Wavelength-tunable colloidal quantum dot laser on
ultra-thin flexible glass
C. Foucher, B. Guilhabert, N. Laurand and M.D. Dawson
Institute of Photonics, SUPA, University of Strathclyde, Glasgow, UK
Supplemental Material
Figure S1 summarizes the full fabrication process of the CQD DFB lasers. The grating-imprinted
polymer layer is fabricated by soft lithography using a glass master grating. This polymer layer is
made of an UV-transparent and photo-curable acrylate-based optical adhesive, Norland NOA85,
which has a refractive index n~1.46 at 589 nm, a viscosity of 200 cps at 25°C and a modulus of
elasticity of 9,340 psi (as stated in the supplier datasheet).1 It is deposited onto the master grating in
its liquid form by spin-coating at 3200 rpm. A 0.1-mm-thick sheet of acetate is used as a temporary
substrate and pressed onto the master grating covered by the adhesive. After photocuring under UV
flooding to a dose of 100 mJ/cm2, the flexible acrylate film is peeled off from the master. It is further
post-cured under UV for about 30 minutes to a total exposure dose of ~9 J/cm2. The replicated
grating is then removed from the acetate substrate. A 43-µm-thick, free-standing flexible film
replicating the features of the master (with Λ = 390 nm and a modulation depth of 25 nm) is thus
obtained. This free-standing film is then transferred onto the thin-glass membrane (AF 32 thin glass
from Schott). A drop of NOA85 is spin-coated at 8000 rpm on top of the 30-µm-thick flexible glass
substrate prior to the transfer. The latter is followed by a final photocuring step under a UV flooding
for a total exposure dose of 100 mJ/cm2.
The active elements of the gain layer are commercial core-shell CdSe/ZnS CQDs (Sigma-Aldrich). The
CQDs are dispersed in a PMMA solution at 1.6 mg/mL in 50% of chloroform and 50% of toluene with
a concentration of 50 mg/mL. This solution is then spin-coated on top of the grating to form a 160nm-thick film. The device is finally annealed for 5 minutes at 35°C on a hot plate.
Figure S1 Fabrication steps of the CQD DFB laser on an ultra-thin flexible glass membrane
Spectra and thresholds at three different positions are measured on the CQD DFB laser on an ultrathin glass membrane. Figure S2 represents the power transfer functions at these different points
with the corresponding values of threshold (595 µJ/cm2, 375 µJ/cm2, 372 µJ/cm2). The spectrum at
each point is plotted in the inset of figure S2, showing that the wavelength does not vary
significantly on the surface of the sample.
Figure S2: Detail of the threshold measured at different position on the laser
1
B. Guilhabert, C. Foucher, A.-M. Haughey, E. Mutlugun, Y. Gao, J. Herrnsdorf, H. D. Sun, H. V.
Demir, M. D. Dawson, and N. Laurand, Opt. Express 22, 7308 (2014)