CA2306325A1 - Mmi thermo-optic coupler - Google Patents
Mmi thermo-optic coupler Download PDFInfo
- Publication number
- CA2306325A1 CA2306325A1 CA 2306325 CA2306325A CA2306325A1 CA 2306325 A1 CA2306325 A1 CA 2306325A1 CA 2306325 CA2306325 CA 2306325 CA 2306325 A CA2306325 A CA 2306325A CA 2306325 A1 CA2306325 A1 CA 2306325A1
- Authority
- CA
- Canada
- Prior art keywords
- cladding
- coupler
- core
- light
- mmi
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
- G02B6/2808—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs
- G02B6/2813—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs based on multimode interference effect, i.e. self-imaging
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/125—Bends, branchings or intersections
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/264—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting
- G02B6/266—Optical coupling means with optical elements between opposed fibre ends which perform a function other than beam splitting the optical element being an attenuator
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12083—Constructional arrangements
- G02B2006/121—Channel; buried or the like
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
- Optical Integrated Circuits (AREA)
Abstract
A multi-mode interference coupler is disclosed for coupling light between ports. The MMI coupler is a planar waveguide having a first input port for launching light into a core of the planar waveguide which has first refractive index n1. The waveguide is dimensioned to have a response that confines light launched therein to a single mode in one dimension, and multi-mode in another dimension. Two other ports are provided for receiving light launched into and propagating through the core from the input port. A polymer cladding of a second material having a refractive index n2 covers at least a portion of the core. A heater is provided and is thermally coupled to the cladding for heating the cladding when a control signal is applied.
Description
Doc. No. 10-312 CA Patent MMI Thermo-Optic Coupler Field of the Invention This invention relates to a mufti-mode (MMI) coupler, and more particularly to an MMI
coupler having a polymer cladding.
Background of the Invention In the processing of light beams for example, in telecommunications applications, important and desired functions are the splitting and combining of light beams. In conventional optics, prisms or pellicle splitters are used for this purpose.
Attempts are continually being made to reduce the dimensions of the optical components to a considerable extent. On the one hand, it is being attempted in three dimensions to realise the processing of light beams by means of interference phenomena such as holography and free space optics. On the other hand, the technique of integrated optics is developing very rapidly. In this technique, waveguides are patterned on thin-film layers.
It is an object of integrated optics to realise the functionality of the components used in 2o conventional optics by new, integrable optical elements. This research field has found important applications in the field of communication.
In fiber-optical communication, data are transmitted by means of optical signals through optical fibers. The optical signals are processed on integrated optical chips which are placed between the fibers. To manufacture these chips, generally thin-film layers are provided on support substrates such as, for example glass, Si, InP, GaAs and subsequently structured.
In optical waveguides the light is guided through a medium referred to as the waveguide 3o core. The guidance is realised in that the waveguide core is bounded by a reflecting transition. In cavity waveguides, a metal is used for this purpose. In dielectric Doc. No. 10-312 CA Patent waveguides, the total reflection on a surrounding medium having a smaller refractive index the waveguide cladding is used. In optical waveguides, only those modes can propagate which fulfil the Maxwell equations. The waveguides are referred to as cut-off, monomode or multimode waveguides, dependent on whether they can guide no mode, only one mode for each polarization or a plurality of modes.
In waveguides, the light propagates in the longitudinal z direction. The x direction is parallel to the waveguide layer and is defined as the horizontal, or lateral direction.
Analogously, the y direction is vertical to the waveguide layer and is defined as the to vertical, or transversal direction. The propagation of light on the chips is computed by means of numerical methods such as beam propagation (BPM) methods, or modal propagation analysis (MPA) methods. In some cases, semi-analytical computations such as the effective index method (EIM) are used. The Maxwell equations are often solved in a scalar approximation. These equations describe the planar optics exactly.
Two 15 polarizations can be distinguished: the TE polarization has the E vector in the x direction and the TM polarization has the H vector in the x direction. For the most frequently used dielectric waveguides in integrated optics, the scalar approximation leads to "quasi-TE"
and "quasi-TM" modes: In such waveguides, the mode forms and the "effective"
indexes may be dependent on the polarization. In many cases it is very much desirable, but very 2o difficult, to produce components which are independent of polarization. It should be noted that "monomode" waveguides often have a mode for each polarization, i.e.
overall, there are often two modes in "monomode" waveguides. These are degenerate modes in normal optical glass fibers.
25 Important components in integrated optics are the beam splitters and combiners.
Generally, one refers to N x M splitters. N x M denote the number of inputs and outputs.
Ideally, these splitters should have the following properties: they should be compact (having small dimensions), independent of polarization, not very sensitive to manufacturing inaccuracies and easy to produce. Moreover, it should be possible to 3o readily adapt the splitting or combining ratios to the various applications by geometrical changes in the design. Various beam splitters and combiners have already been realised:
coupler having a polymer cladding.
Background of the Invention In the processing of light beams for example, in telecommunications applications, important and desired functions are the splitting and combining of light beams. In conventional optics, prisms or pellicle splitters are used for this purpose.
Attempts are continually being made to reduce the dimensions of the optical components to a considerable extent. On the one hand, it is being attempted in three dimensions to realise the processing of light beams by means of interference phenomena such as holography and free space optics. On the other hand, the technique of integrated optics is developing very rapidly. In this technique, waveguides are patterned on thin-film layers.
It is an object of integrated optics to realise the functionality of the components used in 2o conventional optics by new, integrable optical elements. This research field has found important applications in the field of communication.
In fiber-optical communication, data are transmitted by means of optical signals through optical fibers. The optical signals are processed on integrated optical chips which are placed between the fibers. To manufacture these chips, generally thin-film layers are provided on support substrates such as, for example glass, Si, InP, GaAs and subsequently structured.
In optical waveguides the light is guided through a medium referred to as the waveguide 3o core. The guidance is realised in that the waveguide core is bounded by a reflecting transition. In cavity waveguides, a metal is used for this purpose. In dielectric Doc. No. 10-312 CA Patent waveguides, the total reflection on a surrounding medium having a smaller refractive index the waveguide cladding is used. In optical waveguides, only those modes can propagate which fulfil the Maxwell equations. The waveguides are referred to as cut-off, monomode or multimode waveguides, dependent on whether they can guide no mode, only one mode for each polarization or a plurality of modes.
In waveguides, the light propagates in the longitudinal z direction. The x direction is parallel to the waveguide layer and is defined as the horizontal, or lateral direction.
Analogously, the y direction is vertical to the waveguide layer and is defined as the to vertical, or transversal direction. The propagation of light on the chips is computed by means of numerical methods such as beam propagation (BPM) methods, or modal propagation analysis (MPA) methods. In some cases, semi-analytical computations such as the effective index method (EIM) are used. The Maxwell equations are often solved in a scalar approximation. These equations describe the planar optics exactly.
Two 15 polarizations can be distinguished: the TE polarization has the E vector in the x direction and the TM polarization has the H vector in the x direction. For the most frequently used dielectric waveguides in integrated optics, the scalar approximation leads to "quasi-TE"
and "quasi-TM" modes: In such waveguides, the mode forms and the "effective"
indexes may be dependent on the polarization. In many cases it is very much desirable, but very 2o difficult, to produce components which are independent of polarization. It should be noted that "monomode" waveguides often have a mode for each polarization, i.e.
overall, there are often two modes in "monomode" waveguides. These are degenerate modes in normal optical glass fibers.
25 Important components in integrated optics are the beam splitters and combiners.
Generally, one refers to N x M splitters. N x M denote the number of inputs and outputs.
Ideally, these splitters should have the following properties: they should be compact (having small dimensions), independent of polarization, not very sensitive to manufacturing inaccuracies and easy to produce. Moreover, it should be possible to 3o readily adapt the splitting or combining ratios to the various applications by geometrical changes in the design. Various beam splitters and combiners have already been realised:
2 Doc. No. 10-312 CA Patent Symmetrical Y branches are simple solutions for lx 2 splitters with a 50%/50%
intensity ratio. Asymmetrical Y branches yield other intensity ratios but, due to coupling effects, they are often polarization-dependent between the two outputs. For manufacturing Y
branches, a high resolution, particularly in the sharp bifurcation, is required. They are very sensitive to manufacturing inaccuracies.
Directional couplers with two parallel waveguides separated by means of a narrow slit operate as 2 x 2 sputters. However the coupling length is, however, very sensitive to 1 o manufacturing parameters, particularly as regards slit width and depth.
The coupling length is also very much dependent on polarization. "Two-mode" interference (TMI) couplers without a slit also operate as 2 x 2 splitters. The intensity ratio is, however, very much dependent on the coupling into the input and output Y branches.
Consequently, they are very sensitive to manufacturing conditions. United States Patent 5,857,039 15 describes a thermo-optically activated directional coupler having a polymer guide buffer layer and a heater which allows the refractive index of the polymer to be varied. Of course it is well known that polymer has a higher refractive index variation with temperature than silica and better heat confinement. The '039 patent extols the virtues of polymer over silica especially in the interguide space. When the interguide space is small 2o in relation to the dimensions of the cross section, the guides can only be properly covered by the mineral layer, particularly in the case of silica coverings, by a so-called "FHD"
technique which is extremely difficult to apply. Therefore, the '039 patent provides a solution which is tailored to providing a more practicably directional coupler.
25 It is somewhat obvious, in hindsight, that in a directional coupler wherein coupling of light across a cladding boundary between two closely spaced waveguides is to be accomplished, that the boundary region must be controlled to increase or decrease the coupling across this region. Ergo, in order to allow the two single mode signals to couple, or to remain isolated, in a controlled manner, this intermediary cladding region must be 30 highly manufacturable and controllable. As the '039 patent purports, a polymer disposed between these cores, provides a practicable solution.
intensity ratio. Asymmetrical Y branches yield other intensity ratios but, due to coupling effects, they are often polarization-dependent between the two outputs. For manufacturing Y
branches, a high resolution, particularly in the sharp bifurcation, is required. They are very sensitive to manufacturing inaccuracies.
Directional couplers with two parallel waveguides separated by means of a narrow slit operate as 2 x 2 sputters. However the coupling length is, however, very sensitive to 1 o manufacturing parameters, particularly as regards slit width and depth.
The coupling length is also very much dependent on polarization. "Two-mode" interference (TMI) couplers without a slit also operate as 2 x 2 splitters. The intensity ratio is, however, very much dependent on the coupling into the input and output Y branches.
Consequently, they are very sensitive to manufacturing conditions. United States Patent 5,857,039 15 describes a thermo-optically activated directional coupler having a polymer guide buffer layer and a heater which allows the refractive index of the polymer to be varied. Of course it is well known that polymer has a higher refractive index variation with temperature than silica and better heat confinement. The '039 patent extols the virtues of polymer over silica especially in the interguide space. When the interguide space is small 2o in relation to the dimensions of the cross section, the guides can only be properly covered by the mineral layer, particularly in the case of silica coverings, by a so-called "FHD"
technique which is extremely difficult to apply. Therefore, the '039 patent provides a solution which is tailored to providing a more practicably directional coupler.
25 It is somewhat obvious, in hindsight, that in a directional coupler wherein coupling of light across a cladding boundary between two closely spaced waveguides is to be accomplished, that the boundary region must be controlled to increase or decrease the coupling across this region. Ergo, in order to allow the two single mode signals to couple, or to remain isolated, in a controlled manner, this intermediary cladding region must be 30 highly manufacturable and controllable. As the '039 patent purports, a polymer disposed between these cores, provides a practicable solution.
3 Doc. No. 10-312 CA Patent The use of a polymer cladding on an silica filament strand of optical fibre is well known, and has been disclosed in United States Patent 4,116,654 issue September 26, 1978.
In this patent it is stated that "Where low attenuation of transmitted light in an optical fiber material is critical, the preferred material for the filamentary core is silica, since it has one of the lowest attenuations presently known. Suitable cladding materials known in the art include thermoplastic polymers which have an index of refraction lower than that of the core; and which preferably are substantially amorphous."
I o A further mention of polymer cladding is found in United States Patent 5,873,923 in the name of DiGiovanni, with reference to optical amplifiers.
In this patent, a polymer cladding is suggested in a mufti-clad fibre amplifier, where the 923 patent states that "Any polymer cladding serves little purpose beyond guiding".
Considering the teaching of DiGiovanni, and that of United States Patent 5,857,039, it is evident that the cladding gu~~e~ the liht within a waveguide or optical fibre and when the relative refractive index difference between the cladding and the core is varied the confinement of light within a guide varies as well.
What is surprising however, is that significance of providing a cladding on a mufti-mode coupler which operates under a very different regime. What is further surprising is how coupling within a wide MMI core is affected by varying the cladding on top.
Notwithstanding, this will be explained.
In the last few years, multimode interference (MMI) couplers have become more and more popular. These components are waveguide sections guiding a plurality of modes.
They are produced, for example by widening a conventional waveguide structure until it guides a sufficient number of modes. The lateral guidance is then, for example, also often 3o increased. Thanks to their self imaging property, these couplers operate as N x M
splitters in two or three dimensions. "Conventional" MMI couplers as used throughout
In this patent it is stated that "Where low attenuation of transmitted light in an optical fiber material is critical, the preferred material for the filamentary core is silica, since it has one of the lowest attenuations presently known. Suitable cladding materials known in the art include thermoplastic polymers which have an index of refraction lower than that of the core; and which preferably are substantially amorphous."
I o A further mention of polymer cladding is found in United States Patent 5,873,923 in the name of DiGiovanni, with reference to optical amplifiers.
In this patent, a polymer cladding is suggested in a mufti-clad fibre amplifier, where the 923 patent states that "Any polymer cladding serves little purpose beyond guiding".
Considering the teaching of DiGiovanni, and that of United States Patent 5,857,039, it is evident that the cladding gu~~e~ the liht within a waveguide or optical fibre and when the relative refractive index difference between the cladding and the core is varied the confinement of light within a guide varies as well.
What is surprising however, is that significance of providing a cladding on a mufti-mode coupler which operates under a very different regime. What is further surprising is how coupling within a wide MMI core is affected by varying the cladding on top.
Notwithstanding, this will be explained.
In the last few years, multimode interference (MMI) couplers have become more and more popular. These components are waveguide sections guiding a plurality of modes.
They are produced, for example by widening a conventional waveguide structure until it guides a sufficient number of modes. The lateral guidance is then, for example, also often 3o increased. Thanks to their self imaging property, these couplers operate as N x M
splitters in two or three dimensions. "Conventional" MMI couplers as used throughout
4 Doc. No. 10-312 CA Patent the specification and the following claims are understood to be those elements having parallel sides. It is to be noted that MMI couplers can also be made with slanting sides.
Several prior art patents describe the function and operation of the MMI
couplers, such as United States Patent 5,698,597 in the name of Besse, issued November 18, 1997, and United States Patent 5,953,467 in the name of Madsen issued September 14, 1999, both incorporated herein by reference. Since the invention deals exactly with this point, it is necessary to elucidate the properties of the "conventional" MMI couplers.
Heretofore, MMI couplers have been very difficult to manufacture with a great deal of to accuracy. Notwithstanding, since these devices are not highly tolerant to imperfect manufacturing, producing MMI couplers has been a feat, and until now, has remained a costly process. The invention discovered here concerns providing a polymer layer atop the MMI wide core and lessens the requirement for accuracy in manufacturing and allows a device to be tuned to meet required specifications, within predetermined limits. For 15 example, a poorly manufactured device can be tuned to perform as a perfectly manufactured device that meets its original specifications. Hence, many fewer devices are rejected and discarded as rejects.
A second advantage of this invention is that devices can be tuned to provide a controlled 20 and variable output. For example, the MMI coupler can function as a switch or a variable coupler.
In hindsight, after considering this invention, it is not intuitive, since multi-modes are mixed with a single wide guide having confinement only in the vertical dimension 25 wherein the modes are "essentially" free to mix in a lateral dimension;
thus it is quite surprising that the discovery of the provision of a polymer confining layer over top of the single multi-mode guide would yield any significant advantage.
Notwithstanding, best mode working embodiments will be described.
Doc. No. 10-312 CA Patent Summary of the Invention It is an object of the invention to provide an MMI coupler that is tunable and that is more tolerant to manufacturing inaccuracies due to its tunability.
In accordance with the invention a mufti-mode interference coupler for coupling light between ports is provided, comprising:
a first input port for launching light into a core of a substantially planar waveguide-of a 1o first material having a first refractive index n,, the substantially planar waveguide having a response that confines the light to a single mode in one dimension, and mufti-mode in another dimension;
at least two output ports for receiving light launched into and propagating through the core from the input port;
a polymer cladding of a second material having a refractive index n2 covering at least a portion of the core; and, a heater thermally coupled to said cladding for heating the cladding in dependence upon a control signal, to vary at least one of a) the amount of light received at the at least two output ports and, b) the ratio of light distributed between the output ports, wherein at least one of the first material and the second material is a polymer.
Brief Description of the Drawings Exemplary embodiments of the invention will now be described in conjunction with the drawings in which:
Fig. la is a top view of an MMI-based thermo-optic switch/attenuator;
3o Fig. lb is a cross-section of the device having a polymer cladding;
Fig. 2 is a typical plot of the ratio WelW of a MMI coupler against the refractive index Doc. No. 10-312 CA Patent of the cladding, wherein the refractive index of the core has been kept fixed at 1.5.
Detailed Description Referring now to Figs. 1 a and 1 b, a thermo-optic optical switch or attenuator in the form of an MMI couplers as shown. The MMI coupler has two input ports and two output ports. Alternatively one input port can be provided. This device can be used as a switch or an attenuator. Switching is done by changing the temperature of the device through the heating element placed on top of the device. Alternatively, the same thermo-optic 1 o effect can be used to initially compensate for the fabrication variations of the coupler.
A most important parameter in the design of MMI couplers is their beatlength, L,~. After fabrication of a device, tuning and switching can be performed by varying its beatlength.
For MMI couplers, the beat length at a wavelength ~ is defined as L - 7Z' 4Yl~erWe (1) where ,Qo and ,13, are the propagation constants of the fundamental and first order modes, respectively, n,,e~ is the slab effective index at the guiding region, and We is the effective width of the fundamental transverse mode. The effective width (We) is slightly larger than the actual width ( W) of the multimode waveguide and takes into account the lateral 2o penetration depth of the modal field. The effective width depends on the waveguide characteristics. It can be approximated by the effective width of the fundamental mode and is given by 2a We - W + ~ ~~ ~ n2 ~ ~n~ - n2 ) ~ 1~2~ (2) n~
where a= 0 for TE, a= 1 for TM, and n~ and n2 are the refractive indices of the core and cladding, respectively.
To change the beatlength, n,,er and/or We can be varied. As indicated in Equation ( 1 ), the beatlength is directly dependent on the square of We and, therefore, varying We rather Doc. No. 10-312 CA Patent than n,,e~ has much more pronounced effect on the beatlength. We can be changed by varying the index contrast between the core and cladding of the waveguide. If core and cladding have similar themo-optic coefficients (dn/dT), then we can only change n,,er ~d not We by changing the.temperature of the device. However, If the core and cladding of the waveguides are selected to have suitable refractive indices and of different materials with different thermo-optic coefficients, then the effective width We can be altered by changing the temperature.
Fig. 2 illustrates a variation of the ratio WelW against the changes of the refractive index l0 of the cladding for a given MMI coupler. It can be seen that the rate of change of the ratio WelW is faster as the refractive indices of the core and cladding become close together. This is evident from Equation (2) wherein the difference between We and W
gets smaller for waveguide with higher contrast (i.e., larger difference between n, and n2). Thus, if the MMI coupler is weakly confining, the effective width of the MMI
coupler can be changed efficiently by varying the refractive index of either the core or the cladding, while keeping the other one relatively unchanged. This method is much more effective than changing n~er~
Exemplary embodiment The parameter values shown in the following table show a design example. A
change of 0.01 in the refractive index value of the cladding is required for the switching operation.
Assuming a dn2/dT--2.5* 10~/K, which is a typical value for polymers, the required change in the temperature of the device for 0.01 change in refractive index of the cladding is about 40 degrees Centigrade. The coupler length is about 670 ,um.
An extinction ratio of more than 20 dB can be easily achieved. The device has a wide bandwidth.
Doc. No. 10-312 CA Patent MMI in/out guidesmore = 1.50 Width 8 ,cmi3 ,um n~tad ~ = 1.49 L,~, = 167.5 ,um # of modes2/3 1 n~rpa2 = 1.48 L,~2 = 133.5 ~cm Of course, numerous other embodiments may be envisaged, without departing from the spirit and scope of the invention.
Several prior art patents describe the function and operation of the MMI
couplers, such as United States Patent 5,698,597 in the name of Besse, issued November 18, 1997, and United States Patent 5,953,467 in the name of Madsen issued September 14, 1999, both incorporated herein by reference. Since the invention deals exactly with this point, it is necessary to elucidate the properties of the "conventional" MMI couplers.
Heretofore, MMI couplers have been very difficult to manufacture with a great deal of to accuracy. Notwithstanding, since these devices are not highly tolerant to imperfect manufacturing, producing MMI couplers has been a feat, and until now, has remained a costly process. The invention discovered here concerns providing a polymer layer atop the MMI wide core and lessens the requirement for accuracy in manufacturing and allows a device to be tuned to meet required specifications, within predetermined limits. For 15 example, a poorly manufactured device can be tuned to perform as a perfectly manufactured device that meets its original specifications. Hence, many fewer devices are rejected and discarded as rejects.
A second advantage of this invention is that devices can be tuned to provide a controlled 20 and variable output. For example, the MMI coupler can function as a switch or a variable coupler.
In hindsight, after considering this invention, it is not intuitive, since multi-modes are mixed with a single wide guide having confinement only in the vertical dimension 25 wherein the modes are "essentially" free to mix in a lateral dimension;
thus it is quite surprising that the discovery of the provision of a polymer confining layer over top of the single multi-mode guide would yield any significant advantage.
Notwithstanding, best mode working embodiments will be described.
Doc. No. 10-312 CA Patent Summary of the Invention It is an object of the invention to provide an MMI coupler that is tunable and that is more tolerant to manufacturing inaccuracies due to its tunability.
In accordance with the invention a mufti-mode interference coupler for coupling light between ports is provided, comprising:
a first input port for launching light into a core of a substantially planar waveguide-of a 1o first material having a first refractive index n,, the substantially planar waveguide having a response that confines the light to a single mode in one dimension, and mufti-mode in another dimension;
at least two output ports for receiving light launched into and propagating through the core from the input port;
a polymer cladding of a second material having a refractive index n2 covering at least a portion of the core; and, a heater thermally coupled to said cladding for heating the cladding in dependence upon a control signal, to vary at least one of a) the amount of light received at the at least two output ports and, b) the ratio of light distributed between the output ports, wherein at least one of the first material and the second material is a polymer.
Brief Description of the Drawings Exemplary embodiments of the invention will now be described in conjunction with the drawings in which:
Fig. la is a top view of an MMI-based thermo-optic switch/attenuator;
3o Fig. lb is a cross-section of the device having a polymer cladding;
Fig. 2 is a typical plot of the ratio WelW of a MMI coupler against the refractive index Doc. No. 10-312 CA Patent of the cladding, wherein the refractive index of the core has been kept fixed at 1.5.
Detailed Description Referring now to Figs. 1 a and 1 b, a thermo-optic optical switch or attenuator in the form of an MMI couplers as shown. The MMI coupler has two input ports and two output ports. Alternatively one input port can be provided. This device can be used as a switch or an attenuator. Switching is done by changing the temperature of the device through the heating element placed on top of the device. Alternatively, the same thermo-optic 1 o effect can be used to initially compensate for the fabrication variations of the coupler.
A most important parameter in the design of MMI couplers is their beatlength, L,~. After fabrication of a device, tuning and switching can be performed by varying its beatlength.
For MMI couplers, the beat length at a wavelength ~ is defined as L - 7Z' 4Yl~erWe (1) where ,Qo and ,13, are the propagation constants of the fundamental and first order modes, respectively, n,,e~ is the slab effective index at the guiding region, and We is the effective width of the fundamental transverse mode. The effective width (We) is slightly larger than the actual width ( W) of the multimode waveguide and takes into account the lateral 2o penetration depth of the modal field. The effective width depends on the waveguide characteristics. It can be approximated by the effective width of the fundamental mode and is given by 2a We - W + ~ ~~ ~ n2 ~ ~n~ - n2 ) ~ 1~2~ (2) n~
where a= 0 for TE, a= 1 for TM, and n~ and n2 are the refractive indices of the core and cladding, respectively.
To change the beatlength, n,,er and/or We can be varied. As indicated in Equation ( 1 ), the beatlength is directly dependent on the square of We and, therefore, varying We rather Doc. No. 10-312 CA Patent than n,,e~ has much more pronounced effect on the beatlength. We can be changed by varying the index contrast between the core and cladding of the waveguide. If core and cladding have similar themo-optic coefficients (dn/dT), then we can only change n,,er ~d not We by changing the.temperature of the device. However, If the core and cladding of the waveguides are selected to have suitable refractive indices and of different materials with different thermo-optic coefficients, then the effective width We can be altered by changing the temperature.
Fig. 2 illustrates a variation of the ratio WelW against the changes of the refractive index l0 of the cladding for a given MMI coupler. It can be seen that the rate of change of the ratio WelW is faster as the refractive indices of the core and cladding become close together. This is evident from Equation (2) wherein the difference between We and W
gets smaller for waveguide with higher contrast (i.e., larger difference between n, and n2). Thus, if the MMI coupler is weakly confining, the effective width of the MMI
coupler can be changed efficiently by varying the refractive index of either the core or the cladding, while keeping the other one relatively unchanged. This method is much more effective than changing n~er~
Exemplary embodiment The parameter values shown in the following table show a design example. A
change of 0.01 in the refractive index value of the cladding is required for the switching operation.
Assuming a dn2/dT--2.5* 10~/K, which is a typical value for polymers, the required change in the temperature of the device for 0.01 change in refractive index of the cladding is about 40 degrees Centigrade. The coupler length is about 670 ,um.
An extinction ratio of more than 20 dB can be easily achieved. The device has a wide bandwidth.
Doc. No. 10-312 CA Patent MMI in/out guidesmore = 1.50 Width 8 ,cmi3 ,um n~tad ~ = 1.49 L,~, = 167.5 ,um # of modes2/3 1 n~rpa2 = 1.48 L,~2 = 133.5 ~cm Of course, numerous other embodiments may be envisaged, without departing from the spirit and scope of the invention.
Claims (5)
1. A multi-mode interference coupler for coupling light between ports, comprising:
a first input port for launching light into a core of a substantially planar waveguide-of a first material having a first refractive index n1, the substantially planar waveguide having a response that confines the light to a single mode in one dimension, and multi-mode in another dimension;
at least two output ports for receiving light launched into and propagating through the core from the input port;
a polymer cladding of a second material having a refractive index n2 covering at least a portion of the core; and, a heater thermally coupled to said cladding for heating the cladding in dependence upon a control signal, to vary at least one of a) the amount of light received at the at least two output ports and, b) the ratio of light distributed between the output ports, wherein at least one of the first material and the second material is a polymer.
a first input port for launching light into a core of a substantially planar waveguide-of a first material having a first refractive index n1, the substantially planar waveguide having a response that confines the light to a single mode in one dimension, and multi-mode in another dimension;
at least two output ports for receiving light launched into and propagating through the core from the input port;
a polymer cladding of a second material having a refractive index n2 covering at least a portion of the core; and, a heater thermally coupled to said cladding for heating the cladding in dependence upon a control signal, to vary at least one of a) the amount of light received at the at least two output ports and, b) the ratio of light distributed between the output ports, wherein at least one of the first material and the second material is a polymer.
2. A coupler for coupling as defined in claim 1, wherein the first material is a non-polymer.
3. A coupler as defined in claim 2, wherein first material is glass.
4. A coupler as defined in claim 3 further wherein the MMI coupler is a thermo-optic switch, splitter, or attenuator and wherein the first input port is at a first end and wherein the at least two output ports are at a second end.
5. A coupler as defined in claim 2, further comprising a second input port, adjacent the first input port.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2306325 CA2306325A1 (en) | 1999-04-30 | 2000-04-20 | Mmi thermo-optic coupler |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002271159A CA2271159A1 (en) | 1999-04-30 | 1999-04-30 | Optical hybrid device |
| CA2,271,159 | 1999-04-30 | ||
| CA 2306325 CA2306325A1 (en) | 1999-04-30 | 2000-04-20 | Mmi thermo-optic coupler |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2306325A1 true CA2306325A1 (en) | 2000-10-30 |
Family
ID=25680930
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2306325 Abandoned CA2306325A1 (en) | 1999-04-30 | 2000-04-20 | Mmi thermo-optic coupler |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2306325A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1378776A1 (en) * | 2002-07-01 | 2004-01-07 | Agilent Technologies, Inc. | Optical attenuator using a multi-mode waveguide with a perturbation element |
| WO2006012141A1 (en) * | 2004-06-29 | 2006-02-02 | E.I. Dupont De Nemours And Company | Ultrahigh-index-contrast planar strictly non-blocking high-port-count cross-connect switch matrix |
| SG125124A1 (en) * | 2004-06-30 | 2006-09-29 | Agency Science Tech & Res | Enhanced multimode interference coupler |
| CN110426865A (en) * | 2019-07-31 | 2019-11-08 | 长春理工大学 | The thermo-optical switch of guided mode specular displacement effect and multimode interference effect is utilized in silicon waveguide corner mirror |
-
2000
- 2000-04-20 CA CA 2306325 patent/CA2306325A1/en not_active Abandoned
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1378776A1 (en) * | 2002-07-01 | 2004-01-07 | Agilent Technologies, Inc. | Optical attenuator using a multi-mode waveguide with a perturbation element |
| US6868222B2 (en) | 2002-07-01 | 2005-03-15 | Agilent Technologies, Inc. | Optical attenuator using a perturbation element with a multi-mode waveguide |
| WO2006012141A1 (en) * | 2004-06-29 | 2006-02-02 | E.I. Dupont De Nemours And Company | Ultrahigh-index-contrast planar strictly non-blocking high-port-count cross-connect switch matrix |
| SG125124A1 (en) * | 2004-06-30 | 2006-09-29 | Agency Science Tech & Res | Enhanced multimode interference coupler |
| CN110426865A (en) * | 2019-07-31 | 2019-11-08 | 长春理工大学 | The thermo-optical switch of guided mode specular displacement effect and multimode interference effect is utilized in silicon waveguide corner mirror |
| CN110426865B (en) * | 2019-07-31 | 2023-08-18 | 长春理工大学 | Thermo-optical switch utilizing guided mode reflection displacement effect and multimode interference effect in silicon waveguide corner mirror |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US6353694B1 (en) | MMI thermo-optic coupler | |
| Suzuki et al. | Integrated-optic double-ring resonators with a wide free spectral range of 100 GHz | |
| US7587110B2 (en) | Multicore optical fiber with integral diffractive elements machined by ultrafast laser direct writing | |
| US7376307B2 (en) | Multimode long period fiber bragg grating machined by ultrafast laser direct writing | |
| US8064741B2 (en) | Optical coupling device | |
| US6208798B1 (en) | Variable optical attenuator with thermo-optic control | |
| US5703975A (en) | Interferometric switch | |
| US9057839B2 (en) | Method of using an optical device for wavelength locking | |
| JP3349950B2 (en) | Wavelength demultiplexing circuit | |
| EP1509792A2 (en) | Integrated splitter with reduced losses | |
| Chen | A broadband wavelength demultiplexer assisted by SWG-based directional couplers | |
| CA2369191A1 (en) | Optical coupling structure | |
| CA2306325A1 (en) | Mmi thermo-optic coupler | |
| US6453094B1 (en) | All fiber DWDM multiplexer and demultiplexer | |
| KR20000059922A (en) | Add-drop wavelength filter using mode discrimination couplers and tilted Bragg gratings | |
| AU697911B2 (en) | Mach-zehnder switch | |
| JP2002511157A (en) | Narrowband transmission filter using Bragg grating for mode conversion | |
| KR100281552B1 (en) | Integrated Optical Variable Optical Attenuator Using Thermo-optic Effect | |
| Park et al. | Optimization of tilted Bragg grating tunable filters based on polymeric optical waveguides | |
| Melloni et al. | TriPleX: A new concept in optical waveguiding | |
| GB2329721A (en) | Optical attenuator | |
| Kohtoku | Low-loss compact silica-based AWG using deep ridge waveguide | |
| Mansuripur et al. | The beam propagation method | |
| Venghaus et al. | Polarization-independent Mach-Zehnder interferometer on III-V semiconductors | |
| Kavian et al. | Reza Talebzadeh, Mohammad Soroosh |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |