PAM4 dominates equipment design test at OFC 2018

Test equipment suppliers must keep at least one step ahead of their technology design customers. The right test capabilities must be available to enable designers to beat their competitors to market with products that meet emerging standards or anticipate new user requirements. Thus, with several module vendors using OFC 2018 to demonstrate their first 400 Gigabit Ethernet modules, as well as derivative products such as single-lambda 100G QSF28 devices, it's not surprising that PAM4 test capabilities dominated the booths of test instrument suppliers in San Diego.

Test equipment suppliers must keep at least one step ahead of their technology design customers. The right test capabilities must be available to enable designers to beat their competitors to market with products that meet emerging standards or anticipate new user requirements. Thus, with several module vendors using OFC 2018 to demonstrate their first 400 Gigabit Ethernet modules, as well as derivative products such as single-lambda 100G QSF28 devices, it's not surprising that PAM4 test capabilities dominated the booths of test instrument suppliers in San Diego. Test companies demonstrated their high-speed Ethernet chops as well by taking part in interoperability demonstrations conducted by the Ethernet Alliance and OIF.

These interops, as intended, showed how well both the IEEE 802.3bs 400 Gigabit Ethernet specifications and OIF FlexE 1.1 Implementation Agreement have led to compatible products from multiple vendors. Test vendors that participated in the combined demos (as well as other demos, particularly in the OIF booth) included Anritsu, EXFO, Keysight Technologies, Spirent Communications, Tektronix, Teledyne LeCroy, and VIAVI Solutions.

Meanwhile, equipment developers looking for the right test tool for their requirements also likely visited the inaugural Test and Measurement Resource. The display and demonstration area featured test gear for both network and lab requirements. Companies highlighting or discussing instruments or services for technology designers included Anritsu, Arden Photonics, EXFO, Experior Laboratories, Fiberpro, Finisar, JGR, Keysight Technologies, Luna, OptoTest, OZ Optics, Photon Kinetics, Santec, VIAVI Solutions, and Yokogawa. For a full list of participants in the Test and Measurement Resource Center, see "Test and Measurement Resource Center debuts at OFC 2018."

Keeping up with PAM4

The introduction of PAM4 to optical communications, and specifically to the applications IEEE 802.3bs covers, means the introduction of new test procedures. These procedures include new ways to measure extinction ratio and optical modulation amplitude. But the biggest measurement change for equipment designers is Transmission Dispersion and Eye Closure Quaternary (TDECQ), a procedure that replaces both eye mask testing as well as traditional Transmitter Dispersion Penalty (TDP) measurements (see "Optical technology designers add TDECQ to their test lexicon"). TDECQ procedures evolved significantly during the 802.3bs specification process – and likely will continue to do so, according to sources on the show floor in San Diego.

Several announcements highlighted efforts to make PAM4 testing easier, more accurate, and less expensive:

  • Anritsu showed its how its BERTWave MP2110A and MP1900A 56G PAM4 BERT could combine to provide TDECQ measurements for 400-Gbps optical chips and modules. It also highlighted use of the MP1900A, MP2110A, and G0375A PAM4 Encoder to enable victim/aggressor tests on 400G OSFP direct attach copper cable (DAC) and module compliance boards.
  • Keysight Technologies saw several of its instruments used to demonstrate PAM4-based capabilities. For example, Accelink Technologies was revealed to have used Keysight's N1092A DCA-M Sampling Oscilloscope with a N1077A Clock Recovery (CR) unit as well as M8040A High-Performance BERT to develop its 100G single-lambda DR1 module. Similarly, Applied Optoelectronics, Inc. was named as a customer for Keysight's N1092C DCA-M and 86100D DCA-X mainframe with 86116C optical electrical module, which the company used in the development of its single-lambda 100G DR1 device. Meanwhile, MaxLinear showed off the capabilities of its 400-Gbps transceiver chipset with the help of Keysight's N1092A Digital Communications Analyzer and M8196A Arbitrary Waveform Generator.
  • Tektronix upgraded the PAM4 capabilities of its DPO70000SX Series real-time oscilloscopes for design applications. The 59-GHz DPO7OE2 single-mode optical probe offers increased bandwidth over the earlier 33-GHz DPO7OE2 probe, enabling access to the benefits of real-time scopes for 400G PAM4 applications. The company also announced a pair of optical modules and software-based 400G PAM4 TDECQ measurement capabilities for use with the DSA8300 equivalent-time oscilloscope, particularly for manufacturing and production applications.

More on the floor

While most of the test news for equipment designers focused on PAM4, those working on line-side coherent applications weren't ignored. The emphasis here was on meeting the requirements for 64 GBaud and higher capabilities. While it was listing PAM4 customers, Keysight also included the news that engineers at NeoPhotonics used the test systems vendor's N4391A Optical Modulation Analyzer (OMA), M8196A Arbitrary Waveform Generator (AWG), and N4373D Lightwave Component Analyzer (LCA) as they developed NeoPhotonics' line of 64-GBaud coherent optical components (see, for example, "NeoPhotonics shipping 64-GBaud coherent optical components for 600-Gbps, 1.2-Tbps designs"). Other vendors of coherent transmission test suites, including Tektronix and Teledyne LeCroy, showed off similar capabilities. With companies such as Infinera discussing plans to move to 100 GBaud, it would seem these test vendors have more R&D in their future.

Outside of PAM4 and coherent, there were other announcements at OFC 2018 designed to catch the eye of technology designers:

  • Bristol Instruments unveiled the 828A Optical Wavelength Meter. The instrument uses a Fizeau etalon design to measure the absolute wavelength of CW and modulated optical signals to an accuracy as high as ± 0.3 pm (see "Bristol Instruments offers 828A Optical Wavelength Meter for CW and modulated optical signals").
  • Coherent Solutions and National Instruments displayed the results of a collaboration focused on PXI. The new range of PXI optical test modules is designed to complement National Instruments' PXI instruments for mixed-signal test applications.
  • EXFO revealed they have leveraged last year's acquisition of Yenista Optics to relaunch the CTP10 Component Test Platform for component characterization applications, including those that involve photonic integrated circuits (PICs). Yenista had debuted the original version of the CTP10 at OFC 2017.
  • VeEX introduced the RXT-6200 Universal 100G Test Module for the company's RXT-1200 test platform. The module features CFP4, dual QSFP28/QSFP+, dual SFP28/SFP+/SFP optical transceiver ports, as well as standard legacy electrical interfaces, for use in a wide variety of applications, including the lab.
  • VIAVI Solutions announced a collaboration with Microsemi that combines the former's ONT-600 with the latter's DIGI-G5 Optical Transport Network (OTN) processor to provide a pathway toward development of optical network hardware that will support OTUCn, Flexible OTN (FlexO), and Flexible Ethernet (FlexE). The ONT-600 provides test support of each of these transmission formats, as well as a wide range of 400 Gigabit Ethernet module form factors.

Such announcements represent only a sampling of the test and measurement activity on the show floor of OFC 2018. But they indicate the variety of initiatives underway to meet the increasingly complex requirements of optical communciations technology developers.

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