SE534346C2 - Integrated chip including trench - Google Patents

Description

534 346 without joints in the waveguide. The chip includes a number of waveguides and components, all of which are formed by etching this basic structure. Such a chip offers low manufacturing cost in combination with a high manufacturing yield.

One problem with transmitting and receiving optical signals is the risk of optical and electrical crosstalk between different components. This is particularly true when laser components and light detector components are arranged on the same integrated chip. There can be problems with unwanted reflections at joints or interfaces such as the connection port to the optical fiber or from other interfering stray light.

In addition, there may be unwanted light from externally arranged components such as lasers, LEDs and the like, as well as scattered light from imperfections in waveguides and gratings and spontaneous emission from optically active material in the chip itself.

Especially in integration applications, the physical distance between components is often small, and the risk of both electrical and optical crosstalk is therefore high.

Thus, the invention relates to an integrated chip for data or telecommunications or optical analysis for one, two or more wavelengths, where the chip has a basic structure that is the same from a carrier and upwards over the entire surface of the chip, where formed at the upper surface of the chip, and where the chip comprises monolithically the basic structure comprises protruding waveguides, integrated components, and is characterized in that a trench is etched down along at least one of the sides of one of the waveguides and down to an etching depth that is at least so great that the trench is optically insulating and in that at least 10 15 20 25 534 346 a wall of the trench that is arranged closest to a waveguide has at least one of the properties firstly that it is corrugated, whereby the corrugated wall constitutes a grating-based optical component, and secondly that it is angled so that light incident on the waveguide is reflected towards the trench wall and towards the substrate of the chip alternatively out of the the chip.

The invention will now be described in detail, with reference to exemplary embodiments of the invention and the accompanying drawings, in which: Figure 1 is a perspective view of a monolithic integrated chip for optical signals according to a first preferred embodiment of the present invention; Figure 2 is a top view of the integrated chip shown in Figure 1; Figure 3 is a perspective view of a monolithic integrated chip for optical signals according to a second preferred embodiment of the present invention; Figure 4 is a top view of the integrated chip shown in Figure 3; and Figures 5a-5c are cross-sectional views through A-A in Figure 2, illustrating the detailed design of a trench wall according to the present invention.

Figure 1 schematically shows a monolithic integrated chip 1, before metallization, with an input waveguide 2, an optical coupler 6 and two output waveguides 4, 5. 4. One or both of the waveguides 4, 5 can also function as input waveguides to the coupler 6. 10 15 20 25 30 534 345 According to the invention, the chip 1 is intended for data or telecommunications or optical analysis for one, two or more wavelengths.

The chip 1 comprises a waveguide 2 with a first port 3, where the port 3 is arranged to guide light into or out of the waveguide 2. The waveguide 2 is expanded, in an expanded part in the form of an optical coupler 6, from the first port 3 in the direction of a second waveguide 4 and a third waveguide 5. The various components of the chip 1 are monolithically integrated. In other words, the chip has a basic structure that is the same from a carrier upwards over the entire surface of the chip, and the waveguides 2, 4, 5 are formed at the upper surface of the chip by etching the basic structure down so that protruding waveguides are formed.

Figure 2 shows an integrated chip similar to that in Figure 1.

Corresponding parts have the same reference numerals in all figures.

The monolithically integrated components included in chip 1 share a common ground plane, namely the substrate in chip 1, which constitutes the n-side of the structure. Above this are layers of material that constitute a p-side of chip 1, whereby a pn junction arises.

Along at least one of the sides of one of the waveguides there is a trench 7. The trench 7 is produced by etching the monolithically integrated material structure in the chip 1 from the top of the chip 1 down to an etching depth that is at least so great that a trench is created that is optically and preferably also electrically insulating. According to a preferred embodiment, etching is carried out at least down to an n-layer of the chip 1. According to another preferred embodiment, etching is carried out to at least a depth where all p-layers in the structure above the pn junction itself have been etched through, or at least to a depth that reaches down to the pn junction itself or down to the pn junction itself so that only a few, preferably a maximum of 3, material layers, alternatively at least down to the first occurring, in the etching direction down through the material, n-layer so that only a few, preferably a maximum of 3, material layers, alternatively to a depth that at least passes through the pn junction itself.

It is particularly preferred that the trench 7 reaches down to a depth of between 50 and 5000 nm, preferably between 200 and 2000 nm.

Such etching depths result in good insulating properties optically as well as electrically (see below).

The trench 7 illustrated in the figures runs on both sides of all waveguides 2, 4, 5 of the chip 1. However, the trench 7 can run either along only parts of one or more waveguides, surround one or more waveguides or surround one or more components on the chip 1. This is evident from the following.

With the help of the trench 7, effective optical isolation of the relevant waveguide is achieved with respect to stray light incident on the waveguide from directions that are shielded by the trench 7. Such stray light may originate from nearby components or subcomponents such as from an integrated laser, but may also consist of, for example, spontaneously emitted light from the coupler 6 itself or light incident on the chip 1 from the outside.

Figure 5a illustrates in cross-section a preferred embodiment of a trench 7 according to the present invention. A waveguide, in this case the third waveguide 5, is provided with a trench 7. The figure is not to scale for clarity. According to a preferred embodiment, at least one wall 55 of the trench 7 which is arranged closest to the waveguide 5 is vertical.

In this case, the chip 1 is advantageously formed in absorbing material 8 on the side of the trench 7 on which the waveguide 5 is not located.

Since incident, unwanted stray light L is reflected back into the absorbing material 8 by the vertical wall 55, such stray light L can be prevented from spreading further. It is preferred that the amount of absorbing material 8 between mutually isolated components or sub-components in the chip 1 is sufficient to extinguish substantially all such re-reflected stray light L. According to a preferred embodiment, the minimum distance between two adjacent, parallel trenches, each of which is arranged to isolate a respective waveguide, is thus at least 25 pm. It is also preferred that grounded or reverse biased contact surfaces are used with the chip 1 to improve the absorption of unwanted light L in the absorbing material 8.

Figure 5b illustrates, in a similar manner to Figure 5a, a second preferred design of the wall 55. At least one wall of the trench 7 which is arranged closest to the waveguide 5 is thus angled so that light L which falls onto the waveguide 5 is reflected towards the trench wall 55 out of the chip 1.

Correspondingly, Figure 5c illustrates a third preferred embodiment of the wall 55, wherein at least one wall of the trench 7 which is arranged closest to the waveguide 5 is angled so that light L incident on the waveguide 5 is reflected against the trench wall 55 down towards the substrate of the chip 1, which is generally not absorbent. This can in many cases lead to the unwanted stray light being distributed over a larger volume of material, which is desirable. On the other hand, there is a risk that the light will be reflected back to sensitive areas of the chip. In addition, there is a risk that disturbing interference patterns will arise between the walls of the chip 1. Therefore, in certain applications it is preferable to use either the first or the second preferred design of the wall 55 as described above.

As is apparent from Swedish patent 0501217-4, the material system in a monolithically integrated chip 1 according to the present invention can be designed with different materials. However, the material structure usually consists of a number of layers of different semiconducting materials, mainly consisting of As, P, Ga, In and/or Al. There are several suitable ways to manufacture a monolithically integrated grating that can be used as a laser cavity or filter in accordance with the present invention. The active material can further consist of a bulk layer, an MQW structure (Multiple Quantum Well) or a combination of QDs (Quantum Dots).

In order to achieve good insulation of a particular waveguide, it is preferred that a respective trench runs along both sides of at least one waveguide. In other words, the waveguide in question is optically isolated by means of a trench in accordance with the invention along both its sides, so that the influence of incident stray light in the waveguide and on components arranged along the waveguide is significantly reduced.

According to a particularly preferred embodiment, which is also illustrated in Figures 1-4, the trench 7 is arranged to run along and around all waveguides 2, 4, 5 arranged in a component, so that all these waveguides 2, 4, 5 are surrounded by the trench 7. In fact, the trench 7 as illustrated in Figures 1 and 2 does not describe a closed curve. The reason for this is that light is guided in and out of the first waveguide 2 through the port 3, which is why an opening in the trench 7 must be arranged in front of the port 3. The fact that the trench 7 "surrounds" all waveguides 2, 4, 5 is herein intended to also encompass designs where the trench 7 has such openings where connections to one or more waveguides are found. As mentioned above, the waveguides 4, 5 may also include ports for conducting light in and out, in which case the trench 7 is arranged with openings in front of such ports.

In the case where several components are arranged side by side with transport waveguides arranged to conduct light between components, it is preferred that a trench is arranged to surround all of these components including the transport waveguides, however with openings for any external ports. In the case where a chip is to be cleaved, it is preferred that no trench is arranged along a waveguide at the site of cleavage, since such a trench may cause cleavage defects.

The unwanted currents that cause electrical crosstalk between different components in the chip 1 occur largely in the p-material or via the pn-junction. In the case where the trench 7, when surrounding the group of waveguides 2, 4, 5, cuts off the p-side and the pn-junction in the chip 1 around the entire group, the group will thus be substantially electrically isolated from disturbing electrical crosstalk from other parts of the chip 1. Such an arrangement thus means that a very good optical as well as electrical isolation can be achieved by a group of waveguides 2, 4, 5 on the chip 1.

According to a particularly preferred embodiment, an array of components is arranged on one and the same chip 1. Such a chip may, for example, comprise a number of components of the type illustrated in Figures 1 and 2, wherein each component comprises a first waveguide 2, a second waveguide 4 and a third waveguide 5. The second waveguide 4 comprises a laser for emitting light. The third waveguide 5 comprises a light detector for detecting light. The subcomponents may in this case advantageously be monolithically integrated.

Through an expanded part in the form of an optical coupler 6, light is guided from the laser to the first waveguide 4 and further out through the port 3, and light is guided from the port 3, via the first waveguide 2 and up to the light detector in the third waveguide. Various components are arranged with respective lasers and light detectors to emit and receive light with different respective wavelengths.

Each component is in this case preferably isolated from the other components by means of a respective surrounding trench in accordance with the above-described, which means that a number of such components can be manufactured on one and the same chip 1 and can be operated there without significant crosstalk between components. Such manufacturing of a plurality of components guides on one and the same chip entails low manufacturing costs, for example for applications in which light with a plurality of different wavelengths is to be handled in parallel.

The skilled person will recognize that a plurality of components can be arranged on one and the same monolithic integrated chip 1 in several different ways. For example, a plurality of lasers and/or light detectors for different wavelengths can be arranged in separate waveguides isolated from each other on one and the same chip 1. Certain components on the chip 1 can also be cascaded one after the other, using optical couplers, where each respective component is optically and electrically isolated from the other components in the manner described above, with openings in the trench for transport waveguides and so on. In this way, for example, triplexers can be built up, with two lasers and a photodetector each operating at a separate wavelength.

The individual components on the chip can then be encapsulated individually without the material itself being divided. A chip with arrays of components can then be packaged (optically aligned) onto a fiber ribbon, or a ribbon cable of parallel optical fibers, which allows all components in the array to be connected to a common multi-channel control electronics circuit, which is cost-saving and also saves physical space. This in turn means that less premises are required and therefore means energy savings.

In many applications, optical filters are used as components in monolithically integrated chips 1 of the present type. According to a preferred embodiment, at least one such optical filter is provided in the chip 1 by modifying a trench running along the waveguide in which the filter is to be arranged.

This is illustrated in Figures 3 and 4, in which an optical filter 52 is arranged along the third waveguide 5.

Thus, the part of the trench 7 that runs along the section of the third waveguide 5 at which the filter 52 is arranged is located at such a distance from the waveguide 5 that the optical mode in the waveguide 5 is influenced by the inner wall 53 of the trench 7 arranged closest to the waveguide 5, and also possibly the bottom of the trench 7. 54, so the trench wall 53 and/or the bottom of the trench is corrugated so that a first-order filter function is achieved.

The corrugation 54 of the trench wall 53 or the trench bottom is, like the trench 7 itself, preferably produced by means of etching, in a manner known per se. The distance of the trench 7 from the waveguide 5 and the physical geometry of the corrugated wall 53 determine the functionality of the filter 52 in terms of filtration strength, pass/stop band, etc., in a manner that is conventional per se.

The present inventors have surprisingly discovered that the size, in the plane 2 and 4 of the chip 1), (the plane illustrated in the figures of the etched away area of the trench 7 and the total volume of material etched away affect the quality of the corrugated side wall 53 or trench bottom. Too small an area makes it difficult for the process gases to access the etching front, which results in a deteriorated physical structure of the corrugated wall. This is of course not desirable, since this affects the properties of the filter 52. Too large a total volume of material etched away, on the other hand, leads to severe regrowth during etching, which also deteriorates the structure of the corrugated side wall 53 or trench bottom.

It has been found that good etching results can be obtained with respect to the corrugation of the trench wall 53 if the trench 7 is at least 0.1 µm, preferably at least 0.5 µm, wide and at most 1000 µm, preferably at most 250 µm wide. The width of the trench 7 is the dimension of the trench 7 that is visible in Figure 4 perpendicular to the longitudinal direction of the third waveguide 5.

It has also been found that particularly good etching results can be achieved in the case where the cross-sectional area of the trench 7, perpendicular to its main direction of propagation, is between 0.005 and 5000 µm, preferably between 0.1 and 500 µm.

In order to achieve good filtering performance, it is preferred that such a monolithically integrated filter 52 comprises at least about 100 grating periods, each grating period being about between 50 and 300 nm. 10 15 20 25 30 534 345 12 The distance between the trench 7 and the waveguide 5 is preferably between 0 and 10 µm at the location of the filter 52, and at other locations preferably between 0 and 500 µm.

In accordance with a preferred embodiment, the trench may be exposed to air, which provides a high refractive index difference.

It can also be covered by a dielectric such as SiO,, SiNm BCB or equivalent, which provides lower refractive index difference but on the other hand better physical protection for the filter and/or trench. This choice depends, for example, on the packaging used for the chip 1.

It is also possible to achieve other grating-based optical sub-components by adapting a wall of the trench 7 that is closest to a particular waveguide. Examples include lasers and diffractive couplers, the latter of which can be used to couple light out of the waveguide into an adjacent waveguide.

By providing grating-based optical sub-components in the wall of the existing trench 7 rather than as stand-alone, separately manufactured, either monolithically integrated or not, components, it is achieved that the manufacture of the chip 1 becomes simpler and therefore cheaper. Specifically, in many cases the trench 7 and the filter 52 can be manufactured in one and the same step.

The above has described preferred embodiments. However, it is obvious to those skilled in the art that many changes can be made to the described embodiments without departing from the spirit of the invention. Thus, the invention should not be limited by the described embodiments, but can be varied within the scope of the appended claims.

Claims (10)

10 15 20 25 30 534 346 13 P A 1? E N T IC R A V Integrated chip (1) for data or optical analysis for one, or telecommunication two or more wavelengths, wherein the chip (1) has a basic structure which is equal from a carrier and upwards over the entire surface of the chip, where the basic structure comprises suspension waveguides (2; 4; 5), formed at the upper surface of the chip (1), and where the chip (1) comprises monolithically integrated components, characterized in that a trench (7) is present etched along at least one of the sides of a of the waveguides and down to an etching depth which is at least so large that the ditch is optically insulating and that (53:55) closest to a waveguide has at least one of the properties at least one wall of the ditch (7) which is arranged first to it is corrugated, the corrugated wall constituting a lattice-based optical component, and secondly that it is angled so that light incident on wave (55) (1) substrate or out of the chip (1). the daren is reflected against the ditch wall and towards the chips An integrated chip (1) according to claim 1, characterized in that the etching depth is at least so large that a ditch is provided which is also electrically insulating. Integrated chip (1) according to claim 1 or 2, characterized in that the chip (1) is arranged for data or telecommunication or optical analysis for one, two or more wavelengths and can be used to emit light and to be able to detect light, and since the chip (1) comprises- (3), is expanded from the first port, a first waveguide (2) takes a first port where the first waveguide (2) (3) in the direction of at least a second waveguide (4) and a third waveguide (5). 10 15 20 25 30 35 534 345 14 An integrated chip (1) according to claim 1, 2 or 3, characterized in that at least one wall (55) of the trench (7) arranged closest to a waveguide is vertical. Integrated chip (1) according to one of the preceding claims, characterized in that the width of the ditch (7) is between 0.1 and 1000 μm. Integrated chip (1) according to one of the preceding claims, characterized in that the width of the ditch (7) is between 0.5 and 250 μm. An integrated chip (1) according to any one of the preceding claims, characterized in that the etching depth of the ditch is between 50 and 5000 nm. Integrated chip (1) according to one of the preceding claims, characterized in that the trench (7) is arranged to run along both sides of at least one waveguide. An integrated chip (1) characterized according to any one of the preceding that the ditch (7) claims, is arranged to run along all waveguides (2; 4; 5) in a component of the chip (1), on all sides of all these waveguides (2; 4; 5), so that the waveguides (2; 4; 5) are surrounded by the ditch (7) except for openings for ports in the component. An integrated chip (1) according to any one of the preceding claims, characterized in that at least one wall (53) of the ditch (7) arranged closest to a waveguide is corrugated, the corrugated wall (53) and that the grating-based optical component a grid-based optical component, nenten is an optical filter.