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Tunable Multicast Laser Transmitter using Space Division Routing

IP.com Disclosure Number: IPCOM000110748D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 3 page(s) / 139K

Publishing Venue

IBM

Related People

Li, CS: AUTHOR [+3]

Abstract

This article discloses a novel fast-tunable laser transmitter that is based on the integration of a laser diode array together with a tree of optical waveguide couplers. Tuning is accomplished by electronically enabling array elements which emit light at the desired wavelengths and routing the light to a single output.

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This is the abbreviated version, containing approximately 52% of the total text.

Tunable Multicast Laser Transmitter using Space Division Routing

       This article discloses a novel fast-tunable laser
transmitter that is based on the integration of a laser diode array
together with a tree of optical waveguide couplers.  Tuning is
accomplished by electronically enabling array elements which emit
light at the desired wavelengths and routing the light to a single
output.

      Laser transmitters which have narrow emission spectra and which
can be tuned quickly have wide applications in WDMA networks [1].
Several tunable lasers have been proposed, but they all have one or
more serious limitations, such as limited tuning range, limited
tuning speed, complex control, or lack of multicast capability.

      One approach is to build a single multi-section tunable laser
as described in [2].  Another approach is based on a phase-matched
grating [3].  These devices have good bandwidth and high speed, but
their control is complex and they do not support multicast.  An array
of laser diodes on a chip, where each element in the array emits
light at a different wavelength is described in [4].  The array
consists of 20 DFB lasers with 1 nm separation in wavelength and
could potentially be the basis for a tunable transmitter.

      While generating different wavelengths with the laser array is
feasible, it is generally difficult to couple the light into a single
output fiber.  A grating can be used to collect the light and couple
it into the output, but this approach requires that the laser diodes
emit light at wavelengths determined by their positions relative to
the grating.  Since absolute wavelength accuracy is difficult to
achieve in practice, this is at present a significant problem.

      Another approach to solving the coupling problem is to employ a
binary tree of wavelength independent Y-junction couplers which
combine their two inputs into a single output.  However, since the Y-
junction coupler has an intrinsic loss of 3 dB, an n stage binary
tree of such devices will have a loss of at least 3n dB.  Wavelength
dependent directional couplers can also be used to select between two
different wavelengths appearing on separate input ports; however,
this method is only applicable for two specific wavelengths.  Thus,
this form of coupler cannot be used in a tree structure where
couplers at the kth stage of the tree are required to select one of
2k possible wavelengths.

      The proposed invention is illustrated in the figure.  The
tunable laser transmitter consists of (1) an electronic selector, (2)
a laser diode array, and (3) an optical switch consisting of a tree
of directional couplers interconnected by waveguides.  Laser
radiation from the laser diodes is coupled to the input waveguides of
the tree.  The light is then routed through the tree to a single
waveguide output which can then be coupled to a single-mode fiber.
Two sele...