Programmable multiphoton quantum interference in a single spatial mode.

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.

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.

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 propose to use four-wave mixing inside silicon waveguides for generating quantum-correlated photon pairs in a single spatial mode. Such silicon-based photon sources not only exhibit high pair correlation but also have high spectral brightness. As the proposed scheme is based on mature silicon technology, it has the potential of becoming a cost-effective platform for on-chip quantum information processing applications.

We experimentally demonstrate a violation of local realism with highly spatially multimode polarization-entangled two-photon states produced by spontaneous parametric down-conversion (SPDC) pumped by a spatially incoherent light source---a light-emitting diode (LED). While existing studies have observed such a violation only by postselecting the LED-pumped SPDC photons into a single spatial detection mode, we achieve a Clauser-Horne-Shimony-Holt inequality violation of $S=2.532\ifmmode\pm\else\textpm\fi{}0.069>2$ using a spatially multimode detection setup that collects nearly 4080 SPDC spatial modes. These results indicate that coherent pump sources, such as lasers, are not required for SPDC-based entanglement generation. Our work could enable novel and practical sources of entangled photons for quantum technologies such as device-independent quantum key distribution and quantum-enhanced sensing.

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.

We report a continuous-wave (CW) optical parametric oscillator (OPO) based on a MgO-doped periodically poled LiNbO(3) (MgO:PPLN) crystal. The 532 nm pump generates coherent radiation that is tunable from 800 to 920 nm for the signal and from 1250 to 1580 nm for the idler, respectively. The OPO output power exhibits a slowly varying instability that we attribute to a thermal effect induced by the pump. This instability is truncated by means of a low-pass servo that includes a single-mode fiber that filters the beam into a single spatial mode. The resulting output characteristics are promising for radiometric applications in the near infrared including most fiber-optic communication bands.

Phase-locked operation of an array of semiconductor lasers has been extensively studied in recent years [1-12] with the eventual goal of obtaining high power (several hundreds of milliwatts) into a single spatial lobe of radiation. Earlier, the studies were concentrated on the integration of two types of lasers, namely, gain guided [1,2,5,6,] and index guided [7] stripe geometry lasers into an array with different stripe widths and varied spacing between the stripes. Phase lock of these lasers can only be achieved with a proper combination of width, stripe spacing and driving current. A considerable amount of interest has since been focused on the study of conditions under which a single spatial mode with narrow divergence angle can be produced. At present there is no reproducible process that can be used to fabricate single lobe phase-locked semiconductor arrays. The main application of the semiconductor array now is to pump solid state lasers. In this case we do not require phase locking or single lobe far field. In this paper we report fabrication of a different kind of semiconductor laser array, i.e. incoherent laser array. The main features of the incoherent laser arrays are : 1) Low threshold index-guided laser elements, 2) Single lobe far-field pattern, 3) Low astigmatism, 4) Low current operation, 5) Densely packed and 6) Total electrical and optical isolation. We expect such laser arrays will have important applications in multi-head optical-disk reading and writing, multi-fiber optical communications and line of sight communications.

We report on infrared supercontinuum generation extending over more than one octave of bandwidth, from 850nm to 2.35μm, produced in a single spatial mode from a robust, compact, composite chalcogenide glass nanotaper. A picosecond laser at 1.55μm pumps a high-index-contrast, all-solid nanotaper that strongly confines the field to a 480nm diameter core, while a thermally compatible built-in polymer jacket lends the nanotaper mechanical stability.

Based on the quantum dot-photon molecular coupling system, we proposed an efficient and stable single photon source. The system uses photon molecules formed by the coupling of two optical microcavities A and B, one of which contains a quantum dot. The excitation laser act on the quantum dot in cavity A, and through the interaction between the light field in cavity A and cavity B, single photon is generated in cavity B and output extraction is performed therein. The system maintains good sub-Poisson characteristics over a wide range of dot-cavity coupling strength variation (0.25κ<;g<;κ) and at low cavity tunneling strength (J≥0.5κ) as well. It also has excellent robustness and is easy to construct. Under the optimal experimental parameters that can be realized, the zero-delay second-order correlation function g <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (0) of the system can be as low as 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> with a relatively large intra cavity photon number. We theoretically explains the reason why the system produces sub-Poisson light, and analyzed the impact of system parameters change. Meanwhile, the system spatially separates the output light from the excitation light, making it easy to extract single photons, and has potential application value for easier integration. The model proposed in this paper will bring important guiding value to the efficient and integrated single photon sources in future quantum information processing.

Fourier methods are widely used in optical information processing for time domain waveform synthesis and detection. In such approaches an input pulse is spectrally decomposed and modulated by an appropriately designed spectral filter. In general, various ultrafast applications may need either generation or characterization of waveforms depending whether their frequency response is or is not known a priori. Ultrafast pulses prove useful in driving or probing such systems because their broad, deterministic complex spectral amplitude “sees” a large continuous portion of the system transfer function. Traditionally, space domain spectral decomposition is used to perform optical Fourier processing, where pairs of gratings and lenses are used to decompose the spectral content of the pulsed, optical waveforms. Liquid crystal and acousto-optic (AO) modulators provide a means for introduction of somewhat arbitrary system transfer functions. More recently, compact waveguide-based approaches have used arrayed waveguide gratings (AWGs) to perform an analogous spectral decomposition to those achieved with traditional, free-space coupled gratings. Information processing arrangements using the space domain for transverse spectral decomposition benefit from the maturity of such techniques, with respect to basic understanding, component quality, and the excellent phase control that free-space manipulations provide. Component insensitivity to optical power permits the shaping and detecting of high peak power pulses used to drive nonlinear optical systems. Furthermore, nonlinear optical elements can be introduced directly into these processors to provide unique ultrafast waveform synthesis capabilities with response times in the range of femtoseconds. Drawbacks to free-space approaches include scaling in volume to achieve large time bandwidth products (TBWPs) and limiting the temporal extent of waveforms coupled back into a single-mode fiber (SMF). The origin of this last restraint is the time∕space interrelation inherent in traditional pulse shaping devices. AWG approaches rely on complex waveguide elements to circumvent large processor volumes and time∕space coupling issues, but they too are practically limited by fabrication requirements. The number of resolvable spots in the output waveform for both Fourier synthesis and direct space-to-time AWG approaches is equal to the number of waveguide channels. An alternative approach to Fourier processing relying on a single transverse spatial mode can better integrate with fiber systems and photonic lightwave circuits and will scale in length only for the achievement of large TBWPs. Fiber-based and fiber-integrated processors can manipulate optical waveforms in the time domain exploiting chromatic dispersion for longitudinal spectral decomposition and applying to it Fourier synthesis techniques. Drawing on the identical mathematical treatments of diffraction in space and dispersion in time, an approximate Fourier transform (FT) of an incident optical signal is achieved via chromatic dispersion after reaching the so-called “far-field approximation.” With such an amount of dispersion, the temporal waveform closely resembles the spectrum. Such a waveform is called a longitudinal spectral decomposition wave (SDW). A time-variant element (e.g., modulator) filters this SDW. And it is possible to recompose the pulse waveform through propagation in a conjugate dispersion source matched (i.e., of opposite sign but equal magnitude) to the first dispersive element. The number of resolvable spots that such a processor offers relies on a suitable modulation scheme and the experimental ability to disperse a sub-picosecond pulse using second-order dispersion.

Distributed-Bragg-reflector (DBR) ring oscillators are the first monolithic semiconductor lasers containing broad-area active regions which operate in a single mode to several times their threshold current. Orthogonally oriented diffraction gratings surrounding an unpatterned active region select a single spatial and temporal mode of oscillation. The authors present both analytic and experimental verification of single mode operation for active dimensions up to 368 mu m*1000 mu m. Threshold current densities under 200 A/cm/sup 2/ and total differential efficiencies greater than 60% have been measured. DBR ring oscillators have demonstrated over 1 W of single frequency output power, 460 mW of spatially coherent, single frequency output power, and nearly circular diffraction limited output to 4xI/sub th/. The performance potential of these devices is enormous, considering that the output apertures are nearly two orders of magnitude wider than conventional single-mode sources which generate up to 0.2 W of coherent output.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>