Mitsubishi develops new device for optical networks

Mitsubishi Electric Corp has developed a new semiconductor optical modulator which can double the distance over which data can travel within optical fiber metropolitan or backbone networks at 40G bps (bits per second), the company said last week.

Existing modulators can send data signals for around 20 kilometers at 40G bps. The new modulator can extend that distance to more than 40 kilometers, which is far enough to cover metropolitan network areas, Mitsubishi said.

A semiconductor optical modulator takes a light wave, adds in modulations corresponding to data bits on a designated wavelength and sends the pulse down the line. Many engineers have been developing network devices such as this modulator for the expected next-generation standard speed of 40G bps. Currently, the speed offered by conventional optical fiber network services is around 10G bps.

A bottleneck for fiber-optic transmission of data at high speeds is a phenomenon called wavelength chirping. This causes distortion of the optical pulse shape, because the propagation speed of the optical pulse is different at different wavelengths as the optical fiber material displays a different refractive index at different wavelengths. This distortion becomes more significant as transmission speed and transmission distance increase.

Mitsubishi achieved the breakthrough by changing the structure of the modulator. Instead of two layers -- one known as the barrier layer and one as the well layer -- the new modulator consists of three layers, with two barrier layers and one well layer, the company said.

Mitsubishi's semiconductor optical modulator is expected to be sample shipped in November at ¥200,000 (US$1,600) and a version packaged into a module is to be shipped in December at ¥800,000, the company said.

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