Abstract
We demonstrate 64 Gbps operation in a compact Si photonic crystal optical modulator that employs meander line electrodes and compensate for the phase mismatch between slow light and RF signals. Although low dispersion slow light increases the modulation efficiency, maintaining a sufficiently wide working spectrum, the phase mismatch becomes a limiting factor on the operation speed even when the phase shifter length is as short as 200 μm. Meander line electrodes broke this limit and enhanced the cutoff frequency by up to 31 and 38 GHz using 50 Ω and 20 Ω termination resistors, respectively. This allowed to use a group index of slow light higher than 20, and greatly improved the quality of the modulation characteristics at 25 and 32 Gbps. Clear open eye was observed even at 40-64 Gbps.
Highlights
In recent years, a large number of low-cost and high-speed optical transceivers have come into use as optical interconnects
We have studied Si photonic crystal waveguide (PCW) and lattice-shifted PCW (LSPCW) slow light modulators, which have a short phase shifter length, L = 200 μm, and a wide working spectrum of 15–20 nm [9,10,11,12], assuring a wide temperature tolerance; we have demonstrated the operation from 19°C to 124°C
We theoretically suggested that the phase mismatch could be compensated for by meander line electrodes and termination resistors that delay the RF signals, and predicted that the operation speed can be Received 22 Feb 2019; revised 25 Apr 2019; accepted 25 Apr 2019; published 2 May 2019
Summary
A large number of low-cost and high-speed optical transceivers have come into use as optical interconnects. High-speed small modulators that are currently being studied include resonators; plasmon waveguides; and those using Si photonics, electro-optic (EO) polymers, etc [6,7,8] They have some disadvantages: a narrow working spectrum, a large optical loss, and/or low compatibility with complementary metal-oxide-insulator (CMOS) processes. The on-chip passive loss was approximately 5 dB, and it demonstrated a wellbalanced performance It did not reach a bit rate over 40 Gbps; we only observed a barely open eye in the old study [9]. One reason for this is the phase mismatch between slow light and RF signals. We report the experimental demonstration of this prediction
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