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Wavelength Locking Scheme using a Grating Demultiplexer for Applications in WDMA Networks and WDM Links

IP.com Disclosure Number: IPCOM000115551D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 93K

Publishing Venue

IBM

Related People

Janniello, FJ: AUTHOR [+4]

Abstract

WDMA networks and WDM links can exploit the vast bandwidth offered by optical fiber at 1.3&mu.m and 1.55&mu.m windows of low attenuation loss. In both environments, the different emission wavelengths of the transmitters are required to be maintained accurately. Although the transmitter wavelength can be accurately controlled by a thermo-electric cooler (0.1A) attached close to the laser chip, long-term effects due to aging will alter the emission wavelength. Any change in emission wavelength introduces loss in optical power for the individual channel and an increase in crosstalk for neighboring channel in a dense WDMA and WDM environment. Therefore, it is important to monitor and lock the emission wavelengths of the transmitters. Any failure of the laser components, e.g., the thermo-electric cooler, can also be detected.

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Wavelength Locking Scheme using a Grating Demultiplexer for Applications
in WDMA Networks and WDM Links

      WDMA networks and WDM links can exploit the vast bandwidth
offered by optical fiber at 1.3&mu.m and 1.55&mu.m windows of low
attenuation loss.  In both environments, the different emission
wavelengths of the transmitters are required to be maintained
accurately.  Although the transmitter wavelength can be accurately
controlled by a thermo-electric cooler (0.1A) attached close
to the laser chip, long-term effects due to aging will alter the
emission wavelength.  Any change in emission wavelength introduces
loss in optical power for the individual channel and an increase in
crosstalk for neighboring channel in a dense WDMA and WDM
environment.  Therefore, it is important to monitor and lock the
emission wavelengths of the transmitters.  Any failure of the laser
components, e.g., the thermo-electric cooler, can also be detected.

      Fig. 1 shows the schematic of the wavelength sensing and
locking scheme.  As shown in the figure, a small fraction of the
transmitter output optical power (~5-10%) is tapped and
coupled to a SiO sub 2 planar waveguide grating demultiplexer (1).
Nominally, the emission wavelength should match with one of the
output wavelengths as dictated by the positioning of output
waveguides.  An optical fiber is connected from the output waveguide
to a photodetector.  Total optical power from the grating as well as
its time derivative are monitored.  The measured signals can then be
used to lock the emission wavelengths using the scheme implemented in
the IBM* Rainbow network (2).  The details of the locking electronics
are given in Fig. 2.  Modulation of the transmitter can be provided
by ramping the temperature with the thermo-electric cooler by a...