-
[show abstract]
[hide abstract]
ABSTRACT: We experimentally and theoretically study the characteristics of
semiconductor ring lasers bidirectionally coupled by a single bus waveguide.
This configuration has, e.g., been suggested for use as an optical memory and
as an optical neural network motif. The main results are that the coupling can
destabilize the state in which both rings lase in the same direction, and it
brings to life a state with equal powers at both outputs. These are both
undesirable for optical memory operation. Although the coupling between the
rings is bidirectional, the destabilization occurs due to behavior similar to
an optically injected laser system.
02/2013;
-
[show abstract]
[hide abstract]
ABSTRACT: 'Conventional' protocols of high-frequency repetitive transcranial magnetic stimulation (rTMS) delivered to M1 can produce analgesia. Theta burst stimulation (TBS), a novel rTMS paradigm, is thought to produce greater changes in M1 excitability than 'conventional' protocols. After a preliminary experiment showing no analgesic effect of continuous or intermittent TBS trains (cTBS or iTBS) delivered to M1 as single procedures, we used TBS to prime a subsequent session of 'conventional' 10 Hz-rTMS.
In 14 patients with chronic refractory neuropathic pain, navigated rTMS was targeted over M1 hand region, contralateral to painful side. Analgesic effects were daily assessed on a visual analogue scale for the week after each 10 Hz-rTMS session, preceded or not by TBS priming. In an additional experiment, the effects on cortical excitability parameters provided by single- and paired-pulse TMS paradigms were studied.
Pain level was reduced after any type of rTMS procedure compared to baseline, but iTBS priming produced greater analgesia than the other protocols. Regarding motor cortex excitability changes, the analgesic effects were associated with an increase in intracortical inhibition, whatever the type of stimulation, primed or non-primed.
The present results show that the analgesic effects of 'conventional' 10 Hz-rTMS delivered to M1 can be enhanced by TBS priming, at least using iTBS. Interestingly, the application of cTBS and iTBS did not produce opposite modulations, unlike previously reported in other systems. It remains to be determined whether the interest of TBS priming is to generate a simple additive effect or a more specific process of cortical plasticity.
European journal of pain (London, England) 04/2012; 16(10):1403-13. · 3.37 Impact Factor
-
W Ding,
O K Staines,
G D Hobbs,
A V Gorbach,
C de Nobriga,
W J Wadsworth,
J C Knight,
D V Skryabin,
M J Strain, M Sorel,
R M De La Rue
[show abstract]
[hide abstract]
ABSTRACT: We report frequency conversion experiments in silicon-on-insulator (SOI) directional couplers. We demonstrate that the evanescent coupling between two subwavelength SOI waveguides is strongly dispersive and significantly modifies modulational instability (MI) spectra through the coupling induced group velocity dispersion (GVD). As the separation between two 380-nm-wide silicon photonic wires decreases, the increasing dispersion of the coupling makes the GVD in the symmetric supermode more normal and suppresses the bandwidth of the MI gain observed for larger separations.
Optics Letters 02/2012; 37(4):668-70. · 3.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrated room-temperature continuous-wave (RTCW) operation of electrically driven in-plane emitting micro-disc lasers with radius of 10 μm. The disk cavity was fabricated using high resolution electron beam lithography based on hydrogen silsesquioxane (HSQ) and BCl<sub>3</sub>-Cl<sub>2</sub>-Ar inductively coupled plasma etching. By using circular bump or notch defects on the circumference as output coupling as well as mode control mechanisms, single-mode operation for large bump defect lasers with sidemode suppression ratio larger than 30 dB was observed, with highly directional output emission.
IEEE Photonics Technology Letters 12/2011; · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The resonant defect-enhanced photodiode has received recent attention for its potential use in silicon photonic applications such as wavelength division multiplexing (WDM). Here, we analyze the nature of the resonant enhancement in micro-ring photodiodes by exploring the roles of defect content and ring geometry. Through the use of post-processing to gradually reduce the defect concentration, we demonstrate an optimized peak responsivity of 160 mA W−1 in a ring resonator having a linewidth of 0.12 ± 0.01 nm and 12.8 ± 0.9 dB extinction. We also show that the responsivity is insensitive to ring radius in the range between 10 µm and 20 µm , demonstrate the influence of a drop port waveguide on the resonant enhancement, and discuss design methodologies to enhance performance further.
Journal of optics 11/2011; 13(12):125503. · 1.57 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate a method for the efficient modulation of optical wavelengths around 1550 nm in silicon waveguides. The amplitude of a propagating signal is mediated via control of the charge state of indium centers, rather than using free-carriers alone as in the plasma-dispersion effect. A 1×1 switch formed of an integrated p-i-n junction in an indium-doped silicon on insulator (SOI) waveguide provides 'normally-off' silicon absorption of greater than 7 dB at zero bias. This loss is decreased to 2.8 dB with application of a 6 V applied reverse bias, with a power consumption of less than 1 μW.
Optics Letters 10/2011; 36(19):3717-9. · 3.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report the first realization of integrated, all-optical first- and higher-order photonic differentiators operating at terahertz (THz) processing speeds. This is accomplished in a Silicon-on-Insulator (SOI) CMOS-compatible platform using a simple integrated geometry based on (π-)phase-shifted Bragg gratings. Moreover, we achieve on-chip generation of sub-picosecond Hermite-Gaussian pulse waveforms, which are noteworthy for applications in next-generation optical telecommunications.
Optics Express 09/2011; 19(20):19514-22. · 3.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Quantum cascade lasers (QCLs) are semiconductor lasers based on intersubband transitions in quantum wells. Semiconductor lasers in ring format do not need cleaved facets or gratings to achieve optical feedback required for lasing and could support either bidirectional or unidirectional operation. In this paper, we report on QCL in this ring format for unidirectional operation and coupled ring tuning.
Lasers and Electro-Optics Europe (CLEO EUROPE/EQEC), 2011 Conference on and 12th European Quantum Electronics Conference; 06/2011
-
[show abstract]
[hide abstract]
ABSTRACT: The authors present all-optical differentiators based on Silicon-on-Insulator (SOI) Bragg grating technology. It has been shown that the spectral transfer function required for the realization of an N<sup>th</sup>-order all-optical temporal differentiation can be provided by a uniform multiple-π-phase-shifted Bragg grating. The device operates in reflection and consists of a uniform Bragg grating with π-phase-shift sections along its length. The desired spectral response of these devices is achieved within their reflection notch around the Bragg wavelength. Furthermore, the high coupling coefficients of these gratings, in the order of 10<sup>2</sup>-10<sup>3</sup> cm<sup>-1</sup>, produce grating responses with notch bandwidths of a few nanometres for device lengths less than 100μm, allowing the processing of sub-picosecond pulses.
Lasers and Electro-Optics Europe (CLEO EUROPE/EQEC), 2011 Conference on and 12th European Quantum Electronics Conference; 06/2011
-
D Duchesne,
K A Rutkowska,
M Volatier,
F Légaré,
S Delprat,
M Chaker,
D Modotto,
A Locatelli,
C De Angelis, M Sorel,
D N Christodoulides,
G Salamo,
R Arès,
V Aimez,
R Morandotti
[show abstract]
[hide abstract]
ABSTRACT: We report modal phase matched (MPM) second harmonic generation (SHG) in high-index contrast AlGaAs sub-micron ridge waveguides, by way of sub-mW continuous wave powers at telecommunication wavelengths. We achieve an experimental normalized conversion efficiency of ~14%/W/cm2, obtained through a careful sub-wavelength design supporting both the phase matching requirement and a significant overlap efficiency. Furthermore, the weak anomalous dispersion, robust fabrication technology and possible geometrical and thermal tuning of the device functionality enable a fully integrated multi-functional chip for several critical areas in telecommunications, including wavelength (time) division multiplexing and quantum entanglement.
Optics Express 06/2011; 19(13):12408-17. · 3.59 Impact Factor
-
D. Duchesne,
K.A. Rutkowska,
M. Volatier,
F. Legare,
S. Delprat,
M. Chaker,
D. Modotto,
A. Locatelli,
C. De Angelis, M. Sorel,
D.N. Christodoulides,
G. Salamo,
R. Ares,
V. Aimez,
R. Morandotti
[show abstract]
[hide abstract]
ABSTRACT: Modal phase-matched second harmonic generation is obtained in sub-micron AlGaAs waveguides using a continuous-wave laser at telecommunication wavelengths. The tunability and robust fabrication process make this device ideal for integrated wavelength conversion.
Lasers and Electro-Optics (CLEO), 2011 Conference on; 06/2011
-
[show abstract]
[hide abstract]
ABSTRACT: Passively mode-locked laser devices are presented incorporating chirped distributed Bragg reflectors. The Bragg grating sections consist of post-growth, sidewall relief, tapered gratings, offering continuous chirp and modulation of the coupling coefficient. Blue-chirped gratings are found to compensate for the pulse chirp accumulated in the laser gain and absorption sections. Pulses are measured with the largest 3 dB bandwidths, up to 2.3 nm, and smallest pulsewidths, 1.49 ps, achieved in passively mode-locked DBR lasers.
IEEE Journal of Quantum Electronics 05/2011; · 1.88 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present an investigation on the nonlinear dynamics of intense pulses in an AlGaAs Bragg waveguide and we report the experimental observation of an intensity dependent blue-shift of the Bragg notch spectral line.
2011 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO); 01/2011
-
[show abstract]
[hide abstract]
ABSTRACT: A novel 40 GHz passively mode-locked AlGaInAs/InP 1.55 micron laser was demonstrated with low divergence angle, timing jitter of 440 fs (100 Hz - 100 MHz), and RF linewidth of 25 kHz.
Conference on Lasers and Electro-Optics (CLEO) - Laser Applications to Photonic Applications, Baltimore, USA; 01/2011
-
SPIE Photonics West, San Francisco; 01/2011
-
[show abstract]
[hide abstract]
ABSTRACT: We report on the chirp measurements of low peak power optical pulses, generated by AlGaInAs semiconductor mode-locked lasers at repetition frequency of 40 GHz, with a sonogram technique including high-sensitivity TPA waveguide detector.
IEEE Photonics Society, 2010 23rd Annual Meeting of the; 12/2010
-
[show abstract]
[hide abstract]
ABSTRACT: We report time domain measurements of the group-velocity-dispersion-induced and nonlinearity-induced chirping of femtosecond pulses in subwavelength silicon-on-insulator waveguides. We observe that at a critical input power level, these two effects compensate each other leading to soliton formation. Formation of the fundamental optical soliton is observed at a peak power of a few Watts inside the waveguide. Interferometric cross-correlation traces reveal compression of the soliton pulses, while spectral measurements show pronounced dispersive waves emitted by solitons into the wavelength range of normal group velocity dispersion.
Optics Express 12/2010; 18(25):26625-30. · 3.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We describe the fabrication and characterization of a silicon waveguide resonant photodetector compatible with the optical-to-electrical conversion of wavelengths at, or around, 1550 nm. Sub-band responsivity is provided through the introduction of defects via inert self-implantation and subsequent annealing. The detector is located within a 20- m radius silicon microring resonator. An 18-dB resonant enhancement in absorption coefficient and 12-dB enhancement in photocurrent were measured, leading to a resonant responsivity of approximately 39 mA/W at 20-V reverse bias.
IEEE Photonics Technology Letters 11/2010; · 2.19 Impact Factor
-
F. Morichetti,
A. Canciamilla,
C. Ferrari,
M. Torregiani,
M. Ferrario,
R. Siano,
P. Boffi,
L. Marazzi,
P. Martelli,
P. Parolari,
M. Martinelli,
A. Samarelli, M. Sorel,
R.M. De La Rue,
L. O'Faolain,
D.M. Beggs,
T.F. Krauss,
A. Melloni
[show abstract]
[hide abstract]
ABSTRACT: We show a direct comparison between silicon reconfigurable delay lines based on coupled resonator optical waveguides and photonic crystal waveguides. The structures are used to selectively delay the two orthogonally polarized channels of a RZ-PolDM-DQPSK format at 100 Gbit/s.
Optical Communication (ECOC), 2010 36th European Conference and Exhibition on; 10/2010
-
[show abstract]
[hide abstract]
ABSTRACT: We study the Mode-Locking dynamics of 40-GHz semiconductor Fabry-Pérot lasers with intracavity saturable absorber by using a Traveling-Wave-Model and a time-domain response of the semiconductor material. We analyze the influence of key parameters and compare our predictions with experimental results.
Optical Communication (ECOC), 2010 36th European Conference and Exhibition on; 10/2010
