Lightwave Catalog: 2015 Bit Error Ratio and Waveform Analysis Volume 3 - Catalog

The Keysight Technologies, Inc. J-BERT M8020A is the first in a series of new BER test solutions. It enables fast, accurate receiver characterization of single- and multi-lane devices. With today’s highest level of integration, this J-BERT stream -lines your test setup. In addition, automated in-situ calibration of signal conditions ensures accurate and repeatable measurements. An interactive link training allows the M8020A to behave like a real partner.

Keysight J-BERT M8020A high performance BERT

• Data rates up to 16 Gb/s and 32 Gb/s
• Scalable from 1 to 4 BERT channels
• Integrated jitter interference, 8-tap de-emphasis
• Interactive link training
• Built-in clock recovery and equalization

Introduction

Manufacturers of optical transceivers are faced with increasing challenges to their businesses, particularly how to reduce product cost. Pressures to reduce cost as data rates rise means manufacturing engineering managers and their engineers must be more creative in how to reduce costs before their competitors do. Traditional methods of eliminating tests or trying to make tests run faster may not be feasible, may not yield the intended benefit or may provide results that don’t agree well with their customer’s measurements. The use of parallel testing promises huge improvements, but more innovation is needed. Read below, how Keysight helps to optimize the manufacturing processes of optical components.

Common transceiver types and manufacturing flows

The number of communications standards and transceiver types has proliferated during the last decade creating more complexity for the typical manufacturing test facility. Mass market and other high volume transceivers typically have fewer tests and less temperature cycling. More complex transceivers at higher data rates have more extensive tuning, temperature cycling and challenges to meet high desired yields.

The ultimate goal of Keysight’s approach is to provide a sufficiently accurate answer, very quickly, which is enabled by these recently introduced capabilities:

• DCA with parallel characterization of multiple devices, or characterization of parallel optics, Improved autoscale performance, eye tuning, rapid eye, faster eye mask testing
• Multi-channel BERTs for characterizing multi-channel devices and multi-channel standards (4 x 25 G)
• Great improvements in cost of test are achieved by testing multiple transceivers in parallel, either several single channel transmitters at once or several channels on a multi-channel transmitter
• Multi-port optical attenuator with up to four separate attenuators that are settable in parallel and provide fast settling times, a significant improvement in both multi-device and multi-lane testing
• Newly designed attenuation devices that ensure high modal fidelity in multimode fiber based transceiver testing, a contribution to narrower test margins and thus better yield

Implementing these innovations in your production line can improve by 2X to 10X the number of units tested per station per year, and result in a 2X to 5X improvement in the cost-of-test per transmitter.

Applications:

Optical Receiver Stress Test

The fundamental test for these network elements is the bit error ratio, demonstrating reliable operation in digital data transmission systems and networks. The basic principle is simple: the known transmitted bits are compared with the received bits over a transmission link including the device under test. The bit errors are counted and compared with the total number of bits to give the bit error ratio (BER). The applied test data signal can be degraded with defined stress parameters, like transmission line loss, horizontal and vertical distortion to emulate worst-case operation scenarios at which the device under test has to successfully demonstrate error free data transmission. Obviously, this test is of fundamental importance for receiving network elements, due to the manifold impairments occurring on optical transmission lines. Therefore, many all optical transmission standards define such stressed receiver sensitivity on the basis of a BER measurement. The basic test methods and setups are usually very similar. However, the test conditions, the stress parameters or methods of stress generation vary from standard to standard, depending on the application area, transmission medium, data rate or data protocol.

Oscilloscope:

Use clean, un-jittered clock to verify stressed signal.

Optical receiver devices, especially those for data rates in the higher Gbps-range, are commonly exposed to extensive stressed receiver sensitivity tests during their design and qualification phase to verify their performance and to determine their margin against the requirements. The BER is measured under standard compliant stressed conditions at various optical modulation amplitudes (OMA) to BER down to 10-12 or lower. In the manufacturing phase, BER tests are performed at a few different OMA points down to only BER of 10-9 to reduce test time and cost. Applying this reduced test scheme in series implies that the device manufacturer knows very well the device margins. This leads to the requirements for a test solution with high accuracy and reproducibility regarding the stressed test signal generation. For the optical part of the stressed signal generation, this means maintaining high signal fidelity. This demand may lead especially for multimode fiber devices to some interesting test challenges. This catalog covers the test equipment needed to perform these tests. Get more detail about Keysight’s N4917A Optical Receiver Stress Test Solution on page 30.

There are three topologies in this type of network including point-to-point, arbitrated loop, and switched fabric. The connections between devices use transceivers for optimization. For example, in a switched fabric topology, SFP+ (8 GFC and 16 GFC), XFP (10 Gb/s) and SFP (≤ 4 Gb/s) are types of transceivers that connect between the switched fabric and various devices such as storage and computing equipment. Typical patterns used to test transceiver devices include PRBS series, JSPAT, and K28 series which are part of the preloaded library of patterns in the N4960A 32 G BERT.

For 16 GFC applications (14.025 Gb/s), the N4960A can perform BER measurements and can provide a stressed pattern generator signal for receiver tests. 16 GFC devices must be accurately characterized to strict tolerances. The N4960A, used with the N4980A multi-instrument BERT software, can also provide jitter tolerance tests for accurate characterization.

Transmitter compliance testing and eye-diagram analysis

Viewing the eye-diagram is the most common method to characterize the quality of a high-speed digital transmitter signal. Industry standards such as SONET, SDH, Fibre Channel and Ethernet rely on eye-diagram analysis to confirm transmitter specifications. The eye is examined for mask margin, amplitude, extinction ratio and overall quality. Tests are commonly performed using a well defined reference receiver to provide consistent results both in manufacturing test, incoming inspection, and system level applications. Standards based reference receivers and test procedures are built into the DCA’s to provide compliance test capability.