JPS58190921A - Optical demultiplex element - Google Patents

Abstract

PURPOSE:To vary the wavelength of the light which should be divided, by forming an optical waveguide on a substrate with a material which can vary reversibly its refractive index and then writing a diffraction grating by a double luminous flux interference method or an optical beam scanning method. CONSTITUTION:An otical waveguide 2 using single crystals of BSO and BGO is formed on a substrate 1. Transparent electrodes 3 and 3 are formed by vapor deposition on both end surfaces of the substrate 1 and the waveguide 2 respectively. Then the DC voltage is impressed to the electrodes 3 and 3 from a power supply 4 via a switch 5. Both BSO and BGO show an electro-optical effect only when a DC field exists and produces the photosensitivity. The diameter is enlarged for two lumnous fluxes given from a laser, and these luminous fluxes are irradiated to the waveguide 2 of an electro-optical material with equal incident angle phi. An interference is given to the two luminous fluxes when an electric field exists to generate a change of refractive index in response to the interference fringes. The change of the refracive index corresponds to the interference fringes. When the space between gratings is set as (d), only lambda1 is diffracted for mlambda1=2nd cosQ (Q: incident angle of waveguide light 8 and m: number of order).

Description

[Detailed description of the invention] The present invention relates to a reversible optical demultiplexing device.

Optical wavelength division multiplexing (WDM), which simultaneously transmits multiple light waves with different wavelengths through a single optical fiber, is currently in the 1. It is being extensively researched.

An optical demultiplexing element is an element for extracting light of a certain wavelength λ from a multiplexed optical signal.

It is one of the elements that plays an important role in optical wavelength division multiplexing communication systems.

Currently, the demultiplexing elements that are in practical use are three-dimensional structures such as diffraction gratings and multilayer filters.

FIG. 11 is a sectional view showing an example of a known diffraction grating type demultiplexing element.

This demultiplexing element houses a diffraction grating 3 in a box-shaped casing 30, receives light from an optical fiber 32 containing light of wavelength λl and light of wavelength formula 2, and receives light from an optical fiber 32 containing light of wavelength λl and light of wavelength formula 2. , by diffracting the light with the wavelength λ1 and the light with the wavelength λ2 in different directions. Light having wavelengths λl and λ2 can be extracted from the light exits 33 and 34 provided at positions corresponding to predetermined diffraction angles.

FIG. 12 is a sectional view showing an example of a known multilayer filter type demultiplexing element.

It is a three-dimensional demultiplexing element in which a multilayer filter 35 is housed in a box-shaped casing 30. Light incident from the optical fiber 32 is separated by the multilayer filter 35 into light with a wavelength λl,
It is divided into λ2 light. A multilayer film is made by stacking many dielectric thin films with different refractive indexes, and the reflected light from the boundary surfaces interferes with each other. Light of a specific wavelength can be almost 100% reflected, and conversely, light of a specific wavelength can be transmitted almost 100%.

These demultiplexing elements are three-dimensional, three-dimensional, and large-sized elements. A smaller element is desirable.

Aiming at miniaturization, a two-dimensional waveguide-type demultiplexing element was proposed. This is considered promising because it is small and stable.
There is a lot of research and development going on.

FIG. 13 is a perspective view of a known waveguide type demultiplexing element.

The waveguide-type demultiplexing element 36 is a diffraction grating 39 in which periodic irregularities are formed on a photosensitive material 38 on a substrate 37 using, for example, a photosensitive material 37 technique.

A two-dimensional waveguide 40 having a shape that penetrates or bends through the diffraction grating 39 is provided, and the wavelength is λ1. λ2, 1
1. [Suppose that a wave of P is introduced from an optical fiber. Only the light of wavelength λ2 that satisfies the Bragg condition is diffracted by the diffraction grating, and the remaining light travels straight.

The waveguide-type demultiplexing element has the waveguide and the diffraction grating on the same east plane and is two-dimensional, so it can be made into a small element.

There are several methods for creating a diffraction grating on a plane that includes a waveguide, such as three-beam interferometry and optical beam scanning.

FIG. 14 is a schematic diagram of the optical system configuration of the two-dimensional beam interference method.

The light from the laser 41 is divided into two beams a and b by a half mirror 42 and expanded by collimators 43 and 43 to form parallel beams with a wide beam diameter. The substrate 3
The light enters the photosensitive material 38 on the photosensitive material 7 from the left and right sides at the same angle of incidence φ.

Since the two beams a and l) are coherent laser beams,
Creates interference fringes on the surface of the substrate. The interval d between the interference fringes is given by 2 sinφ (1). The exposed photosensitive material is developed and IF sinusoidal irregularities are created to form a diffraction grating.

FIG. 15 is a schematic diagram of the optical system configuration of the light beam scanning method. The laser beam 45 is focused by a lens 46 and onto the photosensitive material 38.
Scanning is performed to draw parallel grid lines 47.

A laser beam is scanned to draw grating lines one by one, forming a diffraction grating.

The three-beam interferometry and the light beam scanning method are known methods for optically producing a diffraction grating.

The waveguide type demultiplexing element 3G shown in FIG. 13 can be manufactured by such an optical method and is a promising element, or the wavelength of the light to be split is fixed. Since the grating spacing of the diffraction grating is fixed, the wavelength that satisfies Bragg's diffraction conditions is defined in advance.

If there is a demultiplexing element that allows you to freely select the limb length to be demultiplexed,
More useful.

If the wavelength can be selected freely, there is no need to fabricate many types of diffraction gratings for each wavelength. Furthermore, if the selected wavelength can be changed instantly, it can also function as an optical switch.

The object of the present invention is thus to provide a demultiplexing element that can vary the wavelength of light to be demultiplexed.

According to the present invention, a waveguide type demultiplexing element is manufactured using a reversible photosensitive material.

Certain electro-optic crystals, amorphous semiconductors, and thermoplastic devices can have their refractive index changed by an electric field. The change in refractive index is reversible, and it returns to its original state when heat is applied. Can be used over and over again.

Bix2Si02o (Bismuth silicon oxide,
Bso element) single crystal, Bi 1zGeo2o (abbreviated as Bso element)
A single crystal (77° germanium oxide, abbreviated as BGO element) exhibits an electro-optic effect when a DC voltage is applied in a certain direction, and when irradiated with light waves, it produces a refraction change according to the light waves. . There is no photosensitivity when there is no DC electric field.

When a DC electric field is applied, light waves are transmitted to the BSO element, BG
When the O element is irradiated, its refractive index changes, but this change in refractive index is memorized for a relatively long time if kept in a dark state. When the light wave is irradiated again, the previous change in the refractive index is erased, and a change in the refractive index corresponding to the new irradiation light occurs.

When an amorphous semiconductor (chalcogenide glass) based on Se or S is irradiated with light waves, the refractive index changes depending on the electric field of the light waves. It is therefore possible to write diffraction gratings into amorphous semiconductors by optical methods. The written refractive index distribution can be erased by heating.

It is known that a thermoplastic element can become a reversible optical recording element by being combined with a photoconductive material.

6 to 10 are cross sections IZ+ showing the optical recording process of the thermoplastic element.

Thermoplastics have the property of softening and exhibiting plasticity when heated, and solidifying when cooled.

In FIG. 6, a thermoplastic element in which photoconductive material B is combined with the back surface of thermoplastic A is charged by corona discharge.

In FIG. 7, the thermoplastic is irradiated with light C. During this exposure process, the portion of the photoconductive material B that receives the light C becomes a conductor, and negative charges move to the back surface of the thermoplastic A.

FIG. 8 shows the recharging process. Positive and negative charges are added to the front side of thermoplastic A and the back side of photoconductive material B.

When heated in this state, the thermoplastic softens. The positive and negative charges between the front and back surfaces of thermoplastic A exert electrostatic attraction to each other, causing plastic deformation of the thermoplastic. FIG. 9 shows the state after heat development. Roughness is formed on the thermoplastic surface depending on the intensity of the irradiated light. Upon cooling, this unevenness is retained.

When reheated, it returns to its original uniform thickness as shown in Figure 10.

Using an optical recording element that allows writing and erasing in this way,
It is possible to create a demultiplexing element that can freely select the wavelength of light.

Below, the structure, operation, and effects of the present invention will be explained with reference to drawings showing embodiments.

FIG. 1 is a perspective view of a branching element according to an embodiment using an electro-optic crystal as a waveguide.

A waveguide 2 made of an electro-optic material is formed on the substrate 1. The electro-optic material waveguide 2 is, for example, the above-mentioned BSO,
BGO single crystal, etc.

Transparent electrodes 3.3 are provided on both end faces of the substrate 1 and the electro-optic material waveguide 2 by vapor deposition or the like. The transparent electrode 3 is A
u thin film, I n 203, etc.

The DC power supply 4 connects the transparent electrodes 3 on both end faces via the switch 5.
．． Apply DC voltage to 3. BSO, BCO elements have an electro-optical effect only in the presence of a DC electric field and do not exhibit photosensitivity in the absence of a DC electric field.

Two light beams emitted from the same laser are expanded in diameter and irradiated onto the electro-optic material waveguide 2 at the same incident angle φ. This is exposure using the three-beam interferometry described above.

When the wavelength of the exposure laser beam is λ, the interval between interference fringes created by irradiating the three beams is given by equation (1).

When the switch 5 is closed and a DC electric field is applied to the electro-optic material waveguide 2, when the three beams irradiate the waveguide 2, a change in the refractive index corresponding to the interference fringes appears on the waveguide 2. It happens. Since the refractive index change corresponds to parallel, equally spaced interference fringes, it functions as a diffraction grating 7.

When the grating spacing of the diffraction grating is d, only light with a wavelength λl that satisfies the formula (2) is diffracted. 0 is the incident angle of the guided light 8, defined as an included angle between a line perpendicular to the grating line of the diffraction grating 7 and the optical axis of the guided light.

n is the refractive index of the waveguide for guided light. m is an integer indicating the order of diffraction.

The guided light 8 has a wavelength λ1. λ2. It is assumed that light of λ3 is included. Among these, if λl satisfies equation (2), only the light of wavelength λ1 is diffracted by the diffraction grating 7. In this example, the diffracted light 9 is extracted from a certain surface of the transparent electrode 3. The remaining λ2. Since the light of λ3 does not satisfy equation (2), it is not diffracted.

Go straight through the diffraction grating 7.

In this way, only the light of wavelength λ1 can be separated from the guided light of (λ1+λ2+λ3).

If it is necessary to change the wavelength λ1 of the diffracted light, it is better to change the grating spacing d of the diffraction grating 7. To this end, it is best to change the incident angle φ of the exposure light beam 6.6 or change the length of the exposure laser.

If φ or λ is changed and λ2 satisfies equation (2), then out of the guided light of (λ1+λ2+λ3), λ
You will be able to split the waves.

In this way, by appropriately changing φ and λ while applying a DC electric field, it is possible to make only light of a given wavelength conform to equation (2), and to extract only light of this wavelength.

As long as the DC electric field continues to be applied, the diffraction grating 7 is recorded and remains on the electro-optic material waveguide 2 even if the irradiation of the exposure light beam 6.6 is simultaneously stopped. Guided light λ
1+λ2+... is usually longer than the wavelength of the exposure laser, and the electro-optic effect is also small. This is to prevent the diffraction grating 7 from being erased by the guided light.

Even if a DC electric field is continuously applied, among the three luminous fluxes,
If one of the light beams is cut off and the waveguide 2 is irradiated with only the light beam, the diffraction grating 7 will disappear.

- Electro-optic material waveguide 2, which causes interference due to the large luminous flux
This is because standing waves due to the three beams are no longer formed on the surface of .

The diffraction grating 7 can also be eliminated by removing the DC electric field.

FIG. 2 is a perspective view of the state in which the diffraction grating has disappeared.

Is switch 5 turned off and no electric field is applied?
Alternatively, when only one beam is illuminating the waveguide, no grating is present. The guided light 8 passes through as it is. There is no demultiplexing function.

Since the diffraction grating can be instantaneously formed or destroyed, it can also be used as an optical switch for the diffracted light λ1.

An amorphous semiconductor (chalcogenide glass) can also be used as the electro-optic material waveguide 2. As a chalcogenide amorphous semiconductor, (1) As −
S-based systems (2) As-S-Ge-based systems (3) As-S-Se-Ge systems have electro-optical effects, so diffraction gratings can be reversibly produced using a similar method. .

The writing uses the three-beam interference method and the light beam scanning method, as in the case of making conventional irreversible waveguide type diffraction gratings.

The refractive index changes depending on the light, and this becomes a diffraction grating.

This is memorized, but can be erased by heating.

As shown in FIG. 3, erasing is performed by uniformly irradiating an infrared lamp 13 to erase the diffraction grating on the electro-optic material waveguide 2 made of an amorphous semiconductor.

Further, FIG. 4 shows a configuration for erasing by Joule heat. A resistive layer 15 is provided between the substrate 1 and the amorphous semiconductor waveguide, and when electricity is applied to it, Joule heat is generated and the written diffraction grating is erased. The resistance layer 15 is connected to a power source 16 and a switch 17.

Thermoplastic elements can be used as waveguides. As already explained, this material softens and becomes plastic when heated, and solidifies when cooled.

There is no electro-optic effect and no refractive index distribution is generated by light waves. However, when combined with a photoconductive element, charged and exposed to light, irregularities appear on the thermoplastic surface depending on the energy of the light. This can be used as a diffraction grating. As in the previous two examples, writing can only be done by the three-beam interferometry or the light beam scanning method.

FIG. 5 is a sectional view showing an example of a wavelength splitting element using a thermoplastic material.

Thermoplastic material 23 is further layered.

In addition, an electrode for corona discharge is provided above, and a sixth electrode is provided above.
Processes such as charging, exposure, recharging and heating as shown in FIGS. 10 to 10 are performed.

For heating, the conductor waveguide 21 may be energized to generate Joule heat.

According to the present invention, a reversible demultiplexing element can be manufactured using a diffraction grating that can be written and erased using light.

Since the wavelength of the light to be selected is made variable, it has a wide range of applications in optical wavelength division multiplexing communication systems.

Furthermore, since a diffraction grating can be instantly erased or formed, it can also be used as an optical switching element.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a demultiplexing element according to an embodiment of the present invention.
This figure shows a state in which a diffraction grating is generated on an electro-optic material waveguide using three-beam interferometry. FIG. 2 is a perspective view of the same demultiplexing element, showing a state in which one of the light beams is absent and the diffraction grating is erased. FIG. 3 is a cross-sectional view showing a configuration in which a diffraction grating is created on the waveguide using an amorphous semiconductor by three-beam interferometry and is erased by irradiation with an infrared lamp. FIG. 4 is a sectional view showing a configuration in which a diffraction grating is created on the waveguide using an amorphous semiconductor as a waveguide by three-beam interference method, and the grating is heated and erased by passing current through a resistor. FIG. 5 is a cross-sectional view of an embodiment of the splitting element of the present invention made of thermoplastic material. FIG. 6 is a cross-sectional view showing the charging process of an element combining photoconductive material and thermoplastic. FIG. 7 is a sectional view showing the exposure process of the same thing. FIG. 8 is a sectional view showing the recharging process of the same material. FIG. 9 is a sectional view showing the heat development process of the same product. FIG. 10 is a sectional view showing the same state after heating and erasing. FIG. 11 is a sectional view of a known diffraction grating type demultiplexing element. FIG. 12 is a sectional view of a known multilayer filter type demultiplexing element. FIG. 13 is a perspective view of a known waveguide type demultiplexing element. FIG. 14 is a configuration diagram of an optical system for exposure using three-beam interference method. FIG. 15 is an optical system configuration diagram showing the diffraction grating manufacturing process using the light beam scanning method. 1... Substrate 2... Electro-optic material waveguide 3... Transparent electrode 4... DC power supply 5... Switch 6... ...Light beam for exposure 7...Diffraction grating 8...Guided light 9...Diffracted light 10...Transmitted light 13... ... Infrared lamp 15 ... Resistance layer 20 ... Substrate 21 ... Conductor waveguide 22 ... Photoconductive thin film 23 ... Thermoplastic material Inventors: Yu Nishiwaki, Haru Kazumatsu, Kenji Moto, Patent applicant: Sumitomo Electric Industries, Ltd. Figure 1 Figure 2 Figure 3 Figure 5 Figure 10 Figure 11 Figure 12 Figure 13 Figure 6 Figure δ figure

Claims (6)

[Claims] (1) A waveguide that guides light in a plane is formed on the substrate using a material that can reversely change the refractive index i1 by light irradiation, and the waveguide is 1. A splitting element characterized in that a diffraction path T is written or erased in the wavelength division element. (2) The demultiplexing element according to claim (1), wherein the material of the waveguide is an electro-optic crystal. (3) The splitting element according to claim 2, wherein the electro-optic crystal is B112SiOzo (bismuth silicon oxide) or Bir2GeOzo (bismuth germanium oxide). (4) The splitting element according to claim (1), wherein the material of the waveguide is an amorphous semiconductor. (5) Amorphous semiconductors include As-5 series, As-
Force/l of S-Ge system, As-S-Se-Ge system
/ The branching element according to claim (4), which is D genide glass. (6) The demultiplexing element according to claim (1), wherein the material of the waveguide is thermoplastic.