Multiple-input multiple-output (MIMO) transmission can be used to increase the throughput of visible light communication (VLC) systems. This approach is highly compatible with the use of arrays of micro light emitting diodes (µLEDs).In this work, we demonstrate an imaging-MIMO VLC system using a two dimensional individually addressable array of µLEDs and an integrated CMOS-based receiver. An aggregate data rate of ~920 Mbps is realized using four parallel channels at a link distance of 1 m. Further improvement in the data rates is feasible by optimizing the system components and operating conditions.
Optical wireless LANs have the potential to provide bandwidths far in excess of those available with current or planned RF networks. There are several approaches to implementing optical wireless systems, but these usually involve the integration of optical, optoelectronic, and elec-I Figure 5. Demonstration system optomechanics. Transmitter optomechanics Receiver optomechanics Detector array flip-chip bonded to CMOS integrated circuit Ceramic package Ceramic package Source array flip-chip bonded to CMOS integrated circuit
155Mb/s operation of an optical wireless link is achieved by using the spectral characteristics and angular emission spectra of a 7-element tracking array of 980nm RC-LEDs. Preliminary results show extension to 200 Mb/s/channel. Resonant-cavity, quantum well, light-emitting diodes (RC-LEDs) were shown, some time ago, to have significantly better efficiencies and controllable spectral characteristics than conventional LEDs [1][2]. Further work highlighted the importance of the relationship between the cavity resonance wavelength and the emission characteristics of the quantum wells on the angular spectrum of the emitted light [3]. In this paper we show how these characteristic can be used to advantage in a free-space tracking optical line-of sight communication link. Free-space optical communication can provide very high bandwidths, significantly higher than available from conventional wireless connections. However, they need either precise optical alignment or, in the case of mobile links, tracking of users within the field of view. We show that using arrays of RC-LEDs in combination with appropriate optics it is possible to achieve high data rates and tracking without mechanical or additional beam steering elements.The system concept and RC-LED array are shown in fig. 1 and fig. 2. The transmitters consists of an array of RC-LEDs that emit through their substrate, as show in figure 2. This configuration allows flip-chip bonding and direct addressing of each element from custom designed CMOS drivers, as well as subsequent integration with transmitter optics. Tracking or beam scanning is achieved by sending data via different elements in the array. Elements off-set from the optical axis of the transmitting optics send light in off-axis directions so optimum link alignment can be achieved rapidly by an iterative sequential scanning procedure across elements in the array.The devices use emission from four GaInAs/GaAs quantum wells located in a hybrid resonant cavity, and light is emitted at approximately 980nm with a spectral linewidth of 20-30nm. The cavity is formed by a metal reflector (and associated phase matching layer) and an AlAs/GaAs Bragg reflector. Fig.1. System concept for free-space line-of-sight link Fig.2. Hexagonal 7-element array of RC-LEDs. Base station Terminal Fig. 3 shows the electrical and optical characteristics of the RC-LEDs. Drive currents of around 100mA were provided by CMOS circuitry capable of rise times of several nsec. A useful feature of the RCLED devices is that the cavity can be detuned to provide a beam profile that is optimum for the application, and an optical model of the system shown in figure 1 ([4]) was developed to ascertain this. The desired angular emission spectrum was achieved by selecting the emission wavelength of the quantum wells to be approximately 10-20 nm shorter than the resonance wavelength of the cavity as shown in fig. 3(c). Receivers produced using back-illumination detectors flip-chip bonded to custom CMOS circuitry allowed 155 Mb/s (Manchester coded) opera...
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