group/presentation title agilent restricted month ##, 200x using the new agilent 81495a o/e with...

Group/Presentation TitleAgilent Restricted Month ##, 200X

Using the New Agilent 81495A O/E with

Infiniium Real-time Oscilloscopes


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


81495A Frequency Response

81495A opt.085DE47900007

-35

-30

-25

-20

-15

-10

-5

0

5

0.0E

+00

5.0E

+09

1.0E

+10

1.5E

+10

2.0E

+10

2.5E

+10

Frequency [Hz]

rel.

Am

pli

tud

e [d

B]

SN007 @ 25°C

SN007 @ 0°C

SN007 @ 45°C

• The linear transfer characteristics of the 81495A makes it a very suitable optical front-end for the real-time oscilloscopes.


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.


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


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


Diagram Showing How Filtered Measurements are Made

Optical-to-electricalconverter

Low-passfilter

Opticalsignal

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

Unfiltered optical

waveform


Calibrated Reference Receiver

• 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.

The figure above shows a sample frequency response plot of an HP83485A OC-48

measurement module.


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


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


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.


Next: The Channel Setup Dialog will reflect the changes


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


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.


Settings of the Low Pass Filter

0.75 * 3.125 Gbps


Screenshot after turning on Low Pass Filter function


Screenshot after turning off the source channel, to only see the filtered data.


Screenshot of eye diagram using the Serial Data Analysis

CR Settings: 1st Order PLL, 1.875 MHz loop bandwidth (Data-rate/1667)


Turning on color-graded display.


Using Histogram to analyze the optical eye diagram

The “Mode” is the peak of the Histogram. The “1” level is 3.210 mW


Using Histogram to analyze eye diagram, continued.

The “0” level is 347 uW. Rough calculation for ER or OMA can be done.


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’.


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.


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


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


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

http://www.agilent.com/find/ref

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