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.
Laser (VCSEL) with a liquid crystal (LC) microcell monolithi-2 cally integrated on its surface for spectral tuning is investigated. 3 Unlike tunable VCSELs integrating a movable membrane, here 4 the physical length of the cavity remains unchanged and only the 5 voltage applied on the LC ensures a refractive index modification 6 for a particular polarization emitted by the VCSEL. This tunable 7 VCSEL operates in CW at room temperature and exhibits 8 more than 23 nm wavelength tuning around 1.55 µm at a 9 maximum applied voltage of 20 V. The measured laser threshold 10 around 6.5 mW is still comparable to VCSEL without 11 LC microcell, a clear indication that the optical losses related 12 the LC are very low. On the other hand, for this first optically 13 pumped device, the lasing characteristics suggest that the LC 14 birefringence is lower than expected. To assess this hypothesis, 15 thermo-optical simulations have been conducted.
Liquid crystal (LC) microcells monolithically integrated on the surface of InGaAs based photodiodes (PDs) are demonstrated. These LC microcells acting as tunable Fabry-Perot filters exhibit a wavelength tunability of more than 100 nm around 1550 nm with less than 10V applied voltage. Using a tunable laser operating in the S and C bands, photocurrent measurements are performed. On a 70 nm tuning range covered with a driving voltage lower than 7V, the average sensitivity for the PD is 0.4 A/W and the spectral linewidth of the LC filter remains constant, showing a FWHM of 1.5 nm. Finally, the emission spectrum from an Er-doped fiber is acquired by using this tunable PD as a micro-spectrometer.
In this work, the thermo-optical properties of a nematic liquid crystal are determined through reflectance measurements performed on a high finesse tunable filter fabricated using a polymer-based microcell technology. The final aim is to insert such material in the optical cavity of a 850 nm tunable VCSEL device, in which local self-heating due to CW pumping must be taken into account. These localized interferometric experiments are performed in the near-infra-red range and at temperatures up to 115 °C. A thermal model is derived from the acquired data. Finally, we demonstrate that the birefringence of QYPDLC-36 liquid crystal remains higher than 0.18 at 60 °C, feature well suited to real device operation.
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