Coherent Optical Subassembly (COSA)
Coherent optical front ends powered by silicon photonic integrated circuits
What is a Coherent Optical Subassembly (COSA)?
A Coherent Optical Subassembly (COSA) is a compact optical front-end that enables a coherent transceiver to transmit and receive high-speed data over fiber networks.
In the transmit direction, it converts electrical signals from a coherent Digital Signal Processor (DSP) into modulated optical signals, usually with the use of an external laser. In the receive direction, it translates the incoming light into electrical signals for the DSP to decode.
A COSA typically integrates:
- Photonics, including Mach-Zehnder modulators and photodetectors.
- RF integrated circuits, including modulator drivers and transimpedance amplifiers.
Nokia CSTAR™ COSAs, designed for pluggable and embedded digital coherent optics (DCO), are implemented in silicon photonics (SiPh). This technology enables large-scale integration of optical functions, leveraging standard CMOS manufacturing and the global semiconductor ecosystem for cost-efficient, high-volume production. SiPh supports uncooled, non-hermetic packaging and close co-packaging with electronic ASICs (such as DSPs, switches, and compute chips), reducing interconnect losses and power consumption. SiPh can also serve as a platform for heterogeneous integration, combining native silicon with materials like Thin-Film Lithium Niobate (TFLN) and Indium Phosphide (InP) to maximize bandwidth and performance.
What are the benefits of Nokia CSTAR SiPh COSAs?
Performance
Maximize wavelength capacity, achieved with the co-design, co-packaging and high-density integration of SIPh/hybrid integrated circuits and mixed-signal RF integrated circuits.
Efficiency
Leverage SiPh and advanced ASIC fabrication to deliver low power consumption in a compact, low-cost footprint, with fast development and manufacturing plus proven reliability from established silicon foundry processes.
Ease of integration
Simplify transceiver assembly and enable quick and easy deployment into DCOs in various embedded and pluggable form factors.
Products
Nokia CSTAR optics are available as stand-alone COSA modules, for third-party integration into pluggable or embedded DCO applications.
They can be combined with an external amplifier/laser source, and with Nokia Coherent Digital Signal Processors or with third party DSPs.
CSTAR™-800 module
The CSTAR-800 is a compact integrated coherent optical front-end featuring a heterogenous SiPh/TFLN transmit and receive photonic integrated circuit (PIC). It integrates drivers and transimpedance amplifiers (TIAs) in a non-hermetic package, for use in 800Gb/s high-performance DCOs, and operating at Baud rates up to 135 Gbaud.
CSTAR-800 is ideally suited for high-capacity pluggable optics applications such as data center interconnect (DCI) and metro, regional and long-haul transport applications. It is designed for up to +3dBm Tx output power with an external EDFA & ITLA and supports C- and Super C-band operation.
CSTAR-800 is designed for OSFP form factors and available for integration into 800Gb/s modules. It and can be combined with the Nokia Tahoe DSP or with a third-party coherent DSP.
CSTAR™-400 module
The CSTAR™-400 is a small form factor BGA packaged, DSP-agnostic Silicon Photonics COSA transmitter and receiver operating up to 67Gbaud and optimized for use in 400G DCOs. The CSTAR-400 is designed with high density and low power to enable integration into QSFP-DD, OSFP and CFP2 pluggable form factors. CSTAR-400 is ideally suited for high-capacity pluggable optics applications such as data center interconnect (DCI) and metro, regional and long-haul transport applications. CSTAR™-400 is available for integration into 400Gb/s DCO modules.
CSTAR™-200+ module
The CSTAR™-200+ is a small form factor, Ball Grid Array (BGA) packaged Silicon Photonics COSA transmitter and receiver for use in 100G/200G DCOs operating up to 34Gbaud. The CSTAR-200+ is designed with high density and low power to enable integration into QSFP-DD, OSFP and CFP2 pluggable form factors for use in 5G fronthaul, access, metro, regional and long-haul applications, or for use in 100/200Gb/s coherent embedded transponders.
Nokia CSTAR SiPh COSAs
Offering large-scale integration of a wide range of optical functions and enabling high-performing devices.
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