Periodic Reporting for period 3 - TWILIGHT (Towards the neW era of 1.6 Tb/s System-In-Package transceivers for datacenter appLIcations exploiting wafer-scale co-inteGration of InP membranes and InP-HBT elecTronics)
Reporting period: 2022-08-01 to 2024-05-31
TWILIGHT is a 4-year Horizon 2020 ICT project funded by the European Commission under the Photonics Public Private Partnership (PPP) which addresses the transformation of datacenters to support the modern Internet of Things (IoT), 5G and emerging Artificial Intelligence (AI) applications. TWILIGHT targets to develop the next generation of optical transceivers and optical space switches for datacenter interconnect applications targeting a) 112 Gbaud per lane speed (i.e. up to 224 Gb/s using PAM4 modulation) and b) scalable ultra-fast optical switching.
WP2: Starting from the system requirements for short and longer distance datacenter interconnect links and in close monitoring of the industrial trends in WP7, TWILIGHT partners defined the specifications of the components for 1.6T optical transceivers and ultra-fast optical space switches. Initial system-level simulations were carried out based on reference components which were later updated with the components specs fed from fabrication and characterization activities. The necessary DSP tools including novel equalization techniques for high-speed performance evaluation of TWILIGHT transmitters and receivers were investigated and further optimized by means of machine learning algorithms. System-level simulations for deriving the high-level specifications of the optical space switches and on-chip semiconductor optical amplifiers (SOAs) were also performed.
WP3: The photonics components for the transmitters, receivers and switches were developed. An advanced Selective Area Growth (SAG) technology was implemented on InP membrane platform, enabling multiple MQW bandgaps on the same wafer (Figure 2). DFB lasers were designed and fabricated with stable operation and high side-mode-suppression ratio (SMSR) across a record wavelength tuning range (1458.9 to 1592.4 nm). Thermally shunted EMLs were designed and fabricated with significantly reduced thermal resistance and enhanced dissipation efficiency, improving the operation stability and longevity under high-power conditions. In addition, new thermal models and parameter extraction techniques were developed to assess and optimize device heating, allowing precise control over performance characteristics under various operating conditions. Two generations of UTC photodetectors were designed and fabricated (Figure 3) and a final run of UTC-PDs based on the developed co-integration process was designed and processed (see WP5 below). Finally, polarization insensitive semiconductor optical amplifiers (PI-SOAs) were designed and fabricated showing low polarization dependence. C-band 8x8 switch PICs based on different architectures were developed (Figure 4).
WP4: 0.5-µm InP DHBTs with improved performances have been developed demonstrating 450/530 GHz cut-off frequencies, along with a breakdown voltage above 4V. Based on this technology, a monolithically integrated analog multiplexer-driver (AMUX-driver) IC has been designed, fabricated and characterized demonstrating record performances up to 200 GSa/s operation in NRZ with a 1.4 Vppd output swing, without any support of DSP or equalization (Figure 5(a)). A second generation of AMUX-driver IC was designed and fabricated in the same technology and showed 4-Vppd at 100 Gb/s for NRZ modulation (Figure 5(b)). Both AMUX-driver IC generations show the highest performances in terms of driving efficiency with respect to the current state-of the-art. At the receiver side, standalone linear transimpedance amplifiers (TIAs) were designed and fabricated on the 0.5-µm InP DHBT process showing 50~GHz electrical bandwidth with 220 mVppd output swing at 64 Gb/s (Figure 6(a)). In addition, an analog demultiplexer (ADeMUX) was developed with good functionality at 50 GSa/s (Figure 6(b)).
WP5: TWILIGHT has achieved one of its most challenging and innovative milestones which is the development and validation of a significantly improved process flow for the co-integration of photonics and electronics components at wafer scale and for the first time for InP-to-InP technologies (Figure 7). Multiple co-integration tests were performed based on dedicated wafers of InP membranes and InP DHBTs to define the max temperatures and strain tolerated by the DHBTs. Post bonding alignment tests relying on soft-baked anchors achieved very high alignment accuracy (~ 2μm). Thermal studies for the co-integrated optoelectronic structure were carried out. RF Interconnection of photonics and electronics components was realized based on ultra-short vias minimizing parasitics. The developed process flow was validated by means of active dedicated wafers (Figure 8). Furthermore, the ceramics interposers for assembly of the optoelectronic chips were designed and fabricated. Further assembly was performed on the host PCB which was designed and developed to carry also the driving and control electronics and the DSP chip. Two variations of receiver modules were delivered on evaluation board suitable for testing with external test and measurement laboratory equipment (Figure 9 and Figure 10). The corresponding receiver PCBAs were prepared and tested (Figure 11 and Figure 12). Finally, the 8x8 switch modules were fully assembled on PCBA and tested (Figure 13).
WP6: Performance evaluation was carried out exploiting the developed DSP tools in WP2. A full high-speed testbed was setup capable of testing the TWILIGHT devices at 112 Gbaud and beyond. Preliminary experiments were carried out using existing high speed EMLs that were repackaged within TWILIGHT, yielding new performance records. In addition, a software orchestrator was generated to control the laboratory test and measurement equipment and to estimate semi-real time bit-error rate (BER). The receiver modules were tested under laboratory conditions with a commercial off-the-shelf modulator. Further evaluation was performed using a commercial 800G PAM4 ASIC.
WP7: The TWILIGHT partners have made substantial progress in tracking technology advances in the rapidly evolving datacenter application field and in identifying exploitation opportunities in the datacenter market. Each partner has elaborated on an exploitation plan whereas a supply chain has been outlined towards generating products through the project technology. IPR has been well managed with IPR reports generated and 2 patent applications prepared. Three innovations have been submitted to the EU Innovation Radar. The project has been very well disseminated through its website and social accounts and has produced up to now 68 publications. Overall, all dissemination KPIs have been achieved.
WP3: The photonics components for the transmitters, receivers and switches were developed. An advanced Selective Area Growth (SAG) technology was implemented on InP membrane platform, enabling multiple MQW bandgaps on the same wafer (Figure 2). DFB lasers were designed and fabricated with stable operation and high side-mode-suppression ratio (SMSR) across a record wavelength tuning range (1458.9 to 1592.4 nm). Thermally shunted EMLs were designed and fabricated with significantly reduced thermal resistance and enhanced dissipation efficiency, improving the operation stability and longevity under high-power conditions. In addition, new thermal models and parameter extraction techniques were developed to assess and optimize device heating, allowing precise control over performance characteristics under various operating conditions. Two generations of UTC photodetectors were designed and fabricated (Figure 3) and a final run of UTC-PDs based on the developed co-integration process was designed and processed (see WP5 below). Finally, polarization insensitive semiconductor optical amplifiers (PI-SOAs) were designed and fabricated showing low polarization dependence. C-band 8x8 switch PICs based on different architectures were developed (Figure 4).
WP4: 0.5-µm InP DHBTs with improved performances have been developed demonstrating 450/530 GHz cut-off frequencies, along with a breakdown voltage above 4V. Based on this technology, a monolithically integrated analog multiplexer-driver (AMUX-driver) IC has been designed, fabricated and characterized demonstrating record performances up to 200 GSa/s operation in NRZ with a 1.4 Vppd output swing, without any support of DSP or equalization (Figure 5(a)). A second generation of AMUX-driver IC was designed and fabricated in the same technology and showed 4-Vppd at 100 Gb/s for NRZ modulation (Figure 5(b)). Both AMUX-driver IC generations show the highest performances in terms of driving efficiency with respect to the current state-of the-art. At the receiver side, standalone linear transimpedance amplifiers (TIAs) were designed and fabricated on the 0.5-µm InP DHBT process showing 50~GHz electrical bandwidth with 220 mVppd output swing at 64 Gb/s (Figure 6(a)). In addition, an analog demultiplexer (ADeMUX) was developed with good functionality at 50 GSa/s (Figure 6(b)).
WP5: TWILIGHT has achieved one of its most challenging and innovative milestones which is the development and validation of a significantly improved process flow for the co-integration of photonics and electronics components at wafer scale and for the first time for InP-to-InP technologies (Figure 7). Multiple co-integration tests were performed based on dedicated wafers of InP membranes and InP DHBTs to define the max temperatures and strain tolerated by the DHBTs. Post bonding alignment tests relying on soft-baked anchors achieved very high alignment accuracy (~ 2μm). Thermal studies for the co-integrated optoelectronic structure were carried out. RF Interconnection of photonics and electronics components was realized based on ultra-short vias minimizing parasitics. The developed process flow was validated by means of active dedicated wafers (Figure 8). Furthermore, the ceramics interposers for assembly of the optoelectronic chips were designed and fabricated. Further assembly was performed on the host PCB which was designed and developed to carry also the driving and control electronics and the DSP chip. Two variations of receiver modules were delivered on evaluation board suitable for testing with external test and measurement laboratory equipment (Figure 9 and Figure 10). The corresponding receiver PCBAs were prepared and tested (Figure 11 and Figure 12). Finally, the 8x8 switch modules were fully assembled on PCBA and tested (Figure 13).
WP6: Performance evaluation was carried out exploiting the developed DSP tools in WP2. A full high-speed testbed was setup capable of testing the TWILIGHT devices at 112 Gbaud and beyond. Preliminary experiments were carried out using existing high speed EMLs that were repackaged within TWILIGHT, yielding new performance records. In addition, a software orchestrator was generated to control the laboratory test and measurement equipment and to estimate semi-real time bit-error rate (BER). The receiver modules were tested under laboratory conditions with a commercial off-the-shelf modulator. Further evaluation was performed using a commercial 800G PAM4 ASIC.
WP7: The TWILIGHT partners have made substantial progress in tracking technology advances in the rapidly evolving datacenter application field and in identifying exploitation opportunities in the datacenter market. Each partner has elaborated on an exploitation plan whereas a supply chain has been outlined towards generating products through the project technology. IPR has been well managed with IPR reports generated and 2 patent applications prepared. Three innovations have been submitted to the EU Innovation Radar. The project has been very well disseminated through its website and social accounts and has produced up to now 68 publications. Overall, all dissemination KPIs have been achieved.
TWILIGHT has advanced the state-of-the-art significantly with respect to the development of new processes, components and systems towards 1.6T co-packaged optical transceivers and scalable fast optical space switches for datacenter interconnect networks. Every partner has defined their exploitation strategy and the consortium value chain ensures a secure pathway of the developed technologies to the market. For the optical transceivers, cost analysis based on TWILIGHT technologies is in alignment with the 1.6 Tb/s transceiver cost estimates, assuming high volumes (~250k units per quarter). For the 8x8 switches, and assuming medium volumes (~1k units per quarter) a significant undercut of the cost/port pair with respect to commercial devices was estimated.