Ultra-compact integrated coherent receiver with grating-based beam splitter

Moore's law has successfully predicted that the density of the transistors in integrated circuits (ICs) will double for every 18 months, which enables better performance of electronic components and systems but with almost the same price over four decades. The telecommunication industry is eager to duplicate this phenomenal success to their photonic counterpart. Photonic integration can provide not only reductions in size, weight, and power consumption, but also advancements in reliability and performance. To keep up the anticipated explosive growth rate, innovation in optical components of photonic integrated circuits (PICs) plays a key role to support a steady reduction in both circuit sizes and manufacturing costs.;In analog optical links, phase modulation can provide high dynamic range provided the transmitted radio frequency (RF) signal phase can be demodulated linearly. However, the linearity of conventional interferometer-based coherent receivers is limited by their sinusoidal response, which counterbalances the advantage of phase modulation. In order to achieve high linearity, an optical phase-locked loop (OPLL) configuration is introduced to reduce the net phase swing across the demodulator such that it operates within the linear regime without penalty in signal-to-noise ratio (SNR). The challenge is to make a receiver operable at high frequencies. Because high loop gain as well as a wide bandwidth is required for efficient phase tracking, the physical delay in the OPLL must be kept sufficiently short to prevent oscillation.;In this work, an ultra-compact coherent integrated receiver in which an OPLL is incorporated to suppress the non-linearities arising from phase demodulation has been successfully demonstrated. An ultra-compact grating-based beam splitter with only 10 mumsplitting length has been developed that can significantly reduce the signal loop delay and improves the system performance when compared with other types of beam splitters. A shot-noise limited spur-free dynamic range (SFDR) of 118 dB·Hz2/3 is achieved at 100 MHz with 10 mA photocurrent in each photodiode.