Using the New Agilent 81495A O/E with Infiniium Real-time Oscilloscopes

1. Using the New Agilent 81495A O/E with Infiniium Real-time Oscilloscopes Group/Presentation Title Agilent Restricted

2. Have Your Customers Asked for an Optical Front-end for the Infiniium Real-time Scopes? • In Jan 2008, the DPT (PL3E) released a multi-mode version of the 81495A optical-to-electrical converter for the LMS (816xA/B) mainframes • The 81495A has a reference receiver response with a modulation bandwidth of 9 GHz 81495A module 8163B Lightwave Multi-meter Group/Presentation Title Agilent Restricted

3. 81495A Frequency Response • The linear transfer characteristics of the 81495A makes it a very suitable optical front-end for the real-time oscilloscopes. Group/Presentation Title Agilent Restricted

4. Basic Features of the 81495A • Fiber input: Standard Multi-mode 62.5µm/125µm with Agilent universal adapter connector. • Will accept both single-mode and multi-mode inputs • Wavelength: 750nm – 1650nm • Covers the main wavelengths: 850nm, 1310nm, 1550nm • Bandwidth up to 9 GHz allows optical data-rate measurements from 622Mb/s to 12.5Gb/s (filtered). • Make average power measurements on the LMS multi-meter. Group/Presentation Title Agilent Restricted

5. Two Types of Optical Measurement Needs • Unfiltered: • Customers who want to see the raw response of their optical transmissions • Basically scientist and researchers • The rise-time rule for required bandwidth applies to this kind of measurements • The bandwidth required to make these measurements depends on the rise-time • The 81495A has a Gaussian-like roll-off Unfiltered response of an 3.125Gbps optical signal Group/Presentation Title Agilent Restricted

6. Two Types of Optical Measurement Needs … continued • Filtered: • Customers who want to make industry standard optical measurements on their optical transmitters, basically for implementing data transmission designs. • The measurement system response is intentionally reduced in bandwidth in a highly controlled fashion • This provides for a consistent measurement method for characterizing optical transmitters • In addition, a reduced bandwidth receiver will behave similarly to receivers typically used in a real-world transmission system. • This controlled bandwidth reduction is achieved using a calibrated reference receiver Group/Presentation Title Agilent Restricted

7. Diagram Showing How Filtered Measurements are Made Unfiltered optical waveform Optical-to-electrical converter Low-pass filter Optical signal The Infiniium real time oscilloscope has software filters to take the place of a hardware filter for the optical waveform which can then be used to make measurements on Group/Presentation Title Agilent Restricted

8. A typical reference receiver follows a 4th order Bessel-Thompson low-pass response -3dB bandwidth is set to 75% of the optical bit-rate A reference receiver for a 2.5Gb/s system would have a bandwidth of 1.88 GHz Standards usually specify the upper and lower limits that the measurement system has to meet in order to be called a calibrated reference receiver. Calibrated Reference Receiver The figure above shows a sample frequency response plot of an HP83485A OC-48 measurement module. Group/Presentation Title Agilent Restricted

9. How do we set up the Oscilloscope to make optical measurements? • Optical measurements are typically made in units of power (watts) • The most basic information that is needed is the optical-to-electrical conversion ratio, also known as conversion gain. This number specifies how much optical power is represented by the output voltage of the O/E. • Different optical wave-lengths have different optical-to-electrical conversion ratios Table from the 81495A data sheet showing the conversion ratios at different wavelengths Group/Presentation Title Agilent Restricted

10. Configuring the Oscilloscope • Open the Channel Setup dialog by clicking on the channel button indicated below. We are using channel 2 as an example. Click Here Then Click Here Group/Presentation Title Agilent Restricted

11. Probe Configuration • Click on Configure Probing System, turn on External Scaling. • Under External Scaling, change the Units to Watt, and then input the conversion gain as desired. Group/Presentation Title Agilent Restricted

12. Next: The Channel Setup Dialog will reflect the changes Group/Presentation Title Agilent Restricted

13. Channel Behavior Setup • Because optical signals are DC-coupled – the signals are all seen to be offset above the ground reference. • There is no negative optical power • Adjusting the vertical Volts/div knob should expand the waveform about the ground reference Ground reference Group/Presentation Title Agilent Restricted

14. To Turn on Low Pass Filters • Because the source used in this example is a 3.125 Gbps signal, I will turn on a Low Pass Filter function on the oscilloscope. • The Low Pass Filter Function on the oscilloscope is a 4th order Bessel-Thompson filter, which is suitable for filtering optical signals. Group/Presentation Title Agilent Restricted

15. Settings of the Low Pass Filter 0.75 * 3.125 Gbps Group/Presentation Title Agilent Restricted

16. Screenshot after turning on Low Pass Filter function Group/Presentation Title Agilent Restricted

17. Screenshot after turning off the source channel, to only see the filtered data. Group/Presentation Title Agilent Restricted

18. Screenshot of eye diagram using the Serial Data Analysis CR Settings: 1st Order PLL, 1.875 MHz loop bandwidth (Data-rate/1667) Group/Presentation Title Agilent Restricted

19. Turning on color-graded display. Group/Presentation Title Agilent Restricted

20. Using Histogram to analyze the optical eye diagram The “Mode” is the peak of the Histogram. The “1” level is 3.210 mW Group/Presentation Title Agilent Restricted

21. Using Histogram to analyze eye diagram, continued. The “0” level is 347 uW. Rough calculation for ER or OMA can be done. Group/Presentation Title Agilent Restricted

22. Typical Optical Measurements • Extinction Ratio (ER) with Dark Calibration • Ratio of the energy (power) used to transmit a logic level ‘1’, to the energy used to transmit a logic level ‘0’. • Dark calibration is the process of factoring out the power transmitted by the O/E when there is no light being transmitted. Typically, the optical input of the O/E is covered, and the optical power reading is stored. This reading is then subtracted from the measurements of the logic levels “1’ and ‘0’. Group/Presentation Title Agilent Restricted

23. Dark Calibration example • Use the Vavg (Entire Display) measurement to measure the optical power when there is no input into the O/E. • Averaging can be used to improve accuracy. Group/Presentation Title Agilent Restricted

24. Optical Measurements .. continued • Optical Modulation Amplitude (OMA) • OMA represents the separation between the logic ‘1’ and logic ‘0’ levels. The difference between these 2 levels describes the modulation power of the signal. The larger the modulation power, the easier it is for the system receiver to accurately determine the logic signal. • OMA = Logic ‘1’ power level – Logic ‘0’ power level Group/Presentation Title Agilent Restricted

25. Demos at FOE 2008 (Japan)OFC 2008 and ECOC 2008 (BELGIUM) The demo on the left was displayed at FOE Japan (Jan 2008) The demo in the bottom picture was displayed at ECOC 2008 BELGIUM Group/Presentation Title Agilent Restricted

26. References • 81495A Reference Receiver – http://www.agilent.com/find/ref • Data Sheet pub number: 5989-7536EN • Agilent Application Note 1550-8, Measuring Extinction Ratio of Optical Transmitters, Pub number: 5966-4316E • Agilent Application Note 1550-9, Improving the Accuracy of Optical Transceivers Extinction Ratio Measurements, Pub number: 5989-2602EN Group/Presentation Title Agilent Restricted