Ashok V. Krishnamoorthy,
Fang Xu,
Joseph E. Ford,
and Yeshayahu Fainman
A. V. Krishnamoorthy and J. E. Ford are with the Advanced Photonics Research Department, Bell Laboratories, Lucent Technologies, Holmdel, New Jersey 07733.
F. Xu and Y. Fainman are with the Electrical and Computer Engineering Department, University of California, San Diego, La Jolla, California 92093-0407.
Ashok V. Krishnamoorthy, Fang Xu, Joseph E. Ford, and Yeshayahu Fainman, "Polarization-controlled multistage switch based on polarization-selective computer-generated holograms," Appl. Opt. 36, 997-1010 (1997)
We describe a polarization-controlled free-space optical multistage
interconnection network based on polarization-selective computer-generated
holograms: optical elements that are capable of imposing arbitrary,
independent phase functions on horizontally and vertically polarized
monochromatic light. We investigate the design of a novel nonblocking
space-division photonic switch architecture. The multistage-switch
architecture uses a fan-out stage, a single stage of 2 × 2 switching
elements, and a fan-in stage. The architecture is compatible with several
control strategies that use 1 × 2 and 2 × 2 polarization-controlled
switches to route the input light beams. One application of the switch is in
a passive optical network in which data is optically transmitted through the
switch with a time-of-flight delay but without optical-to-electrical
conversions at each stage. We have built and characterized a
proof-of-principle 4 × 4 free-space switching network using three
cascaded stages of arrayed birefringent computer-generated holographic
elements. Data modulated at 20 MHz/channel were transmitted through the
network to demonstrate transparent operation.
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The architecture was circuit switched.
For the worst-case optical path loss.
αs is the insertion loss per switch, in decibels.
For the worst-case SNR. βs
is the cross-talk isolation per switch, in decibels.
In the entire network.
The SNR in this case is due to second-roder cross talk.
Table 2
Performance Scaling for Various Configurations of the Stretch Network versus the Network Size Na
Stretch AS/PC tied control lines; fan-in to receivers
(log2N)αs
βs - 10 log10(N/2)
log2N
N(N/2 - 1) + (N2/4)
1 × 2 2 × 2
Stretch PS/PC separate receivers
αs + 3(log2N - 1)
βs
1
(N2/4)
2 × 2
Full space-division switch AS/AC fan-out equals
N
(2 log2N)αs
2βs - 10 log10(log2N) (second-order cross talk)
2 log2N
2N(N - 1)
1 × 2
Either AS or PS may be used in the
fan-out module. For small networks, the fan-in modules may use PC
with either optical fan-in or separate receivers. For large
networks, the fan-in modules should use AC. The control signals
in a stage of an active splitting (fan-out) or an active combining
(fan-in) module can be tied together to reduce the number of
separate control lines.
The architecture is circuit switched.
For the worst-case optical path
loss. αs is the insertion loss per
switch, in decibels.
For the worst-case
SNR. βs is the cross-talk isolation
per switch, in decibels. SNR is limited by first-order cross talk
unless otherwise noted.
Number in the entire network.
Table 3
Performance Estimates for a Scalable Switch (N ≥ 1024 Channels) and Best Experimental Results to Date for 1 × 2, 2 × 2, and 4 × 4 BCGH Switches
Performance Estimates
Experimental Results
η = 98%
η ≈ 60% (four-level phase)
Rg = Rm = 99%
Rg = Rm ≈ 99%
C = 98%
C = 98%
2 × 2 switch efficiency of 98% insertion loss of -0.64 dB
2 × 2 switch efficiency of ≈36% insertion loss of -4 dB
2 × 2 switch SNR of 20–30 dB
1 × 2 switch SNR of 22 db (160:1)
2 × 2 switch SNR of 16 dB (40:1)
4 × 4 switch SNR of 13 dB (20:1)
Tables (3)
Table 1
Performance Scaling for Several Well-Known Photonic Switch Architectures in Terms of the Network Size N
The architecture was circuit switched.
For the worst-case optical path loss.
αs is the insertion loss per switch, in decibels.
For the worst-case SNR. βs
is the cross-talk isolation per switch, in decibels.
In the entire network.
The SNR in this case is due to second-roder cross talk.
Table 2
Performance Scaling for Various Configurations of the Stretch Network versus the Network Size Na
Stretch AS/PC tied control lines; fan-in to receivers
(log2N)αs
βs - 10 log10(N/2)
log2N
N(N/2 - 1) + (N2/4)
1 × 2 2 × 2
Stretch PS/PC separate receivers
αs + 3(log2N - 1)
βs
1
(N2/4)
2 × 2
Full space-division switch AS/AC fan-out equals
N
(2 log2N)αs
2βs - 10 log10(log2N) (second-order cross talk)
2 log2N
2N(N - 1)
1 × 2
Either AS or PS may be used in the
fan-out module. For small networks, the fan-in modules may use PC
with either optical fan-in or separate receivers. For large
networks, the fan-in modules should use AC. The control signals
in a stage of an active splitting (fan-out) or an active combining
(fan-in) module can be tied together to reduce the number of
separate control lines.
The architecture is circuit switched.
For the worst-case optical path
loss. αs is the insertion loss per
switch, in decibels.
For the worst-case
SNR. βs is the cross-talk isolation
per switch, in decibels. SNR is limited by first-order cross talk
unless otherwise noted.
Number in the entire network.
Table 3
Performance Estimates for a Scalable Switch (N ≥ 1024 Channels) and Best Experimental Results to Date for 1 × 2, 2 × 2, and 4 × 4 BCGH Switches
Performance Estimates
Experimental Results
η = 98%
η ≈ 60% (four-level phase)
Rg = Rm = 99%
Rg = Rm ≈ 99%
C = 98%
C = 98%
2 × 2 switch efficiency of 98% insertion loss of -0.64 dB
2 × 2 switch efficiency of ≈36% insertion loss of -4 dB