Abstract:We demonstrate a wavelength domain-multiplexed (WDM) optical link relying on a single section semiconductor mode-locked laser (SS-MLL) with quantum dash (Q-Dash) gain material to generate 25 optical carriers spaced by 60.8 GHz, as well as silicon photonics (SiP) resonant ring modulators (RRMs) to modulate individual optical channels. The link requires optical reamplification provided by an erbium-doped fiber amplifier (EDFA) in the system experiments reported here. Open eye diagrams with signal quality factors (Q-factors) above 7 are measured with a commercial receiver (Rx). For higher compactness and cost effectiveness, reamplification of the modulated channels with a semiconductor optical amplifier (SOA) operated in the linear regime is highly desirable. System and device characterization indicate compatibility with the latter. While we expect channel counts to be primarily limited by the saturation output power level of the SOA, we estimate a single SOA to support more than eight channels. Prior to describing the system experiments, component design and detailed characterization results are reported including design and characterization of RRMs, ring-based resonant optical add-drop multiplexers (RROADMs) and thermal tuners, S-parameters resulting from the interoperation of RRMs and RR-OADMs, and characterization of Q-Dash SS-MLLs reamplified with a commercial SOA. Particular emphasis is placed on peaking effects in the transfer functions of RRMs and RR-OADMs resulting from transient effects in the optical domain, as well as on the characterization of SS-MLLs in regard to relative intensity noise (RIN), stability of the modes of operation, and excess noise after reamplification.

We experimentally investigate an optical link relying on silicon photonics transmitter and receiver components as well as a single section semiconductor mode-locked laser as a light source and a semiconductor optical amplifier for signal amplification. A transmitter based on a silicon photonics resonant ring modulator, an external single section mode-locked laser and an external semiconductor optical amplifier operated together with a standard receiver reliably supports 14 Gbps on-off keying signaling with a signal quality factor better than 7 for 8 consecutive comb lines, as well as 25 Gbps signaling with a signal quality factor better than 7 for one isolated comb line, both without forward error correction. Resonant ring modulators and Germanium waveguide photodetectors are further hybridly integrated with chip scale driver and receiver electronics, and their co-operability tested. These experiments will serve as the basis for assessing the feasibility of a silicon photonics wavelength division multiplexed link relying on a single section mode-locked laser as a multi-carrier light source.

Based on the single channel characterization of a Silicon Photonics (SiP) transceiver with Semiconductor Optical Amplifier (SOA) and semiconductor Mode-Locked Laser (MLL), we evaluate the optical power budget of a corresponding Wavelength Division Multiplexed (WDM) link in which penalties associated to multi-channel operation and the management of polarization diversity are introduced. In particular, channel cross-talk as well as Cross Gain Modulation (XGM) and Four Wave Mixing (FWM) inside the SOA are taken into account. Based on these link budget models, the technology is expected to support up to 12 multiplexed channels without channel pre-emphasis or equalization. Forward Error Correction (FEC) does not appear to be required at 14 Gbps if the SOA is maintained at 25 °C and MLL-to-SiP as well as SiP-to-SOA interface losses can be maintained below 3 dB. In semi-cooled operation with an SOA temperature below 55 °C, multi-channel operation is expected to be compatible with standard 802.3bj Reed-Solomon FEC at 14 Gbps provided interface losses are maintained below 4.5 dB. With these interface losses and some improvements to the Transmitter (Tx) and Receiver (Rx) electronics, 25 Gbps multi-channel operation is expected to be compatible with 7% overhead hard decision FEC.

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