Jan Hendrik Wülbern

Electro-optic modulation in slotted resonant photonic crystal heterostructures

Two dimensional photonic crystal waveguides in high index materials enable integrated optical devices with an extremely small geometrical footprint on the scale of micrometers. Slotted waveguides are based on the guiding of light in low refractive index materials and a field enhancement in this particular region of the device. In this letter we experimentally demonstrate electro-optic modulation in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with nonlinear optical polymers. A photonic crystal heterostructure is used to create a cavity, while simultaneously serving as an electrical connection from the slot to the metal electrodes that carry the modulation signal.

Electro-optical modulator in a polymer-infiltrated silicon slotted photonic crystal waveguide heterostructure resonator

We present a novel concept of a compact, ultra fast electro-optic modulator, based on photonic crystal resonator structures that can be realized in two dimensional photonic crystal slabs of silicon as core material employing a nonlinear optical polymer as infiltration and cladding material. The novel concept is to combine a photonic crystal heterostructure cavity with a slotted defect waveguide. The photonic crystal lattice can be used as a distributed electrode for the application of a modulation signal. An electrical contact is hence provided while the optical wave is kept isolated from the lossy metal electrodes. Thereby, well known disadvantages of segmented electrode designs such as excessive scattering are avoided. The optical field enhancement in the slotted region increases the nonlinear interaction with an external electric field resulting in an envisaged switching voltage of approximately 1 V at modulation speeds up to 100 GHz.

40 GHz electro-optic modulation in hybrid silicon–organic slotted photonic crystal waveguides

In this Letter we demonstrate broadband electro-optic modulation with frequencies of up to 40 GHz in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with a nonlinear optical polymer. Two-dimensional photonic crystal waveguides in silicon enable integrated optical devices with an extremely small geometric footprint on the scale of micrometers. The slotted waveguide design optimizes the overlap of the optical and electric fields in the second-order nonlinear optical medium and, hence, the interaction of the optical and electric waves.

Omnidirectional photonic band gap in polymer photonic crystal slabs

In this letter, we report on the experimental observation of a complete in-plane photonic band gap for transverse-electric-like polarized modes in a polymer photonic crystal slab with a triangular array of holes. We performed transmission measurements on two-dimensional photonic crystal slabs in both principal directions of the triangular lattice. For a propagation distance of 40 lattice constants, the transmission was effectively suppressed regardless of propagation direction below −15dB over a bandwidth of 65nm. The experimental results are in excellent agreement with theoretical predictions obtained from band diagram calculations and finite integration time domain techniques.

Electro-optically tunable photonic crystals

We report on electro-optical modulation with a sub-1-V sensitivity in a photonic crystal slab waveguide resonator which contains a nanostructured second-order nonlinear optical polymer. The electro-optical susceptibility in the core was induced by high electric-field poling. A square lattice of holes carrying a linear defect was transferred into the slab by electron-beam lithography and reactive ion etching, creating a photonic crystal slab-based resonator. Applying an external electric modulation voltage to electrodes leads to a linear electro-optical shift of the resonance spectrum and thus to a modulation of the transmission at a fixed wavelength based on the electronic displacement polarization in a noncentrosymmetric medium (Pockels effect). This effect is therefore inherently faster than other reported electro-optic modulation effects in nanophotonics.

Photonic crystal cavity definition by electron beam bleaching of chromophore doped polymer cladding

We demonstrate a novel concept for the fabrication of high Q photonic crystal heterostructure cavities. First, photonic crystal waveguides without cavities are fabricated. The cavities are defined in a later fabrication step by spatially resolved bleaching of a chromophore doped polymer cladding. Bleaching of polymer films either by UV light or by electron beam illumination is well known to reduce the refractive index of the film. The reduction of the cladding refractive index leads to a reduction of the effective lattice constant of the photonic crystal waveguide. The maximum refractive index change was found to be 6•10-2 which corresponds to the effective lattice constant change of 12.2 nm. With this approach it is also possible to achieve very small effective lattice constant shifts of 0.02 nm which is not possible with state of the art lithography. Being able to precisely define the effective lattice constant at every point of the photonic crystal waveguide we are able to impose cavity mode profiles which closely resemble a Gaussian envelope. This leads to a dramatic increase of the Q-factor. In simulations we have obtained Q-factors as high as 3.0•106 for a vertically symmetric polymer cladding. First results for non-vertically symmetric structures are presented.

Hybrid silicon-organic racetrack resonator designs for electro-optical modulation

Racetrack resonators based on the silicon-on-insulator platform are proposed for electro-optical modulation. The resonators are functionalized by a cladding of a second order nonlinear optical polymer. Two different concepts for the racetrack design employing different waveguide geometries for quasi-TE and quasi-TM polarization operation are presented. In both resonator designs the electrical contact is established by fully etched segmented electrode sections to allow for an easy fabrication process. For quasi-TM polarization the width of the strip waveguide is optimized to 400 nm. The Q factor of 2000 is measured for a sample with segmented electrode. A loss of 0.4 dB per segmented waveguide is deducted. For the quasi-TE polarization the slot waveguide geometry is optimized to 470 nm total width including a vertical slot of 90 nm width. Only the straight parts of the racetrack are slotted, while the bends are built from strip waveguides. To convert the mode from strip to slot geometry stub like couplers of 100 nm length are employed. The measured Q factor is 550. The in device Pockels coefficient is measured to r33 = 1 pm/V. This small value indicates a very low poling induced polar order which needs to be improved. This is a topic of current investigation.

Modulation and dispersion control in photonic crystals

We report on electrooptical modulation with a sub 1Volt sensititivity in a photonic crystal slab waveguide resonator which contains a nanostructured nonlinear optical polymer. This modulation effect is based on the electronic displacement polarization in a noncentrosymmetric medium (Pockels-effect) and is therefore inherently by more than three orders of magnitude faster than any other reported electrooptic modulation effect in nanophotonics. We also show concepts for extremely high and zero dispersion as well as for time delay in photonic crystal waveguides. Tuning can be achieved by hybrid combination of Si-based PCs and organic EO-materials.

High speed electro-optic modulation in hybrid silicon on insulator slotted photonic crystal

We demonstrate GHz electro-optic modulation in a slotted silicon photonic crystal infiltrated with nonlinear optical polymer material.

Multi GHz modulation in ultra compact organic-inorganic structures

In this letter we demonstrate broadband electro-optic modulation with frequencies up to 40 GHz in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with a nonlinear optical polymer. Two dimensional photonic crystal waveguides in silicon enable integrated optical devices with an extremely small geometrical footprint on the scale of micrometers. The slotted waveguide design optimizes the overlap of the optical and electric field in the second order nonlinear optical medium and hence the interaction of the optical and electric wave.