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Development Of An Optical Isolator For A FP-CW-QCL At 8.5 μ m Using An Experimental Faraday Rotator

Development Of An Optical Isolator For A FP-CW-QCL At 8.5 μ m Using An Experimental Faraday Rotator. Brian E. Brumfield* Scott Howard ** Claire Gmachl ** Donald K. Wilson † Mark Percevault † Benjamin McCall ‡. *Department of Chemistry, University of Illinois, Urbana, IL

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Development Of An Optical Isolator For A FP-CW-QCL At 8.5 μ m Using An Experimental Faraday Rotator

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  1. Development Of An Optical Isolator For A FP-CW-QCL At 8.5μm Using An Experimental Faraday Rotator Brian E. Brumfield* Scott Howard** Claire Gmachl** Donald K. Wilson† Mark Percevault† Benjamin McCall‡ *Department of Chemistry, University of Illinois, Urbana, IL **Department of Electrical Engineering, Princeton University, Princeton Institute for the Science and Technology of Materials, Princeton, NJ †Optics For Research, Division of Thor Labs, Caldwell, NJ ‡Departments of Chemistry and Astronomy, University of Illinois, Urbana, IL

  2. Motivation/Problem • Development of (EC)-QCL in mid-IR • Acquire high-resolution spectrum of C60~8.5μm • Back-reflection introduces • Intensity fluctuations • Frequency instability “Collimating” Optics Mode-matching optics High Finesse Cavity AOM QCL

  3. AOM High Finesse Cavity Mode-matching optics Isolator Potential Solution • Employ Optical Isolator “Collimating” Optics QCL

  4. The Faraday Effect • Discovered 1845 by Michael Faraday • Amount of rotation found equal to product of: • V: Verdet constant (degrees/ G*cm) • B: Magnetic field strength (G) • L : Length of material traversed (cm)

  5. Essentials of An Optical Isolator • Gap in commercially available Faraday Rotators from 3.5 to 10 μm! • Three components • Pair of polarizers • Faraday rotator (FR) P1 P2 FR 45° 0° 45° 90°

  6. Faraday Effect In n-InSb CO2 Lasers: n-InSb Interband Effect Free Carrier Effect • Independent of Ne • Dependent on high B • Ne (cm-3) free charge carrier electron concentration • Dominates when: • B field >10 kG • Ne < 1x1016 cm-3 • Dominates when: • High n-doping: • Ne > 1x1016 cm-3 Melngailis et. al. J. Quantum Electron. 1996, 84, 227. • Advantages: • Low optical insertion loss • Disadvantage: • Need very strong magnets >15 kG • Advantages: • Table top design • Disadvantage: • Increased optical insertion loss

  7. Testing Set-Up PC Lock-in HgZnCdTe Beam Chopper HgCdTe P2 P1 FR Wire Grid Polarizers ~400:1

  8. Single-Pass Analysis • Transmission curve recorded 10° increments • Fit to: • Measured 6 ± 1° rotation

  9. Triple-Pass • Single-pass rotation provided undesirable ~6 ± 1° • Why? • Can increase power throughput by multi-passing • Z-Pass Configuration M1 P1 P2 FR M2

  10. Triple-Pass Results/Comparisons • Rotation Low • High temperature • Thickness • Wavelength • Insertion Loss High • Reduction of transmission due to P2 setting • Triple Pass 100 West 18th Tomasetta et. al. J Quantum Electron. 1979, QE-15, 266.

  11. P4 P3 P2 P1 FR Future Directions • Short Term • Test for adequate isolation • Inadequate isolation-additional WG polarizers • Acquisition of highly doped n-InSb • Long Term • Optimization of n-InSb material

  12. Acknowledgements Brian Siller NASA Laboratory Astrophysics Dreyfus UIUC

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