Abstract
We report a CMOS integrated micro-LED array capable of generating discrete optical output power levels. A 16 × 16 array of individually addressable pixels are on-off controlled through parallel logic signals. With carefully selected groups of LEDs driven together, signals suitable for discrete transmission schemes are produced. The linearity of the device is assessed, and data transmission using pulse amplitude modulation (PAM) and orthogonal frequency division multiplexing (OFDM) is performed. Error-free transmission at a symbol rate of 100 MSamples/s is demonstrated with 4-PAM, yielding a data rate of 200 Mb/s. For 8-PAM, encoding is required to overcome the baseline wander from the receiver, reducing the data rate to 150 Mb/s. We also present an experimental proof-of-concept demonstration of discrete-level OFDM, achieving a spectral efficiency of 3.96 bits/s/Hz.
Highlights
Demand for wireless data communications is constantly increasing, putting further strain on the limited radio frequency (RF) spectrum
The simplest modulation scheme that can be performed in this way is on-off keying (OOK), where the light-emitting diodes (LEDs) brightness is modulated between a high and low state to represent a high or low logic level, respectively
The LED arrays used for this work consist of 16 × 16 individually addressable gallium nitride (GaN) LED elements fabricated in flip-chip configuration
Summary
Demand for wireless data communications is constantly increasing, putting further strain on the limited radio frequency (RF) spectrum. Multi carrier modulation schemes such as orthogonal frequency division multiplexing (OFDM) overcome these problems by adapting the channel loading to channel capacity using adaptive bit and energy loading algorithms This allows OFDM to skip subcarriers where the signal to noise ratio (SNR) is low. We present a highly compact integrated approach to discrete optical signal generation: an array of micro-LED pixels integrated with complementary metal-oxide semiconductor (CMOS) driving electronics. This provides a mm scale device capable of using CMOS logic signals to control groups of LEDs in an on-off fashion, and generate discrete output levels without the need for a DAC. This "digital-to-light" transmitter can be scaled to provide higher output power or a higher number of discrete output power levels
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