Patent Publication Number: US-8111965-B2

Title: Waveguide for thermo optic device

Description:
This application is a Continuation of U.S. application Ser. No. 12/780,601, filed May 14, 2010 now U.S. Pat. No. 7,936,955, which is a Continuation of U.S. application Ser. No. 12/047,927, filed Mar. 13, 2008, now issued as U.S. Pat. No. 7,720,341, which is a Continuation of U.S. application Ser. No. 10/929/271, filed Aug. 30, 2004, now issued as U.S. Pat. No. 7,359,607, which is a Divisional of U.S. application Ser. No. 10/233,000, filed Aug. 29, 2002, now issued as U.S. Pat. No. 7,006,746. These applications are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to thermo optic devices, such as optical waveguides. In particular, it relates to efficiently formed input and output waveguides having increased bandwidth. 
     BACKGROUND OF THE INVENTION 
     The art of making and developing new uses for thermo optic devices continues to emerge. Presently, thermo optic devices are used as filters, switches, multiplexers, waveguides, and a host of other semiconductor and optical transmission devices. 
     With reference to  FIGS. 1A and 1B , a prior art thermo optic device in the form of an optical waveguide is shown generally as  110 . It comprises a grating  112  formed of a lower cladding  114 , an upper cladding  116 , an input waveguide  118 , an output waveguide  120  and a grating waveguide and an optional resonator  122 . As is known, the waveguides and resonator are formed of a material having a higher refractive index than that of the upper and lower claddings to propagate light therein during use. The grating  112  is disposed on a substrate  124 . In many thermo optic devices the substrate is a printed circuit board or some form of silicon. 
     In forming the device, the lower cladding is deposited on the substrate. An intermediate layer, for the waveguides and resonator, is deposited on the lower cladding, photo patterned and etched. The upper cladding is deposited on the waveguides and resonator. In an alternate formation process, the lower cladding  206  is an oxidation of a silicon substrate with the waveguides, resonator and upper cladding being formed in the same manner. 
     The inherent characteristics of waveguides and resonators, such as their sizes, shapes, compositions, etc., may vary greatly from application to application. The characteristics of all waveguides and resonators, however, are generally selected in such a manner to eliminate crosstalk between the input and output waveguides at undesirable frequencies and to resonate signals (i.e., prolong and/or intensify) which allows transfer between the waveguides at desirable frequencies. The undesirable frequencies are not transferred between the two waveguides. The range of frequencies that are not transferred is determined by the properties of the grating, and is typically referred to as the bandwidth. The frequencies that are transferred are determined by the specific designs of the grating resonator waveguides. 
     In the representative prior art embodiment shown in  FIG. 1B , the resonator  122  has a generally symmetrical tooth-shaped pattern. To set the center frequency, the grating corrugation period is adjusted by adjusting the pitch (distance) between the teeth. 
     As part of the task of setting the bandwidth, an aspect ratio is adjusted in an area where the waveguide and resonator front or face one another. It is not possible to change the bandwidth by only changing the aspect ratio. The grating strength changes the bandwidth and it is necessary to change the aspect ratio to allow the device to operate appropriately. 
     For example, in  FIG. 1A , resonator  122  has a surface  123  facing a surface  119  of input waveguide  118 . The aspect ratio (a.r.) in this area is defined as the area of the input waveguide surface to the area of the resonator surface (a.r.=area of input waveguide surface/area of resonator surface). A large bandwidth corresponds to a small aspect ratio while a small bandwidth corresponds to a large aspect ratio. Correspondingly, a large bandwidth can be achieved by either increasing the area of the resonator surface, decreasing the area of the input waveguide surface, or adjusting both surface areas in such a manner to achieve a relatively small ratio number. A small bandwidth can be achieved by either decreasing the area of the resonator surface, increasing the area of the input waveguide surface, or adjusting both surface areas in such a manner to achieve a relatively large ratio number. Even further, increases or decreases of surface area can be achieved by adjusting one or both of the surface dimensions of the waveguide or resonator surfaces. For example, depth “D” of surface  119  or  123  may be increased or decreased according to desired bandwidth. 
     In other words, to set the bandwidth, the strength of the grating between the input and output waveguides is increased. As the grating strength is increased, the difference in effective index for waveguides with and without gratings becomes increasingly difficult to maintain. The difference in effective index for coupled devices such as these is typically referred to as asynchronicity. The term asynchronicity indicates that the propagation constant at the resonant wavelength is different for the waveguide and grating, which limits the amount of light that can be coupled between them. The problem of asynchronicity becomes even more problematic when it is desirable to achieve polarization independent devices, as is required for commercial fiber optic components. In this case, coupling between the grating and waveguide requires synchronicity for both of the orthogonal polarization states of the system. 
     Methods for trimming the effective index of the waveguide to match the grating, or grating to match the waveguide, are required to achieve optimal performance from coupled systems such as the waveguide/grating coupler system. Trimming approaches have been defined elsewhere (See “Integrated-Optic Grating-Based Filters For Optical Communication Systems” by Jay Northrop Damask, Massachusetts Institute of Technology thesis, available Jul. 16, 1996, chapter 4), but are not generalized for addressing arbitrary waveguide combinations, or are not compatible with standard processing techniques. 
     Since the resonator  122  and the input and output waveguides  118 ,  120  are formed together during the same process steps as described above, the depth, D, of the resonator is essentially fixed as the same depth of the waveguides and therefore the asynchronicity limits the bandwidths and grating strengths that can be used. 
     Accordingly, the thermo optic arts desire waveguides having increased bandwidths that are relatively cheap and quick to produce without sacrifices in quality, reliability or longevity. 
     SUMMARY OF THE INVENTION 
     The above-mentioned and other problems become solved by applying the apparatus and method principles and teachings associated with the hereinafter described waveguide for thermo optic device. 
     In one embodiment, a waveguide and resonator are formed on a lower cladding of the thermo optic device, each having a formation height that is substantially equal. Thereafter, the formation height of the waveguide is attenuated. In this manner, the effective index between the waveguide and grating can be matched, thereby allowing the synchronicity requirements to be met for larger bandwidth devices. The waveguide attenuation is achieved by photomasking and etching the waveguide after the resonator and waveguide are formed. In one embodiment the photomasking and etching is performed after deposition of the upper cladding. In another, it is performed before the deposition. 
     In another embodiment, a plurality of waveguides, an input and output waveguide, are attenuated from their respective formation heights to a different or substantially equal waveguide height. In still another embodiment, a plurality of resonators are formed between the input and output waveguides. 
     In still another embodiment, resonator(s) are attenuated before or after deposition of the upper cladding. 
     Thermo optic devices, thermo optic packages and fiber optic systems having these waveguides are also taught. 
     These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross sectional view of a thermo optic device in the form of an optical waveguide in accordance with the prior art; 
         FIG. 1B  is a planar view of the thermo optic device of  FIG. 1A ; 
         FIG. 2A  is a cross sectional view of a lower cladding on which a waveguide in accordance with the teachings of the present invention will be formed; 
         FIG. 2B  is a cross sectional view in accordance with the teachings of the present invention of a first photomasking step in a processing step subsequent to  FIG. 2A ; 
         FIG. 2C  is a cross sectional view in accordance with the teachings of the present invention of waveguides and resonators formed on a lower cladding in a processing step subsequent to  FIG. 2B ; 
         FIG. 2D  is a cross sectional view in accordance with the teachings of the present invention of an upper cladding deposited on the waveguides and resonator in a processing step subsequent to  FIG. 2C ; 
         FIG. 2E  is a cross sectional view in accordance with the teachings of the present invention of a second photomasking step in a processing step subsequent to  FIG. 2D ; 
         FIG. 2F  is a cross sectional view in accordance with the teachings of the present invention of an attenuated height waveguide in a processing step subsequent to  FIG. 2E ; 
         FIG. 2G  is a cross sectional view in accordance with the teachings of the present invention of an attenuated height waveguide in a processing step subsequent to  FIG. 2F ; 
         FIG. 3  is a cross sectional view in accordance with the teachings of the present invention of an alternate embodiment of an attenuated height waveguide; 
         FIG. 4  is a cross sectional view in accordance with the teachings of the present invention of a plurality of attenuated height waveguides having the same height; 
         FIG. 5  is a cross sectional view in accordance with the teachings of the present invention of another embodiment of a plurality of attenuated height waveguides having different heights; 
         FIG. 6A  is a cross sectional view in accordance with the teachings of the present invention of an alternate embodiment of a second photomasking step in a processing step subsequent to  FIG. 2D ; 
         FIG. 6B  is a cross sectional view in accordance with the teachings of the present invention of an attenuated height waveguide in a processing step subsequent to  FIG. 6A ; 
         FIG. 6C  is a cross sectional view in accordance with the teachings of the present invention of an upper cladding formed on the waveguides and resonator in a processing step subsequent to  FIG. 6B ; 
         FIG. 7  is a cross sectional view in accordance with the teachings of the present invention of an alternate embodiment of an attenuated height waveguide; 
         FIG. 8  is a cross sectional view in accordance with the teachings of the present invention of a plurality of attenuated height waveguides having the same height; 
         FIG. 9  is a cross sectional view in accordance with the teachings of the present invention of another embodiment of a plurality of attenuated height waveguides having different heights; 
         FIG. 10  is a cross sectional view in accordance with the teachings of the present invention of an attenuated height resonator; 
         FIG. 11  is a cross sectional view in accordance with the teachings of the present invention of another embodiment of an attenuated height resonator; 
         FIG. 12A  is a cross sectional view in accordance with the teachings of the present invention of waveguides and a resonator formed on a lower cladding; 
         FIG. 12B  is a cross sectional view in accordance with the teachings of the present invention of an attenuated height input waveguide, an attenuated height output waveguide and an attenuated height resonator all having different heights; 
         FIG. 13  is a cross sectional view in accordance with the teachings of the present invention of an attenuated height waveguide coupled to an output waveguide via a plurality of resonators; 
         FIG. 14  is a block diagram of a system having a thermo optic package comprising waveguides formed in accordance with the teachings of the present invention; and 
         FIG. 15  is an alternative embodiment of a thermo optic package comprising waveguides formed in accordance with the teachings of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration, specific embodiments in which the inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that process, electrical or mechanical changes may be made without departing from the scope of the present invention. The term substrate used in this specification includes any base semiconductor structure such as silicon-on-sapphire (SOS) technology, silicon-on-insulator (SOI) technology, thin film transistor (TFT) technology, doped and undoped semiconductors, epitaxial layers of a silicon supported by a base semiconductor structure, as well as other semiconductor structures well known to one skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and their equivalents. 
     The following description and figures use a reference numeral convention where the first digit of the reference numeral corresponds to the figure and the following two digits correspond to like elements throughout the specification. For example, the lower cladding of a thermo optic device of the present invention has a reference number of  202 ,  302 ,  402 , etc. corresponding to the lower cladding X 02  in  FIGS. 2 ,  3 ,  4 , etc. where X is the number of the figure in which the reference numeral appears. 
     For definition purposes: a “formation height,” either waveguide or resonator, is a height before any attenuation is performed to a structure and is to be distinguished from a resonator “height” or waveguide “height” which is the height of a structure after some attenuation has been performed. In other words, the two words “formation height” will be used to identify heights of structures pre-attenuation and the single word “height” will be used to identify structures post-attenuation. For example, in the event a structure itself was not attenuated, its “formation height” will be the same as its “height” after another structure has been attenuated, i.e., the resonator formation height in  FIG. 2C  is the same as the resonator height in  FIG. 2F . In contrast, in the event a structure has been attenuated, its “formation height” will be taller than its “height” after attenuation, i.e., the input waveguide formation height of  FIG. 2C  is taller than the input waveguide height of  FIG. 2F . 
     With reference to  FIG. 2A , a substrate  200  is provided upon which a waveguide for use with a thermo optic device will be formed. In one embodiment the substrate is silicon. In another, it is a printed circuit board. In still another, it is any surface upon which a layer may be deposited. 
     A first layer  202  or lower cladding is formed on the substrate. In one embodiment, the substrate is some form of silicon and the first layer is a grown layer via oxidation of the substrate. In another embodiment, the first layer is a deposited layer. 
     Some techniques for depositing the first layer, and all remaining deposited layers, include, but are not limited to, any variety of chemical vapor depositions (CVD), physical vapor depositions (PVD), epitaxy, evaporation, sputtering or other known or hereinafter developed techniques. Specific CVD techniques include low pressure (LP) ones, but could also be atmospheric pressure (AP), plasma enhanced (PE), high density plasma (HDP) or other. 
     In still another embodiment, the first layer is a silicon oxide that is deposited via a LPCVD technique using a tetraethyl orthosilicate or TEOS source. 
     After depositing the first layer, a second layer  204  is deposited on the first layer using one of the above or other deposition techniques. In one embodiment, the second layer is a silicon oxynitride deposited with a PECVD technique using a silane with nitrous oxide reaction in an argon or helium plasma, under the conditions of 450° C., 450 watts and 13.56 MHz. In another embodiment, the second layer is a translucent material. 
     While the lower cladding, in one embodiment, was formed of a silicon oxide and the second layer was formed of silicon oxynitride, it should be appreciated that numerous other materials for these first and second layers exist. One skilled in the art will understand that a variety of anneal steps can follow the above steps. 
     The selection of the layers is dictated by the index of refraction, absorption in the wavelength range of interest, thermo-optic coefficients and other optical and mechanical properties. The second layer will be formed into the waveguide and grating and light will propagate there by virtue of total internal reflection of light. So long as the second layer is a material having an index of refraction that is higher than the index of refraction for the first layer at the wavelength of interest, light signals will be guide and propagated in the device. 
     In  FIG. 2B , a first mask  206  is provided to photo impact  208  the second layer  204  in a photomasking step thereby producing a photo impacted region  210  in the second layer on top of the lower cladding. 
     In one embodiment, the photo impacting is accomplished with an ultraviolet light from a photolithography device well known to those skilled in the art. The photo impacting, however, should not be limited to such an embodiment and may alternatively include X-rays or other light sources. 
     The first mask  206  may be configured as a clear-field or dark-field mask, as those terms as well understood by skilled artisans, according to the desired design of the photo impacted region  210  in the second layer. 
     Thereafter, with reference to  FIG. 2C , the second layer  204  is etched so that the photo impacted region  210  remains thereby leaving or forming a waveguide and resonator on the surface  220  of the lower cladding, first layer  202 . In particular, an input waveguide  212 , an output waveguide  214  and a resonator  216 , between the input and output resonators to couple light signals from the input to the output during use, are formed on the surface  220 . Each of the waveguides and resonator have a formation height that is substantially equal since they were formed together in the same process. This height is measured from the surface  220  of the first layer  202  to plane  218 . Although no particular formation height is required for this invention, for reference purposes, the formation height is often about 1 to about 2 microns. The height depends upon the particular application in which the thermo optic device will be used and the optical properties of the layers. 
     Some particular etching techniques embraced by this invention for forming the waveguides and resonators by leaving the photo impacted region  210  on the lower cladding include, but are not limited to, any variety of wet etches including immersion or spray, or dry etches including plasma, barrel or planar, ion milling, reactive ion etches (RIE) or deep RIE. 
     In one particular embodiment of the invention, the second layer is dry etched with a photo resist pattern and CF 4  or CF 4 CHF 3  Argon based chemistry in a parallel plate reactor under the conditions of about 50 militorr, 600 watts and 13.56 MHz. 
     With reference to  FIG. 2D , a third layer  222  or upper cladding is deposited on the surface of the waveguides  212 ,  214  and resonator  216  and portions of the first layer  202  not having such structures formed thereon. The upper cladding is deposited to a thickness sufficient to prevent external films and circuitry from interfering with the light propagated in the waveguide during use. For reference purposes only, the upper cladding and lower cladding are, in one embodiment, deposited to the same thickness of about 4 microns nominally. 
     In another embodiment, the third layer is a second silicon oxide layer deposited in the same manner as previously described for the first layer. In still another embodiment, the third layer has an index of refraction that is substantially equal to the index of refraction of the first layer. 
     It will be appreciated that the third layer  222  has an upper surface that can be used to stack multiple thermo optic devices by continuing the deposition, patterning and etching processes described herein. The upper surface may alternatively contain a heater (not shown) for changing a thermo optical property of the device as light propagates in the waveguide during use. 
     With reference to  FIG. 2E , after depositing the third layer  222 , a second mask  224  is provided to attenuate the top of a waveguide as shown in  FIG. 2F . In particular, the top  226  of input waveguide  212  is attenuated a height, H, from the top  228  of the resonator  216  by means of etching, especially dry etching. 
     Many things should now be apparent to those skilled in the art. For example, the input waveguide has a waveguide height that is shorter than the resonator height while the output waveguide remains the same height as the resonator height which is the same as their respective formation heights. As a result, the aspect ratio between the resonator and the input waveguide has decreased (in comparison to the prior art,  FIG. 1A , for example) thereby maintaining the synchronicity condition. 
     In particular, the aspect ratio (a.r.) in area  213  has decreased where the input waveguide  212  and resonator  216  front one another along resonator surface  217  and input waveguide surface  211 , wherein (a.r.) in area  213  is defined as the area of the input waveguide surface  211  to the area of the resonator surface  217  or (a.r.=area of input waveguide surface  211 /area of resonator surface  217 ). 
     The resonator height from the surface  220  to the top  228  of the resonator  216 , like the input or output waveguide height from surface  220  to top  226  or top  227  of the input waveguide  21  or output waveguide  214 , respectively, is not required to be any particular height and is dictated according to the frequency characteristics demanded by the particular application in which the thermo optic device is used. For reference purposes, however, each of the heights can be found in a range from about 1 to about 2 microns in one embodiment. 
     In still a similar manner, the horizontal spacing (as viewed in the figure from left-to-right) between the grating and the waveguides, and length over which the grating and waveguides couple to each other, is determined by the performance requirements of the device. For reference purposes, however, the resonator is separated from the waveguide in one embodiment in a range from about 1 to about 2 microns. 
     To complete one embodiment of the thermo optic device, a fourth layer  250  may be deposited on the attenuated waveguide, the input waveguide, and the upper cladding, third layer  222 . The fourth layer, like the upper cladding is deposited to a thickness sufficient to prevent outside light from interfering with the light propagated in the waveguide during use. 
     In one embodiment, the fourth layer is a third silicon oxide layer deposited in the same manner as previously described for the third layer. In another embodiment, the fourth layer has an index of refraction that is substantially equal to the index of refraction of the first and third layers. 
     It will be appreciated that the fourth layer  250  has an upper surface that can be used to stack multiple thermo optic devices by continuing the deposition, patterning and etching processes described herein. The upper surface may alternatively contain a heater (not shown) for changing a thermo optical property of the device as light propagates in the waveguide during use. 
     With reference to  FIG. 3 , it will be appreciated that a reciprocal embodiment of the one shown in  FIG. 2F  can be achieved with respect to the output waveguide. In particular, the output waveguide  314  is attenuated in height from its formation height, which was substantially the same as the top  328  of the resonator  316 , to the top  327 . The input waveguide  312  remains the same height as the resonator. 
     Correspondingly, in area  315 , the aspect ratio has decreased (in comparison to the prior art,  FIG. 1A , for example) where the output waveguide  314  and resonator  316  front one another along resonator surface  319  and output waveguide surface  321 , wherein (a.r.) in area  315  is defined as the area of the output waveguide surface  321  to the area of the resonator surface  319  or (a.r.=area of output waveguide surface  321 /area of resonator surface  319 ). As such, synchronicity between the output waveguide and the grating has been achieved, even for high bandwidth gratings. 
     In  FIG. 4 , both the input and output waveguides  412 ,  414  have been attenuated in height, H 1  and H 2 , respectively, where H 1  is measured from the top  428  of the resonator to the top  426  of the input waveguide and H 2  is measured from the top  428  of the resonator to the top  427  of the output waveguide  414 . It will be appreciated that the resonator height from the lower cladding to the top  428  of the resonator  416  is the same height as the resonator formation height ( FIG. 2C , for example) because the resonator has not been attenuated. In the embodiment shown, H 1  is substantially equal to H 2 . 
     In  FIG. 5 , both the input and output waveguides are attenuated but are attenuated to different heights. In this embodiment, H 1  is taller than H 2 . 
     With reference to  FIGS. 6A through 6C , it will be appreciated that the attenuation of a waveguide, in another embodiment, can occur before the deposition of the upper cladding layer. In particular, a second mask  624  masks resonator  616  and output waveguide  614  on the surface  620  of the lower cladding  602  so that the input waveguide  612  may be attenuated in height via an etching process similar to the process steps of  FIGS. 2E and 2F  before deposition of the upper cladding. As a result, the input waveguide is attenuated in height, H, as defined from the top  628  of the resonator  616  to the top  626  of the input waveguide  612 . 
     To complete the thermo optic device, an upper cladding  622  is then deposited on the surface of the waveguides  612 ,  614  and resonator  616  and portions of the first layer  602  or lower cladding not having such structures formed thereon. As before, the upper cladding is deposited to a thickness sufficient to prevent external films and circuitry from interfering with the light propagated in the waveguide during use. The upper cladding may still have a resistive heater or other thermo optic devices formed on an upper surface thereof as the application demands in which the device is to be used. 
     The input waveguide still has a waveguide height that is shorter than the resonator height while the output waveguide remains the same height as the resonator height which is the same as their respective formation heights. Like before, the aspect ratio of the resonators and the input waveguide has been altered to maintain synchronicity and allow higher bandwidth devices to be used. 
     In particular, the aspect ratio (a.r.) in area  613  has decreased where the input waveguide  612  and resonator  616  front one another along resonator surface  617  and input waveguide surface  611 , wherein (a.r.) in area  613  is defined as the area of the input waveguide surface  611  to the area of the resonator surface  617  or (a.r.=area of input waveguide surface  611 /area of resonator surface  617 ). 
     In  FIG. 7 , in another embodiment of waveguide attenuation before deposition of the upper cladding, it is the output waveguide  714  that is attenuated in height, not the input waveguide  712 . The aspect ratio (a.r.) in area  715  has decreased where the output waveguide  714  and resonator  716  front one another along resonator surface  719  and output waveguide surface  721 , wherein (a.r.) in area  715  is defined as the area of the output waveguide surface  721  to the area of the resonator surface  719  or (a.r.=area of input waveguide surface  721 /area of resonator surface  719 ). 
     With reference to  FIG. 8 , in still another embodiment of attenuating the waveguide before deposition of the upper cladding, both the input and output waveguides  812 ,  814  have been attenuated. In particular, they have been attenuated a height H 1  and H 2 , respectively, wherein H 1  spans the distance from the top  828  of resonator  816  to the top  828  of the input waveguide and H 2  spans the distance from the top  828  of resonator  816  to the top of the output waveguide  827 . As shown, H 1  is substantially equal or the same as H 2 . Correspondingly, the aspect ratios in areas  813  and  815  have decreased (in comparison to the prior art) where synchronicity can be maintained for higher bandwidth devices. In  FIG. 9 , a view similar to  FIG. 8 , H 1  is less than H 2 . 
     While the foregoing teaches thermo optic devices where synchronicity is achieved by attenuating the thickness of the waveguides, in an alternate embodiment of the present invention, it may be desirable to attenuate the thickness of the grating to limit the synchronicity. 
     For example, in  FIGS. 10 and 11 , it is the resonator having an attenuated height, not the waveguides. In particular, in  FIG. 10 , the resonator  1016  is attenuated in height from its formation height, which was substantially co-equal with the top  1026  of the input waveguide  1012  and the top  1027  of the output waveguide, to the top  1028 . The upper cladding  1022 , in this embodiment, is formed on the resonator, waveguides and lower cladding  1002  after the resonator is attenuated from its resonator formation height. 
     In  FIG. 11 , the upper cladding  1122  is formed on the resonator  1116 , the input waveguide  1112 , the output waveguide  1114  and the lower cladding  1102  before the resonator  1116  is attenuated in height to top  1128  from its formation height which was substantially equal to top  1126  and  1127  of the input and output waveguides, respectively. 
     It should be appreciated that even further embodiments of the present invention include attenuating the heights of all the waveguides and the resonator and attenuating them to different heights. For example, in  FIGS. 12A and 12B , a resonator  1216  and a plurality of waveguides, input waveguide  1212  and output waveguide  1214 , are formed on a lower cladding, first layer  1202  in accordance with the previously described techniques. Each has a formation height, H, which is substantially equal and spans the distance from the surface  1220  of the lower cladding to their respective top surfaces,  1228 ,  1226  and  1227 . 
     After attenuation ( FIG. 12B ), the resonator  1216  has a resonator height, H 3 , shorter than its formation height and spans the distance from the surface  1220  to top  1228 . The input waveguide  1212  has an input waveguide height, H 2 , shorter than its formation height and spans the distance from the surface  1220  to top  1226 . The output waveguide  1227  has an output waveguide height, H 3 , shorter than its formation height and spans the distance from the surface  1220  to top  1227 . As shown, H 3  is greater than H 2  which is greater than H 1 . It should be appreciated, however, that the heights could all be variously arranged so that the waveguides are taller than the resonator or that the output waveguide is the tallest, etc. As with previous embodiments, these attenuated structures could be attenuated before or after the deposition of an upper cladding layer, not shown. 
     In  FIG. 13 , it will be appreciated that thermo optic devices of the present invention may be formed with a more than a single resonator to achieve even further variations in the frequency characteristics of the device as application demand varies. In particular, a plurality of resonators  1328 A and  1328 B are formed on a surface  1320  of the lower cladding between the input and output waveguides  1312 ,  1314 , to couple a light signal from the input to the output waveguide during use. As previously described for single resonator embodiments, the plurality of resonators are formed in the same process steps as the waveguides and are formed of the second material. Each resonator has a formation height that is substantially equal with the waveguides when formed. After the input waveguide is attenuated, as shown in this embodiment, the input waveguide is shorter than either of the resonators and output waveguide. In particular, it is shorter by distance, H, spanning from the top  1328 A and  1328 B to the top  1326  of the input waveguide  1312 . The output waveguide  1314  has a top  1327  that is substantially equal to the top  1328  of the resonators. It will be appreciated, that the pluralities of resonators may also be attenuated in accordance with previously shown single resonator embodiments Likewise, the output waveguide may also be attenuated from its formation height. All embodiments may attenuate heights before or after the deposition of an upper cladding, not shown. Those skilled will appreciate that still other numbers of resonators, beyond the two shown, could be formed. 
     With reference to  FIG. 14 , a system, having as part thereof a resonator or waveguide formed in accordance with the teachings of the present invention, is shown generally as  1441 . The system may be an exclusively fiber optic system or may be a system having other software and hardware devices, as indicated by the dashed line  1445 , operably coupled to at least one fiber optic component thereof. 
     In either system, a light source  1443  will be provided as the source for propagating light signals along at least one fiber optic line  1447 . Well known light sources include, but are not limited to, laser light sources. In the embodiment shown, the system  1441  includes a plurality of fiber optic lines  1447 . 
     Coupleable to the fiber optic lines via a plurality of input fiber optic ports  1451  is a thermo optic package  1449 . Contained within the thermo optic package is at least one thermo optic device  1453  having at least one waveguide or resonator formed in accordance with the present invention. In the embodiment shown, the thermo optic device  1453  is coupled to the input fiber optic port  1451  via an input connector  1455  while an output connector  1457  couples the thermo optic device to an output fiber optic port  1459 . In turn, the output fiber optic port  1459  is coupled to another fiber optic line  1447  of system  1441 . 
     During use, a system user merely needs to couple fiber optic lines  1447  to the input and output fiber optic ports of the package  1449  to readily achieve at least one resonator or waveguide having an increased or decreased bandwidth as necessary. 
     With reference to  FIG. 15 , an alternative embodiment of a thermo optic package  1549  is shown having a thermo optic device  1553  with a single input connector  1555  and a plurality of output connectors  1557 . The input connector  1555  connects with input fiber optic port  1551  which is readily matable with a fiber optic line  1547  of a system. The output connectors  1557  of thermo optic device  1553  are each matable with an output fiber optic port  1559 . 
     It will be appreciated that while shown as a single input connector with two output connectors, the thermo optic device  1553  having a resonator or waveguide formed in accordance with the present invention may alternatively have two or more input connectors and one or more output connectors depending upon the type and desired use of the thermo optic device  1553 . 
     CONCLUSION 
     The above structures and fabrication methods have been described, by way of example, and not by way of limitation, with respect to waveguides for thermo optic devices. 
     In particular, a waveguide and resonator are formed in the same process steps on a lower cladding of the thermo optic device and each have a formation height that is substantially equal. Thereafter, the formation height of the waveguide is attenuated. In this manner, the aspect ratio as between the waveguide and resonator in an area where the waveguide and resonator front or face one another decreases (in comparison to the prior art) thereby restoring the synchronicity between the waveguide and the grating and allowing higher bandwidth configurations to be used. The waveguide attenuation is achieved by photomasking and etching the waveguide after the resonator and waveguide are formed. In one embodiment the photomasking and etching is performed after deposition of the upper cladding. In another, it is performed before the deposition. 
     In another embodiment, a plurality of waveguides, an input and output waveguide, are attenuated from their respective formation heights to a different or substantially equal waveguide height. In still another embodiment, a plurality of resonators are formed between the input and output waveguides. 
     In still another embodiment, resonator(s) are attenuated before or after deposition of the upper cladding. In this manner, the aspect ratio increases thereby decreasing the available signal bandwidth. 
     Thermo optic devices, thermo optic packages and fiber optic systems having these waveguides are also taught. 
     As a result, waveguides of this invention can be formed quicker and cheaper without any corresponding sacrifice in quality, reliability or longevity. 
     The present invention has been particularly shown and described with respect to certain preferred embodiment(s). However, it will be readily apparent to those of ordinary skill in the art that a wide variety of alternate embodiments, adaptations or variations of the preferred embodiment(s), and/or equivalent embodiments may be made without departing from the intended scope of the present invention as set forth in the appended claims. Accordingly, the present invention is not limited except as by the appended claims.