Rgf Roel Baets

Laser emission and photodetection in an InP/InGaAsP layer integrated on and coupled to a Silicon-on-Insulator waveguide circuit

Laser emission from an InP/InGaAsP thin film epitaxial layer bonded to a Silicon-on-Insulator waveguide circuit was observed. Adhesive bonding using divinyl-tetramethyldisiloxane-benzocyclobutene (DVS-BCB) was used to integrate the InP/InGaAsP epitaxial layers onto the waveguide circuit. Light is coupled from the laser diode into an underlying waveguide using an adiabatic inverted taper approach. 0.9mW optical power was coupled into the SOI waveguide using a 500mum long laser. Besides for use as a laser diode, the same type of devices can be used as a photodetector. 50mum long devices obtained a responsivity of 0.23A/W.

Adhesive bonding of InP/InGaAsP dies to processed silicon-on-insulator wafers using DVS-bis-benzocyclobutene

The process of bonding InP/InGaAsP dies to a processed silicon-on-insulator wafer using sub-300 nm layers of DVS-bis-benzocyclobutene (BCB) was developed. The planarization properties of these DVS-bis-BCB layers were measured and an optimal prebonding die preparation and polymer precure are presented. Bonding quality and bonding strength are assessed, showing high-quality bonding with sufficient bonding strength to survive postbonding processing.

Ultralow-loss 3-dB photonic crystal waveguide splitter

A photonic crystal waveguide splitter that exhibits ultralow-loss 3-dB splitting for TE-polarized light is fabricated in silicon-on-insulator material by use of deep UV lithography. The high performance is achieved by use of a Y junction, which is designed to ensure single-mode operation, and low-loss 60 degrees bends. Zero-loss 3-dB output is experimentally obtained in the range 1560-1585 nm. Results from three-dimensional finite-difference time-domain modeling with no adjustable parameters are found to be in excellent agreement with the experimental results.

Improved performance of AR-coated DFB lasers for the introduction of gain coupling

Antireflection (AR)-coated distributed-feedback (DFB) lasers with both gain- and index-coupled distributed feedback are studied numerically with respect to mode losses, mode suppression, and spatial hole burning. The mode losses and the spatial hole burning decrease with increasing gain coupling, while the mode suppression increases. It is shown that a large improvement in performance can already be obtained for small fractions of gain coupling.<<ETX>>

Integration of InP/InGaAsP photodetectors onto silicon-on-insulator waveguide circuits

The integration of optical functionalities on a chip has been a long standing goal in the optical community. Given the call for more integration, Silicon-on-Insulator (SOI) is a material system of great interest. Although mature CMOS technology can be used for the fabrication of passive optical functionality, particular photonic functions like efficient light emission still require III-V semiconductors. We present the technology for heterogeneous integration of III-V semiconductor optical components and SOI passive optical components using benzocyclobutene (BCB) die to wafer bonding. InP/InGaAsP photodetectors on SOI waveguide circuits were fabricated. The developed process is compatible with the fabrication of InP/InGaAsP light emitters on SOI.

Monolithic integration of a spot size transformer with a planar buried heterostructure InGaAsP/InP-laser using the shadow masked growth technique

We present a vertically tapered InGaAsP/InP planar buried heterostructure (PBB) laser for low loss coupling to single-mode fibers. To achieve the vertical tapering we make use of the shadow masked growth technique. Tapered lasers with beam divergences of 15/spl deg/ in both lateral and transverse directions were realized. In comparison with untapered lasers, the coupling losses to cleaved single-mode fibers could be reduced by 4.8 dB down to 5.8 dB.<<ETX>>

Reduction of Propagation Loss in Pillar-Based Photonic Crystal Waveguides

Out-of-plane losses are the major issue in the integration of two-dimensional photonic crystal devices in photonic integrated circuits. In this paper, we show that the out-of-plane losses of pillar-based photonic crystal waveguides can be vastly reduced, even for pillars with a low vertical index contrast, such as in InP/InGaAsP/InP technology. These low losses are obtained by creating confinement between the pillars with a polymer layer stack. We show that the spatial frequency component of the Bloch mode in the first Brillouin zone (i.e., the component inside the light cone), is significantly suppressed by the optimized polymer layer stack.

Heterogeneously integrated III-V-on-silicon multibandgap superluminescent light-emitting diode with 290 nm optical bandwidth.

A broadband superluminescent III-V-on-silicon light-emitting diode (LED) was realized. To achieve the large bandwidth, quantum well intermixing and multiple die bonding of InP on a silicon photonic waveguide circuit were combined for the first time, to the best of our knowledge. The device consists of four sections with different bandgaps, centered around 1300, 1380, 1460, and 1540 nm. The fabricated LEDs were connected on-chip in a serial way, where the light generated in the smaller bandgap sections travels through the larger bandgap sections. By balancing the pump current in the four LEDs, we achieved 292 nm of 3 dB bandwidth and an on-chip power of -8  dBm.

Ultrafast and bias-free all-optical wavelength conversion using III-V-on-silicon technology

Using a 7.5 μm diameter disk fabricated with III-V-on-silicon fabrication technology, we demonstrate bias-free all-optical wavelength conversion for non-return-to-zero on-off keyed pseudorandom bit sequence (PRBS) data at the speed of 10 Gbits/s with an extinction ratio of more than 12 dB. The working principle of such a wavelength converter is based on free-carrier-induced refractive index modulation in a pump-probe configuration. We believe it to be the first bias-free on-chip demonstration of all-optical wavelength conversion using PRBS data. All-optical gating measurements in the pump-probe configuration with the same device have revealed that it is possible to achieve wavelength conversion beyond 20 Gbits/s.

Very steep optical thresholding Characteristic using a DFB laser diode and an SOA in an optical feedback scheme

A new optical decision or thresholding circuit, composed of a semiconductor optical amplifier (SOA) and a distributed feedback (DFB) laser diode in an optical feedback scheme is proposed. This new circuit has been studied both by simulations and experiments. Simulations show a very steep optical decision characteristic that rises more then 5 dB over an input power range of less then 0.5 dB. It is also demonstrated that the decision point can easily be shifted by tuning the drive currents of both the laser diode or the SOA or the feedback ratio between them. The principle has been experimentally verified as well, using a discrete SOA and DFB laser diode. We showed a good agreement with the simulation results. Again a very steep optical decision characteristic, combined with the possibility to adjust the decision point was obtained.