nonlinear drivers strongly coupled via a large passive network. While the simulation of clock meshes is already very time consuming, tuning such networks under tight performance constraints is an even daunting task. Same is the case with the phase locked loop. Being composed of multiple individual analog blocks, it is an extremely challenging task to optimize the entire system considering all block level trade-offs. In this work, we address these two challenging optimization problems i.e.; clock mesh skew optimization and PLL locking time reduction. The expensive objective function evaluations and difficulty in getting explicit sensitivity information make these problems intractable to standard optimization methods. We propose to explore the recently developed asynchronous parallel pattern search (APPS) method for efficient driver size tuning. While being a search-based method, APPS not only provides the desirable derivative-free optimization capability, but also is amenable to parallelization and possesses appealing theoretically rigorous convergence properties. In this work it is shown how such a method can lead to powerful parallel optimization of these complex problems with significant runtime and quality advantages over the traditional sequential quadratic programming (SQP) method. It is also shown how design-specific properties and speeding-up techniques can be exploited to make the optimization even more efficient while maintaining the convergence of APPS in a practical sense. In addition, the optimization technique is further enhanced by introducing the feature to handle non-linear constraints through the use of penalty functions. The enhanced method is used for optimizing phase locked loops at the system level.

This thesis establishes a quantization noise model of a delta-sigma modulator (DSM), which is utilized to estimate the phase noise performance of a fractional-N frequency synthesizer. In delta-sigma modulator structures, we choose multi-stage noise shaping (MASH) and single-loop structure for investigating the advantages and disadvantages. We have implemented a 3rd order single-loop and a 3rd order MASH DSM by using Verilog codes and a Xilinx field-programmable gate-array (FPGA). With a reference frequency of 12MHz, the fractional-N frequency synthesizer has an output frequency band of 2400~2500MHz, and a frequency resolution of 183 Hz. The measured phase noise is lower than -54 dBc/Hz at 10 kHz offset frequency. The PLL settling time is less than 29us with a 48 MHz frequency hopping.

Ultra-Wideband ¡}UWB¡~Communication Technology is one of the potential technologies in indoor wireless communication applications. Because of the property of fine resolution of transmitted signal by UWB, it is powerful on indoor location applications. In the first place, we need to estimate the time of arrival based on the wireless location applications. Whether synchronization between the template signals and received signals affects directly the SNR of the estimator output and decreases the ranging accuracy. Because of the transmitted signal is the type of impulse radio for UWB system, it is more important on the time accuracy of the internal oscillator. In the thesis, we utilize the Delay-Locked Loop ¡}DLL¡~ structure with Self-tuning function to reduce the timing jitter in the internal oscillator. We can improve the stability in the tracking loop and utilize multipath canceller to cancel the multipath interference in the indoor environment. When reaching synchronization between the template signal and received signal by using the tracking loop, we can improve ranging accuracy and increase location precision according to the received signal.

Abstract¡G For the fractional-N frequency synthesizers using delta-sigma modulation techniques, the noise source dominant to degrade the spectral purity comes from phase intermodulation of quantization noise due to the PLL nonlinearity. To study and improve the PLL nonlinearity effect, this thesis applies the theory of white quantization noise and nonlinear analysis method to simulate the frequency responses of quantization noises in delta-sigma modulators (DSM) with different order and in various architecture. With the help of Agilent EEsof¡¦s ADS tool, the phase noise performance of the studied fractional-N frequency synthesizers can be well predicted. For demonstration, this thesis work implements a 2.4 GHz fractional-N frequency synthesizer hybrid module, and measures the phase noise under considering various combinations of DSM order and architecture, PLL bandwidth and reference frequency. Another demonstration of this thesis is to implement a PLL IC using 0.18 £gm CMOS process. The implemented PLL IC operates in the frequency range from 2120 to 2380 MHz with a supply voltage of 1.8 V and a current consumption of 27 mA. Under the test condition of reference frequency and PLL bandwidth equal to 20 MHz and 50 kHz, respectively, the measured phase noise is 90 dBc/Hz at an offset frequency of 100 kHz and the measured stable time is about 40 £gs for a frequency jump of 80MHz.

Phase locking of external-cavity diodes laser¡]ECDL¡^ to the stabilized optical frequency combs of a femtosecond mode-locked laser. Optical frequency combs of a femtosecond mode-locked laser can be the reference standard of dual-wavelength external-cavity diode lasers (ECDLs). Frequency stabilization of two external-cavity diode laser is also demonstrated simultaneously.Suppression of the frequency fluctuation of two ECDLs from hundreds MHz to 200 Hz is demonstrated and characterized. Meanwhile, frequency tunable continuous-wave Tera-Hertz (cw THz) wave is generated and observed by photomixing of the output of two frequency stabilized ECDLS with tunable relative frequency difference on a photoconductive antennas. In our experiment, cw THz wave is demonstrated and with tuning range from 0.200 to 1.240THz and could be attribute as frequency standard of THz.

In this study we use AFM-based nanolithography technique to produce nanofeatures of the single strand DNA and LNA probe molecules which are prepared via thiolated nucleic acid self-assembled monolayers (SAMs) on gold substrates. The goal is to observe the topographic changes of the DNA film structures resulting from the formation of rigid double strand DNA when the target and probe DNAs bind together. The so-called hybridization depends strongly on the probe density on the substrate surface. To find the proper probe density for hybridization, we vary the concentration of the probe DNA and search for the optimal conditions for measuring the height changes of the nanofeatures. We also monitor the topographic changes of the DNA nanofeatures in the different target DNA concentrations as a function of time, and the binding isotherms are fitted with the Langmuir adsorption model to derive the equilibrium dissociation constant and maximum hybridization efficiency. In addition, we extend the nanoscale hybridization reaction detection to mismatched DNA:DNA and LNA:DNA hybridization, and observe that topographic change of mismatched hybridization is inconspicuous and rapidly reach equilibrium. The results reveal the apparent difference between the perfect match and mismatch conditions, and validate that this approach can be applied to differentiate the situations for both perfect match and mismatch cases, demonstrating its potentials in the gene chip technology.