NRT-2500 Polarization Control Platform

The NRT-2500 is a polarization controller designed to implement a variety of very fast, very accurate and very reliable polarization applications such as:

1. Versatile Polarization Platform for multiple lab purposes
2. Scramble & Randomize Polarization
3. Set Polarization
4. Very fast, robust & endless Polarization Tracking
5. Coherent detection
6. Polarization De-multiplexing of
   Dual-Polarization signals
7. Customizable for new applications

Download the NRT-2500 Datasheet.

Key Specifications

Insertion Loss	<3 dB
PDL	<0.3 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
Speed distribution parameters2 (in scrambling operation)	rmode ≡ b0.5 up to ~2,300 radians/second <r>≡ 1.25rmode up to ~2,875 radians/second rmax~ 3.76rmode up to ~8,650 radians/second
Slew speed (for SOP-to-SOP transition in randomizer operation)	≥ 1 microseconds (up to 1,500,000 radians/second)3
Tracking Speed (closed loop in tracking mode)	~20 microseconds4
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. Subject to change at any time by New Ridge Technologies, LLC. 2. For a Rayleigh distribution: rmode is the mode of the distribution, <r> is the mean SOP change, and 99.9% of all SOP changes occur by rmax = 3<r> ~ 3.76rmode 3. 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.

Versatile Polarization Platform for Multiple Lab Applications

NRT's polarization control platform combines an integrated-optic Lithium Niobate (LiNbO₃) waveguide polarization-controller device for super-fast polarization response driven by a customizable DSP/FPGA platform for functional flexibility. Together they enable NRT to provide a wide range of polarization operations in one product. The four functions currently offered are:

1. Set Polarization

Perhaps the most often used polarization operation in the lab. The NRT-2500 provides the electronic equivalent of 4 Lefevre fiber-optic paddles to align the pump to the probe or the signal to the local oscillator, maximize light through a polarization element, or polarization-demultiplex optical communication signals. 

Each 'electronic paddle' is controlled through the user interface to set the polarization where you need it. Move the sliders or enter a values
from 0 to 1000.
 

2. Polarization Scrambler

Scrambling the State of Polarization (SOP) is another common fiber optic lab function. Scrambling is invaluable to test the robustness of polarization diversity detection schemes or polarization multiplexed optical communication signals. For these applications it is important that the polarization fully and evenly covers the Poincaré sphere. Such truly random SOP changes obey Rayleigh statistics. The NRT-2500's scrambler repeatably generates this well-known and analytic distribution of SOP statistics. No more guessing about the coverage of the Poincaré sphere or the distribution of SOP change rates. Just enter the desired Rayleigh distribution scrambling rate and you're on your way. The NRT-2500 combines its programmable DSP and the ultrafast speed of the LiNbO₃ polarization controller to generate the fastest, yet truly random, SOP scrambler available.

Polarization Scrambler setup yielding even SOP coverage on the Poincaré sphere. At the right is a histogram of the SOP scrambling fit to the theoretical Rayleigh distribution for random scrambling with the peak at b0.5= 1,940 radians/sec, and a tail that extends past 7,300.

3. Polarization Randomizer

Need more speed? The NRT-2500 Polarization Randomizer mode allows you to set the slew time between polarization states and dwell time at a state. At each cycle the NRT-2500 sends each waveplate to a unique random position at the predetermined slew speed, and then holds it there till the next cycle. Settable slew speeds as fast as 1 µs enable changes in the SOP up to about
1,500,000 radians/second (or about 500,000 Hz)!

The NRT-2500's scrambler and randomizer are perfect for evaluating and validating the performance of DSP-based equalizer CDR chips used in new coherent fiber optic transponders for 40G and 100G. See our white paper on the SOP changes seen in the network and verify these SOP speeds in transponders.

4. Fast Robust and Endless Polarization Tracker

NRT's unique tracking algorithm enables virtually perfect SOP tracking with no dropouts or glitches for your new applications and prototypes. The NRT-2500's open architecture allows you to optimize the performance for your specific application:

• Create a unique error signal from four A/D converter inputs
• Optimize algorithm parameters with tracker optimization program

New Ridge has leveraged >4 years of time and effort in the tracker, and has packaged it all together for you. This tracking technology is so robust it was qualified for network deployment at multiple carriers around the world after proving its 'five-9s' tracking capabilities.

NRT-2500 in Polarization Tracker mode stabilizing a scrambled SOP input using the light passing through a polarizer as the feedback.

In the figure is a set up for polarization tracking. The goal for the control algorithm is to very quickly adjust the LiNbO₃ polarization controller to maximize the light passing the polarizer and reaching the photodiode.

The tracking results are shown at the right of the figure. The sophisticated algorithm offered by NRT is clearly able to track the scrambled input the optical polarization; maintaining a tight clean locus circle of output polarization states, demonstrating very fast and very accurate tracking, with no glitches!

Tracking Example 1: Polarization Demultiplexing

An optical polarization demultiplexer can be built as shown here, where a tone or RF-power on one of the polarization-tributaries is used as the feedback to lock the NRT-2500.

Tracking Example 2: 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.

New Ridge also welcomes licensing of the NRT-2500’s design
and tracking algorithm for OEM solutions.

Do you have a polarization control problem or function the NRT-2500
can solve? Then please contact us to discuss implementation.

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