1,721,024 research outputs found
Passive mode-locking in semiconductor lasers with saturable absorbers bandgap shifted through quantum well intermixing
Full text linkPassive mode-locking in semiconductor lasers in a Fabry–Perot configuration with a bandgap blueshift applied to the saturable absorber (SA) section has been experimentally characterized. For the first time a fully post-growth technique, quantum well intermixing, was adopted to modify the material bandgap in the SA section. The measurements showed not only an expected narrowing of the pulse width but also a significant expansion of the range of bias conditions generating a stable train of optical pulses. Moreover, the pulses from lasers with bandgap shifted absorbers presented reduced chirp and increased peak power with respect to the nonshifted case
Optimized coupler design for slot waveguide ring resonators
No full textThe highly sensitive nature of slot waveguide micro-resonator power couplers is discussed with respect to the resonator geometry and evanescent coupler design. A modified, tri-bar, evanescent field coupler is demonstrated that shows reduced sensitivity to ring radius as compared with conventional couplers, while maintaining a compact beat-length of only a few micrometers. With the measurement of bending losses of curved slot waveguides, critically coupled ring resonators were designed and fabricated, exhibiting a resonance extinction exceeding 22 dB
Ultra-low power four wave mixing wavelength conversion in silicon micro-ring resonators with tunable Q-factor
No full textThe development of highly non-linear silicon devices is a fundamental step towards the realization of low power optical signal processing devices. In order to achieve this final goal several constraints have to be overcome. In particular, the next generation of opto-electronic integrated devices must be ultra-compact, compatible with foundry model fabrication processing and exhibit low power consumption [1]. In recent years, many non-linear photonic devices have been demonstrated based on the Silicon On Insulator (SOI) technology platform allowing for an unprecedented level of integration. Many research groups have demonstrated non-linear devices that can perform wavelength conversion [2], demultiplexing operations [3] and all-optical switching [4]. In particular, in order to perform wavelength conversion, Four Wave Mixing (FWM) effects are typically used in silicon, showing conversion efficiencies that have ranged from -40 dB to -8 dB [5]. The latter figure was demonstrated on a 8-cm long waveguide with a very high pump peak power (Pp=5 W) and a lateral pin junction to reduce the free carrier losses due to two photon absorption. In order to decrease the pump power, resonant devices have been considered and demonstrated in the past few years [6]. In such structures the non-linear response is substantially improved due to the field enhancement of the cavity, which is proportional to the cavity Q-factor
Active on-chip dispersion control using a tunable silicon Bragg grating
Full text linkActively controllable dispersion in on-chip photonic devices is challenging to implement compared with free space optical components where mechanical degrees of freedom can be employed. Here, we present a method by which continuously tunable group delay control is achieved by modulating the refractive index profile of a silicon Bragg grating using thermo-optic effects. A simple thermal heater element is used to create tunable thermal gradients along the grating length, inducing chirped group delay profiles. Both effective blue and red chirp are realised using a single on-chip device over nanometre scale bandwidths. Group delay slopes are continuously tunable over a few ps/nm range from red to blue chirp, compatible with on-chip dispersion compensation for telecommunications picosecond pulse systems
Continuously tunable, narrow linewidth mm-wave generation from a monolithically integrated triple DFB laser chip
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Measurement of Optical Pulsewidth in the Picosecond Regime Using a Non-linear Fiber and Power Meter
No full textA technique for the characterization of picosecond pulse widths is presented, based a non-linear optical fiber loop mirror and power meter measurement. Pulse-widths in the 2-10ps range are successfully recovered with a resolution of 0.25ps
Photonic integrated filter with widely tunable bandwidth
No full textWe present a comprehensive design, fabrication, and characterization analysis of compact silicon-on-insulator bandpass filters with widely tunable bandwidth. The filter architecture is based on an unbalanced Mach-Zehnder interferometer loaded with a pair of ring resonators. A wide bandwidth tunability (from 10% to 90% FSR) can be achieved by controlling the resonant frequency of the rings while preserving a good filter off-band rejection. Design rules are provided that take into account fabrication tolerances as well as losses. Furthermore, the use of tunable couplers allows a more flexible shaping of the spectral response of the filter. The sensitivity with respect to nonlinear effects is carefully investigated. Operation over a wavelength spectrum of 20 nm is demonstrated, making the device suitable for channel subset selection in WDM systems, reconfigurable filters for gridless networking and adaptive filtering of signals. © 1983-2012 IEEE
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