CN104849807A - Turning device of high-density waveguide superlattice - Google Patents

Abstract

Recently, the inventors have developed a technique to make the arrayed waveguide spacing down to half a wavelength and still have low crosstalk. One of the basic ideas is to design the waveguides of the waveguide array to have different widths, and form several waveguides with different widths into a waveguide sub-array. Then the waveguide sub-arrays are periodically arranged to form an arbitrarily large waveguide array, which is called a waveguide superlattice. The inventors' studies have shown that, with proper design, the crosstalk between arbitrary waveguides in a waveguide superlattice remains low even when the waveguide spacing is as low as half a wavelength. But when the waveguide superlattice makes a turn at such a small pitch, the mode field leaking from one of the waveguides will couple strongly with the other waveguides, leading to increased crosstalk. In the present invention, the inventor uses a special coupling structure containing curved waveguides to widen the high-density waveguide superlattice into a waveguide array with a large spacing before making a turn, and first staggers the high-density waveguide superlattice by a certain distance before turning . These approaches allow high-density waveguide superlattices to turn with very low crosstalk.

Description

Turning devices for high-density waveguide superlattices

technical field

The present invention relates to the turning problem of high-density waveguide superlattice (waveguide array whose pitch can be as low as half wavelength) to overcome crosstalk.

Background technique

Silicon-based photonics has great potential in the field of low-loss, large-scale photonic integration. Existing silicon-based photonics technology has not reached the integration level of one waveguide per micron, or although it has achieved high-density photonic integration, it has sacrificed other aspects of performance, such as insertion loss and crosstalk. Therefore, finding a method that can achieve the purpose of high integration and have the least impact on other aspects of performance is the central issue in the field of photonic systems. As we all know, the smaller the waveguide spacing, the greater the crosstalk between each other, which is a basic factor that limits the improvement of integration. Although the silicon-based waveguide with high refractive index difference can easily reduce the waveguide spacing to a few microns and the crosstalk is not obvious, but continuing to reduce the waveguide spacing on this basis will make the crosstalk surge to an unbearable value.

For two waveguides, when they are close together, their coupling constants are generally expressed by κ. According to the optical power coupling formula of the asymmetric waveguide directional coupler [1]

$\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&Right\; Arrow;</span>\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&beta;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&kappa;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\sqrt{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;\&beta;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&kappa;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; )</span>$

It can be seen that when the difference Δβ of the transmission constant between the waveguides is large to a certain extent (Δβ>>κ), the optical power coupling ratio between the waveguides, that is, the crosstalk will be reduced to a smaller value. However, this technique is only suitable for two waveguides and is not suitable for extending to large waveguide arrays. The inventor's research shows that in a large-scale waveguide array with a relatively close spacing, not only the two directly adjacent waveguides have strong coupling, but also the overlap integral of the mode field between the second nearest neighbor, the third nearest neighbor and even further adjacent waveguides is sufficient Large, so there is also obvious coupling, that is, there is obvious crosstalk.

The inventors of the present application have proposed a technique [2,3] that can make the crosstalk still very low when the pitch of the waveguide array is as low as half the wavelength. One of the basic ideas is to design the waveguides of the waveguide array to have different widths, and form several waveguides with different widths into a waveguide sub-array. Then the waveguide sub-arrays are arranged periodically to form an arbitrarily large waveguide array. In terms of semiconductor device physics, the above-mentioned waveguide sub-array can also be called a waveguide supercell, and the above-mentioned waveguide array constructed on this basis can also be called a waveguide superlattice. The inventor's research shows that when the waveguide supercell contains 5 waveguides, through a waveguide supercell design called "staggered-composite", even if the waveguide spacing is as low as half a wavelength, the distance between any waveguides in the waveguide superlattice Crosstalk remains low.

But at this point, a new question arises, that is, how does a high-density waveguide superlattice with such a small pitch turn? The reason for this problem is that when making a turn when the waveguide spacing is so small, the mode field leaking from one of the waveguides will couple strongly with the other waveguides, resulting in increased crosstalk.

For this problem, the inventor will propose a solution in this application.

The prior art documents are referenced as follows:

[1] Saleh, B.E.A. & Teich, M.C., Fundamentals of Photonics. (Wiley-Interscience, New York, 1991).

[2] Wei Jiang, "Waveguide Superlattices For High Density Photonics Integrations," U.S.Provisional Application no.61/877,052, filed on September 12, 2013.

[3] Wei Jiang, "Waveguide Superlattices For High Density Photonics Integrations," PCT application No.PCT/US2014/055442, filed on September 12, 2014.

Invention content:

The object of the present invention is to solve the turning problem of high-density waveguide superlattice.

Technical scheme of the present invention is as follows:

A device for high-density waveguide superlattice turning. At the end of the high-density waveguide superlattice, a section of coupling structure including curved waveguides is used to widen the high-density waveguide superlattice into a waveguide array with a larger pitch required. , use the curved waveguide to realize the turning; and then use the aforementioned coupling structure in reverse to restore the waveguide array with a large spacing back to the high-density waveguide superlattice.

The coupling structure of at least one waveguide in the high-density waveguide superlattice includes an S-shaped waveguide.

The starting points of the above-mentioned adjacent S-shaped waveguides are staggered by a certain distance.

The S-shaped waveguide includes a first curved waveguide, a straight waveguide and a second curved waveguide, or the S-shaped waveguide includes a first curved waveguide and a second curved waveguide.

Wherein the starting points of the first section of curved waveguides of the adjacent S-shaped waveguides are staggered by a certain distance or wherein the starting points of the adjacent S-shaped waveguides are staggered by a certain distance.

The S-shaped waveguide includes a waveguide in the shape of a cosine function.

At the end of the high-density waveguide superlattice, each waveguide starts to turn one by one, and the turning start points of adjacent waveguides are staggered by a certain distance.

The turning device is used end-to-end with a second identical turning device to reduce the waveguide array back to a high density waveguide superlattice.

Between the two turning devices there is a straight waveguide array or a straight waveguide superlattice.

The high-density waveguide superlattice is widened into a waveguide array with a larger pitch due to the sequentially staggered turning start points for coupling.

Beneficial effects: when solving the turning problem of the high-density waveguide superlattice, the high-density waveguide superlattice is first widened into a waveguide array with a large spacing before turning. Among them, curved waveguides are used in the process of widening the distance, but the present invention adopts the method of staggering the starting point of curved waveguides to make the distance between each curved waveguide and adjacent curved waveguides larger, so that the additional mode field leakage caused by bending is different from other The coupling of the curved waveguide is so weak that it can be ignored and will not affect the low crosstalk characteristic of the high-density waveguide superlattice. Then operate in reverse according to the above-mentioned method of widening the waveguide spacing, and restore the waveguide array with a wider spacing to a high-density waveguide superlattice. Among them, the curved waveguide connected with the high-density waveguide superlattice also adopts the method of staggering the starting point, and the turning process occurs in the part of the waveguide array with a large spacing, which is easy to do.

Description of drawings

Figure 1 is a schematic diagram of a device in which a high-density waveguide superlattice first widens and then turns;

Fig. 2 is the schematic diagram of the device turning after the high-density waveguide superlattice is staggered successively;

Fig. 3 is a schematic diagram of the device for turning and restoring after the high-density waveguide superlattice is staggered successively;

Among them: 100. The device of high-density waveguide superlattice widening first and then turning; 110. High-density waveguide superlattice; 120. Coupling structure; 130. Larger spacing array waveguide; 140. Turning waveguide; 200. High-density waveguide 210. High-density waveguide superlattice; 220. Turning waveguide; 300. Device for turning and restoring high-density waveguide superlattice after successive staggering; 310. High-density waveguide superlattice; 320. Bend waveguide.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and example.

The basic idea of the present invention is to widen the high-density waveguide superlattice into a waveguide array with a larger pitch by special means, and then turn or start turning after the high-density waveguide superlattice is staggered successively.

1. The high-density waveguide superlattice first widens and then turns;

The turning device 100 of the high-density waveguide superlattice is designed by adopting the scheme shown in FIG. 1 to realize the turning of the high-density silicon-based waveguide superlattice 110 . (In fact, a high-density waveguide superlattice may be composed of multiple waveguide supercells, and each waveguide supercell is composed of several waveguides with different widths, and the waveguide spacing is very small. Here, 5 waveguides are taken as an example, for illustration purposes only .)

In this example, the light wavelength is between 1500 nanometers and 1570 nanometers, the waveguide uses silicon as the core, silicon dioxide is the cladding, and each waveguide of the high-density waveguide superlattice 110 is single-mode, with a width between 200 and 500 nm. Among the five unequal values selected, the waveguide spacing is 0.78 μm. Use the S-shaped waveguide as the coupling structure 120 to widen the waveguide spacing (composed of two curved waveguides and one straight waveguide), where the radius of the curved waveguide is 20 microns, the bending angle is 60 degrees, and the starting point of the adjacent first curved waveguide is staggered by 10 μm , the waveguide spacing is widened to 5 μm, and the turning waveguide 140 is used to realize the turning of the waveguide array 130 with a large waveguide spacing. At this time, due to the large waveguide spacing, the coupling between the mode field leaked from the turning waveguide 140 and other waveguides is very weak and can be ignored. . Afterwards, reverse the method of widening the waveguide spacing as described above, and restore the waveguide array with a wider spacing to a high-density waveguide superlattice. Realized turning of high-density silicon-based waveguide superlattice. The S-shaped waveguide 120 can use the first curved waveguide to expand the angle, then use the straight waveguide to expand the distance between the waveguides, and then use the second curved waveguide to select the extension direction of the subsequent straight waveguide.

In another specific design example, some or all of the S-shaped waveguides 120 can be composed of two curved waveguides without adding a straight waveguide. In other specific design examples, the S-shaped waveguide 120 can also be designed as a waveguide in the shape of a cosine function. In these designs, the shortest distance between adjacent curved waveguides in the z direction should generally be relatively large, such as 2 μm or more.

2. The high-density waveguide superlattice is staggered successively and then turned

The turning device 200 of the high-density waveguide superlattice is designed by adopting the scheme shown in FIG. 2 to realize the turning of the high-density silicon-based waveguide superlattice.

In this example, the light wavelength is between 1500 nanometers and 1570 nanometers, the waveguide uses silicon as the core, and silicon dioxide is the cladding. Among the five unequal values selected, the waveguide spacing is 0.78 μm. The turning is realized by using the turning waveguides 220, wherein the start points of adjacent turning waveguides 220 are sequentially staggered by 10 μm. At this time, due to the large distance between the waveguides, the coupling between the mode field leaked from the bend waveguide 220 and other waveguides is very weak and can be ignored.

In Fig. 2, the arrayed waveguide pitch is widened, and it can also be used to couple with another large-pitch waveguide superlattice or ordinary waveguide array.

3. The high-density waveguide superlattice is staggered successively and then turned and restored

The turning device 300 of the high-density waveguide superlattice is designed by adopting the scheme shown in FIG. 3 to realize the turning and restoration of the high-density silicon-based waveguide superlattice.

On the basis of the specific implementation example 2, as shown in FIG. 3 , connecting an identical device end-to-end behind this device can restore the waveguide array back to a high-density waveguide superlattice. There can be a section of straight waveguide array or straight waveguide superlattice between two turning devices, and the distance between the two turns can be adjusted according to actual needs.

In some applications (including the above three specific implementation examples), the waveguide can also be made of other materials, such as silicon nitride as the core, and the cladding material includes silicon dioxide; or silicon oxynitride as the core, the cladding The material contains silicon dioxide; or silicon dioxide doped with germanium is used as the core, and the cladding material contains silicon dioxide; or compound semiconductor materials with different refractive indices are used as the core and cladding; or compound semiconductor materials with different refractive indices are used as the The core and cladding materials contain oxides; or polymer materials with different refractive indices are used as the core and cladding. When the refractive index difference between the core and the cladding material is small, the waveguide spacing in the waveguide superlattice should be enlarged accordingly to reduce crosstalk. The distance between the starting points of adjacent curved waveguides or the starting points of the S-shaped waveguides should also be enlarged accordingly. The turning angle can be any value.

The specific embodiment of the present invention has been described above in conjunction with the accompanying drawings, but these descriptions can not be interpreted as limiting the scope of the present invention, the protection scope of the present invention is defined by the appended claims, any claims on the basis of the present invention All modifications are within the protection scope of the present invention.

Claims (10)

1. A device for high-density waveguide superlattice turning is characterized in that at the end of high-density waveguide superlattice, a section of coupling structure comprising curved waveguide is used to widen the high-density waveguide superlattice to a relatively high density waveguide superlattice. The large-pitch waveguide array uses the curved waveguide to realize the turning; and then reverses the aforementioned coupling structure to restore the large-pitch waveguide array back to the high-density waveguide superlattice. 2. The turning device according to claim 1, characterized in that the coupling structure of at least one waveguide in the high-density waveguide superlattice comprises an S-shaped waveguide. 3. The turning device according to claim 2, characterized in that the starting points of the adjacent S-shaped waveguides are staggered by a certain distance. 4. The turning device according to claim 2 or 3, wherein the S-shaped waveguide comprises a first section of curved waveguide, a section of straight waveguide and a second section of curved waveguide or wherein the S-shaped waveguide comprises a first section of curved waveguide, and The second section of the curved waveguide. 5. The turning device according to any one of claims 2-3, wherein the starting points of the first curved waveguides of adjacent S-shaped waveguides are staggered by a certain distance or wherein the starting points of adjacent S-shaped waveguides are staggered by a certain distance. 6. The turning device according to any one of claims 2-3, wherein the S-shaped waveguide comprises a cosine function shaped waveguide. 7. A device for turning a high-density waveguide superlattice, characterized in that at the end of the high-density waveguide superlattice, each waveguide begins to turn one by one, and the turning starting points of adjacent waveguides are staggered by a certain distance. 8. The turning device of claim 7, wherein said turning device is used end-to-end with a second identical turning device to restore the waveguide array back to a high-density waveguide superlattice. 9. A device as claimed in claim 7, between two turning means there is a straight waveguide array or a straight waveguide superlattice. 10. The turning device according to claim 7, characterized in that the high-density waveguide superlattice is widened into a waveguide array with a larger pitch due to the sequentially staggered turning starting points for coupling.