Introduction
Silicon photonics (SiP) is a key enabling technology for future high-speed optical interconnects and communications systems. SiP allows for dense integration, high yield, and low energy consumption, making it an attractive solution for scalable and energy-efficient 800 Gbps and 1.6 Tbps data links. Recent advances in SiP have demonstrated impressive capabilities, such as compact arrayed waveguide grating routers extremely efficient wavelength division multiplexing filters, and high-bandwidth modulators.
In this article, we will explore a record-breaking demonstration of a 170 Gbaud on-off-keying (OOK) SiP ring resonator modulator (RRM)-based transmitter, capable of achieving performance below the 6.7% overhead hard-decision forward error correction (HD-FEC) threshold of 4.5×10^-3 for both optical back-to-back (ob2b) and transmission over 100 meters of single-mode fiber (SMF).
Experimental Setup
The experimental setup for testing the SiP RRM is shown in Fig. 1(a). The signal bit sequence for OOK is generated offline in MATLAB, pulse-shaped with a root-raised-cosine filter, and loaded into an arbitrary waveform generator (AWG). The RRM is reverse-biased at 1.5 V, and the signal and bias are applied using 110 GHz RF probes. A tunable laser with an output power of 15.5 dBm is coupled into the RRM using grating couplers.
The RRM's insertion loss at different bias voltages (Fig. 1(b)) and relative responses at different detuning levels (Fig. 1(c)) are measured using an integrated photonics test setup. The modulator extinction ratio at different detuning values is shown in Fig. 2(c).
After optical modulation, the signal is transmitted over 100 m of SMF. An erbium-doped fiber amplifier (EDFA) and wavelength selective switch (WSS) are used to overcome coupling losses and filter out amplified spontaneous emission noise. The signal is then detected by a 100-GHz PIN photodiode and captured by a real-time digital storage oscilloscope (DSO). Finally, the signal is processed offline with a matched filter, timing recovery, decision-feedback equalizer (DFE), and the bit error rate (BER) is calculated.
Results and Discussion
The performance of the SiP RRM transmitter is evaluated for OOK modulation at 150 Gbaud, 160 Gbaud, and 170 Gbaud, targeting the 6.7% OH HD-FEC threshold of 4.5×10^-3 for both ob2b and after transmission over 100 m of SMF. Fig. 2(a) shows the BER as a function of received optical power, using a DFE with 99 feedforward taps and 7 feedback taps.
As can be seen from Fig. 2(a), the SiP RRM transmitter achieves performance below the HD-FEC threshold for all data rates in the ob2b scenario, as well as after transmission over 100 m of SMF. A power penalty is observed after fiber transmission due to the high chromatic dispersion coefficient in the C-band.
Fig. 2(b) shows the eye diagrams for the different data rates at the highest received optical power. Open eye diagrams are observed for all cases, with a slight reduction in eye-opening after fiber transmission due to chromatic dispersion.
Conclusion
This tutorial has covered the demonstration of a record-breaking 170 Gbaud OOK SiP RRM-based transmitter, achieving performance below the 6.7% OH HD-FEC threshold for both ob2b and after transmission over 100 m of SMF. The experimental setup, results, and analysis have been presented, highlighting the potential of SiP RRM modulators for compact, high-symbol-rate transceivers in short-reach applications.
References
[1] Ostrovskis, T. Salgals, M. Koenigsmann, et al., "170 Gbaud On-Off-Keying SiP Ring Resonator Modulator-based Link for Short-Reach Applications," in IEEE Journal of Selected Topics in Quantum Electronics, vol. xx, no. xx, pp. 1-8, 2024.
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