JP5691034B2 - Waveguide type optical protection device and waveguide type optical protection device - Google Patents

Description

  The present invention relates to a waveguide-type optical protection element and a waveguide-type optical protection device, and, for example, relates to a configuration for improving the sensitivity of a waveguide-type optical protection device for a waveguide-type optical circuit.

  In recent years, with the progress of optical communication systems, the capacity of optical communication networks has been increased, and optical devices having various functions have been developed accordingly. In particular, in an optical network that uses a semiconductor optical amplifier, the optical signal suddenly changes after the average optical signal input power to the semiconductor optical amplifier continues to be very low in operations such as switching an optical switch or instantaneous interruption of the device. When the power increases, an optical surge is generated, and the receiving circuit connected in the subsequent stage is damaged by the optical surge.

  Therefore, the circuit design or the like has been devised so as not to generate a large optical surge, but the conventional optical surge suppression method has a problem that the optical communication apparatus is increased in size or complexity and is expensive. In some cases, the optical surge cannot be sufficiently suppressed in terms of speed.

  Therefore, it has been proposed that an optical limiter circuit or an optical limiter element is provided in front of the light receiving element to reduce damage to the receiving circuit due to an optical surge. As a conventional optical limiter circuit, an optical limiter circuit using a nonlinear etalon in which an optical nonlinear material is inserted in an optical resonator or a nonlinear element in which a saturable absorber is inserted in an asymmetric Fabry-Perot resonator has been proposed. Yes.

  However, since these elements have a planar configuration and are difficult to integrate into various optical circuits composed of waveguides, optical limiter circuits using Mach-Zehnder interference waveguides have been proposed. (For example, refer to Patent Document 1).

  FIG. 5 is a conceptual configuration diagram of an optical limiter circuit using a conventional Mach-Zehnder type interference waveguide. The optical input waveguide 201 and an optical branching waveguide 202 that branches an optical signal input to the optical input waveguide 201 are shown in FIG. The first arm waveguide 203 and the second arm waveguide 204 connected in parallel to the optical branching waveguide 202, and the optical coupling waveguide 205 connected to the output ends of the first arm waveguide 203 and the second arm waveguide 204. The optical output waveguide 206 is connected to the optical coupling wave waveguide 205 and outputs an optical signal.

  This Mach-Zehnder type interference waveguide is formed by sequentially forming an InP lower cladding layer, an InGaAsP core layer, and an InP upper cladding layer on an InP substrate and etching them into a predetermined shape. Here, the absorption coefficient is increased in the first arm waveguide 203 by impurity doping or the like, and the respective absorption coefficients are set so that a difference occurs in the absorption coefficient between the first arm waveguide 203 and the second arm waveguide 204.

  Further, by adjusting the branching ratio of the optical branching waveguide 202 and the lengths of the first arm waveguide 203 and the second arm waveguide 204, the first arm waveguide 203 and the second arm waveguide are reduced when the optical input is weak. The light intensity immediately before the waveguide 204 is coupled to the optical coupling waveguide 205 is made equal and in phase.

When the optical circuit is configured in this way and the optical input power is increased, only the temperature of the first arm waveguide 203 is locally increased by light absorption. Since a semiconductor generally has a large thermo-optic coefficient of about 10 ⁻⁴ K ⁻¹ , if the first arm waveguide 203 has a length of about 1 mm, the light phase shifts by about π with a temperature increase of about 10 ° C. To do.

  In the Mach-Zehnder type interference waveguide, the coupling efficiency to the optical output waveguide 206 decreases unless the phases of the light from the first arm waveguide 203 and the second arm waveguide 204 are in phase immediately before the optical coupling waveguide 205. . Therefore, the output power of the transmitted output light increases in proportion to the incident power in the region where the incident power is low, but the limiter type light input / output characteristics that the output power is relatively suppressed when the incident power exceeds the predetermined intensity Therefore, it has a function of an optical protection circuit.

JP 2009-2222796 A

  However, since the effect of increasing the absorption coefficient by heat is small, it is insufficient as a highly sensitive photoprotection circuit. Therefore, it can be considered that the first arm waveguide 203 is made of an optical nonlinear material. Since the refractive index of the nonlinear material changes according to the light intensity, the phase difference when the light propagated through the two waveguides of the first arm waveguide 203 and the second arm waveguide 204 is combined is the light intensity. As a result, the transmittance depends on the light intensity.

  Therefore, nonlinear input / output characteristics can be obtained by setting the branching ratio of the optical branching waveguide 202 to an appropriate value and adjusting the initial phase difference between the waveguides. FIG. 6 is a light input / output characteristic diagram. When high-intensity light of a certain level or more is incident, the light output is attenuated due to a decrease in transmittance, and functions as a light protection circuit.

  However, even in this case, since there is no material having a large optical nonlinearity, there is a problem that the light intensity required for lowering the transmittance is high, which is insufficient as a protective circuit for a highly sensitive optical circuit. Furthermore, the Mach-Zehnder type interference waveguide requires a high accuracy when forming the two arm waveguides, and has a problem that the planar size becomes large.

  Therefore, an object of the present invention is to realize a highly sensitive optical protection function with a simple and small configuration without using the light intensity dependency of the refractive index change of the waveguide itself.

To solve the above problem,
(1) According to the present invention, in the waveguide type optical protection element, an input waveguide, a waveguide on which a phase change material film is laminated, and an output waveguide are connected in series, and a part of the phase change material film There is a crystal phase, Ri remain amorphous phase der, the phase change material film is made of a material having absorptive to guided light guided through the waveguide in a state of crystalline phase, and the guided wave It has a light protection function of blocking the guided wave of the guided light to the output waveguide when the light intensity of the light exceeds a preset threshold value .

  In this way, by providing a waveguide in which a phase-change material film partly in a crystalline phase is laminated between the input waveguide and the output waveguide, a highly sensitive optical protection function with a simple and small configuration Can be realized. That is, since the portion that has become the crystal phase becomes the nucleus of the phase change, even if a light pulse with a weak light intensity is input, the phase changes from the amorphous phase to the crystalline phase, thereby realizing a highly sensitive light protection function.

(2) Regarding the above (1), by controlling the ratio of the crystal phase of said phase change material film, and controlling said threshold. Since the phase change threshold value in which the crystal phase portion becomes a nucleus depends on the ratio of the crystal phase in the phase change material film, the light protection threshold value is controlled by the ratio of the crystal phase in the phase change material film. It becomes possible.

  (3) Further, in the above (2), the present invention provides that the ratio of the crystal phase in the phase change material film is 0.1% to 10.0% of the whole phase change material film by volume ratio. It is characterized by being. If it is less than 0.1%, the light intensity for causing a phase change is increased, so that the sensitivity is lowered. On the other hand, if it exceeds 10.0%, loss is large and malfunction is likely to occur.

  (4) Moreover, the present invention is characterized in that, in any one of the above (1) to (3), the thickness of the phase change material film is 10 nm to 100 nm. If it is less than 10 nm, even if the entire phase change material film is crystallized, it is insufficient to effectively absorb the signal light. On the other hand, if it exceeds 100 nm, it is meaningless to make it thicker.

(5) Further, in the waveguide type optical protection circuit device according to the present invention, an input waveguide, a waveguide in which a phase change material film is laminated, and an output waveguide are connected in series, and the phase change material film is part of the crystal phase, Ri remain amorphous phase der, the phase change material film is made of a material having absorptive to guided light guided through the waveguide in a state of crystalline phase, and A waveguide-type optical protection element having an optical protection function for blocking the waveguide of the guided light to the output waveguide when the light intensity of the guided light exceeds a preset threshold, and the phase change material film And a light irradiation means for irradiating light for controlling the crystal state of the phase change material film.

  As described above, the above-mentioned waveguide type optical protection element needs to be returned to the initial state when it is used continuously when the phase is changed to the crystalline phase. It is necessary to provide light irradiation means for irradiating light for controlling the crystal state of the material film.

  (6) Further, in the above (5), the present invention is characterized in that the light irradiation means includes an optical fiber whose position can be adjusted. As described above, when the light irradiating means includes the position-adjustable optical fiber, an optical system for spot irradiation to a minute region and wide area irradiation can be configured by a single optical system.

  According to the disclosed waveguide-type optical protection element and waveguide-type optical protection device, by using a phase change material, a simple and compact configuration can be achieved without using the light intensity dependency of the refractive index change of the waveguide itself. A highly sensitive light protection function can be realized.

It is a notional perspective view of the waveguide type optical protection device of an embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS It is structure explanatory drawing of the waveguide type optical protection element of Example 1 of this invention. It is an optical input-output characteristic figure of the waveguide type optical protection element of Example 1 of this invention. It is a notional block diagram of the waveguide type optical protection apparatus of Example 2 of this invention. It is a conceptual block diagram of the optical limiter circuit using the conventional Mach-Zehnder type | mold interference waveguide. It is an optical input / output characteristic diagram of an optical limiter circuit using a Mach-Zehnder type interference waveguide using an optical nonlinear material.

  Here, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a conceptual perspective view of a waveguide type optical protection apparatus according to an embodiment of the present invention. The waveguide type optical protection device includes a substrate 11, a lower cladding layer 12, a waveguide 13, an upper cladding layer 14, and a phase change material film 15 provided on a part of the top surface of the waveguide 13. One end side of the waveguide 13 becomes the input waveguide 16, the other end side becomes the output waveguide 18, and the phase change material film 15 becomes the light absorbing portion 17.

This length of the optical propagation direction of the phase change material layer 15 is arbitrary, for example, a 2Myuemu～15myuemu, mostly an amorphous phase portion 15 _1, the crystal phase portion 15 ₂ provided on the surface side phase The change material film 15 has a volume of 0.1% to 10.0%. The crystalline phase section 15 ₂ may be a single spot, may be a plurality of spots, the crystal phase section 15 ₂ is the core of the phase change, entering the weak light intensity light pulses, an amorphous phase To a crystalline phase.

When the signal light incident from the input waveguide 16, when the intensity of the signal light is small, since the absorption in the amorphous phase portion 15 ₁ hardly occurs, and transmitted as it is, is output as it is from the output waveguide 18.

On the other hand, when the intensity of the signal light exceeds the threshold, the whole undergoes a phase change to a large crystal phase section 15 ₂ of the absorption coefficient of the light absorbing portion 17 as a nucleus is a crystal phase. Since the crystalline phase has a large absorption coefficient, the transmittance of the waveguide 13 is lowered, and the light to the output waveguide 18 in the subsequent stage is blocked, thereby functioning as a light protection device. In this case, it is possible to adjust the threshold light protection device operates by the shape and volume of the crystal phase portion 15 _2.

When the phase change material film 15 becomes a crystalline phase, it is necessary to return to the initial state. For this purpose, the laser beam irradiation optical system 19 irradiates a pulse laser beam to change the phase to the amorphous phase. For example, pulse laser light with a high intensity of about 1 ns to 100 ns, for example, about 20 ns, for example, about 100 mW is irradiated. Meanwhile, in order to form a crystalline phase 15 ₂ as a phase change of the nucleus surface of the phase change material layer 15, the pulse width of 100Ns～500ns, for example, low intensity of about 500 ns, for example, 10 mW approximately spot pulse Irradiate with laser light. Note that the wavelength of the laser light to be irradiated may be any wavelength that can be absorbed by the phase change material regardless of the state of the phase change material, but normally, 650 nm which is an easily available laser emission wavelength is used.

  In this case, the waveguide 13 is preferably a semiconductor single crystal such as Si, SiGe, InP, GaAs, InGaAsP, InAlAs, InGaAs, GaN, or GaNAs. In selecting the material, it is necessary to select a material having a low absorption rate in the wavelength band of the optical signal. For example, Si or InGaAsP is desirable in the 1.3 μm to 1.55 μm band.

  Also, as a substrate structure, in order to make the waveguide a single crystal core layer, an SOI (Sbmicductor on Insulator) substrate formed by a substrate bonding technique or a lateral seeding method, or a sapphire substrate having high thermal conductivity is used. It is desirable to use a conventional SOS (Silicon on Sapphire) substrate.

Examples of the phase change material constituting the phase change material film 15 include tetrahedral materials such as α-Si, α-Ge, α-GaSb, α-GaAs, α-Sb, GeSe, and Ge-Sb-Te chalcogenides. Phase change type optical discs such as Ni-based materials, Sb-Te based chalcogenite materials, chalcogenide materials such as As ₂ Se ₃ or As ₂ S ₃ , NiO, HfO ₂ , ZrO ₂ , or transition metal oxide materials such as ZnO Proven materials are desirable. In particular, the change in the optical absorption due to the phase change large _{Ge 2 -Sb 2 -Te 5, Ge} 1 -Sb 4 -Te 7, Ge 1 -Sb 2 -Te 4, Ge 6 -Sb 2 -Te 9 etc. A Ge—Sb—Te chalcogenide material is desirable.

  As described above, in the embodiment of the present invention, since the waveguide having the phase-change material thin film partially crystallized is used, an optical protection device having a simple and small configuration and a low threshold power is provided. It becomes possible to configure.

  In addition, an optical system that can control the phase change between the crystal phase and the amorphous phase of the phase change material thin film portion and the size and number of the crystal phase portions is provided to restore the light protection device to the initial state or to protect the light. It is possible to adjust the operation threshold of the apparatus.

  Based on the above, the waveguide type optical protection element according to the first embodiment of the present invention will be described next with reference to FIGS. FIG. 2 is a configuration explanatory view of the waveguide type optical protection element of Example 1 of the present invention, FIG. 2 (a) is a schematic perspective plan view, and FIG. 2 (b) is FIG. 2 (a). It is a schematic sectional drawing in alignment with the surface of the dashed-dotted line in.

As shown in the figure, using a SOI substrate, a 200 nm thick SiO ₂ film formed on the silicon substrate 21 is used as the lower cladding layer 22, and the single crystal silicon layer formed thereon is etched in a stripe shape. For example, the single crystal silicon core layer 23 having a width of 400 nm and a height of 220 nm is formed.

A portion of the surface of the monocrystalline silicon core layer 23, in 30nm thickness by using a mask sputtering method using a metal mask, the light propagation direction length 10μm _Ge 2 _-Sb 2 -Te ₅ of composition A GST film 24 is formed. At this time, the entire GST film 24 is in an amorphous phase.

Next, an SiO ₂ film having a thickness of 1.5 μm is formed on the entire surface at a film forming temperature of 100 ° C. to form the upper clad layer 25. At this time, since the deposition temperature of the upper cladding layer 25 is 100 ° C., the entire GST film 24 remains in an amorphous phase. Note that when the deposition temperature of the upper cladding layer 25 is increased, a crystalline phase is obtained.

Next, by irradiating a pulse laser beam having a spot diameter of 1500 nm, a wavelength of 650 nm, an intensity of 10 mW / μm ² and a pulse width of 500 ns, a part of the GST film 24 is phase-transitioned into the crystal phase, and the crystal phase by a part 24 _2, optical waveguide protection element 20 of example 1 of the present invention is completed. Incidentally, the remaining portion will remain in the amorphous phase portion 24 _1. Here, one end side of the single crystal silicon core layer 23 becomes the input waveguide 26, the other end side becomes the output waveguide 28, and the portion provided with the GST film 24 becomes the light absorbing portion 27.

Ge ₂ -Sb ₂ -Te ₅ GST film 24 composition, with respect to light having a wavelength of 1.3μm~1.65μm utilized in optical communication, large absorption in the crystal phase, absorption in the amorphous phase The imaginary part k of the complex refractive index is less than 0.1 in the amorphous phase and about 1.0 in the crystal phase. For example, when input light having a wavelength of 1.5 μm is weak, the transmittance is high because most of the GST film 24 is in an amorphous phase.

  FIG. 3 is a light input / output characteristic diagram of the waveguide-type photoprotective element according to Example 1 of the present invention. As is apparent from the comparison of the inclinations of the straight lines in the partial crystal state and the straight line in the entire crystal state, The larger the value, the higher the transmittance.

Thus, although also increases the output power to increase both the incident power, the temperature rise due to light absorption exceeds a certain threshold optical power and in the crystalline phase section 24 ₂ is advanced beyond the crystallization temperature at around, GST film 24 Crystallization proceeds. As the crystallization progresses, the surrounding temperature exceeds the crystallization temperature one after another, and the whole crystallizes, the absorption of the waveguide increases rapidly, and changes to a state showing transmittance on a straight line with a small inclination.

  Since the phase change process from the partial crystal state to the full crystal state progresses in a time of about 1 μs, it is excessive to an optical element such as a light receiving element, a light modulating element, a light deflecting element, or an optical amplifying element in the subsequent stage. Function as a light protection element.

  In order to return the light protection element to the initial state, the entire GST film 24 is amorphized by irradiating the GST film 24 in an all-crystal state with strong laser light, and then the weak laser light is irradiated in a spot shape. As a result, part of the surface of the GST film 24 is crystallized.

Note that when the GST film 24 is not crystallized at all, light absorption in the GST film 24 is small, and unless it is very strong input light, it does not function as a light protection element because it does not change into a crystalline phase. The crystal phase portion 24 ₂ of the size, by changing the number, it is possible to adjust the threshold protection circuit operates.

  Next, with reference to FIG. 4, the waveguide type optical protection apparatus of Example 2 of this invention is demonstrated. FIG. 4 is a conceptual configuration diagram of the waveguide-type photoprotection device according to the second embodiment of the present invention. The waveguide-type photoprotection element 20 according to the first embodiment and a laser beam irradiation optical system that irradiates pulse laser light. 30.

  The laser light irradiation optical system includes an optical fiber 31, a collimating lens 32, and a converging lens 33. The converging lens 33 uses a lens shorter than the focal length of the collimating lens 32. As the optical fiber 31, a circular core, an elliptical core, a fiber composed of a plurality of cores, a photonic crystal fiber, a holey fiber, or the like can be used.

A mode field cross-sectional shape at the end face of the optical fiber 31, by adjusting the fiber end face position, it is possible to adjust the condensing spot shape and number of the vicinity of the crystal phase portion 24 _2. When the entire GST film 24 is in an amorphous phase, the position of the optical fiber 31 is adjusted to reduce the spot on the GST film 24, and the light pulse with a wavelength of 650 nm, an intensity of about 10 mW / μm ^{2 and} a pulse width of about 500 ns is weak. Is partly transformed into a crystalline phase.

When the entire GST film 24 is crystallized by the incidence of a strong optical signal, the position of the optical fiber 31 is adjusted to increase the spot on the GST film 24, and the intensity is about 650 nm, 100 mW / μm ^2. By irradiating with a light pulse having a strong pulse width of about 20 ns, it becomes amorphous, and then a part thereof is crystallized.

  As described above, the second embodiment of the present invention has the laser beam irradiation optical system including the position-adjustable optical fiber. Therefore, by adjusting the position of the optical fiber, the amorphization and the partial crystal can be achieved. Can be switched.

The beam spot size at the time of some crystallization, laser light intensity, by adjusting the pulse width or the like, the position of the crystal phase portion 24 _2, the size, number and can be set arbitrarily, thereby light The threshold value of the protection element can be set arbitrarily.

  In the above description, the case where the GST film is in an amorphous state even after the upper clad layer is formed has been described. However, the GST film may be in a crystalline state by increasing the film formation temperature of the upper clad layer. In this case, in order to cause the entire phase to transition to the amorphous phase in advance, the entire surface is irradiated with intense laser light to cause the entire phase to transition to the amorphous phase. Needless to say, the phase transition between the amorphous phase and the crystalline phase can be achieved by preparing a heater in the vicinity of the GST film and heating only a part or the whole of the heater.

DESCRIPTION OF SYMBOLS 11 Substrate 12 Lower clad layer 13 Waveguide 14 Upper clad layer 15 Phase change material film 15 ₁ Amorphous phase portion 15 ₂ Crystal phase portion 16 Input waveguide 17 Light absorption portion 18 Output waveguide 19 Laser light irradiation optical system 20 Waveguide type Optical protection element 21 Silicon substrate 22 Lower clad layer 23 Single crystal silicon core layer 24 GST film 25 Upper clad layer 24 ₁ Amorphous phase portion 24 ₂ Crystal phase portion 26 Input waveguide 27 Light absorption portion 28 Output waveguide 30 Laser light irradiation optics System 31 Optical fiber 32 Collimating lens 33 Converging lens 201 Optical input waveguide 202 Optical branching waveguide 203 First arm waveguide 204 Second arm waveguide 205 Optical coupling waveguide 206 Optical output waveguide

Claims (6)

An input waveguide;
A waveguide on which a phase change material film is laminated;
The output waveguide is connected in series,
Some of the phase change material film is in the crystalline phase, Ri remain amorphous phase der,
The phase change material film is made of a material that absorbs guided light guided through the waveguide in a crystalline phase, and the light intensity of the guided light exceeds a preset threshold value. A waveguide-type optical protection element characterized by having an optical protection function that blocks the guided light from being guided to an output waveguide . 2. The waveguide type optical protection element according to claim 1, wherein the threshold value is controlled by controlling a ratio of a crystal phase in the phase change material film.   3. The waveguide type according to claim 2, wherein a ratio of a crystal phase in the phase change material film is 0.1% to 10.0% of the whole phase change material film in volume ratio. Light protection element.   4. The waveguide-type photoprotective element according to claim 1, wherein the phase change material film has a thickness of 10 nm to 100 nm. An input waveguide;
A waveguide on which a phase change material film is laminated;
The output waveguide is connected in series,
A partially crystalline phase of the phase change material film, Ri remain amorphous phase der, the phase change material layer has an absorption against guided light guided through the waveguide in a state of crystalline phase A waveguide-type optical protection element made of a material and having an optical protection function for blocking the guided light to the output waveguide when the light intensity of the guided light exceeds a preset threshold ;
A waveguide type optical protection device comprising: a light irradiation means for irradiating the phase change material film with light for controlling a crystal state of the phase change material film.   6. The waveguide type optical protection device according to claim 5, wherein the light irradiation means includes an optical fiber whose position is adjustable.

Images