E. L. Portnoi

Mode-locking at 9.7 GHz repetition rate with 1.7 ps pulse duration in two-section QD lasers

Ultrashort pulses of 1.7 ps at frequency as low as 9.7 GHz are demonstrated by passive mode-locking of monolithic two-section InAs/InGaAs (/spl lambda/=1.28 /spl mu/m) quantum-dot laser. Pulse shortening with the absorber section bias increase is observed.

RF linewidth in passively mode locked quantum well lasers

Investigation of the stability of pulse repetition rate emitted with semiconductor lasers in the regime of passive mode locking has been conducted. It was shown experimentally that the decrease of an overlap integral of the quantum-sized active layer with the waveguide mode and the increase of the time of the carrier capture on the emitting level resulted in narrowing of the radio-frequency linewidth.

Features of mode locking in laser with quantum well in broad waveguide layer

Passive mode locking (PML) regimes in two-section lasers with quantum wells in broad waveguides operating at λ = 1.06 μm have been studied. The room temperature spectrum of the saturable absorber section retains exciton peak at the absorption edge, which decreases in amplitude shifts toward longer wavelengths by 18 meV when the reverse bias voltage is varied from 0 to 14 V. The PML regime is observed at relatively large voltages (above 9 V) that are necessary to compensate for the effect of band broadening in the gain section by the Stark shift of absorption in the reversely biased section. The PML regime exists, beginning with threshold values of the pumping current, and is characterized by a narrow RF signal with a 20-kHz linewidth. As the reverse bias voltage on the absorber section is increased, a low-frequency amplitude modulation superimposes on the mode-locked laser radiation.

Picosecond semiconductor lasers with a multisection saturable absorber, fabricated by heavy ion implantation

A method of implanting high-energy heavy ions across the emitter layer of a semiconductor laser has been developed to create distributed regions of ultrafast saturable absorber integrated into the cavity of a quantum-well laser. This method was used to fabricate picosecond laser diodes having high average powers and to demonstrate colliding-pulse mode-locking of a diode laser with a multisection saturable absorber.

Gain switching of an external cavity grating-coupled surface emitting laser with wide tunability

The gain-switched, single frequency operation of an external cavity grating-coupled surface emitting laser with a wavelength tuning range of 100 nm was presented. The light in the grating section was coupled out of the laser at a specific angle to the surface of the device. Analysis showed that within the driving current range, lasing in the device only occurred when the external cavity was properly aligned.

Alx Ga1-x As-GaAs Heterojunctions

Electrical properties and injection luminescence were studied in Alx Ga1-xAs-GaAs n-p and p-n heterojunctions containing various amounts of aluminum (Eg = 1.52–1.9 eV at 300°K). A band model of the heterojunctions was established and its principal parameters were determined. It is shown that the main discontinuity occurs in the conduction band. The size ΔEc of this discontinuity varies linearly with the aluminum content in Alx Ga1-xAs; the discontinuity ΔEv in the valence band is almost zero. The injection luminescence spectra agree with the proposed model. The mechanism of current flow is compared with features of the electroluminescence spectra. At room temperature and above, the initial (low-current) section, the forward branch of the current-voltage characteristic for n-p heterojunctions is determined by recombination in the space-charge layer, and at current densities above 1–5 A/cm2, by recombination in the bulk of the diode. At low temperatures, the forward branch is given by the theory of Shockley, Noyce, and Sah. For p-n heterojunctions, the initial section of the current—voltage characteristic is of the tunnel type; at about 5 A /cm2 and above, the mechanism of current flow is similar to that in n-p heterojunctions.

Power increase in Q-switched two-sectional quantum well lasers due to Stark effect

Two-sectional laser diodes emitting light pulses in Q-switched (QS) mode are investigated. The active region of lasers contains three quantum wells. The shift of absorption edge due to Stark effect leads to red shift of lasing wavelength and pulse power doubling in QS mode.

Generation of high repetition frequency subpicosecond pulses at 1.535 /spl mu/m by passive mode-locking of InGaAsP/InP laser diode with saturable absorber regions created by ion implantation

Summary form only given. We report obtaining optical pulses 0.64 ps wide at a 104 GHz repetition rate from a passively mode-locked InGaAsP/InP laser diode. The laser emission spectrum corresponds to the amplification band of erbium-doped fiber amplifiers.

The effect of barrier width in coupled asymmetric double quantum well structure on passive mode-locking region of existence

Semiconductor two-sectional laser diodes with active region, consisting of two InGaAs quantum wells of different width separated with GaAs barrier are investigated. At barrier thickness of 2 nm quantum wells are coupled and diagonal optical transition originates between them. Peak in absorption spectra of lasing structure related to this diagonal transition is observed. An additional region of passive mode-locking due to this absorption peak takes place at low reverse biases on absorber section.

Passive mode-locked laser based on quantum dot superlattice

Passive mode-locking is achieved in two sectional lasers with an active layer based on superlattice formed by ten layers of quantum dots. Tunnel coupling of ten layers changes the structural polarization properties: the ratio between the TE and TM polarization absorption coefficients is less by a factor of 1.8 in the entire electroluminescence spectrum range for the superlattice.