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Optical sub-systems: powering the next generation of coherent transport

How DSPs and silicon photonics enable the next generation of coherent transceivers

At the heart of our next-generation Photonic Service Engines (PSE), our vertically integrated optical sub-systems are advancing coherent transport technology and powering urgently needed optical network scaling. They incorporate our latest coherent digital signal processors (DSPs) and silicon photonic (SiP) optical front-ends for increased baud rates, enhanced performance, lower power per bit, smaller form factors, and improved integration.

Our optical subsystems are powered by advanced electro-optics solutions like our super-coherent DSPs, optimized for maximum performance, or compact DSPs, optimized for low power applications and in pluggable modules. Our  CSTAR (TM) silicon photonic (SiP) modules provide a coherent optical subassembly (COSA) optical front-end for use in both pluggable and embedded digital coherent optics (DCO) transceiver modules. Our CSTAR modules are used in both Nokia and third-party pluggable DCOs to power 100, 400 and 800Gb/s DCOs in QSFP-DD and CFP2 form factors, as well as powering the optics for our high-performance super-coherent PSEs.

How do coherent DSPs enable more scale and performance?

Introduced just over a decade ago, coherent transport technology has achieved a remarkable 100-fold increase in wavelength speed. Sustained progress across six generations of coherent optics has enabled us to scale fiber capacity and increase transmission distance, all while reducing power per bit.

Coherent optics relies on the use of digital signal processors (DSPs) and the application of phase modulation techniques to shape the optical signals generated by optical front-ends. Instead of simply turning the laser transmitting data on or off, coherent transmission modulates the periodic waveform, or carrier signal, making it possible to encode more data per wavelength.

The digital-to-analog modulation is implemented using a DSP. In transmitting mode, the DSP converts the electronic digital data, the “zeros” and “ones” that encode the information, by applying sophisticated coherent modem algorithms to modulate the phase, amplitude and polarization of the carrier signal waveform. The re-encoded information, now embedded in the modulated signal waveform, is received by a DSP at the other end of the optical fiber, which de-modulates it back into the original digital data. 


Our extended pedigree of internally developed coherent DSPs have enabled many “firsts” for optical transport networks. We were the first to introduce 100Gb/s coherent optics, which provided a 10x increase in data transmission speed over a single wavelength compared to 10Gb/s on-off keyed (OOK) optics that were the norm. Since then, we have introduced the industry’s first probabilistic constellation shaping (PCS) algorithms, which allow continuous optimization of coherent modulation, and the first continuously tunable baud rate, to maximize spectral efficiency. We led the industry transformation to application-optimized coherent optics, whether for ultimate capacity and reach performance, or optimized for low power applications in pluggable transceivers for metro and regional applications.

Whether measured in bits per second, spectral efficiency or capacity-reach, coherent optics have enabled exponential increases in wavelength speeds. They have increased all-optical transmission reach from hundreds to tens of thousands of kilometers. Our sixth generation super-coherent Photonic Service Engine, the PSE-6s, drives wavelength speeds to 1.2 Terabits per second and ushers in new frontiers in network scale, performance and sustainability. The sixth-generation Compact PSE (PSE-6c) extends these benefits to low-power 800G pluggable coherent optics  for use in metro and regional applications across optical transport and routing platforms. 

Silicon Photonics CSTAR

Silicon Photonics CSTAR optics are used either as stand-alone COSA modules or in integrated multi-chip modules. They provide the optical front end for coherent transceivers


Photonic Service Engine pluggable DCOs  deliver electro-optic integrated modules in standardized pluggable QSFP and CFP2 form factors

PSE-6 super-coherent 130Gbaud DCOs

PSE-6 super-coherent 130Gbaud DCOs deliver record scale and performance in real-world optical networks, and have demonstrated 800Gb/s single wavelength transport over trans-oceanic distances subsea links

How Silicon Photonics enable the next generation of coherent transceivers

Our Silicon Photonics provide a revolutionary technology platform to enable large-scale integration and scaling of a wide range of optical functions — similar to how electronic ASIC integration has increased exponentially over the past 40 years.

Silicon photonics benefit from leveraging the same advanced capabilities of electronic ASIC fabrication facilities. They create highly integrated photonic circuits and devices with world-leading performance. They also enjoy faster development and manufacturing timelines than is possible with traditional optical materials technologies.


Silicon photonics enable complex opto-electronic functions using well-established silicon foundry processes

Our Silicon Photonics are used to power our range of CSTAR optics modules, which are then integrated with application-optimized coherent DSPs to implement sophisticated coherent modem and signal processing algorithms that optimize for maximum performance and lowest power.

Silicon Photonics integrate the complex optical, opto-electronic and electronic functions needed in a coherent transceiver, otherwise unachievable using discrete devices. The co-design, co-packaging and multi-chip integration of silicon photonic integrated circuits (SiP ICs), mixed-signal RF integrated circuits (RFICs), and coherent DSPs enables the high-performance, high density, low power consumption, and low cost needed for high data rate transceivers operating at speeds of 400Gb/s, 800Gb/s, 1.2Tb/s and beyond.


Optical Transmitter/Receiver Optics


The CSTAR™-200+ is a small form factor, 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 as a COSA module for use in 100/200G coherent on-board optics.



CSTAR™-400 is a next-generation, small form factor BGA packaged, DSP-agnostic Silicon Photonics COSA transmitter and receiver operating up to 69Gbaud 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, and for integration into third-party 400G DCO modules.