PAS Lambda Scan Engine: Wavelength-dependence Test Solution

Introduction

The Lambda Scan (LS) engine is the primary measurement software in the Keysight Photonic Applications Suite (PAS) for measuring wavelength and polarization dependence. Measurements using signals from continuously-swept tunable lasers are controlled and automated. This guide describes configurations for testing optical-to-optical and optical-to-electrical fiberoptic components.

Background

The LS software engine is the successor to the PAS IL/PDL engine and FSIL engine and benefits from years of development in close cooperation with users working in R&D and manufacturing of components for fiberoptic networks. Features that were in either of those two engines are now implemented together in LS, as well as measurement of DGD and PMD. Support for more and newer instruments and greater flexibility in choosing measurement parameters have been included while keeping a high level of compatibility in the GUI and automation interfaces to make migration from the earlier software engines easy.

Generalized Configuration Outline

A basic configuration for the measurement setup is shown in Figure 1, that can be generalized with the following outline to choose the best arrangement for a particular application. Different software licenses are also adapted to the application.

1.     Tunable laser source for wavelength scans at constant sweep speeds from 0.5 nm/s to 200 nm/s (expandable to switch 2 or 3 TLS for extended wavelength coverage)

2.     Polarization control, only if polarization dependence is needed, to stabilize or switch the polarization rapidly and repeatedly while the wavelength is scanned

3.     Detection instruments (optical power meter, photocurrent meter: SMU, or polarimeter) to measure signal from the device under test, DUT, in response to input optical signal, often multiple channels

4.     LS software engine to synchronize setup, run measurements and analyze results.

Tunable laser source configuration

The selection of the tunable laser models is based primarily on the desired wavelength range and required wavelength accuracy, using models that support continuous-sweep measurements. These are measurements made while the laser scans the wavelength at a constant speed, while regulating power, triggering the sampling and logging the internally measured wavelength values. The most current models are:

• N7776C, specified with ± 1.5 pm / ± 1 pm absolute/relative wavelength uncertainty or

• N7778C, specified with ± 10 pm / ± 5 pm absolute/relative wavelength uncertainty

Wavelength range options for these models are:

• Option 113: 1240 to 1380 nm

• Option 114: 1340 to 1495 nm

• Option 116: 1490 to 1640 nm

• Option 216: 1450 to 1650 nm

Equivalent laser sources in the older modular style are the:

• 81606A (like N7776C)

• 81608A (like N7778C)

• 81607A with intermediate performance and lower power for Option 116 only

• 81602A for extra high power level up to above +18 dBm at the peak-power wavelength and covering 1250 to 1370 nm (Option 013 only). The 81602A does not have the very low spontaneous emission level that is often desired for measuring spectra with high dynamic range, like wavelength multiplexers.

Older modular laser models may also be used with the software, if available. Please refer to the Technical Overview for a list of supported models. www.keysight.com/find/n7700 Generally the newer models are advantageous with higher maximum sweep speeds and use of wavelength scans in both directions, as well as support for more data points and faster data transfer.

The configuration can include more than one TLS instrument to extend the wavelength range. A combination of options 113, 114 and 116 provides gapless coverage from 1240 to 1640 nm.