Optofluidic platform using liquid crystals in lithium niobate microchannel

Abstract

We demonstrate the all optical control of the molecular orientation of nematic liquid crystals confined in microfluidic channels engraved in lithium niobate. Microchannels are obtained by a novel approach based on femtosecond pulse laser micromachining carried on in controlled atmosphere. The combined effect of photovoltaic and pyroelectric fields generated by light in lithium niobate crystals on the liquid crystal orientation, is reported for the first time. The total space charge field and its dependence on the incident light intensity can be controlled by changing the direction of pump light propagation through the microfluidic chip. The results reported in this manuscript demonstrate that liquid crystals and lithium niobate can efficiently be combined in microfluidic configuration, in order to push forward a novel class of optofluidic devices.

Opto-Microfluidic System for Absorbance Measurements in Lithium Niobate Device Applied to pH Measurements

“…As is possible to notice in Figure 4 a,b, the Ti:LN waveguide allows an efficient propagation of light beams at both wavelengths; similarly, Figure 4 a–c clearly demonstrate that the light polarization does not significantly change the transmission property of the waveguide, neither in terms of the beam shape nor its intensity. This feature can be relevant for specific applications, where the light polarization could play a key role, such as applications involving Liquid Crystal [ 33 , 48 ]. Notably, all the beam outputs in Figure 4 show a monomodal behavior, which is ideal for realizing in the future a fiber pigtailing of the waveguides, thus assuring the complete portability of the final devices.…”

“…Then, the coupling between the optical and fluidic components of the device has been demonstrated to efficiently work for different channel sizes—i.e., 50 and 200 µm. Therefore, the proposed optofluidic device can be easily integrated within more complex fluidic geometries, which can be obtained in LN substrate by other fabrication techniques, such as laser ablation [ 24 , 33 ] or Focused Ion Beam [ 56 ]. Additionally, the Ti:LN waveguides have been demonstrated to be able to guide laser beams with different polarizations and wavelengths in the visible range—i.e., 533 and 632 nm.…”

“…Therefore, the combination of the optical capabilities typical of this material with microfluidic tools can offer unprecedented fertile ground for the development of advanced LOCs made using the same monolithic substrate. Additionally, during recent years LN has been also exploited for the realization of photovoltaic tweezers in iron-doped substrates, where photoinduced electric fields [26] were used to trap small particles [27]; to manipulate droplets [28], bubbles [29], or biological samples [30]; and to control liquid crystal cells [31][32][33][34]. Similarly, the pyroelectric effect of this material promotes creating local electric fields on its surface by means of temperature gradients, thus generating liquid microlenses [35], nano-pipetting [36], and 3D photorefractive red blood cell imaging [37].…”

Real-time precise microfluidic droplets label-sequencing combined in a velocity detection sensor

“…In fact, Lithium Niobate is a well-known material for the creation of stages for integrated optics 39 , 40 and, more recently, for actuating micro- and nano-objects, thanks to its physical properties such as pyroelectricity 41 – 43 , piezoelectricity 44 , 45 and photorefractivity 46 , 47 . Furthermore, the feasibility to integrate such optical and manipulation stages in a fluidic circuit 34 , 48 – 50 has definitively contributed to include LN among the materials eligible for realizing lab-on-a-chips demonstrating to be more versatile and flexible in multi-functional platforms’ delivery respect to any material in which optical waveguide 30 – 32 , 37 have been already employed. Specifically, in this work we realized the MZI configuration by means of titanium in-diffusion, which is a standard technique for the realization of waveguides in this material 39 .…”

Fabrication and Characteristics of Heavily Fe-Doped LiNbO3/Si Heterojunction

“…As a strong contender for "optical silicon", LN is applied for optical waveguides, electro-optical modulation, holographic storage, optical parametric oscillators, etc. [3,4,5,6,7,8]. However, LN is generally considered to be an insulator, and acts as a passive component in the above applications [9].…”