The cost effective comb based laser sources are considered to be one of the prominent emitters used in optical communication (OC) and photonic integrated circuits (PIC). With the rising demand for delivering triple-play services (voice, data and video) in FTTH and FTTP-based WDM-PON networks, metropolitan area network (MAN), and short-reach rack-to-rack optical computer communications, a versatile and cost effective WDM transmitter design is required, where several DFB lasers can be replaced by a cost effective broadband comb laser to support on-chip optical signaling. Therefore, high performance quantum dot (Q.Dot) comb lasers need to satisfy several challenges before real system implementations. These challenges include a high uniform broadband gain spectrum from the active layer, small relative intensity noise with lower bit error rate (BER) and better temperature stability. Thus, such short wavelength comb lasers offering higher bandwidth can be a feasible solution to address these challenges. However, they still require thorough characterization before implementation. In this project, we briefly characterized the novel quantum dot comb laser using duty cycle based electrical injection and temperature variations where we have observed the presence of reduced thermal conductivity in the active layer. This phenomenon is responsible for the degradation of device performance. Hence, different performance trends, such as broadband emission and spectrum stability were studied with pulse and continuous electrical pumping. The tested comb laser is found to be an attractive solution for several applications but requires further experiments in order to be considered for photonic intergraded circuits and to support next generation computer-communications.

<p>Kerr frequency comb, a sequence of equally spaced sharp lines in frequency domain generated via four-wave mixing process, has multiple applications such as spectroscopy, metrology, and atomic clocks. Conventional frequency combs generated from mode-locked laser have the limitations of low repetition rate and large volume. One novel platform, silicon nitride (SiN) microring resonator (MRR), can overcome such disadvantages. The SiN MRR is a low loss waveguide resonator and has good reliability and capacity for on-chip integration, which enables a portable solution for Kerr frequency comb.</p><p>This thesis focuses on the design and characterization of the SiN MRR to optimize the important performance characteristics for the applications.<br></p><p>In Kerr comb applications, phase coherence between the comb lines is required to eliminate unwanted signals in the systems. Therefore, the investigation of the coherent state in MRR based comb generation can benefit the development of comb generation techniques. In particular, dark pulses exhibit much higher comb conversion efficiency than the single soliton combs.<br></p><p>The tunability of Kerr comb is another important performance characteristic of the applications, which is useful for multiple applications, such as matching the comb line spacing to the wavelength multiplexing grid for coherent communication or aligning the on-chip laser wavelength and MRR resonance frequency during the integration. The theoretic analysis of thermal tuning and experimental characterization of resonance frequency tuning via an on-chip microheater are performed in this thesis to explore the thermal tuning efficiency and its limitation.<br></p><p>Another important performance characteristics of the frequency comb is the comb bandwidth. Large bandwidth comb will be beneficial for application like dual comb spectroscopy. In addition, octave-spanning Kerr comb is desired due to its capacity of f-2f self-referencing for comb line frequencies stabilization for the applications like atomic clocks. To demonstrate on-chip octave-spanning Kerr soliton, the dispersion engineering is utilized in the device design to optimize the pump dispersion and dispersive wave generation simultaneously. The octave-spanning solitons are achieved on SiN MRRs with around 900 GHz repetition rate.<br></p><p>Finally, two optical division approaches are demonstrated to read out the large repetition rate of the octave-spanning soliton on all-SiN platform with auxiliary combs to enable the locking of undetectable repetition rate with less complexity in the fabrication and integration. The first approach uses a 25 GHz soliton; whose repetition rate is directly detectable via a photodiode. The second approach employs a Vernier scheme with an 880 GHz soliton to provide an alternative optical division scheme with lower requirements in fabrication ultrahigh Q MRRs. The divided repetition rate can be locked to enable the fully stabilization of frequency comb to provide an on-chip high stability and low noise frequency comb source.<br></p><p></p>

The report aims to investigate the influence of chemical reactions on comb crack formation and propagation in coated cemented carbide milling inserts with different compositions. A series of novel experimental techniques have been developed and applied to understand oxidation and corrosion effects on comb cracks. Furthermore microstructure changes in the region of the comb cracks on worn milling inserts were studied by high resolution microscopy. It has been observed that the main effect of the oxidation and corrosion on comb cracks is connected to an attack of the binder phase, affecting its composition, distribution and morphology. Different comb crack types for dry and wet milling have been observed. In the presence of cooling media (wet machining) inserts present lateral cracks (fatigue induced) connected to the principal comb crack, which form at regions where the binder has been strongly corroded. Despite the addition of Cr and (Ta,Nb)C enhance both the oxidation and corrosion attack resistance have a minor effect on the formation and propagation of comb cracks. Schematic models based on the experimental results and scientific discussions are presented to understand the influence of oxidation and corrosion in the formation and propagation of comb cracks.

The paper covers the use of a COMB generator to detect and diagnose RF problems related to cable and shielding problems in data acquisition systems in situ. The setup and method to conduct these tests is discussed in detail. Circuit design for a COMB generator is covered, as well as commercially available units. The use of a spectrum analyzer for the detector is covered and characteristic outputs are examined. Low cost alternatives to the spectrum analyzer are also examined. The COMB generator and the spectrum analyzer used for the test are portable devices and so, lend themselves to field use where access to alternating current sources is problematic.

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<p>In this Thesis I report on my work done in replicating the Pound-Drever-Hall (PDH) laser stabilization technique as well as applications of PDH to microring resonators and generated Optical Frequency Combs (OFC). These works have been broken down into three sections. First, I replicated the PDH method with a continuous wave (CW) laser along with a Fabry-Pérot Cavity (FPC). Second, I applied the same technique to a 25 GHz Free Spectral Range (FSR) microring resonator fabricated in Silicon Nitride. Third, I applied the PDH technique to a high Quality Factor (Q) high Free Spectral Range (FSR) microring resonator in preparation to lock the repetition rate of two soliton combs beat together. The last experiment was for an application towards a compact optical clock system; such systems will have a wide impact on the infrastructure of our navigation and communication structures in use today.</p>

Modern Automatic Blood Pressure Measurement Techniques are based on measuring the cuff pressure and on sensing the pulsatile amplitude variations. These measurements are very sensitive to motion of the patient or the surroundings where the patient is. The slightest unexpected movements could offset the readings of the automatic Blood Pressure meter by a large amount or render the readings totally meaningless. Every effort must be taken to avoid subjecting the body of the patient or the patient's surroundings to motion for obtaining a reliable reading. But there are situations in which we need Blood Pressure Measurements with the patient or his surroundings in motion; for instance in an ambulance while a patient is being transported to a hospital. In this thesis, we present a technique to reduce the effect of motion artifact from Blood Pressure measurements. We digitize the blood pressure waveform and use Digital Signal Processing Techniques to process the corrupted waveform. We use the differences in frequency spectra of the Blood Pressure signal and motion artifact noise to remove the motion artifact noise. The motion artifact noise spectrum is not very well defined, since it may consist of many different frequency components depending on the kind of motion. The Blood Pressure signal is more or less a periodic signal. That translates to periodicity in the frequency domain. Hence, we designed a digital filter that could take advantage of the periodic nature of the Blood Pressure Signal waveform. The filter is shaped like a comb with periodic peaks around the signal frequency components. Further processing of the filtered signal: baseline restoration and level shifting help us to further reduce the noise corruption.

This dissertation details work on high repetition rate semiconductor mode-locked lasers. The qualities of stable pulse trains and stable optical frequency content are the focus of the work performed. First, applications of such lasers are reviewed with particular attention to applications only realizable with laser performance such as presented in this dissertation. Sources of timing jitter are also reviewed, as are techniques by which the timing jitter of a 10 GHz optical pulse train may be measured. Experimental results begin with an exploration of the consequences on the timing and amplitude jitter of the phase noise of an RF source used for mode-locking. These results lead to an ultralow timing jitter source, with 30 fs of timing jitter (1 Hz to 5 GHz, extrapolated). The focus of the work then shifts to generating a stabilized optical frequency comb. The first technique to generating the frequency comb is through optical injection. It is shown that not only can injection locking stabilize a mode-locked laser to the injection seed, but linewidth narrowing, timing jitter reduction and suppression of superfluous optical supermodes of a harmonically mode-locked laser also result. A scheme by which optical injection locking can be maintained long term is also proposed. Results on using an intracavity etalon for supermode suppression and optical frequency stabilization then follow. An etalon-based actively mode-locked laser is shown to have a timing jitter of only 20 fs (1Hz-5 GHz, extrapolated), optical linewidths below 10 kHz and optical frequency instabilities less than 400 kHz. By adding dispersion compensating fiber, the optical spectrum was broadened to 2 THz and 800 fs duration pulses were obtained. By using the etalon-based actively mode-locked laser as a basis, a completely self-contained frequency stabilized coupled optoelectronic oscillator was built and characterized. By simultaneously stabilizing the optical frequencies and the pulse repetition rate to the etalon, a 10 GHz comb source centered at 1550 nm was realized. This system maintains the high quality performance of the actively mode-locked laser while significantly reducing the size weight and power consumption of the system. This system also has the potential for outperforming the actively mode-locked laser by increasing the finesse and stability of the intracavity etalon. The final chapter of this dissertation outlines the future work on the etalon-based coupled optoelectronic oscillator, including the incorporation of a higher finesse, more stable etalon and active phase noise suppression of the RF signal. Two appendices give details on phase noise measurements that incorporate carrier suppression and the noise model for the coupled optoelectronic oscillator.

No description available.

No description available.