51 research outputs found
Injection-locked Semiconductor Lasers For Realization Of Novel Rf Photonics Components
This dissertation details the work has been done on a novel resonant cavity linear interferometric modulator and a direct phase detector with channel filtering capability using injection-locked semiconductor lasers for applications in RF photonics. First, examples of optical systems whose performance can be greatly enhanced by using a linear intensity modulator are presented and existing linearized modulator designs are reviewed. The novel linear interferometric optical intensity modulator based on an injection-locked laser as an arcsine phase modulator is introduced and followed by numerical simulations of the phase and amplitude response of an injection-locked semiconductor laser. The numerical model is then extended to study the effects of the injection ratio, nonlinear cavity response, depth of phase and amplitude modulation on the spur-free dynamic range of a semiconductor resonant cavity linear modulator. Experimental results of the performance of the linear modulator implemented with a multi-mode Fabry-Perot semiconductor laser as the resonant cavity are shown and compared with the theoretical model. The modulator performance using a vertical cavity surface emitting laser as the resonant cavity is investigated as well. Very low VÏ€ in the order of 1 mV, multi-gigahertz bandwidth (-10 dB bandwidth of 5 GHz) and a spur-free dynamic range of 120 dB.Hz2/3 were measured directly after the modulator. The performance of the modulator in an analog link is experimentally investigated and the results show no degradation of the modulator linearity after a 1 km of SMF. The focus of the work then shifts to applications of an injection-locked semiconductor laser as a direct phase detector and channel filter. This phase detection technique does not iv require a local oscillator. Experimental results showing the detection and channel filtering capability of an injection-locked semiconductor diode laser in a three channel system are shown. The detected electrical signal has a signal-to-noise ratio better than 60 dB/Hz. In chapter 4, the phase noise added by an injection-locked vertical cavity surface emitting laser is studied using a self-heterodyne technique. The results show the dependency of the added phase noise on the injection ratio and detuning frequency. The final chapter outlines the future works on the linear interferometric intensity modulator including integration of the modulator on a semiconductor chip and the design of the modulator for input pulsed light
Optical Modulator with Linear Response
A purely linear resonant cavity interferometric modulator with a potential infinite spurious free dynamic range and multi-gigahertz bandwidth is described
Baseline-free Quantitative Absorption Spectroscopy Based on Cepstral Analysis
The accuracy of quantitative absorption spectroscopy depends on correctly
distinguishing molecular absorption signatures in a measured transmission
spectrum from the varying intensity or "baseline" of the light source. Baseline
correction becomes particularly difficult when the measurement involves
complex, broadly absorbing molecules or non-ideal transmission effects such as
etalons. We demonstrate a technique that eliminates the need to account for the
laser intensity in absorption spectroscopy by converting the measured
transmission spectrum of a gas sample to a modified form of the time-domain
molecular free induction decay (m-FID) using a cepstral analysis technique
developed for audio signal processing. Much of the m-FID signal is temporally
separated from and independent of the source intensity, and this portion can be
fit directly with a model to determine sample gas properties without correcting
for the light source intensity. We validate the new approach in several complex
absorption spectroscopy scenarios and discuss its limitations. The technique is
applicable to spectra obtained with any absorption spectrometer and provides a
fast and accurate approach for analyzing complex spectra
Single-cycle all-fiber frequency comb
Single-cycle pulses with deterministic carrier-envelope phase enable the
study and control of light-matter interactions at the sub-cycle timescale, as
well as the efficient generation of low-noise multi-octave frequency combs.
However, current single-cycle light sources are difficult to implement and
operate, hindering their application and accessibility in a wider range of
research. In this paper, we present a single-cycle 100 MHz frequency comb in a
compact, turn-key, and reliable all-silica-fiber format. This is achieved by
amplifying 2 m seed pulses in heavily-doped Tm:fiber, followed by cascaded
self-compression to yield 6.8 fs pulses with 215 kW peak power and 374 mW
average power. The corresponding spectrum covers more than two octaves, from
below 700 nm up to 3500 nm. Driven by this single-cycle pump, supercontinuum
with 180 mW of integrated power and a smooth spectral amplitude between 2100
and 2700 nm is generated directly in silica fibers. To broaden
applications,few-cycle pulses extending from 6 m to beyond 22 m with
long-term stable carrier-envelope phase are created using intra-pulse
difference frequency, and electro-optic sampling yields comb-tooth-resolved
spectra. Our work demonstrates the first all-fiber configuration that generates
single-cycle pulses, and provides a practical source to study nonlinear optics
on the same timescale.Comment: Revised versio
Complete reactants-to-products observation of a gas-phase chemical reaction with broad, fast mid-infrared frequency combs
Molecular diagnostics are a primary tool of modern chemistry, enabling
researchers to map chemical reaction pathways and rates to better design and
control chemical systems. Many chemical reactions are complex and fast, and
existing diagnostic approaches provide incomplete information. For example,
mass spectrometry is optimized to gather snapshots of the presence of many
chemical species, while conventional laser spectroscopy can quantify a single
chemical species through time. Here we optimize for multiple objectives by
introducing a high-speed and broadband, mid-infrared dual frequency comb
absorption spectrometer. The optical bandwidth of >1000 cm-1 covers absorption
fingerprints of many species with spectral resolution <0.03 cm-1 to accurately
discern their absolute quantities. Key to this advance are 1 GHz pulse
repetition rate frequency combs covering the 3-5 um region that enable
microsecond tracking of fast chemical process dynamics. We demonstrate this
system to quantify the abundances and temperatures of each species in the
complete reactants-to-products breakdown of 1,3,5-trioxane, which exhibits a
formaldehyde decomposition pathway that is critical to modern low temperature
combustion systems. By maximizing the number of observed species and improving
the accuracy of temperature and concentration measurements, this spectrometer
advances understanding of chemical reaction pathways and rates and opens the
door for novel developments such as combining high-speed chemistry with machine
learning
Broadband dual-frequency comb spectroscopy in a rapid compression machine
We demonstrate fiber mode-locked dual frequency comb spectroscopy for broadband, high resolution measurements in a rapid compression machine (RCM). We apply an apodization technique to improve the short-term signal-to-noise-ratio (SNR), which enables broadband spectroscopy at combustion-relevant timescales. We measure the absorption on 24345 individual wavelength elements (comb teeth) between 5967 and 6133 cm-1 at 704 microsecond time resolution during a 12-ms compression of a CH4-N2 mixture. We discuss the effect of the apodization technique on the absorption spectra, and apply an identical effect to the spectral model during fitting to recover the mixture temperature. The fitted temperature is compared against an adiabatic model, and found to be in good agreement with expected trends. This work demonstrates the potential of DCS to be used as an in situ diagnostic tool for broadband, high resolution, measurements in engine-like environments.</p
Spatially resolved mass flux measurements with dual comb spectroscopy
Providing an accurate, representative sample of mass flux across large open
areas for atmospheric studies or the extreme conditions of a hypersonic engine
is challenging for traditional intrusive or point-based sensors. Here, we
demonstrate that laser absorption spectroscopy with frequency combs can
simultaneously measure all of the components of mass flux (velocity,
temperature, pressure, and species concentration) with low uncertainty, spatial
resolution corresponding to the span of the laser line of sight, and no
supplemental sensor readings. The low uncertainty is provided by the broad
spectral bandwidth, high resolution, and extremely well-known and controlled
frequency axis of stabilized, mode-locked frequency combs. We demonstrate these
capabilities in the isolator of a ground-test supersonic propulsion engine at
Wright-Patterson Air Force Base. The mass flux measurements are consistent
within 3.6% of the facility-level engine air supply values. A vertical scan of
the laser beams in the isolator measures the spatially resolved mass flux,
which is compared with computational fluid dynamics simulations. A rigorous
uncertainty analysis demonstrates a DCS instrument uncertainty of ~0.4%, and
total uncertainty (including non-instrument sources) of ~7% for mass flux
measurements. These measurements demonstrate DCS as a low-uncertainty mass flux
sensor for a variety of applications.Comment: Main Text: 15 pages, 7 figure; Supplement: 6 pages, 4 figures;
Submitted to Optic
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