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. 2018 Nov;24(6):6101806.
doi: 10.1109/JSTQE.2018.2866677. Epub 2018 Aug 23.

Indium Phosphide Photonic Integrated Circuits for Free Space Optical Links

Hongwei Zhao  1 , Sergio Pinna  2 , Bowen Song  3 , Ludovico Megalini  4 , Simone Tommaso Šuran Brunelli  5 , Larry A Coldren  6 , Jonathan Klamkin  7
Affiliations

Indium Phosphide Photonic Integrated Circuits for Free Space Optical Links

Hongwei Zhao et al. IEEE J Sel Top Quantum Electron. 2018 Nov.

Abstract

An indium phosphide (InP)-based photonic integrated circuit (PIC) transmitter for free space optical communications was demonstrated. The transmitter consists of a sampled grating distributed Bragg reflector (SGDBR) laser, a high-speed semiconductor optical amplifier (SOA), a Mach-Zehnder modulator, and a high-power output booster SOA. The SGDBR laser tunes from 1521 nm to 1565 nm with >45 dB side mode suppression ratio. The InP PIC was also incorporated into a free space optical link to demonstrate the potential for low cost, size, weight and power. Error-free operation was achieved at 3 Gbps for an equivalent link length of 180 m (up to 300 m with forward error correction).

Keywords: Free space communication; Mach-Zehnder modulator; optical interconnect; photonic integrated circuit; sampled grating DBR laser; semiconductor optical amplifier.

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Figures

Fig. 1.
Fig. 1.
Microscope image of fabricated InP-based PIC transmitter comprising of a five-section SGDBR laser (all sections are labeled in the figure), a high-speed SOA (SOA 1), a 1-mm long MZM, and a high-power two-section output booster SOA (SOA 2).
Fig. 2.
Fig. 2.
(a) Epitaxial structure in the active region; (b) Sideview of the active/passive interface following regrowth.
Fig. 3.
Fig. 3.
SEM images at various stages of the fabrication process: (a) The sampled gratings of the front mirror of the laser; (b) Top view of a 1×2 MMI structure; (c) Cross section of a MMI with silicon nitride passivation; (d) Cross section of the high-speed SOA.
Fig. 4.
Fig. 4.
Overlaid lasing spectra of the SGDBR laser.
Fig. 5.
Fig. 5.
SGDBR laser LIV curve (with CW current source) measured by using the SOA as a photodiode.
Fig. 6.
Fig. 6.
Measured SMSR across the tuning range.
Fig. 7.
Fig. 7.
Lasing spectrum near 1550 nm with a 55-dB SMSR measured by an optical spectrum analyzer with a resolution bandwidth of 0.02 nm.
Fig. 8.
Fig. 8.
Measured heterodyne laser linewidth spectrum demonstrating a 3-dB linewidth of 6.4 MHz.
Fig. 9.
Fig. 9.
MZM response under forward bias at various laser wavelengths.
Fig. 10.
Fig. 10.
MZM response under reverse bias at various laser wavelengths.
Fig. 11.
Fig. 11.
Gain as a function of current density for the high-speed SOA (3 μm x 400 μm) with different input power levels at a wavelength of 1560 nm.
Fig. 12.
Fig. 12.
Off-chip optical power of the PIC transmitter versus the current in the flared-waveguide section of the booster SOA.
Fig. 13.
Fig. 13.
Eye diagrams for 1 Gbps and 3 Gbps NRZ OOK modulation.
Fig. 14.
Fig. 14.
Schematic of free space optical link setup.
Fig. 15.
Fig. 15.
BER for 1 Gbps and 3 Gbps NRZ OOK transmission.
See this image and copyright information in PMC

References

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