Top PDF Fiber-coupled ultra-high-Q microresonators for nonlinear and quantum optics

Fiber-coupled ultra-high-Q microresonators for nonlinear and quantum optics

Fiber-coupled ultra-high-Q microresonators for nonlinear and quantum optics

The optical modes of a toroidal dielectric cavity are not analytically solvable, as Helmholtz’s equation is not separable in this coordinate system. However, the ability to predict the optical properties, especially the resonance wavelengths, mode volumes, and radiation quality factors, is very important in understanding the utility and applicability of these structures to both pas- sive and active optical studies. The microtoroid geometry, which exhibits a dumbbell-shaped cross section, can in most cases be considered a torus (expressed in terms of the principle di- ameter D, and the minor or inner diameter d). The presence of the supporting structure only affects the optical mode when the toroid diameter becomes comparable to the radial extent of the optical mode which occurs at an inner diameter below approximately 1.5 microns for an optical mode with a wavelength of 850 nm, and approximately 2.8 microns for at a wavelength of 1550 nm. Furthermore, through improvements in fabrication the influence of the toroid support can in principle be minimized. While approximate expressions for the optical behav- ior of these structures for both the low compression (sphere-like) and high compression (step index fiber-like) regimes can be derived, operation in the intermediate geometrical regime is desired, as these are both experimentally accessible and retain the most desirable properties of whispering-gallery-type microcavities. Therefore, I developed a numerical approach to char- acterize the optical modes of the cavity over the complete geometrical range possible, using a two-dimensional finite element eigenmode/eigenvalue solver, after explicitly accounting for the rotational symmetry, as described in more detail in Appendix A. The optical modes are cal- culated in a full-vectorial model, which provides the complete electric field dependence. The accuracy of the numerical technique was carefully verified by comparison with the solution for a microsphere cavity. The results for the mode volumes, resonance wavelengths, and field profiles were in excellent agreement. Furthermore, the error in the radiation quality factor was less than 10% over a wide value of radiation Q’s (10 3 to 10 14 ), demonstrating that this
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Research on nonlinear and quantum optics at the photonics and
quantum information group of the University of Valladolid

Research on nonlinear and quantum optics at the photonics and quantum information group of the University of Valladolid

comes into play, for a specific value of pulse energy, it can compensate the slow pulse broadening and result in a robust periodic evolution with the peridiodicity of the dispersion map. This nonlinear pulse is called a DM soliton. The DM soliton has larger energy [19] than its conventional NLS counterpart for the same average dispersion and, thus, a better signal to noise ratio (SNR) and is more robust against amplifier-noise Gordon-Haus timing jitter [20]. Furthemore, the large magnitude of the local dispersion results in a lessen- ing of four wave mixing effects.

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Linear, nonlinear and quantum optics in Silicon Photonics

Linear, nonlinear and quantum optics in Silicon Photonics

sampled points. Since the derivative stage enhances the high frequency electronic noise superimposed to the deterministic signal, a moving average lter has been used on the rough sequence to increase the signal to noise ratio (SNR). With this step, the random properties of the nal bit sequence would arise mostly from the deterministic part of the signal and less from the stochastic noise. The lter allows to achieve a SNR of ≈ 16 (on the derived sequence) and at the same time does not tailor the sharp spikes of the deterministic signal. The randomness of the nal sequence is evaluated using the statistical test suite provided by the National Institute of Standards and Technology (NIST) [197]. This consist in a series of tests that a sequence of bits has to pass in order to be classied as a random sequence. In a perfectly random bit sequence, each bit has an equal probabily to be zero or one. The highest bitrate that passed all the NIST tests is 1 Gbps , and has been reached using the post processing parameters listed in Table 2.3. The reports of the statistical tests are shown in Table 2.4. It has been found that the sampling rate of 200M Hz was too high to generate uncorrelated points, so the latter has been halved. To verify that the SNR iwas suciently high to exclude any contribution from the stochastic noise to the randomicity of the nal bit sequence, the NIST tests were performed on the electronic noise alone, using the same post processing parameters of Table 2.3. As it can be seen from the report of Table 2.4, the electronic noise did not pass three tests, meaninig that the noise level superimposed to the deterministic signal was indeed very low after the averaging stage. Furthermore, to also exclude that the randomicity of the sequence may have originated from the post processing steps, the NIST tests have been performed on a quasi-periodic signal, recorded at an input wavelength of 1543.893 nm and at 15 mW of input power. The signal is quasi-periodic in the sense that a small jitter ∆T on the period T is present, but ∆T /T 1 holds. The post processing parameters were again the ones listed in Table 2.3. The reports of Table 2.4 show that the bit sequence did not pass many tests, meaning that the random properties of the bit sequence arised from the chaotic nature of the signal seed.
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Electrical control of nonlinear quantum optics in a nano-photonic waveguide

Electrical control of nonlinear quantum optics in a nano-photonic waveguide

Integrated quantum photonic systems, in which quantum states of light are generated, manipulated, and detected on-chip, are rap- idly evolving as a scalable approach for quantum information sci- ence and technologies. Efficient generation of indistinguishable single photons and control of photon–photon interactions are es- sential requirements for the practical implementation of inte- grated quantum photonics in quantum optical networks and photonic quantum computing. Integrated architectures in which embedded, waveguide-coupled quantum emitters can act as pho- ton sources and also provide the saturable nonlinearity to mediate photon–photon interactions provide a particularly compact and scalable solution. Further key advantages of this approach include efficient coupling of the quantum emitter to a single optical mode [1] and wide bandwidth waveguide operation [2], with recent work demonstrating the significant potential of this approach us- ing InGaAs quantum dots (QDs) [3,4] and color centers in dia- mond [5,6]. The deterministic nature of the nonlinearity can be exploited in future photonic gates such as the controlled-phase [7–9] and controlled-NOT [10] gates, the building blocks for
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Quantum Optics Properties of QCD Vacuum

Quantum Optics Properties of QCD Vacuum

Therefore we believe that the non-perturbative stage of gluon evolution can be one of sources of the gluon SS in QCD by analogy with nonlinear medium for photon SS in QO. Gluon MD in the range of the small transverse momenta (thin ring of jet) is Poissonian [8]. Quark-gluon MD in the whole jet at the end of the perturbative cascade can be represented as a combination of Poissonian distributions each of which corresponds to a coherent state. Studying a further evolution of gluon states at the non-perturbative stage of jet evolution we obtain new gluon states. These states are formed as a result of non-perturbative self-interaction of the gluons expressed by nonlinearities of Hamiltonian. Using the Local parton hadron duality it is easy to show that in this case behaviour of hadron multiplicity distribution in jet events is differentiated from the negative binomial one that is confirmed by experiments for pp, pp-collisions [9]-[11].
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Quantum optics for space platforms

Quantum optics for space platforms

Our photon source itself is fairly conventional, using a nonlinear process called spontaneous parametric down Conversion (SPDC). In the laboratory, SPDC-based sources have been used in many ground-breaking experiments, demonstrating their viability. However, the constraints of our satellite platform have forced us to reexamine nearly every aspect of the design. In order to fit our source aboard a CubeSat, we are restricted to a volume of about 300 ml, which is smaller than a can of soda. Our entangled photon source must weigh less than 300 g and

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Integrated Ultra-High-Q Nonlinear Photonic Platform for On-Chip Optoelectronic Systems

Integrated Ultra-High-Q Nonlinear Photonic Platform for On-Chip Optoelectronic Systems

mode waveguide coupler. However, the mode coupling is only 25 % level so that might not be sufficient to use the coupling for nonlinear optics application – generally coupling strength also determines operating power of both frequency comb and lasers[22, 55]. Besides, TM0 mode has higher Q 0 , but it is even not coupled with straight nitride waveguide because of insufficient field overlap between TE waveguide mode and quasi-TM resonator mode. In order to strengthen the mode coupling with fundamental modes, cavity-waveguide gap can be one of methods that adjust the magnitude of field overlap. This approach corresponds to the gap adjustment between taper fiber and WGM resonator, and it can cause an additional scattering loss because then waveguide needs to be on the outward sidewall of the ridge resonator. Pulley waveguide structure[4] is also another approach, and this method can avoid an additional scattering loss caused in narrower gap. Fig.5.20 shows optical microscope image of pulley nitride waveguide featured on integrated resonator system. As has been discussed in 5.4.3, the width of nitride waveguide is constant in the bending region so as to keep the same phase-matching condition with longer interaction length. The designed waveguide dimension is same with the straight waveguide (900 nm × 250 nm).
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Nonlinear Optics in Chip-based Microresonators and their Applications

Nonlinear Optics in Chip-based Microresonators and their Applications

Stable optical frequency reference has been studied for decades [90, 91] and has revo- lutionized many application areas such as communication, time keeping, low noise mi- crowave generation, and basic science[26, 92, 93]. Such optical frequency references ben- efit from high optical Q factor or equivalently long optical storage time. Fabry-Perot cavi- ties [94, 95, 96], absorption spectral-hole burning in cryogenically cooled crystals [97, 98], and long-delay-line interferometers [99, 100] are examples of such stable optical reference systems. Allan deviation (i.e. fractional frequency instability, which is a standard measure of frequency stability) of 1x10 −16 at 1 s averaging [95] has been attained from the state- of-the-art Fabry-Perot optical cavities. In these systems, a narrow resonator line for laser locking is created by high-finesse-mirrors and the resonance frequency is immune to ther- mal fluctuations by using low-thermal-expansion housings and low-thermal-noise mirror coating [95, 94, 96, 101, 102]. However, these optical frequency reference systems remain as laboratory systems, because they are rather bulky and sometimes use cryogenic systems. While pursuing the ultimate stabiltiy, there has been a continuing need for portable optical frequency references. Bench-top or rack-mount optical frequency systems with Hz- level linewidth is developed by miniaturizing Fabry-Perot optical cavity[103, 104]. Besides miniaturization of conventional Fabry-Perot optical cavity, attention has naturally turned towards miniature devices such as ultra-high optical-Q, solid-state resonator systems based on silica [105, 106, 107] and crystalline fluoride materials [108, 109, 110]. Besides the compact size of these devices, their reduced mass can offer improved performance with respect to shock and acceleration. Some systems are chip-based and there is the possibility of integration with other components. These compact solid-state microresonators are also demonstrated as optical reference cavities [111, 112, 113].
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Nonlinear Optics in Ultra high Q Whispering Gallery Optical Microcavities

Nonlinear Optics in Ultra high Q Whispering Gallery Optical Microcavities

The ultra-high-Q optical modes in toroid microcavities, as well as the observed strongly reduced azimuthal mode spectrum, make toroid microcavities a promising candidate for nonlinear optical oscillators. In contrast to spheres, toroid microcavities are wafer-scale, and as such allow possible integration with other functionality. In this chapter the particular suitability of toroid microcavities as nonlinear Raman oscillators is shown, and the first Raman laser on a chip demonstrated. As in the case of microspheres, the long photon storage times in conjunction with the high ideality of a tapered optical fiber coupling junction[31], allows stimulated Raman lasing to be observed at ultra-low threshold (as low as 74 µW of fiber-launched power at 1550 nm). High efficiency (up to 45% at the critical coupling point) is obtained and in good agreement with theoretical modeling. In addition the emission is observed to be single mode over a large range of pump powers, which was not attainable in microspheres, due to the presence of nearly degenerate azimuthal modes. In addition, numerical modeling shows that the optical modes of toroid microcavities, possess a lower effective mode volume compared to microspheres. While the mode volume is readily calculated using numerical tools, it is experimentally difficult to access. In
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Crystalline Whispering Gallery Mode Resonators for Quantum and Nonlinear Optics

Crystalline Whispering Gallery Mode Resonators for Quantum and Nonlinear Optics

Quality factors were obtained by fitting the cavity response curves to a Lorentzian for both laser frequency scan directions. We fit the dependence of the quality factor on power to exponentials for illustration — to delineate the data points. These exponentials converge to a single value of Q for low optical power, as expected. It should be noted that the intrinsic Q factor of a cavity generally should not depend on the optical excitation power. The observed divergence is generated by the method used to derive the Q factors. Fig. 4.5 serves to clarify this statement. It represents four measurements of the same WGM at coupled pump powers of 60 nW and 1 µW. These measurements correspond to points A,B,C,D in Fig. 4.4. For the upper trace the pump power is well below the threshold of nonlinearities and the resonant curve is Lorentzian. For the lower trace the higher pump power causes the curves to deviate from the Lorentzian shape and become non-symmetric. The asymmetry arises from thermal nonlinearity, which in our case causes the cavity eigen-frequency to decrease as the laser beam begins to heat up the cavity material. As will be discussed in the following sections, measurements A and B correspond to a power level that is below the Raman lasing threshold, and thresholds of other nonlinear effects. For these measurements one may observe the linear oscillator response independent of the direction of the frequency scan and thus be able to obtain a reliable estimate for the cavity’s intrinsic Q factor. Occasional deviations from a Lorentzian were still observed, due to the acoustic noise perturbations and the high-pass filter in the AC-coupled input of the oscilloscope.
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Fiber coupled nanophotonic devices for nonlinear optics and cavity QED

Fiber coupled nanophotonic devices for nonlinear optics and cavity QED

between waveguides. Full power transfer requires that, in addition, no other radiation or guided modes of either waveguide participate in the coupling, either due to a large phase mismatch and/or weak transverse overlap. Fiber taper coupling has been shown to be extremely valuable in this regard (in comparison to simple prism coupling, which involves a continuum of modes), and was first used to provide near perfect single mode coupling to dielectric microsphere [61, 42, 62] and toroid [14] resonators for ultra sensitive measurement of high-Q whispering gallery modes. In a similar manner, fiber taper probes can be used to couple to two dimensional PC membrane waveguides, thanks to their undercut air-bridge structure that suppresses radiation from the fiber into the substrate, and their zone-folded dispersion that enables phase matching between the dissimilar fiber and PC modes. Thus, by designing a PC waveguide whose defect mode has a transverse field profile that sufficiently overlaps the fiber taper’s, efficient power transfer between the waveguides can be achieved. Furthermore, the flexibility in lattice engineering afforded by PCs allows this waveguide to be designed to couple efficiently to PC defect cavities, providing a fiber-PC waveguide-PC cavity optical probe.
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Ultra high Q planar microcavities and applications

Ultra high Q planar microcavities and applications

Re-circulation of light within small dielectric volumes enables the storage of optical power near specific resonant frequencies and is important in a wide range of fields such as cavity quantum electrodynamics[1, 2], photonics[3, 4], nonlinear optics[5-7], and sensing[8, 9]. The performance of these structures is strongly dependent upon the surface quality. With a nearly atomic-scale surface finish, dielectric micro-cavities formed by surface tension are superior to all other micro-resonant structures by many orders of magnitude when comparing photon lifetime (cavity Q). Droplets and solid spheres or spheroids[10-13] (formed from droplets) are so far the only known examples of surface- tension, induced micro-cavities (STIM); in particular, silica based microsphere resonators have attained Q values in excess of 9 billion. Despite their unique properties and
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High density InAlAs/GaAlAs quantum dots for non-linear optics in microcavities

High density InAlAs/GaAlAs quantum dots for non-linear optics in microcavities

chosen so as to lie rather close to the maximum of the QD absorption line. Transmission measurements, as expressed by Eq. (9), give, indeed, access to absorption. These were done, as previously, by ramping the incident intensity and meas- uring the transmittance. The right side of Fig. 12 shows the transmission as a function of the incident intensity. It is com- pared to theoretical curves deduced from Eqs. (12) and (7). The left side of Fig. 12 plots the absorption, as deduced from Eq. (9), applied to the experimental data and fitted with the ansatz of Eq. (10). The difficulty lies in the dependence of T upon the nonlinear index via /. Therefore, instead of using the intracavity intensity, which depends on this phase term, we used the measured incident intensity with the assumption that they are in a quasi-constant ratio. We first adjusted the saturation parameters of the absorption in Eq. (12) so as to obtain the best possible fit. However, we noted that, in a sec- ond step, additional adjustments could be made by fine tuning the wavelength, i.e., the position with respect to the resonance and the saturation index. Further experiments will attempt to elucidate this point. However, from these adjusted values, we could extract the significant parameters of the QD material.
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Ultra high performance fiber reinforced concrete as strengthening material

Ultra high performance fiber reinforced concrete as strengthening material

The safety of structures is of high importance affecting people’s lives. Structural evaluation, and possibly intervention, is considered necessary for old structures, structures which have been affected by accidental actions and also for structures in high seismic risk areas. Research should now focus on the development of new sustainable techniques which increase the safety of existing structures, and at the same time minimize the necessary to build new structures and to consume new materials and resources. The present research investigates the effectiveness of an advanced material, such as Ultra High Performance Fiber Reinforced Concrete (UHPFRC), for the strengthening of existing Reinforced Concrete (RC) structures. For this reason, an extensive experimental study on the properties of the material and the application for strengthening of RC beams has been conducted. More specifically, parameters such the effect of fiber content on the performance, the workability and the cost of the material have been investigated first. Based on the analysis, an optimum mixture design has been selected and has been applied for strengthening of RC beams using different configurations. The results indicated that the strengthening with UHPFRC is a well promising technique and the performance of the strengthened elements has been increased in all the examined cases.
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Linear optics and quantum maps

Linear optics and quantum maps

In the previous subsection we have shown that it is pos- sible to generate two-qubit states represented by points upon and below the Werner curve in the linear entropy-tangle plane, by operating on a single qubit 共local operations兲 be- longing to a pair initially prepared in the entangled singlet state. In another paper 关40兴 we have shown that it is also possible to generate MEMS states 共 see, e.g., Refs. 关 41,44 兴 , and references therein兲, via local operations. However, the price to pay in that case was the necessity to use a dichroic device that could not be represented by a “physical,” namely, a trace-preserving, quantum map. In the present subsection, as an example illustrating the usefulness of our conceptual scheme, we show that by allowing bilocal operations per- formed by two separate optical devices T A and T B located as
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Development of ultra-high performance fiber Reinforced Ductile concrete

Development of ultra-high performance fiber Reinforced Ductile concrete

The purpose of this research is to develop the ultra-high performance, fibre reinforced ductile concrete. The fibres which are used for research are PVA fibre. Hollow microspheres are also used to develop a new type of concrete. The compressive strength and flexural strength of the new developed concrete has been investigated in concrete lab. Further to the literature review on fibre reinforced concretes, engineered cementations composites, polyvinyl alcohol fibres and glass hollow microspheres; physical samples of Lightweight PVA-ECC's with hollow glass microsphere additives have been created and tested under external loading conditions. In order to achieve the objectives, hollow microspheres are added to the PVA fiber to eliminate the need of coating the surface of PVA fiber with oily substance. These hollow microspheres may decrease chemical bond as of surface coating. Samples were produced by mixing all the components together. The first stage involved the preparation of mix designs. The second stage attempted to make beams, small and large cubes and kept for curing. The third stage looked into characterization of design such as flexural strength and compression strength by performing test in the lab. The last stage evaluated the properties such as stress, strain and putting all the data on the graphs and did comparison of the graphs. The results analyzed and reported on in order to determine the characteristics and behavior and of lightweight PVA-ECC when exposed to these loadings. Below is the methodology of carrying out these tests and analysis of results.
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Fundamental aspects of quantum optics : a dissertation

Fundamental aspects of quantum optics : a dissertation

changes in the dynamics of the scaled means as S is varied are not accompanied by changes in the classical dynamics. The changes are due to the transition between the quantum and classical regime. Figs. 13 — 15 are the numerical results of a single quantum trajectory evolving in time for the second harmonic system in the regime of the classically chaotic region that comes from Eq.(4.8) and Eq.(4.9). The Figures 13a,14a and 15a are the scaled mean photon numbers (hi) and Figures 13b, 14b and 15b are the phase space trajectories of the mean field amplitude (ä\) with different values of S ( i.e. different intensity of pumping field ). They should be compared with the classical results (Fig.7). They are very different from the results that come from the master equation. When we reduce the pump field (S increased), the quantum jumping becomes larger, and the behavior of the mean photon number is far from the behavior of classical result. When the pumping field is increased (S decreased ), the mean photon number of the quantum trajectory is qualitatively similar to the classical photon number. A similar conclusion follows from the phase space trajectories of the mean field amplitudes. From Fig. 13b,14b and 15b, we can see that with increased optical field (i.e. S decreased ), the quantum jumping becomes smaller and the trajectory evolving in phase space tends to be similar to the classical orbit.
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Using supermodels in quantum optics

Using supermodels in quantum optics

the operator E denoting the identity map on the maximal common domain of A, A † . By Definition 4.4, we give an abstract formulation of the ladder operator formalism for which the self-similar supermodels from Section 3 and the discrete Schr¨odinger models from Section 4 so far are two different realizations. Therefore, an eigenvalue distribution of type (4.34) has indeed a physical interpretation in Schr¨odinger theory. We now may ask what is the impact of this type of spectrum for coherent state theory within quantum optics. A discussion on this topic will be started by the next section.
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Parity time symmetric coupled microresonators with a dispersive gain/loss

Parity time symmetric coupled microresonators with a dispersive gain/loss

Abstract: The paper reports on the coupling of Parity-Time (PT)- symmetric whispering gallery resonators with realistic material and gain/loss models. Response of the PT system is analyzed for the case of low and high material and gain dispersion, and also for two practical scenarios when the pump frequency is not aligned with the resonant frequency of the desired whispering gallery mode and when there is imbalance in the gain/loss profile. The results show that the presence of dispersion and frequency misalignment causes skewness in frequency bifurcation and significant reduction of the PT breaking point, respectively. Finally, we demonstrate a lasing mode operation which occurs due to an early PT-breaking by increasing loss in a PT system with unbalanced gain and loss.
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Quantum Optics of Polaritonic Nanocomposites

Quantum Optics of Polaritonic Nanocomposites

The aim of the thesis is to study the quantum optics of polaritonic nanocomposites. These systems are made by the combination of two or more micro- or nano-scale structures with complementary optical properties. One of these components is a material that is capable of carrying propagating phonon-, exciton-, or surface plasmon-polaritons. The combined optical properties of the composite will have capabilities that go beyond those of their constituent parts. The motivation behind this work is driven by the common scienti…c knowledge that our current electronic technology is reaching intrinsic speed and e¢ciency limits that simple advances will not …x. Switching mechanisms, like those laid out in this thesis, can be applied to make new types of optoelectronic devices that operate at faster speeds and higher e¢ciencies. This would allow these new components to circumvent the fundamental limits of the common electronic components. As a further application, these one- and two-photon mechanisms can also be made into sensing components. By this function, the presence of particular substances may be detected or have its own optical properties probed by a change in an optical response of a nanocomposite. The sheer number of available nanostructure components is ever growing along with recent advances in nanofabrication techniques. Nanocomposites hybrid systems have the potential to be the next generation of nano-sensors, communication networks, and computational devices. In this thesis, the optical properties of several types of nanocomposite hybrid systems are theoretically and numerically investigated.
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