Supercontinuum generation is an extensively studied and arguably the most important and all-encompassing nonlinear phenomenon. Yet, we do not have a good control over all the signals generated in this process. Usually, a large part of an octave spanning spectrum has an orders of magnitude weaker signal than the peak to be useful for any application. In this work, we show strong signal generation within a supercontinuum generated in a complementary metal-oxide-semiconductor compatible silicon Bragg grating waveguide. We show up to 23dB of signal enhancement over a 10nm full-width-at-half-maximum bandwidth at the Bragg resonance in the telecom window. Additionally, the grating is made by depositing charge carriers periodically, thus avoiding any dimensional change in the waveguide, and it can allow other functionalities offered by the induced electric field, such as second harmonic generation and free carrier sweeping. We believe this work opens up an avenue for research in nonlinear integrated photonics and signal enhancement in the supercontinuum by the Bragg effect (whether created through grating formation with dimensional variation in insulators and/or periodic charge carrier doping in semiconductors).

We present on recent progress on a hybrid tellurite glass and silicon nitride photonic platform. We show low loss waveguides and Q factors < 10^6 in microring resonators. We also show rare-earth-doped active devices, including erbium-doped and thulium-doped waveguide amplifiers and thulium-doped microring lasers. Using the same approach, we demonstrate nonlinear functionalities including efficient four-wave-mixing, supercontinuum generation and third harmonic generation in compact microring resonators and waveguides. The platform is highly promising for compact and low-cost passive, active and nonlinear photonic integrated circuits for applications in computing, communications, sensing and metrology.

Integrated modelocked lasers with high power are of utmost importance for next generation optical systems that can be field-deployable and mass produced. Here we study fully integrated modelocked laser designs that have the potential to generate ultrashort, high power, and high quality pulses. We explore a large mode area laser for high power pulse generation and study the various mode-locking regimes of dispersion managed soliton pulses in net anomalous and net normal dispersion cavities. Furthermore, we study numerically and experimentally general properties and tunability of a fast integrated saturable absorber based on low loss silicon nitride nonlinear interferometer. We believe this work guides the exploration of the future for integrated high power modelocked lasers.

Silicon photonics is coming of age; however, it is still lacking a monolithic platform for optical sources and nonlinear functionalities prompting heterogeneous integration of different materials tailored to different applications. Here we demonstrate tellurium oxide as a complementary metal oxide semiconductor silicon photonics platform for nonlinear functionalities, which is already becoming an established platform for sources and amplifiers. We show broadband supercontinuum generation covering the entire telecom window and show for the first time to our knowledge third-harmonic generation in its integrated embodiment. Together with the now-available lasers and amplifiers on integrated TeO 2 this work paves the way for a monolithic TeO 2 -based nonlinear silicon photonics platform.

We demonstrate a self-calibrated optical frequency synthesizer using a fully-integrated erbium-doped tunable laser. A 20 nm tuning range from 1544 nm to 1564 nm is achieved with~10−13 frequency instability at 10s averaging time. © 2019 The Author(s)

We present a CMOS-compatible, Q-switched mode-locked integrated laser operating at 1.9 µm with a compact footprint of 23.6 × 0.6 × 0.78mm. The Q-switching rate is 720 kHz, the mode-locking rate is 1.2 GHz, and the optical bandwidth is 17nm, which is sufficient to support pulses as short as 215 fs. The laser is fabricated using a silicon nitride on silicon dioxide 300-mm wafer platform, with thulium-doped Al2O3 glass as a gain material deposited over the silicon photonics chip. An integrated Kerr-nonlinearity-based artificial saturable absorber is implemented in silicon nitride. A broadband (over 100 nm) dispersion-compensating grating in silicon nitride provides sufficient anomalous dispersion to compensate for the normal dispersion of the other laser components, enabling femtosecond-level pulses. The laser has no off-chip components with the exception of the optical pump, allowing for easy co-integration of numerous other photonic devices such as supercontinuum generation and frequency doublers which together potentially enable fully on-chip frequency comb generation.

Ability to selectively enhance the amplitude and maintain high coherence of the supercontinuum signal with long pulses is gaining significance. In this work, an extra degree of freedom afforded by varying the dispersion profile of a waveguide is utilized to selectively enhance supercontinuum. As much as 16 dB signal enhancement in the telecom window and 100 nm of wavelength extension is achieved with a cascaded waveguide, compared to a fixed dispersion waveguide. Waveguide tapering, in particular with increasing width, is determined to have a flatter and more coherent supercontinuum than a fixed dispersion waveguide when longer input pulses are used. Furthermore, due to the strong birefringence of an asymmetric silicon waveguide the supercontinuum signal is broadened by pumping simultaneously with both quasi-transverse electric (TE) and quasi-transverse magnetic (TM) mode in the anomalous dispersion regime. Thus, selective signal generation is obtained by controlling the dispersion for the two modes. Such waveguides offer several advantages over optical fiber as the variation in dispersion can be controlled with greater flexibility in an integrated platform. This work paves the way forward for various applications in fields ranging from medicine to telecom where specific wavelength windows need to be targeted.

We demonstrate a silicon photonics optical frequency synthesizer (SPOFS). The frequency instability obtained in the telecom band is 1×10−12 at 1s level, comparable to a bench-top commercial optical frequency synthesizer system.

Efficient complementary metal-oxide semiconductor-based nonlinear optical devices in the near-infrared are in strong demand. Due to two-photon absorption in silicon, however, much nonlinear research is shifting towards unconventional photonics platforms. In this work, we demonstrate the generation of an octave-spanning coherent supercontinuum in a silicon waveguide covering the spectral region from the near- to shortwave-infrared. With input pulses of 18 pJ in energy, the generated signal spans the wavelength range from the edge of the silicon transmission window, approximately 1.06 to beyond 2.4 μm, with a -20 dB bandwidth covering 1.124-2.4 μm. An octave-spanning supercontinuum was also observed at the energy levels as low as 4 pJ (-35 dB bandwidth). We also measured the coherence over an octave, obtaining , in good agreement with the simulations. In addition, we demonstrate optimization of the third-order dispersion of the waveguide to strengthen the dispersive wave and discuss the advantage of having a soliton at the long wavelength edge of an octave-spanning signal for nonlinear applications. This research paves the way for applications, such as chip-scale precision spectroscopy, optical coherence tomography, optical frequency metrology, frequency synthesis and wide-band wavelength division multiplexing in the telecom window.

We demonstrate silicon-photonics-based octave spanning optical frequency combs phase coherently locked to a microwave oscillator for optical frequency synthesis. This system offers capability for precision optical synthesis of CW laser over the entire C-band.

Many spectroscopic techniques today rely on time-resolved measurements under short excitation pulses. Instead of using a chopped pump excitation, or ultrafast optical pulses, we expand on and apply the previously developed set of frequency domain methods to analyze the population level dynamics in rare-earth-doped media. By identifying the full frequency response of the gain medium, this method can accurately yield excited state lifetimes and can also be used to estimate transition cross-sections. The accuracy of the frequency domain methods are verified with Er 3+ -and Tm 3+ -doped fibers, and an Al 2 O 3 :Tm 3+ waveguide, recovering similar results as reported by time-resolved techniques. The complete frequency domain model presented here can be used in characterization of novel optical gain media, and can provide insights into population dynamics in solid state amplifiers and lasers.

We present a CMOS-compatible, Q-switched mode-locked integrated laser at 1.9µm with a compact footprint of 23.6×0.6×0.78mm, a Q-switched rate of 720kHz, a mode-locked rate of 1.2GHz, and pulse durations of 215fs.

Many optical systems require broadband filters with sharp roll-offs for efficiently splitting or combining light across wide spectra. While free space dichroic filters can provide broadband selectivity, on-chip integration of these high-performance filters is crucial for the scalability of photonic applications in multi-octave interferometry, spectroscopy, and wideband wavelength-division multiplexing. Here we present the theory, design, and experimental characterization of integrated, transmissive, 1 × 2 port dichroic filters using spectrally selective waveguides. Mode evolution through adiabatic transitions in the demonstrated filters allows for single cutoff and flat-top responses with low insertion losses and octave-wide simulated bandwidths. Filters with cutoffs around 1550 and 2100 nm are fabricated on a silicon-on-insulator platform with standard complementary metal-oxide-semiconductor processes. A filter roll-off of 2.82 dB nm −1 is achieved while maintaining ultra-broadband operation. This new class of nanophotonic dichroic filters can lead to new paradigms in on-chip communications, sensing, imaging, optical synthesis, and display applications.

Mode-locked lasers provide extremely low jitter optical pulse trains for a number of applications ranging from sampling of RF-signals and optical frequency combs to microwave and optical signal synthesis. Integrated versions have the advantage of high reliability, low cost and compact. Here, we describe a fully integrated mode-locked laser architecture on a CMOS platform that utilizes rare-earth doped gain media, double-chirped waveguide gratings for dispersion compensation and nonlinear Michelson Interferometers for generating an artificial saturable absorber to implement additive pulse mode locking on chip. First results of devices at 1.9 μm using thulium doped aluminum-oxide glass and operating in the Q-switched mode locking regime are presented.

An integrated artificial fast saturable absorber at 1.9 μm is demonstrated in a CMOS-compatible process. It is based on the Kerr effect in a nonlinear Mach-Zehnder Interferometer using silicon nitride waveguides embedded in SiO2.

This thesis discusses a series of advances toward–and resulting in–the demonstration of the first ultrafast THz-driven electron gun, a technology with the potential to deliver unprecedented electron beam quality to scientists studying matter at the ultrafast and ultrasmall scale via electron diffraction or x-ray imaging. In Part 1, we discuss various advances in generation of high energy pulsed THz radiation, a spectral regime uniquely effective at accelerating electrons but historically lacking in efficient sources. In particular, through various improvements to the grating-based tilted pulse front (TPF) technique, we demonstrate a record conversion efficiency of 1%. We also implement echelon-based TPF, achieving 3.5x higher efficiency than grating-based TPF for short (∼100 fs) pulses. Finally, we reuse the residual pump to obtain a recycled efficiency around half to a quarter that of the original. This reduced efficiency can be linked to spatio-spectral distortions in the residual pump, and we characterize these distortions to better understand the asymmetric dynamics of the THz generation process. In Part 2, we discuss the design, testing, and commissioning of an electron gun driven exclusively by THz radiation. The accelerating structure, capable of broadband, dispersionless THz propagation and sub-wavelength confinement, is analyzed through electromagnetic simulations and experimental tests. We also characterize the accelerated electrons in absolute charge and spectrum as a function of emission phase and THz energy, while showing that the behavior matches well with theory and simulation. Our first-version THz gun delivers near 1 keV electrons accelerated by field strengths surpassing that of the best operational RF guns. The gun also delivers narrowband electron spectra which can already be used for low-energy electron diffraction. Thesis Supervisor: Franz X. Kärtner Title: Professor of Electrical Engineering Thesis Supervisor: Erich P. Ippen Title: Elihu Thomson Professor of Electrical Engineering

Mid-infrared laser sources are of great interest for various applications, including light detection and ranging, spectroscopy, communication, trace-gas detection, and medical sensing. Silicon photonics is a promising platform that enables these applications to be integrated on a single chip with low cost and compact size. Silicon-based high-power lasers have been demonstrated at 1.55 μm wavelength, while in the 2 μm region, to the best of our knowledge, high-power, high-efficiency, and monolithic light sources have been minimally investigated. In this Letter, we report on high-power CMOS-compatible thulium-doped distributed feedback and distributed Bragg reflector lasers with single-mode output powers up to 267 and 387 mW, and slope efficiencies of 14% and 23%, respectively. More than 70 dB side-mode suppression ratio is achieved for both lasers. This work extends the applicability of silicon photonic microsystems in the 2 μm region.

The spontaneous emission lifetime in Al2O3:Tm3+ waveguides is measured to be 568 +/- 48 mu s, using a frequency-domain method. The method is studied and verified in Er3+-doped silica fiber, yielding a measured lifetime of 9.73 +/- 0.08 ms.