U.S. patent application number 13/527573 was filed with the patent office on 2013-08-29 for time/wavelength-division multiplexed passive optical network (twpon).
This patent application is currently assigned to National Taiwan University of Science and Technology. The applicant listed for this patent is San-liang Lee. Invention is credited to San-liang Lee.
Application Number | 20130223841 13/527573 |
Document ID | / |
Family ID | 49002987 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130223841 |
Kind Code |
A1 |
Lee; San-liang |
August 29, 2013 |
TIME/WAVELENGTH-DIVISION MULTIPLEXED PASSIVE OPTICAL NETWORK
(TWPON)
Abstract
The present invention discloses a time/wavelength-division
multiplexed passive optical network (TWPON), which has an optical
splitter (21) and a waveguide grating router (WGR) (22) disposed at
a remote node (RN) (20). The optical splitter (21) and the WGR (22)
can be connected in a cascade or in a parallel such that the
present invention can use less number of wavelengths to increase
transmission capacity or increase the number of users. The TWPON of
the present invention can provide TDM-PON, WDM-PON, and Hybrid PON
co-existing platform with less wavelengths channel fault monitoring
mechanism.
Inventors: |
Lee; San-liang; (Taipei
City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; San-liang |
Taipei City |
|
TW |
|
|
Assignee: |
National Taiwan University of
Science and Technology
Taipei City
TW
|
Family ID: |
49002987 |
Appl. No.: |
13/527573 |
Filed: |
June 19, 2012 |
Current U.S.
Class: |
398/72 |
Current CPC
Class: |
H04J 14/0235 20130101;
H04J 14/0282 20130101; H04J 14/02 20130101; H04J 14/0232 20130101;
H04J 14/0265 20130101; H04J 14/0246 20130101; H04J 14/0247
20130101; H04J 14/0227 20130101; H04J 14/08 20130101; H04J 14/0252
20130101; H04J 14/025 20130101 |
Class at
Publication: |
398/72 |
International
Class: |
H04J 14/02 20060101
H04J014/02; H04J 14/08 20060101 H04J014/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 29, 2012 |
TW |
101106524 |
Claims
1. A time/wavelength-division multiplexed passive optical network
(TWPON), which is divided into an optical line terminal, a remote
node, and a plurality of optical network units in structure,
characterized in that the TWPON comprises: an optical splitter for
splitting a mixed optical signal, comprising a set of wavelengths
that are different from each other, received from the optical line
terminal to form multi-way mixed optical signals; and a
multiple-input and multiple-output waveguide grating router,
coupled to the optical splitter, having a plurality of input ports
and a plurality of output ports, wherein the input ports
respectively receive the multi-way mixed optical signals, and the
output ports respectively output wavelength components of each
mixed optical signal of the multi-way mixed optical signals to the
optical network units, wherein at least two optical network units
receive optical signals, which are coded and transmitted with a
time-division manner, having the same wavelength component.
2. The TWPON according to claim 1, wherein one of the input ports
of the multiple-input and multiple-output waveguide grating router
receives another mixed optical signal, the multiple-input and
multiple-output waveguide grating router respectively outputs
component signals of said another mixed optical signal to
predetermined optical network units.
3. The TWPON according to claim 2, further comprising a wavelength
band filter coupled to the optical splitter and the multiple-input
and multiple-output waveguide grating router, the wavelength band
filter is utilized to allow merely the mixed optical signal to
enter the optical splitter and allow merely said another mixed
optical signal to enter one of the input ports of the
multiple-input and multiple-output waveguide grating router.
4. The TWPON according to claim 1, wherein the optical splitter and
the multiple-input and multiple-output waveguide grating router are
located at the remote node.
5. A time/wavelength-division multiplexed passive optical network
(TWPON), which is divided into an optical line terminal, a remote
node, and a plurality of optical network units in structure,
characterized in that the TWPON comprises: a first-stage optical
splitter for splitting a received time-division optical signal to
form multi-way time-division optical signals; a multiple-input and
multiple-output waveguide grating router, coupled to outputs of the
optical splitter, having a plurality of input ports and a plurality
of output ports, wherein the input ports respectively receives the
multi-way time-division optical signals, the output ports
respectively outputs the multi-way time-division optical signals,
and each output port outputs a single time-division optical signal;
a plurality of second-stage optical splitters respectively coupled
to the output ports of the multiple-input and multiple-output
waveguide grating router, wherein each second-stage optical
splitter is utilized to split the single time-division optical
signal outputted from each output port of the multiple-input and
multiple-output waveguide grating router again, and the
time-division optical signals split and obtained from the
second-stage optical splitters are respectively transmitted to the
optical network units; and a wavelength band filter disposed at a
front end of the first-stage optical splitter, wherein the
wavelength band filter is utilized to select a mixed optical
signal, which comprises a set of wavelengths that are different
from each other, from the optical line terminal, and make the mixed
optical signal entering one of the input ports of the
multiple-input and multiple-output waveguide grating router, the
output ports of the multiple-input and multiple-output waveguide
grating router respectively output wavelength components of the
mixed optical signal to the respective second-stage optical
splitters, and each second-stage optical splitter splits the
received wavelength component again, wherein at least two optical
signals having the same wavelength component received by optical
network units are coded and transmitted with a time-division
manner.
6. The TWPON according to claim 5, wherein the wavelength band
filter is utilized to select another mixed optical signal, which
comprises another set of wavelengths that are different from each
other, from the optical line terminal and make the another mixed
optical signal entering one of the input ports of the
multiple-input and multiple-output waveguide grating router, and
the output ports of the multiple-input and multiple-output
waveguide grating router respectively output component signals of
the another mixed optical signal to predetermined optical network
units.
7. The TWPON according to claim 5, further comprising a
bidirectional transceiver disposed at the optical line terminal for
transmitting and receiving the time-division optical signals.
8. The TWPON according to claim 5, wherein the first-stage optical
splitter, the multiple-input and multiple-output waveguide grating
router, the second-stage optical splitters, and the wavelength band
filter are located at the remote node.
9. A time/wavelength-division multiplexed passive optical network
(TWPON), which is divided into an optical line terminal, a remote
node, and a plurality of optical network units in structure,
characterized in that the TWPON comprises: an optical splitter for
splitting a time-division optical signal received to form multi-way
time-division optical signals; a waveguide grating router, arranged
in parallel with the optical splitter, receives a mixed optical
signal, which comprises a set of wavelengths that are different
from each other, from the optical line terminal and outputs
wavelength components of the mixed optical signal; and a plurality
of wavelength band filters respectively disposed between
corresponding output ports of the optical splitter and the
waveguide grating router, wherein each wavelength band filter is
connected to one optical network unit for selecting the
time-division optical signal to be transmitted with a time-division
manner or selecting one of the wavelength components of the mixed
optical signal to be transmitted with a wavelength-division
manner.
10. A time/wavelength-division multiplexed passive optical network
(TWPON), which is divided into an optical line terminal, a remote
node, and a plurality of optical network units in structure,
characterized in that the TWPON comprises: a first-stage optical
splitter for splitting a time-division optical signal received to
form multi-way time-division optical signals; a waveguide grating
router, arranged in parallel with the first-stage optical splitter,
receives a mixed optical signal, which comprises a set of
wavelengths that are different from each other, from the optical
line terminal, and respectively outputs wavelength components of
the mixed optical signal; and a plurality of wavelength band
filters respectively disposed between corresponding output ports of
the first-stage optical splitter and the waveguide grating router;
and a plurality of second-stage optical splitters, connected to the
wavelength band filters in a one-to-one relationship, utilized for
splitting the time-division optical signals or the wavelength
components of the mixed optical signal from the respective
wavelength band filters again and then transmitting them to the
respective optical network units.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a passive optical network
(PON), and more particularly, to a passive optical network capable
of giving much flexibility to increase transmission capacity and
the number of users.
BACKGROUND OF THE INVENTION
[0002] Generally, a passive optical network comprises an optical
line terminal (OLT), a remote node (RN), and a plurality of optical
network units (ONUs). A terminal such as a personal computer (PC)
is connected to the ONU and the ONU will transform a signal
transmitted from the terminal into an optical signal. The optical
signal is split by an optical splitter at the RN and then
transmitted to a central office (CO) of a service provider, i.e.,
the aforesaid OLT, through an optical fiber. After the OLT performs
various types of signal processing, communication between one ONU
and another ONU or communication between the ONU and another
terminal on network can be carried out.
[0003] Currently, an optical access network can be classified into
a time-division multiplexed passive optical network (TDM-PON), a
wavelength-division multiplexed passive optical network (WDM-PON),
and a hybrid passive optical network (Hybrid PON).
[0004] For TDM-PON, 10G-PON was accomplished and standardized in
2010 and next generation will be 40G-PON or 100G-PON. For 10G-PON,
each concurrent user can have 10/N Gb/s bandwidth in average, where
N is the number of ONUs. In another aspect, the WDM-PON is not
standardized yet. Current technology can offer each user with 1.25
to 10 Gb/s bandwidth. The WDM-PON is a virtual point-to-point
topology, which needs a pair of transceivers at the OLT for each
ONU.
[0005] The TDM-PON structure may not serve the needs when the
demand for larger bandwidth is increased. This is because it might
be more difficult in system design and costly to use higher speed
transceivers that are required in 40G-PON or 100G-PON. Especially,
it might require burst mode transceivers for higher data rate.
Also, power budget might be a problem. It may need avalanche
photo-diode (APD) receivers, forward error correction (FEC)
encoders, or optical amplifiers at the OLT or even at the ONUs.
Further, it may eventually need to use cooled laser sources to
avoid signal fluctuation caused by temperature variation.
[0006] The advantages of the WDM-PON structure is that it has
larger bandwidth and gives much flexibility for different types of
services and different bandwidths, and at the same time has better
security. However, the WDM-PON structure is costly. If services are
provided to N users, N dense wavelength-division multiplexing
(DWDM) transceivers and N colorless ONU light sources are needed at
the OLT.
[0007] However, the DWDM transceivers and colorless light sources
are still quite expensive. In addition, different wavelength bands
may be needed for upstream and downstream transmission. For
example, assuming that the channel spacing is 0.8 nm and the
structure is designed to provide for 32 users, the total optical
bandwidth in use is required to be 51.2 nm, and this occupies a
quite large optical bandwidth.
[0008] Further, for the channel fault monitoring (CFM) issues for
TDM-PON, special high-sensitivity OTDR (optical time-domain
reflectometer) such as a photon-counting OTDR needs to be used for
the monitoring due to large splitting loss of the optical splitter
at the RN. Meanwhile, it is also proposed to add optical filters or
wavelength-selective reflectors (e.g., fiber Bragg gratings, FBG)
to the distribution fibers and use tunable OTDR (T-OTDR) to locate
fiber breaks among the distribution fibers. The tunable OTDR is
relatively high in cost and the use of the tunable OTDR requires a
larger optical bandwidth for the channel monitoring.
[0009] For the channel fault monitoring issues for WDM-PON, a large
optical bandwidth for the channel fault monitoring is needed
because it requires an OTDR with a tunable light source or a
broadband light source to reach each distribution fiber due to the
wavelength selective characteristic of the WGR at the RN. For
example, assuming that the channel spacing is 0.8 nm and the
WDM-PON structure is designed to provide for 32 ONUs, the required
optical bandwidth for the channel fault monitoring is 25.6 nm
besides the possible 51.2 nm bandwidth for the upstream and
downstream transmission. Optical bandwidth might be very tight if
more service channels (e.g., video, audio, or radio over fiber
(RoF)) are going to be added to the WDM-PON structure.
[0010] In addition, Hybrid PON generally has following two types:
(1) cascading WDM-PON with a TDM-PON for extended services to more
users and/or longer distance with an extended box; (2) connecting
WDM-PON and TDM-PON in parallel to provide both point-to-point
(i.e., WDM) and broadcasting (i.e., TDM) services.
SUMMARY OF THE INVENTION
[0011] An objective of the present invention is to provide a
time/wavelength-division multiplexed passive optical network
(TWPON) for giving much flexibility to increase transmission
capacity and the number of users.
[0012] To achieve the above objective, the present invention is to
provide a time/wavelength-division multiplexed passive optical
network (TWPON), which is divided into an optical line terminal, a
remote node, and a plurality of optical network units in structure,
characterized in that the TWPON comprises: an optical splitter for
splitting a mixed optical signal, comprising a set of wavelengths
that are different from each other, received from the optical line
terminal, to form multi-way mixed optical signals; and a
multiple-input and multiple-output waveguide grating router coupled
to the optical splitter, having a plurality of input ports and a
plurality of output ports, wherein the input ports respectively
receive the multi-way mixed optical signals, and the output ports
respectively output wavelength components of each mixed optical
signal of the multi-way mixed optical signals to the optical
network units, wherein at least two optical network units receive
optical signals, which are coded and transmitted with a
time-division manner, having the same wavelength component.
[0013] In another aspect, the present invention provides a
time/wavelength-division multiplexed passive optical network
(TWPON), which is divided into an optical line terminal, a remote
node, and a plurality of optical network units in structure,
characterized in that the TWPON comprises: a first-stage optical
splitter for splitting a received time-division optical signal to
form multi-way time-division optical signals; a multiple-input and
multiple-output waveguide grating router, coupled to outputs of the
optical splitter, having a plurality of input ports and a plurality
of output ports, wherein the input ports respectively receives the
multi-way time-division optical signals, the output ports
respectively outputs the multi-way time-division optical signals,
and each output port outputs a single time-division optical signal;
a plurality of second-stage optical splitters respectively coupled
to the output ports of the multiple-input and multiple-output
waveguide grating router, wherein each second-stage optical
splitter is utilized to split the single time-division optical
signal outputted from each output port of the multiple-input and
multiple-output waveguide grating router again, and the
time-division optical signals split and obtained from the
second-stage optical splitters are respectively transmitted to the
optical network units; and a wavelength band filter disposed at a
front end of the first-stage optical splitter, wherein the
wavelength band filter is utilized to select a mixed optical
signal, which comprises a set of wavelengths that are different
from each other, from the optical line terminal, and make the mixed
optical signal entering one of the input ports of the
multiple-input and multiple-output waveguide grating router, the
output ports of the multiple-input and multiple-output waveguide
grating router respectively output wavelength components of the
mixed optical signal to the respective second-stage optical
splitters, and each second-stage optical splitter splits the
received wavelength component again, wherein at least two optical
signals having the same wavelength component received by optical
network units, are coded and transmitted with a time-division
manner.
[0014] In yet another aspect, the present invention provides a
time/wavelength-division multiplexed passive optical network
(TWPON), which is divided into an optical line terminal, a remote
node, and a plurality of optical network units in structure,
characterized in that the TWPON comprises: an optical splitter for
splitting a time-division optical signal received to form multi-way
time-division optical signals; a waveguide grating router, arranged
in parallel with the optical splitter, receives a mixed optical
signal, which comprises a set of wavelengths that are different
from each other, from the optical line terminal, and outputs
wavelength components of the mixed optical signal; and a plurality
of wavelength band filters respectively disposed between
corresponding output ports of the optical splitter and the
waveguide grating router, each wavelength band filter is connected
to one optical network unit for selecting the time-division optical
signal to be transmitted with a time-division manner or selecting
one of the wavelength components of the mixed optical signal to be
transmitted with a wavelength-division manner.
[0015] In still yet another aspect, the present invention provides
a time/wavelength-division multiplexed passive optical network
(TWPON), which is divided into an optical line terminal, a remote
node, and a plurality of optical network units in structure,
characterized in that the TWPON comprises: a first-stage optical
splitter for splitting a time-division optical signal received to
form multi-way time-division optical signals; a waveguide grating
router, arranged in parallel with the first-stage optical splitter,
receives a mixed optical signal, which comprises a set of
wavelengths that are different from each other, from the optical
line terminal, and respectively outputs wavelength components of
the mixed optical signal; and a plurality of wavelength band
filters respectively disposed between corresponding output ports of
the first-stage optical splitter and the waveguide grating router;
and a plurality of second-stage optical splitters, connected to the
wavelength band filters in a one-to-one relationship, utilized for
splitting the time-division optical signals or the wavelength
components of the mixed optical signal from the respective
wavelength band filters again and then transmitting them to the
respective optical network units.
[0016] Compared to a traditional time-division multiplexed passive
optical network (TDM-PON), the TWPON implemented according to the
present invention can carry out high-capacity transmission at
relatively low cost, and does not have a problem of unable to
increase transmission capacity in the traditional TDM-PON, caused
by the limitation of high-speed transceivers themselves. Compared
to a traditional WDM-PON, the TWPON implemented according to the
present invention can use less numbers of wavelengths to carry out
the same transmission capacity, and meanwhile occupied optical
wavelength bands are relatively small and the cost of used light
sources is relatively low as well. The TWPON of the present
invention can efficiently integrate and access to the network as
desired, is able to provide different services in response to
different demands for transmission bandwidth, and also can increase
transmission capacity at relatively low cost in response to the
increasing of users.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic structural diagram showing a
time/wavelength-division multiplexed passive optical network
(TWPON) according to a first embodiment of the present
invention.
[0018] FIG. 2 is a schematic diagram showing input and output of a
waveguide grating router.
[0019] FIG. 3 is a schematic structural diagram showing a TWPON
according to a second embodiment of the present invention.
[0020] FIG. 4 is a schematic diagram showing an optical network
unit in the second embodiment of the present invention.
[0021] FIG. 5 is a schematic structural diagram showing a TWPON
according to a third embodiment of the present invention.
[0022] FIG. 6 is a schematic structural diagram showing a TWPON
according to a fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] FIG. 1 is a schematic structural diagram showing a
time/wavelength-division multiplexed passive optical network
(TWPON) according to a first embodiment of the present invention.
The TWPON according to the first embodiment of the present
invention is a wavelength-division multiplexed passive optical
network (WDM-PON) based on a time-division manner, or called a
WDM-PON like architecture. As shown in FIG. 1, The TWPON of the
first embodiment is divided into an optical line terminal (OLT) 10
(for example, located at a central office (CO) of a service
provider), a remote node (RN) 20, and a plurality of optical
network units (ONUs) 30 in structure. Optical fibers 55 are
distributed therebetween for transmitting optical signals.
[0024] As shown in FIG. 1, a 1.times.n optical splitter 21 and a
M.times.N multiple-input and multiple-output waveguide grating
router (WGR) 22 are arranged at the RN 20.
[0025] The optical splitter 21 receives a mixed optical signal
{.lamda.1, .lamda.2, . . . .lamda.m} from the OLT 10. The mixed
optical signal {.lamda.1, .lamda.2, . . . .lamda.m} comprises a set
of wavelengths (e.g., m wavelengths) that are different from each
other. The optical splitter 21 will split or shunt the mixed
optical signal {.lamda.1, .lamda.2, . . . .lamda.m} to form
multi-way (e.g., n ways) mixed optical signals {.lamda.1, .lamda.2,
. . . .lamda.m}, wherein each way or each channel is constituted of
wavelengths {.lamda.1, .lamda.2, . . . .lamda.m}. The WGR 22 is
coupled to the optical splitter 21 for receiving the multi-way
mixed optical signals from the optical splitter 21.
[0026] The WGR 22 has a plurality of input ports and a plurality of
output ports. Each input port of the WGR 22 receives one mixed
optical signal {.lamda.1, .lamda.2, . . . .lamda.m}. After the
multi-way mixed optical signals from the optical splitter 21 are
routed by the WGR 22, each output port of the WGR 22 will output
one of wavelength components of each mixed optical signal of the
multi-way mixed optical signals, in which one output port can
output one wavelength component to an ONU 30. In such a manner, it
can provide for n.times.m (=N) ONUs 30 as shown in FIG. 1.
[0027] In above arrangement, the WDM-PON like structure merely uses
m wavelengths and n ONUs 30 share the same optical wavelength for
the transmission. Herein, the shared ONUs 30 receiving the same
wavelength component will adopt a time-division manner (i.e., TDM)
for the optical signal coding and transmission. For example,
assuming that 8 wavelengths (m=8) are used and the WDM-PON like
structure is designed to provide for 32 ONUs 30 (N=32), then every
4 ONUs (n=4) shares the same wavelength by using the TDM.
Meanwhile, the ONUs 30 can be equipped with burst mode upstream
transmitters (Tx) for the TDM transmission. In an aspect of
transmission speed, each ONU has B/n bandwidth in average, where B
is the bit rate of each transmitter.
[0028] FIG. 2 is a schematic diagram showing input and output of a
waveguide grating router. The w-th wavelength to connect between an
input port x and an output port y can be expressed as:
w=(N-x+y+1) mod N,
wherein w represents w-th wavelength and N is a maximum input or
output of the array. Therefore, if the mixed optical signal
{.lamda.1, .lamda.2, . . . .lamda.m} is inputted to port 1, m+1,
2m+1, . . . , the output wavelength at port 1, m+1, 2m+1, . . . ,
is all .lamda.1. Likewise, the output wavelength at port 2, m+2,
2m+2, . . . , is all 22, and so on. With such kind of input/output
port connection, output ports k, m+k, 2m+k, . . . , will share the
same wavelength. These ports need to use burst-mode transmitters at
the corresponding ONUs 30 for the TDM transmission. As shown in
FIG. 2, the wavelengths sets enclosed by solid lines show an
example of how 4 wavelengths are used to connect all the output
ports of the WGR.
[0029] Compared to a traditional time-division multiplexed passive
optical network (TDM-PON), the TWPON of the first embodiment of the
present invention can carry out high-capacity transmission at
relatively low cost, and does not have a problem of unable to
increase transmission capacity in the traditional TDM-PON, caused
by the limitation of high-speed transceivers themselves. Compared
to a traditional WDM-PON, the TWPON of the first embodiment of the
present invention can use less numbers of wavelengths to carry out
the same transmission capacity, and meanwhile occupied optical
wavelength bands are relatively small and the cost of used light
sources is relatively low as well. The TWPON of the first
embodiment of the present invention can efficiently integrate and
access to the network as desired for quickly increasing numbers of
users and bandwidth.
[0030] Referring to FIG. 1, the TWPON of the first embodiment of
the present invention further comprises a wavelength band filter 23
disposed at the RN 20. The wavelength band filter 23 is coupled to
the optical splitter 21 and the WGR 22. The wavelength band filter
23 can make the mixed optical signal {.lamda.1, .lamda.2, . . .
.lamda.m} from the OLT 10 to pass the optical splitter 21 and make
another mixed optical signal {.lamda.e1, .lamda.e2, . . .
.lamda.eN} from the OLT 10 to pass one of the input ports of the
WGR 22 such that the mixed optical signal {.lamda.1, .lamda.2, . .
. .lamda.m} is merely allowed to enter the optical splitter 21 and
said another mixed optical signal {.lamda.e1, .lamda.e2, . . .
.lamda.eN} is merely allowed to enter one of the input ports of the
WGR 22. Moreover, the WGR 22 will respectively output component
signals of said another mixed optical signal {.lamda.e1, .lamda.e2,
. . . .lamda.eN} to predetermined ONUs 30. As shown in FIG. 1, a
WDM band filter 24 may be arranged between each output port of the
WGR 22 and corresponding ONU 30. The WDM band filter 24 is utilized
to select the wavelength component of the mixed optical signal or
the wavelength component of said another optical signal as an
output, or select both of them together. If there needs larger
bandwidth or provides other services in the future, said another
mixed optical signal {.lamda.e1, .lamda.e2, . . . .lamda.eN} can be
used to provide for ONUs 30 for greatly increasing transmission
capacity, or served as security channels for improving the ability
to protect the optical distribution network (ODN).
[0031] As shown in FIG. 1, a set of transmitters 11 is arranged at
the OLT 10 and optical wavelengths emitted therefrom are
multiplexed into the mixed optical signal {.lamda.1, .lamda.2, . .
. .lamda.m} by a WGR 13 upon downstream transmission. In upstream
transmission, the mixed optical signal is demultiplexed by a WGR 14
and then received respectively by receivers 12. Extended light
sources also can be disposed at the OLT 10 to generate said another
mixed optical signal {.lamda.e1, .lamda.e2, . . . .lamda.eN} for
increasing transmission capacity or increasing security. A band
filter 15 arranged at the OLT can be utilized to filter wavelengths
adaptively.
[0032] Also, the OLT 10 further comprises a channel fault
monitoring (CFM) module 16 utilized to locate fiber breaks among
distribution fibers. In the first embodiment of the present
invention, the channel fault monitoring only needs an optical
bandwidth covering m wavelengths rather than N wavelengths, and
therefore the number of wavelengths used for the channel fault
monitoring is reduced efficiently. Compared to the traditional
WDM-PON, the present invention uses less numbers of wavelengths for
the channel fault monitoring. If the number of ONUs 30 using the
same wavelength is small (e.g., n=4), the OTDR should be able to
resolve the reflected signals or the distribution fibers can be
easily arranged to have different lengths among the shared ONUs. In
addition, the upstream transmitters can be implemented by adopting
an m-wavelength tunable laser as the light source. Since m is
relatively small (m=4 or 8) in the present embodiment, it can adopt
a standard distributed Bragg reflector (DBR) laser as the light
source. The cost of the DBR is relatively effective as compared to
an injected locked FP laser or a colorless transmitter such as a
reflective semiconductor optical amplifier (RSOA).
[0033] FIG. 3 is a schematic structural diagram showing a
time/wavelength-division multiplexed passive optical network
(TWPON) according to a second embodiment of the present invention.
The TWPON of the second embodiment of the present invention is a
TDM-PON like architecture. The present embodiment mainly uses
two-stage optical splitters provided for time-division optical
signals transmitted in a time-division manner (i.e., TDM). An
M.times.N multiple-input and multiple-output waveguide grating
router is inserted between the two-stage optical splitters. The
TWPON of the second embodiment of the present invention can provide
three classes of services, which respectively are (1) pure TDM-PON
services, (2) Hybrid PON services, and (3) pure WDM-PON services.
Therefore, the TWPON of the second embodiment can provide different
services in response to different demands for transmission
bandwidth and also can increase transmission capacity at relatively
low cost in response to the increasing of users.
[0034] (1) Pure TDM-PON services: a 1.times.n first-stage optical
splitter 27, an M.times.N WGR 28, and a plurality of 1.times.m
second-stage optical splitters 29 are disposed at the RN 20. The
first-stage optical splitter 27 receives a time-division optical
signal .lamda.t from the OLT 10, and splits or shunts the
time-division optical signal .lamda.t to form multi-way (e.g., n
ways) time-division optical signals. The WGR 28 is coupled to the
outputs of the first-stage optical splitter 27. The WGR 28 has n
input ports that respectively receive the aforesaid multi-way
time-division optical signals. The multi-way time-division optical
signals are outputted respectively by output ports of the WGR 28,
wherein each output port outputs a single-way time-division optical
signal. The second-stage optical splitters 29 are respectively
coupled to the output ports of the WGR 28. Each second-stage
optical splitter 28 will split the time-division optical signal
outputted from corresponding output port of the WGR 28 again, for
example, splitting into m ways. The time-division optical signals
from the second-stage optical splitters are respectively
transmitted to the respective ONUs 30. In such a manner, it can
serve n.times.m (=N) ONUs 30 as shown in FIG. 3.
[0035] The time-division optical signals at the wavelength of
.lamda.t can be transmitted and received by using bidirectional
(BiDi) transceivers 17, 34 that are disposed at the OLT 10 and the
respective ONUs 30 (see FIG. 3 and FIG. 4). For example, burst mode
transmitters at the ONUs 30 and burst mode receivers at the OLT 10
are needed for transmitting an upstream time-division optical
signal .lamda.tu in the upstream transmission. Burst mode
transmitters at the OLT 10 and burst mode receivers at the ONUs 30
are needed for transmitting a downstream time-division optical
signal .lamda.td in the downstream transmission. In an aspect of
transmission speed, each ONU 30 has a bandwidth of B1/N, where B1
is the bandwidth of the TDM-PON service.
[0036] (2) Hybrid PON services: a wavelength band filter 26 is
disposed at the RN 20. The wavelength band filter 26 is arranged at
a front end of the first-stage optical splitter 27. The wavelength
band filter 26 is utilized to select a mixed optical signal
{.lamda.1, .lamda.2, . . . .lamda.n} , which comprises a set of
wavelengths (e.g., n wavelengths) that are different from each
other, from the OLT 10, and make the mixed optical signal
{.lamda.1, .lamda.2, . . . .lamda.n} entering one of the input
ports (e.g., (n+1)th input port) of the WGR 28. After the mixed
optical signal {.lamda.1, .lamda.2, . . . .lamda.n} is routed by
the WGR 28, the output ports of the WGR 28 will respectively output
the respective component signals {.lamda.1, .lamda.2, . . .
.lamda.n} of the mixed optical signal to the respective
second-stage optical splitters 29. For example, an optical signal
of i-th wavelength .lamda.i is transmitted to i-th second-stage
optical splitter 29. The component signal received by each
second-stage optical splitter 29 is split to form m ways again, for
example. Therefore, m ONUs 30 share the same wavelength such that
it can serve n.times.m (=N) ONUs 30 as shown in FIG. 3.
[0037] In above arrangement, the WDM-PON merely uses n wavelengths
and every m ONUs shares the same wavelength for the transmission.
The shared ONUs 30 receiving the same wavelength component will
adopt a time-division manner (i.e., TDM) for the optical signal
coding and transmission. For example, assuming that 4 wavelengths
(n=4) are used and the structure is designed to provide for 32 ONUs
30 (N=32), then every 8 ONUs (m=4) shares the same wavelength by
using the TDM. Meanwhile, the ONUs 30 can be equipped with burst
mode upstream transmitters (Tx) for the TDM transmission. In an
aspect of transmission speed, each ONU 30 has B2/m bandwidth in
average, where B2 is the bit rate of each transmitter of the Hybrid
PON.
[0038] (3) Pure WDM-PON services: the wavelength band filter 26
disposed at the RN 20 further can be used to select another mixed
optical signal {.lamda.e,n+1, .lamda.e,n+2, . . . .lamda.e,N} from
the OLT 10 and make said another mixed optical signal
{.lamda.e,n+1, .lamda.e,n+2, . . . .lamda.e,N} entering one of the
input ports of the WGR 28. Said another mixed optical signal
comprises another set of wavelengths that are different from each
other. The output ports of the WGR 28 will respectively output
component signals {.lamda.e,n+1, .lamda.e,n+2, . . . .lamda.e,N} of
said another mixed optical signal to predetermined ONUs 30, for
example, (n+i)th ONU. In such a manner, it can efficiently increase
the number of users. Meanwhile, each ONU 30 can be equipped with a
WDM bidirectional transceiver 36 for the WDM transmission (see FIG.
4). The wavelength components {.lamda.e,n+1, .lamda.e,n+2, . . .
.lamda.e,N} of said another mixed optical signal can be an integer
multiplicity of .lamda.FSR (free spectral range) away from the
wavelength components {.lamda.1, .lamda.2, . . . .lamda.n} of the
mixed optical signal. If there needs larger bandwidth or provides
other services in the future, said another mixed optical signal
{.lamda.e,n+1, .lamda.e,n+2, . . . .lamda.e,N} can be used to
provide for each ONU 30 for greatly increasing transmission
capacity. In an aspect of transmission speed, the bandwidth of each
ONU 30 is B3, where B3 is the bit rate of each transmitter of the
WDM-PON.
[0039] In addition, each ONU 30 may need a WDM band filter 32 to
separate the three classes of service channels. The WDM band filter
32 can also be placed at the output port of the second-stage
optical splitter 29 to provide signals for the ONUs 30.
[0040] A channel fault monitoring (CFM) module 16 located at the
OLT 10 can be utilized to locate fiber breaks among distribution
fibers. In the second embodiment of the present invention, the
channel fault monitoring can follow any of the signal paths of the
three classes of services by using a wavelength band that is an
integer multiplicity of .lamda.FSR away from the signal band and a
suitable band filter. However, it also can merely use the Hybrid
PON path because of its compromised optical bandwidth and splitting
loss for the monitoring signal. This can be implemented by using a
tunable laser or a broadband light source that covers an optical
bandwidth of n wavelengths rather than N wavelengths. In such a
manner, the number of used wavelengths for the channel fault
monitoring is reduced efficiently. If the number of the shared ONUs
30 is relatively small (e.g, m=4), the OTDR should be able to
resolve the reflected signals or the distribution fibers can easily
arranged to have different lengths among the shared ONUs 30 for
performing the channel fault monitoring.
[0041] FIG. 5 is a schematic structural diagram showing a
time/wavelength-division multiplexed passive optical network
(TWPON) according to a third embodiment of the present invention.
As shown in FIG. 5, a 1.times.N optical splitter 27, a 1.times.N
waveguide grating router 28, and a plurality of WDM wavelength band
filters 25 are arranged at the RN 20. The optical splitter 27
receives a time-division optical signal .lamda.t from the OLT 10
and splits the time-division optical signal .lamda.t to form
multi-way (e.g., N ways) time-division optical signals. The WGR 28
is arranged in parallel with the optical splitter 27. The input
port of the WGR 28 receives a mixed optical signal {.lamda.1,
.lamda.2, . . . .lamda.N} from the OLT 10 and the mixed optical
signal {.lamda.1, .lamda.2, . . . .lamda.N} comprises a set of
wavelengths (e.g., N wavelengths) that are different from each
other. The N output ports of the WGR 28 respectively output
wavelength components .lamda.1, .lamda.2, . . . .lamda.N of the
mixed optical signal. The WDM wavelength band filters 25 are
respectively disposed between corresponding output ports of the
optical splitter 27 and the WGR 28. Each one of the WDM wavelength
band filters 25 is connected to one ONU 30 for selecting the
time-division optical signal .lamda.t to be transmitted with a
time-division manner or selecting one of the wavelength components
.lamda.1, .lamda.2, . . . .lamda.N of the mixed optical signal to
be transmitted with a wavelength-division manner. Compared to the
second embodiment, the third embodiment of the present invention
can reduce the number of the WDM wavelength band filter 25. It is
also easier for photonic integration of all passive components at
the RN 20 due to less number of crossovers in the third
embodiment.
[0042] FIG. 6 is a schematic structural diagram showing a
time/wavelength-division multiplexed passive optical network
(TWPON) according to a fourth embodiment of the present invention.
Compared to the third embodiment, the fourth embodiment of the
present invention further comprises a plurality of second-stage
optical splitters 29. Each second-stage optical splitter 29 is
arranged between one WDM wavelength band filter 25 and one ONU 30.
The second-stage optical splitters 29 are connected to the WDM
wavelength band filters 25 in a one-to-one relationship. Each of
the second-stage optical splitters 29 is utilized for splitting a
time-division optical signal .lamda.t or one of wavelength
components .lamda.1, .lamda.2, . . . .lamda.N of a mixed optical
signal from corresponding WDM wavelength band filter 25 again, and
then transmitting them to the respective ONUs 30. In the fourth
embodiment of the present invention, it also can provide another
mixed optical signal {.lamda.e,n+1, .lamda.e,n+2, . . . .lamda.e,N}
for each ONU 30 for further increasing the number of users.
[0043] The advantage of the fourth embodiment of the present
invention is that the TDM-PON transmission does not have extra
insertion loss from the WGR 28.
[0044] While the preferred embodiments of the present invention
have been illustrated and described in detail, various
modifications and alterations can be made by persons skilled in
this art. The embodiment of the present invention is therefore
described in an illustrative but not restrictive sense. It is
intended that the present invention should not be limited to the
particular forms as illustrated, and that all modifications and
alterations which maintain the spirit and realm of the present
invention are within the scope as defined in the appended
claims.
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