1. Related Applications
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.
2. The Field of the Invention
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.
3. The Background Art
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.
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.
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.
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.
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
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
An object of the present invention is to provide an apparatus and method of converting parallel digital information input to photonic serial information.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.