assembly of channels
total internal reflection
I.N. Kompanets, T.A. Neevina, S.I. Kompanet
This article relates to solution of actual problem of creating the all-optical communication networks and is devoted to the development of multi-channel parallel switch, which carries out an optical connection any given input optical channel with given output optical channel.
A new method for the parallel (without intersections) bitwise NxN switching of optical channels is proposed. It is illustrated in the example of a three-bit device (8-channel). The process of switching consists of n stages, where n = lg2N. At each stage the operations of doubling the number of channels are performed and the subsequent assembly (sealing) for those channels through which a light signal propagates.
Addresses for connection N input optical channels with N output optical channels are set by means of arrays of N optical modulators. Doubling is performed by using an optical splitter, for example, an optical cube, made up of two prisms. Two different variants are suggested to perform the assembly, which are described in more detail.
According to the first variant the switch includes waveguide channels, made of electro-optical crystal (lithium niobate), and at each stage the total internal reflection (TIR) cells with control electrodes are built-in each waveguide, so that a pair of adjacent cells provides a given optical connection between two adjacent waveguides. The photo detectors arrays are used to register a presence or absence of optical signal in waveguide channels. They are associated by means of the feedback with the voltage source and the control electrodes of TIR cells. Connection of optical channels is performed on a small level of the optical signal, which is sufficient for its registration by the photo detectors in the feedback system. The information light beam is applied to the switch after completing of the channels connection, i.e. after installing all the cells to the appropriate state (light transmitting or deflecting).
According to the second variant the switch includes the waveguide channels, made of photorefractive material (eg, lithium niobate, lithium tantalate, barium titanate, etc.), which changes it’s refractive index when exposed by the light. The address connection of any optical input with given optical output is provided due to control optical signals with the wavelength, to which junctions of waveguide channels are sensitive. A map of switched junctions is determined by a computer in accordance to input and the output addresses. In compliance with this map the two-dimensional array of control optical signals is formed by means of LED display or the laser source and spatial light modulator. It is also possible to include into the optical scheme a holographic optical element, which specifies the desired configuration of control signals. Switching of optical channels in photorefractive waveguides is performed simultaneously for all bit addresses that is a big advantage of this variant of switch.