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Dynamic Gain Equalization Scheme for MAN/WAN using WDMA and Semiconductor Optical Amplifiers

IP.com Disclosure Number: IPCOM000112077D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 126K

Publishing Venue

IBM

Related People

Choy, MM: AUTHOR [+4]

Abstract

Disclosed is a dynamic equalization scheme using planar gratings and semiconductor optical amplifier arrays to overcome the near-far problem and nonequal transmission spectra present in a MAN/WAN.

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This is the abbreviated version, containing approximately 51% of the total text.

Dynamic Gain Equalization Scheme for MAN/WAN using WDMA and Semiconductor
Optical Amplifiers

      Disclosed is a dynamic equalization scheme using planar
gratings and semiconductor optical amplifier arrays to overcome the
near-far problem and nonequal transmission spectra present in a
MAN/WAN.

      A metropolitan area network or wide area network (MAN/WAN)
using WDMA has the potential near-far problem where the optical
signals originating from different location experience different
attenuation.  Furthermore, fibers and optical amplifiers used in such
a network also have nonflat transmission spectra and thus different
wavelengths experience different gain and attenuation even though
they travel through the same physical path.  Most of the existing
studies on gain equalization has been focused on equalizing the
nonflat gain spectra of the optical amplifiers.  Gain equalization
using fiber grating embedded in the 'Er' sup 3+ fiber amplifier was
proposed in [1].  Although a larger equalization bandwidth is
achieved, this scheme can not adjust the gain dynamically.  Two-stage
fiber amplifier with offset gain peaks was proposed in [2] to
dynamically equalize (by means of pump power) the optical signal
power among different channels in a WDMA system.  This scheme,
however, has a very limited equalized bandwidth of &app.2.5nm.  Gain
equalization can also be achieved through controlling the
transmission spectra of the optical filters.  Using this principle,
an equalized 29-channel WDM system spanning 7 nm was demonstrated
using a Mach-Zehnder Interferometric filter [3].  Acousto-optic
tunable filter (AOTF) has also been used to equalize gain spectra for
a very wide transmission window [4].  Through the injection of
multiple RF frequencies with each RF signal transmitting at a
different magnitude, an arbitrary transmission characteristic can be
established.  The resolution of this scheme, however, is limited by
the resolution of an an AOTF.

Fig. 1 shows the proposed scheme which consits of:

o   wavelength demultiplexer (e.g., grating), which demultiplexes the
    incoming multiple optical signals into individual wavelength
    channels,

o   optical amplifier arrays, which are responsible for the gain
    adjustment of individual wavelength channels,

o   wavelength multiplexer (e.g., grating) which multiplexes the
    gain-equalized optical signals into a single output.

      The essence of this gain equalization scheme relies on the
dynamic adjustment of the gain of each optical amplifier through
modifying the injection current of each amplifier.  Furthermore, the
gain of the optical amplifier is dynamically adjusted to achieve a
constant optical signal power at the output of the optical amplifier
in case of an increase/decrease of the incoming optical power.  This
dynamic gain adjustment is achieved by a close loop monitoring
circuitry, as shown in Fig. 2, which

o   measures the voltage drop across th...