Recirculating Loop System

To simulate and test long distance fiber optic communication lines, Brimrose has developed a fiber-coupled AO modulation system. The recirculating loop system consists of two fiber-coupled AO modulators/switches and a corresponding RF driver. One of the AO modulators/switches is placed outside the loop to define the loading time and the second AOM is placed inside the loop to define the recirculating time or distance of the pulse transmission, which corresponds directly to the length of the long distance fiber optic line. 
Since conventional Acousto-Optic devices will frequency shift the transmitted light by the acoustic carrier frequency, the Brimrose recirculating loop system utilizes a no-shift AO device inside the loop that will keep the frequency of light at a constant value even after multiple passes. The no-shift AO device does not complicate testing nor degrade system performance.


  • Low Insertion Loss

  • No O-rings

  • Rack-mount Enclosure

  • High Extinction Ratio

  • No Frequency Shift

  • Inside Loop Recirculating Switch

  • Outside Loop Loading Switch

  • Custom Configurations Available


  • Simulating and Testing of Long Distance Fiber Optic Communication Lines

  • OEM Designs



Model # AMM-100-4-140-1550-2FP/nfs AMM-100-8-70-1550-2FP
Max. Input Optical Power (mW) 300 300
Polarization Dependent Loss (dB) 0.2 0.2
Extinction Ratio (dB) * >50 >50
Input Impedance (ohms) 50 50
Case Type 2-Port Fiber-coupled 2-Port Fiber-coupled
Type of Fiber 9µm Core, 125µm Cladding Single-Mode 9µm Core, 125µm Cladding Single-Mode
Fiber Connector Type FC/SC/LC FC/SC/LC
Polishing of the Fiber End PC/SPC/UPC/APC PC/SPC/UPC/APC
Fiber Jacket Type 900µm/3mm 900µm/3mm
Back Reflection (dB) ** 40/50 40/50
Total Insertion Loss (dB) *** ~5.6 2.5-3.0

Brimrose offers 2-Port Fiber-coupled AO Modulators (transmitter switch is used for outside the loop) and 2-Port Fiber-coupled AO Modulators (no frequency shift switch is used for inside the loop).  
* The RF driver must match this extinction ratio.  

** Back reflection at FC connector is not included.

*** This spec includes: coupling losses, optical transmission through the crystal and diffraction efficiency losses. FC connector losses are not included. 

The RLS models shown in the table represent some examples of our fabrication capabilities.  In addition, other wavelengths, frequencies or configurations are available. 

Complete the form to receive a quote for one of our standard models or get a custom quote.

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