JP2006267888A - Semiconductor optical control element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To not only allow a delay time to be controlled but also make a semiconductor optical control element compact while suppressing the increase in power consumption of the semiconductor optical control element. <P>SOLUTION: The semiconductor optical control element is provided with quantum dots 12 and a controlling light source 13, and the controlling light source 13 is so configured that the quantum dots 12 is irradiated with control light L12 having a wavelength corresponding to energy of exciton molecules wherein excitons are bound, and a wavelength of signal light L11 is set so as to correspond to energy of excitons enclosed in the quantum dots 12, and a differential of an absorption spectrum of the signal light L11 is changed by an interference effect between excitons and exciton molecules, whereby an optical output pulse L11b resulting from delaying an optical input pulse L11a is emitted. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor optical control element, and is particularly suitable for application to a method for realizing an optical delay operation by an interference effect between excitons and exciton molecules.

  In response to the speeding up of information communication accompanying the recent development of the Internet and the like, optical communication using optical fibers has become widespread (Non-Patent Documents 1 and 2). In this optical communication, an optical pulse is used as information transmission means, and a technique is employed in which the temporal density and size of the optical pulse are changed according to the information content. This light pulse operation can also be realized by a direct modulation operation of the light source. Alternatively, it can be realized by emitting a light pulse from the light source at a constant period and then delaying the light pulse using another element. This method of delaying an optical pulse using another element has an advantage that the light source can be stably operated, and is widely used.

  This optical pulse delay processing is extremely important not only in communication in which transmission and reception are performed one-to-one, but also in communication in which transmission and reception are performed in a many-to-many manner. That is, in many-to-many communication, it is necessary to accurately send information to a recipient designated by the sender. Usually, signals from multiple senders are collected in one place and then distributed to multiple receivers. In this case, signals from different senders may arrive at the same place where signals from the senders are collected. With current technology, it is difficult to simultaneously deliver light pulses that arrive simultaneously from multiple senders to different recipients. For this reason, optical pulses that have simultaneously arrived from a large number of transmitters are sequentially distributed while any optical pulse that has simultaneously arrived from a large number of transmitters is delayed by an optical delay element.

FIG. 19 is a diagram illustrating an example of a conventional optical delay element.
In FIG. 19, the optical delay element is provided with an optical switch 61 and an optical fiber 62 that change the path of the signal light L61. Here, the trigger voltage TG4 is input to the optical switch 61. The optical switch 61 can switch the path of the signal light L61 to the optical fiber 62 side when the trigger voltage TG4 is turned on, and pass the signal light L61 as it is when the trigger voltage TG4 is turned off.

FIG. 20 is a timing chart showing an optical delay operation in the optical delay element of FIG.
In FIG. 20, it is assumed that an optical input pulse L61a is input to the optical switch 61 as the signal light L61. Here, when the trigger voltage TG4 is OFF, the optical input pulse L61a passes through the optical switch 61 as it is, and the optical output pulse L61b is not delayed. On the other hand, when the trigger voltage TG4 is turned on, the optical input pulse L61a input to the optical switch 61 is introduced into the optical fiber 62. Therefore, the optical output pulse L61b emitted from the optical switch 61 has a delay corresponding to the length of the optical fiber 62, and is delayed by the delay times D11 and D12 for each optical input pulse L61a.
In this optical delay element, attenuation due to light absorption occurs when the signal light L61 passes through the optical switch 61 and the optical fiber 62, but the amount of attenuation can be ignored in normal optical communication.

FIG. 21 is a diagram showing another example of a conventional optical delay element.
In FIG. 21, the optical delay element is provided with a photodetector 71 that converts signal light L71 into an electric signal, a buffer memory 73 that stores the electric signal, and a laser light source 72 that converts the electric signal into signal light L71 ′. The optical delay element is provided with a trigger circuit 74 that supplies an electrical signal to the laser light source 72. Here, the trigger voltage TG <b> 5 is input to the trigger circuit 74. The trigger circuit 74 can supply the electrical signal stored in the buffer memory 73 to the laser light source 72 only when the trigger voltage TG5 is turned on.

FIG. 22 is a timing chart showing an optical delay operation in the optical delay element of FIG.
In FIG. 22, when an optical input pulse L 71 a is input to the photodetector 71 as the signal light L 71, the optical input pulse L 71 a is converted into an electric signal and stored in the buffer memory 73. When the trigger voltage TG5 is turned on, the electrical signal stored in the buffer memory 73 is supplied to the laser light source 72, and the light output pulse L71b corresponding to the light input pulse L71a is emitted from the laser light source 72. Here, since the optical output pulse L71b is emitted according to the input timing to the trigger voltage TG5, the delay times D21 and D22 of the optical output pulse L71b can be individually changed by controlling the input timing of the trigger voltage TG5. The delay times D21 and D22 of the light output pulse L71b can be made different for each light input pulse L71a.

In the optical delay element shown in FIG. 21, the photodetector 71, the buffer memory 73, and the laser light source 72 can all be configured to have a size of 1 mm square, and it is sufficient that the entire optical delay element has a size of several mm square. Compact size is possible.
Yamashita, “A book that understands the mechanism of optical fiber communication”, Technical Review, pp. 162-163, pp226-227 Suematsu, Iga, “Introduction to Optical Fiber Communication”, Ohm, pp. 148-149

However, in the optical delay element of FIG. 19, the delay times D11 and D12 of the optical input pulse L61a are determined by the length of the optical fiber 62, and it is difficult to control the length of the optical fiber 62. For this reason, the delay times D11 and D12 of the optical input pulse L61a are the same, and there is a problem that the delay time of the optical input pulse L61a cannot be controlled for each optical input pulse L61a.
The optical switch 61 of FIG. 19 can be configured with a size of 1 mm square, but the length of the optical fiber 62 is required to be about several centimeters to several tens of centimeters in order to obtain a necessary delay amount. Therefore, there is a problem that the entire optical delay element is the largest among the elements currently used in optical communication.

In the optical delay element shown in FIG. 21, the light-to-electricity conversion efficiency of the photodetector 71 is at most several tens of percent. Therefore, it is difficult to drive the laser light source 72 with only the converted electric signal. is there. For this reason, an external power source is required to drive the laser light source 72, and there is a problem that power consumption increases. In addition, the photodetector 71 has a problem that, when optical pulses are converted into electrical signals, phase information of the optical pulses is completely lost, and communication cannot be performed by writing information in the phase of the light. It was.
SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor light control element that can control the delay time while suppressing an increase in power consumption and can be made compact.

In order to solve the above-described problem, according to the semiconductor optical control element according to claim 1, the quantum dot for confining the exciton and the control light having a wavelength corresponding to the energy of the exciton molecule to which the exciton is coupled are provided. And a control light source for irradiating the quantum dots.
Thereby, the level corresponding to the energy of the exciton molecule can be oscillated by irradiating the quantum dot with the control light. For this reason, it becomes possible to change the derivative of the absorption spectrum and to change the refractive index after almost eliminating the light absorption between the levels corresponding to the energy of the exciton constituting the exciton molecule. . As a result, signal light having a wavelength corresponding to the energy of the exciton is incident on the quantum dot, so that it is possible to delay the signal light while suppressing absorption loss of the signal light, and convert the signal light into an electrical signal. Therefore, it is possible to reduce the power consumption of the optical delay element, and it is not necessary to use an optical fiber to delay the signal light, and the optical delay element can be made compact. Become.
Further, since it is not necessary to convert the signal light into an electric signal in order to delay the signal light, the phase information of the signal light can be preserved and the amount of information transmitted can be increased.

According to the semiconductor optical control element of claim 2, signal light having a wavelength corresponding to the energy of the exciton is incident on the quantum dot, and a level corresponding to the energy of the exciton and the exciton molecule A three-level system having one level in common is formed by levels corresponding to the energy of.
As a result, the level corresponding to the energy of the exciton molecule is oscillated, so that the optical absorption between the levels corresponding to the energy of the exciton can be almost eliminated and the derivative of the absorption spectrum can be changed. It becomes. For this reason, it is possible to delay the signal light while suppressing the absorption loss of the signal light by irradiating the quantum dot with the control light having a wavelength corresponding to the energy of the molecular molecule, thereby reducing the power consumption of the optical delay element. And it becomes possible to realize compactness.

The semiconductor light control element according to claim 3 further comprises a trigger circuit that controls the power of the control light emitted from the control light source in accordance with a delay time of the signal light. .
As a result, by changing the power of the control light, it becomes possible to control the optical response characteristics due to the bonding state between the levels corresponding to the energy of the exciton molecule, and the level corresponding to the energy of the exciton. It is possible to control the differentiation of the absorption spectrum while substantially eliminating the light absorption between the two. Therefore, it is possible to control the delay time of the signal light without converting the signal light into an electric signal, to reduce the power consumption of the optical delay element, and to delay the signal light There is no need to use an optical fiber, and the optical delay element can be made compact.

According to another aspect of the semiconductor optical control element of the present invention, the width and length of the quantum dots are in the range of 2 to 10 times the Bohr radius, and the height of the quantum dots is 0.1 to 1 times the Bohr radius. It is characterized by being in the range of
As a result, the excitons can be stably present in the quantum dots, and the exciton molecule energy can be made larger than the temperature energy in the environment where the semiconductor light control element is used. It is possible to make the dots stably exist. Therefore, both excitons and exciton molecules can be stably present in the quantum dots, and the semiconductor light control element can be stably operated.

According to another aspect of the semiconductor optical control device of the present invention, the quantum dot has a structure in which the first semiconductor layer is completely surrounded by the second semiconductor layer having a larger band gap than the first semiconductor. It is characterized by.
As a result, quantum dots can be formed by using a semiconductor manufacturing process, and quantum dots can be formed with high accuracy, and semiconductor light control elements can be easily mass-produced.

Further, according to the semiconductor light control element of claim 6, the control light source is a Fabry-Perot semiconductor laser, a surface emitting semiconductor laser, a light emitting diode or a superluminescent diode, and the control light source and the light source The active region provided with the quantum dots is formed on the same semiconductor substrate.
As a result, the light source for control and the active region provided with the quantum dots can be integrated on the same semiconductor substrate, so that the semiconductor light control element can be made compact and the semiconductor manufacturing process can be achieved. The alignment of the control light source and the quantum dots can be performed, and the assembly work of the semiconductor light control element can be simplified.

According to a seventh aspect of the present invention, the active layer of the control light source has the same structure as the quantum dots.
As a result, the power consumption of the control light source can be reduced, and even when the control light source is incorporated in the semiconductor light control element, the power consumption of the entire semiconductor light control element can be reduced.

  As described above, according to the present invention, an optical delay operation can be realized by the interference effect between excitons and exciton molecules, and the delay time can be controlled. As a result, the phase information of the signal light can be preserved and the amount of information transmitted can be increased.

Hereinafter, a semiconductor optical control device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing a schematic configuration of the semiconductor light control element according to the first embodiment of the present invention.
In FIG. 1, the semiconductor light control element is provided with quantum dots 12 and a control light source 13. Here, the quantum dots 12 can constitute an active region that causes light absorption and refraction. The quantum dots 12 can have a structure in which the periphery is completely surrounded by an energy barrier layer 11 for confining excitons generated by the signal light L11 in the quantum dots 12. Further, the control light source 13 can irradiate the quantum dots 12 with a control light L12 having a wavelength corresponding to the energy of the exciton molecules to which the excitons are bonded. Further, the wavelength of the signal light L11 can be set so as to correspond to the energy of excitons confined in the quantum dots 12.

  A semiconductor can be used as the material of the energy barrier layer 11 and the quantum dots 12, and the semiconductor layer constituting the energy barrier layer 11 is selected so as to have a larger band gap than the semiconductor layer constituting the quantum dots 12. be able to. Further, the quantum dot 12 can constitute a three-level system in which one level is shared by a level corresponding to the energy of the exciton and a level corresponding to the energy of the exciton molecule. In addition, it is preferable to set the width r1 and length r2 of the quantum dots 12 in a range of 2 to 10 times the Bohr radius, and the height r3 of the quantum dots 12 in a range of 0.1 to 1 times the Bohr radius.

  When the optical input pulse L11a enters the quantum dot 12 as the signal light L11, excitons corresponding to the energy of the signal light L11 are generated in the quantum dot 12. When the excitons are generated in the quantum dots 12 and the control light L12 is incident on the quantum dots 12, exciton molecules corresponding to the energy of the control light L12 are generated in the quantum dots 12, and the excitons and excitons are generated. The level corresponding to the energy of the exciton and the exciton molecule shifts to the drezed state due to the interference effect with the molecule. For this reason, it is possible to change the derivative of the absorption spectrum of the signal light L11 while substantially eliminating the light absorption between levels corresponding to the energy of the exciton, while suppressing the absorption loss of the signal light L11. It becomes possible to emit the light output pulse L11b obtained by delaying the light input pulse L11a.

FIG. 2 is a diagram illustrating a photoexcited state in a two-level system when light having a frequency ν _p is incident.
In FIG. 2, it is assumed that the signal light L11 having energy hν _p is incident on a two-level system composed of levels 1 and 2. Here, when the energy hν _p of the signal light L11 is made to correspond to the energy difference between the levels 1 and 2, excitons corresponding to the energy hν _p of the signal light L11 can be generated in the two-level system. Here, h is the Planck constant, and ν _p is the frequency of the signal light L11.

FIG. 3 is a diagram showing optical response characteristics in the two-level system of FIG.
3, it can be seen that in the two-level system of FIG. 2, the absorption coefficient has a peak at the energy hv _p corresponding to the energy difference D12 between the levels 1 and 2. The absorption coefficient represents the amount of light absorbed by the two levels. The refractive index is an amount proportional to the light delay time, and is approximately proportional to the derivative of the absorption coefficient.
Here, if the refractive index is n (hν), the speed of light v _g in the two-level system can be expressed by the following equation (1) as a function of the light energy (hν).
v _g = c / (n (hν) + hν (∂n (hν) / ∂ (hν))) (1)
Where c is the speed of light in vacuum. Therefore, if the refractive index n (hv) or refractive index differential ∂n (hν) / ∂ (hν ) is increased, the speed of light v _g is slow, the light can be delayed.

FIG. 4 is a diagram showing a photoexcited state in a three-level system when light of two types of wavelengths ν _p and ν _c is incident.
In FIG. 4, it is assumed that signal light L11 with energy hν _p and control light L12 with energy hν _c are incident on the three-level system in which level 3 is added to the two-level system in FIG. Here, when the energy hν _p of the signal light L11 is made to correspond to the energy difference between the levels 1 and 2, and the energy hν _c of the control light L12 is made to correspond to the energy difference between the levels 2 and 3, this three-level system. Can generate excitons corresponding to the energy hν _c of the control light L12 after generating excitons corresponding to the energy hν _p of the signal light L11. Here, h is the Planck constant, ν _p is the frequency of the signal light L11, and ν _c is the frequency of the control light L12. Further, the optical power of the control light L12 having the energy hν _c can be increased by about 10 times the optical power of the signal light L11 having the energy hν _p , for example.

Then, when an exciton molecule corresponding to the energy hν _c of the control light L12 is generated, the control light L12 having the energy hν _c is strongly coupled to the levels 2 and 3 between the levels 2 and 3, and the level 2, Rabi vibration occurs in No.3. Then, when Rabi vibration occurs in the levels 2 and 3, the levels 2 and 3 are changed to the levels 2D and 3D wearing light clothes, and the state shifts to the dressed state. When the levels 2 and 3 change to the levels 2D and 3D, the state corresponding to the energy between the levels 1 and 2 disappears, and the light between the levels 1 and 2 corresponding to the energy hν _p of the signal light L11. Absorption can be almost eliminated. Therefore, in the three-level system in FIG. 4, the absorption coefficient can have a minimum value at the frequency ν _p corresponding to the energy difference D12 between the levels 1 and 2.

FIG. 5 is a diagram showing optical response characteristics in the three-level system of FIG.
In FIG. 5, it can be seen that in the three-level system of FIG. 4, the absorption coefficient becomes almost zero in the vicinity of the energy hv _p corresponding to the energy difference D12 between the levels 1 and 2. In addition, it can be seen that the positive gradient of the refractive index is remarkably large in the vicinity of the energy hν _p . This can also be interpreted as an interference between the light absorption process between the levels 1 and 2 and the light absorption process that returns from the level 1 to the level 2 through the levels 2 and 3 again. .

Therefore, in the vicinity of the energy hν _p corresponding to the energy difference D12 between the levels 1 and 2, the refractive index differential ∂n (hν) / ∂ (hν) of the equation (1) becomes large, and the speed of light v _g is Become slow. Therefore, if a three-level system having one level in common can be formed, an optical delay operation can be realized. The optical response characteristic of the three-level system depends on the optical power of the control light L12 having the energy hv _c . Therefore, by controlling the optical power of the control light L12 with energy hν _c , the refractive index can be changed, and the delay time of the signal light L11 with energy hν _p can be controlled.

FIG. 6 is a diagram showing the relationship between the change in refractive index and the optical power at the frequency ν _c according to an embodiment of the present invention. FIG. 6 plots the derivative of the refractive index in the vicinity of the region where the energy hν _p of the signal light L11 is equal to the energy difference D12 between the levels 1 and 2 against the optical power of the control light L12 having the energy hν _c . Is.
In FIG. 6, it can be seen that when the optical power of the control light L12 having the energy hv _c is increased, the derivative of the refractive index is decreased. Therefore, increasing the optical power of the control light L12 energy hv _c, it is possible to increase the speed v _g of light, it is possible to shorten the delay time of the signal beam L11 energy hv _p. Therefore, it becomes possible to control the delay time by changing the refractive index of the light, and it is not necessary to convert the signal light L11 into an electric signal. Therefore, the loss in converting the signal light L11 into an electric signal is eliminated. The phase information of the signal light L11 can be preserved, and the amount of information transmitted can be increased.

FIG. 7 is a diagram schematically showing a sample structure used for demonstrating the action of the present invention.
In FIG. 7, an AlGaAs barrier layer 21 is formed on a GaAs (311) B substrate 20, and InGaAs quantum dots 22 are embedded in the AlGaAs barrier layer 21. The InGaAs quantum dots 22 were 3 nm in height and 30 nm in width. In addition, a wavelength tunable laser 24 for generating the signal light L21 incident on the quantum dots 22 is provided, and a control light source that emits light at a wavelength that allows the light absorption and refractive index of the quantum dots 22 to be changed. 23 is provided. Furthermore, a photodetector 25 that detects the signal light L21 that has passed through the quantum dots 22 is provided.

  When the signal light L21 generated by the wavelength tunable laser 24 is incident on the quantum dot 22, the exciton K1 in FIG. 8 is generated, and an exciton state corresponding to the two-level state in FIG. 2 is generated. . Then, when the control light L22 generated by the control light source 23 is incident on the quantum dot 22 and the wavelength of the control light L22 is made to correspond to the energy of the exciton molecule K2 in which the excitons K1 are bonded to each other, 3 in FIG. An exciton molecular state corresponding to the level state is generated.

FIG. 9 is a diagram showing a light absorption spectrum in an exciton state.
In FIG. 9, when signal light L21 generated by the wavelength tunable laser 24 is incident on the quantum dot 22, a plurality of sharp absorption peaks X1 to X4 appear. The absorption peaks X1 to X4 correspond to the high-order states from the lowest order to the fourth order of the exciton K1 in FIG. 8, and each exciton state forms the two-level state in FIG. When the light irradiation power is increased in the quantum dots 22, another exciton K1 is formed in the quantum dots 22, and an exciton molecular state in which the excitons K1 are coupled to each other is generated.

FIG. 10 is a diagram showing light absorption spectra in an exciton state and an exciton molecular state.
In FIG. 10, when the exciton molecule state is generated after the exciton state is generated, the absorption peaks XX1 to XX4 of the exciton molecule are generated corresponding to the absorption peaks X1 to X4 of the exciton K1. . Here, the absorption peaks XX1 to XX4 of the exciton molecules are shifted to the lower energy side by the exciton molecule binding energy Ek with respect to the absorption peaks X1 to X4 of the exciton K1. In addition, since the exciton molecule K2 is formed after the exciton K1 is formed, the energy state when the exciton molecule state is generated is, for example, the energy of the absorption peak X1 of the exciton K1 and the exciton molecule. A three-level system is formed for the energy of the absorption peak XX1.

FIG. 11 is a diagram showing the state of the three-level system generated in the exciton state and the exciton molecular state.
In FIG. 11, it is assumed that the signal light L21 of energy hν _X is incident on the quantum dot 22 with respect to the two-level system having the level X1 corresponding to the absorption peak X1 of the exciton K1. Here, when the energy hν _X of the signal light L21 is made to correspond to the energy difference between the levels 1 and X1, an exciton K1 corresponding to this energy difference is generated. Then, it is assumed that the control light L22 having the energy hν _XX is incident on the quantum dot 22 in a state where the exciton K1 is generated. Here, when the energy hv _XX of the control light L22 is made to correspond to the energy difference between the levels X1 and XX1, an exciton molecule K2 corresponding to this energy difference is generated. Therefore, an absorption peak XX1 of the exciton molecule K2 corresponding to this energy difference appears, and a three-level system is formed for the levels X1 and XX1.

Further, the exciton molecule-exciton energy is smaller by the exciton molecule binding energy Ek than the exciton-ground state energy. For this reason, by making the energy hν _XX of the control light L22 coincide with the exciton molecule-exciton energy, the optical response characteristic of FIG. 12 can be obtained, and the optical delay is obtained with the absorption coefficient having a minimum value. Operation can be realized.
Here, since the optical delay effect increases as the denominator of the equation (1) increases, the optical delay factor S can be defined by the following equation (2).
S = n (hν) + hν (∂n (hν) / ∂ (hν)) (2)

FIG. 13 is a diagram illustrating measurement results of the delay factor and the optical input power of the frequency ν _{XX according to} the embodiment of the present invention.
In FIG. 13, it can be seen that the delay factor S can be controlled by changing the optical input power of the control light L22 of energy hv _XX . Further, if properly choose the optical input power of the control light L22, the velocity v _g of light may be 10 parts per million or less.
Since the exciton molecule binding energy Ek determines the stability of the exciton molecule K2, in order to stably perform the delay operation of the semiconductor light control element, the temperature energy in the use environment of the semiconductor light control element is used. It is also preferable to increase the exciton molecule binding energy Ek.

FIG. 14 is a diagram showing the relationship between the lateral size of quantum dots and exciton molecule binding energy according to an embodiment of the present invention.
In FIG. 14, it is understood that the exciton molecule binding energy Ek changes with the width r1 and the length r2 of the quantum dot 12 of FIG. Here, the exciton molecule binding energy Ek is maximized when the width r1 and the length r2 of the quantum dot 12 is about 3 times the Bohr radius, and is larger than the temperature energy En in the range of 2 to 10 times the Bohr radius. I understand. Further, in order to allow not only the exciton molecule K2 but also the exciton K1 to exist stably, it is necessary to set the height r3 of the quantum dot 12 within a range of 0.1 to 1 times.

FIG. 15 is a cross-sectional view showing a schematic configuration of a semiconductor optical control device according to the second embodiment of the present invention.
In FIG. 15, an energy barrier layer 31 is formed on a semiconductor substrate 30, and quantum dots 32 are embedded in the energy barrier layer 31. The size of the quantum dots 32 can be set, for example, such that the height is 3 nm (0.3 times the Bohr radius) and the width is 30 nm (three times the Bohr radius). In addition, a semiconductor laser 33 that emits light at a wavelength that allows the light absorption and refractive index of the quantum dots 32 to be changed is provided. Furthermore, a trigger circuit 34 that applies a trigger voltage TG1 for causing the semiconductor laser 33 to emit light is connected to the semiconductor laser 33. As the semiconductor substrate 30, for example, a GaAs (100) substrate or an InP substrate may be used in addition to the GaAs (311) B substrate. Further, as a semiconductor constituting the quantum dots 32 and the energy barrier layer 31, any material such as InP, GaInAsP, GaAs, AlGaAs, InGaAs, and GaInNAs can be applied in addition to the InGaAs / AlGaAs system. In addition to the Fabry-Perot semiconductor laser, a surface emitting semiconductor laser, a light emitting diode, a super luminescent diode, or the like may be used as the semiconductor laser 33.

FIG. 16 is a timing chart showing an optical delay operation in the semiconductor optical control element of FIG.
In FIG. 16, when the optical input pulse L31a is incident on the quantum dot 32 as the signal light L31, excitons corresponding to the energy of the signal light L31 are generated in the quantum dot 32. Then, in the state where excitons are generated in the quantum dots 32, the trigger voltage TG <b> 1 is applied from the trigger circuit 34 to the semiconductor laser 33, thereby causing the control light L <b> 32 to enter the quantum dots 32. When the control light L32 is incident on the quantum dots 32, exciton molecules corresponding to the energy of the control light L32 are generated in the quantum dots 32, and the refractive index changes due to the interference effect between the excitons and the exciton molecules. . For this reason, the light output pulse L31b obtained by delaying the light input pulse L31a is output from the quantum dot 32.

Here, since the derivative of the refractive index of the quantum dot 32 changes depending on the optical power of the control light L32, the optical output pulse is controlled by controlling the magnitude and input timing of the trigger voltage TG1 applied to the semiconductor laser 33. The delay times D1 and D2 of L31b can be individually changed, and the delay times D1 and D2 of the optical output pulse L31b can be made different for each optical input pulse L31a. That is, increasing the optical power of the control light L32, it is possible to increase the speed v _g of light, it is possible to shorten the delay time of the signal light L31. For this reason, if the trigger voltage TG1 applied to the semiconductor laser 33 is increased, the delay time D1 of the light output pulse L31b can be decreased, and if the trigger voltage TG1 applied to the semiconductor laser 33 is decreased, the light output pulse L31b. The delay time D2 can be increased.
Note that the active layer of the semiconductor laser 33 may have the same structure as the quantum dots 32. As a result, the power consumption of the semiconductor laser 33 can be reduced, and even when the semiconductor laser 33 is incorporated in the semiconductor light control element in which the quantum dots 32 are formed, the power consumption of the entire semiconductor light control element is reduced. be able to.

FIG. 17 is a cross-sectional view showing a schematic configuration of a semiconductor optical control device according to the third embodiment of the present invention.
In FIG. 17, an energy barrier layer 41 is formed in a partial region on the semiconductor substrate 40, and quantum dots 42 are embedded in the energy barrier layer 41. Further, in other regions on the semiconductor substrate 40, a lower clad layer 43, an active layer 44, and an upper clad layer 45 are sequentially laminated so that the light absorption and refractive index of the quantum dots 42 can be changed. A semiconductor laser 48 that emits light is configured. Further, a DC bias power source 46 for applying a voltage to the semiconductor laser 48 is connected between the semiconductor substrate 40 and the upper clad layer 45, and the DC bias power source 46 is for causing the semiconductor laser 48 to emit light. A trigger circuit 47 for applying the trigger voltage TG2 is connected. As the semiconductor substrate 40, for example, a GaAs (100) substrate or an InP substrate may be used in addition to the GaAs (311) B substrate. Further, as semiconductors constituting the quantum dot 42, the energy barrier layer 41, the lower cladding layer 43, the active layer 44, and the upper cladding layer 45, InGaAs, AlGaAs, InP, GaInAsP, GaAs, AlGaAs, InGaAs, GaInNAs, etc. It can be applied to any material. In addition to the Fabry-Perot type semiconductor laser, a surface emitting semiconductor laser, a light emitting diode, a super luminescent diode, or the like may be used as the semiconductor laser 43.

When the optical input pulse L41a enters the quantum dot 42 as the signal light L41, excitons corresponding to the energy of the signal light L41 are generated in the quantum dot 42. Then, the control light L42 is caused to enter the quantum dot 42 by supplying the trigger voltage TG2 in a state where excitons are generated in the quantum dot 42. When the control light L42 is incident on the quantum dots 42, exciton molecules corresponding to the energy of the control light L42 are generated in the quantum dots 42, and the refractive index changes due to the interference effect between the excitons and the exciton molecules. . For this reason, the light output pulse L41b obtained by delaying the light input pulse L41a is output from the quantum dot 42.
Here, since the derivative of the refractive index of the quantum dot 42 changes depending on the optical power of the control light L42, the delay time of the optical output pulse L41b is changed by controlling the magnitude of the trigger voltage TG2 and the input timing. The delay time can be controlled without converting the signal light L41 into an electric signal.

FIG. 18 is a cross-sectional view showing a schematic configuration of a semiconductor optical control device according to the fourth embodiment of the present invention.
In FIG. 18, an energy barrier layer 51 is formed in a partial region on the semiconductor substrate 50, and quantum dots 52 are embedded in the energy barrier layer 51. Further, on the energy barrier layer 51, a Bragg distribution reflection layer 53, an active layer 54, a Bragg distribution reflection layer 55, and a voltage application layer 56 are sequentially stacked so that the light absorption and refractive index of the quantum dots 52 can be changed. A surface emitting laser 60 that emits light with a wavelength of Here, a part of the Bragg distribution reflection layer 53 is exposed from the active layer 44, the Bragg distribution reflection layer 55 and the voltage application layer 56, and the voltage application layer 57 is formed on the exposed Bragg distribution reflection layer 53. Has been. Further, a DC bias power source 58 for applying a voltage to the surface emitting laser 60 is connected between the voltage application layers 56 and 57, and a trigger voltage for causing the surface emitting laser 60 to emit light is connected to the DC bias power source 58. A trigger circuit 59 for applying TG3 is connected. As the semiconductor substrate 50, for example, a GaAs (100) substrate or an InP substrate may be used in addition to the GaAs (311) B substrate. Further, as semiconductors constituting the Bragg distribution reflection layer 53, the active layer 54, the Bragg distribution reflection layer 55, the quantum dots 52, and the energy barrier layer 51, in addition to InGaAs / AlGaAs, InP, GaInAsP, GaAs, AlGaAs, InGaAs, Any material such as GaInNAs can be applied. In addition to the surface emitting semiconductor laser, a light emitting diode or a super luminescent diode may be used.

  When the light input pulse L51a enters the quantum dot 52 as the signal light L51, excitons corresponding to the energy of the signal light L51 are generated in the quantum dot 52. Then, by supplying a trigger voltage TG3 in a state where excitons are generated in the quantum dots 52, the surface emitting laser 60 is caused to emit light, and the control light emitted from the surface emitting laser 60 is incident on the quantum dots 52. When the control light is incident on the quantum dots 52, exciton molecules corresponding to the energy of the control light are generated in the quantum dots 52, and the refractive index changes due to the interference effect between the excitons and the exciton molecules. For this reason, the light output pulse L51b obtained by delaying the light input pulse L51a is output from the quantum dot 52.

  Here, since the derivative of the refractive index of the quantum dot 52 changes depending on the optical power of the control light emitted from the surface emitting laser 60, the light output pulse is controlled by controlling the magnitude of the trigger voltage TG3 and the input timing. The delay time of L51b can be changed, and the delay time can be controlled without converting the signal light L51 into an electric signal.

As a method of forming the Bragg distribution reflection layer 53, the active layer 44, the Bragg distribution reflection layer 55, and the voltage application layer 56, MBE (Molecular Beam Epitaxy), MOCVD (Metal Organic Chemical Vapor Deposition), or ALCVD (Atomic Layer) is used. Epitaxial growth such as chemical vapor deposition can be used. In addition, as a method of forming the energy barrier layer 51 in which the quantum dots 52 are embedded, a semiconductor layer constituting the quantum dots 52 is formed by epitaxial growth, and then this semiconductor layer is formed using a resist pattern formed by a lithography technique as a mask. The quantum dots 52 can be embedded in the energy barrier layer 51 by etching into the shape of the quantum dots 52 and forming the energy barrier layer 51 on the quantum dots 52 by epitaxial growth.
In the embodiment of FIG. 18, the method of laminating the surface emitting semiconductor laser 60 on the energy barrier layer 51 in which the quantum dots 52 are embedded has been described. However, the energy barrier layer 51 in which the quantum dots 52 are embedded is formed on the surface. It may be laminated on the light emitting semiconductor laser 60.

  INDUSTRIAL APPLICABILITY The present invention can realize an optical delay element capable of controlling power consumption and downsizing while allowing delay time to be controlled, and can be used in fields such as optical communication.

1 is a perspective view showing a schematic configuration of a semiconductor light control element according to a first embodiment of the present invention. It is a figure which shows the photoexcited state in a 2 level system when the light of frequency (nu) _p injects. It is a figure which shows the optical response characteristic in the two level system of FIG. It is a figure which shows the photoexcited state in a 3 level system when the light of two types of wavelengths of frequency (nu) _p and (nu) _c injects. FIG. 5 is a diagram showing optical response characteristics in the three-level system of FIG. 4. It is a figure which shows the relationship between the change part of the refractive index which concerns on one Embodiment of this invention, and the optical power of frequency (nu) _c . It is a figure which shows typically the sample structure used in order to demonstrate the effect | action of this invention. It is a figure which shows the exciton molecular state produced | generated by the quantum dot. It is a figure which shows the light absorption spectrum in an exciton state. It is a figure which shows the light absorption spectrum in an exciton state and an exciton molecular state. It is a figure which shows the state of the three level system produced | generated in the exciton state and the exciton molecular state. It is a figure which shows the optical response characteristic in the 3 level system of FIG. It is a figure which shows the measurement result of the delay factor which concerns on one Embodiment of this invention, and the optical input power of frequency (nu) _XX . It is a figure which shows the relationship between the magnitude | size of the horizontal direction of the quantum dot which concerns on one Embodiment of this invention, and an exciton molecule | numerator binding energy. It is sectional drawing which shows schematic structure of the semiconductor optical control element concerning 2nd Embodiment of this invention. 16 is a timing chart showing an optical delay operation in the semiconductor optical control element of FIG. It is sectional drawing which shows schematic structure of the semiconductor optical control element concerning 3rd Embodiment of this invention. It is sectional drawing which shows schematic structure of the semiconductor optical control element which concerns on 4th Embodiment of this invention. It is a figure which shows an example of the conventional optical delay element. FIG. 20 is a timing chart showing an optical delay operation in the optical delay element of FIG. 19. FIG. It is a figure which shows the other example of the conventional optical delay element. It is a timing chart which shows the optical delay operation | movement in the optical delay element of FIG.

Explanation of symbols

11, 31, 41, 51 Energy barrier layer 12, 32, 42, 52 Quantum dot 13, 23 Control light source L11, L21, L31, L41, L51 Signal light L11a, L31a, L41a, L51a Light input pulse L11b, L31b, L41b, L51b Light output pulse L12, L22, L32, L42 Control light 20 GaAs (311) B substrate 21 AlGaAs barrier layer 22 InGaAs quantum dot 24 Wavelength tunable laser 25 Photodetector K1 Exciton K2 Exciton molecule 30, 40, 50 Semiconductor substrate 33, 48 Semiconductor laser TG1 to TG3 Trigger voltage 43 Lower cladding layer 45 Upper cladding layer 44, 54 Active layer 46, 58 DC bias power supply 34, 47, 59 Trigger circuit 53, 55 Bragg distribution reflection layer 56, 57 Voltage application 70 layers Light emitting laser

Claims (7)

Quantum dots that confine excitons;
A semiconductor light control element comprising: a control light source that irradiates the quantum dots with control light having a wavelength corresponding to energy of exciton molecules to which the excitons are bonded.   Signal light having a wavelength corresponding to the energy of the exciton is incident on the quantum dot, and one level is shared by the level corresponding to the energy of the exciton and the level corresponding to the energy of the exciton molecule. The semiconductor light control element according to claim 1, wherein a three-level system is configured.   3. The semiconductor light control element according to claim 2, further comprising a trigger circuit that controls the power of the control light emitted from the control light source in accordance with a delay time of the signal light.   The width and length of the quantum dots are in the range of 2 to 10 times the Bohr radius, and the height of the quantum dots is in the range of 0.1 to 1 times the Bohr radius. The semiconductor light control element of any one of Claims 1.   5. The quantum dot has a structure in which the first semiconductor layer is completely surrounded by a second semiconductor layer having a larger band gap than that of the first semiconductor. 6. Semiconductor light control element. The control light source is a Fabry-Perot semiconductor laser, a surface emitting semiconductor laser, a light emitting diode or a superluminescent diode,
6. The semiconductor light control element according to claim 1, wherein the control light source and the active region provided with the quantum dots are formed on the same semiconductor substrate.   7. The semiconductor light control element according to claim 1, wherein an active layer of the control light source has the same structure as the quantum dots.

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