JP2937442B2 - WDM optical element, WDM optical system, and optical modulation method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing optical element used for light modulation, image processing, and the like.

[Conventional technology]

2. Description of the Related Art Conventionally, a nonlinear optical function element having a function of performing optical modulation, optical frequency conversion, and the like using a nonlinear optical effect in an optical waveguide has been proposed. For its operating characteristics, see, for example, “Journal of Applied Physics, No. 58.
Volume (1985), pages R57 to R78 (J. Appl. Phys., 58
(1985), pp. R57-R78).
In the above document, in an optical waveguide under a condition that light of a single wavelength is guided, light modulation is performed by using a change in refractive index due to a nonlinear optical effect, and a second order due to a second-order nonlinear optical effect.
Optical frequency conversion such as harmonic generation has been attempted. The change in the refractive index due to the nonlinear optical effect is about 10%, and the length of the optical waveguide is about 1 cm. In addition, a pulse laser having an output of about 100 W is used as a light source.

An optical modulation technique using the nonlinear optical effect is also disclosed in Japanese Patent Application Laid-Open No. 2-124540.

[Problems to be solved by the invention]

In the above prior art, there are problems such as a large size of an element for realizing the function, a low integration degree, and a need for a high output light source. It is difficult to construct the device.
Further, in the above-described conventional technology, it is difficult to process three primary colors of light in parallel with one optical waveguide, or to compare two images to recognize a common portion or the like.

It is an object of the present invention to have a characteristic of high integration and low input operation, and to be able to perform optical logic modulation operation in parallel with a single optical waveguide for three primary colors of light, or to perform image processing with natural colors. To provide a wavelength division multiplexing device capable of performing the following.

[Means for solving the problem]

The above object includes a plurality of (for example, three) semiconductor thin films having different thicknesses, each of which has a band gap in a near-infrared region and is sandwiched between barrier materials having a band gap of near ultraviolet. In this case, the wavelength of the energy level of the excited state of the electron-hole formed in the thin film of each layer corresponds to a predetermined visible light (for example, in the case of three layers, the visible light red, green, and blue). The optical waveguide is formed as described above, and light that resonates at the respective energy levels is incident on each layer of the optical waveguide, and the other light is irradiated as modulated light or reference light, whereby the phase or refractive index of the incident light is increased. Is achieved, and the wavelength multiplexing optical element is configured to perform light intensity modulation, color tone modulation, and switching of a propagation path in an arbitrary region of visible light.

As a specific configuration example, the semiconductor thin film of the optical waveguide is formed so that the wavelength of the excitation energy level of each electron-hole corresponds to red, green, and blue of visible light.

Further, as another example, the optical waveguide may be configured to include a closed circuit, or may be configured as two optical waveguides arranged so as to generate electromagnetic coupling.

In a more limited aspect, the semiconductor thin film layer is a III-V compound (for example, GaAs), and the barrier layer is
The barrier layer is preferably formed of an I-VI group compound (for example, ZnS _0.15 Se _0.85 ), and the mismatch between the lattice constant of the barrier layer and the semiconductor thin film is desirably 0.5% or less. In another limited aspect, the refractive index of the semiconductor thin film layer is set to 10 times or more that of the air, and the width of the optical waveguide is set to 1/5 or less of the wavelength of red light in the air. I do. The optical waveguide layer may be formed by processing the semiconductor thin film layer on a fine wire having a width of 40 nm or less in the direction along the substrate surface, and reducing the width of the optical waveguide to 50 nm or less, and narrowing down the end portion in a fan shape. A part may be provided. In order to irradiate the modulated light or the reference light to the optical waveguide, a new optical waveguide layer may be provided.

As an application example of the wavelength tunable optical element of the present invention, this is constituted by two optical waveguides which are close to each other so that electromagnetic coupling occurs, and one element corresponds to one pixel and four or more elements are integrated. I do. According to such a configuration, the original image of the natural color is divided into pixels and the pixels are incident on the elements, and the incident pixels are compared with the pixels of the reference image. Can be separated and extracted, the output light of each element is two-dimensionally arranged, and image processing for outputting images of the common portion and the non-common portion can be performed.

[Action]

In the above configuration, when light having a wavelength that resonates with the exciton level is incident, polariton is formed by coherent interaction between the exciton and light. And when polaritons are present, the interaction between excitons and light is very strong, and the refractive index of the medium at the resonance wavelength increases significantly from the value in air. In particular, when a quantum well structure is formed using a material having a much larger band gap than a quantum well layer made of a semiconductor thin film for a barrier layer, the interaction between excitons formed in the quantum well and light is further strengthened, and the resonance state is increased. The refractive index at is more than 10 times that of air. Such a situation can be realized, for example, by using a II-VI group compound such as ZnS _0.15 Se _0.85 or a mixed crystal thereof as a barrier and using a III-V group compound such as GaAs as a quantum well. In this system, it can be said that the lattice mismatch is as low as 0.42%, so that the influence of distortion can be ignored.

When the above system is used, since the refractive index is 10 or more with respect to the light having the wavelength in the resonance region, it is possible to guide the light to the optical waveguide having the width of the nanometer size, and the integration degree of the optical element. Can be dramatically increased. In addition, since the band gap of the barrier layer is in the near ultraviolet region and the band gap of the quantum well layer is in the near infrared region, when the thickness of the quantum well is changed, the wavelength of light that resonates with the quantum well excitons becomes visible in the entire visible light region. It is variable. Therefore, by providing three quantum well layers having different thicknesses,
Polaritons corresponding to red (R), green (G), and blue (B) can be propagated through a single optical waveguide. This R, G, B are the three primary colors of light, guide the natural color,
An element for performing an optical operation can be configured.

Also, utilizing the fact that the phase of polaritons changes due to exciton scattering, an interference-type optical waveguide is constructed, and the electron-hole system created by modulated light changes the phase of polaritons formed by input light. The intensity of light can be modulated by changing the interference conditions. in this case,
Since the exciton component of the polariton is the highest at the exciton resonance wavelength, scattering becomes strong when the wavelength of the modulated light is close to that wavelength. Therefore, if the wavelength component of the modulated light is selected, modulation of an arbitrary component among R, G, and B can be performed, and color tone modulation and
It can be applied to wavelength multiplexing logic and the like. Note that the intensity of the modulated light required to cause this effect may be about 1 mW, which has the advantage that an element that operates with low input can be configured.

In addition, exciton scattering weakens the interaction between excitons and light, reducing the refractive index. Therefore, by irradiating the optical waveguide with light and inducing exciton scattering, the confinement of light in the optical waveguide is weakened, and the amount of light leaking out of the electric field is increased, so that the components are adjacent to each other. It can also be taken out to another optical waveguide provided. This enables RGB image processing, as shown in Example 2 described later, and allows comparison between the original image and the reference image in natural colors according to the wavelength component of the reference light. Also in this case, similarly to the above modulation, the intensity of the reference light may be about 1 mW.

The device according to the present invention uses the interaction between excitons and light using polaritons as described above.To sufficiently exhibit this effect, when light is incident on the quantum well layer, It is necessary to take structural considerations such that light is incident in the longitudinal direction of the layer.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 In this embodiment, an optical waveguide for inputting modulated light is connected to a part of an optical waveguide of a Mach-Zehnder interferometer, and three primary colors of red (R), green (G), and blue (B) light are used. This is an embodiment in which an element for guiding and modulating light is formed. FIG. 1 (a) shows a schematic external view of the Mach-Zehnder interferometer of this embodiment, and FIG. 1 (b) shows a configuration of the optical waveguide (shown in a horizontal direction).

First, a manufacturing method will be described. In FIG. 1 (b), a semi-insulating GaAs wafer is used as a substrate 1, and undoped GaAs is first formed on the substrate 1 as a cladding layer 4.
0 μm, ZnS _0.15 Se _0.85 to become barrier layer 8 1.5 μm, 19.
8Å GaAs quantum well layer 5, 100Å barrier layer 8, 11.3Å
Epitaxial crystal growth is performed by a molecular beam epitaxy method (MBE method) in the order of a GaAs quantum well layer 6, a 100 ° barrier layer 8, an 8.5 ° GaAs quantum well layer 7, a 1.5 μm barrier layer 8, and a cladding layer. The cladding layer 4 and the region sandwiched between them constitute the core. In the quantum well layer 5, an exciton level 9 serving as a source of a red-band polariton is generated. The energy of exciton level 9 at liquid helium temperature is 1.77 eV and the wavelength
It becomes 707 nm. In the exciton level 10 of the quantum well layer 6 corresponding to the green band polariton, the energy is 2.30 eV and the wavelength is 542 nm. In the exciton level 11 of the quantum well layer 7 corresponding to the blue band polariton, the energy is Is 2.89 eV and the wavelength is 430 nm.

After the crystal is grown, it is processed into a Mach-Zehnder interferometer as shown in FIG. Here, the width of the optical waveguide is 4 μm, the length of the interferometer is 200 μm, and the length of the optical waveguides connected to both ends of the interferometer is 25 μm. Therefore, the total length of the interferometer optical waveguide 2 is 250 μm. It is. The length of the modulated light incident optical waveguide 3 connected to a part of the interferometer is 100 μm.

The above elements were cooled with liquid helium, and each wavelength was
707 nm, 542 nm, 430 nm R incident light 21, G incident light 22, B
The incident light 23 enters the interferometer optical waveguide 2. Then, each incident light resonates with the corresponding quantum well exciton, and R
It propagates as a polariton of a band, a G band, and a B band. Here, the wavelengths of the modulated light incident optical waveguides 3 are 707 nm and 54 nm, respectively.
When the R, G, and B lights of 2 nm and 430 nm are incident as modulated lights 41, 42, and 43, respectively, the interference condition changes because the phase of the resonating polariton changes, and the outgoing light 31 of the R, G, and B light changes. , 32,33 change in intensity. Therefore, by selecting the R, G, and B components incident as modulated light, the emitted light can be obtained as modulated light of any color.

FIG. 2 is a block diagram showing the configuration of the entire optical system including the optical element. In the figure, 50 is an input light source that emits three primary colors of red (R), green (G), and red (R) light, and 51 is an optical element according to the present invention. 52 is a light source for modulation,
The configuration is the same as that of the input light source 50, except that the R, G, and B components can be selected. The light emitted from the input light source 50 is guided to the optical fiber 53 and enters the optical element 51 as incident light. On the other hand, the light emitted from the light source 52 for modulation is
The light is guided to 54, enters the optical element 51 as modulated light, and performs the above-described modulation. The light emitted from the optical element 51 is guided to an optical fiber 55 and enters a wavelength resolving prism 56,
Here, the light is divided into R, G, and B lights, and the R detector 61,
It is detected by a G detector 62 and a B detector 63.

Example 2: This example is an example in which two optical waveguides optically coupled to each other are extracted, and a specific component is extracted from R, G, and B light components, and an optical element that performs image processing and the like is manufactured. It is.

At low temperatures, the exciton state in the quantum well is stable and there is no disturbance due to thermal oscillations, so the interaction between the quantum well exciton and light increases, and the refractive index of the quantum well becomes more than 10 times that of air . The interaction between the quantum well exciton having a large confinement effect and light at liquid helium temperature, which is the object of the present invention, is exactly the condition for realizing such a huge refractive index, and therefore, the width of the optical waveguide is large. And 100nm,
It can be reduced to nanometer size less than one-fifth of the wavelength of light in air.

FIG. 3A shows the appearance of an optical device having an optical waveguide having a width of nanometer size and performing image processing and the like according to the present embodiment. As in the first embodiment, a semi-insulating GaAs wafer was used as the substrate 101, and crystal growth was performed under exactly the same conditions as in the first embodiment. Next, after resist exposure by electron beam lithography, dry etching was performed to form an optical waveguide 102 having a width of 100 nm and two curved portions and an optical waveguide 103 also having a width of 100 nm and one curved portion. As shown in FIG. 2 (a), the optical waveguides 102 and 103 are partially close to each other, and the distance between the optical waveguides in that region is 50 nm. here,
The optical waveguide 102 is called an input optical waveguide, and the optical waveguide 103 is called an extraction optical waveguide. Also, as shown in FIG. 3B, a 500 nm aluminum film is applied so that the reference light 110 is irradiated only on the side of the input optical waveguide 102 near the input optical waveguide 102 and the takeout optical waveguide 103. After deposition of 119, a reference light irradiation window 120 was formed by ion milling.

Hereinafter, the operation will be described. The input light 107 is incident on the input optical waveguide 102 by the spherical fiber 104. First, consider a case where light that resonates with an R-band exciton is input as input light. The input light becomes R-band polariton and propagates through the optical waveguide. Since the input optical waveguide 102 has a refractive index of 10 or more,
It propagates stably even in an optical waveguide with a nanometer width. In this case, even if there is a portion where the extraction optical waveguide 103 is close, the exudation of the electric field from the input optical waveguide 102 is extremely small, so that the transfer of polaritons to the extraction optical waveguide 103 does not occur. Therefore, the output light 108 from the input optical waveguide 102 is emitted, but the output light 109 from the extraction optical waveguide 103 is not emitted. However, when the coupling region between the two optical waveguides, that is, the input optical waveguide 102 in the approaching portion, is irradiated with R light having the same wavelength as the input light as the reference light 110, the refractive index decreases due to exciton scattering. Wave path 10
The seepage of the electric field from 2 increases, and the optical waveguide for extraction 1
Shift of R-band polaritons to 03 occurs. In this case,
Output light 109 from the extraction optical waveguide 103 is observed.

Next, a description will be given of an example in which utilization of the integrated optical elements described above for image processing is attempted. First, six of the above optical elements are integrated on one substrate, and each optical element is placed in order from top to bottom.
Numbered from to 6. Next, the same thing is produced in six substrates, and each substrate is numbered from I to VI. Then, the input light 107 is made incident by the spherical fiber 104, and the output lights 108 and 109 are extracted by the spherical fibers 105 and 106. Further, an optical demultiplexer (not shown) is connected to the fiber for guiding the input light 107 and the reference 110, and a monitor fiber is attached. The monitoring fibers were classified by number for each substrate and each element, and arranged in a matrix. This is shown in FIG. In the figure, each circle corresponds to a light spot from the fiber. As a test pattern, each input light 107 has a pattern similar to the input light pattern shown in FIG.
R light on optical elements 1 and 2 on all substrates, G on optical elements 3 and 4 on all substrates
B light is used for light and optical elements 5 and 6 on all substrates. On the other hand, as a test pattern of the reference light, as shown in FIG.
R light is used for the all-optical elements of the substrates I and II, G light is used for the all-optical elements of the substrates III and IV, and B light is used for the all-optical elements of the substrates V and VI. At this time, if the pattern of the output light 109 from the extraction optical waveguide 103 is shown as a light spot array from the spherical fiber 106, it becomes the output light spot array 123 in FIG. 4C. At this time, only when the wavelengths of the input light 107 and the reference light 110 match, the extraction optical waveguide 103 is extracted from the input optical waveguide 102.
The input light pattern 12
Considering that the output light 109 is emitted only when 1 and the reference light pattern 122 overlap, the output light spot array 12
The pattern of 3 is understandable. On the other hand, the pattern of the output light 108 from the input optical waveguide 102 becomes the output light spot array 124 in FIG. Here, the intensity of the output light corresponding to the polariton that has moved to the extraction optical waveguide 103 decreases, and the intensity of the other output light relatively increases.

In the above description, it is assumed that monochromatic light of R, G, or B is input to each optical element as a test pattern. However, mixed light of R, G, and B is actually incident, and the input image is a reference image. And the remaining part can be extracted. In the above description, the case where six elements are integrated is described. However, the number of pixels can be increased by increasing the degree of integration of the elements on the substrate. For example, considering a width of 1 mm and arranging each element at an interval of 1 μm, 1000 elements can be integrated. Then, if ten substrates on which 1000 are integrated are used, image processing of 100 × 100 pixels in vertical and horizontal directions can be performed.

Embodiment 3 A third embodiment of the present invention will be described with reference to FIG. In this embodiment, in order to further confine polaritons in a nanometer-sized optical waveguide, each quantum well layer in the first embodiment is processed into a fine line shape by electron beam lithography and dry etching. It also aims to enhance the confinement of polaritons. In the figure, 131 is a substrate, 1
32 is a 19.81 GaAs quantum well thin wire, 133 is a 11.3Å GaAs quantum well thin wire, 134 is an 8.5Å GaAs quantum well thin wire, and 135 is a cladding layer. The width of the fine wire is 40 nm, and the width of the optical waveguide including the cladding is 50 nm. According to this embodiment, the size of the optical element can be further reduced. When the characteristics of a single device were evaluated, results equivalent to those of the device used in Example 2 were obtained.

Embodiment 4: In the optical device described above, the optical waveguide is thin and the incident end is narrow, so that the light incident efficiency is only about 10%. Therefore, in this embodiment, as shown in FIG. 6, a fan-shaped narrowing portion 142 is provided on the end surface of the nanometer optical waveguide 141. Here, the width of the end face of the narrowed portion is 1 μm, and the length of the narrowed portion is 10 μm. According to this embodiment, the incident efficiency is 50%
Or more.

Embodiment 5: A fifth embodiment of the present invention will be described with reference to FIG. In this embodiment, as shown in FIG. 7, in order to make the reference light 110 incident, an element is constructed by newly connecting the reference light incident optical waveguide 151 to the input optical waveguide 102. Is the same as in the second embodiment. Also in this example, as a characteristic of a single element, a result equivalent to that of the element used in Example 2 was obtained.

In this embodiment, the reference light is incident. However, even when the modulated light is incident, the same effect can be obtained with the completely same configuration.

〔The invention's effect〕

According to the present invention, light modulation can be performed in parallel with a single optical waveguide using three primary colors of light as basic wavelength components, or image processing can be performed with natural colors, and the characteristics of high integration and low input operation can be achieved. Can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a wavelength division multiplexing optical element for performing optical modulation according to a first embodiment of the present invention, FIG. 2 is a block diagram showing an entire configuration of an optical system including the optical element of the embodiment, FIG. FIG. 4 is an explanatory view of a wavelength multiplexing optical element for performing image processing and the like according to a second embodiment of the present invention. FIG. 4 is an explanatory view of image processing by the optical element. FIG. 5 is a third embodiment of the present invention. FIG. 6 is a cross-sectional view of an optical waveguide including a semiconductor thin film layer processed into a quantum wire in the example, FIG. 6 is an explanatory view of a fourth embodiment of the present invention, and FIG.
FIG. 4 is an explanatory diagram of the embodiment. DESCRIPTION OF SYMBOLS 1 ... substrate 2 ... interferometer optical waveguide 3 ... modulated light incidence optical waveguide 4 ... cladding layer 5 ... 19.8Å GaAs quantum well layer 6… 11.3Å GaAs quantum well layer 7… 8.5Å GaAs quantum well layer 8… Barrier layers 21, 22, 23 ... incident light 31, 32, 33 ... outgoing light 41, 42, 43 ... modulated light 50 ... input light source, 51 ... optical element 52 ... modulation light source, 56 ... prism 53, 54, 55 ... optical fibers 61,62,63 ... detector 101 ... substrate, 102 ... input optical waveguide 103 ... extraction optical waveguides 104,105,106 ... spherical fiber 107 ... input light, 108,109 ... output light 110 ... reference light, 131 ... substrate 132 … 19.8Å GaAs quantum well thin wire 133… 11.3Å GaAs quantum well thin wire 134… 8.5Å GaAs quantum well thin wire 135… cladding layer 141… nanometer optical waveguide 142… narrowed part 151… reference light incidence optical waveguide

Claims (5)

(57) [Claims] 1. A semiconductor device comprising: a plurality of quantum well layers comprising a semiconductor having a band gap in the near infrared region; and a barrier layer comprising a semiconductor having a band gap in the near ultraviolet region joined to both sides of the quantum well layer. An optical waveguide extending from the light incident portion to the light emitting portion, and a light irradiating portion for irradiating the optical waveguide with light between the light incident portion and the light emitting portion; A wavelength-division multiplexing optical element, wherein layers have different thicknesses. 2. The optical waveguide according to claim 1, wherein the optical waveguide branches into a first optical waveguide and a second optical waveguide between the light incident portion and the light emitting portion and then joins the first and second optical waveguides. The wavelength division multiplexing optical element according to claim 1, wherein the wavelength multiplexing optical element is provided so as to irradiate light to a wave path. 3. A separate optical waveguide is provided on the side of the optical waveguide to be irradiated with light so that electromagnetic coupling is generated in the optical waveguide at a position where the light irradiating section is arranged. 2. The wavelength division multiplexing optical device according to claim 1, wherein: 4. An optical waveguide having a structure in which a plurality of quantum well layers having different thicknesses from each other are sandwiched by barrier layers having a band gap larger than that of the quantum well layer, and a first light is applied to the optical waveguide. Means for injecting, and means for injecting the second light for modulating the first light into the optical waveguide, wherein one of the plurality of quantum well layers includes the first light and the second light. 2. A wavelength division multiplexing optical system having an exciton level of energy corresponding to a wavelength component contained in the second light. 5. A first light including a wavelength component corresponding to the energy of an exciton level is propagated through a first optical waveguide layer formed by stacking a plurality of quantum well layers having different exciton levels, By irradiating the optical waveguide layer with a second light having a wavelength component that resonates with at least one of the exciton levels and having the same wavelength as the first light, the phase of the first light or A light modulation method comprising changing a refractive index of the quantum well layer.