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81195A Optical Modulation Generator Software

Data Sheets

81195A Optical Modulation Generator Software

Product Description

The latest developments in 200G, 400G and 1Tb coherent optical transmission systems are challenging test engineers. More and more flexibility is required to generate clean modulated signals as well as signal impairments to stress coherent receivers over multiple test scenarios.

The 81195A optical modulation generator software introduces an innovative soft-ware-defined test approach. It enables generation of dual-polarization complex modulated signals as well as elec-tronic synthesis of optical signal impairments such as phase noise, polarization rotation, and polarization mode dispersion (PMD), both in real time with M8195A or in a traditional waveform generation mode using M8195A, M8196A or M8194A Arbitrary waveform generators.

Combined with the M8195A 65 GSa/s arbitrary waveform generator hardware Digital Signal Processor functions it improves up to 100x the speed of test, the cost and the predictability of the output.

In traditional fiber transmission and optical receiver testing, which uses optical elements for stress conditioning, the stress conditions can only be changed in a stochastic way resulting in long test times.

In contrast, this new test approach allows you to generate and reproduce dynamic stress conditions with precise time evolution or stress statistics, increasing test coverage and reducing test time. The 81195A software in conjunction with a four-channel Keysight Technologies arbitrary waveform generator can generate cleanand distorted signals.

With the digital signal processing (DSP) block of the M8195A, the parameters of the waveform (e.g. the pulse-shaping filter coefficients) and the impairments can be adjusted at run time without downloading a new waveform. The real-time waveform generation enables deterministic emulation of optical signal properties over a long period of time, which previously has not been possible.

Key Features

– Waveform calculation for dual-polarization, complex modulated signals (up to 256QAM)

– Supporting hardware DSP in M8195A for real-time waveform generation

– Off-line waveform generation for M8196A, M8194A and multi-module M8195A AWGs setups

– Effective use of the available M8195A module memory in real-time waveform generation mode for complex modulated signals (up to 8 GSym per channel on two IQ channels simultaneously at up to 32.5 GBaud)

– Realistic emulation of optical signal properties and impairments, including phase noise, polarization mode dispersion, and polarization rotation over a long period of time

– Change signal properties, ‘on-the-fly’ without needing to re-calculate the entire waveform (saves valuable time during debug and characterization)

– Output triggers synchronized with impairment generation

– Corresponding analysis capabilities in the Keysight Technologies optical modulation analyzer portfolio

Waveform Creation Methods

The 81195A software provides two means of generating waveforms. As shown in the figure below, waveform mode creates them using software algorithms. Real-time mode uses the M8195A hardware DSP block to create the waveforms.

Each method has distinct benefits:

– In waveform mode

– A wide range of baud rates are available (real-time mode is limited to certain ranges)

– Signal waveforms with non-integer number of samples per symbol can be generated using waveform resampling

– In real-time mode

– Signal properties like pulse shaping parameters and signal impairments can be modified at run-time without need for re-calculating and re-downloading a new waveform, significantly reducing test time

– Real-time operation allows signal property generation and variation, such as polarization rotation, either as fast transients or slowly changing effects over a long period of time

– Trigger output, which is aligned with the signal impairment pattern, can be used to synchronize test equipment, e.g. time-to-error measurement with BERT

Real Time DSP Engine

The real time DSP engine on the AWG chip of the M8195A arbitrary waveform generator consists of a fixed concatenation of pre-defined DSP functions and FIR filters, with programmable coefficients. Coefficient memories of various sizes are available to change the DSP characteristic upon external triggering or according to a repetitive dynamic impairment pattern. Output triggers are generated in sync with the coefficient patterns.

PSK/QAM encoder

For the real-time DSP operation, the AWG memory stores the data pattern symbols which are then encoded using the PSK/QAM encoder based on reconfigurable look-up tables (LUT), instead of storing the pre-calculated waveform samples of the desired signal.

IQ rotator

The IQ rotator consists of two identical blocks where an instantaneous rotation angle, controlled from a pre-programmed coefficient pattern memory, is applied to the complex IQ signal for both the X and Y polarization, emulating, for example, carrier phase noise or a frequency offset.

Polarization controller

The polarization controller is a one-tap butterfly filter and alters the state of polarization (SOP) by acting like a concatenation of a circular and linear retarder. Rotation angle and retardation can be controlled from a pre-programmed pattern memory, which allows complex SOP trajectories on the Poincare sphere to be synthesized.

PMD emulator

Based on the model of multi-segment concatenation of birefringent elements, the PMD emulator block is a complex FIR butterfly structure in which its filter coefficients represent the optical channel’s PMD impulse response.

Pulse shaper FIR

For a spectrally efficient transmission channels, the data symbols can be filtered with a general 16-tap FIR filter to flexibly vary the pulse shaping such as raised or root-raised cosine or the roll-off factor.

Non-linear equalizer

The non-linear equalizer applies a non-linear transfer function based on a broken line approximation algorithm to the data signal, allowing, for example, the equalizer to compensate for the transfer characteristic of an electro-optical modulator.

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