Supplementary Information
Wavelength-converted wave-guiding in dye-doped polymer nanofibers
Huaqing Yu1,2 and Baojun Li1,* 1State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275, China 2School of Physics and Electronic-information Engineering, Hubei Engineering University, Xiaogan 432000, China *Address correspondence to [email protected]
1. Propagation distance-dependent PL peak
The 532-nm blue light (0.12 W) was evanescently coupled into a 480-nm diameter nanofiber, and the nanofiber exhibited different emission colors at different positions along the nanofiber as shown in Fig. 3a. Figure S1 is the corresponding propagation distance- dependent PL peak (i.e., maximum PL wavelength, also referred to as center wavelength λc) in the nanofiber, which reveals that, with an increase in propagation distance, the PL peak of the guided PL spectrum in the nanofiber generally experienced a first rapid increase and followed by a slow increase, and finally got saturated. This is good agreement with earlier reports in dye-doped polymer optical fiber.1 It is worth noting that the dynamical range of PL peak in the nanofiber can be improved through properly controlling the concentration of the doped dyes.
2. PL spectra at different positions in the nanofiber
By launching the 473-nm blue light (0.12 W) into the nanofiber in Fig. 3c, the nanofiber exhibited different emission colors such as yellow-orange, orange, and red-orange at the positions of C1, C2, and C3, respectively. The corresponding PL peaks for the three positions are 582, 590, and 595 nm, respectively. Moreover, the PL intensity at the positions of from C1 to C3 got weaker and weaker due to self-absorption of excited light as shown in Fig. S2.
1 Figure S1. PL peak as a function of propagation distance for a 480-nm diameter nanofiber under excitation light of 532-nm wavelength at power of 0.12 μW.
Figure S2. PL spectra at positions of C1, C2, and C3 of a 480-nm diameter nanofiber under excitation light of 473-nm wavelength at power of 0.12 μW.
3. Branching angle-dependent output power at different branches
To investigate the influence of branching angle on the device performance, we launched the
532-nm green light (0.12 μW) into the 22 splitter in Fig. 4a. We measured the normalized output power at the branches 1 and 2 with respect to the input power as a function of branching angle (the straight line distance between the coupling region and the measuring position is about 15 μm) as shown in Fig. S3. The input/output branching angles of the splitter
2 were changed from 7° to 90°. It was found that the sum of relatively output power at the branches 1 and 2 at the measured positions almost remained unchanged, but each of them experienced cyclical change processes. It should be pointed out that the angle-dependent output power at different branches is related to the modal properties such as momentum components and propagation constant as well as the coupling region properties such as distance between the waveguide.
Figure S3. Relative output power versus branching angle for a 22 splitter with diameters of 630 and 500 nm for branches A-1 and B-2, respectively, by injecting the 532-nm green light with the power of 0.12 μW.
Reference 1. Sheeba, M., Rajesh, M., Mathew, S., Nampoori, V. P. N., Vallabhan, C. P. G. & Radhakrishnan, P. Side illumination fluorescence emission characteristics from a dye doped polymer optical fiber under two-photon excitation. Appl. Opt. 47, 1913–1921 (2008).
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