Semiconductor optical fibers

We review the recent advancements in the fabrication and application of semiconductor optical fibers. Particular focus is placed on novel materials and device designs for use in optical signal processing systems

Depth resolution of Piezoresponse force microscopy

Given that a ferroelectric domain is generally a three dimensional entity, the determination of its area as well as its depth is mandatory for full characterization. Piezoresponse force microscopy (PFM) is known for its ability to map the lateral dimensions of ferroelectric domains with high accuracy. However, no depth profile information has been readily available so far. Here, we have used ferroelectric domains of known depth profile to determine the dependence of the PFM response on the depth of the domain, and thus effectively the depth resolution of PFM detection

Development of polycrystalline silicon waveguides by laser crystallization

Silicon (Si) is an excellent material for integrated photonics devices as its high refractive index allows for small device footprints. To date, most of the work in this area has leveraged the single crystal silicon-on-insulator platforms, which are relatively expensive to produce and thus drive up component costs. Here we propose an alternative method to fabricate crystalline silicon waveguides by laser processing of an amorphous starting material. As well as reducing production costs, this approach has the added advantage of removing the substrate dependence so that more flexible alternatives can be considered. This method has previously been applied to a-Si wires grown inside silica capillaries and shown to produce very large crystallites [1]. Here we demonstrate preliminary results of laser-induced crystallization of a-Si films and micro-patterned wires produced by chemical vapor deposition (CVD) on SiO2 substrates. The samples have been crystallized using a c.w. argon-ion laser at 488nm. Crystallized tracks have been written by scanning the focused beam across the samples using different laser intensities and scanning speeds. The resulting material quality is then studied using Raman spectrometry, optical and electronic microscopy and X-ray diffraction. For the planar films, we have produced crystallite sizes on the order of hundreds of nanometers to a few microns; similar to those obtained via conventional pulsed Excimer laser crystallization [2]. However, for the micro-patterned samples, we have found that it is possible to grow crystals that almost cover the entire width of the wire, over lengths of up to 18µm, considerably larger than what is typically reported for polysilicon waveguide devices [3]. Furthermore, this laser crystallization method has been observed to reform the surface of the Si wires resulting in very smooth sidewall profiles (as shown in Fig. 1) which is very important for low loss optical transmission in photonic devices

Ultraviolet writing of channel waveguides in proton-exchanged LiNbO₃

We report on a direct ultraviolet (UV) writing method for the fabrication of channel waveguides at 1.55 µm in LiNbO3 through UV irradiation of surface and buried planar waveguides made by annealed proton exchange and reverse proton exchange. A systematic study of the guidance properties as a function of the UV writing conditions is presented

A silicon/lithium niobate hybrid photonic material platform produced by laser processing

Silicon (Si) and lithium niobate (LiNbO3) are two materials that are synonymous with the electronics and photonics industries respectively and are supported by a significant amount of technological know-how. It has been suggested and demonstrated recently that Si could also be used for the production of integrated photonic devices, however its performance can be limited by the transmission cutoff at short wavelengths, a relatively high two-photon absorption, and a zero second order nonlinear optical susceptibility. LiNbO3 on the other hand is a very good dielectric material with very little electronic functionality and high second order nonlinearity. Thus, as these two materials have complementary properties, there is significant merit in combining them into a single hybrid system that will benefit from the properties of its constituents, as demonstrated via direct bonding in [1]. Here we propose a route for producing such a hybrid material system via local laser processing of a low cost, easy to produce amorphous silicon (a-Si) film deposited onto a single crystal LiNbO3 substrate. This research is based on recent encouraging results of a laser based crystallization process obtained in a-Si core optical fibres that not only produced crystallites with very large aspect ratios, but also allowed for tuning of the Si bandgap [2].The emphasis of this laser-processing route has been on achieving structures with large crystals and low surface roughness in order to obtain good photonic and electronic device performance. Interestingly it was revealed that, apart from the expected local crystallization of the a-Si film, this particular system exhibited a plethora of interesting and potentially useful effects including the direct formation of optical waveguides in LiNbO3, enabled ferroelectric domain reversal and the spontaneous formation of periodic structural features on the Si film, shown in the figure below

Laser processing of amorphous silicon on lithium niobate for photonic applications

Silicon (Si) and lithium niobate (LiNbO3) are two materials that are synonymous with the electronics and photonics industries respectively and are supported by a significant amount of technological know-how. It has been suggested and demonstrated recently that Si could also be used for the production of integrated photonic devices, however its performance can be limited by the transmission cutoff at short wavelengths, a relatively high two-photon absorption, and lack of second order nonlinear optical susceptibility. LiNbO3 on the other hand is a very good dielectric material with high second order nonlinearity but with very little electronic functionality. It can be envisaged however that these two materials have complementary properties therefore there is significant merit in combining them into a single hybrid system that will benefit from the properties of its constituents as demonstrated in [1] on a directly bonded single crystal hybrid. In this contribution we will present results on laser processing of amorphous silicon films deposited on LiNbO3 and other substrates suggesting a new route for the fabrication of Si based photonic circuits. This research is based on recent encouraging results of a laser based crystallization process obtained in a-Si core optical fibres that not only obtained crystallites with very large aspect ratio but also allowed for tuning of the Si bandgap [2]. &more..

Microstructuring lithium niobate

Lithium niobate is among the most important nonlinear optical materials used today in the photonics industry as it combines a variety of very important optical and electromechanical properties. Microstructuring of this material opens new possibilities for the utility of lithium niobate into a wider range of applications beyond the area of optoelectronics. In this talk a synopsis of methods, developed at the ORC, for the fabrication of refractive, diffractive, nonlinear and actual microstructures on congruent lithium niobate single crystals will be given. The development of such methods shows the potential for using this nonlinear ferroelectric crystal as the base for the development of integrated miniature multifunctional devices

Self-adaptive laser resonators using degenerative four-wave mixing in a proximity-coupled side-pumped Nd:YVO₄ amplifier

Degenerate four-wave mixing (FWM) techniques used to produce self-adaptive laser resonator based on diffraction from a gain grating have shown considerable promise for correction of distortion in high-power solid-state laser systems. In these systems, the gain grating is formed by spatial hole burning caused by interference of coherent beams in the laser amplifier and modulation of the population inversion. The gain grating formation can be used for phase conjugation by using the amplifier in a four-wave mixing geometry, for self-pumped phase conjugation by using an input beam in a self-intersecting loop geometry and for formation of a self-starting adaptive oscillator by providing additional feedback from an output coupler and requiring no external optical input. Successful demonstrations of such a self-adaptive resonator have been performed recently in diode side-pumped Nd:YVO4 [1] whose operation is based on the very high reflectivities (>800%) [2] and more recently (>10,000%) of a gain grating formed in a diode-bar side-pumped NdYVO4, amplifier. This resonator has been shown to correct for severe distortions introduced inside the loop with a maximum output of ~7.2 W so far achieved. We will present results of increased resonator outputs by proximity-coupling of the pump diode straight to the FWM amplifier region resulting in higher gains, whereby the diode emitting facet is placed around 50 microns from the pump face of the amplifying crystal. Output powers of the order ~10 W should be achievable, and we will present modelling data for such proximity-coupled geometries

Continuous wave ultra violet laser induced frustration of etching in congruent lithium niobate

Surface relief patterns have been fabricated on the z face of congruent lithium niobate single crystals by illumination of the surface with continuous wave 244 nm laser radiation followed by chemical etching with hydrofluoric acid