N77-Series Attenuators
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The Keysight Technologies, Inc. N775xA and N776xA series compact multi-channel attenuators and power meters are a new class of remote controlled fiberoptic instruments for optical transceiver and network integration test. High setting speed of attenuation and power as well as power measurement capability, combined with USB, LAN and GPIB interfaces provides increased throughput and operational efficiency to meet today’s challenges in manufacturing.
Operation Modes
All attenuators feature both attenuation mode and power control mode.
In attenuation mode, the calibrated value of attenuation in dB can be set. The attenuation can be changed at up to 1000 dB/s or the rate can be set to values in the range 0-1000 dB/s for single-mode and 0-80dB/s for multimode units.
The power control functionality allows you to set the power level at the attenuator output. The instrument uses the feedback signal from a photodiode after a monitor tap, both integrated in the instrument, to set the desired power level at the output of the module (Figure 1 and Figure 2).
When the power control mode is enabled, the module automatically corrects for power changes at the input so that the output power level you set is maintained. Absolute power levels can be set with high accuracy after an initial offset calibration for the uncertainties at connector interfaces.
Power measurements
In addition, the Keysight N7751A and N7752A attenuators include two extra optical power meter channels for convenient power measurements and setup calibration.
User calibration processes
Comprehensive offset functionality allows you to calibrate the optical path in various test set-ups. There is an offset for the attenuation factor, and an independent offset for the output power level, to calibrate for losses due to patch cords, connectors and switches. Additionally, wavelength and offset value pairs can be stored in a table to compensate for wavelength-dependent effects in the optical path of the set-up. This allows you to precisely set the optical power level directly at the input interface of your device under test. With the extra optical power meter channel, calibration is even easier and more convenient. All power related offsets can be determined by a firmware function that reads a value from the reference power meter. The difference between the power value read by the reference power meter and the actual value of the attenuator is automatically stored as the offset
Key specifications and features
- 0.05 dB relative power setting accuracy, 0.1 dB for multimode
- Settling time: 20 ms attenuation, 100 ms power, 200 ms multimode
- Accurate built-in power monitor
- Miniature bulk optics for multimode for best transfer of modal distribution
- Choice of FC/PC or FC/APC connectors for 9/125 μm SMF models
- Choice of 50, 62.5 or 80 μm core fiber type for multimode models
- 0.1 to 1000 dB/s or for multimode to 80 and 1000 dB/s attenuation transition speed (selectable)
- +23 dBm max. input power
- ≤ 1.2 dB (typ. 1.3 dB MMF) insertion loss
- 45 dB single-mode attenuation range (typ.)
- 35 dB multimode attenuation range
- –50 dBm to +20 dBm power setting range (–35 to +20 dBm MMF)
- One half-width rack unit
- Fully compatible with setups and programs developed using the Keysight 8157x modular attenuators
- Powerful and user-friendly GUI software
- Two instrument configurations can be stored and recalled
N776xA multi-channel optical attenuators with internal power control
The Keysight N776xA multichannel optical attenuators with 1, 2 and 4 attenuator channels
in one unit provide an excellent combination of versatility and density
Benefits
Compact instrument combines and integrates multiple functions for setting attenuation and power levels and optical power measurement to reduce CAPEX and floor space.
Fast and precise setting of optical power levels in parallel with settling times of 100 ms (200ms multimode) for improved throughput.
The multichannel attenuator sets and measures several ports at the same time, saving significant time characterizing multiport and multi-channel components and network equipment.
Miniature bulk optics for multimode avoids distortion of modal distribution and assures stability and accurate power monitoring.
Active power control keeps output power constant.
The instrument can be controlled via LAN and USB, as well as GPIB for compatibility with existing equipment.
An easy-to-use and intuitive graphical user interface speeds up the integration process.
The N77xx-Viewer: An easy-to-use graphical user interface
The N77xx Windows-based graphical user interface offers flexible and convenient control of the instrument.
Easy switching between channels with tabs.
Overview window with all channels at a glance.
Two instrument configurations can be stored and recalled.
Enable or disable the attenuator’s output with one click.
Choose between setting an attenuation or an output power.
Applications
Optical transceiver testing
One of the challenges in testing transceivers is parallelization of bit-error-ratio measurements for multiple-device and multichannel device measurements. Sensitivity measurements require fast and precise setting of optical power levels in parallel at the receiver inputs with settling times like 100 ms for improved throughput.
Modal fidelity for multimode fiber setups
Signals in multimode fibers are distributed over a range of mode groups that can have different loss and delay in a link. For dependable multimode transceiver testing, the instrument used to set the power level should not change this modal distribution. The bulk-optic filter and collimated beam path of Keysight multimode attenuators are the best way to assure homogeneous attenuation of all input modes and to optimize stability.
Optical network integration testing
When integrating and testing network equipment to test network transmission performance and network management, including meshed networks using ROADMs, attenuators represent link spans between network nodes or amplifier stages.
The very fast attenuation and power setting response of the Keysight N775xA and N776xA attenuators allows simulation of many network configurations in a short time. In the path-blocking mode, fiber network cuts are emulated. With the attenuation and power ramp feature, the attenuation and/or the output power is changed at a defined rate of 0.1 dB/s to 1000 dB/s. This feature simulates slow and fast changes in the fiber network for testing the network management system.