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High speed GaN micro-LED arrays for data communications

High speed GaN micro-LED arrays for data communications. N. Laurand (1 ) , J.J.D . McKendry (1 ) , A.E. Kelly (2 ) , S. Zhang (1 ) , J. Vinogradov (3 ) , D. Massoubre (1 ) , B.R. Rae (4 ) , R.P. Green (5 ) , E. Gu (1 ) , O. Ziemann (3 ) , R.K. Henderson (4 ) and M.D. Dawson (1)

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High speed GaN micro-LED arrays for data communications

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  1. High speed GaN micro-LED arrays for data communications N. Laurand(1), J.J.D. McKendry(1), A.E. Kelly(2), S. Zhang(1), J. Vinogradov(3), D. Massoubre(1), B.R. Rae(4), R.P. Green(5), E. Gu(1), O. Ziemann(3), R.K. Henderson(4) and M.D. Dawson(1) 1: Institute of Photonics, University of Strathclyde, Glasgow, UK 2: School of Engineering, University of Glasgow, Glasgow, UK 3: POF-Application Center, Georg Simon Ohm University, Nürnberg, Germany 4: School of Engineering, University of Edinburgh, Edinburgh, UK 5: Department of Physics, University College Cork, Cork, Ireland

  2. Introduction to micro-LEDs 0.5mm Matrix-addressable Micro-stripes • III-nitride wafers grown on sapphire • UV (370nm), violet (405nm) blue (450 and 470nm) and green (520nm) • Patterned by standard photolithography M.D. Dawson and M.A.A. Neil, “Micro-pixellated LEDs for science and instrumentation” J Phys D. 41090301 (2008).

  3. Individually-addressable micro-LEDs • 16 × 16 array • 72µm diameter • 100µm pitch • 370, 405, 450nm emission • 8 × 8 array • 10, 20…80µm diameter • 200µm pitch • 370, 405, 450, 520, 560nm emission

  4. CW power output • Up to 5mW from a single micro-LED pixel (450nm peak emission) • Smaller pixels – higher output power densities & current densities

  5. Micro-LEDs for communications • Our GaN-based micro-LEDs emit at wavelengths corresponding to attenuation minimum in POF • Data transmission using white LEDs also topical • Possible advantages of micro-LEDs? • faster response? • multi-channel output?

  6. Visible-light communications using micro-LEDs

  7. Bandwidth of micro-LEDs • ‘Bare’ pixels individually-addressed using a high-speed probe • Bandwidth strongly dependent on current density

  8. Bandwidth of micro-LEDs • General trend that smaller micro-LEDs have higher maximum bandwidths. • Attributed to higher maximum current densities for smaller pixels (reduced current crowding and device self-heating).

  9. Data transmission demo. • Single micro-LED addressed using high-speed probe. Emission imaged onto Si photodetector. • NRZ modulation (modulation depth 2V, DC bias ~7V).

  10. Data transmission demo. 622 Mbit/s 155 Mbit/s 1.2 Gbit/s • 520nm-emitting micro-LED, diameter 34µm • i = 35mA, output power ≈ 0.2mW • “Error-free” up to 1.1 Gbit/s

  11. Visible-light communications using CMOS-controlled micro-LEDs

  12. CMOS-driver array • Primarily designed for generating intense (sub)ns-duration pulses for OSL pumping • 16×16 array of individually-addressable drivers, 100×100µm2, 100µm pitch • Multiple modes of operation – CW, pulsed, NRZ modulation • Each of the 16 columns may be modulated with independent data inputs (MIMO data transmission) • CMOS and micro-LED chips integrated by flip-chip bonding process 1.6mm

  13. Bandwidth of CMOS-micro-LEDs • NRZ signal from BERT used to trigger CMOS drivers. Micro-LEDs bias voltage modulated between 0V and LED_VDD (variable) • Increasing V = higher bandwidth. Higher bandwidths obtained with smaller diameter pixels.Max bandwidth from single pixel ≈185MHz (450nm device) • ‘Error-free’ data transmitted at up to 512 Mbit/s (450nm device)

  14. Data transmission over POF • Work done in collaboration with O. Ziemann’s group, POF-AC, Nürnberg • 450nm-emitting CMOS-controlled micro-LED device used • Micro-LED emission butt-coupled to 1m of 1mm diameter SI-POF • Passive equalisation, low-pass filter and electrical amplifier used

  15. Data transmission over POF • Up to -3dBm of coupled CW power • “Error-free” (BER ≤ 1×10-9) data transmission at 1Gbit/s from pixel diameters ranging from 34 to 84µm • Error-free data transmission also achieved using 520nm-device at up to 500Mbit/s 84µm diameter pixel, 1Gbit/s Received power (a.u.) Time (0.2ns/div)

  16. Multi-channel transmission • Existing CMOS device has up to 16 data inputs – potential MIMO transmitter for high-throughput parallel data transmission • Data transmission using two channels has been investigated. Using two 450nm-emitting 34µm diameter pixels, error free parallel transmission has been achieved up to 600Mbit/s (300Mbit/s per channel) • Data rate per channel limited due to EMI issues between the two channels – this issue appears to be primarily caused by the design of the interface board, not the CMOS or micro-LED arrays themselves.

  17. Conclusions • Micro-LED pixels have been shown to have modulation bandwidths of up to ~450 MHz, with peak emission at wavelengths suitable for transmission over POF. • >1Gbit/s single pixel transmission demonstrated with no equalisation • CMOS control arrays have been shown to provide convenient control over micro-LED arrays, with bandwidth of up to 185MHz possible. With up to 16 independent data channels, these devices are potential MIMO transmitters for VLC. • Key Publications • Jonathan McKendry, Richard P. Green, A. E. Kelly, Zheng Gong, Benoit Guilhabert, David Massoubre, ErdanGu and Martin D. Dawson “High Speed Visible Light Communications Using Individual Pixels in a Micro Light-Emitting Diode Array” Photon. Tech. Lett., Vol 22, No.18, pp 1346-1348, Sept 2010. • McKendry, J. J. D.; Massoubre, D.; Zhang, S.; Rae, B. R.; Green, R. P.; Gu, E.; Henderson, R. K.; Kelly, A. E.; Dawson, M. D.; , "Visible-Light Communications Using a CMOS-Controlled Micro-Light- Emitting-Diode Array," Lightwave Technology, Journal of , vol.30, no.1, pp.61-67, Jan.1, 2012

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