KR100429225B1 - Thermo-Optical Switch - Google Patents

Abstract

The present invention provides a thermo-optic switch, comprising: a substrate; A lower clad layer formed on the substrate; A core layer formed of silica on the lower clad layer; An upper clad layer formed on the core layer and the lower clad layer; It comprises a heater formed in at least one metal pattern on the upper cladding layer formed on the core layer and the lower cladding layer, it is possible to prevent the deterioration of the core layer by using silica as a core layer and light is well It propagates and forms more silica with a smaller thermo-optic coefficient as the cladding layer, thereby reducing the intensity of distribution of the optical mode to the polymer layer and reducing the light loss due to the low temperature and high temperature.

Description

Thermo-optic Switch {Thermo-Optical Switch}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch, and more particularly, to a thermo-optic switch having a small driving power and having a switching speed of several hundreds of kilowatts or less.

Thermo-optic switch is a device that controls the flow of light by using a change in the refractive index of the material according to the temperature, a device for controlling the light path by adjusting the current flowing by attaching the electrode to a specific portion of the optical waveguide.

The structure of the optical waveguide thermo-optic optical switch element is a Mach-Zehnder interferometer using light interference, and a digital thermo-optic switch using optical evolution (DOS) digital optical switch. , Or Y-type), and a directional coupler.

FIG. 1 shows a digital thermo-optic switch comprising a substrate, an underclad layer 20, a core layer 30, an upper clad layer 40, and a heater 50. FIG. .

The optical waveguide principle using the digital thermo-optic switch is as follows.

When electrodes are formed of metal having excellent thermal conductivity such as gold on each branch waveguide of the optical waveguide, and current flows through one electrode, heat is transferred from the heater 50 to generate heat by resistance. Heat is transferred from the electrode to the waveguide portion, and the waveguide through which the heat is transmitted has a small refractive index, so that light does not propagate.

That is, a difference in refractive index between the two branch waveguides occurs due to heat, whereby light propagates in the waveguide having a large refractive index, and light does not propagate in the waveguide having a small refractive index.

A Mach-Zehnder interferometer or directional coupling thermo-optic switch uses interference phenomena, which induces a difference in refractive index by applying heat to one side between two branched waveguides splitting out of one waveguide to generate a path difference, thereby switching to create an interference phenomenon.

The interferometer structure is sensitive to temperature and has a disadvantage of low crosstalk but low switching power.

On the other hand, the DOS switch has a digital response, which is better in temperature and polarization than the interferometer. In addition, the DOS switch is a Y-branch with a very small branch angle of about 0.1 to 0.15 °. Since the mode evolution characteristic is used, the output characteristics are no longer changed when the temperature of one arm increases and the difference in refractive index between the two arms becomes more than one. There is no digital characteristic.

Therefore, the DOS switch has an advantage of operating irrespective of polarization characteristic even in the presence of birefringence of the optical waveguide. Switching crosstalk can also be easily achieved below -25 dB. However, there is a disadvantage that the switching power is higher than the interferometric switch.

For this reason, interferometric switches are mainly manufactured in silica optical waveguide devices with relatively low thermo-optic coefficients, and DOS-type switches are fabricated in polymer optical waveguides with large thermo-optic coefficients.

In order to implement thermo-optic switches, a material having a large thermo-optic coefficient is used. Therefore, a polymer having a large thermo-optic coefficient is used.

Polymers have ten times more thermo-optic coefficients than silica used in waveguides, making it easy to implement thermo-optic switches.

However, polymers have the advantage of being easy to handle, but polymer-based thermo-optic switches easily degenerate in combination with oxygen when exposed to near-infrared rays used in optical communication bands.

To prevent this, a hermetic packing must be made to make the oxygen free. In addition, the loss caused by the waveguide is larger than that of silica, and birefringent optical polymers are birefringence differently and are separated into two lights because the speed of light is different depending on the polarization characteristics (polarization direction) of the light waves. There is a problem, and it is physically weak.

1 × N switches can be fabricated by cascading 1 × 2 thermo-optic switches. In particular, in the case of 1 × 2 thermo-optic switch, it is mainly used in line distribution (O × C, Optical Cross-Connect) of optical signals when a failure occurs in an optical transmission network.

The thermo-optic switch according to the related art described above has a problem in that when the polymer having a large thermo-optic coefficient is used, the polymer is easily degraded in combination with oxygen when exposed to the near infrared rays used in the optical communication band, thereby reducing the reliability of the switch element. .

Therefore, the present invention has been made to solve the above problems, by constituting a core layer of a material that is physically and chemically stronger than the polymer to prevent the deterioration of the core layer, which is an area where the optical signal mainly passes, to reduce the optical loss, and also to the core The purpose of the present invention is to provide a highly efficient and reliable thermo-optic switch by reducing the intensity of distribution of the optical mode to the cladding layer surrounding the layer and preventing the loss of the optical signal.

In addition, the coating of the thermo-optic switch during packaging prevents oxygen permeation on the surface, simplifying packaging, and resulting in much less loss and structural stability, longer life, increased reliability, and greater cost burden due to packaging. It is an object to provide a cheap thermo-optic switch element by shrinking.

1 illustrates a digital thermo-optic switch.

2A and 2B show a cross-sectional view of an embedded waveguide of a thermo-optic switch in a first embodiment according to the present invention.

3A and 3B show a cross-sectional view of a lip waveguide of a thermo-optic switch in a second embodiment according to the present invention.

* Explanation of symbols for main parts of the drawings

10-1, 10-2: substrate

20-1, 20-2, 20-3, 20-4: lower clad layer

30-1, 30-2, 30-3, 30-4: core layer

40-1, 40-2, 40-3, 40-4, 40-5, 40-6: upper cladding layer

50-1, 50-2, 50-3, 50-4: heater

Features of the thermo-optic switch according to the present invention for achieving the above object is a substrate; A lower clad layer formed on the substrate; A core layer formed of silica on the lower clad layer; An upper clad layer formed on the core layer and the lower clad layer; It is configured to include a heater formed in at least one metal pattern on the upper clad layer formed on the core layer and the lower clad layer.

The core layer is characterized in that the Y branched embedded (embedded) structure having a first tube into which light is input on the lower clad layer and a second tube divided into two from the first tube.

In addition, the core layer is characterized in that the Y-branched rib structure (rib) structure is further formed on the upper surface of the lower clad layer the same material layer as the material of the core layer.

The lower clad layer is formed of silica having a refractive index smaller than that of the silica of the core layer, and the upper clad layer is formed of a polymer having a refractive index smaller than that of the silica of the core layer.

The action according to the characteristics of the present invention is that the degradation of the core layer is achieved by using silica as the core layer material and a material having high thermo-optic coefficient as the lower clad layer and silica as the lower clad layer. Can be prevented.

Another feature according to the present invention is to comprise a silica layer between the core layer and the upper cladding layer formed of a polymer having a refractive index smaller than that of the core layer and having a larger refractive index than the polymer.

The action according to the characteristics of the present invention as described above is to use silica as a core layer material is less likely to degenerate, silica having a small thermo-optic coefficient as the upper clad layer, and a polymer having a large thermo-optic coefficient on the silica. As a result, the light propagates well to the core layer, and the upper cladding layer is formed of silica having a small refractive index variation even at low and high temperatures, thereby reducing the intensity of distribution of the optical mode to the polymer layer and reducing the optical loss.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

A preferred embodiment of the thermo-optic switch according to the present invention will be described with reference to the accompanying drawings.

The waveguide structure used in the thermo-optic switch can be divided into an embedded structure and a rib structure.

2A and 2B show a cross-sectional view of an embedded waveguide of a thermo-optic switch in a first embodiment according to the present invention.

As shown in FIG. 2A, the optical waveguide of the thermo-optic switch is formed on the substrate 10-1, the lower cladding 20-1 layer formed on the substrate 10-1, and the lower cladding 20-1 layer. A core 30-1 layer formed of silica (refractive index n1), an upper cladding 40-1 layer formed on the core 30-1 layer and a lower cladding 20-1 layer, and the core 30 And a heater 50-1 formed in at least one metal pattern on the upper cladding 40-1 layer formed on the layer and the lower cladding 20-1 layer.

The core 30-1 layer is a Y-branched embedded having a first tube into which light is input on the lower clad 20-1 layer, and a second tube splitting into two from the first tube. embeded) structure.

The lower clad 20-1 layer is formed of silica (refractive index n2) having a smaller refractive index than the silica of the core 30-1 layer, and the upper clad 40-1 layer is formed of the core 30-1. It is formed from a polymer with a lower refractive index than the silica in the layer.

In the embedded structure, the core 30-1 part and the upper and lower cladding parts 20-1 and 40-1 use a material having a refractive index difference of about 0.3% to 0.6% to reduce coupling loss with the optical fiber.

In addition, since the thickness of the optical fiber core is 8.6 μm, the core 30-1 of the optical waveguide has a thickness of about 6 μm to 8 μm in order to reduce coupling loss between the optical fiber and the light propagated by the optical waveguide.

The thickness of the lower cladding 20-1 is 15 µm or more, and the overall thickness of the optical waveguide is usually about 30 to 40 µm to reduce leakage loss toward the substrate 10-1.

Polymers have ten times more thermo-optic coefficients than silica used in waveguides, making it easy to implement thermo-optic switches. Polymers have the advantage of being easy to handle, but polymer-based thermo-optic switches are easily degenerated in combination with oxygen when exposed to near-infrared radiation used in optical bands.

Degradation of the polymer occurs by reaction with oxygen in the 1550 nm wavelength band, an optical communication frequency domain. Therefore, a hermetic packing with little oxygen is required to prevent oxygen from reacting with the polymer. In addition, the loss caused by the waveguide is larger than that of silica, and due to birefringence, there is a polarization problem and physically weak.

Polymers have a variety of materials, easy to control the refractive index, easy to handle, large thermo-optic coefficient, silica is very stable because the material is very stable, but the thermo-optic coefficient is small.

The polymer used in the thermo-optic switch has a negative thermo-optic coefficient, the silica has a positive thermo-optic coefficient, and the polymer has a refractive index deviation dn / dT of 10 ^-4 greater than 10 ^{-5 of the} silica.

Therefore, when the core 30-1 layer is formed of silica to prevent the birefringence of light due to polarization, it is prevented from being degraded by oxidation.

In the case of the embedded type as shown in FIG. 2A, since the difference in refractive index between the core 30-1 and the clads 20-1 and 40-1 is about 10 ^-3 (0.3%), the polymer has a large thermo-optic coefficient and therefore, The change in temperature also produces this difference in refractive index.

Therefore, when silica is used as the lower cladding 20-1 and the core 30-1 layer and polymer is used as the upper cladding 40-1 layer, since the polymer has a large variation in refractive index with temperature, Mode control requires a very precise temperature controller.

That is, the refractive index of the upper cladding 40-1 layer formed of the polymer should be smaller than the refractive index of the core 30-1 layer even at a low temperature. If the refractive index of the polymer is larger, the optical loss increases and a single mode should be formed at room temperature. Because. At high temperatures, the refractive index of the polymer is so large that the refractive index is greatly reduced, so the optical loss burden is small. On the contrary, at low temperatures, the optical loss burden is large because the change of the refractive index of the polymer is small. Refractive index should be properly adjusted.

On the other hand, in the case of silica, refractive index is easily controlled by doping, and it is very stable thermally or mechanically, and deposition and etching techniques are very well established when forming the lower clad 20-1 layer and the core 30-1 layer. have.

However, when the upper cladding 40-1 layer is deposited with silica, narrow valleys are formed by the pattern by the core 30-1 layer. In this case, it is difficult to deposit between the upper cladding layers. 2) The layer is spin coated with a polymer to facilitate deposition.

In order to solve the problems caused by the thermo-optic coefficient difference between the core layer formed of silica and the upper cladding layer formed of the polymer, the present invention provides a structure as shown in FIG. 2B.

As shown in FIG. 2B, the lower clad 20-2 layer and the core 30-2 layer are formed of silica on the substrate 10-2, and then the first upper clad 40-2 is formed using silica. Form a layer.

The core 30-2 layer includes one first tube through which light is input on the lower clad 20-2 layer, and a second tube splitting into two from the first tube. 30-2 has a rib structure in which the same material layer as that of the core layer is further formed on the upper surface of the lower clad 20-2 layer.

At this time, the thickness is about 1 to several μm, and bending occurs depending on the structure of the core 30-2 layer.

The second upper cladding layer 40-3 is spin-coated by using a polymer on the first upper cladding layer 40-2.

The refractive index of the polymer should be smaller than the refractive index of the core 30-2 layer in the entire temperature range in which it is used.

In this case, when the upper cladding layer 40-2 is further formed with silica, since the variation of the refractive index due to the heat is small because the thermo-optic coefficient of silica is small, the optical loss to the clad layer is reduced, and no additional temperature controller is required. Design is relatively easy.

That is, according to the present invention, silica is used as a material that does not easily degenerate into the core 30-2 layer material, and silica having a small thermo-optic coefficient between the core 30-2 layer and the polymer upper cladding 40-3 layer is used. By further forming the upper cladding layer 40-2, it stably guides the light even at low temperatures, and does not require a temperature controller for controlling the refractive index of the polymer having a large thermal optical coefficient.

In the case of the waveguide of the thermo-optic switch of the embedded structure as shown in Figs. 2A and 2B, when heat is applied from the heaters 50-1 and 50-2 for optical switching, the applied heat is transferred isotropically from the electrode surface. The thicker the entire waveguide, the wider the heat is transferred, the longer the transfer time to the cores 30-1 and 30-2, and the longer the time it takes for the heat to be completely discharged from the waveguide.

In addition, a large amount of heat can be transferred to other branch waveguides in addition to the desired waveguide portion, thereby making it difficult to obtain an efficient thermo-optic effect.

Thus, a lip waveguide as shown in FIGS. 3A and 3B is presented.

3A and 3B show a cross-sectional view of a lip waveguide of a thermo-optic switch in a second embodiment according to the present invention.

First, as shown in FIG. 3A, a lip waveguide of a thermo-optic switch includes a substrate 10-3, a lower cladding layer 20-3 formed on the substrate 10-3, and a lower cladding layer 20-3. A core 30-3 layer formed of silica (refractive index n1) thereon, an upper cladding 40-4 layer formed on the core 30-3 and a lower cladding 20-3 layer, and the core ( 30-3) and a heater 50-3 formed in at least one metal pattern on the upper cladding layer 40-4 formed on the lower cladding layer 20-3.

The lower cladding layer 20-3 is formed of silica (refractive index n2) having a smaller refractive index than that of the core 30-3 layer, and the upper cladding layer 40-4 is formed of the core 30-3. It is formed from a polymer with a lower refractive index than the silica in the layer.

In the case of the rib structure, the difference in refractive index between the core 30-3 layer and the cladding layers 20-3 and 40-4 is large.

Therefore, it is more suitable for depositing silica on the core 30-3 layer and depositing polymer on the upper cladding 40-4 layer than the embedded type.

FIG. 3B is also a structure proposed to improve the problem caused by the thermo-optic coefficient difference between the core 30-4 layer formed of silica and the upper cladding 40-6 layer formed of the polymer as shown in FIG. 2B.

As shown in FIG. 3B, a lower cladding layer 20-4 and a core 30-4 layer are formed of silica on the substrate 10-4, and then the first upper cladding 40-5 is made of silica. Form a layer.

In the case of the lip structure, a material having a refractive index difference of about 1% to 10% by using a difference in refractive index between the core layer and the cladding layer is used.

When the difference in refractive index is large, since the portion of the clad which is affected by the evanescent field formed in the depth direction of the waveguide is thin, the thickness of the lower and upper cladding can be reduced.

Therefore, it can be fabricated to 15 mu m or less as a whole, so that the applied heat is transferred only from the electrode surface to the desired branch waveguide, and heat leakage to the other waveguide is greatly reduced. In addition, since the entire thickness of the waveguide is less than half of that of the embedded structure, heat dissipation is easier due to a short distance from the heat sink. Therefore, the switch speed is faster than the embedded method, and it has the advantage of being able to switch at low driving power.

However, the coupling loss must be taken into account due to the difference in mode size when coupling with the optical fiber.

The manufacturing process of the optical waveguide of the thermo-optic switch of the present invention as described above is as follows.

Typically, the reference numerals of the drawings denote the reference of Fig. 2A.

The lower clad 20-1 layer is first formed on the silicon substrate 10-1.

At this time, there is a method using a deposition method and an oxidation process using PECVD (Plasma Enhanced Chemical Vapor Deposition) or FHD (Flame Hydrolysis Deposition). First, after the oxidation process, the lower clad 20-1 may be formed to a desired thickness by deposition.

Thereafter, the core 30-1 layer is deposited using the above two methods (oxidation deposition process and post-oxidation deposition process).

Then, doping such as germanium (Ge) is used to control the refractive index.

Photographing is performed to form the pattern of the core 30-1 layer. Since the etching is performed 3 ~ 10㎛ depending on the structure to form a metal layer having a good etching selectivity as an etching mask.

In this case, after forming the core layer, a metal layer is deposited using a sputter or the like.

Then, the deposited metal layer is etched after performing a PR spin coating step, alignment and exposure, and photographing work. The etching of the metal layer mainly uses wet etching, and dry etching may also be used.

Therefore, the core 30-1 layer pattern is formed using the metal layer pattern as a mask.

Recently, attempts have been made to form a core layer using PR directly as an etching mask. In this case, etching of the metal layer is omitted. The core layer is dry-etched using the metal layer or PR as an etching mask.

After etching, the etching mask is removed by dry or wet method.

3B and 4B, a thin upper cladding layer 40-2 and 40-5 having a thickness of about 1 to 3 μm is deposited on the core layer with silica.

2A and 3A, the step of forming the upper clad layer with the silica is omitted.

Thereafter, the upper cladding (40-1) layer of the polymer is completed by spin coating and curing by washing at a temperature of about 250 ~ 300 ℃.

When the polymer is deposited, a method of improving step coverage by repeating deposition and sputter etching may be used.

Thereafter, a metal layer is formed for the heater 50-1 by forming a pattern through deposition and photographic work.

In addition, the packaging problem can be easily solved by coating with a material that does not transmit oxygen to the surface when packaging.

The cross-sectional structure formed according to the above process sequence is applied to the structures of Mach-Zehnder interferometer type, directional coupler type, and digital thermo-optic switch.

The thermo-optic switch according to the present invention as described above has the following effects.

First, silica is used as a core material, and silica is used as a lower cladding layer, and a polymer having a high thermo-optic coefficient is used as an upper cladding layer to prevent structural degradation of the core layer. Long service life and increased reliability of the device.

Second, because the upper cladding layer forms more silica with a smaller thermo-optic coefficient, the light propagates well to the core layer, and the upper cladding layer is formed of silica that does not have a large refractive index variation even at low and high temperatures. It reduces the distribution intensity of the light mode and reduces the light loss.

Third, when packaging the device is coated with a material that does not permeate oxygen on the surface it is possible to make a cheap device by significantly reducing the cost burden due to packaging.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (6)

Board; A lower clad layer formed on the substrate; A core layer formed of silica having a refractive index greater than that of the lower clad layer on the lower clad layer; An upper clad layer formed of a polymer having a refractive index smaller than that of the silica of the core layer on the core layer and the lower clad layer; And a heater formed in at least one metal pattern on the upper cladding layer formed on the core layer and the lower cladding layer. 2. The thermo-optic according to claim 1, wherein the core layer has a Y branch having a first tube into which light is input on the lower clad layer and a second tube split into two from the first tube. switch. The thermo-optic switch of claim 2, wherein the core layer further includes a material layer that is the same as that of the core layer on an upper surface of the lower clad layer. The thermo-optic switch of claim 1, wherein the lower clad layer is formed of silica having a refractive index smaller than that of the core layer. delete 6. The thermo-optic switch of claim 5, further comprising silica between the core layer and the polymer material layer, the silica having a lower refractive index than the core layer and having a larger refractive index than the polymer material layer.