L. Legouezigou

Compact wavelength monitoring by lateral outcoupling in wedged photonic crystal multimode waveguides

A device concept for laterally extracting selected wavelengths from an optical signal traveling along a waveguide, for operation in metropolitan area networks, is presented. The signal on the fundamental mode of a multimode photonic crystal waveguide is coupled to a higher-order mode, at a center frequency that spatially depends on the slowly varying guide parameters. The device is compact, intrinsically fault tolerant, and can split any desired fraction of the signal for monitoring purpose. Characterizations by the internal light source technique validate the optical concept whereas an integrated device with four photodiodes qualifies its potential with respect to real-world applications.

Enhanced gain measurement at mode singularities in InP-based photonic crystal waveguides

We present a method of direct measurement of spectral gain and corresponding data in photonic crystal waveguides defined in heterostructures on InP substrates. The method makes use of two photopumping beams, one for gain generation, the other for amplification probing. The results show a clear enhancement of gain at spectral regions of low-group velocity, namely at the edges of the so-called mini-stopband of a three-missing rows wide photonic crystal waveguide.

Discontinuous wavelength super-refraction in photonic crystal superprism

Experimental results on wavelength-dependent angular dispersion in InGaAsP triangular lattice planar photonic crystals are presented. An abrupt variation of the angular dispersion is observed for TM-polarized waves whose frequencies are comprised between those of the fourth and sixth allowed bands. According to the crystal period, the measured angle of refraction is found to either decrease or increase by 30 degrees within a wavelength range smaller than 30 nm. Experimental results are reproduced well from 2D finite difference time domain calculations. The observed phenomena are interpreted from the coupling of the incident light to different modes of the photonic crystal that travel with different group velocities and propagate in different directions within the crystal. Mode dispersion curves and mode patterns are calculated along with isofrequency curves to support this explanation. The observed discontinuous wavelength super-refraction opens a new approach to the application of superprisms.

1.5μm room-temperature emission of square-lattice photonic-crystal waveguide lasers with a single line defect

Narrow waveguides consisting of a single defect-line (W1) in a square lattice photonic crystal are fabricated on InP using the substrate approach. A single-mode distributed-feedback laser emission is obtained under optical pumping at room temperature. Lasing occurs at the second folding point of the dispersion curve of the fundamental waveguide mode (wave vector k=0). The emitted wavelength ranges from 1420to1580nm for a lattice period varying from 460to520nm and a constant air filling factor of ∼26%. The highly monomode behavior is explained using two-dimensional plane-wave models. Similar experiments conducted on triangular lattice W1 waveguides do not yield a laser emission. Three-dimensional simulations confirm that triangular lattice W1 waveguides suffer higher losses than their square homologues.

Quantum dots semiconductor optical amplifier with a-3dB bandwidth of up to 120 nm in semi-cooled operation

More than 120 nm of -3 dB optical bandwidth, together with 10 dB of internal gain at 50°C, are demonstrated and explained with specially designed quantum dot semiconductor optical amplifiers.

Low confinement factor quantum dash (QD) mode-locked Fabry-Perot (FP) laser diode for tunable pulse generation

Electrical spectrum line-width is reduced in mode-locked FP 1.55 μm-QD laser diode through optical confinement factor optimization. From optimized structures, we obtained nearly Fourier-transform limited pulses at 10 GHz, with an averaged width of 8 ps over 10 nm.

Distributed feedback-like laser emission in photonic crystal waveguides on InP substrate

Lasing of triangular and square lattice photonic crystal, waveguides on InP substrate is investigated around the 1.5-/spl mu/m wavelength by optical pumping. The lattice period of the fabricated structures is varied over a very large scale, thereby allowing a detailed exploration of the laser behaviors in the cases of micrometer width waveguides. A genuine distributed feedback (DFB) laser emission is observed in the gap for W2-3 waveguides in the /spl Gamma/M direction of a triangular lattice. A different behavior is obtained for W3 waveguides in the /spl Gamma/K direction of the same lattice as well as for W1 and W3 waveguides in the /spl Gamma/X direction of a square lattice. The laser emission is found to occur at the /spl Gamma/ point of the Brillouin zone (wavevector k=0) when the emission frequency is outside the gap. The DFB-like laser emission is intrinsically single mode in this case. Plane wave calculations show that the field distributions of the two DFB components are radically different. The emitting mode is well localized in the guide core while the non-lasing mode spreads over the whole crystal.

Polarisation insensitive injection locked Fabry-Perot laser diodes for 2.5Gb/s WDM access applications

Polarisation insensitive injection locking of two-section Fabry-Perot laser diodes is demonstrated, allowing to achieve error free transmission through 50 km over 20 nm at 2.5 Gb/s.

Single-mode in-gap emission of medium-width photonic crystal waveguides on InP substrate

In this paper, we present a numerical and experimental study of W3-4 photonic crystal (PhC) waveguide lasers fabricated on InP substrate. In such a PhC waveguide, the dispersion curve of the fundamental mode folds in the two-dimensional gap of the triangular lattice. Folding occurs at the Brillouin zone edge as in the case of genuine distributed feedback (DFB) lasers. Single-mode emission is presently observed in both electrical and optical pumping configurations. This behavior is attributed to the different levels of out-of-plane losses experienced by the two DFB mode components. Three-dimensional finite-difference-time-domain calculations are used to finely quantify the quality factors of the waveguide modes. The modal discrimination is shown to be reinforced when lasing occurs far from the conduction band edge. This trend is also predicted for other canonical waveguides in triangular PhCs as for instance W2-3 waveguides.

Tunable photonic crystal lasers with high side-mode suppression ratio

We demonstrate tunable semiconductor lasers based on three coupled photonic crystal sections, that allows up to 18 nm tuning range with a side-mode suppression ratio greater than 35 dB.