Abstract
A TO-38-can packaged Gallium nitride (GaN) blue laser diode (LD) based free-space visible light communication (VLC) with 64-quadrature amplitude modulation (QAM) and 32-subcarrier orthogonal frequency division multiplexing (OFDM) transmission at 9 Gbps is preliminarily demonstrated over a 5-m free-space link. The 3-dB analog modulation bandwidth of the TO-38-can packaged GaN blue LD biased at 65 mA and controlled at 25°C is only 900 MHz, which can be extended to 1.5 GHz for OFDM encoding after throughput intensity optimization. When delivering the 4-Gbps 16-QAM OFDM data within 1-GHz bandwidth, the error vector magnitude (EVM), signal-to-noise ratio (SNR) and bit-error-rate (BER) of the received data are observed as 8.4%, 22.4 dB and 3.5 × 10(-8), respectively. By increasing the encoded bandwidth to 1.5 GHz, the TO-38-can packaged GaN blue LD enlarges its transmission capacity to 6 Gbps but degrades its transmitted BER to 1.7 × 10(-3). The same transmission capacity of 6 Gbps can also be achieved with a BER of 1 × 10(-6) by encoding 64-QAM OFDM data within 1-GHz bandwidth. Using the 1.5-GHz full bandwidth of the TO-38-can packaged GaN blue LD provides the 64-QAM OFDM transmission up to 9 Gbps, which successfully delivers data with an EVM of 5.1%, an SNR of 22 dB and a BER of 3.6 × 10(-3) passed the forward error correction (FEC) criterion.
Highlights
Over past few decades, the visible light emitting diodes (LEDs) with wavelengths ranging from 350 to 750 nm have been widely used in displays, traffic signals and ubiquitous lighting systems because of its high brightness, low power consumption and long lifetime
The TO-38-can packaged Gallium nitride (GaN) blue laser diode (LD) (OSRAM Opto Semiconductors, PL 450B) mounted with a thermo-electric cooler and a copper-based heat sink is illustrated in Fig. 1 for subsequent 16- or 64-quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM) data transmission over 5 m in free space, in which the single transverse mode GaN blue LD with a lasing wavelength of 450 nm, a spectral linewidth of 0.67 nm and a maximum vertical/horizontal beam divergence of 11/25 degree was packaged in a conventional TO-38-can
The self-feedback temperature controlling system for the TO-38-can packaged GaN blue LD is shown in Fig. 3(a) [23], which consists of a copper mount based heat sink, a SubMiniature version A (SMA) jack connector, a thermoelectric (TE) cooler, a thermistor, two plastic screws and nuts
Summary
The visible light emitting diodes (LEDs) with wavelengths ranging from 350 to 750 nm have been widely used in displays, traffic signals and ubiquitous lighting systems because of its high brightness, low power consumption and long lifetime. The visible light communication (VLC) system implemented with aforementioned LEDs has been considered as a promising candidate for free-space or underwater communications [1,2,3,4], which has distinct features when compared with the traditional radio frequency (RF)- and optical fiber-based communication links, such as electromagnetic interference (EMI) free and free-space data transmission [5,6]. These features provide a new level of flexibility for applications in different environments including flying aircrafts, hospitals and indoor wireless networks. Watson et al have preliminarily demonstrated a 2.5-Gbps nonreturn-to-zero on-off-keying (NRZ-OOK) modulation scheme by using a GaN blue laser diode in a free space link [17]; its transmission capacity is still limited by the inefficient modulation format
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