Top PDF Semiconductor optical microcavities for chip-based cavity QED

Semiconductor optical microcavities for chip-based cavity QED

Semiconductor optical microcavities for chip-based cavity QED

To study wavelength-scale cavities, we no longer rely on achieving phase matching, but rather just use the taper as a convenient means to produce a micron-scale evanescent field for sourcing and out-coupling the micron-scale cavity field. The taper effectively serves to bridges the disparate length scales from conventional fiber and free-space optics to chip-based microoptics, and does so entirely off the chip, so that on-chip structures do not require any additional complexity. Although the coupling we observe might not be as efficient as phase matched coupling, the power transfer is more than adequate enough to probe many of the important properties of the cavity. By using an external waveguide as the coupling element, this method is inherently non-invasive, can be used to rapidly characterize multiple devices on a chip, and the ability to vary the position of the taper with respect to the cavity (not an option for microfabricated on-chip waveguides) allows for quantitative investigation of not only the Q factor but also V eff . Furthermore, the resonant coupling from the ex- ternal waveguide is polarization selective, providing additional information about the cavity modes that is not easily obtainable through techniques such as NSOM. Knowledge of a mode’s spectral position, polarization, Q, and V eff will in many cases be enough to unambiguously determine the identity of the mode in comparison to simulation or theoretical results. Thus, in some respects, the versatility of the fiber-based approach that we have described in this chapter makes the technique an optical analog to electrical probes used to study microelectronic devices.
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Influence of optical material properties on strong coupling in organic semiconductor based microcavities

Influence of optical material properties on strong coupling in organic semiconductor based microcavities

for materials with similar chemical characteristics (i.e. the two polyuorene polymers studied) but also for the distinct J-aggregate MEH-PBI. In conclusion, we found clear signatures of strong exciton-photon coupling in metal-clad microcavities for the four investigated organic materials PF8, BBEHP- PPV, F8BT and MEH-PBI. The importance of taking into account the optical anisotropy of the analysed ma- terials, which originates from their dierent ordering in the thin lm, was demonstrated. A comparison of the Rabi splitting to various optical properties of the com- pounds emphasised, in agreement with expectations, the role of the absorption as an important parameter for the coupling strength of the material. Linking the two ob- servations, we deduce that the preferential orientation of transition dipoles in the plane, as seen in all investigated materials, enhances the coupling strength compared to isotropically oriented dipoles due to a more ecient cou- pling to the cavity photons.
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Influence of optical material properties on strong coupling in organic semiconductor based microcavities

Influence of optical material properties on strong coupling in organic semiconductor based microcavities

In conclusion, we found clear signatures of strong exciton-photon coupling in metal-clad microcavities for the four investigated organic materials PF8, BBEHP-PPV, F8BT, and MEH-PBI. The importance of taking into account the optical anisotropy of the analysed materials, which origi- nates from their different ordering in the thin film, was dem- onstrated. A comparison of the Rabi splitting to various optical properties of the compounds emphasised, in agree- ment with expectations, the role of the absorption as an important parameter for the coupling strength of the material leading to a record Rabi splitting observed in organic micro- cavities of 1.09 eV. Linking the two observations, we deduce that the preferential orientation of transition dipoles in the plane, as seen in all investigated materials, enhances the cou- pling strength compared to isotropically oriented dipoles due to a more efficient coupling to the cavity photons.
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Two photon absorption based detection in semiconductor microcavities

Two photon absorption based detection in semiconductor microcavities

Fig. 6.9 TPA photocurrent vs. orientation o f the linear state o f polarisation o f the incident optical signal, recorded for three w avelengths around the cavity resonance. The case for TPA is slightly more complicated, as the TPA process in GaAs is polarisation dependant. From Fig. 6.7 it can be seen that the resonance wavelength of the cavity is not the same for the TPA dominated regime as it is in the SPA dominated regime. This can be explained by the thermal tuning of the cavity because of the large difference in incident power levels used for the TPA and SPA dominant regimes. The dependence of TPA photocurrent on the orientation of the linear polarisation state was recorded at three wavelengths around the cavity resonance, with constant average power incident, as shown in Fig. 6.9. The local maxima {0 = 0° and 90°) correspond to the eigenmodes of the cavity. The difference between the amplitudes of the peaks is due to the birefringence of the cavity. In the absence of birefringence, the amplitude of both peaks would be the same for all wavelengths. The TPA photocurrent was also recorded as the input polarisation state was scanned from circular to linear to circular along four different longitudinal axes of the Poincare sphere, see Fig.
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On-chip High-finesse Fabry-Perot Microcavities for Optical Sensing and Quantum Information

On-chip High-finesse Fabry-Perot Microcavities for Optical Sensing and Quantum Information

Abstract: For applications in sensing and cavity-based quantum computing and metrology, open- access Fabry-Perot cavities – with an air or vacuum gap between a pair of high reflectance mirrors – offer important advantages compared to other types of microcavities. For example, they are inherently tunable using MEMS-based actuation strategies, and they enable atomic emitters or target analytes to be located at high field regions of the optical mode. Integration of curved-mirror Fabry-Perot cavities on chips containing electronic, optoelectronic, and optomechanical elements is a topic of emerging importance. Micro-fabrication techniques can be used to create mirrors with small radius-of-curvature, which is a prerequisite for cavities to support stable, small-volume modes. We review recent progress towards chip-based implementation of such cavities, and highlight their potential to address applications in sensing and cavity quantum electrodynamics.
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Polariton traps in semiconductor microcavities

Polariton traps in semiconductor microcavities

Keywords: Stimulation; Polaritons; Microcavities; Ampli6cation; Condensates Since the 6rst measurement of the angular dis- persion of semiconductor microcavities [1], it has become clear that the in-plane wave vector of the mixed exciton–cavity photons is extremely important for their linear and nonlinear properties. The strong coupling of the highly dispersive cavity photon mode with the rather :at quadratic exciton dispersion, leads to new upper and lower polariton dispersions which are severely distorted, split by the Rabi fre- quency, . The dominant new feature is the deep minimum in the energy–momentum dispersion of the lower polariton, which has a depth =2, and a width,
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Optical devices using an external cavity semiconductor laser

Optical devices using an external cavity semiconductor laser

During operation in the amplification mode, light is input through the front facet and is amplified within the body of the optical gain material. An at least partially optically reflective surface is positioned a first predetermined distance from one of the facets during operation of the device in the amplification mode. In the signal generation mode, the at least partially optically reflective surface is positioned a second

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Raman transitions in cavity QED

Raman transitions in cavity QED

Abstract In order to study quantum effects such as state superposition and entanglement, one would like to construct simple systems for which the damping rates are slow relative to the rate of coherent evolu- tion. One such system is strong-coupling cavity quantum electrodynamics (QED), in which a single atom is coupled to a single mode of a high finesse optical cavity. In recent years, optical trapping techniques have been applied to the cavity QED system, allowing an individual atom to remain coupled to the cavity for long periods of time. For the purpose of future cavity QED experiments, one would like to gain as much control over the trapped atom as possible; in particular, one would like to cool the center of mass motion of the atom, to measure the magnetic field at the location of the atom, and to be able to prepare the atom in a given internal state. In the first part of this thesis, I present a scheme for driving Raman transitions inside the cavity that can be used to achieve these goals. After giving a detailed theoretical treatment of the Raman scheme, I describe how it can be implemented in the lab and discuss some preliminary experimental results.
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Cavity QED with multilevel atoms

Cavity QED with multilevel atoms

Access You should consider how your vacuum system will interface to the rest of your ex- periment. This means, for example, providing optical access for beams and cameras. You should consider how many windows you will need and whether they will require antireflective coatings. AR coated windows are more delicate, so windows should not be coated unless it is necessary. If you need electrical access to your chamber, you should consider how many pins you need and how much noise is allowable. If you need low noise then you may want to use coaxial feedthroughs, but if you need many pins on a small flange then this will not be possible. Anecdote: we once had an electrical feedthrough that had long metal pins that went through a piece of ceramic. Electrical connection was made to the pins on the outside by soldering. The feedthrough de- veloped a leak, which was attributed to mechanical stress on the pins causing a leak in the ceramic. Since then, we have had success using feedthroughs that end in BNC jacks. Liz Wilcut has successfully used fiber optic feedthroughs based on a Swagelock fitting with a Teflon ferrule (following Ref. [80]) in chambers achieving 10 −9 Torr.
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Coherent Control in Cavity QED

Coherent Control in Cavity QED

After the PBS, the cavity output is collimated, and an angle-tuned mirror sepa- rates the 836 nm light for the cavity lock. A series of four dichroic mirrors and two interference filters suppresses the remaining 836 nm and 936 nm light in the path be- fore the light is finally coupled into optical fiber. In December 2005, we measured the propagation efficiency p table to be 66% before fiber coupling, with losses attributed to individual elements listed in Table 2.1. This measurement is roughly consistent with the values of p path = p couple p table = 32% and 40% given in Refs. [16, 29], where p couple includes fiber coupling losses; in November 2006, we improved the fiber alignment, which boosted p path from 30% to 50%. The dichroic elements are relatively ineffective at suppressing FORT light — each dichroic removes less than half of incident light at 936 nm — and should probably be removed from future beam paths, as they are also not perfect at 852 nm. Each interference filter, on the other hand, has a measured suppression of 10 4 at 936 nm. It is interesting to note that given the measured FORT propagation losses at each step of the path, we would still expect the FORT power to saturate our detectors, while in fact we see fewer than 5 photon counts/second due to 936 nm light. It must be true that optimizing the probe coupling into fiber at 852 nm results in very poor FORT fiber coupling. We believe that this is due to refraction in the PBS cube at the cavity output, which causes light at the two wavelengths to
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Optical properties and resonant cavity modes in axial InGaN/GaN nanotube microcavities

Optical properties and resonant cavity modes in axial InGaN/GaN nanotube microcavities

4 Department of Physics, SUPA, University of Strathclyde, G4 0NG, UK * P.Coulon@bath.ac.uk Abstract: Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers. Disk or tube geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes. In this article we present the fabrication of homogenous and dense arrays of axial InGaN/GaN nanotubes via a combination of displacement Talbot lithography (DTL) for patterning and inductively coupled plasma top-down dry-etching. Optical characterization highlights the homogeneous emission from nanotube structures. Power-dependent continuous excitation reveals a non-uniform light distribution within a single nanotube, with vertical confinement between the bottom and top facets, and radial confinement within the active region. Finite- difference time-domain simulations, taking into account the particular shape of the outer diameter, indicate that the cavity mode of a single nanotube has a mixed WGM-vertical Fabry-Perot mode (FPM) nature. Additional simulations demonstrate that the improvement of the shape symmetry and dimensions primarily influence the Q-factor of the WGMs whereas the position of the active region impacts the coupling efficiency with one or a family of vertical FPMs. These results show that regular arrays of axial InGaN/GaN nanotubes can be achieved via a low-cost, fast and large-scale process based on DTL and top-down etching.
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Optical properties and resonant cavity modes in axial InGaN/GaN nanotube microcavities

Optical properties and resonant cavity modes in axial InGaN/GaN nanotube microcavities

4 Department of Physics, SUPA, University of Strathclyde, G4 0NG, UK * P.Coulon@bath.ac.uk Abstract: Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers. Disk or tube geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes. In this article we present the fabrication of homogenous and dense arrays of axial InGaN/GaN nanotubes via a combination of displacement Talbot lithography (DTL) for patterning and inductively coupled plasma top-down dry-etching. Optical characterization highlights the homogeneous emission from nanotube structures. Power-dependent continuous excitation reveals a non-uniform light distribution within a single nanotube, with vertical confinement between the bottom and top facets, and radial confinement within the active region. Finite- difference time-domain simulations, taking into account the particular shape of the outer diameter, indicate that the cavity mode of a single nanotube has a mixed WGM-vertical Fabry-Perot mode (FPM) nature. Additional simulations demonstrate that the improvement of the shape symmetry and dimensions primarily influence the Q-factor of the WGMs whereas the position of the active region impacts the coupling efficiency with one or a family of vertical FPMs. These results show that regular arrays of axial InGaN/GaN nanotubes can be achieved via a low-cost, fast and large-scale process based on DTL and top-down etching.
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Elastomer based electrically tunable, optical microcavities

Elastomer based electrically tunable, optical microcavities

Electrically tunable optical microcavities are used for versatile applications in the field of sensing, spectroscopy as well as telecommunications 1 . Particularly for bio- medical applications or chemical point-of-care analysis, it is desirable to develop simple, compact, and easily processable devices. For this purpose, optical sensing promises high sensitivity and a reduced response time 2 . Reconfigurable filters with small bandwidth were re- alized up to now by microelectromechanical systems (MEMS) 3,4 which require complicated etching and lithography or the application of thin membranes as tun- able elements. By comparison, our approach is based on tuning microcavity resonance via an electroactive elas- tomer, is easy and cost-effective. Due to simple design, various structures and scaling to large area arrays are en- visioned.
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Asymmetric angular emission in semiconductor microcavities

Asymmetric angular emission in semiconductor microcavities

population, a normally incident probe pulse can be set to arrive simultaneously with the pump pulse. In order to inject polaritons at specific ( v ,k), the optical pulses are spectrally filtered and aligned along particular incident angles, without grossly modifying their time of arrival at the sample. To achieve this we constructed the femtosecond-stable goniom- eter shown in Fig. 1, which rotates under the center of the sample. The arms for pump, probe, and detection beams each allow access to u < 6 80°. A 100-fs Ti:S laser is used to generate the different 3-ps pulses which are shaped in the spectral plane using computer-controlled liquid crystal modulators. 10 The pump powers are kept sufficiently low so that the exciton oscillator strength suffers no appreciable bleaching. 11 The emitted light from the sample is collected in a detection cone of 6 0.14° and is coupled through polarization-sensitive optics into a multimode fiber. To avoid averaging across regions of different excitation intensity, only the inner part ~50 m m! of the PL spot is sampled. A monochromator with nitrogen-cooled charge-coupled device
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Experiments with Toroidal Microresonators in Cavity QED

Experiments with Toroidal Microresonators in Cavity QED

Obtaining critical coupling with P F dark enough to observe atom transits by means of contact mode is significantly more difficult and potentially damaging to the toroid than non-contact mode and should therefore only be used when an appropriate positioning system is unavailable. Rather than arbitrarily choosing the separation between taper and toroid, we are only able to choose the point at which we attach the taper to the toroid. Each time the toroid is contacted with the taper we are potentially damaging the fine surface that is responsible for high quality factors. To simplify the process of finding resonance locations, as well as to minimize damage from contacting the taper, toroids should be characterized in a setup external to the vacuum chamber that is capable of operating in non-contact mode. This is more feasible without the constraints of a vacuum chamber and optics. Additionally, these parts are all commercially available and can be obtained rather reasonably compared to a system which is vacuum-compatible. For this experiment, the toroid chip was mounted to a stage attached to an xyz translation stage. Piezo-tipped micrometers were used to control the fine and coarse motion; the taper was rigidly mounted. A pair microscopes were used to image the toroid from above and from the side. A model of the system we used is shown in Figure 2.12 and the process of characterizing toroids is described in Chapter 4.
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Bifurcations in Single Atom Cavity QED

Bifurcations in Single Atom Cavity QED

Using this procedure I obtained a nominal value of l = 71.6µm, implying an axial mode spacing, F SR = 2.1THz. The cavity linewidth was measured by monitoring the transmitted intensity while sweeping, in time, the length of the cavity over a resonance. The sweep rate was calibrated by placing frequency sidebands on the laser, and the digitized transmission signal was fit with a Lorentzian. The obtained value was, δf = 16MHz, implying a cavity decay parameter, κ = 2π · 8MHz, and a finesse, F = 130, 000. Assuming a symmetric cavity, this constrains the total losses to T + A ≈ 24ppm. Since the cavity was mode matched to > 95%, the mirror loss parameters were inferred through a measurement of the cavity transmission alone, Eq. 2.85. From the ≈ 20% of the incident power that was measured exiting the cavity, I inferred the transmission and absorption losses to be T ≈ 10ppm and A ≈ 14ppm. This is quite unfortunate, as it implies that only a fraction η T ≈ 0.2 of the intracavity power makes it into the cavity output mode (i.e., the mode that we measure.) It should be noted, however, that I made no attempts to characterize the optical scattering due to the (uncoated) vacuum chamber view ports, so that the quantity T is probably a bit larger than quoted above, while A is equally smaller. This fact is irrelevant, however, for determining the quantity κ. Furthermore, although η T was estimated using only transmission measurements, subsequent analysis of the cavity reflection signal was found to be consistent with this value of η T .
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GaInNAs based Hellish vertical cavity semiconductor optical amplifier for 1 3 μm operation

GaInNAs based Hellish vertical cavity semiconductor optical amplifier for 1 3 μm operation

The operation of Hellish device is based on the longitu- dinal injection of electron and hole pairs in their respective channels, due to the diffusion of both top contacts through all layers. Without the applied electric field, if the sample is illuminated, photogenerated carriers will even- tually recombine radiatively in the QW without drifting laterally in the longitudinal channels. On the other hand, when the device is biased, the energy bands tilt up, with the degree of tilting being proportional to the applied vol- tage. At low bias, a quasi-flat region is established by the tilted energy bands, and a small number of carriers are then able to drift diagonally into the p-n junction. This is illustrated in Figure 3. With an increase in the electric field, the energy bands will tilt up more, so that more car- riers will flow into the active region, enhancing the
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GaInNAs-based Hellish-vertical cavity semiconductor optical amplifier for 1.3 mu m operation

GaInNAs-based Hellish-vertical cavity semiconductor optical amplifier for 1.3 mu m operation

The operation of Hellish device is based on the longitu- dinal injection of electron and hole pairs in their respective channels, due to the diffusion of both top contacts through all layers. Without the applied electric field, if the sample is illuminated, photogenerated carriers will even- tually recombine radiatively in the QW without drifting laterally in the longitudinal channels. On the other hand, when the device is biased, the energy bands tilt up, with the degree of tilting being proportional to the applied vol- tage. At low bias, a quasi-flat region is established by the tilted energy bands, and a small number of carriers are then able to drift diagonally into the p-n junction. This is illustrated in Figure 3. With an increase in the electric field, the energy bands will tilt up more, so that more car- riers will flow into the active region, enhancing the
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Relaxation bottleneck and its suppression in semiconductor microcavities

Relaxation bottleneck and its suppression in semiconductor microcavities

~;1 psec! due to their high photon fraction, thus leading to a nonthermal polariton population and the occurrence of a re- laxation bottleneck. Such bottleneck effects have been much discussed theoretically for the cavity polariton system. 4,5 References 4 and 5 calculate the expected population distri- butions for both upper and lower polariton branches, includ- ing exciton-phonon and exciton-exciton scattering. Very large depletions of the low k states, relative to those at high k, by factors up to 10 4 , are predicted. Such relaxation bottle- necks also occur in bulk semiconductors, 6 but are very diffi- cult to study since the polaritons do not decay directly into external photons. In MC’s, by contrast, direct polariton de- cay does occur due to photon leakage out of the cavity, per- mitting direct study of the population distribution. 7
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Collective strong coupling in multimode cavity QED

Collective strong coupling in multimode cavity QED

From the resulting frequency difference between the modes we derive the numbers of quasidegenerate modes contained within a cavity linewidth to be 41 and 3, respectively. One experimental cycle involves loading a magneto-optical trap (MOT), placed into the center of the cavity, from the background gas of the chamber. The loading time is varied between 0.1 and 2 s, resulting in different atom numbers between 8 × 10 4 and 2 × 10 6 . Subsequently the MOT is switched off, and after a delay of 1 ms the cavity is pumped by a linearly polarized laser beam for 1 ms, and its transmission is recorded with the CCD camera. The relevant parameters for the pumping field are the atomic and cavity-field detunings, defined as A = ω P − ω A and C = ω P − ω C , respectively, where ω A is the atomic transition angular frequency; ω C is the cavity resonance frequency, which is the same for all modes, as they are assumed to be degenerate; and ω P is the pump laser frequency. Before measuring the multimode splitting, the cavity is positioned on resonance with the F g = 4 → F e = 5 D 2 line transition, i.e., ω A = ω C and thus A = C . A typical experimental run starts with a probe laser detuning of +100 MHz from the 4–5 transition. This is then successively reduced in steps of 2 MHz until a final detuning of
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