光電所所訊

Plasmon-enhanced Photoluminescence of an Amorphous Silicon Quantum Dot Light-Emitting Device by Localized Surface Plasmon Polaritons in Ag/SiO_x:a-Si QDs/Ag Sandwich Nanostructures

Professor Hoang-Yan Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所林晃巖教授

We investigated experimentally the plasmon-enhanced photoluminescence of the amorphous silicon quantum dots (a-Si QDs) light-emitting devices (LEDs) with the Ag/SiO_x:a-Si QDs/Ag sandwich nanostructures (Fig. 1), through the coupling between the a-Si QDs and localized surface plasmons polaritons (LSPPs) mode, by tuning a one-dimensional (1D) Ag grating on the top. The coupling of surface plasmons at the top and bottom Ag/SiO_x:a-Si QDs interfaces, resulting in the localized surface plasmon polaritons (LSPPs) confined underneath the Ag lines, which exhibit the Fabry–Pérot resonance. From the Raman spectrum, it proves that the existence of a-Si QDs embedded in Si-rich SiO_x film (SiO_x:a-Si QDs) at a low annealing temperature (300℃) to prevent the possible diffusion of Ag atoms from Ag film. The photoluminescence (PL) spectra of a-Si QDs can be precisely tuned by a 1D Ag grating with different pitches and Ag line widths (Fig. 2) were investigated. An optimized Ag grating structure, with 500 nm pitch and 125 nm Ag line width, was found to achieve up to 4.8-fold PL enhancement at 526 nm and 2.46-fold PL integrated intensity compared to the a-Si QDs LEDs without Ag grating structure, due to the strong a-Si QDs–LSPPs coupling (Fig. 3). (International Journal of Photoenergy (Volume 2015 (2015), Article ID 140617)

Fig. 1. Schematic view of a-Si QDs LEDs with a Ag/SiO_x:a-Si QDs/Ag sandwich nanostructures.

Fig. 2. SEM images of a series of Ag gratings (samples B-E). Scale bar is 1 μm.

Fig. 3. The plots of the PL enhancement factor of samples B-E.

Direct QAM-OFDM Encoding of a Master-to-Slave Injection-Locked WRC-FPLD Pair for 28×20 Gbit/s DWDM-PON Transmission

Professor Gong-Ru Lin’s Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所林恭如教授

This work demonstrated a master-to-slave injection-locked weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) pair, which is capable of carrying an orthogonal frequency division multiplexed 16-quadrature amplitude modulation (16-QAM OFDM) data at 20 Gbit/s/channel for 28 channels in a dense wavelength division multiplexing passive optical network (DWDM-PON), as illustrated in Fig. 1. Since the lower front-facet reflectance and longer cavity features of WRC-FPLD, it reveals broader gain spectrum with denser longitudinal modes and higher injection efficiency than a typical FPLD for supporting more DWDM channels. As a result, the optical spectra of master and slave WRC-FPLDs are shown in Fig. 2. After passing through a demultiplexer with a channel spacing of 50 GHz for the central mode of master WRC-FPLD, the filtered single-mode master with a peak power of -4 dBm was employed to injection-lock the slave WRC-FPLD, which achieves a side-mode suppression ratio (SMSR) of 50 dB. Moreover, the bit error rate (BER) performances of back-to-back and 25-km single-mode fiber (SMF) transmitted 20-Gbit/s OFDM data carried by the master-to-slave injection-locked WRC-FPLD pair at different channels are shown in Fig. 3. For the central mode injection case, the back-to-back transmitted BER of 1.6×10^-5 can be improved to 2.9×10^-7 by employing the OFDM subcarrier per-leveling technique, and it is inevitably degraded to 2.1×10^-4 due to the fiber dispersion after 25-km SMF transmission. To meet the forward error correction (FEC) the required BER of 3.8×10^-3, 28 DWDM channels can be obtained to reveal a total data-rate of 28×20=560 Gbit/s. Therein, a slightly decreased SMSR of 35 dB is also obtained for the farthest side-mode injection case. In conclusion, the master-to-slave injection-locked WRC-FPLD pair has shown its competitive performance and superior flexibility to fit multi-channel DWDM-PON transmission.

Fig. 1. The schematic diagram of the master-to-slave injection-locked WRC-FPLD pair based DWDM-PON system for direct 16-QAM OFDM modulation and transmission.

Fig. 2. The optical spectra of master and slave WRC-FPLDs.

Fig. 3. The BER performances of back-to-back and 25-km SMF transmitted 28-Gbit/s 16-QAM OFDM data.