KR100892427B1 - Mach-Zhender Interferometers Structure And Triplexer Using The same - Google Patents

Abstract

The present invention relates to a Mach-Zehnder interferometer structure for a triplexer and a triplexer using the same, wherein the difference in length of the Mach-Zehnder interferometer arm is adjusted to the first wavelength to be an integer multiple of the first wavelength plus half wavelength, and the 3dB coupler is Disclosed is a Mach-Zehnder interferometer structure for a triplexer that stably separates three wavelength bands over a wide band by being optimized for a second wavelength to a third wavelength, and a triplexer using the same.

Triplexer, Machender, Interferometer, PLC

Description

Mach-Zhender Interferometers Structure And Triplexer Using The Same}

The present invention relates to a Mach-Zehnder interferometer structure for a triplexer and a triplexer using the same. More specifically, the length difference of two arms is set to an integer multiple of a first wavelength, and the optical coupler is the first wavelength. And a Mach-Zehnder interferometer structure that adjusts to separate the second and third wavelength bands and a triplexer implemented using the same.

Recently, as the high-speed subscriber transmission service network of about 2 to 10 Mbps provided through the ADSL / VDSL subscriber network has been established, the related service industry has been activated, and the domestic internet industry has made rapid progress. Nevertheless, it is recognized that a transmission capacity of ADSL / VDSL is insufficient in providing HDTV-class video services and the like, and efforts to smoothly provide a high-speed service of about 100 Mbps continue.

As part of this effort, in Japan, 100 Mbps is a system that can smoothly provide 100 Mbps, and the construction of FTTH (Fiber-to-the-Home) system based on Passive Optical Network (PON) has been supported by the government such as NTT. The company is actively progressing mainly. Accordingly, the number of FTTH subscribers is expected to surpass that of ADSL / VDSL subscribers by 2008. Stimulated by such a situation in Korea, the government has set up BcN (Broadband Convergence Network) and FTTH as the driving force for the next generation of national growth, and has expanded the FTTH by conducting FTTH pilot projects centering on KT and Hanaro Telecom. The situation is focused on efforts.

 The most important issue in the proliferation of Passive Optical Network (PON) -based FTTH systems is the economic cost of having to install ONUs individually.

In the current PON system, the wavelength division multiplexing (WDM) method is used to minimize the use of the optical fiber and reduce the cost. However, in the case of the FTTH where the optical fiber is connected to the home, There is a problem that a huge cost in network construction.

Therefore, in recent years, by using a triplexer module, it is possible to efficiently transmit not only Data and Voice but also HDTV-class video broadcast signals through a single optical fiber. Interest in the TPS (Triple Play Service, International Standard ITU-T G983.3) to provide such uplink (1310nm) and downlink (1490nm) data and downlink video broadcasting (1550nm) is increasing. In other words, the triplexer is expected to be a leading player in the full-scale FTTH era considering the economics of the entire optical network construction. However, most commercialized triplexers are being realized by assembling individual devices such as optical couplers and thin film filters (TFFs).

Hereinafter, a representative triplexer according to the prior art will be described with reference to the accompanying drawings.

1 is a diagram of a bidirectional triplexer of the prior art is disclosed in Korean Patent Publication No. 2005-0045466. Referring to FIG. 1, an optical triplex includes first and second filters FT1 and FT2, first and second optical receivers Rx ₁ and Rx ₂ , and an optical transmitter Tx.

According to this method, after fabricating the Y branch flat waveguide in the silica or polymer platform 12, fine grooves are dug at appropriate branch positions, and the thin film filters 11a and 11b are mounted thereon.

However, this method basically requires an additional precision process of attaching two separately manufactured thin film filters to the grooves of the planar optical waveguide circuit, and because the assembly process is complicated, the yield is low and thus the cost tends to increase. There is this.

2 illustrates another prior art bidirectional priplex. Referring to FIG. 2, there is shown a structure of an optical triplexer having a diffraction grating structure 14 in a directional coupler to separate a 1490 nm wavelength 15b. The wavelength of 1490 nm among the input three wavelengths is emitted to Port B (15b) by the Bragg reflector, and the other two wavelengths are separated by the length (13, 14) of the optical coupler.

1310nm wavelength is half cycle coupler operation, 1550nm wavelength is full cycle coupler operation, so the two wavelengths come out Port C (15c) and Port D (15d), respectively. The reflection at 1490 nm wavelength is determined by the period Z, and the reflection peak magnitude is determined by the diffraction grating spacing.

However, in order to fabricate such a structure, the re-growth process and the etching process are repeated to make the Bragg reflector, which makes the manufacturing difficult and not suitable for mass production.

Therefore, the prior art triplexer requires a further precision machining operation after fabricating a conventional flat plate optical waveguide circuit, and thus has a disadvantage of low production yield and high price.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to design a simplified triplexer by employing a relatively simple structure using an optical coupler and an interferometer, so that mass production is possible at low cost and three wavelengths are reduced. It is to provide a device that can be separated stably.

 Another object of the present invention is to provide a flat waveguide type triplexer which can replace a conventional triplexer which includes a complicated grating structure or a precise process such as an individual lens or a thin film filter.

As a technical means for solving the above-mentioned problems, the first aspect of the present invention comprises two arms; And a Mach-Zehnder interferometer structure for a triplexer having an optical coupler capable of alternating optical power, wherein the length difference of the two arms is set to an integer multiple of one of the first wavelengths, and the optical coupler has a second wavelength to a third wavelength. There is provided a Mach-Zehnder interferometer structure for a triplexer to diverge optical power equally in the wavelength band.

Preferably, the first wavelength is one of 1300-1320 nm, the second wavelength is one of 1470-1500 nm, and the third wavelength is one of 1540-1570 nm.

Preferably, the optical coupler separates the first wavelength and the second wavelength to the third wavelength band based on Equation 1 below.

Meanwhile, the Mach-Zehnder interferometer structure for the triplexer is formed of a waveguide structure including a substrate, a lower cladding of the first dielectric layer, and a second dielectric layer, and the refractive index of the second dielectric layer is larger than the refractive index of the first dielectric layer. Accordingly, an upper cladding of the third dielectric layer may be further provided on the core layer of the second dielectric layer.

Preferably, the dielectric is a polymer, silica, or semiconductor.

The second aspect of the present invention provides two arms; And a first Mach-Zehnder interference portion having an optical coupler capable of alternating optical power, and adapted to separate the first wavelength from the second wavelength to the third wavelength band; And

Provided is a triplexer having a second Mach-Zehnder interference portion for receiving the separated optical signal having the second wavelength to the third wavelength into an optical signal of the second wavelength and the optical signal of the third wavelength.

Preferably, the first Mach-Zehnder interferer and / or the second Mach-Zehnder interferer consists of a plurality of Mach-Zehnder stages.

The length difference between the two arms of the first Mach-Zehnder interference portion is preferably set to an integer multiple of half of the first wavelength.

 The prior art triplexer has disadvantages in that its structure is complicated by assembling individual elements or using a lattice structure. However, unlike the conventional structure, the present invention uses a flat plate optical integrated plate so that a separate thin film filter assembly process is not required. By implementing a Mach-Zhender Interferometer (MZI) optical filter in the form of a Planar Lightwave Circuit (MZI), it is possible to provide an effective triplexer capable of separating three wavelengths.

 In addition, according to the present invention, by removing the additional thin film filter assembly step, the production yield can be significantly improved.

Based on the planar optical waveguide circuit, it can be implemented on silica or polymer material and hybridized (flip chip bonding) of the manufactured triplexer, laser diode and optical receiver can produce low-cost flat panel optical waveguide-based triplexer module. It works.

In addition, even if the wavelength of the 1310nm light source of the subscriber's uplink data transmission channel is changed to 20nm or more, the wavelength separation characteristic is maintained.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. do. The present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, only the embodiments of the present invention to make the disclosure of the present invention complete and complete the scope of the invention to those skilled in the art. It is provided to inform you.

3 is a block diagram of a Mach-Zhender Interferometers (MZI) structure according to a preferred embodiment of the present invention. The Mach-Zehnder interferometer structure has two optical waveguide arms 19a and 19b and an optical coupler 20.

According to the Mach-Zehnder interferometer structure, the length difference ΔL of the two optical waveguide arms is set to an integer multiple of the first wavelength plus half the wavelength, while the optical coupler 20 has the first wavelength and the second wavelength to the third wavelength. Adjusted to separate wavelength bands. That is, the optical coupler is adjusted to equally split optical power in the second to third wavelength bands.

Therefore, when the optical signal having the first, second and third wavelengths is input through the input terminal, only the first wavelength is output to the first output terminal, and the optical signal of the second to third wavelength is output through the second output terminal. do.

The two mixed wavelengths incident on the Mach-Zehnder interferometer are distributed through an optical coupler (e.g. 3 dB coupler) and the distributed light waves are due to the difference in the length of the Mach-Zehnder arm (ΔL) 19a, 19b determined by the difference between the two frequencies. Each signal is separated into P _bar and P _cross and its length can be obtained using Equation 2.

Where Δf is the difference between the frequencies of the channels output through the arms, N _eff is the effective refractive index of the waveguide, and c is the speed of light in the vacuum.

Therefore, the length difference (ΔL) 19a, 19b of the arm is an integer multiple of the first wavelength plus half the wavelength to separate the first wavelength, and the first and second to third wavelengths are expressed by Equation (1). We approximate the path difference (ΔL) of a suitable Mach-Zehnder interferometer structure that can be separated, and extract a more accurate range of values through simulation. For example, the first wavelength may be one of 1300 to 1320 nm, the second wavelength may be one of 1470 to 1500 nm, and the third wavelength may be one of 1540 to 1570 nm.

On the other hand, according to the present embodiment, when the 3dB directional coupler is adopted, a waveguide width error (± 0.2 μm) of about 10% occurs in a specific wavelength region (for example, 1.48-1.56 μm) by appropriately selecting the width and height of the waveguide. Even if it can maintain a balance of about 50% ± 5%. Couplers insensitive to process errors can be found by analyzing the waveguide mode of the waveguide constituting the coupler.

On the other hand, in manufacturing a triplexer using the Mach-Zehnder interferometer structure of this embodiment, the width difference of the waveguide (± 0.2㎛) by adjusting the length difference of the Mach-Zehnder arm of each stage in the triplexer and adjusting the characteristics of the 3dB coupler You can maintain the desired crosstalk value even if) occurs. The optical triplexer insensitive to such a process error not only facilitates mass production using a semiconductor process, but also greatly improves a problem such as a decrease in yield caused by an optical waveguide width error.

Diplexers or optical switches that separate the two wavelengths have been previously published. Nevertheless, the reason why commercialization does not proceed in earnest is that it is difficult to increase the yield due to the process error of the waveguide width or the directional coupler spacing.

However, the Mach-Zehnder interferometer structure according to the present embodiment can design a 3dB directional coupler structure that is robust to process error and use it as a basic component, thereby implementing a Mach-Zehnder interferometer structure triplexer that can be produced with high yield. .

When constructing Mach-Zehnder interferometers that normally operate over a wide wavelength range, the 3dB directional coupler uses a wavelength insensitive coupler (WINC). The reason is that in the case of the triplexer implemented with the Mach-Zehnder interferometer structure using the coupler having the flat wavelength characteristic, the light output of each of the three wavelengths can be improved if there is no manufacturing error. In reality, however, the width of the waveguide in the fabrication is more likely to change compared to the original mask, and this change causes the performance of the triplexer to be degraded, resulting in lower yield. In addition, a coupler having a flat wavelength characteristic has a problem in that the waveguide design process is complicated and the waveguide structure length is considerably longer.

4 is a diagram illustrating an inverted rib-type polymer waveguide structure employable in a Mach-Zehnder interferometer structure according to a preferred embodiment of the present invention.

Referring to FIG. 4, the Mach-Zehnder interferometer structure is made of a polymer waveguide structure, and the polymer waveguide structure is a waveguide structure including a substrate 18, a lower cladding 16b of a first polymer, and a second polymer core layer 16a. For example, the upper cladding 17 is air, the core 16a uses a polymer having a refractive index of 1.51, and the lower cladding 16b uses a polymer having a refractive index of 1.43.

Further, for example, the height of the lip is 1.6 mu m and the residual thickness of the core layer in contact with air is 0.5 mu m. Such a waveguide structure can be fabricated using dry etching or nano-imprint processes after polymer layer formation, which is effective when considering suitability for mass production. After forming the bottom cladding layer of the polymer, it can be manufactured by dry etching or by pressing the nano imprint mold to form a shape and then filled with the core polymer.

5A and 5B are graphs illustrating waveguide modes according to waveguide width and waveguide height in the polymer waveguide structure of FIG. 4. FIG. 5A shows only the half region by calculating the waveguide modes in the case of changing between 1.2 μm and 2.2 μm. Referring to FIG. 5B, in the polymer waveguide structure, it can be seen that the tail shape of the waveguide mode is quite similar even when the waveguide width varies between 1.2 μm and 2.2 μm at a portion away from the center of the waveguide by 3.3 μm or more. Therefore, when designing a directional coupler, it can be estimated that a directional coupler that is considerably insensitive to the waveguide width can be obtained when the spacing between the centers of the waveguides is 3.3 µm or more.

The optical coupler insensitive to such a process error not only facilitates mass production of the optical filter in the form of an optical integrated circuit, but also greatly improves the problems such as yield reduction caused by errors in the optical waveguide width. have.

Hereinafter, a triplexer using a Mach-Zehnder interferometer structure will be described in detail with reference to the accompanying drawings.

6 is a schematic diagram of a structure of a triplexer according to an embodiment of the present invention.

The triplexer includes a first Mach-Zehnder interferer MZI1 and a second Mach-Zehnder interferometer structure MZI2. The first Mach-Zehnder interferer MZI1 separates the optical signals of the first wavelength and the second to third wavelengths, and the second Mach-Zehnder interferer MZI2 receives the optical signal having the separated second to third wavelengths. It is configured to receive an optical signal of the second wavelength and the optical signal of the third wavelength.

The first Mach-Zehnder interferer MZI1 sets the length difference between the two arms to an integer multiple of half and the optical coupler adjusts the first and second wavelengths to separate the third to third wavelength bands.

The second Mach-Zehnder interference unit MZI2 separates the remaining two wavelengths, the second wavelength and the third wavelength, on the same principle as when the first wavelength is separated.

On the other hand, it is preferable that the first Mach-Zehnder interferer MZI1 and the second Mach-Zehnder interferer are designed by repeating the Mach-Zehnder type several times. According to this method, it is possible to design such that crosstalk between desired channels is 20 dB or more at three wavelengths (eg, 1310 nm, 1490 nm, and 1550 nm).

Hereinafter, an example of manufacturing the triplex described above with reference to FIG. 6 will be described.

According to the experimental example, the total length of the device composed of the coupler and the Mach-Zehnder interferometer insensitive to the process error is 8350 µm and the width is 190 µm, for obtaining a path difference between ΔL ₁ (24a) and ΔL ₂ (24b). The radius of curvature of the curved waveguides is designed to have 1000㎛ and 1200㎛, respectively. Reference numeral 23 denotes a silica or polymer optical waveguide, and reference numeral 21 denotes a 3 dB directional coupler.

First, the 1310 nm wavelength optical signal 22a among the three wavelengths is separated by the phase difference due to the difference in the lengths DELTA L ₁ of the Mach-Zehnder arm of the first Mach-Zehnder interference section MZI1. However, if we use only one Mach-Zehnder to separate, we can not get more than 20dB of crosstalk, so we design the same Mach-Zehnder interferometer structure.

When the 1310 nm and 1480 to 1560 nm wavelength bands are separated, the length difference (ΔL ₁ ) of the Mach-Zehnder arm is optimized for 1310 nm, that is, an integer multiple of 1310 nm wavelength plus half wavelength, and the 3dB coupler 21 is used at 1480 nm and 1560 nm. By optimizing, the 1310 nm and 1480 nm to 1560 nm wavelength bands are stably separated through the port 1 (22a) over a wide band.

In the second Mach-Zehnder interference section (MZI2), 1490 nm and 1550 nm are separated through Port2 (22c) and Port3 (22b), but the difference in length of the Mach-Zehnder arm of the second Mach-Zehnder interference section (MZI2) (ΔL ₂ ) By the phase difference of the input wavelengths. In this way, a planar optical waveguide-based triplexer separating three wavelengths of 1310 nm, 1490 nm, and 1550 nm can be insensitive to the fabrication process.

On the other hand, the arm 24a or the arm 24b for giving the phase difference in the triplexer does not necessarily have to be a curved structure, but may also be a rectangular structure including a total reflection mirror, and furthermore, there is a triangular structure or a polygonal structure.

The triplexer is composed of a polymer waveguide structure, and the polymer waveguide structure is formed of a waveguide structure including a substrate, a lower cladding of a first polymer, and a second polymer core layer. For example, the upper cladding is air, and the core is The polymer having a refractive index of 1.51 and the cladding below may use a polymer having a refractive index of 1.43. The triplexer manufactured in this way is insensitive to process errors.

Next, the directional coupler manufactured in this manner was analyzed using a three-dimensional beam propagation method (BPM) and a triplexer was analyzed.

5B is a graph showing the output change according to the waveguide width and height change of the directional coupler. If the height of the lip is 1.6 μm and the waveguide width is 1.8 μm, and the waveguide width changes by ± 0.2 μm when 50% coupling is used as the reference design value, the output of the bar port and cross port is about 4 to 6% at 50% It can be seen that the degree of change is limited.

7 is a graph showing the output according to each wavelength of the triplexer. It analyzes the change of phase and amplitude of light passing through the triplexer with C-programming operation with coupler table calculated by 3D beam transmission method.

At this time, when the waveguide width was 1.8 μm, the height was 1.6 μm, and the loss in the waveguide was not considered, the optical power output through each port was 99.8% at 1310 nm, 83.6% at 1490 nm, and 91.4% at 1550 nm. Crosstalk between channels was improved through the repeating structure of the Mach-Zehnder interferometer. The output wavelengths at 1310nm and 6490dB at 1490nm and 1550nm were 22.1dB and 28.5dB, respectively. In addition, it can be seen that the upstream data wavelength (1.31㎛) transmitted from the subscriber is well separated by a wavelength change of ± 20nm.

8 is a graph showing the change in each output wavelength according to the change in the waveguide width that may occur in the actual process. As the waveguide changes in the 1310 nm wavelength band, its output hardly changes, and the output decreases by ± 4% at 1490 nm and ± 8% at 1550 nm. However, even if the waveguide width changes, the desired crosstalk value is maintained at 20dB or more.

9 is a perspective view for showing another embodiment of the present invention.

FIG. 9 is a structure in which an optical transmitter and a receiver are integrated into one module using a surface mount technology based on a triplex manufactured by a planar optical waveguide circuit. Reference numeral 25 denotes a single mode or multimode optical fiber, 26 denotes a planar optical waveguide based triplexer, 27a denotes an optical signal of 1550nm wavelength, 27b denotes an optical signal of 1490nm wavelength, and 27c denotes an optical signal of 1310nm wavelength. Reference numeral 28 denotes a 1310nm optical transmitter, 29a denotes a 1550nm optical receiver, and 29b denotes a 1490nm optical receiver.

According to such a structure, a fabricated optical waveguide-based triplexer is realized using a material such as silica or a polymer, and a Fabry-Perot laser diode is properly etched after part of the implemented silica or polymer. The optical transmitter 28 such as the back is aligned with the linear waveguide through which the 1310 nm wavelength 27a of the triplexer passes.

In addition, the optical receiver manufactured by the InGaAsP series can be aligned with the linear waveguide through which the 1310 nm wavelength 27a passes, thereby implementing a hybrid-based triplex optical waveguide circuit.

In addition, it will be apparent to those skilled in the art from the above description that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

1 and 2 illustrate prior art bidirectional triplexers.

3 is a block diagram of a Mach-Zehnder interferometer structure for a triplexer according to a preferred embodiment of the present invention.

FIG. 4 illustrates a polymer waveguide structure employable in a Mach-Zehnder interferometer structure in accordance with a preferred embodiment of the present invention.

5A and 5B are diagrams showing the results of calculating the waveguide mode according to the waveguide width and depth change in the polymer waveguide structure of FIG. 4.

6 is a schematic diagram of a structure of a triplexer according to a preferred embodiment of the present invention.

7 is a graph showing the output according to each wavelength of the triplexer according to the experimental example of the present invention.

8 is a graph showing a change in each output wavelength according to the change in the waveguide width that may occur in the actual process in the experimental example of the present invention.

9 is a perspective view for showing another embodiment of the present invention.

Claims (14)

Two cancers; And a Mach-Zehnder interferometer structure for a triplexer having an optical coupler capable of alternating optical power. The difference between the lengths of the two arms is set to an integer multiple of half of the first wavelength, And the optical coupler adjusts to equally split optical power in the second to third wavelength bands. According to claim 1, The first wavelength is one of 1300 to 1320 nm, the second wavelength is one of 1470 to 1500 nm, the third wavelength is one of 1540 to 1570 nm Mach for the triplexer Gender interferometer structures. According to claim 1, The difference between the lengths of the two arms is determined based on Equation 3 below to separate the first wavelength and the second wavelength to the third wavelength band Mach-Zehnder interferometer structure.

Where Δf is the difference between the frequencies of the channels output through the arms, N _eff is the effective refractive index of the waveguide, and c is the speed of light in the vacuum. According to claim 1, The Mach-Zehnder interferometer structure for the triplexer is formed of a waveguide structure including a substrate, a lower cladding of the first dielectric, and a second dielectric core layer, wherein the refractive index of the second dielectric is greater than that of the first dielectric. Mach-Zehnder interferometer construction. The method of claim 4, wherein And a top cladding of a third dielectric on top of the core layer of the second dielectric. The method according to claim 4 or 5, And the dielectric material is a polymer, silica, or semiconductor. Two cancers; And a first Mach-Zehnder interference unit having an optical coupler capable of alternating optical power, and adapted to separate the first wavelength from the second wavelength to the third wavelength band; And And a second Mach-Zehnder interference unit for receiving the optical signals having the separated second to third wavelengths and separating the optical signals of the second wavelength into the optical signals of the third wavelength. . The method of claim 7, wherein Wherein the first wavelength is one of 1300 to 1320 nm, the second wavelength is one of 1470 to 1500 nm, and the third wavelength is one of 1540 to 1570 nm. . The method of claim 7, wherein The length difference between the two arms is determined based on Equation 4, thereby separating the first wavelength and the second wavelength to the third wavelength band.

Where Δf is the difference between the frequencies of the channels output through the arms, N _eff is the effective refractive index of the waveguide, and c is the speed of light in the vacuum. The method of claim 7, wherein And the triplexer is formed of a waveguide structure including a substrate, a lower cladding of the first dielectric, and a second dielectric core layer, wherein the refractive index of the second dielectric is greater than that of the first dielectric. The method of claim 10, And a top cladding of a third dielectric over the core layer of the second dielectric. The method of claim 10, Wherein said first and second dielectrics are polymer, silica, or semiconductor. The method of claim 6, And the first Mach-Zehnder interferer and / or the second Mach-Zehnder interferer comprise a plurality of Mach-Zehnder stages. The method of claim 6, The length difference between the two arms of the first Mach-Zehnder interfering portion is set to an integer multiple of half of the first wavelength.

Images