58 research outputs found
Frequency stabilization of a Helium-Neon laser using a microcontroller
Frequency-stabilized internal-mirror Helium-Neon lasers are essential as light sources for high accuracy laser interferometry. A He-Ne laser is coher-ent for a much longer range compared to a regular laser diode, extending its range of use. For example, good long laser beam coherence allows us to keep a high frequency amplitude when we have a setup on a long table (interferometers). One issue with these lasers though is that the power and frequency of the beam tends to fluctuate due to mostly thermal instabilities that cause changes in the length of the laser tube. However, it can be automated using a micro-controller, adjust the position of the S and P polarization on the lasing output power curve in order to make them equal on opposite ends [1-3]. Once stabilized it can be used in applications such as wavelength and vibra-tional metrology, it also serves as the backbone for stabilization of interfer-ometers used for the study of coherence properties of light [4-5]
Photo-oxidative tuning of individual and coupled GaAs photonic crystal cavities
We demonstrate a new photo-induced oxidation technique for tuning GaAs
photonic crystal cavities using a pulsed laser with an
average power of . The laser oxidizes a small diameter spot, reducing the local index of refraction
and blueshifting the cavity. The tuning progress can be actively monitored in
real time. We also demonstrate tuning an individual cavity within a pair of
proximity-coupled cavities, showing that this method can be used to correct
undesired frequency shifts caused by fabrication imperfections in cavity
arrays.Comment: 4 pages, 3 figure
Spontaneous symmetry breaking in a polariton and photon laser
We report on the simultaneous observation of spontaneous symmetry breaking
and long-range spatial coherence both in the strong and the weak-coupling
regime in a semiconductor microcavity. Under pulsed excitation, the formation
of a stochastic order parameter is observed in polariton and photon lasing
regimes. Single-shot measurements of the Stokes vector of the emission exhibit
the buildup of stochastic polarization. Below threshold, the polarization noise
does not exceed 10%, while above threshold we observe a total polarization of
up to 50% after each excitation pulse, while the polarization averaged over the
ensemble of pulses remains nearly zero. In both polariton and photon lasing
regimes, the stochastic polarization buildup is accompanied by the buildup of
spatial coherence. We find that the Landau criterion of spontaneous symmetry
breaking and Penrose-Onsager criterion of long-range order for Bose-Einstein
condensation are met in both polariton and photon lasing regimes.Comment: 5 pages, 3 figure
Inverse design and implementation of a wavelength demultiplexing grating coupler
Nanophotonics has emerged as a powerful tool for manipulating light on chips.
Almost all of today's devices, however, have been designed using slow and
ineffective brute-force search methods, leading in many cases to limited device
performance. In this article, we provide a complete demonstration of our
recently proposed inverse design technique, wherein the user specifies design
constraints in the form of target fields rather than a dielectric constant
profile, and in particular we use this method to demonstrate a new
demultiplexing grating. The novel grating, which has not been developed using
conventional techniques, accepts a vertical-incident Gaussian beam from a
free-space and separates O-band and C-band
light into separate waveguides. This inverse design concept
is simple and extendable to a broad class of highly compact devices including
frequency splitters, mode converters, and spatial mode multiplexers.Comment: 17 pages, 4 figures, 1 table. A supplementary section describing the
inverse-design algorithm in detail has been added, in addition to minor
corrections and updated reference
Selective photoexcitation of exciton-polariton vortices
We resonantly excite exciton-polariton states confined in cylindrical traps.
Using a homodyne detection setup, we are able to image the phase and amplitude
of the confined polariton states. We evidence the excitation of vortex states,
carrying an integer angular orbital momentum m, analogous to the transverse
TEM01* "donut" mode of cylindrically symmetric optical resonators. Tuning the
excitation conditions allows us to select the charge of the vortex. In this
way, the injection of singly charged (m = 1 & m = -1) and doubly charged (m =
2) polariton vortices is shown. This work demonstrates the potential of
in-plane confinement coupled with selective excitation for the topological
tailoring of polariton wavefunctions
Dynamical modeling of pulsed two-photon interference
Single-photon sources are at the heart of quantum-optical networks, with their uniquely quantum emission and phenomenon of two-photon interference allowing for the generation and transfer of nonclassical states. Although a few analytical methods have been briefly investigated for describing pulsed single-photon sources, these methods apply only to either perfectly ideal or at least extremely idealized sources. Here, we present the first complete picture of pulsed single-photon sources by elaborating how to numerically and fully characterize non-ideal single-photon sources operating in a pulsed regime. In order to achieve this result, we make the connection between quantum Monte-Carlo simulations, experimental characterizations, and an extended form of the quantum regression theorem. We elaborate on how an ideal pulsed single-photon source is connected to its photocount distribution and its measured degree of second- and first-order optical coherence. By doing so, we provide a description of the relationship between instantaneous source correlations and the typical experimental interferometers (Hanbury-Brown and Twiss, HongâOuâMandel, and MachâZehnder) used to characterize such sources. Then, we use these techniques to explore several prototypical quantum systems and their non-ideal behaviors. As an example numerical result, we show that for the most popular single-photon sourceâa resonantly excited two-level systemâits error probability is directly related to its excitation pulse length. We believe that the intuition gained from these representative systems and characters can be used to interpret future results with more complicated source Hamiltonians and behaviors. Finally, we have thoroughly documented our simulation methods with contributions to the Quantum Optics Toolbox in Python in order to make our work easily accessible to other scientists and engineers
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