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Fast Tunable Optical Filter for WDMA

IP.com Disclosure Number: IPCOM000109057D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 6 page(s) / 310K

Publishing Venue

IBM

Related People

Choy, MM: AUTHOR [+3]

Abstract

A high-speed, wide-tuning range (1.3 mm-1.6 mm), high-resolution, compact, and potentially low-cost optical tunable filter is proposed for high-density wavelength division multiple access (HD-WDMA) application. The device is based on the design of cascading two electronically tunable filters. The first one, an acousto-optical filter, which acts as a coarse tuning filter has a wide tuning range but with poor resolution. The second one, a carrier-induced index-tuned Fabry-Perot filter, which acts as a fine tuning filter, has a limited tuning range but with high resolution.

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Fast Tunable Optical Filter for WDMA

       A high-speed, wide-tuning range (1.3 mm-1.6 mm),
high-resolution, compact, and potentially low-cost optical tunable
filter is proposed for high-density wavelength division  multiple
access (HD-WDMA) application.  The device is based on the design of
cascading two electronically tunable filters.  The first one, an
acousto-optical filter, which acts as a coarse tuning filter has a
wide tuning range but with poor resolution.  The second one, a
carrier-induced index-tuned Fabry-Perot filter, which acts as a fine
tuning filter, has a limited tuning range but with high resolution.

      A compact, high-speed tunable optical filter with a large
tuning range >200 nm) and narrow bandwidth can significantly improve
the performance of a wavelength division multiple access system.
Currently available devices are limited either by the tuning speed,
the filter bandwidth or the size of the device.  Here, we propose a
compact tunable device that can be tuned over a range from 1.3 to 1.6
mm with tuning speed of N 1 ms, spectral resolution of N 1o, and has
the potential of being integrated on a hybrid silicon bench
micro-optic unit.

      Propose here is a unique combination of coarse-fine filter in
which the acousto-optic tunable filter (AOTF) as the coarse-tuned
filter while a semiconductor index-tuned narrow band filter as the
fine-tuned filter.  The invention is based on the design of cascading
two filters together where the first one serves the coarse tuning
while the second one serves the fine  tuning. In this approach, the
tuning range of the second filter has to cover the passband of the
first filter (1).

      The motivations for cascading filters together in a coarse-fine
manner are:
      o   the wavelength control is much easier as compared to
cascading of two filters of similar bandwidth based on vernier
effect,
      o   requirements on wide tunability and narrow bandwidth are
kept separate in the cascaded configuration.

      The proposed design is shown in the figure, using an AOTF for
the coarse filtering and an index-tuned semiconductor filter for the
fine filtering.  This combination is capable of achieving a wide
tuning range (>200 nm) in microsecond response time with potential
applications to packet switching in the 100 s of Mbps regime.

      The key feature of the coarse-fine approach is that the tuning
range is determined by the coarse filter, while the fine filter gives
the resultant resolution.  Hence, this combination is capable of very
high channel capacity.  Following (2), taking 0.5 o as the resolution
bandwidth, and conservatively doubling the margin, i.e., 2 o channel
spacing would result in 1000 channels, using 2 x 100 nm as the
available laser bands at 1.3 and 1.5 mm (1280-1380 nm and 1480-1580
nm).  The AOTF has demonstrated a wide tuning range of 1.3 - 1.6 mm
(3,4).  Its transfer function is a sinc function with a wide tunin...