DLP® Optical Networking

Adjustable Multiple Wavelength Attenuator/Equalizer Solutions from Texas Instruments.


DLP® technology makes it possible to manipulate and control light in ways that are useful in optical telecommunications networks (OPNET). For example, a DLP® Digital Micromirror Device (DMD) can be used to implement an Optical Add Drop Multiplexer (OADM) to insert (delete) specific wavelength channels into (from) a Wavelength Division Multiplex (WDM) optical signal. This allows for rapid adaptive network configuration and data stream switching.

Another OPNET application is shown in this system block diagram. In-line optical amplifiers are required in long haul optical networks, due to the attenuation of the optical signal with distance. However, different wavelengths are attenuated by different amounts (wavelength dependent differential attenuation). Optical amplifiers are subject to gain saturation (or compression) which can result in the strongest wavelength at the input dominating the amplifier’s output, thereby causing the weaker input wavelengths to fail to be boosted. The DLP® DMD provides precise adjustable attenuation of multiple wavelengths to compensate for the wavelength dependent differential attenuation. This equalization function allows for all of the wavelengths in the optical signal to receive the proper amount of amplification, thereby achieving optimal network performance (high speed, low error rate).

How does it work?

The input optical fiber carries data encoded on different wavelengths of light. The light from the input fiber is dispersed by an optical diffraction grating so that the different wavelengths fall on different regions of the DMD chip. The set of mirrors which correspond to the different wavelengths can be defined as a wavelength region. The amount of light falling on each region will vary because of the selective attenuation which each wavelength has suffered. The mirrors within each wavelength region can be patterned (number of mirrors turned on/off) in such a way as to attenuate the stronger wavelengths to the level of the weaker wavelengths.

The light reflected from all of the wavelength regions of the DMD are recombined by the output diffraction grating into a light beam coupled into the output fiber. The output fiber feeds an optical amplifier which boosts all of the wavelengths to the proper levels for the long trip to the next amplifier, or destination.

The multiple wavelength adjustable equalizer comprises the feedback loop which provides information on the relative power in each wavelength, the embedded processor which calculates the pattern of mirrors to activate on the DMD, and the DMD which provides the spatial optical modulation function to equalize the powers across the wavelengths.

There are many thousands of mirrors on the DMD, but the drawing does not show the level of detail required to see individual mirrors. This means that within each wavelength region on the DMD (marked λ1 – λ4) there are many mirrors. Each mirror can be in either an "on" or an "off" state (±12°). By turning "on" more or fewer mirrors, the amount of light reflected from the input grating to the output grating can be adjusted. In practice, the required number of mirrors for each attenuation value may be achieved by using more complex patterns of on/off mirrors.

The drawing does not show all of the optical or mechanical components which may be required to achieve a functional unit.

The DMD is part of a chipset, and must be utilized with all of the chipset devices.

Application notes & user guides

Application Notes (2)

Title Abstract Type Size (KB) Date Views
PDF 3.85 MB 07 Oct 2013 3362
PDF 529 KB 20 Jul 2010 1962

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