Silicon waveguides for creating quantum-correlated photon pairs

A new class of microelectromechanically tunable vertical-cavity surface-emitting lasers with a half-symmetric cavity structure is described. The cavity is realized by inducing a curvature (R/spl sim/320 μm) in the top movable dielectric mirror. The microcavity forces lasing oscillations in a single fundamental spatial mode of approximately 6 μm despite the 20 μm electrical aperture of the device. The device wavelength was tunable from 863 to 833 nm under a 13-V voltage swing. The device operates in a single fundamental mode with sidemode supression ratio of >20 dB throughout the tuning range.

The interference of nonclassical states of light enables quantum-enhanced applications reaching from metrology to computation. Most commonly, the polarization or spatial location of single photons are used as addressable degrees of freedom for turning these applications into praxis. However, the scale-up for the processing of a large number of photons of these architectures is very resource-demanding due to the rapidly increasing number of components, such as optical elements, photon sources, and detectors. Here, we demonstrate a resource-efficient architecture for multiphoton processing based on time-bin encoding in a single spatial mode. We use an efficient quantum dot single-photon source and a fast programmable time-bin interferometer to observe the interference of up to eight photons in 16 modes, all recorded only with one detector, thus considerably reducing the physical overhead previously needed for achieving equivalent tasks. Our results can form the basis for a future universal photonics quantum processor operating in a single spatial mode.

Development of a compact high brightness X-ray source

By utilizing entanglement property of photons the entangled two-photon absorption (ETPA) effect of an organic material, porphyrin dendrimer, is demonstrated through the comparison of the property of entangled photons to the property of quantum-correlated photons. The ETPA showed a cross-section 31 orders of magnitude higher than the cross-section of the classical two-photon absorption (TPA). This high cross-section is comparable to the cross-section of the resonant single-photon absorption. The entangled absorption effect is compared to the correlated TPA effect to determine the degree of correlation between the entangled and quantum correlated photon pairs. The experimental data describe the different degree of correlation of the non-entangled and entangled photon pairs by demonstrating linear and nonlinear relationship of the absorbed photon flux to the input photon flux. The linearity of the ETPA is an interesting quantum effect because the two-photon absorption is an inherently nonlinear process. Virtual state spectroscopy is also demonstrated as a novel spectroscopic method to investigate the properties of the virtual state from non-monotonic behavior of the cross-section which is represented by controlling temporal property of the entanglement. These results from the quantum spectroscopy methods show a unique quantum property which is not feasible to detect using classical methods.

Evaluation of splicing quality in few-mode optical fibers

Compact, inexpensive laser sources in the 2-4 μm wavelength region are of growing interest for applications in environmental detection of trace gases as well as medical diagnostics, process control and combustion analysis. Many organic compounds, including hazardous pollutants, have characteristic absorption spectra in this region. Although external cavity diode lasers (ECDLs) are commercially available from 0.6 μm to 1.6 μm 1, 2, they have not yet made it into the 2 μm wavelength range. Others have recently demonstrated tunability in an external cavity at 3.3 μm3 which was not continuous or single mode. We present room temperature operation of single longitudinal and single spatial mode, external cavity tunable diode lasers operating around 2 μm. We also present high-resolution absorption measurements of CO2 over the 250 cm−1 laser tuning range.

After characterizing the Raman scattering in a fused silica polarization-maintaining microstructure optical fiber, we built a fiber-based two-photon light source of high spectral brightness, broad spectral range, and very low noise background at room temperature. The resulting bright low-noise two-photon light can be used for a number of quantum information applications.

A VUV and soft x-ray light source based on spontaneous anti-Stokes scattering from atomic population stored in a meta-stable level is described. Unique properties of this source include: narrow linewidth, tunability, linear polarization, picosecond time scale, and quite high spectral brightness. We show how the maximum source brightness, within its narrow linewidth, is that of a blackbody at the temperature T of a metastable storage level. Experimental results showing laser induced emission at 569 Å and 637 Å from a He glow discharge are described. The use of the anti-Stokes process for direct, internal energy transfer from a storage species to a target species is discussed.

This is a study of a group of Czochralski grown rare‐earth‐doped single‐crystal cathodoluminescent phosphors. Such dopants as Ce3+, Tb3+, Eu3+, Sm3+, Tm3+, Gd3+, and some of their combinations were investigated. Activation by, , and by produced the most efficient blue, green, and red phosphors, respectively. In comparison with our previous best garnet single‐crystal phosphor system, the blue, green, and red phosphors are by factors 12.7, 1.23, and 0.7 brighter, respectively. was shown to be an efficient single line (313 nm) emitting phosphor of very high spectral brightness in UV.

In this work, we demonstrated a mid-infrared resonant cavity light emitting diode (RCLED) operating near 4.2 μm at room temperature, grown lattice-matched on a GaSb substrate by molecular beam epitaxy, suitable for CO2 gas detection. The device consists of a 1λ-thick microcavity containing an InAs0.90Sb0.1 active region sandwiched between two high contrast, lattice–matched AlAs0.08Sb0.92/GaSb distributed Bragg reflector (DBR) mirrors. The electroluminescence emission spectra of the RCLED were recorded over the temperature range from 20 to 300 K and compared with a reference LED without DBR mirrors. The RCLED exhibits a strong emission enhancement due to resonant cavity effects. At room temperature, the peak emission and the integrated peak emission were found to be increased by a factor of ∼70 and ∼11, respectively, while the total integrated emission enhancement was ∼×33. This is the highest resonant cavity enhancement ever reported for a mid-infrared LED operating at this wavelength. Furthermore, the RCLED also exhibits a superior temperature stability of ∼0.35 nm/K and a significantly narrower (10×) spectral linewidth. High spectral brightness and temperature stable emission entirely within the fundamental absorption band are attractive characteristics for the development of next generation CO2 gas sensor instrumentation.

High power and efficiency enable new fields of applications for single spatial mode lasers, such as high brightness direct diode laser systems with dense wavelength multiplexing [1,2]. In previous work, we demonstrated that an efficient extreme asymmetric epitaxial structure enables highly efficient high-power single mode Ridge Waveguide (RW) lasers at 970 nm [3]. We will present results of a further optimized vertical and lateral design with increased single-spatial mode power of up to 2.5 W.

Wide stripe semiconductor lasers can be used as optical power amplifiers for obtaining high power single spatial mode output beams. Anti-reflection coatings deposited on the facets of semiconductor lasers effectively suppress any self-oscillation. The input beam from a single spatial mode, low power master oscillator was injected into a laser diode amplifier using microscope objectives and cylindrical lenses. Our system produced up to 300 mW of continuous wave output power with good preservation of the master oscillator beam quality after transmission through the power amplifier.

Continuous-wave operation of a distributed-feedback quantum-cascade laser in a packaged module is demonstrated up to a heat sink temperature of 80 °C with an output power of greater than 10 mW and a power consumption of less than 3.8 W. Single longitudinal mode emission near 5.24 μm is observed over a temperature range from 10 to 80 °C with a side mode suppression ratio greater than 20 dB limited by the instrumentation. A single spatial mode is determined with far-field pattern measurement. The above performance is achieved using a buried heterostructure and a small cavity of 7.6 μm×1.5 mm.

We propose a scalable scheme for optical quantum computing using measurement-induced continuous-variable quantum gates in a loop-based architecture. Here, time-bin-encoded quantum information in a single spatial mode is deterministically processed in a nested loop by an electrically programmable gate sequence. This architecture can process any input state and an arbitrary number of modes with almost minimum resources, and offers a universal gate set for both qubits and continuous variables. Furthermore, quantum computing can be performed fault tolerantly by a known scheme for encoding a qubit in an infinite-dimensional Hilbert space of a single light mode.

We generate quantum-correlated photon pairs using cascaded χ(2):χ(2) traveling-wave interactions for second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC) in a single periodically-poled thin-film lithium-niobate (TFLN) waveguide. When pulse-pumped at 50 MHz, a 4-mm-long poled region with nearly 300%/Wcm2 SHG peak efficiency yields a generated photon-pair probability of 7±0.2 × 10-4 with corresponding coincidence-to-accidental ratio (CAR) of 13.6±0.7. The CAR is found to be limited by Stokes/anti-Stokes Raman-scattering noise generated primarily in the waveguide. A Raman peak of photon counts at 250 cm-1 Stokes shift from the fundamental-pump wavenumber suggests most of the noise that limits the CAR originates within the lithium niobate material of the waveguide.