KR20030041555A - Thermo-Optical Switch - Google Patents

Abstract

PURPOSE: A thermal optical switch is provided to control a refractive index and enhance a switching effect by inserting a polymer into a center portion of a core layer. CONSTITUTION: An under clad layer(20-1) is formed on an upper surface of a substrate(10-1). The first core layer(30-1) is formed on an upper surface of the under clad layer. The first core layer is formed with a silica material. The second core layer(30-2) is formed in the inside of the first core layer. The second core layer is formed with a polymer having a higher refractive index than the refractive index of the first core layer. An upper clad layer(40-1) is formed on the first core layer, the second core layer, and the under clad layer. A heater(50-1) is formed with one or more metallic patterns on the upper clad layer.

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.

Figure 2 shows a Mach-Zehnder interference thermo-optic switch according to the prior art.

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.

In other words, the light from the same light source is split into two and meet again. According to the refractive index and the length of each waveguide, the intensity and phase change when two optical signals meet each other. When light of the same intensity is combined, it is switched by interference depending on the phase. Therefore, if you want to use as a switch, very precise phase control and intensity control is required.

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.

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.

In addition, polymer has an advantage of easy handling, but in the case of thermo-optic switch using polymer, it is easily degenerated by combining with oxygen when exposed to near infrared rays used in optical communication band.

Degradation of the polymer occurs by reaction with oxygen in the 1550 nm wavelength band, an optical communication frequency domain.

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 and are separated into two lights because the speed of light varies depending on the polarization characteristics (polarization direction) of the light waves, and different refractive indices Problem, 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. .

Accordingly, the present invention has been made to solve the above problems, and the object is to improve the switching efficiency by switching the optical signal using the polymer by forming a core layer of the structure wrapped around the polymer in a material stronger than the polymer in physical and chemical have.

Another object of the present invention is to prevent degradation of the core layer, which is a region through which optical signals pass mainly by using silica as a core layer as a material stronger than the physicochemical polymer.

Another object of the present invention is to provide a high efficiency and reliable thermo-optic switch by forming upper and lower cladding layers surrounding the core layer with silica having low thermo-optic coefficients to reduce the intensity of distribution of the optical modes to the clad layer and to prevent light loss. The purpose is.

1 is a plan perspective view of a digital thermo-optic switch according to the prior art.

Figure 2 is a plan perspective view of a Mach-Zehnder interference thermo-optic switch according to the prior art.

3 is a cross-sectional view of a thermo-optic switch in accordance with the present invention.

Fig. 4 is a plan perspective view of a Mach-Zehnder interferometer type thermo-optic switch according to the present invention.

5A and 5B are plan perspective views of a digital thermo-optic switch according to the present invention.

* Explanation of symbols for main parts of the drawings

10-1: Substrate

20-1, 20-2: lower clad layer

30-1, 30-3: first core layer

30-2, 30-4: second core layer

40-1, 40-2: upper cladding layer

50-1, 50-2: 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 first core layer formed of silica on the lower clad layer; A second core layer formed of a polymer having a higher refractive index than the first core layer in the first core layer; An upper clad layer formed on the first 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 positioned on the first and second core layer.

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

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

The action according to the characteristics of the present invention is to form the lower clad and core layer with silica, and then to etch the core portion of the waveguide core portion after etching the core layer, spin coating the polymer to insert the polymer into the core portion of the core layer. In this way, the switching effect can be increased by applying heat to a polymer having a thermo-optic coefficient greater than that of silica with a heater to adjust the refractive index.

In addition, since silica encapsulates the polymer, it prevents the deterioration of the polymer due to oxygen permeation, thereby ensuring the reliability and durability of the device, and forming a silica having a small thermo-optic coefficient as the upper cladding layer. It propagates well to the core layer, allows light to be guided in various temperature ranges of low temperature and high temperature, and reduces the intensity of distribution of the optical mode to the clad layer and prevents light 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.

3 is a cross-sectional view of a thermo-optic switch according to the present invention, showing a cross-sectional view of an embedded waveguide, and is a cross-sectional view taken along the line II ′ of FIGS. 5A and 5B.

4 is a plan perspective view of a Mach-Zehnder interferometer type thermo-optic switch according to the present invention, and FIGS. 5A and 5B are plan perspective views of the digital thermo-optic switch according to the present invention.

As shown in FIG. 3, the optical waveguide of the thermo-optic switch has a substrate 10-1, a lower cladding layer 20-1 formed on the substrate 10-1, and an upper portion of the lower cladding layer 20-1. A first core layer 30-1 formed of silica having a refractive index higher than that of the lower cladding layer 20-1 in the region, and the first core layer 30-1 inside the first core layer 30-1. A second core layer 30-2 formed of a polymer having a higher refractive index than the upper surface of the second core layer 30-2, and an upper layer formed on the first and second core layers 30-1 and 30-2 and the lower cladding layer 20-1. The heater 50- formed on the cladding layer 40-1 and the upper cladding layer 40-1 disposed on the first and second core layers 30-1 and 30-2 in two metal patterns. It is configured to include 1).

The lower clad 20-1 layer is formed of silica having a lower refractive index than the silica of the core 30-1 layer, and the upper clad 40-1 layer is formed of the cores 30-1 and 30-2. It is formed from silica having a refractive index smaller than that of the layer.

The number of the heaters 50-1 varies according to the type of the thermo-optic switch. The thermo-optic switch shown in FIG. 3 is a Y-type digital thermo-optic switch, and the number of heaters 50-1 is two.

In the embedded structure, the cores 30-1 and 30-2 and the upper and lower claddings 20-1 and 40-1 have a refractive index difference of about 0.3% to 0.6% in order to reduce the coupling loss with the optical fiber. Use the material.

The core thickness of the optical waveguide is about 6 μm to 8 μm in order to reduce the coupling loss of the light propagated by the optical fiber and the optical waveguide because the thickness of the optical fiber core is 8.6 μm.

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.

The first core 30-1 layer is formed of silica so that the central portion has a hole, and the polymer is formed of the second core 30-2 in the hole portion, so that the polymer is wrapped with physicochemically durable silica. Because the core is formed into the structure, the polymer is prevented from being degraded by oxidation.

In addition, since the second core 30-2 layer formed of a polymer has a large thermo-optic coefficient, the difference in refractive index can be produced even by a temperature change of several decades, so the light switching effect is excellent.

In order to take advantage of each of the polymer and silica, the upper and lower cladding and the core layer are formed by using silica, and the polymer is inserted into the center portion of the core layer.

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 numerals of FIG. 3.

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.

Accordingly, the first core 30-1 layer pattern is formed of silica using the metal layer pattern as a mask. At this time, the central portion of the first core 30-1 layer is patterned to have holes.

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 first core 30-1 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.

Subsequently, the polymer is spin-coated on the hole, the first core 30-1 layer, and the lower cladding 20-1 layer, and is coated by curing by washing at a temperature of about 250 to 300 ° C. Only the polymer inserted in the center portion of the first core 30-1 layer is removed to form the second core 30-2 layer.

At this time, the polymer is removed using a dry etching method or a chemical mechanical polishing (CMP) method until the surface of the silica first core 30 layer is exposed.

When the surface of the silica first core 30-1 layer is exposed, after the coating is performed by PR, the remaining polymer except for the polymer second core 30-2 layer is removed after photographing. At this time, since PR is removed together with the polymer, the PR continues to be etched even after the polymer is removed until the surface of the core silica is exposed.

After the PR and the polymer are removed in addition to the polymer second core 30-2 layer, the upper cladding layer 40-2 is deposited with silica.

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

By the above process, the Mach-Zehnder interferometer type thermo-optic switch of FIG. 4 and the digital thermo-optic switch of FIGS. 5A and 5B can be made.

In the interferometer type of FIG. 4, after the light splits into two pieces, the two second waveguides into which the polymer second core 30-4 layer is inserted are recombined again, and one waveguide is heated by the heater 50-2. As a result, the refractive index of the polymer second core 30-4 is changed, so that a path difference of light between two waveguides is generated, and a phase change occurs when the light is combined.

The interferometer type thermo-optic switch generates a path difference of light by applying heat through a heater 50-2 on one side between two branch waveguides separated from the waveguide, thereby generating an interference phenomenon and switching.

In other words, the light from the same light source is split into two and meet again. According to the refractive index and the length of each waveguide, the intensity and phase change when two optical signals meet each other. When light of the same intensity is combined, it is switched by interference depending on the phase. Therefore, if you want to use as a switch, very precise phase control and intensity control is required.

5A and 5B, the upper or lower structure may be designed to be optimized according to the heat distribution and the waveguide design.

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

After forming the lower clad and core layer with silica, the core layer of the waveguide is etched when the core layer is etched, followed by spin coating the polymer and inserting the polymer into the core of the core layer. The switching effect can be increased by applying heat to the polymer with a heater to adjust the refractive index.

In addition, since silica encapsulates the polymer, it prevents the deterioration of the polymer due to oxygen permeation, thereby ensuring the reliability and durability of the device, and forming a silica having a small thermo-optic coefficient as the upper cladding layer. It propagates well to the core layer, allows light to be guided in various temperature ranges of low temperature and high temperature, and reduces the intensity of distribution of the optical mode to the clad layer and prevents light loss.

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 (3)

Board; A lower clad layer formed on the substrate; A first core layer formed of silica on the lower clad layer; A second core layer formed of a polymer having a higher refractive index than the first core layer in the first core layer; An upper clad layer formed on the first core layer and the lower clad layer; And a heater formed in at least one metal pattern on the upper clad layer positioned on the first and second core layers. 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. The thermo-optic switch of claim 1, wherein the upper clad layer is formed of silica having a refractive index smaller than that of the core layer.