THz optical pulses from a coupled-cavity quantum-dot laser

Abstract

Optical pulses are generated from a coupled-cavity quantum-dot (QD) laser consisting of a short QD-waveguide Fabry-Perot (F-P) cavity and three long external fiber Bragg grating (FBG) cavities. When the laser is biased at low operation current, the feedback from the external cavities dominates and laser pulses have a 1.01 THz repetition rate, determined by the equal frequency difference of the three FBGs. We are thus able to decouple the repetition rate of a mode-locked laser from the cavity length. With much higher bias current, the QD F-P cavity dominates and the repetition rate is switched to 43.8 GHz, defined by the length of the F-Pcavity.Crown

Self-assembled InAs/InP quantum dots and quantum dashes: Material structures and devices

“…Using the In 0.32 Ga 0.68 As underlying layer, similarly uniform Qdots were observed with an average lateral size and height of 42 nm and 3 nm, respectively, and PL linewidth 64 meV centered at ~1.55 µ m. The improvement in Qdots size uniformity was ascribed to the different growth front, growth behavior of group III elements at the interface between Qdots and barrier, and the modulation in the strain field. Surprisingly, growth of nanostructures directly on AlInAs lattice matched matrix layer without any underlying layer show Qdots formation with slight elongation along [1][2][3][4][5][6][7][8][9][10] direction, as seen in Fig. 6(a), consistent with the results reported by Brault et al [23], while the elongation significantly reduced on InAlGaAs matrix layer (see Fig.…”

“…11. This was attributed to the lower step energy of InAs A steps (along [1][2][3][4][5][6][7][8][9][10]) than B steps (along [110]) and thus of the shorter diffusion length of In in the [110] direction. Furthermore, the effect of growth temperature did not significantly change the Qdot structural and optical characteristics which indicated that the effective diffusion length of the adatoms on the surface is limited by the presence of steps.…”

“…The accomplishment of coupled external cavity InAs/InP Qdots laser based mode locking was brought to the next level by the demonstration of pulse repetition rates in terahertz range by selection of inter frequency spacing of FBG in the terahertz since this spacing determines the repetition rate. A 3×1000 µm 2 InAs/InP Qdot laser with one facet 95% high reflectivity and other 31% reflectivity was utilized with a FBG central wavelengths corresponding to 1.01 THz [10]. It was shown that at low CW bias current below 48 mA, the coupled cavity modes lased with dominant wavelength peaks defined by the three FBG wavelengths.…”

“…The Qdashes were elongated along [110] direction in the former case and [1][2][3][4][5][6][7][8][9][10] direction in the latter case with typical dimensions ~18 nm×60 nm×140 nm. It was until early 2000's that this class of quantum confined nanostructure key features were identified and exploited in the demonstration of various optoelectronic devices.…”

“…An ultrabroad gain profile of > 300 nm from Qdash active elements, as well as lasing and amplified spontaneous emission (ASE) bandwidths crossing more than 50 nm and 700 nm, respectively, from lasers and superluminescent diodes (SLD) are two examples of the recent significant developments in this field of study [5,8,9]. Broadband nature of the InAs/InP Qdot and Qdash laser diodes has been exploited to generate ultra-short femto-second pulses of 158 fs at 2.21THz based on the passive mode-locked scheme [10,11] which find important applications particularly in high speed optical time-domain multiplexer (OTDM), wavelength division multiplexed (WDM) communications, and optical clocking to replace electronic clocking in high-speed electronic circuits, such as a microprocessor.…”