The latest research in the United States: NUV LD or LD laser to accelerate the development of optical wireless communication

The United States and Saudi Arabia, researchers say, they showed for the first time using near UV white in the visible light communication diode laser (NUV LDs) and red green blue (RGB) phosphor. The team of researchers from the University of California at Santa Barbara (UCSB), the Saudi King Abdullah University of science and Technology (KAUST) and the University of Wisconsin at Madison.

Compared with the blue emitter, the advantage of using NUV is to reduce solar radiation noise. Compared with LED, the laser diode can be modulated at a higher speed, this is because the laser diode is the limiting factor is the external cavity laser photon lifetime, unlike LED electron / hole life. The researchers also found that compared with LED, the near ultraviolet laser diode (NUV LDs) with high current and high power density, great potential.

The potential use of white light laser including visible light wireless communication (LiFi) network, underwater wireless optical communication (UWOC) and plastic optical fiber (POF) communication.

The ridge waveguide laser diode of the specifications for the 410nm, 4 m * 1200 m, installed in the semi polar (20-21) free-standing Gan, cross section without coating.

Figure 1: white light (a) communication system based on NUV laser, using RGB phosphor for color conversion, improve the uniformity of the phosphor emission diffuser, transmission (Tx) and receiving (Rx) lens for collimating light, 1GHz APD acquisition and transmission of light. Set the picture (B).

The laser used to stimulate the RGB phosphor mixture in silicone resin, respectively (Ba, CaAlSiN3:Eu2+, Ca, Sr, 2SiO4:Eu2+, BaMgAl10O17:Eu2+ and Mg). These parts of the quantum yield at the wavelength of 410nm were 74%, 78% and 78%. The CIE chromaticity coordinates of the phosphor will respectively marked (0.65,0.36), (0.27,0.64) and (0.14,0.08).

The laser diode is installed in the radiator and the thermoelectric cooler (TEC) on the microwave detection station, between the laser diode and phosphor in the distance between 1cm and 2cm.

Continuous wave laser diode (CW) 15 ~ C threshold current and voltage are respectively 320mA (6.67kA / cm2) and 5.5V. The slope efficiency of 0.36W / A. For the modulation of the -3dB bandwidth is about 1GHz, the bias is higher than that of 400mA. The bandwidth is limited due to the avalanche photodetector (APD), as originally expected laser diode with 5GHz or greater level of bandwidth. The team commented: "with the development of higher bandwidth silicon APD, VLC system for laser based on similar, drive current of 400mA to 600mA is expected to generate higher modulation bandwidth."

When the injection current is increased from 100mA to 600mA, the related color temperature white light excitation (CCT) range from 4700K to 4050K range. The injection current in the 500mA and 600mA, the color rendering index (CRI) increased to 79.

Some members of the team previously used blue laser diode and yellow phosphor YAG:Ce produce white light, but the color index (CRI) to 58. Use a blue laser diode and lead the instability of the perovskite phosphor material, can obtain higher CRI (89) and lower CCT (3236K), but the toxicity and safety issues related to limited commercial potential.

The use of non return to zero (NRZ) / key (OOK) modulation, 210-1 pseudo random binary sequence (PRBS) data stream to 1.5 gigabits per second (Gbps) data flow test, obtains the 3.8x10-3 forward error correction (FEC) error rate and 1.8x10-3 (BER). Have a clear eye diagram in the 1.25Gbps drive current and 570mA.

The team said, "because the APD system will limit bandwidth in 1GHz, is expected to actual data rate higher than 1.5Gbps."

The researchers also hope to use different methods, such as QAM OFDM and the high speed photoelectric detector used in combination to improve data rate. (compiled: LEDinside James)

LED more information, please click on the LED network or the WeChat public account (cnledw2013).