Initial Release: NRT-2500 Polarization Controller Platform

The NRT-2500 is a polarization controller designed for implementing very fast and very reliable polarization tracking applications such as:

1. Polarization demultiplexing of dual polarization modulated fiber optic signals,
2. PMD compensation,
3. Coherent detection, and
4. General lab applications.

Unique Performance

New Ridge's NRT-2500 performance stands alone among available polarization control devices and development platforms. The technologies in the NRT-2500 have already been field-proven and qualified in a commercial fiber optic network element.

Key Specifications

Insertion Loss	<3 dB
Speed (closed loop)	~20 microseconds1
PDL	<0.2 dB
Optical return Loss	>50 dB
Optical Power Handling	<20 dBm
Operating Wavelength	1.55 microns (C- and L-bands)
Optical Connectors	FC/UPC, FC/APC, SC
Power Supply	12 VDC from 100-240 VAC, 50 – 60 Hz wall AC-DC converter
Communication Interfaces	Ethernet, RS-232 (monitor points)
Dimensions	H=4.04” (102.6 mm), W=10.12” (257 mm), D=12.32” (313mm)
1. This speed is feedback/update algorithm loop time based on reading A/DCs and DSP speed and updating polarization controller voltages. The feedback signal level and customization of the algorithm may slow system response.

Best-in-Class Technologies

NRT's polarization controller offering is comprised of four key technologies:

1. Integrated-optic Lithium Niobate (LiNbO3) waveguide polarization controller device. LiNbO3 polarization controllers are known for their super-fast electro-optic response which is useful for tracking polarization as well as polarization scrambling.
2. Unique Control Algorithm running on a custom DSP and FPGA platform. The NRT Control Algorithm control enables:
• Virtually perfect SOP transformations with no dropouts or ‘glitches’
• Accurate and truly 'Endless' control of polarization
• Significant control improvement over other control algorithms
• 10x speed improvement over other control algorithms
• Leverages 4 years of PMD compensator control algorithm development
3. Analog-to-digital converters for external electrical feedback signals
4. The NRT-2500 is supported by a PC software package. Its open architecture allows you to optimize the performance for your application:
• Create your unique error signal from the A/D voltages (such as DOP from the S0, S1, S2, S3 of a polarimeter)
• Adjust algorithm parameters loop gain parameters.
• Run algorithm parameter optimization program

Why recreate the wheel?

Even so-called 'endless' polarization controllers are insufficient for mission critical applications without a robust tracking algorithm. Creating a dither-and-search feedback tracking algorithm is fairly straight forward, and a modestly performing algorithm can be written in relatively short order. However significant time, money manpower and knowledge are required to make an algorithm that is network deployable, capable of 'five-9s' reliability.

New Ridge has invested the time and effort, and has packaged it all together for you. 

The NRT-2500 was derived from hardware and software developed originally for PMD compensation.  This technology was qualified for network deployment at multiple carriers around the world proving its 'five-9s' robust network ready performance capabilities.

Sample Performance

Below is a set up for to test polarization tracking and to compare control algorithms. The goal for the control algorithm is to very quickly adjust the LiNbO₃ polarization controller to minimize the light passing the polarizer and reaching the photodiode.

The results of this demonstration are shown below. The sophisticated algorithm offered by NRT (at the left) is clearly able to track the scrambled input the optical polarization maintaining a tighter locus circle of output polarizations than other common tracking algorithms (on the right).

The output polarization states using the control algorithm in the NRT-2500: notice the clean and tight spot showing very fast and very accurate tracking, with no glitches.   The output polarization states for a common polarization tracking algorithm: the diffuse spot shows instances where the algorithm lost track and could not keep up with the rotating input polarization.

Applications

Polarization Demultiplexing

In this case a tone on one of the polarization-tributaries is used as the feedback to lock the NRT-2500.

PMD Compensation

This NRT-2500 can also be used as the basis for optical PMD compensation development. In this example two NRT-2500s are used to control both the first and second stages of the compensator. New Ridge has included a Master/slave hardware link allowing two NRT-2500s to work as one.

The NRT control algorithm control used here was adapted from a network qualified PMD compensator, proving the NRT-2500's suitability for network applications.

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