Optical digital processing device

This invention consists of three separate functional devices fabricated from a single monolithic semiconductor chip. The three devices may be constructed as a unit to work in concert, or any of the three devices may be constructed alone in order to perform its particular operation independently. The three functional devices are: an optical modulator; an optical demodulator; and, an integrated optical logic device operating in unison and utilizing coherent light from a self contained laser diode for transmitting and receiving data and performing extremely high speed logical operations photonically.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to the manipulation of light waves for 
the purpose of transmitting, receiving and processing digital information, 
and more particularly to the modulating, detecting and performing of 
logical operations with coherent light. 
2. Description of the Prior Art 
It has been known for some time that the use of light as a medium for the 
transmission of information has distinct advantages over conventional 
means, primarily because of the tremendous bandwidth available at such 
short wavelengths. With the introduction of light emitting diodes and more 
particularly of lasers, the technology became a reality and now data 
transmissions at the rate of one billion bits per second can be sent from 
point to point over optical fibers many miles in length. The highest 
transmission rate achieved thus far is about twenty billion pulses per 
second, accomplished by multiplexing several lasers operating at different 
wavelengths. Even this rate, however, is but a fraction of the theoretical 
maximum for a light source operating, for instance, at a wavelength of 900 
nanometers. The primary limiting factor in the transmission rate is the 
frequency at which a light source (typically a light emitting diode or a 
laser) can be turned on and off. The apparent maximum is about one billion 
hertz. The present invention does not turn a laser on and off, but 
modulates the light by an indirect method. 
Likewise, detecting high repetition rate light pulses is difficult, and has 
about the same upper limit with devices now in use (PIN diodes and 
avalanche photodiodes, etc.). The present invention has a means of 
detecting high rate, low power light pulses. 
It has also been known for some time that if a way could be found to use 
photons, as opposed to electrons, as a basis for devices which can perform 
logical operations, that such devices would have substantial advantages 
(primarily in processing speed) over conventional devices. These logical 
operations; logical AND, logical OR, INVERT, and EXCLUSIVE OR are the 
building blocks of most digital electronic circuits. 
An optical logic device would preferably be subject to miniaturization and 
high density packaging, have quantized inputs and outputs, and lend itself 
to inexpensive mass production. The invention described herein performs 
extremely high speed logical operations, can be made to interface with 
most digital devices presently in use, has highly quantized inputs and 
outputs, and can be mass manufactured in high density packaging with 
currently available photolithographic techniques. 
Many optically bistable devices have been proposed, and several have 
recently been constructed. All take advantage of the nonlinearity in the 
refractive index of certain mediums, and most make use of a tuned cavity, 
or interferometer, in which the refractive index is changed by electrical 
or electromagnetic energy injections. I believe that it is unnecessary to 
confine coherent light in a tuned cavity in order to exercise control over 
the phase and amplitude of the light. If the phase of one-half the photons 
in any beam of coherent light can be changed with respect to the other 
half, the amplitude and phase of the composite beam can be controlled. 
Moreover, the use of a tuned cavity incorporates some of the same problems 
that plague the pulsed laser itself. That is, the speed at which it 
operates depends to a great degree on the time it takes for the relections 
inside the cavity to die out after the transition from on to off. The 
length of one bit of information is dependent on the optical length of the 
cavity. The operation of these types of devices, in most instances, 
employs a reference beam to hold the cavity just below a threshold level, 
and a second modulated probe beam to push the cavity past the threshold, 
which exponentially increases the output. This, however, does not address 
the original problem of how to increase the modulation frequency of the 
probe beam. 
The present invention does address this problem and is not restricted by 
the liabilities of a tuned cavity. A tuned cavity or interferometer is 
also extremely temperature sensitive. Since the present invention relies 
on complimentary halves of the same crystal, phase changes due to 
temperature variations are the same in both halves. A tuned cavity also 
requires a full 180.degree. phase shift in the cavity in order to achieve 
true bistability (90.degree. change in the optical length of the cavity). 
In the present invention, any unit of phase shift can be considered a 
transition from an absolute logical low to an absolute logical high. 
SUMMARY OF THE INVENTION 
A digital information processor consisting of three separate functional 
devices fabricated from a single monolithic semiconductor chip utilizing 
coherent-light-for performing extremely high speed digital operations. The 
three devices are: an optical modulator; an optical demodulator; and, an 
integrated optical logic device in which three parallel equally 
dimensioned electrically isolated light channels, transparent at the wave 
length of a selected laser diode, are defined by a crystal deposit of a 
light emitting compound. The position of the laser and the three light 
channels are fixed relative to each other by a grounded metallic 
supporting base. 
The optical modulator and logic device each utilize the laser diode and two 
of the light channels with the optical modulator forming a shift register 
in which binary data from a parallel electrical data bus loaded 
simultaneously into the input of the shift register are emitted as a 
serial) binary train of light pulses at its output. The optical 
demodulator, utilizing the remaining light channel, operates at the speed 
of the optical modulator. 
The primary objective of the invention is to improve upon the speed and 
versatility of photonics.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Like characters of reference designate like parts in those figures of the 
drawings in which they occur. 
In the drawings: 
The optical modulator will be referred to as "the optical modulator". The 
optical demodulator will be referred to as "the optical demodulator". The 
integrated optical logic device will be referred to as "the logic device". 
The photonic integrated circuit which consists of all the above will be 
referred to as "the device". 
The device is constructed in the following manner: 
A crystal C is grown on a conductive metallic base 2 by any crystal growth 
process, such as vacuu evaporation deposition, or molecular beam expitaxy. 
The metal base 2 is a type which resists chemical etching, such as gold. 
The crystal may be any one of several combinations of the light emitting 
binary, ternary, or quaternary compounds composed of the "so called" III-V 
elements (Groups III and V of the periodic table). The crystal will 
consist of three layers, for example they will be (from bottom to top) as 
viewed in FIG. 1: gallium aluminum arsenide GaAlAs, gallium arsenide GaAs; 
and gallium aluminum arsenide GaAlAs. The crystal is capped with a 
conductive metallic top surface S which will not resist etching, such as 
aluminum. The crystal will be doped as shown by FIG. 1. Any semiconductor 
element or compound has a characteristic band gap and other specific 
electrical characteristics. These electrical characteristics can be 
modified or tailored, however, by the introduction of impurities, or 
"dopants" into the crystal structure. Impurities may be electron donors 
such as boron or gallium, or electron acceptors such as arsenic or 
phosphorous. Electron donors are known as "N" dopants and electron 
acceptors are known as "P" dopants. In binary compounds such as gallium 
arsenide, the doping may be accomplished simply by varying the relative 
amounts of each element. 
The dimensions of the device depends upon the application, however for this 
example assume that the device has the relative dimensions shown by FIG. 1 
where: L.sup.0 and L.sup.1 =10.times.10.sup.-6 M, respectively; L.sup.2 
=50.times.10.sup.-6 M; L.sup.3 =2.56.times.10.sup.-3 M; L.sup.4 
=2.615.times.10.sup.-3 M; G=5.times.10.sup.-6 M; W=25.times.10.sup.-6 M; 
and, W'=50.times.10.sup.-6 M. Through industry standard photolithographic 
techniques, the device is etched so that it forms four superposed segments 
mounted on the same conductive metallic surface, as shown by FIG. 1. In 
other words, the crystal C is cut away (separated) along the dual lines 6, 
7 and 8. In addition, the metallic top surface S is transversely etched 
away along lines 9 through 264 (26 through 252, not shown). The 
configuration at this point consists of a laser diode 1, and three 
elongated juxtaposed electrically isolated transparent light channels 3, 4 
and 5 (transparent at the wavelength of the laser diode). The laser and 
the three light channels are mechanically fixed with respect to one 
another by the metallic substrate or base 2 upon which the crystal was 
deposited. (It should be pointed out that the light channels need not be 
of the same material as the laser, however fabrication is simpler if it 
is.) For reasons which will be detailed later, the three light channels 
will also be cleaved at their ends remote from the laser, in the manner 
illustrated by FIG. 1. 
The gap G also defined by the dual lines 8 should be any integral number of 
half wavelengths with respect to the light emitted by the laser, however 
this dimension is not critical to the operation of the device. The gaps 
defined by the dual lines 6 and 7 can be any dimension but should be small 
compared to the width of the light channels. The laser diode 1, of course, 
will be of dimensions so as to be resonant at the frequency of the light 
it is emitting. Since the conductive metallic top S was etched, as 
previously described, the laser diode will have a conductive metallic cap 
1000 for the purpose of attachment of an electrical conductor, not shown. 
Each of the three light channels has 256 conductive metallic caps for the 
same purpose. The metallic base 2 is connected to ground. 
The three light channels are: The 0.degree. (zero degree) channel 4, the 
180.degree. (one hundred and eighty degree) channel 5, and the detector 
channel 3. 
The optical modulator is composed of the laser diode 1, the 0.degree. 
channel 4, and the 180.degree. channel 5. The optical modulator may be 
described as an electrical parallel load, optical serial output shift 
register. In other words, binary data from a parallel electrical data bus 
are loaded simultaneously into the shift register and are then emitted as 
a serial binary train of light pulses. If the two light channels in the 
optical modulator are 2.56 millimeters in length, and consist of 128 
parallel binary inputs, an optical binary output of 4.16 trillion pulses 
per second would be produced. This would represent about a four thousand 
fold improvement over the best pulsed laser performance. 
The optical demodulator is composed of the detector channel 3 and its 
associated circuit (FIG. 3). (In practice the associated circuitry would 
be constructed as an integral part U of the original semiconductor chip, 
however for ease of explanation these parts will be hereinafter discussed 
as if they were discrete components.) The optical demodulator, since it 
has the same dimensions as the two light channels of the optical 
modulator, consists of 128 juxtaposed photodiodes and operates at the same 
speed as the optical modulator. 
The logic device consists of the laser diode 1, the 0.degree. channel 4, 
and the 180.degree. channel 5 and associated circuit (FIG. 2). The logic 
device performs the logical AND, the logical NAND, the logical OR, the 
logical INVERT, and the logical EXCLUSIVE OR. Assuming the same relative 
dimensions given for FIG. 1, a propagation delay per gate of about 240 
femto seconds may be achieved. Again, this is about four thousand times 
faster than the fastest electronic gate. The logical functions are 
performed photonically. 
The light channels 3, 4 and 5 each consist of some number of PN junctions 
(in this example 256) alternated in their polarity as shown by FIG. 1 (the 
doping in channels 3 and 4, not shown, is identical to the doping in 
channel 5). Channel 3 (FIG. 1) consists of PN junctions 3001-3128 in 
alternation with PN junctions 6001-6128. Channel 4 consists of PN 
junctions 2001-2128 in alternation with PN junctions 5001-5128. Channel 5 
consists of PN junctions 1001-1128 in alternation with 4001-4128. As 
stated hereinabove, each of the PN junctions and the laser diode 1 have a 
conductive metallic cap for electrical contact with an electrical 
conductor. The metallic caps 4001-4128, 5001-5128, and 6001-6128 may be 
tied to ground, allowed to float, or reverse biased in order to increase 
the width of the insulating barrier. 
Although in this example the crystal is composed of gallium arsenide and 
gallium aluminum arsenide, the crystal elements actually used will depend 
in some measure on the application. For instance an optical demodulator 
might be constructed from an element with a larger band gap such as 
gallium phosphide or aluminum arsenide in order to attain a higher voltage 
output. An optical modulator might use InGaAsP (indium gallium arsenic 
phosphide) so that the output could be tailored to a particular 
wavelength, for example 1550 nanometers, which is an absorption window in 
some optical fibers. In applications where wavelength is not particularly 
important, such as optical logic elements or photonic amplifiers, 
compounds such as indium antimonide or indium arsenide would generate a 
larger phase shift, and consequently a larger amplification factor. 
Operation 
1. Operation of the optical modulator. 
A constant lasing voltage is applied to the conductive metallic cap 1000 of 
laser diode 1, and ground is applied to the conductive metallic base or 
substrate 2. The active layer of the laser, and the three light channels, 
lies between the "N" doped and "P" doped layers of GaAs. The GaAs layers 
are sandwiched between layers of GaAlAs. This forms what is known as a 
double hetrostructure, wherein the GaAlAs layers have a lower refractive 
index than GaAs layers, and therefore the light and charge carriers are 
trapped in the vicinity of the active layer. This forms a very straight 
and narrow light guide, and insures a maximum interaction between the 
light and the charge carriers in the active layers. Laser light leaving 
the laser portion, and entering the two light channel portions of the 
device will likewise be confined to the active layer, entering at points H 
and J of FIG. 2. Since the two light channels of the optical modulator are 
identical parts of the same crystal, the behavior of the light will be 
identical in each channel, and the phase relationships of the two light 
beams can be very precisely predicted. The optical distance from the input 
point to the output point in each channel is the same, the channel ends 
being at an angle at the output points. This accomplishes two functions. 
It prevents the generation of standing waves due to reflections (and 
consequently prevents resonance) inside the light channels, and it 
projects the light from each channel toward a common convergence point, 
such as a light window, a fiber optic coupling, or the input to an optical 
demodulator or the logic device portion of another device on the same 
substrate, none of the foregoing being shown. The same end could be 
accomplished by directly coupling the outputs of the light channels to the 
desired device. 
The output of a voltage divider network, resistance R140 and R150 (FIG. 2), 
is connected to the conductive metallic cap of PN junction 1001, the first 
element of the 180.degree. channel 5. The output of a voltage divider 
network resistors R160 and R170 is connected to the conductive metallic 
cap 2001 of the first element of the 0.degree. channel 4. Although the 
electrical and optical properties of the two channels are identical, the 
optical length of either channel may be changed by changing the refractive 
index of that portion of the crystal. If a positive voltage from the 
voltage divider network R140 and R150 is applied to the metallic cap of PN 
junction 1001, a current is caused to flow in the PN junction between the 
metallic cap and the metallic substrate 2. 
Referring to FIG. 2, the PN junctions 4001 through 4128 (4002 through 4128 
not shown) and 5001 through 5128 (5002 through 5128 not shown) are not 
biased and serve to electrically insulate PN junctions 1001 from 1002 from 
1003, etc. The refractive index of each element of the crystal is directly 
proportional to the number of charge carriers in the active layer, i.e., 
the current level in the junction. This current level may be any level 
below its threshold. At that point stimulated emission would take place, 
and the applied voltage could no longer control the refractive index. The 
values of R140 and R150 are chosen such that the current through that PN 
junction insures precisely 180.degree. of phase difference in the light 
from channel 5 with respect to the 0.degree. channel 4, as measured at the 
point of convergence of the two beams. The remainder of the 180.degree. 
phase difference results from the fact that, (referring to FIG. 2) in its 
static condition, complimentary logic levels are applied to the junctions 
of the 180.degree. channel, as opposed to the junctions of the 0.degree. 
channel. The outputs transmitted from the two channels then add 
destructively at their convergence point and result in zero output. The 
static state of the optical modulator, therefore, is that the phases of 
the outputs from channels 4 and 5 are 0.degree. and 180.degree. 
respectively which results in no output (or logical zero). 
If a logical high voltage (below the threshold) is applied to input DB00 
and a logical low voltage is applied to its complimentary input DB00 and 
resistors R5 and R205 are of the appropriate values, then the increased 
number of charge carriers in the active layer of PN junction 1002 of the 
180.degree. channel and the decreased number of charge carriers in the 
active layer of the PN junction 2002 of the 0.degree. channel will, 
respectively, cause a phase retardation and a phase advance toward 
270.degree.. The coherent light passing through 2002 of the 0.degree. 
channel 4 will therefore be more in phase with the coherent light passing 
through 1002 of the 180.degree. channel 5 when the convergence point is 
reached. Now, the outputs transmitted from the two channels add more 
constructively for a maximum output (or logical one). 
At the end of a pulse applied to DB00 and DB00, current through the 
junction returns to its static value, and the outputs from the two 
channels again add destructively for no output at the convergence point 
(or logical zero). If a 0.12 pico second pulse is applied to the DB00 and 
DB00 inputs, then a 0.12 pico second light pulse will appear at the 
convergence point (i.e., the light from the two channels will be in phase 
for 0.12 pico seconds). This was accomplished without having to turn the 
laser on or off. If logic levels are applied to all the data bus inputs 
simultaneously (in this case DB00/DB00 through DB132/DB132) then one 
hundred and thirty-two (132) 0.12 pico second pulses of light will appear 
at the convergence point. If the optical length of the light channels is 
30.72 pico seconds (i.e., 2.56.times.10.sup.-3 meters and refractive index 
of 3.6), and there are 132 data bus inputs, then the optical modulator 
will have an output of 4.29.times.10.sup.12 pulses per second. The data 
bus, however, will be operating at only 32.5.times.10.sup.9 hertz since 
132 light pulses are produced for each electrical bus cycle. This is 
analogous to the operation of a parallel load, serial output shift 
register. Each 30.72 pico seconds, 132 data bits are loaded from the bus, 
and then transmitted as a serial optical data stream. The length of the 
electrical pulses from the data bus must not exceed the optical length of 
the individual PN junctions, as this would result in adjacent optical 
pulses overlapping. Although it is doubtful that the electrical bus can 
make a transition in 0.12 pico seconds, a pulse that short can easily be 
produced from the bus transition through RC coupling with a short RC time. 
The optical modulator, therefore, produces encoded light pulses at rates in 
excess of four trillion pulses per second, without having to turn the 
laser on and off. In addition, the power of the light pulses may be 
controlled by simply controlling the amount of phase shift produced by 
each data bus input. The optical modulator, therefore, can function as an 
amplifier, whereas a change in the voltage applied to a PN junction 
results in a proportionate change in the output power. 
2. Operation of the optical demodulator. 
The optical demodulator consists of channel 3 of the device and associated 
circuitry. FIG. 3 shows a horizontal cross section of a portion of the 
detector channel. 
Conventional construction of photodiodes places the PN junction of the 
photodiode as near as possible to the irradiated surface so as to insure a 
maximum interaction of the radiation with the charge carriers in the 
active region. A bias voltage is applied between the cathode and anode so 
as to maximize the number of charge carriers. Photons penetrating the 
irradiated surface (say the anode) and reaching the junction induce 
electrons in the valance band to make a transition to the conduction band. 
This results in current flow across the junction and consequently, a 
voltage drop across a load resistance. A larger irradiated surface insures 
a larger active layer surface area with which the photons can interact 
(and therefore, a larger induced current). Because the light must pass 
through the anode before it reaches the junction, and because any photons 
which pass through the junctions without interacting are absorbed in the 
cathode, only a small portion of the useful radiation results in induced 
voltage. Furthermore the electrical length of a photodiode with a large 
surface area limits the frequency at which the device can operate. For a 
large surface area, cathode/anode capacitance is also a problem. 
The optical demodulator fragmentarily shown by FIG. 3 similarly consists of 
a number of forward biased PN junctions (photodiodes), electrically 
insulated from one another by unbiased reverse PN junctions. Rather than 
being irradiated at the anode surface, the optical demodulator is 
irradiated at point C, which is in line with the active region of PN 
junction 3001. Again, the light is trapped in the active region by the 
double hetrostructure, thereby insuring maximum interaction. Rather than 
irradiating the entire surface at once, however, a short light pulse 
travels through each photodiode individually, irradiating them in 
succession until it reaches point D. If the electrical length of conductor 
F from point A to point B is the same as the optical length from point C 
to point D and the same is true for each of the other conductors with 
respect to their PN junctions, then the photoelectric pulses from each 
individual photodiode will arrive at point B simultaneously, and the 
effect will be the same as if the entire junction (minus the unbiased 
portion) had been irradiated at once. The light, however, is entirely 
confined to the useful region, and the cathode/anode capacitance has been 
reduced. The electrical length of the photodiodes has been reduced by 
breaking it down into many small photodiodes and superimposing their 
outputs. The voltage divider network made up of load resistor R17 and pull 
up resistor R16 insure the proper operating bias for the photodiodes. The 
length of a light pulse must be shorter than the optical length of the 
individual photodiodes to insure that adjacent pulses do not overlap. 
3. Operation of the integrated optical logic device. 
A constant lasing voltage is applied to the conductive metallic cap 1000 of 
laser diode 1, and ground is applied to the conductive metallic substrate 
2. Again the laser light is trapped by the double hetrostructure and 
confined to the active regions of the 0.degree. channel 4 and the 
180.degree. channel 5. Referring to the fragmentary cross section of the 
light channels 4 and 5 (FIG. 2), light enters at points H and J and 
travels from H to K and from J to L. The voltage divider network R140 and 
R150 insures the light from channels 4 and 5 is precisely 180.degree. out 
of phase at the convergence point (or zero output). 
If coherent light (for instance from another logic device on the same 
substrate) is projected onto point P1, which is the active region of PN 
junction 1002, it will cause a small change in the refractive index of 
1002. Because the light projected onto P1 is traveling along a line which 
is perpendicular to the light traveling from J to L, the light projected 
onto P1 will not interfere with the amplitude of the outpu from light 
channel 5. It will however cause a phase change in the laser light moving 
from J to L in channel 5. This is because the refractive index of the 
crystal is not perfectly linear with respect to the amount of light 
passing through it. Because the phase of the light in channel 5 has 
changed with respect to the light in channel 4, the two beams no longer 
completely cancel and there is an output of light at the convergence point 
(or logical one). If a short pulse of light (120 femto seconds, or 
1.2.times.10.sup.-13 sec) is projected onto P1, then a 120 femto second 
pulse will appear at the output. If either of two independent beams of 
light, herein called beam one and beam two, is projected onto P1, the 
above described output would result. If the phase relationships of beam 
one and beam two are 0.degree. and 120.degree. respectively, as shown by 
FIG. 4, and the amplitude of each beam is 1 (one) (in arbitrary units), 
and both beams are projected onto P1 simultaneously, the product of the 
two beams, now called the vector beam, will cause a phase shift in the 
light from channel 5. The phase shift in channel 5, and consequently the 
amplitude of the output pulse, will be the same as if there had been only 
one input. This is because the beams interfere partially destructively in 
accordance with the following formula: (Cos .theta..degree.+Cos 
120.degree.).sup.2 +(Sin.theta..degree.+Sin 120.degree.).sup.2 
=(Vector).sup.2 =1: where: .sqroot.Vector.sup.2 =1 and Vector 
angle=60.degree.. 
The logic device, therefore, has performed a logical OR function, i.e., a 
logical high on either or both inputs, results in a logical high output. 
Since a positive OR is the same function as a negative AND, it also 
performs the AND function if the inputs and outputs are inverted. 
The INVERT function may be performed by the logical NAND. The NAND function 
is accomplished by adding a third input beam, herein called the third 
beam, whose phase angle is 240.degree.. The third beam is displaced from 
both beam one and beam two by 120.degree., and displaced from the vector 
beam by 180.degree.. In this configuration, if both inputs are high, they 
will result in a vector beam of magnitude one (1) at 60.degree., which 
will cancel the third beam of magnitude one (1) at 240.degree. resulting 
in a logical low output. If either beam one or beam two is high and the 
other low, there will be one beam displaced from the third beam by 
120.degree., which will result in a new vector beam of magnitude one (1) 
at either 180.degree. or 300.degree., depending on which input was high. 
This will result in a logical high output pulse. If both input beams are 
low there will remain the third beam of magnitude one (1), which will 
result in a logical high output pulse. In this configuration, therefore, 
the logic device forms the logical NAND function. It should be pointed out 
that since each of the logic elements is also a photodiode, the output of 
each logic element will also be available in voltage form as a voltage 
drop across resistors R1 through R205. 
The logical EXCLUSIVE OR function is performed by the logic device if beam 
one and beam two alone are projected onto P1 as was done with the OR 
function, and the two beams are displaced from one another by 180.degree.. 
In this configuration, a high pulse on either input will result in a high 
output pulse, however if both inputs are high, the two inputs will cancel 
(being 180.degree. out of phase) and a low output will result. 
The precise phase relationships of beam one and beam two with respect to 
the third beam are insured by the selection of the appropriate values for 
resistors R160 and R170 of the logic devices which generated the two 
beams. These phases, and consequently the values of R160 and R170, will 
depend on the physical placement of the individual logic devices on the 
substrate and will be different for different types of integrated 
circuits, but will, of course, be the same for all integrated circuits 
made from the same template. 
Since the logical function performed by each individual element is strictly 
a function of phase relationships of the input beams, and those phase 
relationships can be changed electronically, it is obvious that the 
hardware configuration of each integrated circuit can be changed from 
instant to instant to perform any sequence of operations desired. This 
"dynamic hardware" allows one type of integrated circuit to be used to 
perform any possible combination of logical operations. 
Obviously the invention is susceptible to changes or alterations without 
defeating its practicability. Therefore, I do not wish to be confined to 
the preferred embodiment shown in the drawings and described herein.