Intra-Pulse Intensity Noise Shaping by Saturable Absorbers

In this work, we identify and characterize intra-pulse intensity noise shaping by saturable absorbers applied in mode-locked lasers and ultra-low noise nonlinear fiber amplifiers. Reshaped intra-pulse intensity noise distributions are shown to be inevitably interconnected with self-amplitude modulation, the fundamental physical mechanism for initiation and stabilization of ultra-short pulses in the steady-state of a mode-locked laser. A theoretical model is used to describe the ultrafast saturation dynamics by an intra-pulse noise transfer function for widely-applied slow and fast saturable absorbers. For experimental verification of the theoretical results, spectrally-resolved relative intensity noise measurements are applied on chirped input pulses to enable the direct measurement of intra-pulse noise transfer functions using a versatile experimental platform. It is further demonstrated, how the characterized intra-pulse intensity noise distribution of ultrafast laser systems can be utilized for quantum-limited intensity noise suppression via tailored optical bandpass filtering

Watt-class CMOS-compatible optical high power amplifier

High power amplifiers are critical components in optical systems spanning from long range optical sensing and optical communication systems to micromachining and medical surgery. Today, integrated photonics with its promise of large reductions in size, weight and cost cannot be used in these applications, due to the lack of on-chip high power amplifiers. Integrated devices severely lack in output power due to their small size which limits energy storage capacity. For the last two decades, large mode area (LMA) technology has played a disruptive role in fiber amplifiers enabling a dramatic increase of output power and energy by orders of magnitude. Thanks to the capability of LMA fiber to support significantly larger optical modes the energy storage and power handling capability has significantly increased. Therefore, an LMA device on an integrated platform can play a similar role in power and energy scaling of integrated devices. In this work, we demonstrate LMA waveguide-based CMOS compatible watt-class high power amplifiers with an on-chip output power reaching beyond ~ 1 W within a footprint of only ~ 4 mm2. The power achieved is comparable and even surpasses many fiber-based amplifiers. We believe this work has the potential to radically change the integrated photonics application landscape, allowing power levels previously unimaginable from an integrated device replacing much of today’s benchtop systems. Moreover, mass producibility, reduced size, weight and cost will enable yet unforeseen applications for laser technology

Watt-class CMOS-compatible power amplifier

Power amplifier is becoming a critical component for integrated photonics as the integrated devices try to carve out a niche in the world of real-world applications of photonics. That is because the signal generated from an integrated device severely lacks in power which is due mainly to the small size which, although gives size and weight advantage, limits the energy storage capacity of an integrated device due to the small volume, causing it to rely on its bench-top counterpart for signal amplification downstream. Therefore, an integrated high-power signal booster can play a major role by replacing these large solid-state and fiber-based benchtop systems. For decades, large mode area (LMA) technology has played a disruptive role by increasing the signal power and energy by orders of magnitude in the fiber-based lasers and amplifiers. Thanks to the capability of LMA fiber to support significantly larger optical modes the energy storage and handling capability has significantly increased. Such an LMA device on an integrated platform can play an important role for high power applications. In this work, we demonstrate LMA waveguide based CMOS compatible watt-class power amplifier with an on-chip output power reaching ~ 1W within a footprint of ~4mm2.The power achieved is comparable and even surpasses many fiber-based amplifiers. We believe this work opens up opportunities for integrated photonics to find real world application on-par with its benchtop counterpart

Development of Nonlinear and Ultra-low Noise Fiber Technologies

Fiber-optic technologies for the generation of ultra-low noise optical pulse trains have asevere impact on a great variety of scientific fields and industrial applications such asfrequency metrology, synchronization and timing in free-electron laser facilities and particle accelerators, photonic microwave generation and quantum technologies. The fasttechnological progression of these applications necessitates a constant improvement ofthe underlaying fiber-optic laser systems in every aspect. The scope of this thesis is thedevelopment of novel fiber-optic devices and the discovery of new physical possibilitiesto overcome the currently existing boundaries of ultrafast fiber lasers and their ultra-lownoise applications.To this end, an experimental and theoretical study of state-of-the-art fiber oscillator modelocked with nonlinear amplifying loop mirrors is conducted, a cavity structure thatdemonstrated record ultra-low noise characteristics in conjunction with superior environmental stability. A theoretical model is derived that describes the interaction of the steadystate fluctuating intracavity amplitude with the nonlinear dynamics of the saturable absorber based on amplitude-noise transfer coefficients. To experimentally investigate theinfluence of this interaction decoupled from the optical feedback of the cavity, a novelnonlinear fiber amplifier is constructed which precisely replicates the physical mechanisms of an isolated roundtrip in the oscillator for an auxiliary input generated pulse train.The combined results of the theoretical investigation and the systematic measurementsreveal the existence of an intrinsic amplitude-noise suppressing mechanism that acts onthe circulating intracavity field once per roundtrip. The discovery of this mechanism givesan explanation for the superior noise performance of NALM mode-locked lasers for thefirst time.The second part of this thesis is aimed at the construction and optimization of a devicethat utilizes the discovered nonlinear mechanism for quantum-limited noise suppression.The implementation of an artificial sinusoidal transmission-function in a phase-biased,self-stabilized Sagnac interferometer with all-fiber integrated amplifier enables highlyefficient and broadband suppression of the input amplitude-fluctuations. In the experiment, quantum-limited amplitude-noise suppression by up to 20 dB down to the shotnoise limit at -151.1 dBc/Hz is demonstrated for the frequency range >100 kHz with asimultaneous signal amplification of 13.5 dB. The system shows an extraordinary efficiency in conjunction with a high degree of tunability based on the phase-bias settings.VHence, a great potential for a variety of high-end applications is revealed such as lownoise microwave generation and frequency metrology together with the possibility for thegeneration of squeezed quantum states of light under the right conditions.The third part of this thesis is aimed at the development of a novel I-shaped fiber oscillatormode-locked with the optical Kerr-effect that uses coherent pulse division and recombination to reduce the roundtrip nonlinear phase shift and dramatically increase the achievable intracavity pulse energy by 6.5 dB. In addition, a substantial improvement of thenoise performance is verified for increasing pulse divisions with a suppression of the output amplitude-fluctuations by up to 9 dB for three divisions in the frequency range from10 kHz to 2 MHz. In combination with other established mechanisms to reduce the roundtrip nonlinear phase shift based on dispersion-management or scaling of the fiber coresize, the here developed divided pulse oscillator enables a promising approach for nextgen ultra-low noise and environmentally stable fiber oscillators with high intracavitypower

Large-mode-area soliton fiber oscillator mode-locked with linear self-stabilized Sagnac-interferometer

We demonstrate an all-polarization-maintaining large-mode-area fiber oscillator mode-locked with a Kerr-type linear Sagnac-interferometer. The laser produces low-noise soliton-like pulses with 5.4 nJ pulse energy and 900 fs pulse duration

All-PM Divided Pulse Fiber Oscillator Mode-locked with Optical Kerr-Effect

A Kerr-type mode-locked PM fiber oscillator is demonstrated that utilizes divided pulse bursts to avoid excessive nonlinearities in the fiber segment. Experimental results with one division in the cavity show a 17.5-dB increased output power

Nonlinear fiber amplifier for intensity-noise reduction to the shot-noise limit

We demonstrate an all-PM fiber amplifier for intensity-noise reduction of pulsed input signals. Based on the nonlinear phase difference accumulation of copropagating orthogonal polarization modes in a PM-fiber, shot-noise limited noise reduction is verified

Nonlinear Fiber System for Shot-Noise Limited Intensity Noise Suppression and Amplification

We propose a nonlinear fiber system for shot-noise limited, all-optical intensity noise reduction and signal amplification. The mechanism is based on the accumulation of different nonlinear phase shifts between orthogonal polarization modes in a polarization-maintaining fiber amplifier in combination with an implemented sinusoidal transmission function. The resulting correlation between the input intensity fluctuations and the system transmission enables tunable intensity noise reduction of the input pulse train. In the experiment, the noise spectral density of a mode-locked oscillator is suppressed by up to 20 dB to the theoretical shot-noise limit of the measurement at −151.1dBc/Hz with simultaneous pulse amplification of 13.5 dB

Amplitude-noise suppressing mechanism in fiber lasers mode-locked with nonlinear amplifying loop mirror

We experimentally confirm, that the ultra-low noise characteristics of fiber lasers mode-locked with nonlinear amplifying loop mirror are related to an inherent amplitude-noise suppressing mechanism with its origin in the sinusoidal cavity transmission function