Half-wave voltage

A useful figure of merit for linear electro-optic materials is the half-wave voltage V which is the voltage that must be applied to opposite faces of a unit cube of material to induce a phase difference of % between the extraordinary and ordinary rays. It is discussed further in Section 8.2.2 (see Eq. (8.44)). Values for V, are included in Table 8.1. 

Table 8. Linear EO coefficients (pm/V), reduced half-wave voltages v (kV), dielectric constants Cf, and linear polarization optical coefficients, fyk(m /C) of DAST (Reprinted with permission from (F. Pan, G. Knopfle, Ch. Bosshard, S. Follonier, R. Spreiter, M.S. Wong and P. Gunter, (1996) Appl. Phys. Lett., 69, 13). Copyright (1996), American Institute of Physics)...

The minimum voltage required for a 7t-phase shift, called half-wave voltage Vm can be expressed as ... 

In 2000, an encouragingly low half-wave voltage V of 0.8 V was achieved in a polymer waveguide modulator using highly nonlinear organic chromophores [21],... 

As stated before, electro-optic properties of PLZT materials are related to their ferroelectric properties [131]. For PLDZT, the reduced coercive field (EJ and the enhanced optical transmittance (7) induced by the Dy substitution have led to improved electro-optic properties. Because the working voltage of a device is mainly dependent on the half-wave voltage of the materials, the lowered yi/2 of materials should be favorable to the improvement in performances of the devices. 

The performances of our device are as follows the half-wave voltage is 9 V, the extinction ratio is 31 dB, and the fiber-to-fiber optical loss is 13.2 dB. The bandwidth has been tested up to 2.5 GHz, and further improvement can be expected. The optical stability problem of the polymeric MZ modulator has been identified and characterized in detail. 

Recently, Enami and co-workers [118] presented a hybrid cross-linked EO polymer/sol-gel Mach-Zehnder waveguide modulator with of 0.65 V at 1,550 nm. Such a low value of half wave voltage, which is one of the best results obtained in literature, is related to the combination of a very high electro-optic effect and to the device design that combines physical vertical tapers in the sol-gel core, index tapers in the EO polymer, a suitable electrode structure and a top buffer layer designed for cross-linked EO polymer systems. In such a device also the optical losses result to be reduced with respect to a more traditional configurations. 

Assume that the output power of a laser shows random fluctuations of about 5%. Intensity stabilization is accomplished by a Pockels cell with a half-wave voltage of 600 V. Estimate the ac output voltage of the amplifler driving the Pockels cell that is necessary to stabilize the transmitted intensity if the Pockels cell is operated around the maximum slope of the transmission curve. 

Problem 11.1. A Pockels cell inside a laser resonator is used as Q-switch. It has a maximum transmission of 95% for the applied voltage U = 0. Which voltage U is required to prevent lasing before the gain = exp(aL) of the active medium exceeds the value = 10, when the half-wave voltage" of the Pockels cell is 2 kV What is the effective amplification factor G f immediately after the opening of the Pockels cell if the total cavity losses are 30% per round trip ... 

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