Browse Prior Art Database

Active Optical Star Computer

IP.com Disclosure Number: IPCOM000119627D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 3 page(s) / 121K

Publishing Venue

IBM

Related People

Bowen, DF: AUTHOR [+3]

Abstract

In a wavelength division multiplexed network where an optical star coupler is used to distribute the channels, each at a different wavelength, to multiple users, an ideal optical star coupler will introduce a 1/N power split in the process of broadcasting each input signal equally to all N outputs, given by 10 log10N dB. Though the power from each input is divided by 1/N, the aggregate power on any output remains the same as the input level since N signals are combined in each output. This constant output power at each output port presents a serious saturation problem in optical amplifiers. The typical saturation level of the optical amplifier is Z5 dBm, which is close to the output level of the individual channel transmitter.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Active Optical Star Computer

      In a wavelength division multiplexed network where an
optical star coupler is used to distribute the channels, each at a
different wavelength, to multiple users, an ideal optical star
coupler will introduce a 1/N power split in the process of
broadcasting each input signal equally to all N outputs, given by 10
log10N dB.  Though the power from each input is divided by 1/N, the
aggregate power on any output remains the same as the input level
since N signals are combined in each output.  This constant output
power at each output port presents a serious saturation problem in
optical amplifiers.  The typical saturation level of the optical
amplifier is Z5 dBm, which is close to the output level of the
individual channel transmitter.

      In particular to the computer network environment where the
fiber distances from the coupler to the users are short (Z10 Km) and
the total number of users are large (Z500), the power splitting loss
at the star coupler is the major cause of the signal loss experienced
by each user.  The advent of optical amplifiers, both Er3+ doped
fiber amplifier and semiconductor laser amplifier, at 1.55 mm optical
wavelength, provides an opportunity for recovering the splitting
loss.  However, these amplifiers cannot be placed on the input or
output fiber of the star coupler because power saturation occurs due
to the aggregate power level.  While the amplifier could be placed in
front of a receiver at the user end, this often is not an optimum
placement because the fiber amplifier noise may be comparable to the
desired signal level, thus deteriorating the signal-to-noise level.
Noise and gain saturation considerations require optical gain be
introduced at the region where the loss occurs in the coupler.  It is
the amplifier gain saturation which dominates the number of
amplifiers and pump sources used in the active star coupler. Typical
signal spontaneous noise of 1019A2/Hz/mW dominates over the receiver
thermal noise.

      Our proposal in star coupler may recover all the splitting loss
but the requirement of large number of optical amplifiers
necessitates a new approach.  However, the recent key developments in
device integration suggest a practical and low-cost solution can be
obtained (1).  In particular to this proposal, the semiconductor
amplifier is of interest because (1) its capability in integrating
with InP base optical circuits, (2) multichannel crosstalk impairment
is insignificant since only one or a very few channels are amplified,
and (3) optical coupling could be improved through the use of
low-loss self-aligned waveguides (2), thus reducing the cost in
packaging.

      Many advances have been made in high performance photonic
integrated circuits. These photonic integrated circuits can connect
active lasers, optical combiners, switches and amplifiers, etc, on...