Abstract:
The present invention is a photonic logic circuit for multimode optical signals. The device includes a laser cavity having at least four conduits, the combination forming a substantially X-shaped construction. An output is attached to each conduit for transmission of the optical signals from the cavity. At least one input is connected to the laser cavity. The input is connected to an upper or lower edge of the laser cavity. These are the edges that do not include conduits. A bias contact is connected to the cavity and the two lower conduits. The bias contact is used to pump the photonic device. Preset contacts are attached to each of the upper two conduits and their respective outputs. The preset contacts are used to control the logic function of the photonic logic device. Altering current pump settings between the respective contacts controls the direction of lasing between outputs of the photonic device and the logic function performed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to coherent light generators and, more specifically, to mode discriminating coherent light generators. 
     BACKGROUND OF THE INVENTION 
     Multi-mode laser diodes (MMLDs) are frequently used in electro-optical devices. An MMLD is a laser diode that supports at least two stable modes, though these modes are not necessarily supported at the same time. Typical operation of the laser diode may operate by injection of a current into the device, which causes the coupled lasers to alternate between modes. In many embodiments it is desirable to use MMLDs as optical oscillators, in which case the MMLD include electrical signal inputs along the longitudinal axis of the device. These electrical signals cause perturbations in the mode structure of the MMLD, activating additional modes of the MMLD. The outputs of the MMLD are similarly located along the longitudinal axis of the device. 
     Though these devices are effective in many situations, some problems do exist. One of the most significant limitations is the cross-talk between the input signals and the output signals. As is apparent to those of skill in the art, cross-talk is the phenomenon where signals from one channel cross over into another channel and vice versa in a multi-channel environment. This severely limits the accuracy of the fabricated device and prevents the use of such devices for a number of purposes. Current devices also encounter problems with discrimination between output modes. In most logic devices the output waveguides are closely spaced. This makes discrimination of the modes difficult, resulting in the operation of unwanted modes. MMLDs present the result of the logical operation as the presence or absence of a signal in a specific mode. If the modes can not be accurately discriminated, the logical results can not be cascaded to further logic gates. Finally, MMLDs are generally large in terms of other opto-electronic devices. The length is necessary to allow mode interaction given the typical construction, which includes parallel waveguides and on-axis input signals. 
     U.S. Pat. No. 4,252,403, entitled “COUPLER FOR GRADED INDEX FIBER,” discloses a basic construction for propagation of multiple modes between two fibers. Specifically, this patent discloses a concentric core fiber that is coupled to a graded index fiber by precisely aligning the concentric core fiber with the graded index fiber. Low order modes propagating in the concentric core fiber are coupled to the central region of the graded index fiber and high order modes of the concentric core fiber are coupled to the inner core of the graded index fiber. The present patent does not use this method for propagation of signals. U.S. Pat. No. 4,252,403 is hereby incorporated by reference into the specification of the present invention. 
     U.S. Pat. No. 5,363,463, entitled “REMOTE SENSING OF FIBER OPTIC VARIABLES WITH FIBER OPTIC SYSTEMS,” discloses a variety of fiber optic systems. One such system includes structures for diverting temperature and force information from the optical fiber of the system for measurement, and for reintroducing information into the system at any one of a number of points along the side of the optical fiber. The optical fiber is appropriately prepared along its side to have information reintroduced at certain points. The present invention does not operate according to these principles. U.S. Pat. No. 5,363,463 is hereby incorporated by reference into the specification of the present invention. 
     U.S. Pat. No. 5,764,681, entitled “DIRECTIONAL CONTROL METHOD AND APPARATUS FOR RING LASER,” discloses a method for controlling direction of coupled lasers. Specifically, an asymmetric feedback structure is used to actively or passively control lasing of the system. Active control, which permits directional control of the laser, is achieved through the use of a dielectric stack. Passive control operates through introduction of asymmetry into the path of the laser, preferably by use of a diode to produce cross-coupling of two modes of a laser. The present invention does not operate according to these principles. U.S. Pat. No. 5,764,681 is hereby incorporated by reference into the specification of the present invention. 
     “A New Design for Ultracompact Multimode Interference-Based 2X2 Couplers,” David S. Levy, et al.,  IEEE Photonics Technology Letters , discloses a splitter device that takes a single input and splits the signal into two outputs. The single input is introduced along the axis of the splitter. The structure includes two tapered structures, the tapered ends of the structures being joined in the centers. Both parabolically and linearly tapered devices are proposed. The device includes both two inputs and two outputs, the signal being propagated along the axis of one of the inputs. The present invention does not operate in this manner. This disclosure is hereby incorporated by reference into the specification of the present invention. 
     “Analysis of the Dynamic Behavior and Short-Pulse Modulation Scheme for Laterally Coupled Diode Lasers,” Horatio Lamela, et al.,  IEEE Journal on Selected Topics in Quantum Electronics , discloses a structure having two parallel lasers that allows mode coupling between the lasers. Specifically, the two parallel lasers, given sufficient length, are spaced closely enough to allow switching of power from one laser to the other. To achieve this, the lasers must both be longer than is desirable for most mode switching applications and must be very closely spaced, which makes the modes difficult to isolate. This structure is not the same as that of the present invention. This disclosure is hereby incorporated by reference into the specification of the present invention. 
     “Multimode Interference Bistable Laser Diode,” Mitsui Takenaka, et al.,  IEEE Photonics Technology Letters , discloses a bistable laser structure that switches output modes when an appropriate optical input signal is injected. Specifically, a signal is input along the axis of one of two waveguide inputs. The two waveguides are closely spaced to allow coupling into modes within the bistable laser. The bistable laser must be of sufficient length to allow mode interaction with the injected input signals. As was explained previously, this length is generally greater than is desirable for most multimode applications. Additionally, the close spacing of the output waveguides makes mode discrimination difficult and the on-axis input signal injection is prone to unintended signal scattering back into the input waveguides. The present invention does not operate in this manner. This disclosure is hereby incorporated by reference into the specification of the present invention. 
     Prior art multimode laser diode photonic logic devices have significant limitations in the electro-optical arts. Specifically, to allow interaction between the modes and input signals, most devices must be long. Because a primary goal of electro-optical device designers is to obtain the most compact device possible, this is a significant limitation. Further, most prior art devices operate by closely spacing the output waveguide structures, which results in an inability to accurately discriminate between modes of the output signal. It is therefore desirable in the art to have a compact multimode laser diode photonic logic device that allows accurate discrimination between the modes of the output signal. It is further desirable in the art to have a multimode laser diode photonic logic device that can accept an input signal off-axis with respect to the output signal to prevent unintended signal scattering back into the input waveguides. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a multi-mode photonic logic device for optical input signals. 
     It is a further object of the present invention to provide a multi-mode photonic logic device for optical input signals that allows accurate discrimination between modes of an output signal. 
     It is another object of the present invention to provide a compact multi-mode photonic logic device for optical input signals that allows accurate discrimination between modes of an output signal that is effective for input signals of various wavelengths. 
     The present invention is a photonic logic circuit for multimode optical output signals. The device includes a laser cavity having at least four conduits, the combination forming a substantially X-shaped construction. The upper and lower edges of the laser cavity are preferably curved. An output, preferably a waveguide, is attached to each conduit for transmission of the optical signals from the cavity. 
     At least one input is connected to the laser cavity. The input is connected to an upper or lower edge of the laser cavity. These are the edges that do not include conduits. This configuration is called off-axis input. A bias contact is connected to the cavity and the two lower conduits. The bias contact is used to pump the photonic device. Preset contacts are attached to each of the upper two conduits. The preset contacts are used to control the logic function of the photonic logic device. Altering the application of current between the respective contacts controls the direction of lasing between outputs of the photonic device. This embodiment performs invert and exclusive OR logic functions. 
     In an alternative embodiment, a laser cavity includes only three outputs. In this embodiment a single bias contact may be used to contact all three conduits of the cavity. The alternative embodiment performs invert and exclusive OR logic functions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of the photonic device of the present invention; and 
         FIG. 2  is a top view of an alternative embodiment of the photonic device of the present invention 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is a multimode photonic logic device. Referring to  FIG. 1 , the photonic device  10  of the present invention is shown in greater detail. The photonic device  10  includes four outputs  12 . Each output is a device capable of transmitting an optical signal. Such devices include, but are not limited to, waveguides and optical fibers. As is obvious to those skilled in the art, such devices are common electro-optical devices for transmitting information in the form of light between two electro-optical devices. A waveguide is commonly etched into a semiconductor device to transmit light between other devices located thereon, or between semiconductors. Optical fibers are frequently used to transmit information between electro-optical devices. Any typical electro-optical device capable of transmitting an optical signal may be used as the outputs for the present invention, many of which are well known and commonly used in the art. In the preferred embodiment the outputs  12  are planar waverguides. 
     The photonic device  10  further includes cavity  14  connected to outputs  12 . As is obvious to those skilled in the art, cavity  14  is a chamber in the center of photonic device. Cavity  14  has wide outer edges that taper towards the center of the cavity  14 . In the preferred embodiment the width at the center is approximately 6 um. The outer edges of the cavity  14  are preferably parabolic, however the outer edge may follow a circular curve or have any other suitable shape cavity as would be obvious to those of skill in the art. For example, the cavity  14  may have substantially V-shaped outer edges. In the preferred embodiment the length of the cavity  14  is 45.9 um and the circular curve of the outer edge of the cavity preferably arcs at approximately a 50.2 degree angle given an arc radius of 53.1 um. Cavity  14  is composed of an appropriate semiconductor substrate material. In the exemplified embodiment, the material is a III–V semiconductor material, preferably GaAs. 
     Cavity  14  includes four conduits  16 . Each conduit  16  is preferably a protrusion extending from an edge of the cavity  14 . One conduit  16  extends from the top left side and one from the top right side of the cavity  14 . Similarly, one conduit  16  extends from the bottom left side and one from the bottom right side of the conduit. The conduits  16  preferably protrude from the cavity  14  such that the conduits form a smooth surface with the outer edge of the cavity  14 . Further, each conduit  16  preferably has the same cross-section and epitaxial structure as the cavity  14 . Each conduit  16  is preferably approximately 3 um wide. The cavity  14 , including conduits  16 , is preferably substantially X-shaped. 
     Substrate  15  is connected to the backside of cavity  14 . As is obvious to those of skill in the art, substrate  15  is a conventional semiconductor substrate. In the preferred embodiment, cavity  14  is epitaxially grown on substrate  15 , however cavity  14  may be connected to substrate  15  in any conventional manner many of which are well known and commonly used in the art. In the preferred embodiment substrate  15  is composed of the same material as cavity  14 . In the exemplified embodiment, substrate  15  is composed of GaAs, however other suitable material may also be used such as InP. 
     Bias contact  18  is connected to cavity  14  such that it is in contact with the entire cavity except the two conduits  16  located along the upper edge of the cavity  14 . The connection between bias contact  18  and conduits  16  will be explained in greater detail below. Bias contact  18  is a layer of metal disposed on the photonic device. The metal is composed of an Ohmic material compatible with the material of the laser, and therefore will vary depending on the laser material as would be obvious to those of skill in the art. Typical Ohmic materials used for bias contact  18  include titanium platinum gold, chromium gold p-type contacts for GaAs materials, and gold tin gold n-type contacts for GaAs materials. 
     Preset contacts  20  are connected to conduits  16  such that each preset contact  20  is connected to a conduit  16  not connected to the bias contact  18 . Each preset contact is further connected to the cavity  14  such that the preset contact  20  is not in contact with the bias contact  18 . In the preferred embodiment, each preset contact  20  is connected to its respective conduit  16  such that a gap exists between the joined portion of the conduit  16  and the preset contacts  20  and the juncture of the conduit  16  to the remainder of the cavity  14 . In the preferred embodiment, the gap between these two regions is approximately 2 um. As with the bias contact  18 , preset contacts  20  are a layer of metal disposed on the photonic device. The metal is composed of an Ohmic material compatible with the material of the laser, and therefore will vary depending on the laser material as would be obvious to those of skill in the art. Typical Ohmic materials used for bias contact  18  include titanium platinum gold, chromium gold, and gold tin gold. 
     Mirrors  22  are disposed between cavity  14  and outputs  12 . In the preferred embodiment, four mirrors  22  are disposed between conduits  16  and outputs  12  such that one mirror  22  is disposed between each conduit  16  and its corresponding output  12 . In the preferred embodiment the mirrors  22  are planar, however as is obvious to those skilled in the art the mirrors  22  may be of any other suitable shape, such as curved or confocal. Additionally, three mirrors  22  may be used in place of the four mirrors  22 . If three mirrors  22  are used, one mirror  22  is disposed on each of the left and right side of the photonic device  10  between the conduits  16  and the outputs  12  and a third mirror is disposed on one of the left or right side between a conduit  16  and an output  12  that does not already include a mirror. Mirrors are preferably structures etched in the conduit  16  described above. To achieve this, the preset contacts  20  and bias contact  18  must sufficiently overlap the conduits  16  to allow a mirror to be etched along the junction of the conduits  16  and outputs  12 . Manners of etching mirrors are well known and commonly used in the art and any conventional method could be used in conjunction with the present invention. For example, the edge of a preset contact  20  may be deposited over a conduit  16  in a shape to allow current injection of a specific region of the laser structure. The shapes of the preset contacts  20  and bias contact  18  (which are metal structures) cover the area of the laser that will require current injection. This area is the entire area of the laser cavity  14  and conduits  16 , including the area that will form the mirrors  22 . The only areas that will not be covered by the preset contacts  20  and bias contact  18  are the gaps between the contacts. A photoresist will be patterned such that it protects all surfaces of the semiconductor where etching is not required. A photoresist is not present where etching will occur and mirrors  22  will be formed. The etching will occur at the edges of each of the conduits  16  that are furthest from the cavity  14 . During etching, all other portions of the device are protected by the photoresist. The photoresist opening is overlapped with the edges of the bias contact  18  and the preset contacts  20  where the mirrors will be formed such that the contacts are exposed to the etch along their respective edges. In the exemplified embodiment, the conduits  16  are etched anisotropically to form vertical sidewalls, but may be etched by any other suitable means as would be obvious to those of skill in the art. As was discussed above, any material not covered by photoresist is etched during this process. However, since the edges of the bias contact  18  and preset contacts  20  are not covered by a photoresist at the edges where the mirrors  22  are etched, it is the contacts that protect the semiconductor and allow mirrors  22  to be formed only along the edges of the preset contacts  20  and bias contact  18 . In this manner the contacts actually act as an etch mask to protect the semiconductor region covered by the each contact. The mirrors  22  are formed between the edges of each contact and any area protected by photoresist. A reflective coating may also be applied to the mirrors  22  at this time. Outputs  12 , such as waveguides, may be deposited at this point through any conventional method, as would be obvious to those of skill in the art. 
     Ports  24  are connected to cavity  14 . In the preferred embodiment, at least one port  24  is connected to cavity  14  along a top or bottom edge of cavity  14 . As was discussed previously, cavity  14  preferably includes top and bottom parabolic edges. In the exemplified embodiment, two ports  24  are disposed along the bottom parabolic edge of the cavity  14 . This connection of the port  24  to the cavity is referred to as off-axis input. This is because the input is not along the central axis of the laser cavity. In a more preferred embodiment multiple ports  24  are disposed along each of the top and bottom edges of the cavity  14 , at least one of the ports  24  being disposed along a conduit  16 . In alternative embodiments, ports  24  may be located in any variety of combinations, such as having one port  24  on each of the top and bottom parabolic edges of the cavity, or distributing three ports  24  along the edges of the cavity  14 . A port  24  is preferably an optical port etched into the device that allows optical signals to be transmitted from an external optical device into cavity  14 , but may be any device that allows transmission of optical signals between optical devices. Many such devices are well known and commonly used in the art, and any such conventional device may be used in conjunction with this invention. To reduce reflectance in the ports  24 , an anti reflective coating may be applied to each port  24 . The remaining anti reflective coating prevents excess light from being reflected away from the port  24 . Ports  24  may be omitted if reflectance modification on the input surfaces of the cavity is not required, as described in more detail below. 
     The photonic device  10  further includes inputs  26  connected to ports  24  to conduct optical signals to cavity  14 . As with outputs  12 , an input is any electro-optical device capable of transmitting an optical signal to photonic device  10 . Such devices were discussed in greater detail with reference to outputs  12  above. In the preferred embodiment, inputs  26  are waveguides. As was also discussed in greater detail above, waveguides are conventionally grown, deposited, and/or etched on a semiconductor device, however any conventional waveguide may be used for the inputs  26  of the present invention. If the interface between inputs  26  and cavity  14  were coated by mirror  22  high reflectance coatings, ports  24  may be used to remove the high reflectance coatings deposited on the interfaces between inputs  26  and cavity  14  via an etch process, in an effort to maximize the optical signals present at cavity  14 . 
     To operate the photonic device  10  of the present invention, bias is increased in the bias contact  18  such that two longitudinal (left to right) conduits  16  (as opposed to two lateral (top to bottom) conduits  16  lase. Briefly, the bias is increased in the bias contact  18  causing the electrons within the cavity  14  to be excited to upper energy states, emitting photons, which reflect between the mirrors  22 . When the laser cavity is curved, increased reflectivity may be required at mirrors  22  to mitigate losses. Sufficient excitation of these electrons will result in lasing between two conduits  16 . The photonic device  10  will operate in either cross-mode (meaning one upper conduit  16  and one lower conduit  16  will lase) or bar-mode (meaning both top conduits  16  or both bottom conduits  16  will lase) based on the electrical arrangement of the photonic device  10 , such as the shape of the bias contact  18  and diameter of the edge of cavity  14 . The bias on preset contacts  20  and bias contact  18  of the photonic device  10  dictates which two conduits  16  lase. The specific mechanism by which the optical signal lases between the two conduits is well known to those of skill in the art, and will not be explained in greater detail here. For the purposes of this description it will be assumed that lasing initially occurs between the bottom right conduit  16  and the bottom left conduit  16 . 
     At least one optical signal is transmitted through an input  26  to a port  24 . For the purposes of this description, operation will be discussed with respect to two optical input signals—one each on the top and bottom right sides of the photonic device  10 . In a preferred embodiment, each signal is transmitted through an input  26  to a port  24  that is connected to a conduit  16  (by way of a port  24 .) As was explained in greater detail above, each optical input signal is a light signal containing information to be transmitted through an optical device. By transmitting the optical signal through the port  24 , the optical signal is introduced into a conduit  16 . 
     To cause lasing between the lower two conduits  16 , current is applied to the bias contact  18  under forward bias until the bottom two conduits lase. Current is then introduced to either of the upper two preset contact  20 . For the purpose of this description we will assume current is increased in the upper right preset contact  20 . The current is increased until lasing occurs between the upper right conduit  16  and the lower left conduit  16 . In this state the lower right conduit will normally not lase, or is “off”, and the upper right conduit normally will lase, or is “on,” commonly referred to as a cross-mode. Cavity  14  has only sufficient gain to support lasing between two longitudinal conduits. As such, when the upper right conduit switches on, there is not sufficient gain within cavity  14  to support lasing on the lower right conduit  16  and it switches off. An optical input signal can be introduced through either of ports  24 . If an optical signal is introduced into the lower right conduit  16 , the lower right conduit  16  will begin to lase with the lower left conduit  16 . This is because the electrons in the lower right conduit  16  are stimulated by the external optical signal sufficiently to allow lasing between the lower right and lower left conduits  16 . Because the gain in the cavity  14  region is only sufficient to support lasing between two longitudinal conduits  16 , lasing ceases between the upper right conduit  16  and lower left conduit  16 . When an optical signal was introduced into the upper right conduit  16 , the upper right conduit  16  ceases to lase due to off-axis stimulated emission within the conduit  16  and the lower right conduit  16  starts to lase with the lower left conduit  16 . 
     Alternatively, to cause lasing between the lower two conduits  16  in what is commonly referred to as a bar-mode, after conditions are initially established for a cross-mode as detailed above current is increased to the bias contact  18  under forward bias until the bottom two conduits just begin to lase. The upper right conduit ceases to lase because there is only sufficient optical gain in the cavity  14  to allow lasing between two longitudinal conduits  16  at any given time. In this state the lower right conduit will normally lase, or is “on”, and the upper right conduit normally will not lase, or is “off.” An optical input signal can be introduced through either of ports  24 . If an optical signal is introduced into the upper right conduit  16 , the upper right conduit  16  will begin to lase with the lower left conduit  16 . This is because the electrons in the upper right conduit  16  are stimulated sufficiently to allow lasing between the upper right and lower left conduits  16 . Because the gain in the cavity  14  region is only sufficient to support lasing between two longitudinal conduits  16 , lasing ceases between the lower right conduit  16  and lower left conduit  16 . When an optical signal was introduced into the lower right conduit  16 , the lower right conduit  16  ceases to lase due to off-axis stimulated emission and the lower left conduit  16  lases with the upper right conduit  16 . 
       FIG. 2  shows an alternative embodiment of the alternative photonic device  30  of the present invention. The alternative photonic device  30  preferably includes three outputs  32 . The outputs  32  of the alternative photonic device  30  are essentially identical to the outputs  12  of the photonic device  10  of  FIG. 1 . Because the outputs  12  of the photonic device  10  of  FIG. 1  were described in detail above, the outputs  32  of the alternative embodiment of alternative photonic device  30  will not be described in greater detail. 
     A cavity  34  is connected to the outputs  32  of the alternative photonic device  30 . Each output  32  is connected to a conduit  36  of the cavity  34 . The cavity  34  is an essentially Y-shaped chamber in the center of the alternative photonic device  30 . In the preferred embodiment, the top and bottom edges of the cavity  34  are parabolic, however the edges may be any other suitable configuration allowing two outputs on one side and one output on the opposing side according to user preferences. 
     The alternative photonic device  30  further includes three conduits  36  connected to cavity  34 . Conduits  36  are essentially identical to the conduits  16  of the photonic device of  10  shown in  FIG. 1 , however in the alternative embodiment shown in  FIG. 2 , as was discussed above, the cavity  34  includes only one conduit  36  on one side and two conduits  16  on the opposing side. Although in the embodiment shown the single conduit  36  is shown on the left side of the alternative photonic device  30 , it may be on either the left or right side of the alternative photonic device  30  and the remaining two conduits  36  may be located on the opposite side according to user preferences. 
     Substrate  35  is connected to the backside of cavity  34 . As is obvious to those of skill in the art, substrate  35  is a conventional semiconductor substrate. In the preferred embodiment, cavity  34  is epitaxially grown on substrate  35 , however cavity  34  may be connected to substrate  35  in any conventional manner many of which are well known and commonly used in the art. In the preferred embodiment substrate  35  is composed of the same material as cavity  34 . In the exemplified embodiment, substrate  35  is composed of GaAs, however other suitable material may also be used such as InP. 
     Alternative photonic device  30  includes bias contact  38  connected to cavity  34 . Bias contact is  38  connected to cavity  34  such that it is in contact with the entire cavity  34 , with the exception of a small area left uncovered on one of the conduits  36  located on the edge of the cavity having two conduits  36  due to a notch in bias contact  38 . The uncovered area is the minimum width required to prevent spontaneous lasing in the conduit  36  when biased to allow lasing in the opposite conduit, and accordingly will vary based on the specific dimensions of the alternative photonic device  30 . The connection between bias contact  38  and conduits  36  will be explained in greater detail below. Bias contact  38  is a layer of metal disposed on the photonic device. The metal is composed of an Ohmic material compatible with the material of the laser, and therefore will vary depending on the laser material as would be obvious to those of skill in the art. Typical Ohmic materials used for bias contact  38  include titanium platinum gold, chromium gold, and gold tin gold. 
     The alternative photonic device  30  includes mirrors  42  that are essentially identical to mirrors  22  of the photonic device of  FIG. 1  disposed between conduits  36  and outputs  32 . Mirrors  42  are created in the same manner as mirrors  22 , except that all three mirrors  42  of the alternative photonic device  30  of  FIG. 2  are created using the same bias contact  38 . For a more detailed discussion of mirrors  42 , please reference the discussion of mirrors  22  of photonic device  10  of  FIG. 1  above. 
     A port  44  is connected to a conduit  36  on the side of the alternative photonic device  30  including two conduits  36 . As was explained in greater detail above, a port is an optical device capable of transmitting optical signals to the cavity  34 . In a preferred embodiment the port is connected to the conduit  36  at a portion of the conduit  36  that is in contact with the bias contact  38 . However, the port may also be disposed on a portion of the conduit  36  that is not in contact with the bias contact  38  (this portion being located along the notch in the bias contact  38 ) in an alternative embodiment. The implications of this alternative embodiment will be explained in greater detail below. The port  44  is essentially identical to port  24  of the photonic device of  FIG. 1 , and therefore will not be described in greater detail. 
     Alternative photonic device  30  of  FIG. 2  includes an input  46  connected to port  44 . Input  46  transmits an optical signal to port  44 . Input  46  can be any input capable of transmitting an optical signal to port  44 , but is preferably a waveguide. Input  46  is essentially identical to input  26  of photonic device  10  of  FIG. 1 , and therefore will not be described in greater detail. 
     To operate the alternative photonic device  30  of the alternative embodiment of  FIG. 2 , bias is applied to the bias contact  38  such that a current is created in the bias contact  38 . Bias is increased in the bias contact  38  such that the conduit  36  that does not include the notched region of bias contact  38  lases with the conduit on the opposite side of the alternative photonic device  30 , the alternative photonic device  30  lasing from left to right. Lasing occurs in the same manner in the alternative photonic device  30  as in the photonic device  10  of  FIG. 1 , and will not be explained in greater detail here. The notch in the bias contact  38  prevents sufficient current density from being injected to the conduit  36  in contact with the notched portion of the bias contact  38  to allow that conduit  36  to lase. The specific mechanism by which the optical signal lases between the two conduits is well known to those of skill in the art, and will not be explained in greater detail here. 
     An optical signal is transmitted through input  46  to port  44 . As was explained in greater detail above, the optical signal is a light signal containing information to be transmitted through an optical device. As was further explained in greater detail above, the port is preferably located on the conduit that is entirely in contact with the bias contact  38 . By transmitting the optical signal through the port  44 , the optical signal is introduced into the conduit  36 . 
     The optical signal introduced through port  44  causes lasing to switch from its original configuration to lase between the conduit  36  contacting the notched portion of the bias contact  38  and the opposing conduit  36 . The addition of the optical signal provides sufficient additional off-axis optical power to quench the laser gain, preventing lasing of the conduit  36  attached to the port  44 , allowing lasing at the conduit  36  contacting the notched portion of the bias contact  38 , however does not provide sufficient gain to the alternative photonic device  30  to allow lasing in both conduits  36 . This occurs because, when an optical signal was introduced into the conduit  36 , the conduit  36  ceases to lase due to off-axis stimulated emission. Removal of the optical signal returns the alternative photonic device  30  to its initial lasing state. By this mechanism, a logic operation is performed by the alternative photonic logic device. In the alternative embodiment, port  44  is connected to conduit  36  at a portion not contacting bias contact  38 . Introduction of an optical signal into port  44  causes lasing to occur between the conduit  36  attached to the port  44  and the opposing conduit  44 . This occurs because the electrons in the conduit  36  are stimulated sufficiently to allow lasing between the conduit  36  attached to the port and the opposing conduit  36 . Because the gain in the cavity  34  region is only sufficient to support lasing between two longitudinal conduits  36 , lasing ceases between the conduit  36  that does not include the notched region of bias contact  38  and left conduit  36 .