Showing papers by "Kerstin Worhoff published in 2013"

Observing fermionic statistics with photons in arbitrary processes

Abstract: Quantum mechanics defines two classes of particles-bosons and fermions-whose exchange statistics fundamentally dictate quantum dynamics. Here we develop a scheme that uses entanglement to directly observe the correlated detection statistics of any number of fermions in any physical process. This approach relies on sending each of the entangled particles through identical copies of the process and by controlling a single phase parameter in the entangled state, the correlated detection statistics can be continuously tuned between bosonic and fermionic statistics. We implement this scheme via two entangled photons shared across the polarisation modes of a single photonic chip to directly mimic the fermion, boson and intermediate behaviour of two-particles undergoing a continuous time quantum walk. The ability to simulate fermions with photons is likely to have applications for verifying boson scattering and for observing particle correlations in analogue simulation using any physical platform that can prepare the entangled state prescribed here.

Miniature spectrometer and beam splitter for an optical coherence tomography on a silicon chip.

Abstract: Optical coherence tomography (OCT) has enabled clinical applications that revolutionized in vivo medical diagnostics. Nevertheless, its current limitations owing to cost, size, complexity, and the need for accurate alignment must be overcome by radically novel approaches. Exploiting integrated optics, we assemble the central components of a spectral-domain OCT system on a silicon chip. The spectrometer comprises an arrayed-waveguide grating with 136-nm free spectral range and 0.21-nm wavelength resolution. The beam splitter is realized by a non-uniform adiabatic coupler with its 3-dB splitting ratio being nearly constant over 150 nm. With this device whose overall volume is 0.36 cm3 we demonstrate high-quality in vivo imaging in human skin with 1.4-mm penetration depth, 7.5-μm axial resolution, and a signal-to-noise ratio of 74 dB. Considering the reasonable performance of this early OCT on-a-chip system and the anticipated improvements in this technology, a completely different range of devices and new fields of applications may become feasible.

Energy-transfer-upconversion models, their applicability and breakdown in the presence of spectroscopically distinct ion classes: A case study in amorphous Al2O3:Er3+

Abstract: The influence of energy migration and energy-transfer upconversion (ETU) among neighboring Er3+ ions on luminescence decay and steady-state population densities in Al2O3:Er3+ thin films is investigated by means of photoluminescence decay measurements under quasi-CW excitation. The experimental results are analyzed by several models. As expected from the basic physical assumptions made by these models, only Zubenko’s microscopic model provides good agreement with the experimental data, while other donor−acceptor treatments found in the literature are unsuccessful and the macroscopic rateequation approach provides meaningful results only when misinterpreting the intrinsic lifetime as a free fit parameter. Furthermore, a fast quenching process induced by, e.g., active ion pairs and clusters, undesired impurities, or host material defects such as voids, that is not revealed by any particular signature in the luminescence decay curves because of negligible emission by the quenched ions under quasi-CW excitation, is verified by pump-absorption experiments. This quenching process strongly affects device performance as an amplifier. Since Zubenko’s microscopic model treats all ions equally, it is unable to describe a second, spectroscopically distinct class of ions involving a fast quenching process. The model is extended to take into account the fraction of quenched ions. This approach finally leads to excellent agreement between the luminescence-decay, pump-absorption, and small-signal-gain experiments within the frame of a single theoretical description.

Spectroscopy of upper energy levels in an $Er^{3+}$-doped amorphous oxide

Abstract: A spectroscopic study of the population mechanisms in erbium-doped amorphous aluminum oxide up to the 2H11/2/4S3/2 levels is performed. Via luminescence decay measurements, absorption and emission spectra, and a Judd-Ofelt analysis we determine luminescence lifetimes, radiative and non-radiative decay-rate constants, and branching ratios of the Er3+ inter-manifold transitions. With a continuous-wave pump-probe technique the excited-state absorption (ESA) spectrum is recorded between 900 and 1800 nm and the cross-sections of the ESA transitions 4I13/2 -> 4I9/2, 4I13/2 -> 4F9/2, and 4I11/2 -> 4F7/2 are determined. The microparameters and efficiencies of resonant and phonon-assisted energy-migration and energy-transfer-upconversion (ETU) processes among Er3+ ions occurring from the first and second excited states are evaluated. From the ratio of the 4S3/2 and 4F9/2 luminescence intensities as a function of Er3+ concentration we prove the existence and quantify the macroscopic ETU coefficient of the two-phonon-assisted ETU process (4I13/2, 4I11/2) -> (4I15/2, 4F9/2).

Intra‐laser‐cavity microparticle sensing with a dual‐wavelength distributed‐feedback laser

Abstract: An integrated intra-laser-cavity microparticle sensor based on a dual-wavelength distributed-feedback channel waveguide laser in ytterbium-doped amorphous aluminum oxide on a silicon substrate is demonstrated. Real-time detection and accurate size measurement of single micro-particles with diameters ranging between 1 μm and 20 μm are achieved, which represent the typical sizes of many fungal and bacterial pathogens as well as a large variety of human cells. A limit of detection of ∼500 nm is deduced. The sensing principle relies on measuring changes in the frequency difference between the two longitudinal laser modes as the evanescent field of the dual-wavelength laser interacts with micro-sized particles on the surface of the waveguide. Improvement in sensitivity far down to the nanometer range can be expected upon stabilizing the pump power, minimizing back reflections, and optimizing the grating geometry to increase the evanescent fraction of the guided modes.

Low-temperature deposition of high-quality siliconoxynitride films for CMOS-integrated optics

Abstract: The growth of silicon oxynitride thin films applying remote inductively coupled, plasma-enhanced chemical vapor deposition is optimized toward high optical quality at a deposition temperature as low as 150°C. Propagation losses of 0.5±0.05 dB/cm, 1.6±0.2 dB/cm and 0.6±0.06 dB/cm are measured on as-deposited waveguides for wavelengths of 1300, 1550, and 1600 nm, respectively. Films were deposited onto a 0.25 μm technology mixed-signal CMOS chip to show the application perspective for three-dimensional integrated optoelectronic chips.

Two-photon quantum interference in integrated multi-mode interference devices.

Abstract: Multi-mode interference (MMI) devices fabricated in silicon oxynitride (SiON) with a refractive index contrast of 2.4% provide a highly compact and stable platform for multi-photon non-classical interference. MMI devices can introduce which-path information for photons propagating in the multi-mode section which can result in degradation of this non-classical interference. We theoretically derive the visibility of quantum interference of two photons injected in a MMI device and predict near unity visibility for compact SiON devices. We complement the theoretical results by experimentally demonstrating visibilities of up to 97.7% in 2×2 MMI devices without the requirement of narrow-band photons.

Advanced integrated spectrometer designs for miniaturized optical coherence tomography systems

Abstract: Optical coherence tomography (OCT) has enabled clinical applications that revolutionized in vivo medical diagnostics. Nevertheless, its current limitations owing to cost, size, complexity, and the need for accurate alignment must be overcome by radically novel approaches. Exploiting integrated optics, the central components of a spectral-domain OCT (SD-OCT) system can be integrated on a chip. Arrayed-waveguide grating (AWG) spectrometers with their high spectral resolution and compactness are excellent candidates for on-chip SD-OCT systems. However, specific design-related issues of AWG spectrometers limit the performance of on-chip SD-OCT systems. Here we present advanced AWG designs which could overcome the limitations arising from free spectral range, polarization dependency, and curved focal plane of the AWG spectrometers. Using these advanced AWG designs in an SD-OCT system can provide not only better overall performance but also some unique aspects that a commercial system does not have. Additionally, a partially integrated OCT system comprising an AWG spectrometer and an integrated beam splitter, as well as the in vivo imaging using this system are demonstrated.

Dual-wavelength Narrow-linewidth Lasers and Their Applications

Abstract: Our recent work on distributed-feedback, narrow-linewidth channel waveguide lasers in Er3+- and Yb3+-doped Al2O3 layers deposited on silicon microchips is reviewed.

Toward spectral-domain optical coherence tomography on a silicon chip

Abstract: We present experimental results of a spectral-domain optical coherence tomography system that includes an integrated spectrometer. A depth range of 1 mm and axial resolution of 19 μm was measured. A layered phantom was imaged.

Rare-earth-ion-doped ultra-narrow-linewidth lasers on a silicon chip and applications to intra-laser-cavity optical sensing

Abstract: We report on diode-pumped distributed-feedback (DFB) and distributed-Bragg-reflector (DBR) channel waveguide lasers in Er-doped and Yb-doped Al2O3 on standard thermally oxidized silicon substrates. Uniform surface-relief Bragg gratings were patterned by laser-interference lithography and etched into the SiO2 top cladding. The maximum grating reflectivity exceeded 99%. Monolithic DFB and DBR cavities with Q-factors of up to 1.35×10^6 were realized. The Er-doped DFB laser delivered 3 mW of output power with a slope efficiency of 41% versus absorbed pump power. Single-longitudinal-mode operation at a wavelength of 1545.2 nm was achieved with an emission line width of 1.70 ± 0.58 kHz, corresponding to a laser Q-factor of 1.14×10^11. Yb-doped DFB and DBR lasers were demonstrated at wavelengths near 1020 nm with output powers of 55 mW and a slope efficiency of 67% versus launched pump power. An Yb-doped dual-wavelength laser was achieved based on the optical resonances induced by two local phase shifts in the DFB structure. A stable microwave signal at ~15 GHz with a –3-dB width of 9 kHz and a long-term frequency stability of ±2.5 MHz was created via the heterodyne photo-detection of the two laser wavelengths. By measuring changes in the microwave beat signal as the intra-cavity evanescent laser field interacts with micro-particles on the waveguide surface, we achieved real-time detection and accurate size measurement of single micro-particles with diameters ranging between 1 μm and 20 μm, which represents the typical size of many fungal and bacterial pathogens. A limit of detection of ~500 nm was deduced.