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Publication numberUS20010017721 A1
Publication typeApplication
Application numberUS 09/810,900
Publication dateAug 30, 2001
Filing dateMar 16, 2001
Priority dateMay 8, 1998
Also published asUS6256124, US20020003642
Publication number09810900, 810900, US 2001/0017721 A1, US 2001/017721 A1, US 20010017721 A1, US 20010017721A1, US 2001017721 A1, US 2001017721A1, US-A1-20010017721, US-A1-2001017721, US2001/0017721A1, US2001/017721A1, US20010017721 A1, US20010017721A1, US2001017721 A1, US2001017721A1
InventorsJohn Hait
Original AssigneeHait John N.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Combination photonic time and wavelength division multiplexing method
US 20010017721 A1
Abstract
A method is hereby disclosed for a combination photonic time and wavelength division multiplexing method. Parallel digital inputs of quantity “n” are input into “n” modulator loaders for loading into “n” photonic modulators, each having a setup time required to provide a stable modulation state. Subsequently, a photonic pulse of a specified frequency reads the modulation state of each of the “n” photonic modulators. The “n” modulation states may then be processed by “n” delay mechanisms to time the modulation states into a serial multiplexed output comprising a series of synchronizing pulses and data digits. Several parallel digital to serial multiplexers, operating at distinct frequencies, may be used in parallel or in series to comprise a wavelength division multiplexer in accordance with the invention. The present invention also provides an apparatus for interfacing slower electronic components with the higher speed photonic (optical) components by increasing “n,” the number of parallel digital inputs, therefore maximizing the potential capacity of optical transmission. Moreover, the present invention discloses an apparatus to increase the multiplexer efficiency by beginning to load the next set of data into the photonic modulators shortly after previous set has been read and while the previous data set is being delayed and multiplexed into the serial output.
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Claims(24)
What is claimed and desired to be secured by United States Letters Patent is:
1. A method for converting parallel data signals to serial photonic signals, the method comprising:
providing a pulse train of first photonic pulses having a first wavelength and a first pulse;
providing a first data signal;
providing a first modulator characterized by a first setup time and a first data status;
loading the first data signal into the first modulator following the first pulse and establishing the first data status using the first data signal; and
the first modulator further configured to produce a first data pulse output in response to a selected pulse of the photonic pulses following the first setup time.
2. The method of
claim 1
, further comprising:
providing a second data signal;
providing a second modulator characterized by a second setup time and a second data status;
loading the second data signal into the second modulator following the first pulse and establishing the second data status using the second data signal; and
the second modulator further configured to produce a second data pulse output in response to a first selected pulse of the photonic pulses following the second setup time.
3. The method of
claim 2
, wherein the first and second data pulse outputs occur at different times.
4. The method of
claim 2
, further comprising:
delaying the first data signal by a first delay time to produce a first delayed signal;
delaying the second data signal by a second delay time longer than the first delay time, to produce a second delayed signal.
5. The method of
claim 4
, wherein the first delay mechanism is adjustable.
6. The method of
claim 4
, further comprising combining the first and second delayed signals to provide a multiplexed output.
7. The method of
claim 6
, further comprising selecting the multiplexed output from the group consisting of binary pulses and multi-level semaphores.
8. The method of
claim 6
, wherein the first data signal comprises a first datum followed by a second datum, timed such that the second datum is being loaded into the first modulator while the first datum is being delayed by the first delay mechanism.
9. The method of
claim 6
, further comprising:
providing a synchronization signal synchronized with the first photonic pulses to provide synchronization to the multiplexed output.
10. The method of
claim 9
, wherein the synchronization signal contains information for routing the multiplexed output.
11. The method of
claim 10
, wherein the synchronization signal is a multi-level semaphore.
12. The method of
claim 11
, wherein the multiplexed output contains information produced using modulation techniques selected from the group consisting of amplitude, phase, spatial, and polarization modulation.
13. The method of
claim 12
, wherein the modulation techniques are used to facilitate the separation of the synchronization signal from the first delayed signal.
14. The method of
claim 1
, further comprising selecting the first data signal from the group consisting of a photonic signal and an electronic signal.
15. The method of
claim 1
, further comprising:
providing a pulse train of second photonic pulses having a second wavelength and a second pulse;
providing second and third data signals, respectively;
providing a second modulator characterized by a second setup time and a second data status;
providing a third modulator characterized by a third setup time and a third data status;
loading the second data signal into the second modulator following the second pulse and establishing the second data status using the second data signal;
loading the third data signal into the third modulator following the second pulse and establishing the third data status using the third data signal;
the second modulator further configured to produce a second data pulse output in response to a second selected pulse of the second photonic pulses following the second setup time.
the third modulator further configured to produce a third data pulse output in response to a third selected pulse of the second photonic pulses following the third setup time.
16. The method of
claim 15
, wherein the first modulator further comprises a frequency multiplexed logic device.
17. The method of
claim 15
, further comprising:
delaying the first data signal by a first delay time to produce a first delayed signal;
delaying the second data signal by a second delay time to produce a second delayed signal;
delaying the third data signal by a third delay time longer than the second delay time, to produce a third delayed signal.
18. The method of
claim 17
, further comprising combining the first, second, and third delayed signals to provide a combination time and wave-division multiplexed output.
19. The method of
claim 18
, wherein the combination time and wave-division multiplexed output is launched into an optical fiber having a maximum capacity.
20. The method of
claim 19
, wherein the combination time and wave-division multiplexed output fills the optical fiber to its maximum capacity.
21. The method of
claim 18
, further comprising:
providing a synchronization signal synchronized with the first photonic pulses to provide synchronization to the combination time and wave-division multiplexed output.
22. The method of
claim 21
, wherein the synchronization signal is a multi-level semaphore.
23. The method of
claim 21
, wherein the synchronization signal contains information for routing the combination time and wave-division multiplexed output.
24. The method of
claim 1
, wherein the modulators are photonically controlled.
Description
    BACKGROUND
  • [0001]
    1. Related Applications
  • [0002]
    This application is a continuation of a co-pending patent application, Ser. No. 09/075,046, filed on May 8, 1998 and directed to a Combination Photonic Time and Wavelength Division Multiplexer.
  • [0003]
    2. The Field of the Invention
  • [0004]
    This invention relates to data multiplexing and, more particularly, to novel systems and methods for time and wavelength division multiplexing of binary and non-binary digital information for photonic transmission and information storage systems.
  • [0005]
    3. The Background Art
  • [0006]
    U.S. Pat. No. 5,623,366 to Hait (hereinafter “Hait”), describes a photonic method of parallel to serial conversion. What Hait does not teach is the apparatus and method of providing the proper pulse timing needed in FIG. 24A of Hait, when the parallel information input provides pulses that arrive in parallel at substantially the same time.
  • [0007]
    Hait also does not teach how to use a single pulsed laser system (or other single-pulsed photonic input system) to provide all the required sequential output pulses, including synchronization pulses, needed to provide a complete serial transmission system.
  • [0008]
    Nor does Hait teach how to interface electronic with photonic components to provide serial photonic transmission capable of operating at a rate faster than the rate at which electronic components provide parallel digital data input.
  • [0009]
    In the initial stages of the development of electronic integrated circuit technology, attempts were made at “pulse racing.” That is, attempts were made to time the delay of signals traveling through a computer chip so that a number of signals would arrive at a specific location having a specific timing relationship determined by the various delays applied to each signal. It was found that many of the electronic variables involved, such as capacitance and inductance, made pulse racing impractical and unreliable as chip frequencies increased.
  • [0010]
    Electromagnetic energy, on the other hand, is not affected by the level of capacitance and inductance complexities found in computer chips. The amount of delay that occurs along a photonic delay path may be determined quite accurately even into the sub-picosecond range. The present invention takes advantage of these characteristics of electromagnetic energy and the materials used therewith to provide a complete time-division multiplexing system.
  • BRIEF SUMMARY AND OBJECTS OF THE INVENTION
  • [0011]
    The present invention, a delayed pulse photonic time-division multiplexer, is an apparatus and method of providing parallel digital data to serial data conversion having a photonic serial digital output that may be used with both binary and non-binary transmissions. A series of pulses of photonic energy are input to provide an electromagnetic energy and pulse timing source, which is divided into portions. A portion of the energy of these pulses is directed into the output to provide sync (synchronization) pulses that a photonic receiver uses to time the recovery of serial information and convert it into parallel information. “In serial” as used hereinafter refers to data in serial format (i.e., in series).
  • [0012]
    A portion of the energy of the input pulses is also directed into “n” photonic modulators, the integer “n” being the number of data digits that are to be transmitted in serial within a single data set between sync pulses. For example, if n=8 and the digits are binary, then a byte of serial information would be sent. If n=32, then a 32-bit word is sent. The actual number of digits sent is a matter of engineering choice. The engineer may take into account the need for signal amplification within the receiver and/or the transmitter. He may also need to take into account the accumulation of delay error that may occur using certain types of delay mechanisms.
  • [0013]
    The “n” photonic modulators are first set to their data modulation states, then allowed to complete their setup times, and finally held in those states while a photonic pulse is directed to each one. In the case of binary amplitude modulation, the pulses either are transmitted through each modulator or are inhibited. However, the present invention is not limited to binary transmission only, but may use multistate semaphore digits that use more than two modulation states during each digit time. Thus, the word “digital” in this disclosure may refer to either a binary semaphore or one having more than two modulation states.
  • [0014]
    Associated with the group of “n” photonic modulators is a group of “n” serial timing delay mechanisms. Each modulator has one of these delay mechanisms in series with it so that the photonic pulse reads the condition of the modulator and is delayed sufficiently and directed into the common output so that the resulting modulated digit arrives at the output at its assigned digit time. Therefore, all the “n” modulated and delayed pulses arrive at the output in serial following a sync pulse and prior to the subsequent sync pulse. This produces a complete data set having “n” digit positions filled with the “n” delayed digital pulses.
  • [0015]
    Each serial timing delay mechanism may be placed either before or after its modulator; however, the timing provided by all the delay mechanisms throughout the present invention must be adjusted so as to time the serial digits properly.
  • [0016]
    Photonic modulators have a setup time. That is, it takes a certain amount of time for the modulators to stabilize in response to their controlling electronic inputs. After this setup time has elapsed, the modulators remain stable during the next photonic pulse, which reads the information loaded into the modulators by the electronic inputs.
  • [0017]
    Parallel information is provided through “n” digital information inputs. Each modulator has associated with it one of “n” modulator loaders which load digital information from one of the “n” digital information inputs into its modulator. When triggered, the “n” modulator loaders load the “n” photonic modulators with modulation states from the “n” digital information inputs. To initiate modulator loading and begin the setup time for the next data set, the input pulses are directed into the group of “n” modulator loaders.
  • [0018]
    The present invention is very versatile, since it may be engineered to match a variety of photonic modulators, parallel inputs, optical transmission lines, and demultiplexers. One reason the present invention is superior is that modulators that require a long setup time may be loaded for the next data set while the previous data set is being transmitted. Accordingly, the invention uses time efficiently. As a result, the present invention may be engineered to accommodate slow modulators by increasing the number of digit times and the number of parallel information inputs (that is, by increasing n) without wasting valuable transmission time and effective bandwidth.
  • [0019]
    When photonic parallel inputs are provided along with photonic modulators and loaders, the setup times may be comparatively short. However, the present invention also has the advantage of being able to interface very slow electronics with high-speed photonics. In that case, the modulator loaders may be electronic circuits that control optoelectronic modulators triggered by the photonic pulses using a photo diode. Thus, the complete apparatus for triggering and loading the modulators may involve the use of prior art optoelectronic, electronic, and/or photonic circuitry.
  • [0020]
    The loading circuits load information from the digital information inputs into the modulators and hold that information there until the following trigger pulse occurs. The following trigger pulse occurs after the setup time and the photonic read pulse for that data set.
  • [0021]
    The pulses that trigger modulator loading may require a delay mechanism to prevent a state change within the modulators during the time that photonic pulses are traveling through the modulators. This depends upon the choice of circuitry. This loading delay mechanism may be placed between the input pulse source and the modulators. Individual loading delay mechanisms may be inserted as needed to produce proper output timing before any or all of the “n” photonic modulators.
  • [0022]
    A sync timing delay mechanism may also be inserted between the input pulse source and the output so that sync pulses will be properly timed in the output. All of these various delay mechanisms may be engineered or made adjustable in order to accommodate a great variety of hardware components and transmission protocols.
  • [0023]
    It should be noted that, in the arrangement having the “n” photonic modulators placed before the “n” serial timing delay mechanisms, the first transmitted data set is not yet set up and loaded into the modulators from the parallel digital information input until the first pulse has read the “n” photonic modulators and/or the sync pulse is not delayed by a full data set time. The result is that the first data set following the first sync pulse may be a null data set or may contain spurious or preset information, depending on the circuitry that controls the modulators. Some types of receivers require a specific data set for initialization or calibration. This is one way of providing the beginning data set.
  • [0024]
    The first photonic input pulse triggers the loading of the first data set from the parallel digital information input, which will be transmitted following the second photonic sync pulse. Each modulator is loaded while the previous data set is being transmitted. Following this initialization, sync pulses are interspersed with data set pulses.
  • [0025]
    Wavelength division multiplexing (which may also be referred to as frequency multiplexing) may be accomplished by the present invention in two different ways. If the parallel input information is already wavelength division multiplexed, the present invention may be constructed using frequency multiplexed logic components and by providing frequency matched input pulses. Such components are described in U.S. Pat. No. 5,617,249.
  • [0026]
    Wavelength division multiplexing may also be accomplished through the combination of multiple multiplexers of the present invention routed into a common output. If the pulses of the separate wavelengths used are in sync, only one sync pulse need be sent on one of the wavelengths. However, if the pulses of the separate wavelengths used are not in sync, or if the demultiplexer to be used is not capable of providing synchronization among multiple photonic channels, a sync pulse may be provided for each wavelength channel using the same method as that by which the sync pulses are provided in a single wavelength embodiment. Since each data set-sync pulse data frame may be transmitted asynchronously, the problems associated with wavelength dispersion among the wavelength channels may be minimized.
  • [0027]
    Because the minimum number for “n” is two, the present invention may be described in terms of first and second components. Therefore, the present invention is a method of parallel digital data to photonic serial conversion using delayed-pulse timing that may comprise the elements and methods as described in the following paragraphs.
  • [0028]
    In certain embodiments, an apparatus in accordance with the invention may comprise a first photonic pulse input having a first wavelength, at least first and second digital inputs that constitute a first parallel digital input, a first multiplexer output, at least first and second photonic modulators, and at least first and second modulator loaders for loading the first modulation states into the first and second photonic modulators using information from the first parallel digital input.
  • [0029]
    The first and second digital inputs are input to the first and second modulator loaders, respectively. Subsequently the modulation states from the first and second modulator loaders are transmitted to the first and second modulators where they are converted to photonic digital pulses for output to the first multiplexer output.
  • [0030]
    Similarly, input pulses from the first photonic pulse are input to the first and second modulator loaders to initiate modulator loading to the multiplexer output to provide sync pulses, and to the first and second photonic modulators to read the first modulation states loaded into the first and second photonic modulators to provide first photonic digital pulses of the first wavelength. Moreover, a presently the preferred embodiment may include a delay mechanism as necessary to time the arrival of the first photonic digital output pulses at the multiplexer output in serial between the sync pulses.
  • [0031]
    The capability of the present invention to load information from one data set while simultaneously transmitting another data set enables the present invention to transmit sequential data frames without introducing undesirable delays between frames. This is accomplished because the delay mechanisms are arranged to provide the photonic digital pulses at the multiplexer output from a first data set input to the first parallel data input while the photonic modulators are being loaded with a second data set from the first parallel digital input.
  • [0032]
    A combined wavelength division and time-division multiplexing method of the present invention may be produced by providing multiple multiplexers, as described above, having different photonic wavelength inputs, and combining the time-division multiplexed outputs from all wavelengths into a common output.
  • [0033]
    The method may be implemented by providing a second photonic pulse input having a second wavelength, at least third and fourth digital inputs that constitute a second parallel digital input, a second multiplexer output, at least third and fourth photonic modulators, and at least third and fourth modulator loaders for loading the second modulation states into the third and fourth photonic modulators using information from the second parallel digital input.
  • [0034]
    The third and fourth digital inputs are input to the third and fourth modulator loaders, respectively. Subsequently the modulation states from the third and fourth modulator loaders are transmitted to the third and fourth modulators where they are converted to photonic digital pulses for output to the second multiplexer output.
  • [0035]
    Similarly, input pulses from the second photonic pulse are input to the third and fourth modulator loaders to initiate modulator loading to the multiplexer output to provide sync pulses, and to the third and fourth photonic modulators to read the second modulation states loaded into the third and fourth photonic modulators to provide second photonic digital pulses of the second wavelength.
  • [0036]
    Moreover, one presently preferred embodiment may include a delay mechanism as necessary to time the arrival of the second photonic digital output pulses at the multiplexer output in serial between the sync pulses.
  • [0037]
    Thus, a method of wave division multiplexed time-division multiplexing is made possible by the present invention by combining the first and second multiplexer outputs into a single output.
  • [0038]
    Photonic modulators may be loaded and controlled in a variety of different ways. The most common way is electronic. However, several additional ways exist, including without limitation mechanical, electromechanical, acoustical, and the like. All of the foregoing ways have one thing in common: their top switching speeds are much slower than the short pulse times that may be achieved with electromagnetic energy, including without limitation laser light. Even these slow modulator setup times may be accommodated by the present invention.
  • [0039]
    For example, if the single digit times (as determined by the length of the input pulses) are one femtosecond long and an optoelectronic setup time is one nanosecond, one million serial digits may be placed between sync pulses. Transmission parameters may be engineered to account for the properties of whatever components are available. One of the advantages of the present invention over other devices is that photonic delay mechanisms, including free-flight path differences and/or optical fibers, may be precisely manufactured to provide the precise timing needed to ensure the reliability of a million digits following a single sync pulse. Prior art methods are not sufficiently reliable to make such a transmission protocol practical.
  • [0040]
    Another class of photonic modulators are photonically controlled. With such photonically controlled modulators, high-speed parallel photonic inputs may provide very short setup times. Thus, sync pulse repetition rates, and data transmission rates may be selected to suit the photonic components being used. Such photonic components may include photonic transistors, self-exciting electro-optical devices (SEEDS), and nonlinear optical materials.
  • [0041]
    The use of photonically-controlled photonic modulators also allows for the construction of more complex multiplexers having multiple parallel inputs and various organizations of delay times as needed to match the various parallel digital data sources and transmission protocols to be used.
  • [0042]
    Certain photonic modulators, such as the photonic transistors of U.S. Pat. No. 5,617,249, may provide frequency multiplexed logic, which may be used to frequency 20 multiplex and time-division multiplex information simultaneously using the present invention. Each of the multiplexing frequencies must be provided at the photonic input to provide a series of pulses for each frequency channel. However, with suitable circuitry, sync pulses need only be sent on one of the channels. The result is a combination of wave division and time-division multiplexing.
  • [0043]
    The present invention may be designed to work with amplitude, phase, spatial and polarization modulation techniques, as needed for a particular circumstance. Different forms of modulation may be used to make the separation of sync pulses from data pulses easier at the receiver and to provide multiple states for the transmission of semaphore digits having more than two modulation states. The photonic modulators, support circuitry and delay mechanisms are selected to provide the needed modulation combinations. Sync pulses may even be modulated as multilevel semaphores that may be used for data set routing or other purposes at the receiver. Thus the terms “digit” and “digital,” as used herein include multilevel as well as binary digits.
  • [0044]
    The serial output may be used for direct photonic transmission through free space, waveguides, or optical fibers. The output may also be directed along a delay path such as a free-space path or an optical fiber to provide a method of photonic information storage. The output may also be written onto or into various information storage media including holograms, photographs, CD-ROMS, photo-sensitive materials, and the like.
  • [0045]
    Even though this disclosure uses optical terminology, the present invention may be used with photonic energy anywhere within the electromagnetic spectrum through the selection of appropriate components to match the frequencies being used. Most notable is the microwave region, where the present invention may be used to multiplex information sent via satellite or other microwave links. The recent commercialization of x-ray technology, including x-ray capillaries (like optical fiber for x-rays), may be used to provide multiplexing in the x-ray bands.
  • [0046]
    The use of spatial modulation is not common. While spatial modulation is more complex than the more usual methods, the present invention may use this method of transmission. Spatial modulation is particularly useful when serialization is required inside a photonic computer or mass information storage device. Appropriate components may be used as with the other modulation methods.
  • [0047]
    An object of the present invention is to provide an apparatus and method of converting parallel digital information input to photonic serial information.
  • [0048]
    Another object of the present invention is to provide an apparatus and method for high-speed parallel photonic sampling of preset modulation states loaded into slow modulators followed by transmission of the sampled information in serial during the modulator setup time for the following data frame, thus providing an apparatus and method of maximizing photonic throughput by using the shortest transmissible photonic pulses, while using slow modulators (even electro-photonic modulators) having response times longer than the photonic sampling pulses.
  • [0049]
    Another object of the present invention is to provide an apparatus and method for optimizing data frame repetition rates by matching them to the modulator setup times combined with multilevel semaphores. This may be done to maximize overall transmission rates for each carrier wavelength and then adding separate carrier wavelengths until a selected transmission medium, be it an optical fiber or a free-space beam, has been saturated to its maximum physical information-carrying capacity.
  • [0050]
    Another object of the present invention is to provide an apparatus and method for photonically transmitting electronic information using the fastest available electronic and photonic components.
  • [0051]
    Another object of the present invention is to provide an apparatus and method for transmitting serial information using digital semaphores having more than two modulation states.
  • [0052]
    Another object of the present invention is to provide an apparatus and method for transmitting serial information using a variety of photonic modulation mechanisms and methods.
  • [0053]
    Another object of the present invention is to provide an apparatus and method for transmitting serial information into an optical fiber for the purpose of retrieving the information at a future time.
  • [0054]
    Another object of the present invention is to provide an apparatus and method for transmitting serial information to a satellite reflector or transponder, as the present invention may be designed to use photonic energy in the microwave as well as the optical portions of the electromagnetic spectrum.
  • [0055]
    Another object of the present invention is to provide an apparatus and method for transmitting serial information using the various parts of the electromagnetic spectrum including optical (both visible and invisible,) microwave, and radio frequencies.
  • [0056]
    Another object of the present invention is to provide an apparatus and method for transmitting simultaneous serial (time-division) and wavelength division (frequency multiplexed) information.
  • [0057]
    The foregoing objects and benefits of the present invention will become clearer through an examination of the drawings, description of the drawings, description of the preferred embodiment, and claims that follow.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0058]
    The foregoing and other objects and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which:
  • [0059]
    [0059]FIG. 1 is a schematic block diagram of a parallel digital data to photonic serial data converter that constitutes the multiplexer of the present invention;
  • [0060]
    [0060]FIG. 2 is a pulse timing diagram illustrating the relationship between photonic pulses and modulator setup times; and
  • [0061]
    [0061]FIG. 3 is a pulse diagram showing multistate digit time pulses.
  • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • [0062]
    It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention, as represented in FIGS. 1 through 3, is not intended to limit the scope of the invention, as claimed, but it is merely representative of the presently preferred embodiments of the invention.
  • [0063]
    The presently preferred embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.
  • [0064]
    Those of ordinary skill in the art will, of course, appreciate that various modifications to the details illustrated in the schematic diagrams of FIGS. 1-3 may easily be made without departing from the essential characteristics of the invention. Thus, the following description is intended only as an example, and simply illustrates one presently preferred embodiment consistent with the invention as claimed herein.
  • [0065]
    [0065]FIG. 1 is a block diagram of a delayed-pulse photonic time-division multiplexer which is a parallel digital information to photonic serial information converter of the present invention. Three dots between components indicate identical components for information flow lines up through n−1.
  • [0066]
    [0066]FIG. 2 is a pulse timing diagram that shows how delay times may be organized for the various required pulses and how they relate to each other. Three dots within data sets on time line 35 depict identical digit times up through n−1.
  • [0067]
    The present disclosure is easily understood by examining FIGS. 1 and 2 together. Reference characters 1 through 17 are used in FIG. 1 and reference characters 30 through 47 are used in FIG. 2.
  • [0068]
    Referring to FIGS. 1 and 2, in the depicted embodiment, a series of photonic pulses (optical, microwave, or RF) are provided by photonic source 1 routed into multiplexer input 2 as shown by time line 30. The input pulses 38 a, 45 a, and 40 a are directed through sync delay mechanism 3 to provide sync pulses 38 b, 45 b, and 40 b at photonic output 17, as shown in time line 35.
  • [0069]
    Certain types of time-division demultiplexers require specialized sync waveforms, such as shortened pulses, or specialized modulation characteristics. These may be provided by insertion either with a sync delay mechanism in line 3 or between photonic source 1 and the other components or both for use in demultiplexing. Electronic digital information may be input to photonic modulators 4, 5, 6 through 7 by parallel digital information input 19.
  • [0070]
    Input pulses from multiplexer input 2 as shown on time line 30 are also supplied to a group of “n” photonic modulators to sample their previously loaded and held modulation states. Four of the “n” photonic modulators are shown: photonic modulators 4, 5, 6, and the nth photonic modulator 7. The output of each photonic modulator is directed into its own serial timing delay mechanism. Serial timing delay mechanisms depicted are serial timing delay mechanisms 12, 13, 14 and the nth one 15.
  • [0071]
    The integer “n” may be any integer in which at least one modulator and at least one serial timing delay mechanism are provided for each digit time in output 17, as shown on time line 35, just as with those modulator and serial delay mechanism combinations depicted. Examples of output digit times include the first digit pulse 46 and the nth digit pulse 47 in example data set 44.
  • [0072]
    The output from the group of “n” photonic modulators 4, 5, 6 through 7 and the group of “n” serial delay mechanisms 12, 13, 14 through 15 is “n” delayed digital pulses that are timed to arrive at output 17 in serial. For example, the basic transmission sequence for a single data frame may begin with a modulator loading sequence initiated by a timed photonic pulse from photonic source 1 routed to modulator loaders 8, 9, 10 through 11. In turn, photonic modulators 4, 5, 6, through 7 are loaded during their setup times by modulator loaders 8, 9, 10 through 11, with data from parallel digital information input 19. The loaded modulation states are then held for a period of time to allow photonic sampling of the loaded modulation states.
  • [0073]
    Photonic pulses from photonic source 1 are then routed through photonic modulators 4, 5, 6, through 7 to sample their modulation states. The modulated photonic pulses are then routed and delayed by delay mechanisms 12, 13, 14 through 15 along with a sync pulse to arrive at output 17 in serial. While the photonic pulses are being routed through the delay mechanisms 12, 13, 14 through 15 into the serial output 17, the modulators 4, 5, 6 through 7 are once again prepared by modulator loaders 8, 9, 10 through 11 for data sampling for the next frame.
  • [0074]
    The transmission sequence may be started anywhere in the sequence; however, the information transmitted during the first frame may depend upon several other factors. For example, because photonic modulators that provide more than two stable modulation states may also be used, non-binary semaphores (digits) may be used in the present invention. When only two states are used, the digit times are the same as “bit times,” as commonly used in the electronic serial communications art. Digit times shown in FIG. 2 having both top and bottom lines (for example, as in time line 31) indicate that the actual modulation states depend upon the modulation states of the respective modulators.
  • [0075]
    While FIG. 2 depicts common amplitude modulation form, the actual form of modulation used may be amplitude, phase, spatial, or polarization, or any combination of these. The present invention provides time-division multiplexing by means of pulse delays regardless of the modulation method or methods used for the pulses. Certain modulation combinations may require the use of multiple modulators and/or multiple delay mechanisms for each digit time as the engineering of these components requires. Delay mechanisms may include free-space distances, materials having an index of refraction greater than one, waveguides, optical fibers, one-shot multivibrators, and other more complex circuitry.
  • [0076]
    One advantage of using delaying materials such as glass, optical fibers, and the like is that these may be machined very precisely to maintain digit times within tolerance, while allowing or compensating for temperature and other fluctuations within the materials being used. Changes that do occur may be accurately measured, and such compensating information may be sent to the demultiplexer in order to compensate at the receiving end.
  • [0077]
    Each of the serial timing delay mechanisms 12, 13, 14 through 15 provides a different delay time so that the “n” delayed digital photonic pulses shown on time lines 31, 32, 33 through 34 are combined with the sync pulses at location 16 and arrive at output 17, as 20 shown on time line 35 as data sets 39, 41, and 44 in serial in between sync pulses. As an example, the delay mechanisms may comprise optical fibers, the outputs of which are all directed through a lens and into another optical fiber that comprises output 17.
  • [0078]
    The time spaces shown on either side of the sync pulses, such as sync pulse 45 b between data set times 41 and 44, are optional and may be used if needed by a particular demultiplexer.
  • [0079]
    Each of the “n” photonic modulators has a required setup time that elapses before the modulating information in the modulators is sufficiently stable to be read by sending a photonic pulse into the modulators. This characteristic, which has often been viewed as a detriment in prior systems, is considered useful in the present invention. The summation of digit times that make up a data set, for instance times 39 or 44, may be designed to be at least as long as one of the photonic modulator's setup times shown on time line 37. All modulator setup times depicted on time line 37 are substantially the same as, for example, set up time 42.
  • [0080]
    If the modulators chosen are very slow in comparison with the photonics, more digit times may be added to each data set by adding more parallel inputs in parallel digital information input 19 along with corresponding modulator loader, photonic modulator, serial timing delay mechanisms, and interconnections. These additions increase the size of “n” until the functional limit of the photonics is reached.
  • [0081]
    As an example, if femtosecond pulses, as are commonly produced in the laser art, are used as the photonic source 1 and photonic modulators 4, 5, 6, through 7 having a 2 gHz (0.5 ns) response are used, the parallel digital information input 19 may be expanded to include one half-million parallel lines without the use of non-binary digits (semaphores). When non-binary digits are used during each digit time, the information throughput may be greatly multiplied. As a result, the present invention may be capable of transmitting 1,000 terabits per second and beyond using presently available components, while interfacing inherently slow electronics to high-speed photonics.
  • [0082]
    The length of setup time 42 of photonic modulators 4, 5, 6, through 7 (which depends upon the type of modulators used) and the pulse width of the input pulses such as pulse 40 a will determine the maximum pulse repetition rate for the input and sync pulses as shown on time lines 30 and 35, which in turn will determine the number “n”; that is, the number of digit times such as digit time 47 available between sync pulses.
  • [0083]
    To initiate modulator loading and the setup times as shown on time line 37, input pulses from the series of pulses of photonic energy input at multiplexer input 2 as shown by 110 time line 30 are also directed through delay mechanism 18 as shown on time line 36 and into “n” modulator loaders 8, 9, 10 through the nth one here designated 11. When electronic components are used, these load triggering pulses are directed into a photo diode, which starts an electronic modulator loading circuit as discussed in the summary.
  • [0084]
    Each pulse exiting load delay mechanism 18 triggers loading of the “n” modulators with new information from parallel digital information input 19, starting the modulator setup time, as for example time 42 as shown on time line 37. Pulse setup times as shown on time line 37 may actually be timed events within the “n” modulator loaders 8, 9, 10 through 11 rather than an actual detectable signal having the wave form like that of modulator setup time 42 on time line 37. In view of the foregoing, the present invention is as compatible with optoelectronic modulators and electronic modulator loaders as with photonic, mechanical, acoustic and other modulating and modulator loading. As a result, the present invention may provide photonic serial information at a speed that is considerably faster than that of conventional single electronic modulator methods. This advantage is provided by the use of modulator loading times that occur during the transmission of the previously loaded and sampled data set. The present invention transmits asynchronously, with each sync pulse acting as a start pulse for the data set which follows.
  • [0085]
    Input pulses 38 a, 40 a, and 45 a, shown on time line 30, are directed into the “n” photonic modulators 4, 5, 6, through 7 to read them. This read time may be at any time that is not simultaneous with a setup time such as 42 shown on time line 37. For example, they may be read during time 43, which is between setup times on time line 37.
  • [0086]
    Of particular interest is the relationship between the setup times and the first sync pulse in the embodiment shown. The first input pulse 38 a reads the modulation state of photonic modulators 4, 5, 6, through 7. At that time, the modulators may contain unknown data or may be off or preset since no setup time has yet occurred. This is because modulator read pulses occur before the setup time begins for loading the next data set. Thus, the first data set 41 may be null or may contain unknown or preset data. A null or preset modulation pattern may be used by certain demultiplexers for determining the source of the information that follows, for calibration, or to provide other system information to the demultiplexer.
  • [0087]
    The first parallel digital data set is loaded following pulse 38 a, which is delayed by load delay mechanism 18, which in turn triggers the start of setup time 42. This occurs during the time that the first (possibly null) data set 41 is being transmitted. The photonic modulators are set up and stable at the completion of setup time 42 so that they may be read by the second input pulse 45 a.
  • [0088]
    The modulator outputs are delayed, each one by an amount that differs by at least one digit time (such as 46 and 47), to their individual digit time slots as in time lines 31, 32, 33 through 34 and are combined into output 17 as a complete data set 44, shown in time line 35. The process then continues in the same cyclic manner for the following trigger, setup, read, delay and transmit sequences.
  • [0089]
    The first data set 41 may be eliminated by changing the timing delays of the various delay mechanisms used throughout the invention. In particular, sync delay mechanism 3 may be used to delay the sync pulses so that the first pulse arrives one data frame later; that is, the first sync pulse 38 b would then arrive at 45 b. Certain types of delay, modulation, modulator loading, beam combining, and output mechanisms require the use of amplifiers and pulse shapers that may be inserted, as needed within the present invention.
  • [0090]
    It should be noted that other embodiments of the present invention may place delay mechanisms before the photonic modulators and/or sync output while providing other delays before or within the modulator loaders. However, the disclosed embodiment is simple and compatible with electronic parallel digital information input mechanisms.
  • [0091]
    [0091]FIG. 3 shows a non-binary semaphore quadnary digit having four different amplitude modulated levels 50, 51, 52 through 53, one level of which is transmitted during a digit time (such as digit time 47 of FIG. 2) to indicate one of four digits. The parallel digital information input 19 may be multi-level, or binary to multi-level encoding may be accomplished within the modulator loaders 8, 9, 10 through 11.
  • [0092]
    There are many combinations of non-binary transmission methods that may be used with the “n” photonic modulators. Another example is as shown by waveforms 54, 55, and 56 of FIG. 3, which is ternary. These waveforms indicate the use of a combination of phase and amplitude modulation. The photonic carrier wave 54 is 180 degrees out of phase with carrier wave 56 (as indicated by its position below the zero axis line). On the other hand, carrier wave 55 is amplitude-modulated low; this modulation combination is particularly useful when interference-based photonic components such as those taught in U.S. Pat. No. 5,093,802 are being used at the receiving demultiplexer.
  • [0093]
    If each of the photonic modulators is loaded with non-binary modulation state combinations, considerably more information may be transmitted during each digit time than if binary modulation is used. Any combination of stable modulation states using any combination of modulation methods may be used. The present invention is ideally suited for such modulation techniques because the method provides ample time for loading the modulators, even modulators that are comparatively slow. Multiple modulators may be used for each digit time slot so that the phase, amplitude, polarization, and spatial modulation techniques may be mixed and matched, as the transmitting medium and demultiplexers require. Also, the types of delay mechanisms available are compatible with a variety of modulation methods.
  • [0094]
    The present invention may be used to provide serial photonic information for a variety of tasks. The present invention may be used for fiber optic transmission, satellite and terrestrial microwave links, and for writing to optical devices such as CD-ROMs, holographic storage devices, and fiber optic circulating data storage devices.
  • [0095]
    The photonic components usable in the present invention include those having the capability of frequency multiplexing (or wave division multiplexing) so that multiple frequency channels may be used simultaneously during each digit time. Such a feature is important when transmission or information storage mediums such as optical fibers or microwave links are combined with repeater amplifiers having a limited number of frequency channels available. The present invention may be used with various combinations of frequency channels, pulse repetition rates, and modulation methods to suit the medium to be driven.
  • [0096]
    To accomplish combination wave division and time-division multiplexing, separate carrier wavelengths are routed from photonic source 1 to separate modulators. For example, red light would be routed to modulators 4 and 5 and green light to modulators 6 and 7.
  • [0097]
    The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7957646 *Jan 12, 2006Jun 7, 2011Oki Electric Industry Co., Ltd.Optical time division multiplexing transmitter
US8531761 *May 27, 2010Sep 10, 2013Massachusetts Institute Of TechnologyHigh peak power optical amplifier
US8531772Sep 13, 2011Sep 10, 2013Massachusetts Institute Of TechnologyExternal-cavity one-dimensional multi-wavelength beam combining of two-dimensional laser elements
US8614853Mar 9, 2010Dec 24, 2013Massachusetts Institute Of TechnologyTwo-dimensional wavelength-beam-combining of lasers using first-order grating stack
US9136667Aug 22, 2013Sep 15, 2015Massachusetts Institute Of TechnologyHigh peak power optical amplifier
US20060159458 *Jan 12, 2006Jul 20, 2006Oki Electric Industry Co., Ltd.Optical time division multiplexing transmitter
US20110222574 *Sep 15, 2011Massachusetts Institute Of TechnologyTwo-dimensional wavelength-beam-combining of lasers using first-order grating stack
US20110292498 *May 27, 2010Dec 1, 2011Massachusetts Institute Of TechnologyHigh peak power optical amplifier
Classifications
U.S. Classification398/43, 398/74, 398/75
International ClassificationH04J14/08, H04J14/02
Cooperative ClassificationH04J14/02, H04J14/08
European ClassificationH04J14/08, H04J14/02
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