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• 1.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Quantum error correction2016Doctoral thesis, comprehensive summary (Other academic)

Quantum error correction is the art of protecting quantum states from the detrimental influence from the environment. To master this art, one must understand how the system interacts with the environment and gives rise to a full set of quantum phenomena, many of which have no correspondence in classical information theory. Such phenomena include decoherence, an effect that in general destroys superpositions of pure states as a consequence of entanglement with the environment. But decoherence can also be understood as “information leakage”, i.e., when knowledge of an encoded code block is transferred to the environment. In this event, the block’s information or entanglement content is typically lost.

In a typical scenario, however, not all types of destructive events are likely to occur, but only those allowed by the information carrier, the type of interaction with the environment, and how the environment “picks up” information of the error events. These characteristics can be incorporated into a code, i.e., a channel-adapted quantum error-correcting code.

Often, it is assumed that the environment’s ability to distinguish between error events is small, and I will denote such environments “memory-less”. But this assumption is not always valid, since the ability to distinguish error events is related to the temperature of the environment, and in the particular case of information coded onto photons, kBTR «ℏω typically holds, and one must then assume that the environment has a “memory”. In the thesis I describe a short quantum error-correction code adapted for photons interacting with a “cold” reservoir, i.e., a reservoir which continuously probes what error occurred in the coded state.

I also study other types of environments, and show how to distill meaningful figures of merit from codes adapted for these channels, as it turns out that resource-based figures reflecting both information and entanglement can be calculated exactly for a well-studied class of channels: the Pauli channels. Starting from these resource-based figures, I establish the notion of efficiency and quality and show that there will be a trade-off between efficiency and quality for short codes. Finally I show how to incorporate, into these calculations, the choices one has to make when handling quantum states that have been detected as incorrect, but where no prospect of correcting them exists, i.e., so-called detection errors.

• 2.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Quantum error correction2012Licentiate thesis, comprehensive summary (Other academic)

This thesis intends to familiarise the reader with quantum error correction, and also show some relations to the well known concept of information - and the lesser known quantum information. Quantum information describes how information can be carried by quantum states, and how interaction with other systems give rise to a full set of quantum phenomena, many of which have no correspondence in classical information theory. These phenomena include decoherence, as a consequence of entanglement. Decoherence can also be understood as "information leakage", i.e., knowledge of an event is transferred to the reservoir - an effect that in general destroys superpositions of pure states.

It is possible to protect quantum states (e.g., qubits) from interaction with the environment - but not by amplification or duplication, due to the "no-cloning" theorem. Instead, this is done using coding, non-demolition measurements, and recovery operations. In a typical scenario, however, not all types of destructive events are likely to occur, but only those allowed by the information carrier, the type of interaction with the environment, and how the environment "picks up" information of the error events. These characteristics can be incorporated into a code, i.e., a channel-adapted quantum error-correcting code. Often, it is assumed that the environment's ability to distinguish between error events is small, and I will denote such environments "memory-less".

This assumption is not always valid, since the ability to distinguish error events is related to the \emph{temperature} of the environment, and in the particular case of information coded onto photons, $k_{\text{B}}T_{\text{R}}\ll\hbar\omega$ typically holds, and one must then assume that the environment has a "memory". In this thesis, I describe a short quantum error-correcting code (QECC), adapted for photons interacting with a cold environment, i.e., this code protects from an environment that continuously records which error occurred in the coded quantum state.

Also, it is of interest to compare the performance of different QECCs - But which yardstick should one use? We compare two such figures of merit, namely the quantum mutual information and the quantum fidelity, and show that they can not, in general, be simultaneously maximised in an error correcting procedure. To show this, we have used a five-qubit perfect code, but assumed a channel that only cause bit-flip errors. It appears that quantum mutual information is the better suited yardstick of the two, however more tedious to calculate than quantum fidelity - which is more commonly used.

• 3.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Fidelity as a figure of merit in quantum error correction2013In: Quantum information & computation, ISSN 1533-7146, Vol. 13, no 1-2, p. 0009-0020Article in journal (Refereed)

We discuss the fidelity as a figure of merit in quantum error correction schemes. We show that when identifiable but uncorrectable errors occur as a result of the action of the channel, a common strategy that improves the fidelity actually decreases the transmitted mutual information. The conclusion is that while the fidelity is simple to calculate and therefore often used, it is perhaps not always a recommendable figure of merit for quantum error correction. The reason is that while it roughly speaking encourages optimisation of the "mean probability of success", it gives no incentive for a protocol to indicate exactly where the errors lurk. For small error probabilities, the latter information is more important for the integrity of the information than optimising the mean probability of success.

• 4.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
On the efficiency of quantum error correction codes for the depolarising channelManuscript (preprint) (Other academic)
• 5. Al-Shammari, Rusul M.
KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Tunable Wettability of Ferroelectric Lithium Niobate Surfaces: The Role of Engineered Microstructure and Tailored Metallic Nanostructures2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 12, p. 6643-6649Article in journal (Refereed)

An important aspect of optimizing micro- and optofluidic devices for lab on -a-chip systems is the ability to engineer materials properties including surface structure and charge to control wettability. Biocompatible ferroelectric lithium niobate (LN), which is well-known for acoustic and nonlinear optical applications, has recently found potential micro- and optofluidic applications. However, the tunable wettability of such substrates has yet to be explored in detail. Here, we show that the contact angle of LN substrates can be reproducibly tailored between similar to 7 degrees and similar to 421 degrees by controlling the surface topography and chemistry at the nano- and micrometer scale via ferroelectric domain and polarization engineering and polarization-directed photoassisted deposition of metallic nanostructures.

• 6.
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Orbital angular momentum modes do not increase the channel capacity in communication links2015In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, article id 043040Article in journal (Refereed)

The orbital momentum of optical or radio waves can be used as a degree of freedom to transmit information. However, mainly for technical reasons, this degree of freedom has not been widely used in communication channels. The question is if this degree of freedom opens up a new, hitherto unused 'communication window' supporting 'an infinite number of channels in a given, fixed bandwidth' in free space communication as has been claimed? We answer this question in the negative by showing that on the fundamental level, the mode density, and thus room for mode multiplexing, is the same for this degree of freedom as for sets of modes lacking angular momentum. In addition we show that modes with angular momentum are unsuitable for broadcasting applications due to excessive crosstalk or a poor signal-to-noise ratio.

• 7.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Impact of longitudinal fields on second harmonic generation in lithium niobate nanopillars2016In: APL Photonics, ISSN 2378-0967, Vol. 1, no 6, article id 061302Article in journal (Refereed)

An optimized focused ion beam process is used to fabricate micrometer-long LiNbO3 nanopillars with diameters varying between 150 and 325 nm. Polarimetric mappings of second harmonic generation from a wavelength of 850 nm demonstrate the ability to modify the polarization features of the nonlinearresponse through a fine adjustment of the pillar size. The effect is ascribed to the non-negligible contribution of the longitudinal fields associated with sub-wavelength light confinement in the LiNbO3nanopillars. The results also highlight the importance of a fine control over the nanopillar size in order to effectively engineer their nonlinear response.

• 8.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Low-loss ridge waveguides in thin film lithium niobate-oninsulator (LNOI) fabricated by reactive ion etching2014In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2014Conference paper (Refereed)

We report on the fabrication of waveguides in 300 nm-thick Y-cut lithium niobate on silicon through optimized reactive ion etching, yielding sidewall roughness of 22.9 nm and propagation losses of 8.62 dB/cm at 1550 nm.

• 9.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Low-loss ridge waveguides in thin film lithium niobate-on-insulator (LNOI) fabricated by reactive ion etching2016In: Proceedings Advanced Photonics 2016, OSA Publishing , 2016Conference paper (Refereed)

We report on the fabrication of waveguides in 300 nm-thick Y-cut lithium niobate onsilicon through optimized reactive ion etching, yielding sidewall roughness of 22.9 nm andpropagation losses of 8.62 dB/cm at 1550 nm.

• 10.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Electrical Engineering (EES), Micro and Nanosystems. KTH, School of Electrical Engineering (EES), Micro and Nanosystems. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
Bragg gratings in thin-film LiNbO3 waveguides2017In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Optics Express, ISSN 1094-4087, Vol. 25, no 26, p. 32323-32332Article in journal (Refereed)

We design, fabricate and characterize sidewall corrugated Bragg gratings in a high confinement integrated optics lithium niobate platform, comprising submicrometric photonic wires, tapers and grating couplers to interface off-chip standard telecom optical fibers. We analyze the grating performance as band-rejection filter for TE-polarized signals in the telecom C-band, considering both rectangular and sinusoidal sidewall profiles, and demonstrate record extinction ratios as high as 27 dB and rejection bandwidths as narrow as 3 nm. The results show the potential for an efficient integration of novel photonic functionalities into low-footprint LiNbO3 nonlinear and electro-optical waveguide devices.

• 11.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Electrical Engineering (EES), Micro and Nanosystems. KTH, School of Electrical Engineering (EES), Micro and Nanosystems. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Waveguide Gratings in Thin-Film Lithium Niobate on Insulator2017In: CLEO: 2017, OSA Technical Digest, Optical Society of America, 2017Conference paper (Refereed)
• 12.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Second-harmonic generation engineering in lithium niobate nanopillars2015In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2015Conference paper (Refereed)
• 13. Balobaid, Laila
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Photoreduction of metal nanostructures on periodically proton exchanged MgO-doped lithium niobate crystals2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 18, p. 182904-Article in journal (Refereed)

Local reactivity on periodically proton exchanged lithium niobate (PPE: LN) surfaces is a promising route for the fabrication of regularly spaced nanostructures. Here, using MgO-doped PPE: LN templates, we investigate the influence of the doping on the nanostructure formation as a function of the proton exchange (PE) depth. The deposition is found to occur preferentially along the boundary between MgO-doped LN and the PE region when the PE depth is at least 1.73 mu m, however, for shallower depths, deposition occurs across the entire PE region. The results are found to be consistent with an increased photoconductivity of the MgO-doped LN.

• 14. Balobaid, Laila
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Direct shape control of photoreduced nanostructures on proton exchanged ferroelectric templates2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 4, p. 042908-Article in journal (Refereed)

Photoreduction on a periodically proton exchanged ferroelectric crystal leads to the formation of periodic metallic nanostructures on the surface. By varying the depth of the proton exchange (PE) from 0.59 to 3.10 mu m in congruent lithium niobate crystals, the width of the lateral diffusion region formed by protons diffusing under the mask layer can be controlled. The resulting deposition occurs in the PE region with the shallowest PE depth and preferentially in the lateral diffusion region for greater PE depths. PE depth-control provides a route for the fabrication of complex metallic nanostructures with controlled dimensions on chemically patterned ferroelectric templates.

• 15.
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Quantum-polarization state tomography2016In: PHYSICAL REVIEW A, ISSN 2469-9926, Vol. 94, no 2, article id 020105Article in journal (Refereed)

We propose and demonstrate a method for quantum-state tomography of qudits encoded in the quantum polarization of N-photon states. This is achieved by distributing N photons nondeterministically into three paths and their subsequent projection, which for N = 1 is equivalent to measuring the Stokes (or Pauli) operators. The statistics of the recorded N-fold coincidences determines the unknown N-photon polarization state uniquely. The proposed, fixed setup manifestly rules out any systematic measurement errors due to moving components and allows for simple switching between tomography of different states, which makes it ideal for adaptive tomography schemes.

• 16.
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Humblet's Decomposition of the Electromagnetic Angular Moment in Metallic Waveguides2014In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 62, no 4, p. 779-788Article in journal (Refereed)

In a seminal paper, Humblet decomposed the angular momentum of a classical electromagnetic field as a sum of three terms: the orbital angular momentum (OAM), the spin, and the more unfamiliar surface angular momentum. In this paper, we present the result of such decomposition for various metallic waveguides. We investigate two hollow metal waveguides with circular and rectangular cross sections, respectively. The waveguides are excited with two TE eigenmodes driven in phase quadrature. As references, two better known modes are also analyzed: a plane, a circularly polarized wave (a TEM mode), and a TE-Bessel beam, both of infinite transverse extent and with no metallic boundaries. Our analysis shows that modes carrying OAM and spin can also propagate in the metallic waveguides, even when the cross section of the waveguide is distinctly non-circular. However, the mode density of orthogonal modes carrying OAM is at most equal to that of the waveguides' eigenmodes.

• 17.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
20th Central European Workshop on Quantum Optics, Stockholm, June 16-20, 2013: Book of Abstracts2013Conference proceedings (editor) (Other academic)
• 18.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Classical distinguishability as an operational measure of polarization2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 1, p. 013830-Article in journal (Refereed)

We put forward an operational degree of polarization that can be extended in a natural way to fields whose wave fronts are not necessarily planar. This measure appears as a distance from a state to the set of all of its polarization-transformed counterparts. By using the Hilbert-Schmidt metric, the resulting degree is a sum of two terms: one is the purity of the state and the other can be interpreted as a classical distinguishability, which can be experimentally determined in an interferometric setup. For transverse fields, this reduces to the standard approach, whereas it allows one to get a straight expression for nonparaxial fields.

• 19.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Limits to the efficiency of quantum lithography2011In: Conf. Lasers Electro-Opt. Europe Eur. Quantum Electron. Conf., CLEO EUROPE/EQEC, 2011, p. 5943416-Conference paper (Refereed)

Quantum lithography promises, in principle, unlimited feature resolution, independent of wavelength. The price to be paid is that the lithographic film must consist of a multi-photon absorbing material. If N photons are absorbed, the minimum feature resolution goes from roughly /2 to /2N. However, there has been a discussion in the literature as to what is the probability of N photons in a lithographic exposure field to hit the same detector pixel, thereby enabling the needed N-photon absorption. On one hand it has been claimed that If the optical system is aligned properly, the probability of the first photon arriving in a small absorptive volume of space time is proportional to [the field intensity]. However, the remaining N-1 photons are constrained to arrive at the same place at the same time [1]. On the other hand it has been argued that it is not true that the first arriving photon greatly constrains the arrival location of the following ones Very few photons will be absorbed in one point since they typically arrive far apart. [2]. The answer to this dispute dictate very much the practical feasibility of quantum lithography, because if the few photons in the entangled state are spread out over the exposed area, the probability will quickly become negligible that they arrive at the same spot (causing a N-photon detection event). This will render quantum lithography very inefficient, albeit still feasible in principle.

• 20.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Stars of the quantum Universe: extremal constellations on the Poincare sphere2015In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 10, article id 108008Article in journal (Refereed)

The characterization of the polarization properties of a quantum state requires the knowledge of the joint probability distribution of the Stokes variables. This amounts to assessing all the moments of these variables, which are aptly encoded in a multipole expansion of the density matrix. The cumulative distribution of these multipoles encapsulates in a handy manner the polarization content of the state. We work out the extremal states for that distribution, finding that SU(2) coherent states are maximal to any order, so they are the most polarized allowed by quantum theory. The converse case of pure states minimizing that distribution, which can be seen as the most quantum ones, is investigated for a diverse range of number of photons. Exploiting the Majorana representation, the problem appears to be closely related to distributing a number of points uniformly over the surface of the Poincare sphere.

• 21.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Univ Guadalajara, Dept Fis, Guadalajara 44420, Jalisco, Mexico.. Univ Complutense Madrid, Dept Opt, Fac Fis, E-28040 Madrid, Spain.. Max Planck Inst Phys Lichts, D-91058 Erlangen, Germany.;Univ Erlangen Nurnberg, Inst Opt Informat & Photon, D-91058 Erlangen, Germany.. Max Planck Inst Phys Lichts, D-91058 Erlangen, Germany.;Univ Erlangen Nurnberg, Inst Opt Informat & Photon, D-91058 Erlangen, Germany.. Univ Complutense Madrid, Dept Opt, Fac Fis, E-28040 Madrid, Spain.;Max Planck Inst Phys Lichts, D-91058 Erlangen, Germany.;Univ Erlangen Nurnberg, Inst Opt Informat & Photon, D-91058 Erlangen, Germany..
Extremal quantum states and their Majorana constellations2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 3, article id 031801Article in journal (Refereed)

The characterization of quantum polarization of light requires knowledge of all the moments of the Stokes variables, which are appropriately encoded in the multipole expansion of the density matrix. We look into the cumulative distribution of those multipoles and work out the corresponding extremal pure states. We find that SU(2) coherent states are maximal to any order whereas the converse case of minimal states (which can be seen as the most quantum ones) is investigated for a diverse range of the number of photons. Taking advantage of the Majorana representation, we recast the problem as that of distributing a number of points uniformly over the surface of the Poincare sphere.

• 22.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Deterministic teleportation using single-photon entanglement as a resource2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 2, p. 022316-Article in journal (Refereed)

We outline a proof that teleportation with a single particle is, in principle, just as reliable as with two particles. We thereby hope to dispel the skepticism surrounding single-photon entanglement as a valid resource in quantum information. A deterministic Bell-state analyzer is proposed which uses only classical resources, namely, coherent states, a Kerr nonlinearity, and a two-level atom.

• 23.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
20th Central European Workshop on Quantum Optics Preface2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T160, p. 010301-Article in journal (Refereed)
• 24.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Non-monotonic projection probabilities as a function of distinguishability2014In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 16, p. 013006-Article in journal (Refereed)

Typically, quantum superpositions, and thus measurement projections of quantum states involving interference, decrease (or increase) monotonically as a function of increased distinguishability. Distinguishability, in turn, can be a consequence of decoherence, for example caused by the (simultaneous) loss of excitation or due to inadequate mode matching (either deliberate or indeliberate). It is known that for some cases of multi-photon interference a non-monotonic decay of projection probabilities occurs, which has so far been attributed to interference between four or more photons. We show that such a non-monotonic behavior of projection probabilities is not unnatural, and can also occur for single-photon and even semiclassical states. Thus, while the effect traces its roots from indistinguishability and thus interference, the states for which this can be observed do not need to have particular quantum features.

• 25.
KTH, School of Engineering Sciences (SCI), Applied Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Reply to comment on ‘non-monotonic projection probabilities as a function of distinguishability’2014In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 16, no 11, article id 118004Article in journal (Refereed)
• 26.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. AlbaNova University Center, Sweden.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. AlbaNova University Center, Sweden.
Proposed Implementation of "Non-Physical" Four-Dimensional Polarization Rotations2016In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 34, no 14, p. 3317-3322Article in journal (Refereed)

Recently one of us proposed a new formalism for modeling electromagnetic wave transformations for coherent communication using a real, four-vector description instead of the conventionally used Jones calculus or the Mueller matrices. The four-vector can then handle all superpositions of two orthogonal polarization basis and two orthogonal time bases (e.g., the in-phase and quadrature phase). In developing this formulation it was found that to provide a general but minimal framework for such rotations, it is natural to divide the six generators of four-dimensional (4d) rotations into two groups of three generators, the right-and the left-isoclinic matrices. Of the six transformations these generators define, it was furthermore found that four of them are readily implemented by linear optical components, while two of then were impossible to implement by such means. In this paper, we detail the reason these two "unphysical" rotations cannot be implemented with linear optics. We also suggest how they can be implemented, but at a cost in the signal-to-noise ratio, and give this minimum cost.

• 27. Bouchard, F.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Quantum metrology at the limit with extremal Majorana constellations2017In: Operator Theory: Advances and Applications, ISSN 1004-4469, E-ISSN 2334-2536, Vol. 4, no 11, p. 1429-1432Article in journal (Refereed)

Quantum metrology allows for a tremendous boost in the accuracy of measurement of diverse physical parameters. The estimation of a rotation constitutes a remarkable example of this quantum-enhanced precision. The recently introduced Kings of Quantumness are especially germane for this task when the rotation axis is unknown, as they have a sensitivity independent of that axis and they achieve a Heisenberg-limit scaling. Here, we report the experimental realization of these states by generating up to 21-dimensional orbital angular momentum states of single photons, and confirm their high metrological abilities.

• 28. Carville, N. C.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Growth mechanism of photoreduced silver nanostructures on periodically proton exchanged lithium niobate: Time and concentration dependence2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 18, p. 187212-1-187212-7Article in journal (Refereed)

Photodeposition of metallic nanostructures onto ferroelectric surfaces, which have been chemically patterned using a proton exchange process, has recently been demonstrated. By varying the molar concentration of the AgNO 3 solution and the illumination time, one can determine the initial nucleation sites, control the rate of nucleation and the height of silver nanostructures formed, and study the mechanisms by which these processes occurs. The nanoparticles are found to deposit preferentially in the boundary between ferroelectric and proton exchanged regions, in an area proton exchanged via lateral diffusion under the masking layer used for chemical patterning, consistent with our previous results. Using a short illumination time (3 min), we are able to determine that the initial nucleation of the silver nanostructure, having a width of 0.17 ± 0.02 μm and a height of 1.61 ± 0.98 nm, occurs near the edge of the reactive ion etched area within this lateral diffusion region. Over longer illumination times (15 min), we find that the silver deposition has spread to a width of 1.29 ± 0.06 μm, extending across the entire lateral diffusion region. We report that at a high molar concentration of AgNO3 (10-2 M), the amount of silver deposition for 5 min UV illumination is greater (2.88 ± 0.58 nm) compared to that at low (10-4 M) concentrations (0.78 ± 0.35 nm), however, this is not the case for longer time periods. With increasing illumination time (15 min), experiments at 10-4 M had greater overall deposition, 6.90 ± 1.52 nm, compared to 4.50 ± 0.76 nm at 10 -2 M. For longer exposure times (30 min) at 10-2 M, the nanostructure height is 4.72 ± 0.59 nm, suggesting a saturation in the nanostructure height. The results are discussed in terms of the electric double layer that forms at the crystal surface. There is an order of magnitude difference between the Debye lengths for 10-2 and 10-4 M solutions, i.e., 3.04 vs. 30.40 nm, which suggests the Debye length plays a role in the availability of Ag ions at the surface.

• 29. Carville, N. Craig
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Biocompatibility of ferroelectric lithium niobate and the influence of polarization charge on osteoblast proliferation and function2015In: Journal of Biomedical Materials Research. Part A, ISSN 1549-3296, E-ISSN 1552-4965, Vol. 103, no 8, p. 2540-2548Article in journal (Refereed)

In this work, the influence of substrate surface charge on in vitro osteoblast cell proliferation on ferroelectric lithium niobate (LN) crystal surfaces is investigated. LN has a spontaneous polarization along the z-axis and is thus characterized by positive and negative bound polarization charge at the +z and -z surfaces. Biocompatibility of LN was demonstrated via culturing and fluorescence imaging of MC3T3 osteoblast cells for up to 11 days. The cells showed enhanced proliferation rates and improved osteoblast function through mineral formation on the positively and negatively charged LN surfaces compared to electrostatically neutral x-cut LN and a glass cover slip control. These results highlight the potential of LN as a template for investigating the role of charge on cellular processes.

• 30. Carville, N. Craig
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Photoreduction of SERS-Active Metallic Nanostructures on Chemically Patterned Ferroelectric Crystals2012In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 6, no 8, p. 7373-7380Article in journal (Refereed)

Photodeposition of metallic nanostructures onto ferroelectric surfaces is typically based on patterning local surface reactivity via electric field poling. Here, we demonstrate metal deposition onto substrates which have been chemically patterned via proton exchange (i.e., without polarization reversal). The chemical patterning provides the ability to tailor the electrostatic fields near the surface of lithium niobate crystals, and these engineered fields are used to fabricate metallic nanostructures. The effect of the proton exchange process on the piezoelectric and electrostatic properties of the surface is characterized using voltage-modulated atomic force microscopy techniques, which, combined with modeling of the electric fields at the surface of the crystal, reveal that the deposition occurs preferentially along the boundary between ferroelectric and proton-exchanged regions. The metallic nanostructures have been further functionalized with a target probe molecule, 4-aminothiophenol, from which surface-enhanced Raman scattering (SERS) signal is detected, demonstrating the suitability of chemically patterned ferroelectrics as SERS-active templates.

• 31. Carville, N. Craig
KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Biocompatible Gold Nanoparticle Arrays Photodeposited on Periodically Proton Exchanged Lithium Niobate2016In: ACS BIOMATERIALS SCIENCE & ENGINEERING, ISSN 2373-9878, Vol. 2, no 8, p. 1351-1356Article in journal (Refereed)

Photodeposition of silver nanoparticles onto chemically patterned lithium niobate having alternating lithium niobate and proton exchanged regions has been previously investigated. Here, the spatially defined photodeposition of gold nanoparticles onto periodically proton exchanged lithium niobate is demonstrated. It is shown that the location where the gold nanoparticles form can be tailored by altering the concentration of HAuCl4. This enables the possibility to sequentially deposit gold and silver in different locations to create bimetallic arrays. The cytocompatibility of photodeposited gold, silver, and bimetallic ferroelectric templates to osteoblast-like cells is also investigated. Gold samples provide significantly greater cell biocompatibility than silver samples. These results highlight a potential route for using photodeposited gold on lithium niobate as a template for applications in cellular biosensing.

• 32. Cavalli, Alessandro
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
High-Yield Growth and Characterization of < 100 > InP p-n Diode Nanowires2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 5, p. 3071-3077Article in journal (Refereed)

Semiconductor nanowires are nanoscale structures holding promise in many fields such as optoelectronics, quantum computing, and thermoelectrics. Nanowires are usually grown vertically on (111)-oriented substrates, while (100) is the standard in semiconductor technology. The ability to grow and to control impurity doping of (100) nanowires is crucial for integration. Here, we discuss doping of single-crystalline < 100 > nanowires, and the structural and optoelectronic properties of p-n junctions based on < 100 > InP nanowires. We describe a novel approach to achieve low resistance electrical contacts to nanowires via a gradual interface based on p-doped InAsP. As a first demonstration in optoelectronic devices, we realize a single nanowire light emitting diode in a < 100 >-oriented InP nanowire p-n junction. To obtain high vertical yield, which is necessary for future applications, we investigate the effect of the introduction of dopants on the nanowire growth.

• 33. Cherifi-Hertel, S.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Non-Ising and chiral ferroelectric domain walls revealed by nonlinear optical microscopy2017In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 15768Article in journal (Refereed)

The properties of ferroelectric domain walls can significantly differ from those of their parent material. Elucidating their internal structure is essential for the design of advanced devices exploiting nanoscale ferroicity and such localized functional properties. Here, we probe the internal structure of 180° ferroelectric domain walls in lead zirconate titanate (PZT) thin films and lithium tantalate bulk crystals by means of second-harmonic generation microscopy. In both systems, we detect a pronounced second-harmonic signal at the walls. Local polarimetry analysis of this signal combined with numerical modelling reveals the existence of a planar polarization within the walls, with Néel and Bloch-like configurations in PZT and lithium tantalate, respectively. Moreover, we find domain wall chirality reversal at line defects crossing lithium tantalate crystals. Our results demonstrate a clear deviation from the ideal Ising configuration that is traditionally expected in uniaxial ferroelectrics, corroborating recent theoretical predictions of a more complex, often chiral structure.

• 34. Conforti, M.
KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Broadband parametric processes in quadratic nonlinear photonic crystals2014In: Bragg Gratings, Photosensitivity, and Poling in Glass Waveguides 2014, Optical Society of America, 2014Conference paper (Refereed)

We develop a general model, based on a (2+1)D unidirectional pulse propagation equation, for describing broadband noncollinear parametric interactions in two-dimensional quadratic lattices. We apply it to the analysis of twin-beam optical parametric generation in hexagonally poled LiTaO&#60;inf>3&#60;/inf>, gaining further insights into experimental observations.

• 35. Conforti, Matteo
KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Broadband parametric processes in chi((2)) nonlinear photonic crystals2014In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 39, no 12, p. 3457-3460Article in journal (Refereed)

We develop a general model, based on a (2 + 1)D unidirectional pulse propagation equation, for describing broadband noncollinear parametric interactions in 2D quadratic lattices. We apply it to the analysis of twin-beam optical parametric generation in hexagonally poled LiTaO3, gaining further insights into experimental observations.

• 36. Damm, S.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Formation of ferroelectrically defined Ag nanoarray patterns2014In: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2014Conference paper (Refereed)

In order to produce the most effective Ag nanoarrays for plasmon enhanced fluorescence and Raman scattering made using ferroelectric substrates, the optimum conditions for the creation of arrays must be identified. We study here Ag nanopattern arrays formed using ferroelectric lithography based on periodically proton exchanged (PPE) template methods. We examine different conditions in regard to deposition of Ag nanoparticles and analyze the plasmon enhanced signal from the resulting nanoarray. We apply FLIM (fluorescence lifetime imaging) to assess different Ag nanoarray preparation conditions on fluorescence emission from selected fluorphores. In addition, we apply Raman and luminescence spectroscopy with AFM (atomic force microscopy) to study the plasmon enhancement of luminescence and Raman from the Ag nanoarrays.

• 37. Damm, S.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
SERS from Ag and Au nanoarrays made using photochemical patterning2013In: 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference, CLEO/Europe-IQEC 2013, IEEE Computer Society, 2013, p. 6801468-Conference paper (Refereed)

Metallic nanostructures made from 'coinage' metals such as silver or gold, yield plasmons when light creates a collective oscillation of the conduction electrons on the surface of the metal, creating a greatly enhanced electromagnetic field [1-3]. The specific properties of the plasmonic structures have been found to be greatly dependent on factors such as size, shape, and dielectric environment [1-3]. These properties have been exploited in a variety of plasmonic applications ranging from sensing to enhanced fluorescence [4].

• 38. Damm, Signe
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Surface enhanced luminescence and Raman scattering from ferroelectrically defined Ag nanopatterned arrays2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 8, p. 083105-Article in journal (Refereed)

Ag nanopatterned arrays prepared using periodically proton exchanged templates have been demonstrated to support surface enhanced luminescence. Fluorescence lifetime imaging reveals that luminescence intensity is greatest on Ag and that the lifetime of the molecular probe is reduced, in line with a surface enhanced luminescence mechanism. Studies establish that the substrate simultaneously supports surface enhanced luminescence and Raman scattering. Spatial dependence along the nanopatterned arrays shows <7% variation in Raman scattering signal intensity, offering high reproducibility for practical applications. Fluorophores emitting near the plasmon absorption maxima are enhanced 4-fold.

• 39. de la Hoz, P.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Classical polarization multipoles: paraxial versus nonparaxial2015In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 7, article id 074030Article in journal (Refereed)

We discuss the polarization of paraxial and nonparaxial classical light fields by resorting to a multipole expansion of the corresponding polarization matrix. It turns out that only a dipolar term contributes when one considers SU(2) (paraxial) or SU(3) (nonparaxial) as fundamental symmetries. In this latter case, one can alternatively expand in SU(2) multipoles, and then both a dipolar and a quadrupolar component contribute, which explains the richer structure of this nonparaxial instance. These multipoles uniquely determine Wigner functions, in terms of which we examine some intriguing hallmarks arising in this classical scenario.

• 40. de la Hoz, P.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Unpolarized states and hidden polarization2014In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 4, p. 043826-Article in journal (Refereed)

We capitalize on a multipolar expansion of the polarization density matrix, in which multipoles appear as successive moments of the Stokes variables. When all the multipoles up to a given order K vanish, we can properly say that the state is Kth-order unpolarized, as it lacks of polarization information to that order. First-order unpolarized states coincide with the corresponding classical ones, whereas unpolarized to any order tally with the quantum notion of fully invariant states. In between these two extreme cases, there is a rich variety of situations that are explored here. The existence of hidden polarization emerges in a natural way in this context.

• 41. de la Hoz, P.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Multipolar hierarchy of efficient quantum polarization measures2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 6, p. 063803-Article in journal (Refereed)

We advocate a simple multipole expansion of the polarization density matrix. The resulting multipoles appear as successive moments of the Stokes variables and can be obtained from feasible measurements. In terms of these multipoles we construct a whole hierarchy of measures that accurately assess higher-order polarization fluctuations.

• 42.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
Focused ion beam milling of gallium phosphide nanowaveguides for non-linear optical applications2014In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2014Conference paper (Refereed)

GaP multilayer slab waveguides were fabricated by FIB milling. Limited transmission properties of the nanostructures, due to appreciable residuals of gallium, were recovered by fspulsed laser exposure. The waveguides were assessed by SHG technique.

• 43.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Information and Communication Technology (ICT). KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Modal phase matching in nanostructured zincblende semiconductors for second-harmonic generation2017In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2017Conference paper (Refereed)

Gallium phosphide nanowaveguide arrays, designed to fulfill the phase matching conditions and field-overlap, are characterized by second-harmonic generation. The bandwidth of 30nm with maximum conversion efficiency of 10-3 is measured for 150fs optical pulses.

• 44.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Modal phase matching in nanostructured zinc-blende semiconductors for second-order nonlinear optical interactions2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 7, article id 075303Article in journal (Refereed)

We demonstrate enhanced second-harmonic generation in arrays of nanowaveguides satisfying modal-phase-matching condition, both theoretically and experimentally. The overlap of interacting fields defined by the fundamental mode of the pump and the second-order mode of the second-harmonic wave is enhanced by the longitudinal component of the nonlinear polarization density. For guided modes with significant longitudinal electric field components, the overlap of fields is comparable to that obtained in the quasi-phase-matching technique leading to higher conversion efficiencies. Thus, the presented method is preferable to achieve higher conversion efficiency in second-order nonlinear processes in nanowaveguides.

• 45.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Focused ion beam milling of gallium phosphide nanostructures for photonic applications2016In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 6, no 2, p. 587-596Article in journal (Refereed)

We report on the fabrication of gallium phosphide (GaP) nanowaveguides of controlled dimensions, as small as 0.03 μm and aspect ratio in excess of 20, using focused ion beam (FIB) milling. A known limitation of this fabrication process for photonic applications is the formation of gallium droplets on the surface. We demonstrate a post-fabrication step using a pulsed laser to locally oxidize the excess surface gallium on the FIB milled nanostructures. The process significantly reduces the waveguide losses. The surface optical quality of the fabricated GaP nanowaveguides has been evaluated by second-harmonic generation experiments. Surface and bulk contributions to second-order optical nonlinearities have been identified by polarization measurements. The presented method can potentially be applied to other III-V nanostructures to reduce optical losses.

• 46.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA. Indian Institute of Technology, India. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA. Stockholm University. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Semiconductor Materials, HMA. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence2015In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, no 9, p. 2072-2075Article in journal (Refereed)

We present experimental demonstration and analysis of enhanced surface second harmonic generation (SHG) from hexagonal arrays of silicon pillars. Three sets of Si pillar samples with truncated cone-shaped pillar arrays having periods of 500, 1000, and 2000 nm, and corresponding average diameters of 200, 585 and 1550 nm, respectively, are fabricated by colloidal lithography and plasma dry etching. We have observed strong dependence of SHG intensity on the pillar geometry. Pillar arrays with a 1000 nm period and a 585 nm average diameter give more than a one order of magnitude higher SHG signal compared to the other two samples. We theoretically verified the dependence of SHG intensity on pillar geometry by finite difference time domain simulations in terms of the surface normal E-field component. The enhanced surface SHG light can be useful for nonlinear silicon photonics, surface/interface characterization, and optical biosensing.

• 47. Ehn, A.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Temporal filtering with fast ICCD cameras in Raman studies2013In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 44, no 4, p. 622-629Article in journal (Refereed)

A common problem when applying Raman scattering in applied research is spectral interference from laser-induced fluorescence. Extensive work has been invested in developing spectral and polarization filters as well as modulation schemes to refine spontaneous Raman signals. This current work, however, focuses on utilizing the temporal domain using a picosecond laser system and ICCD cameras with relatively short decay of the camera gate to prevent the fluorescence tail from being captured in Raman experiments. Further, the approach of using an ICCD camera to perform temporal filtering is compared to earlier proposed detection schemes using streak cameras or Kerr gates. The temporal-filtering scheme is evaluated in a spectroscopic investigation where a background subtraction algorithm is presented. The temporal-filtering scheme was also evaluated for Raman imaging of a levitated water droplet surrounded by fluorescing toluene vapor. Furthermore, the temporal-filter detection scheme was simulated in order to provide straight forward evaluation tools to estimate the potential of performing temporal filtering with a laser/camera system considering: laser-pulse duration, time jitter, camera-gate characteristics, gate delay times, fluorescence lifetimes, and relative signal strength between the Raman and fluorescence signal. The fluorescence signal was modeled with a closed two-level system, and the simulated results were compared to results from an investigation of the rising slope of toluene fluorescence. These evaluation tools and experimental investigations may serve as guidelines for planning and performing Raman measurements in situations where traditional filter-rejection schemes are insufficient.

• 48.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. Delft Univ Technol, Kavli Inst Nanosci, Netherlands.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. Delft Univ Technol, Kavli Inst Nanosci, Netherlands. KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Thermo-Optic Characterization of Silicon Nitride Resonators for Cryogenic Photonic Circuits2016In: IEEE Photonics Journal, ISSN 1097-5764, E-ISSN 1943-0655, Vol. 8, no 3, article id 2701009Article in journal (Refereed)

In this paper, we characterize the Thermo-optic properties of silicon nitride ring resonators between 18 and 300 K. The Thermo-optic coefficients of the silicon nitride core and the oxide cladding are measured by studying the temperature dependence of the resonance wavelengths. The resonant modes show low temperature dependence at cryogenic temperatures and higher dependence as the temperature increases. We find the Thermo-optic coefficients of PECVD silicon nitride and silicon oxide to be 2.51 +/- 0.08 E-5 K-1 and 0.96 +/- 0.09 E-5 K-1 at room temperature while decreasing by an order of magnitude when cooling to 18 K. To show the effect of variations in the thermo-optic coefficients on device performance, we study the tuning of a fully integrated electrically tunable filter as a function of voltage for different temperatures. The presented results provide new practical guidelines in designing photonic circuits for studying low-temperature optical phenomena.

• 49.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO. Acreo Swedish ICT AB, Dept Fiber Opt, Sweden.
KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. Acreo Swedish ICT AB, Sweden.
Identification andretrieval of particles with microstructured optical fibers2014Conference paper (Refereed)

A system where laser light is coupled into a fiber with longitudinal holes is used to identify and collect fluorescent particles from a solution, mimicking automatic fiber-based separation of tagged cancer cells in the body.

• 50. Folli, V.
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
Purely nonlinear disorder-induced localizations and their parametric amplification2013In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 38, no 24, p. 5276-5279Article in journal (Refereed)

We investigate spatial localization in a quadratic nonlinear medium in the presence of randomness. By means of numerical simulations and theoretical analyses we show that, in the down conversion regime, the transverse random modulation of the nonlinear susceptibility generates localizations of the fundamental wave that grow exponentially in propagation. The localization length is optically controlled by the pump intensity that determines the amplification rate. The results also apply to cubic nonlinearities.

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