G. Moreau

Subpicosecond pulse generation at 134GHz using a quantum-dash-based Fabry-Perot laser emitting at 1.56μm

We demonstrate passive mode locking in one-section monolithic semiconductor laser diodes based on quantum-dash active layer at very high repetition rate in the 1.5μm window. Transform-limited pulses are generated at 134GHz with subpicosecond width, without any pulse compression scheme. A 50kHz linewidth of the radio-frequency spectrum is also demonstrated at 42GHz, the lowest value reported for any passively mode-locked semiconductor laser. We further show that the saturable absorption section in two-section devices has no significant impact on the mode-locking behavior.

Short pulse generation using a passively mode locked single InGaAsP/InP quantum well laser

We report on subpicosecond pulse generation using passively mode locked lasers (MLL) based on a low optical confinement single InGaAsP/InP quantum well active layer grown in one epitaxial step. Systematic investigation of the performances of two-section MLLs emitting at 1.54 microm evidenced pulse width of 860 fs at 21.31 GHz repetition rate, peak power of approximately 500 mW and a time-bandwith product of 0.57. A 30 kHz linewidth of the photodetected radio-frequency electrical spectrum is further demonstrated at 21 GHz which is, to our knowledge, the lowest value ever reported for a quantum well device.

Comparison of InAs quantum dot lasers emitting at 1.55 µm under optical and electrical injection

InAs/InGaAsP/InP(113)B quantum-dots are studied as active mediums for laser structures emitting near 1.55 µm under optical and electrical injection. In order to precisely tune the emission wavelength of QDs, the double cap growth procedure is used. Laser emission on the ground states is obtained under optical pumping at room temperature. On equivalent structures doped for electrical injection, laser emission is also observed at low temperatures up to 200 K. The difference between the optical and electrical pumping is ascribed to low carrier injection efficiency due to the presence of a 3 nm InP hole blocking barrier at each quantum dot layer which is inherent to the double cap growth procedure. Room temperature laser emission has been reached when the InP first cap layer is substituted by a quaternary GaInAsP (1.18 µm gap) layer in the double cap growth procedure. The threshold current density of the new structure with QD capped only by quaternary is as low as 840 A cm−2 at room temperature.

Effect of layer stacking and p-type doping on the performance of InAs∕InP quantum-dash-in-a-well lasers emitting at 1.55μm

The authors report the growth of 6-, 9-, and 12-layer InAs∕InP quantum-dash-in-a-well (DWELL) laser structures using gas source molecular beam epitaxy. Broad area laser performance has been investigated as a function of number of layers. The highest modal gain at 48cm−1 is achieved for an optimized nine-DWELL layer structure. The effect of layer stacking and p-type doping on the characteristic temperature is also reported. Nine-DWELL layer single mode ridge waveguide lasers showed high slope efficiency (0.2W∕A per facet) and output power (Pout=20mW), close to those of conventional quantum well devices.

Dynamic properties of InAs∕InP (311)B quantum dot Fabry–Perot lasers emitting at 1.52μm

Dynamic properties of truly three-dimensional-confined InAs∕InP quantum dot (QD) lasers obtained by molecular beam epitaxy growth on a (311)B oriented substrate are reported. The relative intensity noise and small signal modulation bandwidth experiments evidence maximum relaxation frequency of 3.8GHz with a clear relaxation oscillation peak, indicating less damping than InAs∕GaAs QD lasers. The Henry factor amounts to ∼1.8 below threshold and increases to ∼6 above threshold, which is attributed to band filling of the thick wetting layer.

Phase-amplitude characterization of a high-repetition-rate quantum dash passively mode-locked laser

We apply a novel phase-amplitude method to a 42.2 GHz one-section quantum dash-based passively mode-locked laser. This new method relies on the measurement of the spectral phase of the longitudinal modes by autocorrelation analysis.

Growth and optical characterizations of InAs quantum dots on InP substrate: towards a 1.55 /spl mu/m quantum dot laser

In recent years, self assembled quantum dots (QDs) have attracted much attention, because of the great potentialities expected from their zero dimensional confinement properties, especially for the realization of opto-electronic devices such as lasers. Indeed, for a QD based laser, a lower temperature dependence (high T/sub 0/), a lower chirp (/spl alpha//sub H/) and a higher modulation bandwidth are predicted compared to the conventional quantum well lasers. Numerous studies have been performed for the growth of InAs/GaAs QDs, and lasers have been realized, presenting improved performances (T/sub 0/=161 K @ 350 K [1], /spl alpha//sub H/=0 @ 1 GHz [2]).

Enhanced In(Ga)As∕GaAs quantum dot based electro-optic modulation at 1.55μm

The authors report a study of the linear electro-optic coefficient in waveguides containing InGaAs∕GaAs quantum dots with a band gap at 1.3μm. The Pockels effect is investigated in the 1.55μm telecommunication window. The measured linear electro-optic coefficient for InGaAs∕GaAs is ∼3.4×10−11m∕V, much higher than that of the bulk or quantum well material. An ∼35% enhancement of the phase variation is achieved compared to that obtained in bulk GaAs waveguides. Finally, a spectral bandwidth of ∼100nm is demonstrated in the 1.5–1.6μm window.

Recent advances in long wavelength quantum dot based lasers

This paper presents recent progress in the field of semiconductor lasers based on self-assembled quantum dots grown either on GaAs or InP substrates. Quantum dot (QD) based lasers are attracting a lot of interest owing to their remarkable optoelectronic properties that result from the three dimensional carrier confinement. They are indeed expected to exhibit much improved performance than that of quantum well devices. Extremely low threshold currents as well as high temperature stability have readily been demonstrated in the InAs/GaAs material system. The unique properties of quantum dot based active layers such as broad optical gain spectrum, high saturation output power, ultrafast gain dynamics and low loss are also very attractive for the realization of mode-locked lasers. Recent results in the field of directly modulated InAs/GaAs lasers emitting in the 1.3 μm window are discussed. We report in particular on temperature independent linewidth enhancement factor (or Henry factor αH) up to 85°C. This is a key parameter which determines many laser dynamic properties. Optical feedback insensitive operation of specifically band-gap engineered devices, compatible with high bit rate isolator-less transmission is also reported at 1.55 μm. Monolithic mode locked lasers based on InAs/InP quantum dashes have been investigated for 1.55 μm applications. Subpicosecond pulse generation at very high repetition rates (> 100 GHz) is reported for self-pulsating one-section Fabry Perot devices. Specific applications based on these compact pulse generators including high bit rate clock recovery are discussed.

Sub-picosecond pulse generation at 134 GHz using a quantum dash-based Fabry-Perot laser emitting at 1.56 /spl mu/m

We report on 800 fs pulse generation, at 134 GHz, using a Fabry-Perot quantum dash laser at 1.56 mum. A 50 kHz RF spectral linewidth at 42 GHz is also demonstrated