Integrated optical router

Details Integrated optical router Integrated optical router

2002-02-22

2004-07-27

Lee, John D. (Department: 2874)

Optical waveguides

Integrated optical circuit

C385S024000, C385S016000, C385S037000, C398S043000, C398S045000, C398S048000, C398S049000, C398S050000, C398S051000, C398S055000, C398S056000, C398S057000

Reexamination Certificate

active

06768827

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to switches used in communications networks. In particular, it relates to optical routers.
2. Background Art
The advancement of telecommunications technology over the past two decades has included two significant developments: (1) large, high-capacity networks based on packet switching; and, (2) optical fiber transmission media and in particular silica fiber and the use of wavelength division multiplexing to further increase the fiber bandwidth. Combining the two has presented some difficulties.
There are several types of commercially important packet networks. Asynchronous transfer mode (ATM) was developed in the telephone industry and is based on ATM cells having a fixed length of 53 bytes. Multiple ATM cells are identified to a virtual communications circuit.
Another type of network assuming greater importance and being implemented in many environments is related to the Internet communications network based on the TCP/IP protocol. The TCP/IP protocol applies to many levels of communications networks, but some of the most challenging applications involve the switched connections between different computer networks. An Internet-type of communications network
10
, as schematically illustrated in
FIG. 1
, connects multiple terminals
12
through nodes
14
interconnected by bi-directional communications links
16
. The terminals
12
can be considered to be ports to other, perhaps different, types of computer networks. The nodes
14
are based on routers which can route sequentially received frames in different directions as the frame propagates through the network
10
from the source terminal
12
to the destination terminal
12
. The preferred term for packets is a frame
18
, which as illustrated in
FIG. 2
, is composed for a serial link of a header
20
and an immediately following data payload
22
. That is, the header
20
and payload
22
are time multiplexed. The header
20
contains among other items a destination for the frame
18
. The data payload
22
is often of variable length, in which case the header
20
includes an indication of the length, but the overall frame is relatively short, on the order of a few hundred bytes. Sometimes a trailer is included to mark the end of the frame.
Although much of the following description is based on the multiply connected fiber network of FIG.
1
and with the routers being based at the nodes
14
, the invention can be used with other types of networks, and routers are used in yet other configurations. In one example, the links may be of different forms linking different types of nodes, including satellites, airplanes, and complexly connected systems of multiple computers. In a second type of networks, as illustrated in the network diagram of
FIG. 3
, an inter-connected ring network
26
includes multiple bi-directional rings
28
a
,
28
b
,
28
c
, each including two counter-propagating optical fibers
30
,
32
, which provide redundant paths in case the pair of fibers
30
,
32
is cut at any one point. That is, the rings
28
are survivable. Terminals
34
are connected to the respective rings
28
through nodes
36
. Cross connects
38
link different ones of the rings
28
. In a more realistic telephone or data network, a cross connect
38
may link more than two rings at a central communications hub.
Each of the rings
28
is typically controlled fairly tightly. A ring network which uses optical fiber for the transmission medium may employ wavelength division multiplexing (WDM), in which a single fiber conveys multiple optical carriers impressed with different data signals. In a WDM environment, packets between different pairs of terminals
34
on the same ring
28
may be identified and switched according to optical wavelength. However, such tight control becomes difficult for switching signals through the cross connects
38
between different rings
28
. A packet switched system typically then requires that the cross connects
38
interrogate the frame header and switch only those frames destined to go outside of the originating ring
28
. That is, the inter-ring cross-connects are advantageously based on routers. For a WDM environment, the cross-ring switching also strongly needs translation between WDM wavelengths to allow reuse of wavelengths and prevent undue constraints on routing and timing. It is also possible that the intra-ring nodes
36
are based on routers which extract from the ring
28
only those frames destined for the associated terminal
34
. Further, the terminals
34
(or terminals
12
of
FIG. 1
) may represent an interface to a local network, such as an Ethernet network, in which only some of the packets need to be transferred from the local network onto the ring
28
, for possible retransmission to yet other rings. Thus, the terminal
34
may additionally incorporate a router to transfer only selected ones of the packets that it receives from within the local network.
Returning to
FIG. 1
, the original TCP/IP networks were based on high-speed digital electrical links
16
, on which the frames
18
are transmitted in sequential fashion. A router receives a frame
18
on an incoming link
16
, determines from the header
20
where the frame
18
should go, and accordingly retransmits the entire frame
18
onto the desired outgoing link
16
. Typically, the received frame is stored in a memory, called a buffer, which allows time for the router to determine from lookup tables which outgoing link corresponds to the destination address. The robustness of the Internet derives from the fact that the nodes
14
are nearly autonomous with very little central control and from the further fact that multiple paths usually exist between the source and destination terminals. In such a loosely controlled network, frames arrive at a node
14
at nearly random times with nearly arbitrary destinations. In particular, two or more frames may arrive nearly simultaneously on different incoming links and require switching to the same outgoing link. The buffer allows for temporary storage of frames awaiting retransmission on a busy link.
The data rate for a network based on electrical links is typically determined by the operating frequency of the electronic routers and their associated electronic receivers and transmitters. At present, the maximum data rate for commonly used electronic systems is about 10 gigabits per second (Gb/s) although 40 Gb/s systems are being developed. Further increases will prove difficult. A 10 Gb/s transmission link conveys a 500 byte frame (each byte being 8 bits) in 400 ns. Since packets need to be individually switched, packet switching times should be substantially less than this time in order to not impact transmission capacity.
Optical fiber presents many advantages in communications network including speed, cost, security, and noise immunity. As originally applied to networks, a fiber was used to carry in one of the fiber transmission bands a single optical signal that had been modulated by an electronic data signal. In a point-to-point system, each link of the network included optical receivers and transmitters including electro-optical (E/O converters at the respective nodes interconnected by an optical fiber. Three commonly used transmission bands extend over wavelengths in the neighborhoods of 850 nm, 1310 nm, and 1550 nm. The 1310 nm band is typically interpreted as extending from 1290 to 1330 nm, and the 1550 nm band extends from 1520 to 1580 nm. The 1310 nm band is usually used in local networks because of its low frequency dispersion and hence high data rates while the 1550 nm band is favored in long distance networks because of its lower absorption. The 850 nm band extending from 800 to 900 nm is also available for less extended networks. The wavelengths between the bands are generally not usable because of excessive fiber absorption. Efforts are continuing to expand the widths of these bands. Optical fibers of other compositions have other transmission bands, but non-silica fibers

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