GB2528896A

GB2528896A - Methods and apparatus for phase shifting and modulation of light

Info

Publication number: GB2528896A
Application number: GB1413730.1A
Authority: GB
Inventors: Shiomo Goldin
Original assignee: Oriel Silicon Photonics Ltd
Current assignee: ORIEL SILICON PHOTONICS LTD.
Priority date: 2014-08-01
Filing date: 2014-08-01
Publication date: 2016-02-10
Anticipated expiration: 2034-08-01
Also published as: GB2528896B; GB201413730D0; WO2016035063A1

Abstract

A waveguide comprising a core and at least 2 photonic crystal mirrors is provided which is adapted to modulate light passing therethrough. The modulation may involve charge carrier density variation or carrier depletion in a reversed biased p-n junction. In some embodiments, the junction direction in which the doping changes is vertical. The waveguide is equipped with electrodes adapted to apply a DC voltage and is tunable to achieve a desired propagation constant of the light.

Description

APPLICATION FOR PATENT

TITLE: Methods and Apparatus for Phase Shifting and Modulation of Light INVENTOR: Shlomo GOLDIN

FIELD OF THE INVENTION

Exemplary embodiments of the invention are in the field of optical modulators.

BACKGROUND OF THE INVENTION

Optical modulators modulate light beams either in free space or as the beam propagates through a waveguide. Various types of optical modulators modulate amplitude, phase or polarization.

Some optical modulators rely upon change in the refractive index of a material resulting from application of a DC voltage or low frequency electric field. The DC voltage or low frequency electric field creates forces that distort the position, orientation, or shape of the molecules constituting the material, Alternatively, the DC voltage or low frequency electric field changes the concentration of free charge carriers in the material, SUM1VL&RY OF THE INVENTION One aspect of some embodiments of the invention relates to tuning a photonic crystal wave guide so that the propagation constant (13) of light passing therethrough is 0 to where is the vacuum wavelength of said light. In some embodiments, a modulation voltage is applied to the WG. In some embodiments, the modulation voltage shifts the dispersion curve so the WG is in a non-propagating state. Alternatively or additionally, in some embodiments the modulation voltage shifts the dispersion curve and contributes to a change in propagation constant 13. According to these embodiments, the group velocity is reduced so that the change in propagation constant is enhanced. Alternatively or additionally, in some O.ic O:lc cc embodiments, the group velocity of the light is 0 to where is the speed of light in vacuum.

Another aspect of some embodiments of the invention relates to photonic crystal optical waveguides which modulate light passing therethrough. In some embodiments, modulation involves charge carrier density variation, h some embodiments, modulation employs carrier depletion in a reversed biased p-n junction. In some embodiments, the junction direction in which the doping changes is the vertical direction. In some embodiments, modulation employs carrier accumulation. In some exemplary embodiments of the invention, the waveguide is equipped with electrodes adapted to apply a DC voltage.

Another aspect of some embodiments of the invention relates to an optical waveguide including photonic crystal mirrors, In some exemplary embodiments of the invention, the waveguide includes one or more series' of layers in a periodic vertical stack. In other exemplary embodiments of the invention, the waveguide includes a series of such layers in a horizontal series, In some exemplary embodiments of the invention, layers of this type are formed by overlaying on a modulator core which extends across only a portion of the width of the waveguide.

Another aspect of some embodiments of the invention relates to use of total internal reflection in the vertical direction in conj unction with periodicity in the horizontal direction and/or to use of total internal reflection in the horizontal direction in conjunction with periodicity in the vertical direction.

Alternatively or additionally, it will be appreciated that the various aspects described above relate to solution of technical problems related to implementation of modulation using microstructures (e.g. in board-to-board, chip-to-chip and on-chip context).

In accordance with some embodiments a method is provided that may include: (a) constructing a wave guide (WG) including at least 2 multilayer photonic crystal mirrors; (b) propagating light through a core of said WG; (c) tuning the WG so that the propagation

AA

constant (13) of the light is 0 to where is the vacuum wavelength of the light; and (d) applying a modulation voltage to the WG.

O.ic O.Ic cc In further embodiments the group velocity of the light is 0 to where is the speed of light in vacuum; and the modulation voltage shifts the dispersion curve so that the a6O.6t_c propagation constant (13) changes but remains in the range of 0 to -In further embodiments the modulation voltage shifts the dispersion curve so that said WG switches between propagating and non-propagating states.

In further embodiments the tuning includes application of a DC voltage to the WG.

In further embodiments the wave guide has a length 100 microns; j 50 microns; i microns or< tO microns or intermediate or shorter lengths.

In accordance with some embodiments, an apparatus is provided that may include: (a) a core bordered on at least two sides by photonic crystal mirrors; (b) a first pair of mirrors which constrain light vertically; (c) a second pair of mirrors which constrain light laterally; and (d a pair of electrodes adapted to apply a modulation voltage.

In further embodiments the first pair of mirrors comprises photonic crystal mirrors.

In further embodiments the first pair of mirrors comprise multilayer photonic crystal mirrors.

In further embodiments the first pair of minors provide total internal reflection to the core.

In further embodiments the second pair of mirrors provide total internal reflection to the core.

In further embodiments the second pair of minors comprise photonic crystal mirrors.

In further embodiments the second pair of minors comprise multilayer photonic crystal minors.

In further embodiments the second pair of mirrors results from bends in at least one minor of the first pair.

In further embodiments the second pair of minors includes two-dimensional photonic crystal mirrors.

In further embodiments the apparatus includes electrodes adapted to apply a DC tuning voltage.

In further embodiments the apparatus includes carrier depletion in a reversed biased p-n junction.

In further embodiments the junction direction in which doping changes is the vertical direction.

In further embodiments the reversed biased p-n junction is at a boundary between the core and one of the multilayer photonic crystal mirrors.

In further embodiments the apparatus includes carrier accumulation.

In accordance with some embodiments, an apparatus is provided that may include: (a) a pair of mirrors with periodically repeating layers I to X having refractive indices n1 to n; (b) a layer between the pair of mirrors contacting each of the mirrors and comprising a core having refractive index n and two flanking sections each having refractive index n. wherein n <nAand n,.)s different from the refractive index of an adjacent layer of either of the minors.

In some embodiments X= 2.

In some embodiments each of the minors includes a multilayer photonic crystal mirror.

In some embodiments the apparatus has carrier depletion in a reversed biased p-n junction.

In some embodiments the junction direction in which the doping changes is the vertical direction.

In some embodiments electrodes may be adapted to apply a DC voltage.

In accordance with some embodiments, an apparatus is provided that may include: (a) a pair of mirrors with periodically repeating layers 1 to X9 having refractive indices n11 to nxa; (b) a layer between the pair of minors contacting each of the mirrors comprising: (iA core having refractive index no: and (ii) two flanking sections each comprising photonic crystal minors.

In some embodiments the photonic crystal mirrors of the flanking sections comprise periodically repeating vertical bridges 1 to X1, having refractive indices n11, to n>,. wherein n0 is different from the refractive index of an adjacent layer of either of the mirrors.

In some embodiments the photonic crystal mirrors of the flanking sections comprise two dimensional photonic crystals.

In some embodiments Xa = 2, In some embodiments Xb = 2.

In some embodiments the apparatus includes carrier accumulation.

In some embodiments the apparatus includes electrodes adapted to apply a DC voltage.

In accordance th some embodiments, an apparatus is provided that may include: (a) a base comprising a multilayer photonic crystal minor; (b) a core contacting an uppermost layer of the base and having a refractive index n different from that of the uppermost layer; and (c) an overlay comprising a second multilayer photonic crystal mirror, each layer in the overlay conforming to a contour of the core, wherein a refractive index of the layer of the overlay contacting the core is different from n.

In some embodiments the base comprises alternating layers of two different materials.

In some embodiments the overlay comprises alternating layers of two different materials.

In some embodiments the apparatus includes carrier depletion in a reversed biased p-n junction.

In accordance with some embodiments, an apparatus is provided that may include: (a) a core which constrains vertical dispersion of light by total internal ref1ectiqiithical1y repeating layers I to X flanking the core laterally and having refractive indices n1 to n; wherein the refractive index of the core is different from the refractive index of an adjacent layer of the periodically repeating layers on either side.

In some embodiments X= 2.

In some embodiments the apparatus may indude carrier depletion in a reversed biased p-n junction.

In some embodiments the apparatus includes caner accumulation.

In some embodiments the apparatus may include electrodes adapted to apply a DC voltage.

In some exemplary embodiments of the invention there is provided a Mach-Zehnder interferometer (MZI) including at least one apparatus as described above. In some embodiments, the MZI includes two apparatus according as described above.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention be'ongs. Although suitable methods and materials are described below, methods and materials similar or equivalent to those described herein can be used in the practice of the present invention. In case of conflict, the patent specification, including definitions, will control. All materials, methods, and examples are illustrative only and are not intended to be limiting.

As used herein, the terms "comprising" and "including" or grammatical variants thereof are to be taken as specifying inclusion of the stated features, integers, actions or components without precluding the addition of one or more additional features, integers, actions, components or groups thereof This term is broader than, and includes the terms "consisting of' and consisting essentially of' as defined by the Manual of Patent Examination Procedure of the United States Patent and Trademark Office, Thus, any recitation that an embodiment "includes" or "comprises" a feature is a specific statement that sub embodiments "consist essentially of' and/or "consist of' the recited feature.

The phrases "adapted to" and "configured to" as used in this specification and the accompanying claims impose additional structural limitations on a previously recited component.

As used in this specification and the accompanying claims the term "vertical" indicates the direction in which material layers are grown in a semiconductor manufacturing process.

As used in this specification and the accompanying claims the terms "horizontal", and "lateral" and conjugates thereof indicate a direction perpendicular to the vertical.

The term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of optics and/or physics.

Implementation of the method and system according to embodiments of the invention involves performing or completing selected tasks or steps manually, automatically, or a combination thereof Moreover, according to actual instrumentation and equipment of exemplary embodiments of methods, apparatus and systems of the invention, several selected steps could be implemented by hardware or by software on any operating system of any firmware or a combination thereof For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit. As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying figures. In the figures, identical and similar structures, elements or parts thereof that appear in more than one figure are generally labeled with the same or similar references in the figures in which they appear. Dimensions of components and features shown in the figures are chosen primarily for convenience and clarity of presentation and are not necessarily to scale. The attached figures are: Fig. 1 is a plot of Frequency as a function of wave vector (dispersion curve); Fig. 2 is a simplified flow diagram of a method according to some exemplary embodiments of the invention; Fig. 3 is a schematic cross section of an apparatus according to an exemplary embodiment of the invention; Fig. 4 is a schematic cross section of an apparatus according to a second exemplary embodiment of the invention; Fig. S is a schematic cross section of an apparatus according to a third exemplary embodiment of the invention; Fig. 6 is a schematic cross section of an apparatus according to a fourth exemplary embodiment of the invention; and Fig. 7 is a schematic cross section of a Mach-Zehnder interferometer (IVIZI) including apparatus according to one or more embodiments of the invention as depicted in Figs. 3 to 6.

DETAILED DESCRIPTION OF EMBODIMENTS

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although suitable methods and materials are described below, methods and materials similar or equivalent to those described herein can be used in the practice of the present invention. In case of conflict, the patent specification, including definitions, will control. All materials, methods, and examples are illustrative only and are not intended to be limiting.

As used herein, the terms "comprising" and "including" or grammatical variants thereof are to be taken as specifying inclusion of the stated features, integers, actions or components without precluding the addition of one or more additional features, integers, actions, components or groups thereof This term is broader than, and includes the terms "consisting of' and "consisting essentially of' as defined by the Manual of Patent Examination Procedure of the United States Patent and Trademark Office. Thus, any recitation that an embodiment "includes" or "comprises" a feature is a specific statement that sub embodiments "consist essentially of' and/or "consist of' the recited feature.

The phrase "consisting essentially of" or grammatical variants thereof when used herein are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof but only if the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method.

The phrase "adapted to" as used in this specification and the accompanying claims imposes additional structural limitations on a previously recited component.

The term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners in the art.

The term "vertical" directions, as used herein, relates to the direction in which material layers are grown in a semiconductor manufacturing process. The terms "horizontal" and "lateral" directions denote any direction perpendicular to the "vertical" direction.

Implementation of the method and system according to embodiments of the invention involves performing or completing selected tasks or steps manually, automatically, or a combination thereof Moreover, according to actual instrumentation and equipment of exemplary embodiments of methods, apparatus and systems of the invention, several selected steps could be implemented by hardware or by software on any operating system of any firmware or a combination thereof, For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit, As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In any case, selected steps of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions, Embodiments of the invention relate methods and apparatus for modulation of light, Specifically, some embodiments of the invention can be used to modulate light passing through a waveguide.

-10 -The principles and operation of methods and/or apparatus according to exemplary embodiments of the invention may be better understood with reference to the drawings and

accompanying descriptions.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and shou'd not be regarded as limiting.

Overview of operatimz principle Voltage applied to multilayer photonic crystal mirrors and/or to a core of a waveguide causes a change in the charge carriers' concentration in the core and/or in the layers of the minors. This change may contribute to a change in the refractive index of the core and/or the minors layers. This change in refractive index contributes to a shift in the dispersion curve (downward shift when the caner concentration is reduced and upward shift when the carrier concentration is increased). Consequently, in some embodiments, the wave vector's parallel-to-the-layers-component Q3) is changed and the phase of light is changed, Working in the slow-light regime enhances the wave vector's change, as depicted in Fig. 1. In some embodiments, the dispersion curve shift causes the waveguide to switch from a propagating to a non-propagating state and vice versa (the waveguide is in a non-propagating state when the whole dispersion curve is above the operation frequency).

According to various exemplary embodiments of the invention the change in the charge carrier concentration and/or the refractive index is made in different ways. In some embodiments, the change in the charge carrier concentration is by carrier depletion (e.g. in a reverse biased PN diode). In some embodiments, the change in the charge carrier concentration is by carrier injunction (e.g. in a forward biased PIN diode). In some embodiments, the change in the charge carrier concentration is by carrier accumulation (e.g. in a MOS capacitor). Additional modulation possibilities include light absorption and/or electro-optics effects.

Exemplarv method Fig. 2 is a simplified flow diagram of a method according to some exemplary embodiments of the invention indicated generally as 10.

Depicted exemplary method 10, includes constructing 20 a wave guide (WG) including at least 2 multilayer photonic crystal mirrors and propagating 30 light through a core of the WG. In the depicted exemplary embodiment, method 10 includes tuning 40 the We so that the propagation constant (13) of the light is 0 to where is the vacuum wavelength of the light and applying 50 a modulation voltage to the We.

In some exemplary embodiments of the invention, the group velocity of the light isO to OJc O.lc c c where is the speed of light in vacuum. According to these embodiments the modulation voltage applied at 50 shifts the dispersion curve so that the propagation constant O.5-O.6 (13) changes but remains in the range of 0 to. A In some embodiments, the modulation voltage applied at 50 shifts the dispersion curve so that the WG switches between propagating and non-propagating states.

According to some embodiments, only the propagation constant (13) changes, i.e. only the phase of the light in the output changes, thereby causing the device as described previously function as an optical phase-shifter. In order to modify the light amplitude, this phase-shifter may be incorporated, for example, into one or both arms of a Mach-Zehnder interferometer (see Fig. 7 below), thereby resulting in a device that functions as an optical modulator. When the phase difference between the two arms is 0 (or 2m times an integer), there is constructive interference between the light waves passing through two arms and the light passes through the device. When the phase difference between the two arms is it (or 2zm+m where m is an integer), there is destructive interference between the light waves passing through two arms and the light does not pass through the device.

According to further embodiments, wherein the modulation voltage shifts the dispersion curve so that the WG switches between propagating and non-propagating states, the device is already functioning as an optical modulator.

-12 -Alternatively or additionally, in some embodiments tuning 40 includes application of a DC voltage to the WG.

Alternatively or additionally, in some embodiments the wave guide has a length 100 microns; < 50 microns; 25 microns or 10 microns or intermediate or shorter lengths.

Exemol an' Anoaratus Figs. 3, 4, 5 and 6 are schematic cross sections of apparatus according to various exemplary embodiments of the invention indicated generally as 100, 200, 300 and 400 respectively.

Apparatus according to various exemplary embodiments of the invention include a core (e.g. 101; 20; 301 and 401 in Figs 3 to 6 respectively) bordered on at least two sides by multilayer photonic crystal mirrors (e.g. 02a and 102b; 202a and 202b; 302a and 302b and 402a and 402b in Figs. 3 to 6 respectively).

Apparatus according to various exemplary embodiments of the invention include a first pair of mirrors which constrain light vertically (e.g. 02a and 102b; 202a and 202b; 303a and 303b and 402a and 402b in Figs. 3 to 6 respectively) and a second pair of mirrors which constrain light laterally (e.g. 103a and 103b; 203a and 203b; 302a and 302b and 402a (vertical portions indicated as 402v) in Figs. 3 to 6 respectively) and a pair of electrodes adapted to apply a modulation voltage (e.g. I 04a and I 04b; 204a and 203b; 304a and 304b and 403a and 403b in Figs. 3 to 6 respectively).

In some exemplary embodiments of the invention, the first pair of mirrors which constrain light vertically include photonic crystal mirrors (e.g. 102a and 102b, 202a and 202b and 402a and 402b in Figs. 3, 4 and 6 respectively). In the depicted embodiments, these photonic crystal mirrors are multilayer photonic crystal mirrors.

In other exemplary embodiments of the invention, the first pair of minors which constrain light vertically provide total internal reflection to the core (e.g. mirrors 303a; 303b and core 301 in Fig 5), Alternatively or additionally, in some embodiments the second pair of mirrors (e.g. 103a and 103 b in Fig. 3) which constrain light laterally provide total internal reflection to core 101.

In some exemplary embodiments of the invention, the second pair of mirrors which constrain light laterally (e.g. 203a and 203b; 302a and 302b and 402a (vertical portions -13 -indicated as 402v) in Figs. 4 to 6 respectively) comprise photonic crystal mirrors. In the depicted embodiments, these photonic crystal mirrors are multilayer photonic crystal mirrors.

Although multilayer photonic crystal minors are depicted, two dimensional or three dimensional photonic crystal mirrors may be substituted to produce additional exemplary embodiments of the invention.

In some exemplary embodiments of the invention, the second pair of mirrors results from bends in at least one minor of the first pair (e.g. 4O2v in Fig. 6).

In some exemplary embodiments of the invention, the apparatus includes electrodes adapted to apply a DC tuning voltage. In some exemplary embodiments of the invention these electrodes are the same electrodes used for modulation as described above and depicted in the figures. In some exemplary embodiments of the invention additional electrodes are provided to apply the DC tuning voltage (not depicted).

Referring again to Fig. 3 Apparatus too can also be described as including a pair of mirrors O2a and 102b with periodically repeating layers I to X having refractive indices n1 to nx and a layer between the pair of minors contacting each of mirrors and including a core 101 having refractive index nA and two flanking sections 105 each having refractive index nB nB < n, and n, is different from the refractive index of an adjacent layer of either of mirrors 102a and 102b. In the depicted exemplary embodiment, X 2. In the depicted exemplary embodiment, each of mirrors 102a and 102b includes a multilayer photonic crystal mirror which constrains light vertically. In some embodiments, of apparatus 100 there is carrier depletion in a reversed biased p-n junction. Optionally, the junction direction in which the doping changes is the vertical direction, The depicted embodiment includes electrodes 104a and 104b adapted to apply modulation voltage and, optionally, a DC voltage.

Referring again to Fig 4, apparatus 200 can also be described as including a pair of mirrors 202a and 202b with periodically repeating layers I to 13(9 having refractive indices n19 to n and a layer between the pair of minors contacting each of the mirrors. In this exemplary embodiment the layer includes comprising: a core 201 having refractive index no: and two flanking sections 203a and 203b each including photonic crystal mirrors, In depicted apparatus 200 the photonic crystal mirrors of flanking sections 203a and 203b include -14 -periodically repeating vertical bridges (between mirrors 202a and 202b) I to Xb having refractive indices nfl, to nXb According to this embodiment n0 is different from the refractive index of an adjacent layer of either of the mirrors.

In some embodiments, Xa = 2. Alternatively or additionally, in some embodiments Xb = 2.

In the depicted exemplary embodiment, each of mirrors 203a, 203b, 202a and 202b includes a multilayer photonic crystal mirror In some exemplary embodiments of the invention, the photonic crystal mirrors of flanking sections 203a and 203b include two dimensional photonic crystals (not depicted).

In some exemplary embodiments of the invention, apparatus 200 has carrier depletion in a reversed biased p-n junction. Optionally, the junction direction in which the doping changes is the vertical direction.

In the depicted exemplary embodiment, apparatus 200 includes electrodes 204a and 204b adapted to apply modulation voltage and, optionally, a DC voltage.

Referring again to Fig. 5 apparatus 300 can also be described as including a core 301 which constrains vertical dispersion of light by total internal reflection and two sets (302a and 302b) of periodically repeating layers I to Xa flanking core 30] laterally and having refractive indices nia to n; wherein the refractive index of core 301 is different from the refractive index of an adjacent layer of the periodically repeating layers on either side. In the depicted exemplary embodiment, wherein X= 2. In the depicted exemplary embodiment, sets (302a and 302b) of periodically repeating layers include multilayer photonic crystal mirrors.

In some exemplary embodiments of the invention, apparatus 300 has carrier depletion in a reversed biased p-n junction.

In the depicted exemplary embodiment, apparatus 300 includes electrodes 304a and 304b adapted to apply modulation voltage and, optionally, a DC voltage.

Referring again to Fig. 6, apparatus 400 can also be described as including a base comprising a multilayer photonic crystal mirror 402b, a core 40] contacting an uppermost layer of the base and having a refractive index n different from that of the uppermost layer and an overlay 402a comprising a second multilayer photonic crystal mirror, each layer in -15-overlay 402a conforming to a contour of core 401 wherein a refractive index of the layer of overlay 402a contacting core 401 is different from n -According to various exemplary embodiments of the invention base 402b and/or overlay 402a include(s) alternating layers of two or more different materials. In some embodiments, apparatus 400 has carrier depletion in a reversed biased p-n junction.

Optionally, the junction direction in which the doping changes is the vertical direction.

Depicted exemplary apparatus 400 includes electrodes 403a and 403b adapted to apply modulation voltage and, optionally, a DC voltage.

Additional Exemplary Annaratus Fig. 7 is a schematic drawing of a Mach-Zehnder interferometer (IvIZI), indicated generally as 500 which incorporates apparatus according to one or more embodiments of the invention as depicted in Figs. 3 to 6 and described hereinabove. The depicted MZI represents an additional class of embodiments of the invention.

Depicted WI 500 is configured to receive light to be modulated via an input waveguide 710. The received light is split by a splitter 720 into a first optical arm 730 and second optical arm 740. Apparatus 752 and 754 according to exemplary embodiments of the invention described above are positioned within optical arms 730 and 740 respectively, if no bias is applied, there is no phase difference in light passing through arms 730 and 740. If a bias is applied, first apparatus 752 creates a m/2 delay, and second apparatus 754 creates a delay, so the phase difference between light passing through arms 730 and 740 arms is it. In the depicted exemplary embodiment, an optical combiner 760 combines the light exiting arms 730 and 740.

Exemplary operating principles In some exemplary embodiments of the invention, the apparatus has carrier depletion in a reversed biased p-n junction. In some embodiments, the junction direction in which doping changes is the vertical direction, In some embodiments, the reversed biased p-n junction is at a boundary between the core and one of the multilayer photonic crystal minors.

In some exemplary embodiments of the invention the light modulation is caused by carrier accumulation. In some embodiments, a MOS capacitor and/or potential well structure -16 -contribute to carrier accumulation. According to various exemplary embodiments of the invention refractive index change and/or absorption change contribute to modulation.

In some exemplary embodiments of the invention the light modulation is caused by carrier injection. According to various exemplary embodiments of the invention refractive index change and/or absorption change contribute to modulation.

According to various exemplary embodiments of the invention the light modulation is caused by electro-optics effects (e.g. Kerr, Pockels effects) or electro-absorption (e.g. QCSE, Frank-Keldysh effect).

In some embodiments, practice of a method according to claim tO (Fig. 2) changes only propagation constant (f3), i.e. only the phase of the light in the output changes. In those cases, the apparatus frmnctions as an optical phase shifter.

Referring again to Fig. 7, incorporation of apparatus according to embodiments of the invention into one or both arms of an MZI contributes to an ability to selectively shift phase.

This phase shifting contributes to an ability to modify amplitude of light passing through the MZI. An MZI so configured functions as an optical modulator, When the phase difference between the two arms of the M.ZI is 0 or 2ir, there is constructive interference between the light waves passing through two arms and the light passes through the device, When the phase difference between the two arms is -hr or -m, there is destructive interference between the light waves passing through the two arms and the light does not pass through the MZI.

Exemplars' materials In some exemplary embodiments of the invention, the mirrors and/or the core comprise layers of Si and SiC. In some exemplary embodiments of the invention, the minors and/or the core comprise layers of Si, SiO and/or SiN.

Exemplars' mariufacturinu techniques Standard semiconductor manufacturing processes are suitable for manufacture of apparatus 100 and/or 200 and/or 300 and/or 400. One common standard semiconductor manufacturing process includes growth of layers of different materials (semiconductors, metals or insulators) on a substrate. Variations on this general strategy include, but are not limited to -17 -using epitaxy (e.g. MBE), different kinds of deposition (e.g. CVD, ALD) and sputtering. The direction of the growth is referred to as vertical.

In some standard semiconductor manufacturing processes the structure is processed in the "lateral" (perpendicular to the "vertical" direction) plane using etching. Common types of etching employed for this purpose are wet chemical etching, reactive ion etching and ion milling. Ion implantation is another type of lateral processing which is frequently used. In some semiconductor manufacturing processes lithography is employed, Alternatively or additionally, in some cases, growth is repeated after some lateral processing (so-called re-growth). Some lateral processing can be then performed again. The growth (re-growth) can be performed on parts of the structure using different kinds of masks etc. Alternatively or additionally, in some cases the fabrication process includes annealing.

It is expected that during the life of this patent many photonic crystal mirror types will be developed and the scope of the invention is intended to include all such new technologies a priori.

Although tM invention hii been described jjj conjunction with specific embodiments thereof. ft j evident ih many alternatives, modifications n4 variations iill k apparent tQ those skilled in the aft Accordinulv. it is intended to embrace all such alternatives.

modifications and variations that fall within the spirit and broad scope of the aupended claims, Specifically, a variety of numerical indicators have been utilized. It should be understood that these numerical indicators could vary even further based upon a variety of engineering principles, materials, intended use and designs incorporated into the various embodiments of the invention. Additionally, components and/or actions ascribed to exemplary embodiments of the invention and depicted as a single unit may be divided into subunits.

Conversely, components and/or actions ascribed to exemplary embodiments of the invention and depicted as sub-units/individual actions may be combined into a single unit/action with the described/depicted function.

Alternatively, or additionally, features used to describe a method can be used to characterize an apparatus and features used to describe an apparatus can be used to characterize a method.

-18 -It should be further understood that the individual features described hereinabove can be combined in all possible combinations and sub-combinations to produce additional embodiments of the invention. The examples given above are exemplary in nature and are not intended to limit the scope of the invention which is defined solely by the following claims.

Each recitation of an embodiment of the invention that includes a specific feature, part, component, module or process is an explicit statement that additional embodiments of the invention not including the recited feature, part, component, module or process exist.

All publications, references, patents and patent applications mentioned in this specification ia herein incorporated th their entirety by reference jn th specification. th same extent as if each individual publication patent or patent application was specifically and individually indicated to be incorporated herein by reference. in addition, citation ut identification jf jy reference in fluii application shall ifl h construed a n admission thai such reference is available as prior art to the present invention.

The terms "include", and "have" and their conjugates as used herein mean "including but not necessarily limited to".