Abstract: A numerical study of threshold gain and modal dispersion in integrated semiconductor laser optical frequency comb sources is presented. We consider an example device where one of the cleaved facets of the laser is replaced by a short Bragg grating section and show that as many as 16 modes can be selected at the first harmonic of the underlying Fabry-Perot cavity. An intracavity approach to limiting the grating-induced dispersion that can be implemented directly through the grating profile is demonstrated.
Notes: Bitauld, David Osborne, Simon O'Brien, Stephen United States Optics letters Opt Lett. 2011 Aug 1;36(15):2985-7. doi: 10.1364/OL.36.002985.
Abstract: We report on the characterization of the timing stability of passively mode-locked discrete mode diode laser sources. These are edge-emitting devices with a spatially varying refractive index profile for spectral filtering. Two devices with a mode-locking frequency of 100 GHz are characterized. The first device is designed to support a comb of six modes and generates near Fourier limited 1.9 ps pulses. The second supports four primary modes resulting in a sinusoidal modulation of the optical intensity. Using a cross-correlation technique, we measured a 20 fs pulse to pulse timing jitter for the first device, while, for the second device, a mode-beating (RF) linewidth of 1 MHz was measured using heterodyne mixing in a semiconductor optical amplifier. Comparison of these results with those obtained for an equivalent Fabry-Perot laser indicates that the spectral filtering mechanism employed does not adversely affect the timing properties of these passively mode-locked devices. (C) 2011 Optical Society of America
Abstract: We demonstrate efficient nanowire superconducting single photon detectors (SSPDs) based on NbN thin films grown on GaAs. NbN films ranging from 3 to 5 nm in thickness have been deposited by dc magnetron sputtering on GaAs substrates at 350 degrees C. These films show superconducting properties comparable to similar films grown on sapphire and MgO. In order to demonstrate the potential for monolithic integration, SSPDs were fabricated and measured on GaAs/AlAs Bragg mirrors, showing a clear cavity enhancement, with a peak quantum efficiency of 18.3% at lambda=1300 nm and T=4.2 K. (C) 2010 American Institute of Physics. [doi:10.1063/1.3496457]
Abstract: We describe how the multimode spectrum of a Fabry-Perot diode laser can be tailored using a non-periodic patterning of the cavity effective index. The cavity geometry is obtained from the solution of an inverse problem based on a perturbative calculation of the threshold gain of the longitudinal modes of the cavity. Experimental measurements are presented that demonstrate an all-optical memory element based on the injection locking bistability of a two-mode device. We also demonstrate passive harmonic mode-locking of a device designed to support a comb of six modes. Near-transform limited pulsed output with 2 ps pulse duration at 100 GHz repetition rate was obtained. Prospects for the extension of our approach to locking of larger numbers of modes over wider bandwidths are discussed. Similarities between the effective index profiles found in these devices and those of related devices and grating structures are also highlighted. (C) 2010 Elsevier B.V. All rights reserved.
Abstract: It is shown that optical synthesis of terahertz and millimeter-wave frequencies can be achieved using two-mode and mode-locked discrete mode diode lasers. These edge-emitting devices incorporate a spatially varying refractive index profile, which is designed according to the spectral output desired of the laser. We first demonstrate a device that supports two primary modes simultaneously with high spectral purity. In this case, sinusoidal modulation of the optical intensity at terahertz frequencies can be obtained. Cross saturation of the material gain in quantum-well lasers prevents simultaneous lasing of two modes with spacings in the millimeter-wave region. We show finally that by mode locking devices that are designed to support a minimal set of four primary modes, we obtain a sinusoidal modulation of the optical intensity in this frequency region.
Abstract: We present the first nanoscale (down to approximate to 50 x 50 nm(2)) detector displaying single-photon sensitivity and a nanosecond response. This type of nanodetector can also be operated in multiphoton mode, where the detection threshold can be set at N = 1, 2, 3, or 4 photons, thus allowing the mapping of photon number statistics on the nanoscale. Its operation principle based on that of hot-spot formation in superconducting nanowires allies the temporal resolution and sensitivity of superconducting single-photon detectors with subwavelength resolution and photon number discrimination. Such detectors can be of great interest for the study of nanophotonic devices at low temperature.
Abstract: We demonstrate passive harmonic mode locking of a quantum-well laser diode designed to support a discrete comb of Fabry-Perot modes. Spectral filtering of the mode spectrum was achieved using a nonperiodic patterning of the cavity effective index. By selecting six modes spaced at twice the fundamental mode spacing, near-transform-limited pulsed output with 2 ps pulse duration was obtained at a repetition rate of 100 GHz.
Notes: Bitauld, David Osborne, Simon O'Brien, Stephen United States Optics letters Opt Lett. 2010 Jul 1;35(13):2200-2. doi: 10.1364/OL.35.002200.
Abstract: We report on the fabrication and characterization of high performance nanowire superconducting single photon detectors (SSPD) on MgO substrates. The deposition of the superconducting material (NbN) has been performed by magnetron sputtering at 400C. This deposition temperature is low enough to be compatible with the fabrication on traditional optical materials like GaAs. First, SSPD meanders covering a surface of 5 5 m2 were characterized. We measured quantum efficiencies up to 20% at 1300 nm. Then, we used a straight 250 m-long NbN nanowire to perform a spatially resolved measurement of the efficiency. Both efficiency dips and peaks were observed. The dips were correlated to lithographic defects, as confirmed by scanning electron microscopy. Conversely, no evidence of a lithographic origin of efficiency peaks was found.
Abstract: The parallel nanowire detector (PND) is a photon number resolving (PNR) detector that uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (approximate to 100 nm wide, a few nm thick), folded in a meander pattern. PNDs were fabricated on 3-4 nm thick NbN films grown on MgO(T(S) = 400 degrees C) substrates by reactive magnetron sputtering in an Ar/N(2) gas mixture. The device performance was characterized in terms of speed and sensitivity. PNDs showed a counting rate of 80 MHz and a pulse duration as low as 660 ps full-width at half-maximum (FWHM). Building the histograms of the photoresponse peak, no multiplication noise buildup is observable. Electrical and optical equivalent models of the device were developed in order to study its working principle, define design guidelines and develop an algorithm to estimate the photon number statistics of an unknown light. In particular, the modeling provides novel insight into the physical limit to the detection efficiency and to the reset time of these detectors. The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed and multiplication noise.
Abstract: We report direct evidence of enhanced spontaneous emission in a photonic crystal light-emitting diode (LED) at telecom wavelength (lambda similar to 1300 nm). This result is crucial to obtain an electrically driven single photon source with high extraction efficiency. This kind of devices can be used for different types of applications in emerging fields like quantum key distribution, quantum information technology as well as in fundamental studies on quantum electrodynamics. In this work we present a device which combines a photonic crystal nanocavity with InAs quantum dots (QDs) and an LED, leading to cavity-enhanced emission at telecom wavelengths under electrical injection. The fabrication process, based on e-beam lithography and additive and subtractive processes, is described in detail. A well-isolated emission peak at about 1300 nm from the PhC mode electrically pumped is obtained (Q similar to 4000), and the enhancement of the spontaneous emission rate (similar to 1.5 fold) is clearly evidenced by time-resolved electroluminescence measurements. (C) 2008 Elsevier B.V. All rights reserved.
Abstract: We present a new photon number resolving detector (PNR), the Parallel Nanowire Detector (PND), which uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (100 nm wide, few nm thick), folded in a meander pattern. Electrical and optical equivalents of the device were developed in order to gain insight on its working principle. PNDs were fabricated on 3-4 nm thick NbN films grown on sapphire (substrate temperature TS = 900C) or MgO (TS = 400C) substrates by reactive magnetron sputtering in an Ar/N2 gas mixture. The device performance was characterized in terms of speed and sensitivity. The photoresponse shows a full width at half maximum (FWHM) as low as 660 ps. PNDs showed counting performance at 80 MHz repetition rate. Building the histograms of the photoresponse peak, no multiplication noise buildup is observable and a one-photon quantum efficiency can be estimated to be 3% (at 700 nm wavelength and 4.2 K temperature). The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed, and multiplication noise.
Abstract: We demonstrate high-performance nanowire superconducting single photon detectors (SSPDs) on bN thin films grown at a temperature compatible with monolithic integration. NbN films ranging from 150nm to 3nm in thickness were deposited by dc magnetron sputtering on MgO substrates at 400 degrees C. SSPDs were fabricated on high quality NbN films of different thickness (7 to 3nm) deposited under optimal conditions. Electrical and optical characterizations were performed on the SSPDs. The highest QE value measured at 4.2K is 20% at 1300nm. (c) 2008 Optical Society of America.
Abstract: Electrical and optical characterization has been performed on several superconducting single photon detectors (SSPDs) consisting of meanders made of ultrathin NbN films. The NbN films, with thickness ranging from 150 nm to 3 nm, were deposited by dc magnetron sputtering on MgO substrates kept at temperature T = 400C. This deposition process carried out at low temperature opens the way of monolithic integration with other photonic devices. The superconducting properties of NbN films and the critical design parameters that affect the quantum efficiency (QE) have been optimized. In particular, by measuring the switching current distribution of each stripe of the meander the process uniformity has been studied. Optical measurements on the fabricated SSPDs showed a QE approximate to 20% at 4.2 K for photons with a wavelength of 1300 nm.
Abstract: A fundamental step towards achieving an "on demand" single photon source would be the possibility of electrical pumping for a single QD and thus the integration of such a device in an opto-electronic circuit. In this work we describe the fabrication process and preliminary results of a Light Emitting Diode (LED) to be integrated with a PhC nanocavity at telecom wavelength. We demonstrate the possibility of an effective electric pumping of the QDs embedded into the membrane by contacting the n-doped and p-doped layers of the thin membrane, which allows the fabrication of a PhC nanocavity on it. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: Optical-to-electrical conversion, which is the basis of the operation of optical detectors, can be linear or nonlinear. When high sensitivities are needed, single-photon detectors are used, which operate in a strongly nonlinear mode, their response being independent of the number of detected photons. However, photon-number-resolving detectors are needed, particularly in quantum optics, where n-photon states are routinely produced. In quantum communication and quantum information processing, the photon-numberre-solving functionality is key to many protocols, such as the implementation of quantum repeaters(1) and linear- optics quantum computing(2). A linear detector with single-photon sensitivity can also be used for measuring a temporal waveform at extremely low light levels, such as in long-distance optical communications, fluorescence spectroscopy and optical time-domain reflectometry. We demonstrate here a photon-number-resolving detector based on parallel superconducting nanowires and capable of counting up to four photons at telecommunication wavelengths, with an ultralow dark count rate and high counting frequency.
Abstract: We report direct evidence of enhanced spontaneous emission in a photonic-crystal (PhC) light-emitting diode. The device consists of p-i-n heterojunction embedded in a suspended membrane, comprising a layer of self-assembled quantum dots. Current is injected laterally from the periphery to the center of the PhC. A well-isolated emission peak at 1.3 mu m from the PhC cavity mode is observed, and the enhancement of the spontaneous emission rate is clearly evidenced by time-resolved electroluminescence measurements, showing that our diode switches off in a time shorter than the bulk radiative and nonradiative lifetimes. (C) 2008 American Institute of Physics.
Abstract: We describe the design and characterization of a fiber-coupled double-channel single-photon detection system based on superconducting single-photon detectors (SSPD), and its application for quantum optics experiments on semiconductor nanostructures. When operated at 2-K temperature, the system shows 10% quantum efficiency at 1.3-mu m wavelength with dark count rate below 10 counts per second and timing resolution < 100 ps. The short recovery time and absence of afterpulsing leads to counting frequencies as high as 40 MHz. Moreover, the low dark count rate allows operation in continuous mode (without gating). These characteristics are very attractive-as compared to InGaAs avalanche photodiodes-for quantum optics experiments at telecommunication wavelengths. We demonstrate the use of the system in time-correlated fluorescence spectroscopy of quantum wells and in the measurement of the intensity correlation function of light emitted by semiconductor quantum dots at 1300 nm.
Abstract: A fast tunable filtering technique is proposed associating a diffraction grating with an intracavity Bragg grating. The bandwidth and the tuning range of this filter can be easily adapted by changing the diffraction grating's orientation, or its period, and its response is uniform over the whole tuning range. A numerical simulation of the filter response to a Gaussian beam has been developed, and it fits the experimental results allowing a calculation of the performances that could be obtained with more specific elements. For example, using a commercial acousto-optic deflector would allow a separation of 500 frequencies. It would then be possible to have a tuning range of 100 nm with a bandwidth of 0.2 nm for optical telecommunications.
Notes: Bitauld, David Zaquine, Isabelle Maruani, Alain Frey, Robert United States Applied optics Appl Opt. 2007 Jul 20;46(21):4728-35.
Abstract: A new filtering technique is proposed that associates the high dispersion of standard reflection gratings with the tuning speed of acousto-optic cells. Tuning is performed by adjusting the grating period so that the chosen wavelength is at Bragg resonance. In this way, the selected wavelength always experiences a maximum diffraction efficiency, ensuring good uniformity. Using a commercial acousto-optic modulator, a wavelength selectivity of 0.075 nm is demonstrated together with a uniformity of +/- 0.2 dB on a tuning range of 2.2 nm corresponding to N = 30 resolvable frequencies. N > 600 could be obtained with an acousto-optic cell specially designed for this device. (c) 2005 Optical Society of America.
Abstract: The diffraction of Gaussian beams on intracavity Bragg gratings is analyzed theoretically. For reasonable waists the associated beam divergence does not significantly influence the diffraction efficiency of such devices. Nevertheless, the tilt angle of the incident beam, imposed by the Bragg resonance condition, strongly reduces the diffraction efficiency at short grating periods. However, the angular selectivity can be maintained if the Fabry-Perot cavity is tuned to the incident beam direction, which allows the use of small-volume holograms together with a dense angular multiplex. This theoretical analysis can be applied to the optimization of the diffraction properties of Gaussian beams on any intracavity Bragg grating, which could then be used for free-space parallel signal processing. (C) 2005 Optical Society of America.
