Liquid-Crystal Alignment by a Nanoimprinted Grating for Wafer-Scale Fabrication of Tunable Devices

Abstract

A simple technology is demonstrated for waferscale fabrication of liquid-crystal (LC) microcells that can be integrated in active optoelectronic devices. Fabrication of 1.55µm tunable Fabry-Perot optical micro-filter arrays is achieved owing to the insertion of a single nanoimprinted polymer grating dedicated to LC alignment and to the soft thermal transfer of a dry thick resist film between two highly reflective mirrors. The filter exhibits a spectral tuning range of 102nm with only 18V applied, as well as negligible internal loss, which makes it suitable for being inserted in a laser cavity. This constitutes a key step toward large-scale integration of widely-tunable photonic devices such as VCSELs using LC technology.

Liquid crystal-based tunable photodetector operating in the telecom C-band

“…In our case, this also confirms that the intra-cavity nanostructured SU-8 layer does not induce diffraction losses as previously mentioned. This was also verified in a previous work by the authors showing the low losses induced by the SU-8 grating and how this grating is efficient to properly align LC molecules [22]. Regarding the responsivity, which is a key parameter for a PD, our results show that over a wide spectral range [1490 nm -1560 nm], the tunable PD provides photocurrent values comprised between 0.5 and 0.65 mA.…”

“…The value deduced for n e is 1.689, i.e. close to that already measured for this type of LC at 25 °C (n e = 1.697) [14,22], confirming that the alignment of the LC molecules along the grating lines is efficient. The linear dependence between the refractive index and the resonant wavelength leads to similar variation behaviors for the shift of the resonant wavelength as a function of the applied LC voltage (green curve in Fig.…”

“…In our fabrication process, this has been done by imprinting a sub-wavelength grating mold in a 700 nm thick SU-8 layer previously spincoated on the bottom DBR surface. Details about this process can be found elsewhere [22]. As for the bottom DBR, the nanoimprinted SU-8 layer has been drawn only on the photosensitive area of the PD in the Fig.…”

Liquid crystal based tunable PIN-photodiodes for detection around 1.55-µm

“…After pattern transfer, the sub-wavelength grating has a period of 800 nm, a duty cycle of 50:50, and a depth in the range of [70-80 nm]. The details of this process are described elsewhere [12] . LC microcells are then defined by polymer walls made of an epoxy photosensitive film named DF-1005.…”

A practical guide to versatile photoalignment of azobenzenes

“…However, novel applications in the fields of light modulation [6] and soft robotics [7] require alignment patterns that vary spatially, i. e. the alignment direction is not uniaxial but follows a specific pattern. To enable this, finer techniques to microstructure the command layer through photo-lithography, soft lithography and maskless lithography have been demonstrated [8][9][10].…”