JP4598382B2 - Optical logic unit - Google Patents

Description

  The present invention relates to an optical logic unit for optical logic operation that can be used as an optical inverter.

  Recent advances in optoelectronic technology are remarkable, and the scope of this technology extends to sensing and computing, centering on optical communications. In the realization of optical computers that apply optoelectronics, light-light control methods that control signal light with control light without any electrical circuit have been attracting attention. Consideration is underway.

  Typical examples of the light-light control method include a method using an absorption saturation type semiconductor element and a method using a side-incident bistable laser diode (see Non-Patent Document 1). In addition, there are a method of performing set-reset with two lights having different polarization planes (see Non-Patent Document 2), a method using nonlinear negative absorption of erbium ions (see Non-Patent Document 3), and the like. The operation of optical logic devices by these methods has also been reported. However, these technologies increase the element size and are not suitable for high-density integration.

  In addition, many methods using nonlinear optical elements have been studied as light-light control methods. In the method using a non-linear optical element, light-light control is enabled by a change in refractive index and absorption coefficient with respect to light intensity. However, since these effects are caused by the third-order polarization of the material, a high-power pulsed laser light source with a high peak value is required simultaneously with a nonlinear optical crystal having a large nonlinear constant. In order to realize this, further high efficiency is required.

In addition, as a basic study, optical switches using two-photon absorption of compound semiconductor optical waveguides (see Non-Patent Document 4) have been reported. Based on these studies, two-photon absorption of silicon photodiodes has been reported. Practical use of an autocorrelator used (see Non-Patent Document 5), an autocorrelator using a silicon CCD camera (see Non-Patent Document 6), a reflectometer using two-photon absorption of a silicon photodiode (see Non-Patent Document 7), etc. There are also reports of typical devices and equipment. However, these require a large group of devices and at the same time have a large element size, so there are no reports of adaptation to optical integrated circuits.
The applicant has not yet found prior art documents related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification.
K. Nonaka, H. Tsuda, H. Uenofara, H. Iwamura, and T. Kurokawa "Optical Nonlinear Characteristics of a Side-injection Light-controlled Laser Diode with a Multiple-quantum-well Saturable Absorption Region", IEEE PHOTONICS TECHNOLOGY LETTERS , VOL.5, NO.2, pp139-141, FEBRUARY 1993. H. Kawaguchi and T. Irie "OPTICALLY TRIGGERED POLARISATION BISTABLE SWITCHING IN LASER DIODES WITH EXTERNAL CAVITIES", ELECTRONICS LETTERS, Vol.28, No.17, pp1645-1647, 13th August 1992. Y.Maeda "All-optical NAND logic device operating at 1.51-1.55μm in Er-doped aluminosilicate glass", ELECTRONICS LETTERS, Vol.35, No.7, pp582-584, 1st April 1999. HKTSANG, RSGRANT, RVPENTY, IHWHITE, JBDSOOLE, E.COLAS, HPLEBLANC, NCANDREADAKIS, MSKIM, W.SIBBETT, "GaAs / GaAlAs MULTIQUANTUM WELLGUIDE FOR ALL-OPTICAL SWITCHING AT 1.55μm", ELECTRONICS LETTERS, Vol. 22, pp1993-1994, 24th October 1991. C.Xu, JMRoth, WHKnox and K. Bergman, "Ultra-sensitive autocorrelation of 1.5μm light with single photon counting silicon avalanche photodiode", ELECTRONICS LETTERS, Vol.38, No.2, pp86-88, 17th January 2002. Dmitriy Panasenko and Yeshaiahu Fainman, "Interferometric correlation of infrared femtosecond pulses with two-photon conductivity in a silicon CCD", APPLIED OPTICS, Vol.41, No.18, pp3748-3752,20 June 2002. Y Tanaka, N Sako, T Kurokawa, H Tsuda, and M Takeda, "Profilometry based on two-photon absorption in a silicon avalanche photodiode", OPTICS LETTERS, Vol.28, No.6, pp402-404, 15 March 2003.

As described above, the conventional optical logic device based on light-light control is highly integrated, such as a large-sized optical logic device that requires a high-output light source due to its large size and low efficiency. There was a problem that it was difficult to apply to circuits.
The present invention has been made to solve the above-described problems, and provides an optical logic unit that has a small element size and can be integrated at high density, and does not require a high-output light source. With the goal.

The optical logic unit according to the present invention includes a plurality of control lights each having a different bit pattern wavelength composed of an on state and an off state having different light intensities, and a second wavelength signal having a wavelength different from these control lights. An optical waveguide configured to combine light, a core made of silicon, and a clad having a refractive index lower than that of the core. At least a filtering circuit that extracts light of the second wavelength from the light that has been combined and guided through the optical waveguide, and the bit pattern has different light intensities at the light intensity at which two-photon absorption occurs in the optical waveguide. a it shall consist of an oN state and an oFF state.
In this optical logic unit, multi-photon absorption occurs in the optical waveguide when the control light guided through the optical waveguide is in one light intensity, and the control light changes into two states, an on state and an off state. The signal light that is simultaneously guided through the waveguide is modulated.

In the optical logic unit, provided before the multiplexer multiplexing circuit may be provided with an attenuator that attenuates the optical intensity of the signal light and control light.

In addition, another optical logic unit according to the present invention includes a first control light having a first wavelength of a bit pattern composed of an on state and an off state having different light intensities, and a wavelength different from that of the first control light. A multiplexing circuit that multiplexes the second control light of the second wavelength and the signal light of the third wavelength different in wavelength from both the first control light and the second control light, a core made of silicon, and lower than this core A third wavelength light is extracted from an optical path configured by a clad having a refractive index and guiding light combined by the multiplexing circuit and light guided by the multiplexing circuit and guided through the optical waveguide. comprising at least a filtering circuit, the bit pattern is shall consist of a boundary of light intensity occurring two-photon absorption is different between on and off states of the light intensity in the optical waveguide.

  As described above, according to the present invention, since an optical waveguide made of a silicon core is used, high-density integration is easy, and it is easy to increase the light intensity density in the optical waveguide. An excellent effect is obtained in that a low-power semiconductor CW laser or the like that is inexpensive and easy to perform hybrid mounting can be used as a light source.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing a configuration example of an optical inverter 100 that is an optical logic unit in the embodiment of the present invention. The optical inverter 100 includes an optical waveguide 101 composed of a silicon core and a clad having a lower refractive index, a multiplexing circuit 104 such as a directional coupler (3 dB coupler), and a bandpass filter. And the filtering circuit 105.

For example, the control light having the wavelength λ ₁ (1.1 μm <λ ₁ <2.2 μm) modulated into the bit pattern by the pattern generator 102 and the optical modulator 103 and the wavelength λ ₂ (1.1 μm <λ ₂ <2.2 μm). ) Is input from the input side of the multiplexing circuit 104, and is multiplexed by the multiplexing circuit 104 and output. The output combined light is input to the optical waveguide 101.

  When only one of the control light and the signal light is input to the optical waveguide 101, each of these wavelengths is longer than the band gap of silicon, so that when the light intensity is low, the light is transmitted (guided) through the optical waveguide 101. Is output (emitted). The light emitted from the optical waveguide 101 passes through the filtering circuit 105, so that only the signal light is extracted. The state of the signal light extracted by the filtering circuit 105 can be measured by the O / E sampling oscilloscope 106. The O / E sampling oscilloscope 106 measures an optical signal having an inverted bit pattern.

  Here, the silicon core optical waveguide 101 can guide light even when the core diameter is 500 nm or less as long as the light has a wavelength of 1.1 to 2.2 μm. The light having a wavelength of 1.1 to 2.2 is remarkably increased in light intensity in the core. In this structure, the intensity of the control light guided through the optical waveguide 101 is increased, and when the intensity exceeds a predetermined value, two-photon absorption occurs, carriers (electron-hole pairs) are generated, and light absorption occurs. It should be noted that multi-photon absorption occurs in the optical waveguide 101 by three-photon absorption, four-photon absorption,...

  Therefore, when the control light of the bit pattern in which the light intensity lower than this is set to the off level and the light intensity higher than this is turned on at the light intensity where the two-photon absorption occurs is incident on the optical waveguide 101, Two-photon absorption occurs. Since the carrier generated by the two-photon absorption also absorbs the signal light, when the control light is on level, the signal light that is combined and incident at the same time by the combining circuit 104 is also absorbed by the optical waveguide 101. .

  In addition, when electron-hole pairs generated by two-photon absorption recombine, light having twice the energy of the control light is emitted, but the energy is larger than the band gap of silicon forming the core of the optical waveguide 101. Since it is large, the light emitted by recombination cannot propagate through the optical waveguide 101. Therefore, according to the optical inverter 100 illustrated in FIG. 1, the signal light can be modulated by the control light combined with the signal light by the multiplexing circuit 104.

  FIG. 2 is a characteristic diagram showing the waveform of the control light. FIG. 3 is a characteristic diagram showing the waveform of the control light measured by the O / E sampling oscilloscope 106 when only the control light is incident. FIG. 4 is a characteristic diagram in which the values of B / A in FIG. 3 are plotted when the input peak intensity of the control light is changed. In these cases, the result of measuring the light emitted from the optical waveguide 101 with the O / E sampling oscilloscope 106 without passing through the filtering circuit 105 is shown.

  As can be seen from FIG. 4, the input peak intensity of the control light and the reciprocal of the transmittance are in a proportional relationship, indicating that the attenuation of the control light shown in FIG. 3 is two-photon absorption in the optical waveguide 101 (references). : JHBechtel and WLSmith, "Two-photon absorption in semiconductors with picosecond laser pulses", PHYSICAL REVIEW B, Vo.13, No.8, pp3515-3522, 15th APRIL 1976.).

Under the condition of the light peak intensity where the control light is attenuated, the generation of carriers (electron-hole pairs) by two-photon absorption occurs, and when signal light enters the waveguide where the electron-hole pairs are generated, The signal light is also attenuated, and the signal light is subjected to inversion modulation by the control light.
FIG. 5 shows the waveform of the output optical signal (signal light) measured by the O / E sampling oscilloscope 106 when the control light and the signal light are combined and incident on the optical waveguide 101. FIG. 6 is a plot of the inversion modulation rate (D / C) in FIG.
As is apparent from these figures, when the input peak intensity is about 20 mW (position E), almost no reversal operation is shown, but when the input peak intensity is about 50 mW (position F), it can be seen that the modulation is about 50%.

Next, another example of the multiplexing circuit and the filtering circuit constituting the optical inverter 100 shown in FIG. 1 will be described with reference to FIG.
First, as shown in FIG. 7A, signal light may be extracted from light emitted from the optical waveguide 101 by a filtering circuit 115 including an optical lattice filter. Further, as shown in FIG. 7B, signal light may be extracted from the light emitted from the optical waveguide 101 by a filtering circuit 125 formed of a ring resonator.

  Further, as shown in FIG. 7C, the signal light and the control light are multiplexed by the multiplexing circuit 114 formed of an optical lattice filter, and the signal light is output by the filtering circuit 115 from the light emitted from the optical waveguide 101. You may make it take out. Further, as shown in FIG. 7D, the signal light and the control light are multiplexed by the multiplexing circuit 114, and the signal light is extracted by the filtering circuit 125 from the light emitted from the optical waveguide 101. Good.

  Further, as shown in FIG. 7E, the signal light and the control light are combined by the multiplexing circuit 124 formed of a ring resonator, and the signal light is output by the filtering circuit 115 from the light emitted from the optical waveguide 101. You may make it take out. Further, as shown in FIG. 7F, the signal light and the control light are multiplexed by the multiplexing circuit 124, and the signal light is extracted by the filtering circuit 125 from the light emitted from the optical waveguide 101. Good.

  Further, as shown in FIG. 7G, the signal light and the control light are combined by a multiplexing circuit 134 made of a reflective diffraction grating, and the light emitted from the optical waveguide 101 is made of a reflective diffraction grating. The signal light may be extracted by the wave circuit 135. Further, as shown in FIG. 7 (h), the signal light and the control light are multiplexed by the multiplexing circuit 144 composed of the transmissive diffracted light value, and the light emitted from the optical waveguide 101 is obtained from the transmissive diffracted light value. The signal light may be extracted by the filtering circuit 145. Further, as shown in FIG. 7 (i), signal light and control light are multiplexed by a multiplexing circuit 154 composed of an arrayed waveguide diffraction grating, and light emitted from the optical waveguide 101 is transmitted from the arrayed waveguide diffraction grating. The signal light may be extracted by the filtering circuit 155.

Next, a configuration example of an optical circuit using the optical inverter in the above-described embodiment will be described.
FIG. 8 is a configuration diagram showing an optical wavelength conversion circuit configured by arranging two optical inverters 100a and 100b in two stages in series. The control light modulated into the bit pattern and the primary signal light composed of continuous light having a wavelength different from that of the control light are input to the optical inverter 100a at the previous stage, and the optical inverter is input to the optical inverter 100b at the subsequent stage. The output light from 100a and the secondary signal light having different wavelengths from the primary signal light are input, and the secondary signal light is output from the optical inverter 100b.

  According to the optical wavelength conversion circuit shown in FIG. 8, the secondary signal light output from the optical inverter 100b is in a state where the modulation pattern of the control light is copied, that is, a state modulated by the control light. Therefore, the input primary signal light is output as the secondary signal light modulated by the control light at a different wavelength by the optical wavelength conversion circuit shown in FIG. Here, the secondary signal light may have a wavelength different from that of the primary signal light, and may be the same wavelength as the control light.

  Note that the optical inverter 100b should have a higher sensitivity than the optical inverter 100a. When the optical inverter 100b is configured in the same manner as the optical inverter 100a, as shown in FIG. 9, the primary signal light output from the optical inverter 100a is amplified by the optical amplifier 200 and then transmitted to the optical inverter 100b. Just input.

  In the above description, one control light is input to the optical inverter. However, the present invention is not limited to this. As shown in FIG. 10, two different control lights are input to modulate the signal light. It may be. The optical logic unit shown in FIG. 10 uses a multiplexing circuit 104a that combines the control light A, the control light B, and the signal light.

According to the optical logic unit shown in FIG. 10, the control light A, the control light B having a wavelength and a bit pattern different from the control light A, and the signal light which is a continuous light having a wavelength different from the control light are input and controlled. The NAND of the light A and the control light B is output from the filtering circuit 105 as signal light.
In this optical logic unit, when at least one of the control light A and the control light B is at the off level, the input peak intensity is equal to or lower than the position E shown in FIG. Further, when both the control light A and the control light B are on level, the input peak intensity at the position F shown in FIG. 6 is obtained.

  Accordingly, when the combined light of the control light A and the control light B enters (inputs) the optical waveguide 101, the optical waveguide undergoes an inversion operation only when both the control light A and the control light B are on level. By filtering the output light 101 by the filtering circuit 105 and taking out the signal light, it operates as a NAND circuit.

  The multiplexing circuit 104a of the optical logic unit shown in FIG. 10 may be configured by two optical lattice filters 114a and 114b, for example, as shown in FIG. At this time, signal light may be extracted from the light output from the optical waveguide 101 by the filtering circuit 115 including an optical lattice filter. Further, as shown in FIG. 11B, signal light may be extracted from the light output from the optical waveguide 101 by a filtering circuit 125 formed of a ring resonator.

  The multiplexing circuit 104a may be constituted by two directional couplers or may be constituted by two ring resonators. The multiplexing circuit 104a may be composed of a reflection type diffraction grating having three or more input channels, may be composed of a transmission type diffraction grating having three or more input channels, You may comprise from the array waveguide diffraction grating which has the above input channels. Further, the filtering circuit is not limited to the optical lattice filter or the ring resonator, but may be composed of a reflection type diffractive photon, a transmission type diffraction grating, or an arrayed waveguide diffraction grating.

  Next, an example of an optical circuit that modulates signal light by inputting three or more different control lights will be described. In FIG. 12, n (n> 2) control light A, control light B, control light C,..., And signal light are respectively input to the multiplexing circuit 164 through the variable optical attenuator 110 and multiplexed. 3 is a configuration diagram showing a configuration of an optical logic unit that inputs light combined by a circuit 164 to a waveguide circuit 101. FIG. A multiplexing circuit 164 multiplexes n + 1 lights.

  In the optical logic unit shown in FIG. 12, n control lights having individual wavelengths are input in individual bit patterns, and signal light that is continuous light having a wavelength different from these control lights is input, and the n control lights The output of the signal light is switched by the sum of the light intensities. A variable optical attenuator 110 is provided for each control light and signal light in the preceding stage of the multiplexing circuit 164 so that the input light intensity can be adjusted.

  For example, when the output bits for the control optical channel pattern are known in advance, an error back-propagation algorithm is used, and the attenuation amount of each variable optical attenuator 110 is set. It can be used as an optical logic unit for a neurocomputer that obtains a high output. In this example, when the control channel pattern to be a teacher pattern is not known in advance, the attenuation amount of each variable optical attenuator 110 may be set using a pattern classification algorithm in the learning process.

  The variable optical attenuator 110 may be a PIN type optical attenuator, for example. Further, as the variable optical attenuator 110, an ND filter type optical attenuator may be used, and an optical attenuator using a magneto-optical effect, an optical attenuator using a Mach-Zehnder interferometer, or the like may be used. May be. If the optical attenuation amount for each input channel can be determined in advance, a fixed optical attenuator may be used instead of the variable optical attenuator.

  The optical logic unit of the present invention described above uses an optical waveguide composed of a silicon core. Silicon is easy to form a fine pattern and can be easily miniaturized. Therefore, according to the optical logic unit of the present invention, high-density integration is easy. In addition, the cross-sectional dimension of the core can be easily set to about 500 nm, and light can be confined in such a minute region, so that it is easy to increase the light intensity density in the optical waveguide. As a result, according to the optical logic unit of the present invention, it is possible to use a low-power semiconductor CW laser or the like as a light source that is inexpensive and easy to perform hybrid mounting.

It is a block diagram which shows the structural example of the optical inverter 100 which is an optical logic unit in embodiment of this invention. It is the characteristic view which showed the waveform of control light. It is a characteristic view showing a waveform of the control light measured by the O / E sampling oscilloscope 106 when the control light is incident with the signal light turned off. FIG. 4 is a characteristic diagram in which values of B / A in FIG. 3 are plotted when the input peak intensity of control light is changed. The waveform of the output optical signal (signal light) measured by the O / E sampling oscilloscope 106 when the control light and the signal light are combined and incident on the optical waveguide 101 is shown. FIG. 6 is a plot of the inversion modulation rate (D / C) in FIG. 5. It is a block diagram which shows the other structural example of the multiplexing circuit and the filtering circuit which comprise the optical inverter 100 shown in FIG. It is a block diagram which shows the optical wavelength conversion circuit comprised by arrange | positioning two optical inverters 100a and 100b in two steps in series. It is a block diagram which shows the optical wavelength conversion circuit comprised by arrange | positioning two optical inverters 100a and 100b in two steps in series. It is a block diagram which shows the other structural example of the optical logic unit in embodiment of this invention. It is a block diagram which shows the other structural example of the optical logic unit in embodiment of this invention. It is a block diagram which shows the other structural example of the optical logic unit in embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Optical inverter, 101 ... Optical waveguide, 102 ... Pattern generator, 103 ... Optical modulator, 104 ... Multiplexing circuit, 105 ... Filter circuit, 106 ... O / E sampling oscilloscope.

Claims (3)

A multiplexing circuit that multiplexes a plurality of control lights having different wavelengths of bit patterns composed of an on state and an off state having different light intensities, and signal light having a second wavelength different from these control lights; ,
An optical waveguide configured of a core made of silicon and a clad having a refractive index lower than that of the core, and guides light combined by the multiplexing circuit;
From light guided through the optical waveguide are multiplexed by the multiplexing circuit, comprising at least a filtering circuit for taking out the light of the second wavelength,
The bit pattern, an optical logic unit, characterized that you have been composed of a border of light intensity occurring two-photon absorption is different between on and off states of the light intensity in the optical waveguide. The optical logic unit according to claim 1,
An optical logic unit comprising an attenuator provided in a preceding stage of the multiplexing circuit and configured to attenuate the light intensity of the signal light and the control light. A first control light having a first wavelength of a bit pattern composed of an ON state and an OFF state having different light intensities, a second control light having a second wavelength different from the first control light, and the first control light A multiplexing circuit that multiplexes a third wavelength signal light having a wavelength different from that of both the light and the second control light;
An optical waveguide configured of a core made of silicon and a clad having a refractive index lower than that of the core, and guides light combined by the multiplexing circuit;
A filtering circuit that extracts light of a third wavelength from the light that has been multiplexed by the multiplexing circuit and guided through the optical waveguide ;
The bit pattern, an optical logic unit, characterized that you have been composed of a border of light intensity occurring two-photon absorption is different between on and off states of the light intensity in the optical waveguide.

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