Electroholography (EH) is a wavelength selective optical switching method based on governing the reconstruction process of volume holograms by means of an electric field. EH was originally invented by A. J. Agranat for the purpose of constructing optoelectronic implementation of artificial neural networks [REF14].

EH provides the underlying principle of operation for a new class of photonic devices that implement fast wavelength selective switching and wavelength tuning that are currently being developed at the OECL. These devices will constitute the physical chassis for implementing wavelength routing schemes in WDM optical communication network in particular for implementing Dynamic Optical Circuit Switching.

The basic electroholographic device is an electrically controlled Bragg grating or a volume hologram stored in a latent state within the volume of an electrooptic crystal. In the g11/g12configurations, (Shown Schematically in Figure 1), the switching operation consists of activating the grating by the application of an electric field. Electroholographic gratings are implemented either by employing the voltage controlled photorefractive effect (REF15), or by employing the principle of the dielectric electroholographic grating [REF16].

As the electroholographic switching operation is the reconstruction of a volume grating (hologram), it is required that the Bragg condition be satisfied. Consequently the EH switch is wavelength selective. In addition the applied field governs the efficiency of the reconstruction. As such electroholographic switches can be the building blocks for complex wavelength selection switching systems which perform grouping, multicasting, power management and non-intrusive data monitoring as an integral part of the switching operation. The basic EH operation is shown in Figure 1. An extensive overview of EH in the g11/g12 configuration can be found in EH Overview.

Figure 1: An Electroholographic g11 switch   (a) The grating is “off”: Both beams pass through;

(b) The beam is “on”: Red beam fulfills the Bragg condition and diffracts.

An array of EH g11 switches providing grouping and multicasting of WDM wavelength channels is shown in the video in Figure 2.

Figure 2: An Array of g11 EH switches operates as a multifunctional Wavelength selective switch.
Figure 3: The inventor of the internet Vinton Cerf explains Electroholography to former secretary of state Alexander Haig

A special variant of EH is EH in the g44 configuration [REF17]. This configuration enables operation at low voltages and provides electrical tunability of the wavelength [REF17]. A tunable laser operating at 1550 nm with spectral tunability over a range of 50 nm was demonstrated by Employing EH in the g44 configuration. [REF10]. A EH switching speeds below 10 nanosecond was demonstrated in the g11 configuration [REF11], and below 1 nanosecond in the g44 configuration [REF12].