Tiny multichannel dispersion compensating grating

Southampton Photonics has released the smallest available multichannel dispersion compensating grating (DCG).

Southampton Photonics has released the smallest available multichannel dispersion compensating grating (DCG).

Measuring only 180 x 6.5mm in packaged format, the BragNet DCG can compensate for chromatic dispersion in up to four optical network channels simultaneously and individually.

It uses a chirped Fibre Bragg Grating (FBG) design to match the dispersion slope of any fibre type to within 99% accuracy per channel and could be used for producing ultra-small sub- or full-band compensation modules.

Supplied either as a packaged device for use in fixed wavelength compensation applications, or in fibre format for use in tuneable compensation modules, the high power handling capability and small size of the BragNet DCGs will offer many advantages to network equipment designers.

They feature a wide range of compensation values from 200 to 2000ps/nm, a maximum insertion loss of 1.5dB, and can operate over the C and L-bands.

Chromatic dispersion is an increasing problem in optical networks and caused by the various wavelengths which make up a single optical data pulse travelling at slightly different speeds down the fibre.

As network datarates increase to 10Gbit/s and beyond, this dispersion causes the pulses to overlap, an effect which worsens with distance travelled.

The result is that the receiver can no longer distinguish the logic 1s from the 0s causing degradation of the data.

Traditionally, the solution has been to use dispersion compensating fibre (DCF), although this cannot compensate for each individual constituent wavelength, and it is limited by its power handling capability and intrinsic high loss characteristics.

Using Southampton Photonics' DCG approach means that the dispersion slope of each individual wavelength can be very accurately compensated at the receiver end, which enables higher datarates and more channels over longer distances.

In many applications, the BragNet DCGs, with their very high power handling capability and low insertion loss, can be used to complement DCF and offer a means of compensating for chromatic dispersion on a per wavelength basis.

The BragNet DCGs are available in one-, two- or four-wavelength formats and all have channel spacings of 100GHz.

The packaged versions are housed in athermal cylindrical packages measuring only 6.5 x 180mm.

Fixed-wavelength dispersion compensating modules (DCMs) are a primary application.

For example, a 32-channel compensation system could be produced from only eight four-channel DCGs which would represent a very large space saving over comparable methods.

Alternatively, the DCGs can be supplied in unpackaged fibre format where they are ideal for use in stretched or thermally tuned applications.

The BragNet DCGs represent a natural product extension for Southampton Photonics as Marketing Director, Vince Sykes, outlined: "We introduced the world's most accurate Fibre Bragg Grating with a channel spacing of 25GHz at last year's OFC, and the dispersion compensating gratings are a natural extension of this breakthrough technology.

They will give subsystem designers enormous flexibility; they can use between one and four channel packaged devices to build the smallest, most cost-effective, multi-channel compensation modules available, or they can use the unpackaged gratings in tuneable systems".

(This was Electronicstalk's Top Story on 20 March 2002).

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