NL1025226C2 - Device, assembly and methods for wavelength-dependent processing of optical signals. - Google Patents

Description

Device, assembly and methods for wavelength-dependent processing of optical signals

Field of the invention. The invention relates to a device for processing wavelength-dependent optical signals, in particular a wavelength multiplexer-demultiplexer or a wavelength-dependent filter, which device comprises one or more input waveguides and two or more output waveguides. assembly of two or more devices according to the invention. The invention further relates to methods for processing wavelength-dependent optical signals by means of a device or assembly according to the invention

BACKGROUND OF THE INVENTION

In J.D. Love, R.C.W. Vance and A. Joblin, Opt Quantum Electron. 28 (1996) 353 discloses adiabatic asymmetric splitters / couplers which can be performed with planar integrated optical techniques. In these splitters / couplers the course of the cross-section with the axial position is always so gradual that the propagation of light from the input to the output proceeds adiabatically and a negligible amount of power is transferred between (system) modes of different order. According to the authors, the "fashion multiplexing" described by them is essentially wavelength independent. It would therefore not be possible to perform wavelength-dependent operations with adiabatic splitters / couplers. According to the present inventors, however, this is indeed possible and adiabatic splitters / couplers can be made suitable for processing wavelength-dependent optical signals, such as wavelength multiplexing-demultiplexing or wavelength-dependent filtering.

The object of the present invention is therefore to provide a device with which wavelength-dependent operations can be performed, starting from adiabatic splitters / couplers and on the basis of per se known mode multiplexing. The device should preferably be capable of being manufactured using integrated optical techniques, wherein the dimensions of the device and the production tolerances are preferably relatively little critical and therefore little or no thermo-optical or electro-optical tuning is required. It is a further object of the present invention to provide a method for wavelength-dependent processing of optical signals by means of such a device, in particular wavelength multiplexing-demultiplexes I and wavelength-dependent filtering, preferably with substantially flat pass-through bands, I preferably having relatively low losses and little crosstalk.

I Summary of the invention I To this end, the invention provides a device of the type mentioned in the preamble, wherein, through a correct choice of geometry and material properties, the device within a first selected wavelength range, going from input to output, everywhere a first I 10 (system) mode of a first determined order / adiabatically conducts I The term "signal" is understood here and hereinafter to mean a luminous flux, whether coded or not. The term 'optical' does not exclude wavelengths outside the visible range. For 'adiabatic', here and in the following always read 'substantially adiabatic', and for 'guide' or 'guided' always 'substantially guide' or "essentially guided".

I Light with a wavelength falling within the first selected wavelength range and within the first (system) mode will be transmitted from the input to the output, while maintaining the order / of the (system) mode By now the involved (system) mode give forms at the input I and at the output (by 'playing' with the geometry and the material properties) that, within the first chosen wavelength range, I wish it mainly coincides with one (or more) input waveguide (s) ) or modes guided by one (or more) output waveguide (s), it becomes possible to 'send' light with a wavelength falling within the first chosen wavelength range from one (or more) input waveguide (s) to one (or more) ) output waveguide (s).

For example, the first (system) mode within the first wavelength range at the input can substantially coincide with a mode guided by a first input waveguide.

Light falling within the first selected wavelength range and the first (system) mode will then be substantially transmitted from the first input waveguide to the output, while maintaining the order / of the (system) mode. Also, if the first (system) mode within the first selected wavelength range at the output substantially coincides with a mode guided by a first output waveguide, this light will be substantially transmitted to the first output waveguide. Light of a first 3 selected wavelength can thus be transmitted from a certain input waveguide to a certain output waveguide.

Also, the first (system) mode within the first selected wavelength range at the input or output may coincide with modes guided by a plurality of input or output waveguides.

Light of a first selected wavelength can thus be transmitted from one (or more) specific input waveguide (s) to one (or more) specific output waveguide (s).

In addition, by a correct choice of geometry and material properties, the device can adiabatically guide a second (system) mode of a second determined order V anywhere within a second chosen wavelength range, going from input to output. In the same manner as described above, light of a second selected wavelength can be transmitted from one (or more) specific input waveguide (s) to one (or more) specific output waveguide (s).

This can of course be repeated for a third selected wavelength range and so on. For example, light of different selected wavelengths can be "steered" from one or more specific input waveguides to one or more specific output waveguides. In principle, any arbitrary nxm wavelength multiplexer-demultiplexer can thus be realized.

The first determined order can be an even order, and the second determined order V can be an odd order, for example / = / '+ 1.

For example, light can be split and / or combined in closely adjacent wavelength regions. This will be explained later in the detailed description.

Also: - the first (system) mode can be a TE (transversally electrically polarized) mode; - the second (system) mode is a TM (transversally magnetically polarized) mode; 30 - / = / '; and - the first selected wavelength region and the second selected wavelength region coincide.

The operations can thus be made polarization dependent.

The invention also provides an assembly for wavelength-dependent processing of optical signals, in particular wavelength multiplexing-demultiplexing and I wavelength-dependent filtering, which assembly comprises two or more devices according to the invention.

By coupling, serially and / or in parallel, a number of devices according to the invention, an in principle unlimited number of wavelength-dependent and / or polarization-dependent splits and / or assemblies can be carried out.

The invention further provides methods for wavelength-dependent monitoring of I optical signals, in particular wavelength multiplexing-demultiplexing and I wavelength-dependent filtering, by means of a device or assembly according to the invention.

All this will become clearer in the following detailed description, with reference to the accompanying figures, of a number of exemplary embodiments of I devices and assemblies according to the invention.

Brief description of the figures. In the following, a number of exemplary embodiments of a device or assembly according to the present invention are described and explained with reference to the accompanying figures. Herein: I - Figs. 1 schematically a first general embodiment of a device according to the invention with an arbitrary number of (> 1) input waveguides and an arbitrary number of I (> 2) output waveguides; FIG. 2a schematically shows a first exemplary embodiment of a device according to the invention with a single multimode input waveguide and two multimode output I waveguides; FIG. 2b schematically dispersion characteristics associated with the device shown in FIG. 2a; FIG. 3a schematically a second exemplary embodiment of a device according to the invention with two input waveguides, a single mode and a multimode, and a single multimode output waveguide. FIG. 3b shows diagrammatically the dispersion characteristics associated with the individual waveguides from the device shown in FIG. 3a; FIG. 3c schematically the common dispersion characteristics associated with the device shown in FIG. 3a; 5 - FIG. 4a shows diagrammatically a first exemplary embodiment of an assembly according to the invention, composed of a number of devices according to the invention, partly in series and partly in parallel, with a combination of, single-mode and multimode, input and output waveguides; FIG. 4b calculated dispersion characteristics associated with the assembly shown in FIG. 4a - FIG. 4c schematically dispersion characteristics associated with the assembly shown in FIG. 4a; FIG. 4d calculated transmission curves of the assembly shown in FIG. 4a; FIG. 5a shows diagrammatically a dead embodiment of a device according to the invention with two, a single-mode and a multimode, input waveguides and three, a multimode and two single-mode, output waveguides; FIG. 5b schematically dispersion characteristics associated with the device shown in FIG. 5a; FIG. 6a schematically a second exemplary embodiment of an assembly according to the invention, constructed from three devices according to the invention, partly in series and partly in parallel, with a combination of single-mode and multimode, input and output waveguides; and FIG. 6b schematically dispersion characteristics associated with the assembly shown in FIG. 6a.

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DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows a general embodiment (1) of a device according to the invention with an arbitrary number (> 1) of input waveguides (10) and an arbitrary number of (> 2) output waveguides (20). The input and output waveguides are designed such that the (system) modal field solutions have desired spatial distributions. The transition zone (30) can in principle have any shape, but it must be adiabatic and conduct the desired (system) modes everywhere within the chosen wavelength ranges involved.

λ λ r »r Λ O C

Devices are said to be adiabatic if changes in the shape and properties of the waveguides along the main direction of propagation of the light are so gradual that there is virtually no power transfer between different (system) modes of order. That means that light will propagate while maintaining (system) fashion order. A prerequisite for this is that everywhere applies κη «A / 0W, where κΜ represents the coupling between the (system) modes p and q as a result of changes in the waveguiding structure, and where Δβκ is the difference I between the propagation constants of the concerning (system) modes. Thus, the <f order I 10 guided (system) mode at the input will ideally be fully passed to the q9 order I (system) mode at the output, provided that the construction is adiabatic and the qe order I (system) mode along the the entire process.

The discussions below are based on two-dimensional (2D) images as shown in the figures, where the dimensionality in the direction perpendicular to the plane of the drawing is assumed to be reduced on the basis of the (approximated) effective I index method (EIM). To reduce the dimensionality, it is assumed that all waveguides are single-mode along the "removed dimension", here always perpendicular to the plane of the drawing. With this more coarsely simplified model, I qualitative results can be derived for channel waveguides, but for the actual design, more sophisticated 3D computer methods should usually be used.

FIG. 2a schematically shows a first exemplary embodiment (2) of a device according to the invention on the basis of an asymmetrical adiabatic plenary splitter. The device comprises an input waveguide (102) with a width Wo, and a first (201) and a second I output waveguide (202) with a width of wa + Δ and w0 - Δ, respectively. The three I waveguides (102,201,202) are all three multimode waveguides. The whole can easily be produced with the aid of known integrated electro-optical techniques. It appears that, in order to meet the adiabaticity requirement, the length of the I 30 transition zone 31, which ends at the place where the output waveguides (201,202) I become substantially parallel, must be at least about 1 mm at a distance between I the parallel output waveguides (201,202) of approximately 50 µm.

7

The dispersion characteristic (effective refractive index NeJgr as a function of wavelength 2) of a multi-mode waveguide generally exhibits a series of curves at substantially regular distances, each corresponding to a guided mode of a certain order, as shown in FIG. 2b. At the input (IN) the (system) modes in this case coincide with the guided modes of the input waveguide (102). Now using the regular spacing of the dispersion curves of the multi-modal waveguides (102,201,202), the cut-off wavelengths (where Nef equals the refractive index n ^ g of the medium surrounding the waveguides) and the adiabatic behavior of the (system) modes, a 1x2 wavelength multiplexer-demultiplexer can be obtained. The device is therefore designed for this purpose, by a correct choice of geometry and material properties, that within a first selected wavelength range δλρ the f order (system) mode is guided everywhere, while also the f order (system) mode at the output (OUT) coincides with a guided mode of the first output waveguide (201). Now when the input waveguide (102) is excited with light with a wavelength falling within the first selected wavelength range and of (system) mode order /, this light will be transmitted to the f order (system) mode at the output (OUT) and thereby to the first output waveguide (201).

The device is also designed so that within a second chosen wavelength range δλρ 'the (system) mode of order V is guided everywhere, whereby the (system) mode of order V at the output (OUT) also coincides with a guided mode of the second output waveguide (202). Now when the input waveguide (102) is excited with light with a wavelength falling within the second selected wavelength range and of (system) mode order, this light will be transmitted to the second output waveguide (202).

By choosing more than two output waveguides and more than two wavelength ranges, an 1 x wavelength multiplexer-demultiplexer can be realized according to the same principle.

FIG. 3a schematically shows a second exemplary embodiment (3) of a device according to the invention with two input waveguides, a multimode (100) and a single-mode (101), and a single multimode output waveguide (200) which is identical in shape and properties is at the multimode input waveguide (100). In fact, the device thus comprises a single multimode waveguide (100/200) to which a single-mode waveguide (101) is adiabatically coupled.

FIG. 3b gives the individual dispersion characteristics for the multimode waveguide I (100/200) and the single-mode waveguide (101). FIG. 3c shows the dispersion characteristics of the (system) modes at the input (IN): the straight lines in the upper part of the I figure), in the transition zone (A): the curved lines in the upper part of the I figure ), and at the output (OUT). The different types of lines indicate different fashion orders. Three selected wavelength regions with widths δλρ + ι, δλρ and I δλρ, ι with central wavelengths of λρ + ι, λρ and λρ, ι are considered. The wavelength ranges I 10 each correspond to a different mode order of / + 1, /, and / -1, respectively.

The single-mode input waveguide (101) exhibits a substantially horizontal dispersion characteristic that intersects the negatively inclined dispersion curves of the multi-mode I waveguide (100/200), see Figure 3b. I light with a wavelength falling within the selected wavelength ranges (δλρ + ι, δλρ and δλρ, ι) I 15 will be in the relevant (system) mode order (/ + 1, /, and / -1) propagating in the output I multi-mode waveguide (200): transmission T = 1 in FIG. 3c. However, outside the selected wavelength ranges, there are no guided (system) modes of the correct order, and there I will radiate light to the environment: transmission T = 0 in FIG. 3c. Thus, the device I will only pass light in certain selected wavelength ranges from the input single mode waveguide I20 (101) to the output multimode waveguide (200) and act as a filter with I flat pass bands. The latter is typical of the adiabatic I devices considered, in contrast to, for example, Mach Zehnder interferometers or Fabry-Perot I cavities.

With the help of FIG. 3b and 3c, it can also be seen that all light within a chosen I wavelength range with width δλρ and central wavelength λρ will be transmitted provided that λι <λρ - 0.5δλρ ·, λα,> λρ + 0.5δλρ \ and λ2> λρ + 0.5 δλρ. A slight shift of the dispersion curves will not negatively influence the operation of the device. Relaxation of the requirements for the positioning of the dispersion curves becomes more pronounced when various devices according to the invention are connected in series, since the mutual distances between the wavelength ranges then become larger. All this allows relatively large production tolerances and makes the device relatively insensitive to temperature, so that only minimal or no optical or electro-optical tuning will be required after production.

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FIG. 4a schematically shows a first exemplary embodiment of an assembly (4) according to the invention, composed of a number of devices according to the invention, partly in series and partly in parallel, with a combination of single-mode and multimode, input and output waveguides. It is a 1x4 wavelength multiplexer demultiplexer with a multimode input waveguide (103) and a single-mode input waveguide (104), and a first intermediate multimode waveguide (203/105) which splits into two second intermediate multimode waveguides (204 / 106; 205/07). The two second intermediate multimode waveguides 204/106; 205/07) again split into four third intermediate multimode waveguides (206/108; 207/109; 208/110; 209 / III) which result in four multimode output waveguides (214 -217) and four single-mode output waveguides (210-213).

Light is coupled into the multi-mode input waveguide (103) from the input single-mode waveguide (104), as in the above-described second embodiment (3). Finally, light is coupled from the third intermediate multimode waveguides (206/108; 207/109; 208/110; 209/111) into the single-mode output waveguides (210-213).

FIG. 4b gives the calculated dispersion characteristics at the input (IN), where virtually no interaction takes place between the input single-mode waveguide (104) and the multi-mode input waveguide (103). The thick solid lines in FIG. 4b correspond to the multimode input waveguide (103), the thin solid line with the input single-mode waveguide (104) and the dotted lines with the multi-mode waveguides (206-209) at the location of section D (D). The width of these multi-mode waveguides (206-209) is indicated as 8.11 µm, 7.77 µm, 7.93 µm and 7.60 µm, respectively.

FIG. 4c shows schematically the dispersion characteristics of the (system) modes at the input (IN), at the location of section C (C) and at the output (OUT).

In FIG. 4d, the calculated transmission curves based on BPM (beam propagation 30 method) calculations are given. Each curve corresponds to the output of one of the single-mode output waveguides (210-213). The flat pass belts are typical of the type of devices according to the invention. The performance of the device depends on the adiabaticity, and therefore on the length of the device. The edges of the transmission curves are not infinitely steep because there are always wave length areas where the condition κη «Δβη (see earlier) is not met everywhere I Fig. 5a schematically shows a third exemplary embodiment (5) of a device according to the invention with two, a single-mode (113) and a multimode (112), input waveguides and three, a multimode (219) and two single-mode (218,220), output waveguides. The I device is again designed such that the input waveguides (112, 113) merge adiabatically into the output waveguides (218-220), the relevant (system) modes within I selected wavelength ranges (δλρ, δλρ *) being guided everywhere.

FIG. 5b shows schematically the corresponding dispersion characteristics at the input (IN) and the output (OUT). The substantially horizontal lines correspond to the I dispersion characteristics of the single-mode waveguides (113,218,220) and the almost I vertical lines to those of the multi-mode waveguide (112/219). The order of the (system) modes is indicated by the different types of lines. In FIG. 5b the production tolerances can be read from the positioning (λ3 - Xi) of the different intersections I in the joint dispersion characteristics with respect to the selected wavelength ranges (δλρ, άί, ρ '). With the help of FIG. 5b, it can be seen that light with an I wavelength falling within the first selected wavelength range δλρ of the single-mode input I waveguide (113) will be transmitted to the first output waveguide (218), while I light with a wavelength falling within the second selected wavelength range δλρ 'from the I single-mode input waveguide (113) to the second output waveguide (220) will be guided.

FIG. 6a, finally, schematically shows a second exemplary embodiment (6) of an assembly I according to the invention, composed of three devices according to the invention, partly in series I and partly in parallel, with a combination of single-mode and multimode, input and output I waveguides. FIG. 6b shows schematically the corresponding dispersion characteristics.

Immediately after the first coupling, the multi-mode waveguide (222) is narrowed somewhat to achieve a shift to the left in the dispersion characteristic of this multi-mode waveguide.

With the help of FIG. 6b it can be seen that the signals with different wavelengths are "routed" according to the indicated arrows. Wavelengths Λ, βη are "routed" to the single-mode waveguide (223) and and / l4 to the single-mode waveguide (221). The wavelengths are then further split to ultimately be led separately to the single-mode output waveguides (224-227).

Devices and assemblies according to the invention can be manufactured using integrated optical technology.

'Integrated optical technology' includes all in the micro-technical field, also known as 'microsystem technology' or 'micro-structural technology', applied design techniques such as wet chemical etching, 'reactive ion etching', 'UGA', 10 'sacrificial layer etching' , and thin film techniques for applying and processing thin layers such as depositing, sputtering, oxidizing, nitrating, implanting or chemical vapor deposition, whether or not in combination with a lithographic technique. Application of said techniques offers the possibility of extensive integration possibilities in the design and production of the device or assembly with additional cost reduction, and the possibility of manufacturing small-sized parts with the required great precision, and the possibility of having the required large number of components on. to achieve a small surface.

It will be clear that the invention, although discussed and elucidated on the basis of a limited number of exemplary embodiments, comprises an in principle unlimited number of possible devices and assemblies with which according to a method according to the invention an in principle unlimited number of types of wavelength-dependent processing of optical signals can be performed, such as wavelength-dependent splitting and merging, wavelength multiplexing-demultiplexing, and wavelength-dependent filtering.

25 λ λ n r λ Λ e

Claims (15)

A device for processing wavelength-dependent optical signals, in particular a wavelength multiplexer-demultiplexer or a wavelength-dependent Alt, which device comprises one or more input waveguides and two or more output waveguides I, wherein, by a correct choice of geometry and material properties, the I device within a first selected wavelength range, going from input to output, I everywhere conducts a first (system) mode of a first certain order / adiabatically. Apparatus as claimed in claim 1, wherein, also by a correct choice of geometry and I material properties, the first (system) mode within the first selected I wavelength range at the input substantially coincides with a mode guided by a first input waveguide. I 15 Apparatus as claimed in claim 1, wherein, also by a correct choice of geometry and I material properties, the first (system) mode within the first selected I wavelength range at the input substantially coincides with a mode guided by a plurality of first I input waveguides. I 20 Device as claimed in any of the claims 1-3, wherein also by a correct choice of I geometry and material properties, the first (system) mode within the first I selected wavelength range at the output substantially coincides with a conductor guided by a first output waveguide fashion. I 25 5. Device as claimed in any of the claims 1-3, wherein also, by a correct choice of I geometry and material properties, the first (system) mode within the first I selected wavelength range at the output substantially coincides with a conductor guided by a plurality of first output waveguides fashion. I 30 A device according to any one of the preceding claims, wherein, also by a correct choice of geometry and material properties, the device within a second chosen H wavelength range, going from input to output, everywhere a second (system) mode of a second determined order V adiabatic conducts 7. Device as claimed in claim 6, wherein also by a correct choice of geometry and material properties, the second (system) mode within the second chosen wavelength range at the input substantially coincides with a mode guided by a second input waveguide. 5 8. Device as claimed in claim 6, wherein also by a correct choice of geometry and material properties, the second (system) mode within the second chosen wavelength range at the input substantially coincides with a mode guided by a plurality of second input waveguides. 10 Device according to any of claims 6-8, wherein, also by a correct choice of geometry and material properties, the second (system) mode within the second selected wavelength range at the output substantially coincides with a mode guided by a second output waveguide. 15 Device as claimed in any of the claims 6-8, wherein also by a correct choice of geometry and material properties, the second (system) mode within the second chosen wavelength range at the output substantially coincides with a mode guided by a plurality of second output waveguides. 20 Device as claimed in any of the claims 6-10, wherein the first determined order / is an even order, and the second determined order / 'is an odd order, wherein for example / = /' + 1. The device of any one of claims 6-10, wherein: 25. the first (system) mode is a TE (transversely electrically polarized) mode; - the second (system) mode is a TM (transversally magnetically polarized) mode; - / = / '; and the first selected wavelength region and the second selected wavelength region 30 coincide. j λ / 1 r λ O /? 13. An assembly for wavelength-dependent processing of optical signals, in particular wavelength multiplexing-demultiplexing and wavelength-dependent filtering, which assembly comprises two or more devices according to one of the preceding claims. A method for processing wavelength-dependent optical signals, in particular wavelength multiplexing-demultiplexing or wavelength-dependent filtering, by means of a device according to any one of claims 1-12. 15. Method for processing wavelength-dependent optical signals, in particular wavelength multiplexing-demultiplexing or wavelength-dependent filtering, by means of an assembly according to claim 13.