JP4913016B2 - Optical transmission line using quantum dots - Google Patents

Description

  The present invention relates to an optical transmission line using quantum dots applied to fields such as a nanoscale optical communication network and optical measurement.

  With the recent development of semiconductor microfabrication technology, a semiconductor element having a fine structure up to a size at which a quantum mechanical effect appears noticeably has been realized (for example, see Non-Patent Document 1). As semiconductor elements utilizing this quantum mechanical effect, for example, HBT (Hetero-junction Bipolar Transistor) and quantum well lasers have been put into practical use. In addition, nanoscale quantum dots that take advantage of the particle properties of electrons by controlling single electrons using quantum mechanical effects have attracted attention.

  Quantum dots are formed by using the above-described semiconductor microfabrication technique to form a box having a potential that is so fine that it gives three-dimensional quantum confinement to the photoexcited carrier. Utilizing this confined system of photoexcited carriers, the energy levels of carriers in the quantum dots become discrete, and the state density sharpens in a delta function. Single-electron memories that use light absorption between the sharpened states of this quantum dot and single-electron transistors that turn on / off single electrons that enter and exit the quantum dot have already been studied. Nanoscale manipulation is being realized.

  By the way, in order to meet future demands for large-capacity information processing, realization of nanoscale arithmetic circuits, delay circuits, etc. that can perform arithmetic processing, information processing, delay processing, etc. without being governed by the diffraction limit of light Is desired. For this purpose, it is necessary to overcome the limitations of electrical wiring, and the realization of nanoscale optical interconnection technology is expected.

  However, in the conventional optical wiring technology, the spatial density is governed by the light diffraction limit, so it is difficult to reduce the occupied volume and wiring density to below the wavelength of light, and high density is expected. In the future, there was a problem that the system requirements could not be met.

  In addition, as the wiring density is increased and complicated, it becomes necessary to cross a plurality of wiring lines. In other words, it is necessary to create an optical interconnection technology that can realize the intersection of wirings on a nano scale. In the case of electrical wiring, in order to avoid short circuiting of wiring, for example, multilayer wiring was used, but in the case of optical interconnection, it is necessary to satisfy the conditions that do not cause interference between signals at the intersection. is there. For this purpose, it is necessary to increase the crossing angle of the waveguides to a certain extent, but there arises a problem that it is extremely difficult to keep the occupied area small.

Furthermore, when a conventional optical wiring has a plurality of input terminals and a plurality of output terminals, an optical switch for switching the light propagation path is required to reconfigure the input / output relationship. An optical switch is controlled by the diffraction limit of light and is configured as a device having a large occupied volume. For this reason, in the configuration in which the optical input / output switching function is performed by this optical switch, there is a problem that it is difficult to finish the entire device compactly.
M. Ohtsu, K. Kobayashi, T. Kawazoe, S. Sangu, and T. Yatsui, IEEE J. Sel. Top. Quantum. Electron., Vol. 8, pp. 839-862 (2002).

For this reason, the present invention has been devised in view of the above-mentioned problems, and its object is governed by the diffraction limit of light in realizing a nanoscale optical interconnection technology. An object of the present invention is to provide an optical transmission line using quantum dots that can function as an optical switch for switching a light propagation path that can be miniaturized without any problem.

In order to solve the above-described problems, an optical transmission line using quantum dots to which the present invention is applied forms a plurality of quantum dots having substantially the same resonance level and having the same resonance level in a row in the transmission direction. The quantum dot array is arranged close to the first quantum dot positioned at the end of the transmission direction, is configured to have a larger volume than the first quantum dot, and a photoexcited carrier is injected from the quantum dot. Two or more output end quantum dots having a resonance level and dissipating the photoexcited carrier from the resonance level to a lower level, based on the dissipation of the photoexcited carrier in the quantum dot at the output end, the photoexcited carrier from a first quantum dot to the quantum dots of the output terminal is transmitted through the resonant level, the occupancy of the photoexcited carriers in the lower level of the quantum dots of the two or more output terminals Flip it, characterized in that it is possible to select the quantum dots of the output moving the excitation carrier.

According to the present invention having the above-described configuration, it becomes possible to realize a nanometer-sized optical switch that is not governed by the diffraction limit of light, and the entire device is made compact by reducing the occupied volume. It becomes possible.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

First, the configuration of an optical transmission line using quantum dots to which the present invention is applied will be described. For example, as shown in the schematic diagram of FIG. 1, the optical transmission line 1 is composed of a plurality of quantum dots 12 arranged in a line on a dielectric substrate made of a material such as NaCl, KCl, or CaF _2. The first quantum dot array 13 and a first output terminal that is disposed close to the quantum dot 12b located at the end of the transmission direction in the first quantum dot array 13 and has a larger volume than the quantum dot 13b. The first transmission line 16 having the quantum dots 14 is provided.

  The optical transmission line 1 includes a second quantum dot array 23 composed of a plurality of quantum dots 22 arranged in a line on the substrate, and a quantum positioned at the end of the second quantum dot array 23 in the transmission direction. A second transmission path 26 having a second output end quantum dot 24 that is arranged close to the dot 22b and has a larger volume than the quantum dot 22b is provided.

  The first transmission path 16 transmits information from the quantum dot 12a located at the start end in the transmission direction to the quantum dot 14 via the quantum dot 12b located at the end. The second transmission path 26 performs information transmission from the quantum dot 22a located at the start end in the transmission direction to the quantum dot 24 via the quantum dot 22b located at the end. This information is transmitted via a photoexcited carrier.

  Incidentally, in the example of FIG. 1, the first transmission path 16 is shown without being crossed with respect to the second transmission path 26, specifically, the first transmission path. 16 and the second transmission path 26 are arranged substantially in parallel. The first transmission path 16 may be separated from the second transmission path 26, or may be arranged close to a position where they are in contact with each other.

  Each quantum dot 12, 14, 22, 24 controls a single electron (photoexcited carrier) based on discrete energy levels formed by confining the photoexcited carrier in three dimensions. In the quantum dots 12, 14, 22, and 24, the energy level of the carriers in the quantum dots becomes discrete due to the confinement system of the photoexcited carriers, and the state density can be sharpened in a delta function. The photoexcited carriers handled in the quantum dots 12, 14, 22, and 24 can be replaced with any photoexcited carriers such as excitons, electrons, and holes.

  The quantum dots 12, 14, 22, and 24 are made of a material system such as CuCl, GaN, or ZnO. When the material system that forms each quantum dot 12, 14, 22, and 24 is CuCl, these are configured as a cube. In addition, when the material system constituting each quantum dot 12, 14, 22, 24 is GaN or ZnO, these are configured as a sphere or a disk. Each of the quantum dots 12, 14, 22, and 24 can have a side length and a diameter of about 4 nm to 10 nm, and can be formed on the substrate with a smaller size than the diffraction limit of light. It becomes possible.

  Here, when the quantum dots 12, 14, 22, 24 are each configured as a cube, when the side length L of the quantum dots 12, 22 is L, the side length of the quantum dots 14, 24 is √2L.

  Each of these quantum dots 12, 14, 22, and 24 may be produced on a substrate based on the Bridgman method or molecular epitaxy (MBE) growth method, or the quantum dot formation position using near-field light CVD. May be accurately controlled.

  Here, the quantum dots 12 constituting the first quantum dot array 13 are close to the quantum dots 14, and the quantum dots 22 constituting the second quantum dot array 23 are close to the quantum dots 24. Causes a field-near field interaction. The quantum dots 14 and 24 emit output light based on the photoexcited carriers that have transitioned from the quantum dots 12 and 22.

Quantum level E in each quantum dot _{12,14,22,24 (n x, n y,} n z) , when the mass of the particle and m, also that the side length of the quantum dot is L, the following formula Defined by (1).

E (n _x , n _y , n _z ) = h ² / 8π ² m (π / L) ² (n _x ² + _ny ² + n _z ² ) (1)

In the present invention, depending on the shape and material of the quantum dot, in addition to the quantum level E ( _nx , _ny , _nz ) defined by the formula (1), other general quantum In some cases, level formulas may apply.

Based on this equation (1), E (n _x , n _y , n _z ) of each quantum dot 12, 14, 22, 24 is calculated. Here, when the side length ratio between the quantum dot 12 and the quantum dot 14 is 1: √2, the quantum level in the quantum dot 12 is (1,1,1) as shown in FIG. E (111) is equal to E (211) when the quantum level in the quantum dot 14 is (2,1,1). That is, the quantum level (1, 1, 1) of the quantum dot 12 and the quantum level (2, 1, 1) in the quantum dot 14 are in a relationship in which the excitation energy levels of the excitons resonate with each other.

  Here, in the case where the photoexcited carrier is transmitted from the quantum dot 12a positioned at the start end in the transmission direction to the quantum dot 14 via the quantum dot 12b positioned at the end in the first quantum dot row 13, the quantum dot 12a Thus, by supplying the optical signal A having the frequency ω1 corresponding to the quantum level (1, 1, 1), the photoexcited carrier is excited to the quantum level. If this excited photoexcited carrier moves to the quantum dot 12b, resonance occurs between (1, 1, 1) in the quantum dot 12b and the quantum level (2, 1, 1) in the quantum dot 14. Occurs. As a result, the photoexcited carrier existing at the quantum level (1, 1, 1) in the quantum dot 12b moves to the quantum level (2, 1, 1) of the quantum dot 14, and further the quantum level of the quantum dot 14 Transition to (1,1,1). As a result, the photoexcited carrier apparently moves from the quantum dot 12b to the quantum dot 14.

  When the quantum level (1, 1, 1) in the quantum dot 12b becomes empty, the photoexcited carrier tends to move toward the quantum dot 12b, and as a result, the photoexcited carrier from the quantum dot 12a to the quantum dot 12b. Can be moved. That is, a quantum dot 14 having a volume larger than that of the quantum dot is disposed close to the quantum dot 12b located at the end of the first quantum dot array 13, and the resonance level in the quantum dot 14 is lower than the lower level. Dissipate photoexcited carriers. As a result, based on the dissipation of the photoexcited carriers in the quantum dots 14, it is possible to transmit the photoexcited carriers between the quantum dots via the resonance levels from the transmission direction start end to the end end of the first quantum dot array 13. It becomes.

  Similarly, the second transmission path 26 can also transmit the photoexcited carrier based on the same mechanism. In the case where the photoexcited carrier is transmitted from the quantum dot 22a positioned at the start end in the transmission direction to the quantum dot 24 via the quantum dot 22b positioned at the end of the second transmission path 26, the quantum dot 22a is subjected to its quantum. By supplying the optical signal B having the frequency ω2 corresponding to the level (1, 1, 1), the photoexcited carrier is excited to the quantum level. If this excited photoexcited carrier moves to the quantum dot 22b, the quantum level (1,1,1) in the quantum dot 22b and the quantum level (2,1,1) in the quantum dot 24 Resonance occurs between them. As a result, the photoexcited carrier existing at the quantum level (1, 1, 1) in the quantum dot 22b moves to the quantum level (2, 1, 1) of the quantum dot 24, and further the quantum level of the quantum dot 24. Transition to (1,1,1). As a result, the photoexcited carrier moves apparently from the quantum dot 22b to the quantum dot 24.

  When the quantum level (1, 1, 1) in the quantum dot 22b becomes empty, the photoexcited carrier tends to move toward the quantum dot 22b. As a result, the photoexcited carrier from the quantum dot 22a to the quantum dot 22b. Can be moved. That is, a quantum dot 24 having a volume larger than that of the quantum dot is disposed close to the quantum dot 22b located at the end of the second quantum dot array 23, and the lower level from the resonance level in the quantum dot 24 is obtained. Dissipate photoexcited carriers. As a result, based on the dissipation of the photoexcited carriers in the quantum dots 24, it is possible to transmit the photoexcited carriers between the quantum dots via the resonance levels from the start end to the end of the first quantum dot array 23 in the transmission direction. It becomes.

  Incidentally, the frequency ω2 of the optical signal B supplied to the quantum dots 22a is different from the frequency ω1 of the optical signal A. For this reason, the quantum level (1, 1, 1) in the quantum dot 22 constituting the second quantum dot row 23 is equal to the quantum level (1, 1, 1) in the quantum dot 12 constituting the first quantum dot row 13. It will have energy levels different from 1). Further, the quantum level (2,1,1) of the quantum dot 24 that resonates with the quantum level (1,1,1) in the quantum dot 22 and the quantum level (1,1,1) in the quantum dot 12 resonate. Thus, the quantum level (2, 1, 1) of the quantum dot 14 has different energy levels.

  Therefore, the optical excitation carrier that transmits the first optical transmission line 16 moves to the second optical transmission line 26 in the middle, or the optical excitation carrier that transmits the second optical transmission line 26 passes the first optical transmission line in the middle. It is possible to prevent the shift to 16. That is, it is possible to prevent information to be transmitted between the first optical transmission line 16 and the second optical transmission line from interfering.

  As described above, the optical transmission line 1 to which the present invention is applied can reduce the occupied volume and the wiring density to about the wavelength of light or less, and can prevent interference between the optical transmission lines. Therefore, it becomes possible to satisfy the requirements of the future system where high density is expected.

  In the present invention, the first optical transmission line 16 and the second optical transmission line 26 may be arranged so as to intersect each other as in the optical transmission line 2 shown in FIG. The energy levels of the quantum dots 12, 14, 22, and 24 constituting the first optical transmission line 16 and the second optical transmission line 26, respectively, and the movement mode of the photoexcited carriers are described with reference to FIG. By quoting, the description below is omitted.

  Such a cross-arranged type optical transmission line 2 can realize crossing of wirings on a nanoscale. In particular, in the present invention, it is possible to realize optical interconnection only by arranging the quantum dots 12 and 14, and it is not necessary to provide, for example, a multilayer wiring in order to avoid a short circuit of the wiring as in the case of an electrical wiring, Interference between signals can be suppressed at the intersection. In addition, the occupied volume and the wiring density can be reduced to about the wavelength of light.

  In addition, by combining the optical transmission lines 1 and 2 as described above, it is possible to realize a nanometer-sized optical interconnection circuit having a size not larger than the wavelength limit of light. In addition, even if the optical transmission lines 1 and 2 are arranged so that the quantum dots 12, 114, 22, and 24 constituting each of them are in contact with each other, the desired effect is obtained, and a more compact size is achieved. It is also possible to realize the interconnection circuit without interference.

  The present invention is not limited to the embodiment described above. For example, as in the optical transmission line 3 shown in FIG. 4, selectivity may be given to the moving direction of the photoexcited carrier.

  The optical transmission line 3 includes a first quantum dot row 13 composed of a plurality of quantum dots 12 arranged in a line on the substrate, and a quantum dot 12b positioned at the end of the first quantum dot row 13 in the transmission direction. And two output end quantum dots 34a and 34b each having a larger volume than the quantum dot 12b. In this optical transmission line 3, the same components and members as those of the optical transmission line 1 described above are denoted by the same reference numerals, and the following description is omitted.

  When the side length ratio between the quantum dot 12 and the quantum dots 34a and 34b at the output end is 1: √2, the quantum level in the quantum dot 12 is (1, 1, 1) as shown in FIG. Is equal to the energy level E2 when the quantum level at the output end quantum dots 34a and 34b is (2,1,1). That is, the quantum level (1, 1, 1) of the quantum dot 12 is in a relationship in which the excitation energy levels of the excitons resonate with the quantum level (2, 1, 1) in the quantum dots 34a and 34b, respectively. .

  As described above, the quantum dots 34a and 34b each having a larger volume than the quantum dot 12b are disposed close to the quantum dot 12b positioned at the end of the first quantum dot array 13, and resonance in the quantum dots 34a and 34b is achieved. The photoexcited carrier is dissipated from the level to the lower level E3. Based on the dissipation of the photoexcited carriers in the quantum dots 34a and 34b, the photoexcited carriers can be moved from the quantum dot 12b to the quantum dots 34a and 34b via the resonance level.

  At this time, the occupation state of the photoexcited carrier at the lower level E3 is controlled for either of the two quantum dots 34a and 34b. As shown in FIG. 5, the lower level E3 of the quantum dot 34b is previously occupied by the photoexcited carrier. As a result, in this quantum dot 34b, the photoexcited carrier cannot be dissipated from the resonance level E2 to the lower level E3, and the photoexcited carrier cannot be transmitted from the quantum dot 12 to the quantum dot 34b. The photoexcited carrier from the quantum dot 12 moves only to the quantum dot 34a. In other words, the quantum dot 34 at the output end where the photoexcited carrier should be moved can be given selectivity to the side where the photoexcited carrier is not occupied in the lower level E3.

  For this reason, it becomes possible to realize a nanometer-sized optical switch that is not subject to the diffraction limit of light by the optical transmission line 3, and it is possible to finish the entire device compactly by reducing the occupied volume. It becomes possible.

It is a block diagram of the optical transmission line using the quantum dot to which this invention is applied. It is an energy band figure of the optical transmission line using the quantum dot to which the present invention is applied. It is a figure which shows the example which has arrange | positioned the 1st optical transmission path and the 2nd optical transmission path mutually crossing. It is a figure for demonstrating the case where selectivity is given to the moving direction of a photoexcitation carrier. It is another figure for demonstrating the case where the selectivity is given to the moving direction of a photoexcitation carrier.

Explanation of symbols

1-3 Optical transmission line 12 14, 22, 24 Quantum dot 13, 23 Quantum dot row 16, 26 Optical transmission line

Claims (1)

Quantum dots having substantially the same size and having the same resonance level are arranged close to the first quantum dot located at the end of the transmission direction in a quantum dot array in which a plurality of quantum dots are arranged in a row in the transmission direction. 2 or more having a resonance level in which a photoexcited carrier is injected from the quantum dot and having a larger volume than the first quantum dot, and dissipating the photoexcited carrier from the resonance level to a lower level With quantum dots at the output end of
Based on the dissipation of the photoexcited carrier in the quantum dot at the output end, the photoexcited carrier is transmitted from the first quantum dot to the quantum dot at the output end via the resonance level,
A quantum dot that is capable of selecting the quantum dot at the output end that moves the photoexcited carrier according to the occupation state of the photoexcited carrier at the lower level of the quantum dot at the two or more output ends. The optical transmission line used.

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