Abstract

Time-multiplexing is a method to increase the brilliance of diode lasers, i.e. a sequence of laser pulses emitted from different laser diodes at different times is guided onto a common optical path via a cascade of polarizing cube beam splitters and polarization switches. The latter are made of piezo-electric crystals oscillating in resonance and making use of the photo-elastic effect to obtain the desired modulation of polarization. We realized a demonstrator for time multiplexing of four laser diodes with such self-excited photo-elastic modulators. The latter is a new alternative to conventional photo-elastic modulators used in ellipsometers.

© 2006 Optical Society of America

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References

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  1. R. DiehlHigh Power Diode Lasers, (Springer-Verlag, Berlin, Heidelberg, New York, 2000).
    [CrossRef]
  2. L. Berger, U. Brauch, A. Giesen, H. Hügel, H. Opower, M. Schubert, and K. Wittig, "Coherent fiber coupling of laser diodes," in Laser Diodes and Applications II, K. J. Linden and P. R. Akkapeddi, eds., Proc. SPIE 2682, 39 46 (1996).
    [CrossRef]
  3. P. J. Winzer, K. Sherman, and M. Zirngibl, "Experimental demonstration of time-division multiplexed Raman pumping," in Proceedings of IEEE Optical Fiber Communication Conference and Exhibit, (2002), pp. 184-185.
  4. F. Bammer and B. Holzinger, "Realization of time-multiplexing for high power diode lasers," in XV International Symposium on Gas Flow, Chemical Lasers and High-Power Lasers, J. Kodymová, ed., Proc. SPIE 5777, 394-397 (2004).
    [CrossRef]
  5. M. Bartram, R. W. De Doncker, J. Gottmann, G. Schlaghecken, D. Hoffmann, and R. Poprawe, "Pulse widths less than 100ns at 500A current: Challenge to explore new applications with high-power laser diode arrays," Proceedings of the second international WLT-conference on lasers in manufacturing 2003 (Europhysics Conference Abstracts).
  6. T. A. Maldonado, "Electro-optic modulators," in Handbook of Optics, M. Bass, ed. (McGraw Hill, Orlando, 1995).
  7. J. F. Nye, Physical properties of crystals, (Clarendon Press, Oxford, 1985).
  8. A. Yariv, Optical waves in crystals (New York: Wiley, 1984).
  9. K. Wong, Lithium Niobate (INSPEC, London, 2002).
  10. E. Collett, Polarized Light in Fiber optics (The PolaWave Group, 2003).
  11. Hinds Instruments, "Principles of operation of photo-elastic modulators" http://www.hindsinstruments.com/PEM_Components/Technology/principlesOfOperation.aspx.

Other

R. DiehlHigh Power Diode Lasers, (Springer-Verlag, Berlin, Heidelberg, New York, 2000).
[CrossRef]

L. Berger, U. Brauch, A. Giesen, H. Hügel, H. Opower, M. Schubert, and K. Wittig, "Coherent fiber coupling of laser diodes," in Laser Diodes and Applications II, K. J. Linden and P. R. Akkapeddi, eds., Proc. SPIE 2682, 39 46 (1996).
[CrossRef]

P. J. Winzer, K. Sherman, and M. Zirngibl, "Experimental demonstration of time-division multiplexed Raman pumping," in Proceedings of IEEE Optical Fiber Communication Conference and Exhibit, (2002), pp. 184-185.

F. Bammer and B. Holzinger, "Realization of time-multiplexing for high power diode lasers," in XV International Symposium on Gas Flow, Chemical Lasers and High-Power Lasers, J. Kodymová, ed., Proc. SPIE 5777, 394-397 (2004).
[CrossRef]

M. Bartram, R. W. De Doncker, J. Gottmann, G. Schlaghecken, D. Hoffmann, and R. Poprawe, "Pulse widths less than 100ns at 500A current: Challenge to explore new applications with high-power laser diode arrays," Proceedings of the second international WLT-conference on lasers in manufacturing 2003 (Europhysics Conference Abstracts).

T. A. Maldonado, "Electro-optic modulators," in Handbook of Optics, M. Bass, ed. (McGraw Hill, Orlando, 1995).

J. F. Nye, Physical properties of crystals, (Clarendon Press, Oxford, 1985).

A. Yariv, Optical waves in crystals (New York: Wiley, 1984).

K. Wong, Lithium Niobate (INSPEC, London, 2002).

E. Collett, Polarized Light in Fiber optics (The PolaWave Group, 2003).

Hinds Instruments, "Principles of operation of photo-elastic modulators" http://www.hindsinstruments.com/PEM_Components/Technology/principlesOfOperation.aspx.

Supplementary Material (1)

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Figures (5)

Fig. 1.
Fig. 1.

Scheme for time-multiplexing of four laser diodes: LD1-4…laser diodes, PF1-3…polarization filters 1-3, Q1-2…quarter-wave-plates, C1-2…LiNbO3-crystals with electrodes on the yz-surfaces, H1-2…half-wave-plates, xyz1-2…local crystal coordinate systems

Fig. 2.
Fig. 2.

Optical switching in Fig. 1(a) retardance course of crystal C1; (b) transmission function Tr(δ) for the laser diode LD1 emitting through the crystal C1, the quarter wave plate Q1 and the polarizers PF1 and PF3; (c) resulting temporal transmission Tr(t); (d) laser pulses from laser diodes LD1, LD3 (dashed) and LD2, LD4 (drawn through)

Fig. 3.
Fig. 3.

Setup to visualize the effect on polarization for different directions of propagation: xyz…crystallographic coordinate system, SC…screen, PF…polarization filter (analyzer), C…LiNbO3-crystal with electrodes on its yz-surfaces, DF…diffuser, QWP…quarter wave plate, LD…laser diode (collimation not shown); α, β… angle coordinates. On the left the pattern, which can be seen on the screen SC in case of a resting crystal, is shown.

Fig. 4.
Fig. 4.

(0.375 MB) Movie of the patterns of the configuration of Fig. 3, when the crystal C oscillates in a shear mode; axis dimension…mrad. The red ellipse indicates the far field spot of the laser diode for removed diffuser and is only shown when a sufficient amount of linear polarization is achieved.

Fig. 5.
Fig. 5.

The prototype (dimensions 115×115 mm) for time–multiplexing of four laser diodes

Equations (6)

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n s n f n 0 3 = Δ B 12 = E x r 22 S + s 12 p 66 E + s 31 p 14 E
δ = 2 π L λ ( n s n f ) ,
Tr ( δ ) = cos 2 ( δ 2 π 4 ) = ( 1 + cos ( δ π 2 ) ) 2 .
P B ( β ) A ( α ) ( N + Δ B ) A ( α ) T B ( β ) T P T ,
M ret = ( 1 0 0 0 0 c φ 2 + s φ 2 cos δ s φ c φ ( 1 cos δ ) s φ sin δ 0 s φ c φ ( 1 cos δ ) s φ 2 + c φ 2 cos δ c φ sin δ 0 s φ sin δ c φ sin δ cos δ ) .
dS ds = 2 π λ ( n f n s ) ( 0 0 0 0 0 0 0 s φ 0 0 0 c φ 0 s φ c φ 0 ) S ,

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