Abstract:
An all-optical device for wavelength conversion, reshaping, modulating, and regenerating. The device includes a splitting device having first, second, third, and fourth terminals and a nonlinear element. The third and fourth terminals are associated with an optical loop including the nonlinear element when the nonlinear element is displaced from the mid-point of the optical loop. The splitting device is arranged to receive a modulated signal from one of the first and second terminals and a continuous beam from one of the first and second terminals to generate a patterned signal based on the continuous beam at one of the first and second terminals when the pattern of the patterned signal is inverted with respect to the pattern of the modulated signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent issued from an application that claims priority of my provisional patent application Ser. No. 60/734,124, filed Nov. 7, 2005 
    
    
     BACKGROUND 
     1. Field 
     Optical communication devices and systems, particularly optical wavelength converters, are used for metro and long-haul communications. 
     2. Prior Art 
     The field of optical communication extensively uses Dense Wavelength Division Multiplexing (DWDM) in which a plurality of information channels corresponding to plurality of different wavelengths are inserted, in parallel, into the same optical fiber. Communication systems have a need to transmit information from one channel having a certain wavelength to another channel with another wavelength. In such a situation (channels operate in different wavelengths) there is a need for wavelength converters to allow the transmission of the information from one information channel to another information channel and without the need for Optical-Electrical-Optical (O-E-O) converters. 
     Wavelength converters may be used also for switching purposes when the wavelength change results with a different port from which the radiation is emitted by wavelength-sensitive demultiplexers (WDM or DWDM). 
       FIG. 1  is a schematic illustration of a prior-art Mach Zhender Interferometer (MZI) wavelength converter  400 . This converter is used to convert signals carried by one wavelength to be carried by another wavelength. Wavelength converters are implemented in the metro area and in the long-haul networks as well. The wavelength converter is designed to convert information generating pulses  402  of wavelength λ 1 , at terminal  404 , into converted information pulses  406  of wavelength λ 2 , at terminal  408 . Continuous Wave (cw) radiation  410 , having a wavelength λ 2 , is inserted at terminal  412  and is split by coupler  414  into cw radiation propagating in branches of radiation guides  416  and  418 . The radiation in branched  416  and  418  passes through Solid-state Optical Amplifiers (SOA)  422  and  420 , respectively, serving as Non Linear Elements (NLE). SOAs  420  and  422  are adjusted to produce relative phase shifts between the cw radiation in guides  416  and  418  for causing the radiation from guides  416  and  418  to be combined destructively in coupler  424 . Accordingly, when no signal  402  is present in terminal  404 , there is no output signal  406  at port  408 . 
     When signal  402  having a wavelength λ 1  is received by terminal  404 , it is coupled by coupler  426  into guide  418  and passes through SOA  420 . For the time duration in which signal  404  passes through SOA  420 , it causes a phase change of π radians to the cw radiation propagating in the opposite direction in SOA  420 . In this case the cw radiation from guides  416  and  418  is combined constructively, by coupler  424 , to produce pulse  406  at output  408  having a wavelength λ 2  and a time duration equal to that of pulse  402 . Accordingly, converter  400  converts pulses  402  of wavelength λ 1  at port  404  into similar pulses  406 , of wavelength λ 2 , at port  408 . The components of the converter of  FIG. 1  are well known. 
     The wavelength converter of  FIG. 1  may have one or more of the following disadvantages: 
     1. The device is phase sensitive and thus electric current injected into SOAs  420  and  422  should be controlled, separately, to each of them to maintain the desired phase relations and to compensate for phase changes resulted from environments changes and/or various drifts in the values of some parameters of device  400 , such as gain drifts of SOAs  420  and  422 . 
     2. In the absence of signals  402  at port  404  and in order to produce zero output signals  406  at port  408 , there is a need to maintain independent gain and phase relations between amplifiers  422  and  420  at branches  416  and  418 , respectively. However the gain and the phase shifts of amplifiers  422  and  420  are dependent parameters, resulting in a situation that may be difficult to control. 
     3. The design of the device requires two SOAs which may reduce manufacturing yield and may increase manufacturing cost and complexity. 
     U.S. patent application Ser. No. 10/845,149 entitled “All optical phase insensitive wavelength converters, apparatus systems and methods” filed May 14, 2004” by Arie Shahar et al. and published Nov. 25, 2004 as Publication Nr. 20040233513 shows a wavelength converter which has one or more of the following drawbacks: 
     1. It is sensitive to the polarization orientation of the converted signal. 
     2. It includes an attenuator in its optical loop that attenuates the converted signal. 
     International patent application PCT/US2004/028588 (International Publication Number WO 2005/022706 A2) by Paul R. Prucnal, filed Sep. 2, 2004 (priority date of Sep. 2, 2003—U.S. Ser. No. 60/499,536) discloses a wavelength converter that suffers from the following disadvantages:
         1. The device is polarization sensitive.   2. The device suffers from high loss due to a coupler in its optical loop. This coupler should have a high coupling coefficient to efficiently couple the converted signal into the optical loop in order to have enough power to produce polarization rotation in the Non Linear Element (NLE) of the optical loop. This means that that the loss in the optical loop is at least equal to the high coupling ratio of the above mentioned coupler.   3. The device suffers from high pattern distortion due to the high power of the converted signal injected from one side only into the NLE in the optical loop.   4. The device suffers from high gain instability due to the high power converted signal that causes the gain of the NLE to be pattern dependent.       

     ADVANTAGES 
     Some advantages of some exemplary embodiments are to provide phase and polarization insensitive wavelength converters, to provide wavelength converters or a regenerator that does not suffers from attenuating devices such as attenuator or coupler in its optical loop, to provide wavelength converters that require only one Non Linear Element, to provide optical re-shapers and regenerators in which a cw beam and a generating signal have the same wavelength, to provide optical modulators to convert direct modulated signals into low chirp signals, to provide a wavelength converter that does not suffer from the above listed disadvantages of the devices of the above Prucnal and Shahar et al. applications. 
     SUMMARY 
     In one embodiment, an all-optical device provides wavelength conversion, reshaping, modulating and regenerating. The device includes a splitting device having first, second, third, and fourth terminals and a nonlinear element. The third and fourth terminals are associated with an optical loop including the nonlinear element when the nonlinear element is displaced from the mid-point of the optical loop. The splitting device is arranged to receive a modulated signal from one of the first and second terminals and a continuous beam from one of the first and second terminals to generate a patterned signal based on the continuous beam at one of the first and second terminals when the pattern of the patterned signal is inverted with respect to the pattern of the modulated signal. 
    
    
     
       DRAWINGS 
         FIG. 1  is a schematic illustration of a wavelength converter known in the art that is phase sensitive and includes two Non Linear Elements (NLEs); 
         FIGS. 2   a ,  2   b , and  2   c  illustrate a polarization insensitive wavelength converter with no excess loss in its optical loop. 
     
    
    
     ABBREVIATIONS AND SYMBOLS 
     ASE—Amplified Spontaneous Emission 
     CCW—Counterclockwise 
     CW—Clockwise 
     cw—Continuous Wave 
     DWDM—Dense Wavelength Division Multiplexing 
     EDFA—Erbium Doped Fiber Amplifier 
     LOA—Linear Optical Amplifier 
     MZI—Mach Zhender Interferometer 
     NLE—Non Linear Element 
     O-E-O—Optical-Electrical-Optical 
     PLC—Planar Circuits 
     PM—Polarization Maintaining 
     PMD—Polarization Mode Dispersions 
     PMF—Polarization Maintaining Fibers 
     S—Distance 
     SMF—Single Mode Fibers 
     SOA—Semiconductor Optical Amplifier 
     XGM—Cross Gain Modulation 
     λ—Wavelength 
     DETAILED DESCRIPTION 
     FIG.  2   a    
       FIG. 2   a  illustrates a wavelength converter. Unlike the devices disclosed by the above Shahar et al. whose principle of operation is based mainly on the phase shift that the converted signal creates at the NLE in the optical loop, the principle of operation of the device of  FIG. 2   a , as explained below, is mainly based upon the polarization rotation that the converted signal creates at NLE  5826 . 
     The device of  FIG. 2   a  includes coupler  5820  having input terminal  5802  and output terminal  5822 . The other two terminals of coupler  5820  form optical loop  5818  having nonlinear element  5826 . Input terminal  5802  includes directing device  5817  that its terminal  5819  may include optional filter  5859 . Output terminal  5822 , optical loop  5818  and input terminal  5802  may include optional polarization controllers  5924 ,  5926  and  5928 , respectively. 
     PRINCIPLE OF OPERATION 
     (a) Polarization Sensitive Wavelength Converter 
     First I will provide an explanation of a situation when there is no arrangement to make the device of  FIG. 2   a . A polarization insensitive device is used when the device is constructed from radiation guides that are not polarization maintaining, such as Single Mode Fibers (SMF). Polarization controllers  5924  and  5926  are adjusted to produce the desired polarization orientation. Under the condition of the desired polarization orientation when no signal  5830  is present at port  5802 , cw radiation  5891 , having wavelength λ 2  and arriving to loop  5818  from terminal  5822 , is transmitted, at least in part, into terminal  5816  and is coupled from guide  5816 , by directing device  5817  (illustrated as coupler  5817 ), to port  5819  to be emitted out of the converter via optional filter  5859 . The injection current into NLE  5826  may also be adjusted to produce optimal polarization rotation in order to maximize the power of cw beam  5891  at port  5819 . 
     Beam  5891  (cw) is split by a splitting device (coupler  5820 ) into two optical components propagating clockwise (CW) and counterclockwise CCW) in loop  5818 . When the CW and the CCW components complete their propagation along loop  5818  they return to coupler  5820  to recombine there by interference. The phase shifts of the CW and CCW optical components produced by the propagation along loop  5818  are equal. Accordingly, if the radiation guides of loop  5818  and NLE  5826  do not produce any polarization rotation, the whole energy of cw beam  5891  would be reflected back into terminal  5822  by a complete constructive interference between the CW and CCW components at coupler  5820 . 
     Polarization Conditions for Continuous Beam 
     However, when varying the polarization orientation, by polarization controller  5926  and NLE  5826 , at least part of the energy of beam  5891  can be emitted out from loop  5818  via coupler  5820  and into radiation guide  5816 . This process is possible since the polarization rotation is not a reciprocal process and the polarization rotation for the CW component is not equal to the polarization rotation for the CCW component. This means that the polarization orientations of the CW and the CCW components returning in loop  5818  to coupler  5820  may be adjusted by the injection current to NLE  5826  and polarization controller  5926  to be in different orientations. In such a case, at least part of the energy of cw beam  5891  is transmitted to guide  5816  via loop  5818  and coupler  5820 . The polarization of the CW and CCW components may even be adjusted, by NLE  5826  and controller  5926 , to be oriented in opposite directions. In such a case, the CW and CCW components interfere completely destructively at coupler  5820  and the whole energy of cw beam  5891  is transmitted from port  5822  to guide  5816 . 
     Influence of Probe Signal 
     A generating signal (known also as converted signal, probe signal or control signal)  5830  appears as signal  5833  in guide  5614  after being amplified by optional optical amplifier  5862 , which may be an SOA. The intensity of signal  5833  is above the power level needed to produce a significant polarization rotation at NLE  5826 . Generating signal  5830 , arriving at guide  5814  as signal  5833 , propagates from there, via a directing device (coupler)  5817 , to radiation guide  5816  and device  5824  that includes splitting device (coupler)  5820  and loop  5818 . At least part of generating signal  5830  is transmitted, by device  5824 , to port  5822  and appears at port  5822  as signal  5834  having wavelength λ 1 . Generating signal  5830 , arriving to directional coupler  5820  as signal  5833 , is split into two optical components  5833 A and  5833 B propagating CW and CCW in the directions of arrows  5842  and  5844 , respectively, in optical loop  5818 . If coupler  5820  is a symmetric coupler, components  5833 A and  5833 B have equal intensity. 
     When generating signal  5830  is present at port  5802  it changes the polarization rotation of NLE  5826  by the high power induced to NLE  5826  from components  5833 A and  5833 B produced by signal  5830 . Components  5833 A and  5833 B propagating in the direction of arrows  5842  and  5844 , respectively, may also cause Cross Gain Modulation (XGM) and phase shift in NLE  5826 , however, the main effect that they produce in NLE  5826  is the relative change of the polarization rotation that NLE  5826  cause to CW and CCW components of cw beam  5891 . This relative change in the polarization orientation for the CW and CCW components of cw beam  5891  is caused, as explained above, due to the non-reciprocal process that produces different polarization rotation to these components during their travel in loop  5818 . The relative polarization rotation applied by NLE  5826  to the CW and CCW components may be adjusted by the power of converted signal  5830  and its components  5833 A and  5833 B. This induces in NLE  5826  a polarization rotation that will cause the CW and CCW components of cw beam  5891  to return to coupler  5820  of loop  5826  with polarization orientations that are opposite. In this case, the CW and CCW of beam  5891  interfere completely constructively in coupler  5820  and thus cw beam  5891  is completely reflected back into port  5822  and no cw beam  5891  appears at port  5819 . 
     Displacement of Nonlinear Element from Mid Point of Optical Loop 
     The absence of signal  5891  at port  5819  lasts for the time period that components  5833 A and  5833 B pass through NLE  5826 . NLE  5826  is displaced by distance S from midpoint  5828 . Displacement S is defined as the distance between midpoint  5828  of loop  5818  and the edge of NLE  5826  marked by line  5850 . As will be explained below, distance S is relatively small and thus components  5833 A and  5833 B pass through NLE  5826  at substantially the same time. This means that the absence of signal  5891 , having wavelength λ 2 , at port  5819  lasts for a time period that is substantially equal to the time width of signal  5830  as shown by signal  5859  at port  5819 . 
     Accordingly, signal  5859  at port  5819  is the inverted signal of generating signal  5830 . However while signal  5830  at port  5802  has a wavelength λ 1  inverted signal  5859  at port  5819  has a wavelength λ 2 . This means that device  5802  operates as inverted wavelength converter. 
     As explained above, cw beam  5891  (like converted beam  5830 ) is also split into CW and CCW optical components at loop  5818 . When NLE  5826  is displaced by a distance S from midpoint  5828 , optical components  5833 A and  5833 B change the polarization orientation of the CW and CCW optical components of cw beam  5891  when they pass through NLE  5826  located asymmetrically in loop  5818 . Thus these CW and CCW components of cw beam  5891  are at a different distance from coupler  5820  where they recombined. The change in the polarization orientation at NLE  5826  and the difference in the distances from NLE  5826  to coupler  5820  for the CW and CCW components of cw beam  5891  cause these CW and CCW components to be combined, by interference, at coupler  5820  with different polarization orientation. 
     The difference between the polarization orientation of the CW and CCW components that experience the change of the polarization orientation at NLE  5826 , due to the generating signal (components  5833 A and  5833 B), may vary periodically at coupler  5820  where the CW and CCW components interfere. This periodic change in the relative polarization orientation between the CW and CCW components of beam  5891  is a function of the displacement distance S. This periodic change is actually the beat length of the birefringence of the radiation guides in loop  5818 , which can be in the range of few millimeters. Thus the displacement S may be equal or smaller than the above beat length or equal to this displacement with the additional length of an integral number of times the beat length. 
     Accordingly, in the presence of generating signal  5830  at port  5802 , distance S may be adjusted to create relative polarization orientation of π radians between the CW and CCW components of beam  5891  at loop  5818  for reducing the power of signal  5859  at port  5819  to substantially zero. This adjustment can improve dramatically the extinction ratio of wavelength converter  5803 . Adjusting the above mentioned distance S of the displacement of NLE  5826  to its optimal distance makes the wavelength converter more efficient and allows the power of generating signal  5830  to be reduced. 
     Wavelength Converter with High Conversion Efficiency and Reduced Pattern Distortions 
     The reduction of the power of signal  5830  reduces the XGM at NLE  5826  as well. This enables inverted signal  5859  to be generated with little delay in the recovery time of NLE  5826 . This allows a high quality converted and inverted signal  5859  to be generated that is pattern insensitive. The efficiency of the wavelength conversion of device  5805  is increased with the birefringence of NLE  5826 . When NLE  5826  has high birefringence, the difference between the indices of refraction of its fast axis and slow axis is high. In this case, NLE  5826  may produce a large change between the polarization orientation of the CW and CCW signals propagating in optical loop  5818 . Accordingly, when NLE  5826  has high birefringence, it may produce a polarization change between the CW and CCW signals propagating in loop  5818 , which is needed for the wavelength conversion even when generating signal  5830  has relatively low intensity. 
     This beat length is equivalent to time delay of 10-30 picoseconds (depends on the birefringence of the radiation guides of loop  5818 ). Thus, when displacement S is equal or smaller than the beat length, the delay time between the arrival time of components  5833 A and  5833 B to NLE  5826  is equal or smaller than 10-30 picoseconds and thus can be regarded, as mentioned above, as passing substantially at the same time through NLE  5826 . The entrance of components  5833 A and  5833 B to NLE  5826  at substantially the same time from two opposite orientations eliminates the pattern distortion exists in the device disclosed by above Prucnal application. 
     Low-Loss Wavelength Converter 
     Another major disadvantage of high loss in the Prucnal device is eliminated by device  5803  by eliminating the need to couple the generating signal into loop  5818  using additional coupler that is integrated into loop  5818 . As mentioned above, such a coupler should have a high coupling efficiency to maintain the high power of the converted signal at the NLE for producing the necessary polarization rotation. However the excess loss that such coupler produces are at least equal to its coupling efficiency and are very high. That means that the device disclosed by Prucnal application suffers from high loss that does not exist in the converter of  FIG. 2   a.    
     The low loss in this device is also a significant advantage over the device disclosed by the Shahar et al. application, which includes an attenuator in its optical loop and produces a major loss for the converted signal. 
       FIG. 2   b  shows circulator  5817 A having input port  5814 , output port  5816  and returning port  5819 . Circulator  5817 A may be used as the directing device of the converter of  FIG. 2   a  by replacing coupler  5817  of the converter. 
     Further reduction in the loss may be achieved by replacing coupler  5817  by circulator  5817 A as indicated by arrows  5916  and shown in  FIG. 2   b . Circulator  5817 A is coupled to guides  5814 ,  5816  and  5819  of  FIG. 2   a  to replace coupler  5817 . Unlike coupler  5817 , circulator  5817 A allows almost complete transmission of generating signal  5833  from guide  5814  to guide  5816  and at the same time it allows almost complete transmission of signal  5891  from guide  5816  to guide  5819  as well. 
     (b) Polarization Insensitive Wavelength Converter 
       FIG. 2   c  shows nonlinear element  5826  of  FIG. 2   a  coupled to polarization maintaining fibers  5818 A and  5818 B of optical loop  5818  in a configuration when the fast axis of fiber  5818 A is aligned towards the slow axis of fiber  5818 B. 
     In order to make the wavelength converter of  FIG. 2   a  polarization insensitive, at least the radiation guides of loop  5818  and coupler  5820  should maintain polarization. For example,  FIG. 2   c  shows radiation guides  5818 A and  5818 B of loop  5818  of  FIG. 2   a  that are Polarization Maintaining Fibers (PMF). PMF  5818 A and  5818 B are shown in cross-sections  5910  and  5902  and have fast axes  5914  and  5904  and slow axes  5912  and  5906 , respectively. 
     PMF fibers  5818 A and  5818 B are coupled to NLE  5826  of  FIGS. 2   a  and  2   c  as indicated by arrows  5920  and  5922 , respectively. Arrows  5920  and  5922  show the coupling points where PMF fibers  5818 A and  5818 B are coupled to NLE  5826 . From cross-sections  5910  and  5902 , it can be seen that PMFs  5818 A and  5818 B are oriented orthogonally to each other. 
     In this situation, when coupler  5820  is a Polarization Maintaining (PM) coupler, fibers  5818 A and  5818 B are PM fibers that are oriented orthogonally to each other, and displacement S is small, the NLE will receive optical components  5833 A and  5833 B in polarization orientations that are substantially orthogonal to each other. 
     The fact that for any polarization orientation of generating signal  5830 , its components  5833 A and  5833 B will arrive to NLE  5826  in loop  5818  with polarization orientations that are orthogonal to each other makes wavelength converter  5803  polarization insensitive to generating signal  5830 . In this case polarization controllers  5926  and  5928  are not needed and can be removed from device  5803  of  FIG. 2   a.    
     Polarization Insensitive Wavelength Converter with Reduced Polarization Mode Dispersions 
     The configuration in which PMFs  5833 A and  5833 B are orthogonal causes the signal from fast axis  5914  of PMF  5818 A to be coupled to slow axis  5906  of PMF  5818 B and vice versa. Similarly, the signal from slow axis  5912  of PMF  5818 A is coupled to fast axis  5904  of PMF  5818 B and vice versa. Since the length of PMF  5818 A and  5818 B is similar, the traveling distance that each signal propagates in the fast and the slow axes is similar. Accordingly, the above mentioned configuration has the advantage of reducing the Polarization Mode Dispersions (PMD). 
     Polarization controller  5924  may be removed from device  5803  of  FIG. 2   a  as well, provided that the polarization of signal  5891  will be aligned to its optimal orientation. This orientation does not change since unlike the converted signal that has random polarization orientation, the light source of signal  5891  has a fixed polarization orientation. 
     Polarization Insensitive Wavelength Converter with Improved Gain Stability 
     To improve the gain stability of device  5803  of  FIG. 2   a , optional optical amplifier  5802  may be a Semiconductor Optical Amplifier (SOA). SOAs are known for their relatively high Amplified Spontaneous Emission (ASE). Accordingly, the use of an SOA may help to achieve constant average power at NLE  5826 , which is independent on the pattern. Adjusting the current injected to SOA  5802  controls the amount of ASE emitted from SOA  5802  and may produce constant average power at NLE  5826  which is independent on the pattern of generating signal  5830 . Such a fixed average power at NLE  5826  make device  5803  very stable and it does not suffers from gain instabilities due to pattern variations of generating signal  5830 . 
     CONCLUSIONS, RAMIFICATIONS, SCOPE 
     Wavelength converter  5803  of  FIGS. 2   a - 2   c  has one or more of the following additional advantages over the devices disclosed by the Prucnal and Shahar et al. applications:
         1. The device is polarization insensitive.   2. The device has an optical loop without an attenuator.   3. The device has very low loss due to the elimination of the need to couple the generating signal into the loop using additional directional coupler.   4. The device does not suffer from high pattern distortion due to the injection of the signal into NLE  5626 , through its both sides, in a collision mode.   5. The device is very stable and does not suffer from high gain instability due to substantially fixed average power at NLE  5826  achieved by the adjustment of the ASE of pre-amplifier  5802 .       

     As explained above, the device of  FIG. 2   a  is phase and polarization insensitive. In a situation where coupler  5820  and directing device  5817  are also wavelength insensitive, the whole device  5805  is wavelength insensitive. 
     While certain features have been illustrated and described, many modifications, substitutions, changes, and equivalents may occur to those of ordinary skill in the art. 
     All the embodiments may include optical isolators in their inputs through which the cw radiation and the pattern of the generating signals are coupled into the wavelength converters. Such optical isolators may block the back reflection and the return of cw radiation and or pulses back into the sources of the cw radiation and the generating signals. 
     All the embodiments may include a continuous sequence of optical components connected by light-guiding media such as, for example, optical fibers, planar waveguides, or planar circuits (PLC), which media may be fabricated using integrated optic techniques and/or on-chip manufacturing. Alternatively, All the embodiments may be constructed from discrete components, in which case the optical guiding media may be replaced by open (free) space, e.g., vacuum, or by a non-solid, e.g., gaseous media, and the directional couplers may be replaced with beam splitters. It should be understood that all amplifiers and controllers may include variable and/or adjustable components. All amplifiers may be made of amplifying media and devices and in particular are made of SOAs, Linear Optical Amplifiers (LOAs) and Erbium-Doped Fiber Amplifier (EDFAs). 
     While the embodiments are described as wavelength converters operate by copying the pulse-pattern signal from one modulated wavelength λ 1  into another Continuous Wave (cw) having another wavelength λ 2 , the embodiments may operate in a similar manner when the modulated signal and the cw beam have the same wavelength λ 1 =λ 2 . When λ 1 =λ 2  the embodiments operate as optical shapers and 2R regenerators by copying the modulated signal onto a cw beam having the same wavelength at the modulated signal for reshaping and regenerating a new signal with a better quality. Accordingly, it should be understood that all the embodiments are devices that operate under various conditions when either λ 1 =λ 2  or λ 1 ≠λ 2  and in any place that symbols λ 1  and λ 2  are used they may be different wavelengths or the same wavelength. All the embodiments may operate as modulators as well when receiving direct modulated pulses with chirp and converting them, by copying on a cw beam, into pulses with reduced or no chirp. 
     Therefore the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments discussed and their legal equivalents.