arXiv subjects

Ingo Breunig

Publications and source records attributed to Ingo Breunig.

21 records · Page 2Linked to original sources

arXiv2018

Frequency comb up- and down-conversion in a synchronously-driven $χ^{(2)}$ optical microresonator

Optical frequency combs are key to optical precision measurements. While most frequency combs operate in the near-infrared regime, many applications require combs at mid-infrared, visible or even ultra-violet wavelengths. Frequency combs can be transferred to other wavelengths via nonlinear optical processes, however, this becomes exceedingly challenging for high-repetition rate frequency combs. Here, it is demonstrated that a synchronously driven high-Q microresonator with a second-order optical nonlinearity can efficiently convert high-repetition rate near-infrared frequency combs to visible, ultra-violet and mid-infrared wavelengths providing new opportunities for microresonator and electro-optic combs in applications including molecular sensing, astronomy, and quantum optics.

physics.optics↗

arXiv2018

Quasi-phase-matched nonlinear optical frequency conversion in on-chip whispering galleries

Chip-integrated whispering-gallery resonators enable compact and wavelength-agile nonlinear optical frequency synthesizers. So far, the most flexible phase-matching technique, i.e. quasi phase matching, has not been applied in this configuration. The reason is the lack of suitable thin films with alternating crystal structure on a low-refractive-index substrate. Here, we demonstrate an innovative method of realizing thin film substrates suitable for quasi phase matching by field-assisted domain engineering of lithium niobate, and subsequent direct bonding and polishing. We are able to fabricate high-Q on-chip WGRs with these substrates by using standard semiconductor manufacturing techniques. The Q-factors of the resonators are up to one million, which allows us to demonstrate quasi-phase-matched second-harmonic generation in on-chip WGRs for the first time. The normalized conversion efficiency is $9\times 10^{-4}\,\textrm{mW}^{-1}$. This method can also be transferred to other material systems.

physics.optics↗

arXiv2017

Giant and accessible conductivity of charged domain walls in lithium niobate

Ferroelectric domain walls are nm-sized interfaces between sections of different allowed values of the spontaneous polarization, the so-called domains. These walls - neutral or charged - can be created, displaced, deleted, and recreated again in ferroelectric materials. [1-3] Owing to the recent progress in the studies of ferroelectrics, they are expected to be functional active elements of the future nano-electronics.[1,4,5] Metallic-like conductivity of charged domain walls (CDWs) in insulating ferroelectrics, predicted in 1970s6 and detected recently,[7-10] is especially attractive for applications. This important effect is still in its infancy. The electric currents are small, the access to the conductivity is hampered by contact barriers, and stability is low because of sophisticated domain structures and/or proximity of the Curie point. Here, we report on giant and accessible persistent CDW conductivity in lithium niobate (LN) crystals (LiNbO3) - a vital material for photonics. [12] Our results are by far superior to the data known for other materials: Increase of LN conductivity by more than 14 orders of magnitude owing to CDWs, access to the effect via Ohmic and semi-Ohmic contacts, and its high stability for temperatures of up to 70 °C are demonstrated. It is made clear why this big effect was missed earlier [11,25] in LN. Our results demonstrate that strong conductivity of CDWs is available in simple ferroelectric materials, possessing only two allowed orientations of the spontaneous polarization, far from the Curie point. Also, CDW functionalities can be combined with linear and nonlinear optical phenomena. [14,15] Our findings allow new generations of adaptive-optical elements, of electrically controlled integrated-optical chips for quantum photonics, and of advanced LN-semiconductor hybrid optoelectronic devices.

cond-mat.mtrl-sci↗