Monolithic photonic integration offers unsurpassed perspectives for higher functional density, new functions, high per-formance, and reduced cost for the telecommunication. Advanced local material growth techniques and the emerging photonic crystal (PhC) technology are enabling concepts towards high-density photonic integration, unprecedented per-formance, multi-functionality, and ultimately optical systems-on-a-chip. In this paper, we present our achievements in photonic integration applied to the fabrication of InP-based mode-locked laser diodes capable of generating optical pulses with sub-ps duration using the heterogeneous growth of a new uni-traveling carrier ultrafast absorber. The results are compared to simulations performed using a distributed model including intra-cavity reflections at the sections inter-faces and hybrid mode-locking. We also discuss our work on InP-based photonic crystals (PhCs) for dense photonic integration. A combination of two-dimensional modeling for functional optimization and three-dimensional simulation for real-world verification is used. The fabricated structures feature more than 3.5μm deep holes as well as excellent pattern-transfer accuracy using electron-beam lithography and advanced proximity-effects correction. Passive devices such as waveguides, 60° bends and power splitters are characterized by means of the end-fire technique. The devices are also investigated using scanning-near field optical microscopy. The PhC activity is extended to the investigation of TM bandgaps for all-optical switches relying on intersubband transitions at 1.55μm in AlAsSb/InGaAs quantum wells.
We report on the investigation of planar photonic crystal waveguide
transitions with a scanning near-field optical microscope (SNOM) in
collection mode. An abrupt and a gradual taper design intended to
couple light from a W3 (three missing rows of holes) to a W1 waveguide
were fabricated in a InGaAsP slab waveguide. SNOM measurements reveal
that a taper design can efficiently funnel light into the W1
waveguide. For both designs a suppressed coupling of light into the W1
waveguide is measured for a frequency which corresponds to a mode
crossing which we determined by 3D plane wave simulations.
We have studied tapers that couple light from a conventional ridge
waveguide into a planar photonic crystal (PhC) waveguide. Tapering
is achieved by changing the PhC waveguide width either in steps or
gradually. Lag effects in fabrication provide an additional
tapering due to the fact that the hole depths scale with the
corresponding hole diameter. Our analysis deals with the
out-of-plane loss that arises within such taper sections. The PhC
consists of a triangular lattice of air holes introduced into an
InGaAsP/InP slab structure. For conceptual studies we use the 2D
multiple multipole method (MMP) in conjunction with an extended
phenomenological model. This model covers the out-of-plane
scattering providing a loss parameter and an effective index
correction for the holes under consideration. This realistic 2D
model is retrieved from full-wave 3D FDTD simulations and
measurements.
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