Coherent Optical Component Test Enables 1.2 Terabit Applications

Optics and Photonics

Coherent Optical Component Test

Enables 1.2 Terabit Applications

Company:

• NeoPhotonics, a designer and manufacturer of optoelectronic solutions for high-speed communication networks

Challenge:

• Difficult to assess new optical components and modules when DSP silicon availability is one year behind

Solutions:

• NeoPhotonics uses Keysight’s N4391A Optical Modulation Analyzer (OMA), M8196A Arbitrary Waveform Generator (AWG), and N4373D Lightwave Component Analyzer (LCA)

Results:

• Accelerated the development of 400G and 600G optical components and sub-assemblies by a year

NeoPhotonics Corporation designs and manufactures optoelectronic solutions for high-speed communication networks in telecom and data center applications. It develops high-speed optical components for 400G, 600G and beyond network communications including data center interconnects (DCI).

Generally, high-speed silicon that drives optical transceivers lags optics by about a year. While developing its latest coherent optical subassembly (COSA) designed for integration into an octal small form factor pluggable (OSFP) module, NeoPhotonics’ engineers worked with Keysight’s state-of-the-art test equipment to demonstrate the expected performance of their final module designs.

The Challenge

Optical coherent transmission technology, initially used in long-haul transmission, is evolving into metro networks and expanding to data center interconnects. Higher order quadrature amplitude modulation (QAM) signaling enables significantly faster data transmission rates and higher levels of spectral efficiency.

QAM is a two-dimensional modulation format that modulates both the phase and amplitude of the signal. QAM combines two carriers that have the same optical frequency but independently modulated amplitudes. The carriers are called in-phase (I) and quadrature (Q). The standard notation is 2n -QAM, with n-bits transmitted per symbol. For example, 16-QAM sends 4 bits per symbol, and 64-QAM sends 6 bits per symbol. The following formula is used to determine the bitrate:

Bitrate = symbol rate (symbols/sec) x coding (bits/symbol) x polarization (typically 2)

Using 16-QAM, a transceiver with a 64 gigabaud (GBaud) raw symbol rate (or 50 GBaud without the overhead) could transmit 400 gigabits per second (Gb/s) on a single channel.

The Optical Internetworking Forum (OIF) is developing the 400ZR implementation agreement (IA) for transmitting a 400 gigabit Ethernet (400GE) payload over data center interconnect links up to 120 km using dense wavelength division multiplexing (DWDM) and higher order modulation. The 400ZR specification recommends 16-QAM at a symbol rate of about 60 GBaud. Achieving this rate within a maximum power consumption of 15 W and considering the space constraints in the target form factors, optical transceivers require dense electronic and photonic integration with tighter specifications and performance margins for all components. These small form factors need small component sizes and low electrical power consumption. These restrictions create challenges for digital signal processor (DSP) and component suppliers. Although not defined by the 400ZR specification, optical transceivers should be in a small format such as octal small format pluggable (OSFP) or double density quad small form factor pluggable (DD-QSFP). NeoPhotonics aims to optimize its products in two directions: for very high speeds and small size. NeoPhotonics’ new COSA product combines its coherent receiver and modulator technologies in a single co-packaged part suitable for use in an OSFP form factor, and eventually also within a DD-QSFP form factor. Unfortunately, the DSP silicon for 400ZR transceivers was still a year out, and NeoPhotonics had no way of assessing its optical components, so they turned to Keysight for help.