Abstract:
A transmitter for transmitting data in the form of an optical signal. The transmitter having: a transmitter chip module having a material capable of radiating light of a first wavelength when both a zero voltage potential exists across the material and when illuminated by light of a second wavelength; a light source optically coupled to the transmitter chip module for illuminating the material with light of the second wavelength; and a voltage controller for controlling the voltage potential across the first material. Also provided is a receiver for receiving data in the form of an optical signal having a first wavelength. The receiver having: a receiver chip module having a material capable of producing a signal in the form of a produced voltage potential or produced current when illuminated by light of both the first wavelength and light of a second wavelength; a light source optically coupled to the receiver chip module for illuminating the material with light of the second wavelength; and a signal detector for detecting presence of the produced signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to VLSI chips and, more particularly, to an optical method for communicating between a transmitter VLSI chip and a receiver VLSI chip such that the noise characteristic of communication between chips is limited. 
     2. Description of the Related Art 
     The bandwidth for the transmission of data between very large scale integrated (VLSI) chips in modern computers is limited by noise. Much of this noise is produced by rapid changes of electrical current, and is called switching noise or Δ-I noise. Because data transmission between devices requires substantial electrical power, interdevice data transmission produces a substantial fraction of observed switching noise, and thereby contributes to the bandwidth limitation on data rate. 
     SUMMARY OF THE INVENTION 
     Therefore it is an object of the present invention to provide an apparatus and method for transmitting data between VLSI chips which reduces the noise characteristic with communications between VLSI chips. 
     It is yet a further object of the present invention to provide an apparatus and method for transmitting data between VLSI chips which increases data transfer rates over methods currently employed in the arts. 
     It is the purpose of this invention to power both the transmission and the reception of data in a manner that contributes minimally to switching noise. The power for both transmission and reception of data is supplied from an external laser in a way that greatly reduces current transients within a VLSI device. Consequently, data rates are potentially faster with this means than with electrical means. 
     Accordingly, a transmitter for transmitting data in the form of an optical signal and a receiver for receiving data in the form of an optical signal are provided. The transmitter comprises: a transmitter chip module having a material capable of radiating light of a first wavelength when both a zero voltage potential exists across the material and when illuminated by light of a second wavelength; a light source optically coupled to the transmitter chip module for illuminating the material with light of the second wavelength; and voltage control means for controlling the voltage potential across the first material. The receiver comprises: a receiver chip module having a material capable of producing a signal in the form of a produced voltage potential or produced current flow when illuminated by light of both the first wavelength and light of a second wavelength; a light source optically coupled to the receiver chip module for illuminating the material with light of the second wavelength; and signal detecting means for detecting the presence of the produced signal. 
     In a first preferred implementation of the transmitter and receiver of the present invention, a first apparatus for transmitting data between first and second VLSI chips is provided. The first apparatus comprises: a transmitter disposed on the first VLSI chip, the transmitter having a first material capable of radiating light of a first wavelength when both a zero voltage potential exists across the first material and when illuminated by light of a second wavelength, the transmitter further having voltage control means for controlling the voltage potential across the first material; a receiver disposed on the second VLSI chip, the receiver having a second material capable of producing a signal in the form of a produced voltage potential or produced current flow when illuminated by light of both the first wavelength and a third wavelength, the receiver further having signal detecting means for detecting the presence of the produced signal; at least one light source optically coupled to the transmitter and receiver for illuminating the first material with light of the second wavelength and for illuminating the second material with light of the third wavelength; and light transmission means for transmitting the light of the first wavelength from the transmitter to the receiver. 
     In a second preferred implementation of the transmitter and receiver of the present invention, a second apparatus for transmitting data between first and second VLSI chips is provided. The second apparatus comprises: a plurality of transmitters disposed on the first VLSI chip, each transmitter having a first material capable of radiating light of a first wavelength when both a zero voltage potential exists across the first material and when illuminated by light of a second wavelength; a plurality of receivers disposed on the second VLSI chip, each receiver corresponding to a transmitter on the first VLSI chip, each receiver having a second material capable of producing a signal in the form of a produced voltage potential or produced current flow when illuminated by light of both the first wavelength and a third wavelength; voltage control means for individually controlling the voltage potential across the first material of each transmitter; signal detecting means for individually detecting the presence of the produced signal from each receiver; at least one light source optically coupled to each of the transmitters and receivers for illuminating the first material of each of the transmitters with light of the second wavelength and for illuminating the second material of each of the receivers with light of the third wavelength; and light transmission means for transmitting the light of the first wavelength from each of the transmitters to a corresponding receiver. 
     In a preferred versions of the first and second apparatus of the present invention, first and second light sources are provided. The first light source providing light of the second wavelength, the second light source providing the light of the third wavelength. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
     FIG. 1 a  illustrates a portion of a transmitter VLSI chip of the present invention in an activated state. 
     FIG. 1 b  illustrates a portion of a transmitter VLSI chip of the present invention in an non-activated state. 
     FIG. 2 a  illustrates a portion of a receiver VLSI chip of the present invention in an excited state. 
     FIG. 2 b  illustrates a portion of a receiver VLSI chip of the present invention in an non-excited state. 
     FIG. 3 illustrates a symbolic description of the transmitter interactions of a transmitter VLSI chip of the present invention. 
     FIGS. 4 a  and  4   b  illustrate the receiver interactions of a receiver VLSI chip of the present invention, with FIG. 4 a  illustrating a graphical comparison of the receiver molecules absorption in the ground state and the shifted absorption band of the excited state and FIG. 4 b  illustrating the phase transitions that the receiver molecules undergo as they receive light of the frequencies which produce a voltage potential. 
     FIG. 5 illustrates a preferred implementation of an embodiment of the apparatus of the present invention for communicating between VLSI chips. 
     FIG. 6 illustrates a version of the embodiment of FIG. 5 wherein multiple transmitter chip modules transmit data to corresponding receiver chip modules. 
     FIG. 7 illustrates a schematic of a junction of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before discussing the preferred implementation of the present invention in detail, a general overview of the physical principles behind the present invention will be discussed with reference to FIGS. 1 a ,  1   b ,  2   a , and  2   b.    
     The present invention transmits data in optical form between two digital devices contained on VLSI chips, a transmitter  100 , and a receiver  200 . The transmitter  100  has a first material  102  of organic molecules that are deactivated by a voltage potential across them. When a first light source, such as a first external laser  104  at a pump wavelength of λ 0  illuminates the first material  102 , the first material  102  radiates an optical signal  106  at wavelength of λ 1 . The radiated optical signal  106  passes through a light path (e.g., optical fibers) that guides it to a receiver chip  200 . At the receiver chip  200 , the optical signal  106  illuminates a second material  202  of organic molecules that are sensitive to wavelength λ 1 , and forces the organic molecules of the second material  202  into an excited state. 
     Subsequently, a second light source, such as a second external laser  206  illuminates the second material  202  at wavelength λ 2 . The second material  202 , if in the excited state, reacts by producing a signal in the form of a produced voltage potential or current flow that can be sensed digitally without further amplification by a signal detector  212 , preferably a voltage detector. If the second material  202  is not in the excited state, no voltage or current is produced when the second external laser  206  illuminates it. It can be appreciated that the power required to convert data from electrical to optical form is supplied by the first external transmitter laser  104 , and the power required to amplify the received signal  106  to a useful voltage level is supplied by the second external receiver laser  206 . Thus, since both the first and second lasers  104 ,  206  are isolated from the power supply that drives the transmitter  100  and receiver  200 , switching noise produced by changes in the optical signal  106  is greatly reduced, thereby enabling faster operation of the digital logic. 
     The overview provided discusses first and second external lasers  104 ,  206 , one each for the transmitter  100  and the receiver  200 . However, it should be appreciated by someone of ordinary skill in the art that a single laser can be utilized for illuminating both the first and second materials  102 ,  202  of the transmitter  100  and receiver  200  without departing from the scope or spirit of the present invention. For instance, a single high bandwidth light source can replace the first and second lasers  104 ,  206 , wherein light of the first and second wavelengths are filtered from the high bandwidth light source and directed at the respective first and second materials  102 ,  202 . 
     In FIG. 1 a , logic device  108  drives a transmitter chip module  103 , which is made of or coated with the first material  102 . The first material  102  reacts to the absence of voltage by being sensitive to external light. In this state, it is said to be “activated”. When the transmitter chip module  103  is in the activated state, and is illuminated by light at wavelength λ 0  it changes state to a “photo-emitting” state and spontaneously emits light at wavelength λ 1  (signal  106 ). In FIG. 1 b , logic device  108  deposits positive charge on the transmitter chip module  103 . The first material  102  reacts to the voltage potential across it by producing, for instance, radicals. In this state, the first material  102  does not photoemit when illuminated by light at wavelength λ 0 , and is said to be in the “deactivated” state. In both FIGS. 1 a  and  1   b , the first external laser  104  illuminates the first material  102  of the transmitter chip module  103  with light of wavelength λ 0 . The activated transmitter chip module  103  in FIG. 1 a  responds by emitting light at wavelength λ 1  (signal  106 ) in response to the absorption of the light at wavelength λ 0 . 
     Note that the amplification of the signal  106  for transmission to the receiver  200  is done within the molecular structure of the first material  102  of the transmitter chip module  103 . The first external laser  104  provides the majority of the energy required to produce the transmitted signal  106 . Fluctuations in the internal state of the transmitter chip module  103  do not lead to large changes in current flow through the logic devices. Consequently, power fluctuations related to transmission of the signal  106  are isolated from the power supply of the logic device  108 , and thus they do not introduce noise into the transmission of a digital logic signal. 
     FIGS. 2 a  and  2   b  show a schematic diagram of what happens when the signal light  106  reaches a receiver chip module  204  and is converted to an electrical signal. Receiver chip module  204  in FIGS. 2 a  and  2   b  has a second material  202  having photosensitive molecules deposited on receiving pads located on the chip module. The receiver  200  operates as follows. First, the received light signal  106  from a transmitter chip module  103  illuminates a corresponding receiver chip module  204  (referred to as a transmitter/receiver chip module pair). In FIG. 2 a , the second material  202  of the receiver chip module  204  receives the signal  106  at wavelength λ 1 , whereas the second material  202  of the receiver chip module  204  in FIG. 2 b  receives no signal  106 . The receiver chip module  204  responds to the signal light  106  by shifting its absorption band to a higher wavelength. Such a receiving site is in the “excited” state. When the second material  202  of the receiver chip module  204  receives signal energy at wavelength λ 1  (signal  106 ), the second material  202  on the chip module  204  changes its state to the excited state. No change of state occurs in the second material  202  on the chip module  204  in FIG. 2 b , because no signal energy  106  is received in this case. Next, the second external laser  206  with light of wavelength λ 2  illuminates the receiver chip module  204 . The second material  202  of the receiver chip module  204 , when in the excited state, responds to the presence of light of wavelength λ 2  by changing its external potential or by emitting a current flow. Thus, the receiver chip module  204  in FIG. 2 a  produces a high external voltage or a high current flow at its terminals  208 ,  210 . However, the receiver chip module  204  in FIG. 2 b  does not respond. The response from the receiver chip module  204  of FIG. 2 a  is treated as a logic value of  1  and the lack or response of the receiver chip module  204  of FIG. 2 b  is treated as a logic value of 0. The amplification power comes from the second external laser  206  emitting at wavelength λ 2 , and thus this power is isolated from the power supply of the receiver  100 . This prevents noise currents due to rapid changes of state from reaching electronic receivers. 
     Although the present invention has thus far been discussed with a single transmitter chip module  103  and a corresponding receiver chip module  204  for simplicity, it should be apparent to one of ordinary skill in the art that a plurality of transmitter chip modules  103  and corresponding receiver chip modules  204  can be provided, each transmitter and corresponding receiver chip module  103 ,  204  being a transmitter/receiver chip module pair. The voltage potential across each transmitter chip module  103 , is controlled via a central processor to place them in either the activated or deactivated states. The transmitter chip modules  103  are then illuminated with light of their respective wavelengths to transmit and receive a signal  106  only for those transmitter chip modules  103  that are in the activated states. In this arrangement, more than one bit of data can be transmitted at a time, for instance, eight transmitter chip modules  103  each having a corresponding receiver chip module  204  can transmit eight bits of data at a time. Any transmitter chip module  103  which is activated and receiver chip module  204  which is energized in a transmitter/receiver chip module pair (the transmitter  100  produces an optical signal  106  and the receiver  200  produces an electrical signal) corresponds to a logical value of 1, and any transmitter chip module  103  which is not activated and receiver chip module  204  which is not energized in a transmitter/receiver chip module pair (the transmitter  100  does not produce an optical signal  106  and the receiver  200  does not produce an electrical signal) corresponds to a logical value of 0. In this way, a data string of eight values is transmitted. This could be done with a multiplicity of lasers, one laser per transmitter chip module  103 , one laser per receiver chip module  204  or with a single light source for each of the transmitter and receiver chip modules that illuminates all the transmitter and receiver chip modules  103 ,  204  concurrently or sequentially. 
     FIG. 3 is a diagram of the state transitions within the molecular material of the first material  102  used in the transmitter chip module  103 . In a preferred embodiment, the first material  102  is a carbozole, and is denoted as M 1 . The activated state is indicated by M 1   * . The deactivated state is M 1   + , a state in which the material gives off or captures electrons. In the activated state, light at wavelength λ 0  causes a transition to the state M 1   * , which is followed by a spontaneous transition back to state M 1  within nanoseconds and is accompanied by light emission at wavelength λ 1 . 
     FIGS. 4 a  and  4   b  are symbolic illustrations of the state transitions within the molecular material of the second material  202  used in the receiver chip module  204 . In a preferred embodiment, the second material  202  is a porphyrin M 2 . Initially, the second material  202  is in a ground state denoted as M 2   0 . When the second material  202  receives light at wavelength λ 1  (signal  106 ) while in the ground state, it changes state to a state called the excited state, denoted as M 2   * . The second material  202  has the property that the light-absorption properties of the two states are different, and that the absorption band for state M 2   *  is shifted in frequency with respect to the absorption band for state M 2   0 . FIG. 4 a  shows the absorption band of the second material  202  in the ground state on the left ( 402 ), and the shifted absorption band of the excited state on the right ( 404 ). The center frequency of the ground state band ( 402 ) is λ 1 , and the center frequency of the excited state ( 404 ) is λ 2 . FIG. 4 b  shows the phases that the receiver undergoes as it receives light successively at frequencies λ 1  and λ 2 . When the second material  202  is in ground state M 2   0  and receives light at wavelength λ 1  (signal  106 ), it absorbs the light and moves to state M 2   * . If the second material  202  receives light at wavelength λ 2  in state M 2   * , the second material  202  responds by changing state to a state called the ionized state M 2   + . In this state, the second material  202  spontaneously emits electrons and produces an electrical current or increases the voltage potential across its terminals  208 ,  210 . If the second material  202  receives light at wavelength λ 2  while in ground state M 2   0 , no absorption (or very little absorption occurs), resulting in virtually no current or voltage change across the terminals  208 ,  210 . It is well known in the art that bifunctional molecules can have this behavior. 
     There are many molecules known in the art; such as anthracenes, pyrenes, perylenes, porphyrins, phthalocyanines, rhodamine dyes, and carbazoles that can be used as the first and second materials  102 ,  202 . In the preferred embodiment, the first material  102  would have as high a photoemission quantum yield as possible (˜1) and the second material  202  would have as high an absorption cross-section as possible as the emission wavelengths of the first material  102 . 
     In the preferred implementation, the first material  102  is a carbazole derivative and the second material  202  is a porphyrin derivative. The first material  102 , a carbazole derivative, has an emission quantum efficiency of about 0.4 and an emission spectrum that overlaps the spectrum of the strongest absorption band of the second material  202 , the porphyrin derivative. As a result, upon activating the first material  102 , the carbazole derivative, with λ 0  (ca. 330 nm), the second material  202 , the porphyrin derivative, is excited to M 2   *  indirectly via λ 1  (ca. 390 nm) emitted by the first material  102 , the carbazole derivative. M 2   *  can be either a singlet or triplet excited state. If it is a single excited state, it may convert rapidly to a triplet excited state. In the case of the preferred embodiment where the second material  202  is a porphyrin derivative, a triplet M 2   *  state is formed. It has a strong absorption peak at λ 2  (ca. 470 nm). When M 2   1  is further excited by λ 2 , it photo-ionizes to give the cation radical M 2   + . This process may be mono-photonic or bi-photonic (i.e. involving either one or two photons.) 
     For the transmitter  100 , it is not important whether the transmitter  100  is illuminated before or after the voltage potential is applied across the first material  102 . Likewise, for the receiver  200 , it is not important in which order the illumination occurs. For some second materials, it may be necessary to illuminate the second material  202  with the second external laser  206  when the second material  202  is in a ground state. The optical signal  106  then trips a transmitter  100  in the active state to emit light or a receiver  200  in the excited state to produce a logic-level voltage at its terminals  208 ,  210 . For some second materials  202  it may be necessary for the electronic or optical signal  106  to reach the second material  202  in the ground state, and for light from the second external laser  206  to operate on the second material  202  only after the second material  202  is active or excited. 
     The preferred implementation of the present invention requires each transmitter chip module  103  and each receiver chip module  204  to be in two different light paths. FIG. 5 shows a preferred embodiment of this arrangement, generally referred to by reference numeral  500 , illustrating the side views of two logic device substrates, a transmitter substrate  502  and a receiver substrate  504 . On each of the substrates is a chip module, a transmitter chip module  103  on the transmitter substrate  502 , and a receiver chip module  204  on the receiver substrate  504 . The signal light  106  from the transmitter  100  to the receiver  200  is transmitted via a light transmission means, such as by traversing a fused fiber bundle array  506  (optical signal path) or similar device for imaging the output of the transmitter chip module  103  (or array thereof) onto a corresponding receiver chip module  204  (or array thereof). The first external laser  104  for the transmitter chip module  103  (or array thereof) is coupled into the fused fiber array  506  in a manner that illuminates the transmitter chip module  103  (or all of the individual transmitter chip modules of an array), preferably by an optical fiber bunch  508  branched into the fused fiber array  506 . Likewise, the second external laser  206  for the receiver chip module  204  (or array thereof) is coupled into the fused fiber array  506  in a manner that illuminates the receiver chip module  204  (or all of the individual receiver chip modules of an array), preferably by an optical fiber bunch  510  branched into the fused fiber array  506 . A processor  512 , preferably the CPU of the computer which houses the VLSI chips, synchronizes the operation of the first and second external lasers  104 ,  206 , as well as the logic device  108  and voltage detectors  212 . 
     Alternatively, it is also possible to illuminate the transmitter and receiver chip modules  103 ,  204  from underneath their respective substrates  502 ,  504  because silicon substrates are virtually transparent to light. However, even if illuminated from below the substrates  502 ,  504 , the signal  106  path continues to lie above the substrate. 
     Other variations of the optical geometry are possible. Instead of placing each transmitter chip module  103  on a separate area of the substrate  502 , the transmitter chip modules  103  can be stacked in a single position. Each first material  102  can be synthesized to emit a different wavelength. The light at different wavelengths can be carried along a common light path to the receiver  200 . At the receiver  200 , the receiver chip modules  204  can also be realized as a stack, each second. material  202  being sensitive to a different wavelength. 
     In a computer system, there are often several hundred signal paths that carry data from one chip module to another. FIG. 6 shows a system implementation that carries data on multiple paths  602  under the control of a single first external laser  104  at wavelength λ 0  and a single second external laser  206  at wavelength λ 2  The signal light  106  path is shown as a bundle or ribbon of fibers  506  that carries signal light from multiple transmitter chip modules  103  to corresponding receiver chip modules  204  via multiple paths  604 . Signal light  106  of wavelength λ 1  is coupled into the light paths at junction  508   a  and light of wavelength λ 2  is coupled into the signal light  106  path at junction  510   a . In this embodiment, the first and second external lasers  104 ,  206  can be turned on and off by external control signals controlled by a central processor  512  which also synchronizes the operation of the logic devices  108  and voltage detectors  212 . In other embodiments, the light from the first and second external lasers  104 ,  206  can be gated onto the signal light  106  path through external modulators (not shown). 
     The substrates that hold the transmitter and receiver chip modules  103 ,  204  are substrates  502 ,  504 , respectively. A single communication works as follows. The logic on the transmitter substrate  502  places each transmitter chip module  103  in either an activated or deactivated state. The first external laser  104  turns on. Its light of wavelength λ 0  passes through fiber bunch  508  and junction  508   a  and into the fused fiber bundle  506  and illuminates the transmitter chip modules  103 . The activated transmitter chip modules  103  (any in which the logic has placed a voltage potential across its first material  102 ) emit the signal light  106  of wavelength λ 1 , which is carried over the fiber bundle  506  to selectively illuminate corresponding receiver chip modules  204 . In the preferred embodiment, each transmitter chip module  103  illuminates one and only one receiver chip module  204 . In other embodiments, light routing and switching can be employed to route light to multiple receivers, and allow the destinations to vary in time. 
     The receiver chip molecules  204  illuminated by the signal light  106  of wavelength λ 1  change state to the excited state. The second external laser  206  turns on and illuminates the receiver chip modules  204  with light of wavelength λ 2 . The second material  202  of the receiver chip modules  204  which are in the excited state (illuminated by the signal light  106  of a corresponding transmitter chip module  103 ) produce an output current or voltage at leads  208 ,  210  when they receive illumination at wavelength λ 2 . Other receiver chip modules produce no output current or voltage. 
     Logic circuits  212  (see FIGS. 2 a  and  2   b ) on the receiver substrate  504  sense the outputs of the receiver chip modules  204  which are summed to provide a data signal. This completes the cycle which can be repeated any number of times to continually transmit data from the transmitter  100  to the receiver  200 . 
     FIG. 7 shows the details of junction  508   a . In general, the first external laser  104  preferably splits into 2 n  output paths through N levels of fiber splitters  702 . In this embodiment, N=2, so that one initial path ( 508 ) splits into 4 outputs after 2 levels of splitting. Each split divides the energy in the light approximately equally among the two outputs. In FIG. 7, the first external laser  104  illuminates fiber  508  with light at wavelength λ 0 . The light passes through 1-to-2 fiber couplings  702  creating a total of 4 outputs  704 , each carrying about one-fourth of the power input to fiber  508 . The four outputs  704  reach four fibers  706  of the optical signal path  506  (alternatively referred to as a data bus), and are coupled onto the optical signal path  506  at coupling points  708 . These are 2-to-1 couplings and are the inverse of couplings  702 . They are directional in the sense that light flowing downward from the first external laser  104  couples onto the optical signal path  506  and continues to travel downward toward the transmitter chip modules  103 . Virtually no light from the first external laser  104  flows upward on the optical signal path  506  towards the receiver chip modules  204 . A similar junction arrangement is also used at the receiver site. 
     While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.