N4917B Optical Receiver Stress Test Solution

Keysight Technologies

N4917B Optical Receiver Stress Test Solution

100GBASE-LR4/ER4/SR4 and 100G MSAs

Solution Brochure

Repeatable Optical Receiver Stress Test for 100GBASE-LR4/ER4/SR4 and 100G Multi Source Agreements

In recent years, transmission speeds in gigabit ethernet have continously increased from 10 Gb/s to 40 Gb/s and are now approaching the 100 Gb/s speed class. 10 Gb/s Ethernet was designed based on a 10.3125 Gb/s line rate on one single-mode fiber per direction. The 40 Gb/s Ethernet speed class changed this to an architecture using the same 10.3125 Gb/s line rate but using four optical wavelengths in the O-Band on one single-mode fiber per direction. This increased the transmission capacity by a factor of four, without a need to make changes to the speed of the electrical components. In the last few years the 100 Gb/s speed class has been established, increasing the electrical line rate from 10.3125 Gb/s to 25.78125 Gb/s. It also uses both four optical wavelengths on one fiber as well as multiple fibers with one optical wavelength per fiber.

The conformance test specification for 100 Gb/s transmission speed class is defined in the IEEE 802.3 standard, clause 88 for 100 Gb/s Ethernet long reach (LR4) and extended reach (ER4) and clause 95 for 100 Gb/s Ethernet short reach (SR4). Several Multi-Source Agreements (MSAs) leverage on the IEEE test procedures to define interface specifications for particular applications.

The N4917B optical receiver stress test solution provides an automated stressed receiver sensitivity test in accordance with the 100GBASE-LR4, ER4 and SR4 and CLR4, CWDM4 and 4WDM MSAs test specifications. In order to do this kind of test, several test instruments such as a bit error ratio tester, digital sampling oscilloscope, optical reference transmitter and tunable laser source are required to operate together to achieve a compliant, repeatable optical stressed eye. This stressed eye is then fed to the receiver under test, where bit error ratio is measured under the stress conditions as defined in the standard.

The N4917B solution provides:

• Automated calibration of the optical stressed eye according to IEEE 802.3 clause 88 and 95, and 100G-CLR4 MSA, 100G CWDM4 MSA, 100G 4WDM-10/-20/40 MSA.
• Calibration of ER, VECP/SEC, J2, J4, J9, OMA parameters
• Repeatable results
• Adjustable target values for ER, VECP/SEC, J2, J4, J9, OMA
• Jitter tolerance compliance and margin test
• Electrical loop back or optional DUT control interface for full automated JTOL test
• Remote control of all the test instrumentation
• For this, the N4917B includes the following key equipment:
• a high performance bit-error-rate tester
• an optical reference transmitter for 25.78125 Gb/s
• a tunable laser covering the O-band for LR4/ER4 and 100G MSAs, or an 850 nm laser for SR4

Optical Stress Test Typical Setup

The N4917B optical receiver stress test solution consists of a BERT plus a sinewave generator for electrical signal and stress generation; an electro-optical converter that modulates the optical signal and a digital sampling oscilloscope/CDR which is required for calibration of the stressed eye. Example setups for single and multimode variants are shown in the figures below. See the configuration guide for a full list of supported instruments.

Setting up a stressed eye according to the standard can be a very time consuming task, even for experienced users it can take a half day. The reason is that the stressed eye parameters are interdependent and therefore several iterations of the optimization cycle are required to converge on the solution. In addition, it is important that the setup is repeatable and remains stable from the time of the stressed eye calibration through to the end of the DUT measurement. Otherwise a drift in the test setup, especially in the electro-optical converter will impair the test results.

The N4917B optical receiver stress test solution provides a repeatable and stable measurement in a fraction of time compared to manual setup of the stressed eye. This offers major time saving during daily measurements and speeds up developing a standard compliant test solution when compared to a self made solution.

N4917B Detailed Test Setup

After the calibration step, each lane of the DUT should be tested in turn, with valid signals present on the other lanes. Exact connection details and setup depend on the type of device being tested. A couple of examples are shown below.

LR4 Transceiver Test

In this example an optical de-multiplexer is used to bring out the four lanes on four individual fibers. Attenuators in each lane are used to set the relative optical modulation amplitude (OMA) with respect to the lane under test. The calibrated stressed eye signal is connected to the lane under test at the optical mulitplexer which combines all four lanes onto one fiber.

BER measurement during the Jitter Tolereance test sweep can either be read from the device under test or optionally looped back to the BERT for fully automated JTOL testing.