JPS6151306B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to an optical logic circuit element that can be constructed in an ultra-small size, can be controlled by optical pulse signals, and can perform ultra-high-speed processing. [Prior Art] Conventionally, silicon (Si)-LSI has been used as logic operation and signal processing elements.
As the computational speed that can be achieved is approaching its physical limit, gallium arsenide (GaAs) LSIs and LSIs using Josephson junctions are being considered to achieve even faster computational processing. However, GaAs-LSI has a calculation speed limit of about 5 pS, and Josephson junction LSI
However, there are problems such as the need for extremely low temperatures due to its operating principle. [Objective] The object of the present invention is to eliminate the above drawbacks,
The object of the present invention is to provide an optical logic circuit element that performs all the main parts of logical operations using light and can operate at ultra high speed at room temperature. [Configuration of the Invention] The present invention has an input optical waveguide, an output optical waveguide, and two single-mode optical waveguides having a nonlinear refractive index that depends on the optical intensity. One end of each of the two single mode optical waveguides is connected to one end of the input optical waveguide so that light of the same power is incident on each of the two single mode optical waveguides, and the other end of each of the two single mode optical waveguides is connected to one end of the input optical waveguide. The end is connected to one end of the output optical waveguide, and the following relationship l ₁・N ₁ ≠ l ₂・N ₂ where, l ₁ : Length of one single mode optical waveguide l ₂ : Length of the other single mode optical waveguide Length N ₁ : refractive index of one single mode optical waveguide N ₂ : configured to satisfy the refractive index of the other single mode optical waveguide. [Example] The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an optical logic circuit element according to the present invention, in which 1 is a single-mode input optical waveguide, 2 is a single-mode output optical waveguide, and 3 is one arm of length l ₁ made of a single mode optical waveguide, and 4 is the other arm of length l ₂ made of a single mode optical waveguide. The two arms 3 and 4 are made to have the same nonlinear refractive index. One end of each of the arms 3 and 4 is connected to the input optical waveguide 1 together with the input optical waveguide 1 so that a Y-shaped branch part 5 is formed, and each other end is connected to the input optical waveguide 1 together with the output optical waveguide 2. It is connected to the output optical waveguide 2 so that a Y-shaped coupling portion 6 is formed. Therefore, the power of the light from the input optical waveguide 1 is
The branching section 5 separates the light by 1/2, and the separated light powers can be completely combined at the coupling section 6. All the optical waveguides mentioned above are single mode waveguides having a core and a clad covering the core, and are constructed of a material whose refractive index changes depending on the intensity of propagating light. Of course, at least one of the core and the cladding, which are the constituent parts of the optical waveguide, may have a nonlinear refractive index. Reference numeral 7 denotes an electrode for applying an electric field to one arm 4. In the above configuration, the input optical waveguide 1
If the intensity of the light incident from the input optical waveguide 1 is _Iio , then the light from the input optical waveguide 1 is divided by 1/2 at the branching part 5.
When separated into two parts, guided to each of the two arms 3 and 4, propagated within both arms 3 and 4, and completely coupled at the coupling part 6, from the output optical waveguide 2. The intensity I _put of the emitted light is I _put =I _io /2 {1+cos(a·n ₂ ·Δl·I _io +δ)}. Here, n ₂ is the refractive index change corresponding to the light intensity I _io within the optical waveguide. Note that the refractive index n of the optical waveguide is expressed by n=n ₀ +n ₂ ·I _io . n ₀ is a refractive index that does not depend on the incident light intensity. Δl is |l ₂ −l ₁ |, i.e., 2
Difference in length of two arms 3 and 4, a=2π/ε
₀ cnλ ₀ , ε ₀ is the permittivity of vacuum, c is the speed of light in vacuum, and λ ₀ is the wavelength of light in vacuum. δ
is the phase difference in the Y-shaped coupling portion 4 of the light that has propagated within the two arms 3 and 4 under conditions that are weak enough that the propagating light does not cause nonlinearity in the refractive index. By appropriately selecting the lengths of the two arms 3 and 4 or the value of the voltage applied to the electrode 7, the phase difference δ at the coupling portion 6 of the light propagating within the two arms 3 and 4 can be adjusted. can be set to 180 degrees, for example. The optical input-output characteristics at this time are shown in FIG. In FIG. 2, the straight line indicates the state of I _put =I _io . As shown in Figure 2, the phase difference δ
= 180 degrees, _Iput changes periodically in response to changes in _Iio . Furthermore, light having a power corresponding to the difference between this curve and the straight line is scattered from the coupling portion 6 as a non-guided mode. Note that, as described above, in this example, the same nonlinear refractive index n ₂
It has a configuration including two arms 3 and 4 of different lengths. However, instead of the two arms 3 and 4, two arms with the same length but different n ₂ and two arms with different Δl and n ₂ may be used to achieve the same effect as described above. The same effect can be obtained. That is, l ₁・N ₁ ≠ l ₂・N ₂ where l ₁ : Length of one single mode optical waveguide l ₂ : Length of other single mode optical waveguide N ₁ : Length of one single mode optical waveguide Refractive index N ₂ of the waveguide: The refractive index N 2 may be set to satisfy the refractive index of the other single mode optical waveguide. Therefore, the optical logic circuit element 8 according to the embodiment of the present invention does not generate reflected light, and as shown in FIG. can be cascaded. FIG. 4 shows an optical logic circuit element 8 according to an embodiment of the present invention.
The I _io -I _put characteristics when the optical logic circuit elements 8 are cascaded in 1st, 2nd, and 3rd stages are shown using the number N of cascaded optical logic circuit elements 8 as a parameter. Note that the electrode 7 is for adjusting the phase difference δ and is not related to the operation itself of the device of the present invention. FIG. 5 is a block diagram of a logic circuit element 9 in which optical logic circuit elements 8 are connected in cascade in three stages.By applying an appropriate optical bias _Ib to this logic circuit element 9, two input Regarding the optical pulse signal I _p ,
AND (AND), OR (OR), NAND (NAND)
and NOR logic circuits can be configured. FIG. 6 shows the intensity _Iio of the incident light on the logic circuit element 9.
An example of the relationship between the I _io -I _put characteristic showing the relationship between the output light intensity I _put and the optical bias I _b and the intensity of the input optical pulse signal I _p in each AND, OR, NAND, and NOR circuit is shown below. show. In Figure 6, a is and, b is or, c is nand, and d
shows the case of each Noah circuit. The truth tables of AND, OR, NAND, and NOR circuits regarding the input optical pulse signal I _p are shown in Table 1 below.

【table】

[Table] As shown in Fig. 7, two NAND circuits 9 configured by the logic circuit elements shown in Fig. 5 are used.
An RS flip-flop circuit can be constructed. As shown in FIG. 7, this RS flip-flop circuit feeds back the outputs of two NAND circuits 9 to one input of the other. Table 2 shows the truth table of this flip-flop circuit.

[Table] As can be seen from this table, as long as R and S are at logic "0", the state of this flip-flop circuit remains stable. If S goes "high", the output Q of the flip-flop circuit goes to logic "1", while if R goes "high", the same output goes to logic "0". Note that if both S and R become "1" at the same time, the output of the flip-flop circuit becomes uncertain. Materials constituting the optical logic circuit element of the present invention based on the operating principle described above include optical nonlinear refractive index
Any substance with n ₂ can be used.
As an example, Table 3 shows the values of n ₀ and n ₂ that are non-resonant to the absorption line for typical semiconductor materials with nonlinear refractive index.

[Table] It is known that the response time of _n2 , which is non-resonant to the absorption line, to Iio is on the order of pS or less _. Using GaAs as a constituent material, we prototyped an optical logic circuit element with an optical waveguide width of 0.08 μm to sufficiently confine light and Δl = 100 μm. I was able to switch the element. That is, a change for one period in FIG. 2 was obtained. When the time response was measured using three stages of optical logic circuit elements each having an element length L (see FIG. 1) connected in cascade of 200 μm, the effective switching speed was 6.4 pS per gate. Since the response speed of the medium is sufficiently fast, the switching speed is determined by the element length. Therefore, by using a larger optical input than the experimental conditions, for example 23 W, it is possible to perform switching even if the element length is reduced to 1/10, and as a result, switching on the order of sub-picoseconds becomes possible. Semiconductors, ferroelectric materials, etc. other than the semiconductors shown in Table 3 can also be used as constituent materials of the optical waveguide. Furthermore, as shown in the literature by Bloss et al. (Applied Physics Letters, Vol. 41, p. 1023 (1982)), GaAs/Al
The GaAs superlattice has an even larger n ₂ than GaAs, and can be used as a material that can switch faster. [Effects] As explained above, according to the present invention, optical logic that operates at room temperature and has a very high operating speed can be widely used as a basic element for signal processing, logical operations, etc. A circuit element can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an optical logic circuit element according to the present invention, FIG. 2 is a diagram showing an example of optical input/output characteristics of the same circuit element, and FIG. 3 is a diagram showing an example of the optical input/output characteristics of the same circuit element. A diagram showing an example of a configuration in which optical logic circuit elements are connected in cascade, FIG. 4 is a diagram showing an example of optical input-output characteristics of the same multi-stage configuration example, and FIG. 5 is a diagram showing a configuration of a logic circuit element in which optical logic circuit elements are connected in cascade in three stages. Figure 6 shows the optical bias and optical pulse signals necessary for the operation of AND, OR, NAND, and NOR circuits constructed using the same logic circuit elements. FIG. 7 is a diagram showing an example of a flip-flop circuit constructed from two NAND circuits constructed from optical logic circuit elements. DESCRIPTION OF SYMBOLS 1... Single mode optical waveguide for input, 2... Single mode optical waveguide for output, 3, 4... Single mode optical waveguide (arm), 5... Y-shaped branch part, 6...
...Y-shaped connecting part, 7...electrode.

Claims (1)

[Claims] 1. An input optical waveguide, an output optical waveguide, and two single-mode optical waveguides having a nonlinear refractive index that depends on light intensity, the two single-mode optical waveguides having a nonlinear refractive index that depends on the optical intensity. One end of each of the two single mode optical waveguides is connected to one end of the input optical waveguide so that light of the same power is incident on each of the waveguides. Each other end is connected to one end of the output optical waveguide, and the following relationship l ₁ · N ₁ ≠ l ₂ · N ₂ where l ₁ : Length of one single mode optical waveguide l ₂ : Length of the other single mode optical waveguide An optical logic circuit element characterized in that the length of one mode optical waveguide N ₁ : the refractive index of one single mode optical waveguide N ₂ : the refractive index of the other single mode optical waveguide. 2. The optical logic circuit element according to claim 1, wherein at least one of the two single mode optical waveguides has an electrode for applying an electric field to control its refractive index. Logic circuit element.