Optical Switch Uses Thin Film and Mirror

Breck Hitz

Sarun Sumriddetchkajorn and Khunat Chaitavon of Thailand's National Science and Technology Development Agency and Ministry of Science and Technology, both in Pathumthani, have developed a novel concept for a 2 x 2 optical switch. The device eliminates the need for separate demultiplexing and multiplexing of wavelength division multiplexed channels, and it can achieve switching speeds in the millisecond range.

A pair of actuators insert either a thin-film filter or a high-quality mirror into the beam path. When the mirror is in the path, all input channels emerge in the "out" fiber. When the thin-film filter — which transmits λ₁ and reflects the other wavelengths -- is inserted, the input signal at λ₁ emerges in the "drop" fiber, and the "add" signal at λ₁ emerges in the "out" fiber (Figure 1).

Figure 1. A reconfigurable 2 x 2 optical switch based on thin-film filters and mirrors eliminates the need for separate demultiplexing and multiplexing of wavelength division multiplexed channels.

Multiple 2 x 2 switches can be ganged to create a multichannel optical add/drop multiplexer (Figure 2). A benefit of the setup is that it does not require the circulators or other components that are in many conventional optical add/drop multiplexers. Inserting optical amplifiers into the system can compensate for the loss that builds up from passage through the array of switches.

Figure 2. An array of the switches creates a multichannel optical add/drop multiplexer that does not require the circulators and other components that are in many conventional systems.

The switching speed of each device depends on the actuator used to move the mirror and the thin-film filter (and on the mass of those items). With an appropriate design, submillisecond speeds should be possible.

In a demonstration model of the device, the researchers used hand-operated mechanical translation stages, so the switching speed was not minimized. They measured an insertion loss of less than 1.3 dB and optical crosstalk well below — 15 dB. The polarization-insensitive switch showed an experimental polarization-dependent loss of 0.07 dB.