1,059 research outputs found
Spectral line-by-line pulse shaping of on-chip microresonator frequency combs
No full textRecently, on-chip comb generation methods based on nonlinear optical modulation in ultrahigh-quality-factor monolithic microresonators have been demonstrated, where two pump photons are transformed into sideband photons in a four-wave-mixing process mediated by Kerr nonlinearity. Here, we investigate line-by-line pulse shaping of such combs generated in silicon nitride ring resonators. We observe two distinct paths to comb formation that exhibit strikingly different time-domain behaviours. For combs formed as a cascade of sidebands spaced by a single free spectral range that spread from the pump, we are able to compress stably to nearly bandwidth-limited pulses. This indicates high coherence across the spectra and provides new data on the high passive stability of the spectral phase. For combs where the initial sidebands are spaced by multiple free spectral ranges that then fill in to give combs with single free-spectral-range spacing, the time-domain data reveal partially coherent behaviour
Laser Cavity-Soliton Micro-Combs
No full textThe field of micro-cavity based frequency combs, or 'micro-combs'[1,2], has recently witnessed many fundamental breakthroughs[3-19] enabled by the discovery of temporal cavity-solitons, self-localised waves sustained by a background of radiation usually containing 95% of the total power[20]. Simple methods for their efficient generation and control are currently researched to finally establish micro-combs as out-of-the-lab widespread tools[21]. Here we demonstrate micro-comb laser cavity-solitons, an intrinsically highly-efficient, background free class of solitary waves. Laser cavity-solitons have underpinned key breakthroughs in semiconductor lasers[22,23] and photonic memories[24-26]. By merging their properties with the physics of both micro-resonators[1,2] and multi-mode systems[27], we provide a new paradigm for the generation and control of self-localised pulses in micro-cavities. We demonstrate 50 nm wide soliton combs induced with average powers one order of magnitude lower than those typically required by state-of-the-art approaches[26]. Furthermore, we can tune the repetition-rate to well over a megahertz with no-active feedback
Phase-coherent lightwave communications with frequency combs
No full textFiber-optical networks are a crucial telecommunication infrastructure in society. Wavelength division multiplexing allows for transmitting parallel data streams over the fiber bandwidth, and coherent detection enables the use of sophisticated modulation formats and electronic compensation of signal impairments. Optical frequency combs can replace the multiple lasers used for the different wavelength channels. Beyond multiplexing, it has been suggested that the broadband phase coherence of frequency combs could simplify the receiver scheme by performing joint reception and processing of several wavelength channels, but an experimental validation in a fiber transmission experiment remains elusive. Here we demonstrate and quantify joint reception and processing of several wavelength channels in a full transmission system. We demonstrate two joint processing schemes; one that reduces the phase-tracking complexity and one that increases the transmission performance.\ua0\ua9 2020, The Author(s)
TiSapphire frequency combs
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis. Vita.Includes bibliographical references (p. 179-186).Femtosecond mode-locked lasers are a unique laser technology due to their broad optical bandwidth and potential for linking the optical and radio frequency domains when these lasers are configured as frequency combs. Ti:Sapphire based mode-locked lasers offer considerable advantages over other laser systems by generating both the broadest optical spectrum and highest fundamental pulse repetition rates directly from the laser cavity. Recent advances in laser diode technology have reduced the cost of pump lasers for Ti:Sapphire based frequency combs considerably, and the recent demonstration of direct diode pumping of a narrowband mode-locked Ti:Sapphire laser suggests that Ti:Sapphire frequency combs may finally be ready to make the transition from an indispensible research tool to a wider set of industrial applications. In this thesis, several applications and fundamental properties of Ti:Sapphire based mode-locked lasers are investigated. To enable more widespread use of Ti:Sapphire based frequency combs, a frequency comb based on an octave spanning 1 GHz Ti:Sapphire laser is demonstrated. The I GHz Ti:Sapphire laser is referenced to a methane stabilized HeNe laser, resulting in a frequency comb with a fractional frequency stability of its optical spectrum of 2x1 0-14 on a 20 second timescale. A recently identified frequency comb application is the calibration of astronomical spectrographs to enable detection of Earth-like planets which are orbiting Sun-like stars. In support of this application, a second frequency comb system was constructed which ultimately was characterized by a 51 GHz pulse repetition rate and 12 nm bandwidth centered at 410 nm. This "astro-comb" system was deployed to the Fred Lawrence Whipple Observatory where preliminary results indicate a 40-fold increase in the spectrograph stability due to calibration by the astro-comb. Finally, the stability of the optical pulse train emitted from femtosecond mode-locked lasers is expected to exhibit the lowest phase noise of any oscillator, with theoretical predictions of phase noise levels below -190 dBc for offset frequencies exceeding 1 kHz. A comparison between the pulse trains of two nearly identical mode-locked lasers resulted in a measured timing error of less than 13 attoseconds measured over the entire Nyquist bandwidth.by Andrew John Benedick.Ph.D
On-chip microresonator frequency combs: Generation dynamics, power transfer, and time-domain characterization
No full textOver the last two decades, optical frequency combs from a mode-locked laser have been used as a ruler in frequency domain for extremely precise measurements. With a series of peaks equally spaced in optical frequency, it gives a significant improvement on the increasing demands of optical frequency metrology, telecommunication, optical clocks and measurements on the atomic level. However, optical frequency combs, based on fiber or free-space optics, are now restricted by further downsizing the optical paths and therefore, with these conventional combs, it is hard to achieve a repetition rate in radio frequencies ranging from several tens GHz to THz. Recently, high-quality (Q) microresonators offer the potential for on-chip comb generation with a repetition rate from tens GHz to several THz. These frequency combs may also support the generation of octave-spanning comb spectra in compact and chip-level devices. This novel Kerr comb technology benefits the developments of integrated photonics. Here, in this thesis, the author discusses the microresonator-based frequency combs from silicon nitride waveguide microrings. Owing to its compatibility with CMOS-compatible fabrication process and large Kerr nonlinearity, silicon nitride has attracted considerable attention for on-chip comb generation. The thesis is organized as follows: Chapter 1 gives brief reviews of optical frequency combs and the properties of silicon nitride waveguide resonators. In Chapter 2, on-chip comb generation and the properties of the generated combs, including communication performance, intensity noise, and time-domain characterization, are investigated. A drop-port study and power transfer in microrings are presented in Chapter 3. The comb-enhanced coupling, comb threshold, and comb efficiency at the through port are also discussed. In Chapter 4, the author compares the comb generation in both normal and anomalous cavity dispersion. Time-domain autocorrelation measurements will be demonstrated to characterize the comb generation in different dispersion regimes. In Chapter 5, the mode-locking transition and soliton formation in anomalous dispersion regime will be discussed. A short, bright, and close to transform-limited pulse is identified in time with a drop-port geometry. Finally, a summary is given in Chapter 6
High-order coherent communications using mode-locked dark-pulse Kerr combs from microresonators
No full textMicroresonator frequency combs harness the nonlinear Kerr effect in an integrated optical cavity to generate a multitude of phase-locked frequency lines. The line spacing can reach values in the order of 100 GHz, making it an attractive multi-wavelength light source for applications in fiber-optic communications. Depending on the dispersion of the microresonator, different physical dynamics have been observed. A recently discovered comb state corresponds to the formation of mode-locked dark pulses in a normal-dispersion microcavity. Such dark-pulse combs are particularly compelling for advanced coherent communications since they display unusually high power-conversion efficiency. Here, we report the first coherent-transmission experiments using 64-quadrature amplitude modulation encoded onto the frequency lines of a dark-pulse comb. The high conversion efficiency of the comb enables transmitted optical signal-to-noise ratios above 33 dB, while maintaining a laser pump power level compatible with state-of-the-art hybrid silicon lasers
Data from: "Larger but not louder: bigger honey bee colonies have quieter combs”
No full textCommunication is impossible if the sender’s signal cannot overcome background noise to reach the receiver. This obstacle is present in all communication modalities, forcing organisms to develop diverse mechanisms to overcome noise. Honey bees will modify combs to improve signal efficiency of substrate-borne vibrations, but it is unknown whether, and if so, how, bees compensate for the largest potential source of noise: the bees themselves. The number of bees in a colony changes markedly throughout the year, but the size of the nest cavity does not, forcing workers into high densities on the combs. How, then, do bees communicate via substrate-borne vibrations on combs that are covered in bees? We used accelerometers to measure comb vibrations, while varying the number of workers on the comb. Surprisingly, comb vibrations decreased with increased worker number. Furthermore, inserting freshly killed bees to the comb demonstrated that it is not simply the bees’ collective mass that damps vibrations, but is probably their behavior. We propose that their posture damps vibrations, with each bee linking up
to six neighboring cells with her legs. This collective damping reduces background noise, and improves the landscape for communication. These results demonstrate how living systems, including superorganisms, can overcome physical obstacles with curiously simple and elegant solutions.MLS is supported by the National Science Foundation Graduate Research Fellowship Program (DGE-1144153). This research was funded with a National Science Foundation Doctoral Dissertation Improvement Grant (1600775), an Andrew W. Mellon research grant, and a Centennial Pollinator Fellowship from the Garden Club of America (to MLS)
All-Linear Phase Retrieval of Optical Frequency Combs via Electric Field Cross-Correlation
No full textSince the invention of optical frequency combs(OFCs), full optical waveform characterization has always been an important topic in ultrafast optics. Traditional measurements either provide only partial information of the waveform(auto-correlation) or require high power and low duty cycle of the waveform for nonlinear effects (FROG and SPIDER). In this thesis, we introduce an all-linear method for the phase retrieval of optical frequency combs. Through the dual-comb electric field cross-correlation between the signal comb and a pre-characterized reference comb, the beat signal is captured by real time oscilloscope in milliseconds. Post digital signal processing could retrieve phase from the sampled signal. The stability and precision of this method are discussed and phase retrieval from different combs generated through microresonators is performed
Mechanical overtone frequency combs
No full textMechanical frequency combs are poised to bring the applications and utility
of optical frequency combs into the mechanical domain. So far, their main
challenge has been strict requirements on drive frequencies and power, which
complicate operation. We demonstrate a straightforward mechanism to create a
frequency comb consisting of mechanical overtones (integer multiples) of a
single eigenfrequency, by monolithically integrating a suspended dielectric
membrane with a counter-propagating optical trap. The periodic optical field
modulates the dielectrophoretic force on the membrane at the overtones of a
membrane's motion. These overtones share a fixed frequency and phase relation,
and constitute a mechanical frequency comb. The periodic optical field also
creates an optothermal parametric drive that requires no additional power or
external frequency reference. This combination of effects results in an
easy-to-use mechanical frequency comb platform that requires no precise
alignment, no additional feedback or control electronics, and only uses a
single, mW continuous wave laser beam. This highlights the overtone frequency
comb as the straightforward future for applications in sensing, metrology and
quantum acoustics
Control and characterization of phase-modulated continuous-wave laser frequency combs
No full textSpectral line-by-line shaping is a key enabler towards optical arbitrary waveform generation, which promises broad impact both in optical science and technology. Significant new physics arises in the line-by-line regime, where the shaped pulse fields generated from one laser pulse now overlap with those generated from adjacent pulses. This leads to coherent interference effects related to the properties of optical frequency combs which serve as the source in these experiments. Phase-modulated continuous–wave (PMCW) laser frequency combs are chosen as the optical source within this dissertation for their relatively high frequency stability and ease of tuning. We experimentally demonstrate the followings: (1) 300 fs optical pulse train generations at 9 and 10 GHz rates by applying line-by-line control to PMCW combs. (2) 5 GHz optical arbitrary waveform generations using more than 100 comb lines. (3) Generations of reprogrammable microwave arbitrary waveforms at rates approaching 10 GHz. (4) Generation of nonlinearly broadened optical frequency combs from PMCW seed pulses using both anomalous and normally dispersive media. Broadened comb coherence properties are further analyzed using differential phase-shift keying decoding. (5) Quantitative analysis on the impact of static comb frequency stability on line-by-line shaped waveforms. (6) Systematic investigations on time-varying comb frequency-noise to intensity-noise conversion in line-by-line shaping
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