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An array of monolithic wide-tunable lasers is integrated using selective area growth to shift the bandgap of their gain section. A gap-free tuning is demonstrated from the combination of the tuning ranges of the lasers, and single-mode operation is verified.

Selective area growth is used for the first time in the TU/e generic integration platform to modify independently the bandgap of active sections. A chip combining 4 tunable lasers with shifted wavelength ranges has been fabricated. A 96 nm wide tuning range is demonstrated.

Summary form only given. In this work, we report a remarkable suppression of the surface recombination rates in passivated III-V undoped InGaAs nanopillars on InP (inset of Fig. 1a). The surface passivation comprises ammonium sulfide, (NH4)2S, chemical treatment followed by encapsulation with a 50 nm layer of SiOx by plasma-enhanced chemical vapor deposition performed at 300°C. Before passivation, fabricated nanopillars with -300 nm lateral width, d, show a very poor photoluminescence (PL) emission (blue curve in Fig. 1a). The corresponding carrier dynamics, measured by time-correlated single-photon counting, Fig 1b, reveal an extremely short lifetime of ~130 ps, related to the well-known strong surface recombination velocity at InGaAs surfaces [3]. After the sulfur treatment followed by SiOx, we observe a substantial increase by almost two orders of magnitude of the PL intensity (red curve in Fig. 1a), while the carrier lifetime increases by more than two orders of magnitude to a value ~23 ns, red curve in Fig 1b. The estimated surface recombination velocity, S, decreases from about 2×104 cm/s in the untreated nanopillars down to around 260 cm/s (inset of Fig. 1b). To our knowledge, this is a record low value in undoped InGaAs semiconductors. Most importantly, our passivation studies reveal that the SiOx capping layer not only protects the pillars' sidewalls against oxidation, as reported in [5], but actively takes part in the passivation process, a result never previously reported.

In this paper, measurements and analysis of the small-signal net modal gain of single-layer InAs/InP(100) quantum-dot (QD) optical amplifiers are presented. The amplifiers use only a single layer of InAs QDs on top of a thin InAs quantum well. The devices have been fabricated using a layer stack that is compatible with active–passive integration scheme, which makes further integration possible. The measurement results show sufficient optical gain in the amplifiers and can thus be used in applications such as lasers for long-wavelength optical coherence tomography and gas detection. The temperature dependence of the modal gain is also characterized. An existing rate-equation model was adapted and has been applied to analyze the measured gain spectra. The current injection efficiency has been introduced in the model to obtain a good fit with the measurement. It is found that only a small portion ($sim$1.7%) of the injected carriers is actually captured by the QDs. The temperature dependence of several parameters describing the QDs is also discovered. The mechanisms causing the blue shift of peak gain as the current density increases and the temperature changes are analyzed and discussed in detail.

We demonstrate all-optical wavelength routing of 80 Gb/s data packets without using electronic control. The system consists of an optical wavelength converter and a monolithically integrated optical flip-flop memory. The integrated optical flip-flop is based on two coupled lasers, exhibiting single-mode operation, having a 35 dB contrast ratio between the states, and switching its state in about 2 ns. The wavelength converter is optically controlled by the optical flip-flop. We show that the optical set and reset pulses can force the optical flip-flop to switch its continuous-wave output light between two specific wavelength positions. The output light feeds the wavelength converter, which, in turn, converts the data packet into the flip-flop's output wavelength, causing the data packet to be routed into a specific port.

We report on a passively mode-locked InP/InGaAsP multiple quantum well semiconductor ring laser that operates at a 20 GHz repetition rate and around 1575 nm wavelength. The device has been realized using the active-passive integration technology in a standardized photonic integration platform. We demonstrate experimentally for the first time to our knowledge that the relative positioning of the amplifier and absorber in a monolithically integrated ring laser can be used to control the balance of power between counterpropagating fields in the mode-locked state. The directional power balance is verified to be in agreement with a model previously reported.

The static and dynamic characteristics of a monolithically integrated InP 1 × 16 optical phased-array switch are presented. The device demonstrates static switching with an average extinction ratio of 18.6 dB, on-chip loss below 7 dB, and wavelength dependence of less than 0.8 dB in the entire C-band. A 40-Gb/s nonreturn-to-zero signal is transmitted through the switch with a power penalty below 0.4 dB. Using a programmable electronic circuit, dynamic switching to all 16 outputs is achieved with response times less than 11 ns.

A versatile fabrication technique for GaAs-AlGaAs wet-etched mirror lasers is presented. This technique works independently of the Al concentration in the cladding layers up to a value of 70%, and it requires four photolithography steps. Ridge waveguide lasers have been successfully processed using a double heterostructure (DHS) as well as graded index separate confinement heterostructures (GRINSCH) having different quantum-well (QW) active layers. This technique is used to fabricate short-cavity lasers in GRINSCH structures having GaAs multiple-quantum-well (MQW) or bulk active layers. Laser operation was obtained in a 29-/spl mu/m-long device using a 5-QW structure. Short lasers with QW active layers show a complex spectral behavior. These lasers operate at higher current densities (/spl sim/20 kA/cm/sup 2/) and emit light at more than one wavelength. This implies that higher order transitions are involved which is not the case when using a bulk GaAs active layer. Besides the two peaks corresponding to the n=1 and n=2 transitions, we found an intermediate peak which corresponds presumably to the forbidden transition E1-HH2.

The authors report lasing of InAs/InGaAsP/InP (100) quantum dots (QDs) wavelength tuned into the 1.55 µm telecom region. Wavelength control of the InAs QDs in an InGaAsP/InP waveguide is based on the suppression of As/P exchange through ultrathin GaAs interlayers. The narrow ridge-waveguide QD lasers operate in continuous wave mode at room temperature on the QD ground state transition. The low threshold current density of 580 A/cm2 and low transparency current density of 6 A/cm2 per QD layer, measured in pulsed mode, are accompanied by low loss and high gain with an 80-nm-wide gain spectrum.

We present a method to prepare a mixed resist material composed of a positive electron-beam resist (ZEP520A) and C60 fullerene. The method is modified from previous methods in literatures to achieve an optimized mixing. An improvement of the mixed material on the thermal resistance respect to the same structures fabricated with normal ZEP resist has been demonstrated by fabricating multimode interference couplers and coupling regions of micro-ring resonators. An improvement on the propagation loss of the InP membrane waveguides from 6.6 to 3.3 dB/cm using this mixed material is also shown.

In this paper, we present mode-locked operation of a monolithic 20GHz integrated extended cavity ring laser. The 4mm-long laser ring cavity incorporates a 750µm-long optical amplifier section (SOA), a separate 40µm-long saturable absorber (SA) section, passive waveguide sections (shallow and deep etch) and a passive MMI-type 50% output coupler. The active sections contain a four quantum well active layer. The output waveguides are tilted under an angle of 7° to minimize back reflections into the device. Device fabrication has been carried out in the JePPIX technology platform [1]. A mask layout image of the device under test is shown in Fig.1.

We present experimental evidence that asymmetric current injection in intracavity contacted vertical-cavity surface-emitting lasers (VCSELs) stabilizes the polarization of the emitted light. Anisotropies in the gain and loss mechanisms introduced by asymmetric current injection are considered to explain this effect. The design scheme opens perspectives to obtain actual polarization control in VCSELs.

A waveguide photodetector (PD) based on semi-insulating (SI) indium phosphide (InP) was simulated, designed, and fabricated. The layer stack for this PD was optimized for use as an optical amplifier or laser and it can be combined with the passive components. By using an SI substrate and deep etching, a small, efficient, and high-speed PD was made, which allows for easy integration of source, detector, and passive optical components on a single chip. A 3-dB bandwidth of 35 GHz and 0.25 A/W external radio-frequency reponsivity is measured at 1.55-mum wavelength for a 1.5-mum-wide and 30-mum-long waveguide PD at -4-V bias voltage. The polarization dependence in the responsivity is less than 0.27 dB.

A versatile sealing process for AlAs layers is presented. This sealing prevents the AlAs layers of AlAs/GaAs top distributed Bragg reflectors from further undesired oxidation during the wet oxidation of the AlAs current constriction layers in vertical cavity surface emitting lasers. This method has been successfully applied to protect the etched pillars in top mirrors although those pillars were plasma dry etched. © 1999 The Electrochemical Society. S1099-0062(98)07-019-9. All rights reserved.

This article reviews the recent progress in the growth and device applications of InAs/InP quantum dots (QDs) for telecom applications. Wavelength tuning of the metalorganic vapor-phase epitaxy grown single layer and stacked InAs QDs embedded in InGaAsP/InP (100) over the [email protected] region at room temperature (RT) is achieved using ultra-thin GaAs interlayers underneath the QDs. The GaAs interlayers, together with reduced growth temperature and V/III ratio, and extended growth interruption suppress As/P exchange to reduce the QD height in a controlled way. Device quality of the QDs is demonstrated by temperature-dependent photoluminescence (PL) measurements, revealing zero-dimensional carrier confinement and defect-free InAs QDs, and is highlighted by continuous-wave ground-state lasing at RT of narrow ridge-waveguide QD lasers, exhibiting a broad gain spectrum. Unpolarized PL from the cleaved side, important for realization of polarization insensitive semiconductor optical amplifiers, is obtained from closely stacked QDs due to vertical electronic coupling.

An integrated InP-InGaAsP two-state coupled-laser device for use in optical packet switching and signal processing is presented. The two states are identified by distinct lasing wavelengths. Single-mode lasing occurs in both states and the contrast ratio between the two states is 35 dB. Switching between states with optical pulses is demonstrated. The use of an arrayed waveguide grating (AWG) and ring laser configuration permits monolithic integration without the need for cleaved facets. How the AWG can be used to obtain partial isolation between multiple interconnected devices is also discussed.

An InP-based integrated beamformer for beamsteering of a four-element Phased-Array Antenna has been designed, fabricated and characterized. This beamformer consists of an AWG, 14 high-speed MZI switches, and 9delaylines integrated on a single compact chip.

We have investigated the potential of asymmetric current injection for polarization switching in GaAs-based intracavity contacted vertical-cavity surface-emitting lasers using two sets of p- and n-type contacts per device. When using the contacts aligned along the [11~0] crystal direction, the observed laser polarization is parallel to [110], whereas, using the contacts along the [110] crystal direction, the polarization of the laser emission switches to a direction making an angle of 25/spl deg/-90/spl deg/ towards [110]. To overcome this peculiar result, a careful design of the contact layers in the intracavity structure is required.

Dynamical microroughening of the etch front of InP[100] due to Electron Cyclotron Resonance plasma etching was investigated. A quantitative study of the etch front morphology shows that the scaling law holds and the observed structure is self-affine. The low value of the growth exponent (/spl beta/=0.37) indicates that neither plasma reemission nor geometrical shadowing controls the Electron Cyclotron Resonance etching of InP.

A low-confinement asymmetric GaAs-AlGaAs double-quantum-well molecular-beam-epitaxy grown laser diode structure with optical trap layer is characterized, The value of the internal absorption coefficient is as low as 1.4 cm/sup -1/, while keeping the series resistance at values comparable cm with symmetrical quantum-well gradient index structures in the same material system. Uncoated devices show COD values of 35 mW//spl mu/m. If coated, this should scale to about 90 mW//spl mu/m. The threshold current density is about 1000 A/cm/sup 2/ for 2-mm-long devices and a considerable part of it is probably due to recombination in the optical trap layer. Fundamental mode operation is limited to 120-180 mW for 6.5-/spl mu/m-wide ridge waveguide uncoated devices and to 200-300 mW for 13.5-/spl mu/m-wide ones, because of thermal waveguiding effects. These values are measured under pulsed conditions, 10 /spl mu/s/l ms.

Three terminal (3T) Double Barrier Resonant Tunneling (DBRT) devices having the base contact to the quantum well have been fabricated from GaAs/AlAs material system. The technological solution is based on high selective etching processes to reach the plane of the very thin quantum well on which, subsequently, a Schottky base contact is obtained using a nonalloyed Ti/Pt/Au metallization scheme. DC and AC electrical measurements demonstrate that the base contact lies on the quantum well of the DBRT structure and the base voltage modulates the collector current. It is shown that the electrical characteristics of these devices enlarge the possibilities of investigations on DBRT structures and suggest important applications in high-speed electronics.

We have developed a scanning tunneling microscope using an optoelectronic switch that gates the tunneling tip current. The switch is fabricated within 30 mm from the tip by photolithography and an accurate cleavage method. We demonstrate this approach by detecting picosecond electrical transients on a coplanar stripline. We have investigated the signal dependence on contact resistance and found significant differences when the tip is brought from low-ohmic contact into the tunneling regime. In this regime, the THz signal amplitude was found to depend linearly on the tunnel conductance, and disappeared when the tip was retracted.

It was recently proposed,1,2 that the power density related to the window width (in W/μm) of a laser diode can be substantially improved using a low confinement epitaxial structure. Keeping a reasonable high value of the intrinsic gain in the active region, a low confinement structure shall work also with a low modal gain value. The power optimization process is essentially connected to the attenuation coefficient of the laser waveguide α. When operating with an α value around 1 cm−1 and pursuing a high differential efficiency, the modal gain should have a value around 5 cm−1 and the laser length should be increased accordingly.2 A beneficial consequence of the low modal gain value is the possibility to increase the stripe width while preserving well the operation in the fundamental lateral mode above the threshold.

A method for back-tracing magnetic field pulses in pump-probe-type magnetization dynamics measurements is presented. Solving vectorially the Landau–Lifshitz–Gilbert equation for our field-induced measurement geometry yields field pulse profiles fulfilling the theoretical expectations on a 100 ps timescale. Applying the method to our earlier, all-optical-type pump-probe measurements, the claim that the optical pulse triggers an ultrafast anisotropy field pulse gets a direct proof: we derive a pulse consisting of a delta-peak type, full width at half maximum