Bessel-Thomson reference filter 622 Mb/s

The TA122 Bessel-Thomson Reference Filter 622 Mb/s is a specialised measurement accessory for engineers working with optical transmission systems, SONET/SDH networks and high-speed telecom signal characterisation.

Pico Technology provides a range of Bessel-Thomson filters matched to standard communication bit rates. The TA122 is specifically intended for:

• 622 Mb/s data rate
• OC12
• STM4
• SONET optical communication systems
• SDH optical communication systems
• Optical waveform characterisation
• Optical eye-diagram measurements

The filter is installed in the electrical signal path after an optical-to-electrical converter. It provides the controlled response required for meaningful receiver-oriented waveform measurements.

Designed for 622 Mb/s OC12/STM4 Signals

The TA122 is the Pico reference filter specifically assigned to 622 Mb/s OC12/STM4 applications.

It is suitable for testing and development involving:

• OC12 optical transmitters
• STM4 transmission systems
• SONET equipment
• SDH equipment
• Fibre-optic communication modules
• Optical transceivers
• Telecom line cards
• Optical networking equipment
• Research communication systems
• Optical test laboratories

Selecting the correct reference filter is important because Pico provides different Bessel-Thomson filters for different standard data rates.

How the TA122 Is Used

The recommended measurement chain is:

Optical signal → O/E converter → TA122 Bessel-Thomson filter → Oscilloscope

The optical-to-electrical converter first converts the incoming optical signal into an electrical waveform.

The TA122 is then placed between the O/E converter output and oscilloscope input.

Pico states that this arrangement enables the oscilloscope to display an accurate representation of the signal that an equalised optical receiver would see.

This distinction is important because the TA122 itself does not process an optical signal directly.

Bessel-Thomson Reference Receiver Response

A Bessel-Thomson reference filter provides a controlled frequency response for communication waveform measurements.

Rather than allowing the oscilloscope to display every high-frequency component passed by its full analogue bandwidth, the filter shapes the signal according to the appropriate reference receiver response.

This helps engineers obtain more meaningful measurements of:

• Pulse shape
• Rise time
• Fall time
• Eye opening
• Signal transitions
• Overshoot
• Undershoot
• Timing behaviour
• Receiver-oriented waveform quality

The result is a waveform that more closely represents how the applicable receiver would respond to the transmitted signal.

Optical Eye-Diagram Analysis

The TA122 can be used as part of an optical eye-diagram measurement setup for 622 Mb/s communication signals.

Eye diagrams help engineers evaluate characteristics such as:

• Eye height
• Eye width
• Rise time
• Fall time
• Crossing behaviour
• Signal amplitude
• Timing variation
• Overshoot
• Undershoot
• Pulse symmetry
• Waveform quality

Using the correct reference receiver filter is important because excessive measurement bandwidth can alter the apparent shape of the eye.

OC12 Optical Communication Testing

OC12 is a SONET optical transmission level associated with approximately 622 Mb/s data transmission.

The TA122 can therefore support measurements involving:

• OC12 optical transmitters
• SONET communication equipment
• Optical line interfaces
• Fibre communication modules
• Optical transceivers
• Telecom equipment validation
• Optical network research

STM4 Optical Communication Testing

STM4 is the corresponding SDH transmission level associated with the 622 Mb/s class.

Typical applications include:

• STM4 transmitter testing
• SDH network equipment
• Optical transport systems
• Fibre communication hardware
• Telecom interface validation
• Research and development
• Educational optical communication laboratories

Compatible PicoScope Oscilloscopes

Pico Technology currently identifies the TA122 Bessel-Thomson filter range for use with:

• PicoScope 9221A
• PicoScope 9231A
• PicoScope 9321

When the correct filter is placed between the O/E converter and oscilloscope input, these instruments can provide measurements representing the response expected from the equalised optical receiver.

Electrical Accessory, Not an Optical Filter

The product page should make this distinction particularly clear.

The TA122 is:

• A Bessel-Thomson reference receiver filter
• Used on the electrical waveform
• Installed after optical-to-electrical conversion
• Used before the oscilloscope input

It is not:

• An optical fibre filter
• An optical attenuator
• An optical-to-electrical converter
• An optical receiver
• A standalone oscilloscope
• A VNA calibration accessory

This wording helps users searching for optical test equipment understand exactly where the TA122 fits into the measurement system.

Passive Measurement Accessory

The TA122 is used as a fixed reference filter within the measurement signal path.

It does not require the types of control functions associated with an active test instrument.

There is no requirement for:

• USB software control
• Automated switching
• PicoSDK programming
• Network connection
• User-selectable filter configuration

The correct model is selected according to the communication bit rate being measured.

Part of the Pico Bessel-Thomson Filter Family

Pico currently lists five reference filters for common serial communication rates.

Why Selecting the Correct BT Filter Matters

Each Bessel-Thomson filter is matched to a particular communication bit rate.

Using a filter designed for another data rate may change the measured:

• Rise time
• Fall time
• Eye opening
• Pulse shape
• Overshoot
• Timing response
• High-frequency content

For a 622 Mb/s OC12/STM4 signal, TA122 is the appropriate Pico reference filter.

Optical Transmitter Characterisation

The TA122 can form part of a test setup used to characterise optical transmitters.

After the transmitted optical waveform has been converted into an electrical signal, engineers can analyse parameters including:

• Pulse transitions
• Signal amplitude
• Eye opening
• Timing behaviour
• Waveform symmetry
• Overshoot and undershoot
• Transmitter output quality

This makes the filter useful in optical communication development and validation environments.

Research and Educational Applications

The TA122 can also support laboratory exercises involving:

• SONET architecture
• SDH architecture
• Optical transmitter behaviour
• Reference receiver concepts
• Eye diagrams
• Fibre communication systems
• Optical-to-electrical conversion
• Communication waveform analysis

It is suitable for university telecom laboratories, engineering research and optical communication training where 622 Mb/s signals are being investigated.

Applications

The TA122 is suitable for:

• 622 Mb/s optical communication testing
• OC12 transmitter characterisation
• STM4 transmitter characterisation
• SONET system development
• SDH system development
• Optical eye-diagram measurements
• Optical transceiver testing
• Fibre-optic system validation
• Telecom line-card testing
• Optical networking research
• Pre-compliance signal evaluation
• Production optical testing
• Telecom R&D
• University optical communication laboratories
• Engineering education

Why Buy from RevineTech?

RevineTech can supply the TA122 for optical and telecom measurement applications and assist engineers in selecting the correct Pico reference filter for their required data rate.

Technical selection support can include:

• TA122 selection for 622 Mb/s systems
• Bessel-Thomson filter comparison
• PicoScope compatibility
• Optical-to-electrical converter configuration
• Sampling oscilloscope selection
• Optical eye-diagram measurement setup
• Related RF cables and adaptors
• Telecom test equipment selection