Subpicosecond pulse generation at 134 GHz and low radiofrequency spectral linewidth in quantum dash-based Fabry-Perot lasers emitting at 1.5 /spl mu/m

Passive modelocking in one-section monolithic semiconductor laser diodes based on a quantum dash active layer at very high repetition rate (>40 GHz), in the 1.5 /spl mu/m window, is demonstrated. 800 fs pulse generation, without any pulse compression scheme, at 134 GHz, is reported. A 50 kHz linewidth of the radiofrequency (RF) spectrum at 42 GHz is also demonstrated, the lowest value reported for any semiconductor passively modelocked laser.     

High performance quantum dot lasers on GaAs substrates operating in 1.5 /spl mu/m range

Stacked InAs/InGaAs quantum dots are used as an active media of metamorphic InGaAs-InGaAlAs lasers grown on GaAs substrates by molecular beam epitaxy. High quantum efficiency (/spl eta//sub i/>60%) and low internal losses (/spl alpha/<3-4 cm/sup -1/) are realised. The transparency current density per single QD layer is estimated as /spl sim/70 A/cm/sup 2/ and the characteristic temperature is 60 K (20-85/spl deg/C). The emission wavelength exceeds 1.51 /spl mu/m at temperatures above 60/spl deg/C.     

Fabrication approach for antiphase narrow linewidth complex coupled 1.55 /spl mu/m DFB lasers

A new method for fabricating narrow linewidth antiphase complex coupled MQW DFB lasers by periodically etching the active layer and quarternary InGaAsP overgrowth is reported. The minimum linewidth for a 375 /spl mu/m long ridge waveguide laser is only 250 kHz at an optical output power of 4 mW.     

1.43 /spl mu/m InAs bilayer quantum dot lasers on GaAs substrate

An edge emitting quantum dot (QD) laser at 1430 nm is demonstrated with a structure grown by molecular beam epitaxy on GaAs substrate. The active region is based on three InAs bilayer QDs embedded in a conventional AlGaAs/GaAs waveguide. The threshold current density is 134 A/cm/sup 2/. Output power of 23 mW per facet is achieved.     

1.5 /spl mu/m GaInNAs semiconductor saturable absorber for passively modelocked solid-state lasers

Fully self-starting and passively modelocking of a 1.5 /spl mu/m solid-state laser with a GaInNAs semiconductor saturable absorber mirror (SESAM) has been demonstrated for the first time. A saturation fluence of 20 /spl mu/J/cm/sup 2/, a modulation depth of 0.39% and a fast temporal decay of 18 ps were measured. These well-suited nonlinear optical SESAM parameters allowed for self-starting and passive modelocking of a diode-pumped Er:Yb:glass laser at 1.534 /spl mu/m with a pulse duration of 5 ps at 61 MHz.     

Short-term wavelength changes in 1.5-/spl mu/m InGaAsP-InP distributed feedback semiconductor lasers

We report short-term lasing wavelength changes in 1.5-/spl mu/m InGaAsP-InP distributed feedback (DFB) lasers. The lasing wavelengths after biasing the lasers have been changed upto 1.2 /spl Aring/ at 20/spl deg/C while maintaining the constant output power. It takes over 700-2000 s, to stabilize the lasing wavelengths in many lasers. The annealing effects could be partially responsible for the wavelength change. It certainly affects the initial performance of cold-start frequency-division-multiplexed systems.     

High-frequency modulation characteristics of 1.3-/spl mu/m InGaAs quantum dot lasers

In this letter, we report results of small-signal modulation characteristics of self-assembled 1.3-/spl mu/m InGaAs-GaAs quantum dot (QD) lasers at room temperature. The narrow ridge-waveguide lasers were fabricated with multistack InGaAs self-assembled QDs in active region. A high characteristic temperature of T/sub o/=210 K with threshold current density of 200A/cm/sup 2/ was obtained. Small-signal modulation bandwidth of f/sub -3 dB/=12 GHz was measured at 300 K with differential gain of dg/dn/spl cong/2.4/spl times/10/sup -14/ cm/sup 2/ from detailed characteristics. We observed that a limitation of modulation bandwidth in high current injection appeared with gain saturation. This property can direct future high-speed QD laser design.     

Antimonide semiconductor saturable absorber for 1.5 /spl mu/m

Self-starting continuous-wave passive modelocking of an Er:Yb:glass laser at 1535 nm is demonstrated with the first antimonide semiconductor saturable absorber mirror (SESAM). The Er:Yb:glass laser produces 20 ps pulses at 61 MHz. This laser was used to characterise the nonlinear optical parameters of the metal organic vapour phase epitaxy grown SESAM.     

Continuous-wave operation of GaInNAsSb distributed feedback lasers at 1.5 /spl mu/m

GaAs-based singlemode emission at 1.5 /spl mu/m has been realised for the first time in continuous-wave operation. GaInNAsSb active-layer material and GaAsN strain-compensating barriers have been used in combination with lateral distributed feedback. Laser diodes with a threshold current of 95 mA, an external efficiency of 0.15 W/A and a maximum output power of more than 10 mW could be demonstrated. A sidemode suppression ratio better than 31 dB could be realised at a singlemode emission wavelength of 1496 nm.     

Optimisation of a-factor for quantum dot InAs/GaAs fabry-perot lasers emitting at 1.3 /spl mu/m

Dynamic measurements of the Henry factor alpha_H of InAs/GaAs Fabry-Perot lasers are compared for 3-, 5- and 10-QD layers. While alpha_H dramatically increases with the bias current for 3- and 5-QD stacks, it only amounts to <4 for the 10-layer stack at high currents, a value similar to that of QW-lasers     

10 Gbit/s data modulation using 1.3 /spl mu/m InGaAs quantum dot lasers

Error-free 8 and 10 Gbit/s data modulation with quantum dot lasers emitting at 1.3 /spl mu/m is presented. 12 Gbit/s open eye patterns are observed. An integrated fibre-optic QD laser module yields error-free data modulation at 10 Gbit/s at a receiver power of -2 dBm.     

High-performance 1.5 /spl mu/m GaInNAsSb lasers grown on GaAs

Substantially reduced threshold current density and improved efficiency in long-wavelength (>1.4 /spl mu/m) GaAs-based lasers are reported. A 20/spl times/1220 /spl mu/m as-cleaved device showed a room temperature continuous-wave threshold current density of 580 A/cm/sup 2/, external efficiency of 53%, and 200 mW peak output power at 1.5 /spl mu/m. The pulsed threshold current density was 450 A/cm/sup 2/ with 1145 mW peak output power.     

InAs/AlSb quantum cascade lasers operating at 6.7 /spl mu/m

Quantum cascade lasers based on the InAs/AlSb material system have been realised. The optical confinement is obtained using a plasmon waveguide with n/sup +/-InAs cladding layers. In pulse mode the lasers emit close to 6.7 /spl mu/m with a threshold current density of 5 kA/cm/sup 2/ at 90 K. The maximum operating temperature is 220 K.     

1.5-/spl mu/m InGaAsP-InP slab-coupled optical waveguide lasers

We report the demonstration of high-power semiconductor slab-coupled optical waveguide lasers (SCOWLs) operating at a wavelength of 1.5 /spl mu/m. The lasers operate with large (4/spl times/8 /spl mu/m diameter) fundamental mode and produce output power in excess of 800 mW. These structures have very low loss (/spl sim/0.5 cm/sup -1/) enabling centimeter-long devices for efficient heat removal. The large fundamental mode allows 55% butt-coupling efficiency to standard optical fiber (SMF-28). Comparisons are made between SCOWL structures having nominal 4- and 5-/spl mu/m-thick waveguides.     

Dynamic properties of 1.5 /spl mu/m quantum dash lasers on (100) InP

The static and dynamic properties of state-of-the-art InP -based QDash lasers around 1.55 mum are reported. Demonstrated are ridge waveguide lasers with a total output power of 37 mW and a total slope efficiency of 0.40 W/A that show a 3 dB modulation bandwidth of 8.0 GHz and a modulation efficiency of 0.76 GHz/y/mA in continuous-wave operation.     

Mid-infrared (8.5 /spl mu/m) semiconductor lasers operating at room temperature

The room-temperature pulsed operation of a semiconductor laser emitting at 8.5 /spl mu/m is reported. This device is an optimized vertical transition quantum cascade (QC) laser. At 300 K the peak output power from a single facet is 15 mW, and the current density at threshold is /spl sim/8 kA/cm/sup 2/. The temperature dependence of the threshold current density is described by a high T/sub 0/ (107 K) in the 200-320 K temperature range.     

GaSb-based tapered diode lasers at 1.93 /spl mu/m with 1.5-W nearly diffraction-limited power

High-power high-brightness 1.93-/spl mu/m wavelength (AlGaIn)(AsSb) tapered diode lasers with a narrow vertical waveguide design are reported for the first time. A nearly diffraction-limited continuous-wave output power of 1.5 W together with a remarkable low fast axis divergence of 43/spl deg/ full-width at half-maximum have been demonstrated. The maximum brightness amounts to 32 MW/cm/sup 2/sr.     

High-power room temperature emission quantum cascade lasers at /spl lambda/=9 /spl mu/m

We present two different techniques for processing InP-based /spl lambda/=9 /spl mu/m quantum cascade lasers which improve the thermal dissipation in the device. The first process is based on hydrogen implantation creating an insulating layer to inject current selectively in one part of the active region. The second process uses a thick electroplated gold layer on the laser ridge to efficiently remove the heat produced in the active region. Each process is designed to improve heat evacuation leading to higher performances of the lasers and will be compared to a standard ridge structure from the same wafer. We give evidence that the process of proton implantation, efficient in GaAs based structures, is not directly applicable to InP based devices and we present a detailed analysis of the thermal properties of devices with an electroplated gold thick layer. With these lasers, an average power of 174 mW at a duty cycle of 40% has been measured at 10/spl deg/C.     

Time-domain modeling of mode suppression in 1.3-/spl mu/m Fabry-Perot lasers

Fabry-Perot lasers still comprise the bulk of lasers used in optical fiber systems. The spectral envelope, of the Fabry-Perot modes, can be modulated either deliberately or as a consequence of processing stages. This can be beneficial, in the case of modal sculpturing where specific Fabry-Perot modes are suppressed, or a hindrance in the case of poor devices. A time-domain model is used to model 1.3-/spl mu/m Fabry-Perot lasers. Simulated power conserving reflective sites are introduced between sections in the model to simulate the effect of reflective sites from etch pits on the output characteristics of real lasers. Spectral modulation of the laser output is reported in agreement with previous experimental results and the strength of reflections required is investigated. We also report the use of the model to investigate the effect of fiber dispersion on the modulated laser output with different spectral mode modulation.     

Bidirectional, subcarrier-multiplexed transmission using 1.3-/spl mu/m Fabry-Perot lasers

We demonstrate a full-duplex, subcarrier-multiplexed, transmission system which employs 1.3-/spl mu/m Fabry-Perot strained layer MQW laser diode transmitters in both directions. Coherent effects are reduced by using lasers with different mode spacing.