Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q11/00—Selecting arrangements for multiplex systems
  • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
  • H04Q11/0062—Network aspects
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/27—Arrangements for networking
  • H04B10/272—Star-type networks or tree-type networks
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0226—Fixed carrier allocation, e.g. according to service
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
  • H04J14/0228—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths
  • H04J14/023—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON]
  • H04J14/0232—Wavelength allocation for communications one-to-all, e.g. broadcasting wavelengths in WDM passive optical networks [WDM-PON] for downstream transmission
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
  • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
  • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
  • H04J14/0245—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU
  • H04J14/0247—Sharing one wavelength for at least a group of ONUs
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
  • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
  • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
  • H04J14/0249—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for upstream transmission, e.g. ONU-to-OLT or ONU-to-ONU
  • H04J14/0252—Sharing one wavelength for at least a group of ONUs, e.g. for transmissions from-ONU-to-OLT or from-ONU-to-ONU
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0278—WDM optical network architectures
  • H04J14/0282—WDM tree architectures
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/0298—Wavelength-division multiplex systems with sub-carrier multiplexing [SCM]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q11/00—Selecting arrangements for multiplex systems
  • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
  • H04Q11/0062—Network aspects
  • H04Q11/0067—Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04Q—SELECTING
  • H04Q11/00—Selecting arrangements for multiplex systems
  • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
  • H04Q11/0062—Network aspects
  • H04Q11/0071—Provisions for the electrical-optical layer interface

Definitions

• Fiber optic local access communication system carrying both addressed and broadcast traffic.
• Fiber optic systems currently in use do not carry signals all the way to the user premise. Copper systems do go to the user premise but usually devote one wire from the head end to each user and do not multiplex multiple signals onto one wire.
• Coax broadcast systems carry signals all the way to the user but carry all signals to each user. Some channels are encrypted lightly and the key to unscramble is made available to selected subscribers only. This facilitates pay-per-view but is often defeated by hackers. In any case present systems carry low bandwidth and do not usually deliver addressed multiple simultaneous signals through one "wire” to the user. By “wire” I mean copper wire, fiber, or coax cable.
• the present invention comprises a fiber optic network and the method embodied in the network, the components of the network, e.g. an optical frequency filter, remote pumping of an amplifier and optical frequency shifter, the network having a fiber leading from a "head-end" station outward toward users and carrying signals to be delivered to those users.
• the fiber branches one or more times but at each branch there is an optical frequency filter which allows certain wavelength channels to travel along one branch and other wavelength channels to travel along another branch. The branching continues until one final twig carries one optical frequency channel to one individual user.
• the branches if any, do not have filters but simply divide the power, and finally the last segment which we call a "street line" taps off a small amount of power to each user.
• the tap is followed by a filter that allows only one channel to pass to the customer premise.
• At the head end one optical frequency channel is allocated to each user.
• These channels are multiplexed onto one fiber leaving the head-end and are routed by means of filters so that the channel allocated to a certain user is delivered only to that user. Therefore, scrambling is not necessary for privacy though it may be provided for additional security against eavesdroppers who may cut into one of the main fibers going along the street.
• the optical frequency channel assigned to each user has a very large bandwidth compared to any single signal now used and is divided into sub-channels as needed by the user with each sub-channel carrying a separate signal.
• Signal traffic from the user back to the head-end is carried, in one embodiment, back to the head-end through a filtered, branched network like the one just described.
• the filters are not absolutely necessary but they conserve signal power at the branch points and they prevent one user from encroaching on the inbound channel of another user.
• the same branched network which carries outbound traffic also carries in-bound traffic.
• an inbound signal obtains an un-modulated source line to be modulated by an electrical signal by either filtering out an un-modulated line sent by the head-end to the user and using that line or by generating the line with an on-premise laser tuned relative to the out-bound un-modulated line.
• the in-bound channel is displaced in optical frequency to lie beside the out-bound channel and the filters have a pass-band sufficient to pass both inbound and outbound.
• the sub-channels assigned to each user are accompanied by a heterodyne line.
• the signals go into a detector which produces electrical signals with beat frequencies corresponding to the optical frequency difference between each signal and the heterodyne line.
• the individual signals are then recovered by electrical filtering of the beat frequencies.
• This has the distinct advantage that the optical signals may be in analog form and the final detected electrical signal will be in a form suitable for the most common kinds of terminal equipment, such as telephones or television.
• other sub-channels can carry signals in digital format destined for computers or the like.
• neodymium doped optical fiber amplifiers operating in the 1.06 micron wavelength window are used. They are preferably side pumped.
• amplifiers may be used if they are so-called "4 level” laser amplifiers. Amplifiers which require the ground state to be depleted go black when pump power fails. 4-level amplifiers remain transparent. It is also desirable to have large gain bandwidth and a fairly smooth gain curve which can be easily flattened by filtering.
• FIG. 1 is an illustration of a fiber optic network distribution system embodying the invention
• Fig. 2 is an illustration of the line drops on a particular street.
• Fig. 3 is an illustration of the optical connections and system of a typical end user.
• Fig. 4 is an alternative embodiment of the invention wherein there are a small number of broadcast channels delivered to all customers leaving the channel selection to be done on premise.
• Fig. 5 is an illustration of a multi-pass Fabry Perot interferometer
• Fig. 6 is an illustration of the head end handling source lines
• Fig. 7 is an illustration of the distribution of un-modulated source lines
• Fig. 8 is an illustration of illustration of sub-channels accompanied by heterodyne lines
• Fig. 9 is an illustration of exemplary frequencies using heterodyne detection
• Fig. 10 is further illustration of various frequencies using heterodyne detection
• Fig. 11 illustrates a frequency shifter
• Fig. 12 is a schematic of multiple detectors at the user end
• Fig. 13 illustrates one signal arrangement for using fiber optic line for both outgoing and incoming traffic.
• the total useful amplification width of Neodymium in the 1.06 micron window is about 10 13 Hz. Assuming the network has 200 users (although a larger number is possible) the bandwidths can be spaced around 10 10 Hz and each customer can be assigned a 1 X 10 9 Hz bandwidth channel.
• broadcast channels are delivered to a user by the user selecting a desired channel from a bus at the head end by means similar to present day channel selection by a TV set.
• the selected channel (electrical signal) then modulates an optical source line at the head end which is assigned to the user making the selection. This signal is then treated like any "addressed" signal destined for that user.
• the first advantage occurs if there are a large number of channels on a bus or buses at the head end. For example, if there are 100,000 channels then it would require a large amount of signal power to deliver them all to all users. Whereas if there are 200 users on one common line then only 200 channels are delivered on that line except that some users will have 2 or 3 TV sets of course.
• the second advantage is that the channel selection occurs beyond the customer's reach and can be programmed and controlled. For example, pay-per-view can be monitored and billed at the head end channel selector so the user cannot by-pass the billing - as is often the case now.
• the user can appear in person at the head end and program the channel selector to reject certain types of programs, such as pornography or violence. If this self- censorship is attempted on the user premise then adolescent children are likely to be able to defeat the self-censorship.
• a small number of channels for example 50 , can be delivered to all customers leaving the channels selection to be done on- premise. Since most users will probably be watching no more than 20 channels total this saves, to some extent, on the cost of channel selectors at the head end.
• a separate fiber carries all these "common” channels.
• bypass filters carry theses broadcast channels (on optical sub-channels within a large channel). Around all filters so that this one broad channel is delivered to many users.
• the head end channel embodiment and the "common channel” embodiment can be done together or separately. That is, a particular system, may embody either scheme or both.
• a system is shown generally at 10 and comprises a head end 12 and single fiber optic lines 14a, 14b, and 14c, each of which branches into a service area 16, only 16a shown.
• Four street lines 18a-18d are shown with the ultimate user or customer designated U.
• the line 18a is shown and comprises neodymium optical amplifiers as needed, a partial lateral couple 22 followed by a filter 24 located between the user and the street line.
• the amplifier is gain flattened as needed. Gain flattening is well understood in the art.
• the bandwidth e.g. lxl 0 9 Hz
• the signal is amplified by a neodymium optical amplifier 26 if needed. If the amplifier is used an additional filter 28 eliminates spontaneous amplifier emission.
• a return signal to the head end flows from the tap 30 to a filter 36 to pick off the heterodyne line.
• a modulator 38 puts the electric signal into optical form. This signal is coupled back into the incoming line.
• An isolator 40 prevents incoming signals from traveling in the reverse direction.
• a system is shown wherein a broad-channel containing several broadcast sub-channels delivered to all customers, for example 50 channels.
• the channel selection for these is done on- premise.
• the filters 52 and the branching of a fiber optic line 54 function as described for the preferred embodiment.
• the filter F n 56 allows the addressed channel to pass to the user which is then combined with broadcast channels C 0 .
• a pump beam is preferably generated on the user premises by laser diode and carried up to the amplifier 20 on the fiber.
• the laser diode on the customer premise is preferably powered by a rechargeable battery so that if the electric power system fails the amplifiers will continue to operate.
• Users are assigned an optical frequency channel and traffic to the user is modulated onto the assigned channel at the head end and routed to the user by optical frequency filtering. To get good separation, the channel widths are made small compared to the channel separation, e.g. 1X10 9 Hz width with 10 10 Hz separation.
• a 2-arm fiber interferometer can be used for filtering and can be temperature stabilized by putting it in a constant temperature housing. Alternatively, a portion of the length of the shorter of the 2 arms can be put in a positive expansion device to compensate for temperature changes. Finally, after all the path splits, a different kind of filter 24 is used to drop to the users on the last branch.
• These filters can be multi-layer dielectric filter which can separate channels 10 11 Hz apart (at 1.06 micron wavelength). With a total spectral width of 10 13 Hz, 100 channels can be separated.
• Fig. 5 This filter is a simple Fabry Perot interferometer with 2 parallel partial mirrors separated by a zero thermal expansion spacer. The mirrors are tilted enough so the reflected light does not go back into the input fiber.
• the filtered light goes back through the mirrors as illustrated in Fig. 5 at 71.
• the output fiber can circle around and send the filtered light back in for two more passes through the filter. This can be continued for several more passes.
• a signal coming from the central system is detected at 60, modulated at 62 and transferred to the main fiber 14 outbound which serves the intended user.
• a "bank" 64 is provided in the head end 10 with 200 unmodulated source lines (if there are 200 users per field line) and split so that each source line serves each of the field lines.
• a wide channel for example 1X10 9 Hz is allocated to each user and is divided into optical frequency sub-channels as needed to carry a variety of signals.
• these channels are de-multiplexed by the receiver using heterodyne detection, Fig. 8.
• the heterodyne line is spaced so that the lowest beat frequency is higher than the highest beat between sub-channels. This reduces interference between signals.
• An optical frequency shifter can be used instead of simply modulating with the RF carriers.
• the "frequency shifter” is simply a single side band device as shown in Fig. 11.
• One modulator drives “in quadrature” with the other and we adjust the phase between the two paths such that one side band exits A and the other B.
• the optical phase adjustment is "semi-permanent" - not variable.
• the RF frequencies can come from an electronic bank of frequencies.
• the total batch of optical signals is detected and RF filters separate the signal channels in the electric domain after detection in much the same way that a channel selector chooses TV channels.
• the head end there can be addressing logic to assign an incoming signal to one of the several RF carriers. For example, if the user has his fax machine permanently tuned to receive channel f 5 , then at the head end the logic will recognize that a certain incoming signal addressed to this user is a fax signal and will modulate it onto f 5 . If the incoming signal is a voice phone signal, it will modulate it onto whatever RF channel the user has his phone tuned to. In one embodiment, the "tuning" can occur at the user end instead of the head end. In a more general embodiment, there is some tuning at head end and some at the user end.
• f 5 , f 6 , f there are 3 voice telephones on the user premises, they can be assigned to f 5 , f 6 , f .
• An incoming call can be addressed at the head end to any one of them that is not in use.
• the next incoming voice call can be directed by local tuning to a certain one of the phones.
• the incoming signals to the user can be detected and distributed in electric from to various pieces of terminal equipment or distributed optically and then detected at the terminal equipment. Both are shown in Fig. 12.
• the signals from the user to the head-end are carried on the same fiber that carries the out-bound traffic.
• sub-channels are assigned for return traffic, see Fig. 13.
• a local laser is provided and is tuned to operate at the heterodyne optical frequency or is tuned at a fixed spacing from the heterodyne.
• Local signals are put on RF carriers just as they are at the head end and combined and modulated onto the local oscillator line. Again, care is taken to displace the unwanted side bands so they cause no confusion or to filter them out.
• the return traffic passes backward through all the routing filters and arrives at the main fiber and is carried back to the head-end. There it passes through a filtered routing system very similar to the one described before — so that each user's inbound signals are directed to one point - where they are heterodyne detected and electronically separated to be used for transmission in the central communication system.
• the power level of the signals should be high enough so that quantum statistics doesn't produce perceptible noise.
• For a "virgin" pulse of photons in digital modulation about 100 photons per bit is sufficient. That is to say 100 detected photons.
• N eff ective is the number of "virgin" photons which would have the same spread as the processed batch.
• the signal is converted to logarithmic form so the number of photons transmitted is proportional to the (log) 2 of the signal and then at the receive end the signal is converted back to its original form then about 900 photons is sufficient for the maximum signal "pixel". What this transformation does is keep the noise level (in decibels) throughout the range from 1 to 1,000. And at 900 photons for the 1,000 level, the noise is such that there is about a 50 % chance of being off by 2 dB - - throughout the whole range.
• heterodyne detection is a form of filtering and is helpful.
• the most economical filter is a planar dielectric milt-layer filter. These can be made at a reasonable expense to pass about 10 11 Hz and reject the rest of the optical spectrum of the amplifier at 1.06 microns.

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• Optical Communication System (AREA)

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• 2001
  • 2001-07-26 AU AU2001280790A patent/AU2001280790A1/en not_active Abandoned
  • 2001-07-26 WO PCT/US2001/023485 patent/WO2002011340A1/en active Application Filing
  • 2001-07-26 EP EP01959208A patent/EP1410543A4/de not_active Withdrawn

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