Abstract:
A wavelength-dependent variable mirror suitable for application in tunable semiconductor lasers is disclosed. The variable mirror comprises a coupler having two input ports and two output ports operable to distribute a known level of light coupled into a first input port, optical channels extending from each of the two coupler output ports of and a wavelength-selective device connected to each of the extended optical channels. In one aspect, the wavelength selective device connects the two extended channels forming an optical loop, which reflects a known level of light back to the coupler input ports. In another aspect, the wavelength selective device reflects a known level of light at a predetermined wavelength back to each of the extended channels to an input port of said coupler. In yet another aspect, a phase controlling element is introduced in at least one optical channel, which introduces a known amount of phase change in the light sent back to the coupler. In one application, a tunable laser is fabricated using a gain medium in conjunction with wavelength-selective variable mirror that operates to reflect a known level of light energy into a gain material to achieve lasing operation at a designated frequency.

Description:
CLAIM OF PRIORITY  
       [0001]    This application claims the benefit pursuant to 35 USC §119, of the earlier filing date of U.S. Provisional Applications;  
         [0002]    Serial No. 60/305,245, entitled, “Tunable Laser Using Half Mach-Zehnder Device with Reflection Grating, having a filed date of Jul. 13, 2001; and  
         [0003]    Serial No. 60/305,244, entitled “Frequency Dependent Variable Mirror And Applications,” having a filing date of Jul. 13, 2001, which are incorporated by reference herein. 
     
    
     
       FIELD OF THE INVENTION  
         [0004]    The present invention is directed to frequency-selective mirrors and more particularly to their application in frequency-selective semiconductor tunable lasers.  
         BACKGROUND OF THE INVENTION  
         [0005]    [0005]FIG. 1 illustrates a cross sectional view of a conventional semiconductor laser  100 . Laser  100  is composed of an active region  110  composed of a light generating and amplifying layered material that generates photons, such as InGaAsP/InP, and providing optical gain to existing photons flowing through the active region, when activated by electrical current driven across the layered structure. Regions  120  and  125  opposing active region  110  create a waveguide that maintains the generated photons guided within active region  110 . Partially reflective materials  130  and  135  at the ends of active region  110  provide reflective surfaces that reflect generated photons and form a cavity. Light propagating back and forth between the reflective cavity ends builds up through a constructive interference process. When sufficient gain within the cavity is provided to overcome propagation and reflection losses, lasing action takes place, resulting in a concentrated beam of light emerging from the ends of the semiconductor structure. In a common configuration one reflecting end surface is partially reflective and one is fully reflective. In this manner the laser light emerges from the semiconductor structure in a known direction. As is known in the art, the reflective surfaces may be facet edges of the semiconductor gain material structure.  
           [0006]    As known in the art, the frequency, wavelength or color, the terms which are interchangeably used herein to describe the spectral characteristics of the lasing light, depends on the material used in the active region and the length of the cavity created between the reflective surfaces, as the constructive interference pattern is frequency dependent. Accordingly, the available frequency, wavelength or color output of each semiconductor laser is limited and predetermined by the choice of material system, the layered structure and the dimensions of the cavity comprising the laser. Conventionally, the structure described above, namely that of gain material placed between two reflecting mirrors, which is referred to as a Fabry-Perot (FP) laser. The FP laser is characterized by having a plurality of equally-spaced operating wavelengths, where the number of lasing wavelengths, their exact position within the gain spectrum and their relative intensity is somewhat random and determined by a variety of operating conditions such as the drive current, the operating temperature, the material system and dimensions of the laser structure. This non-deterministic operation is detrimental for many applications where the precise wavelength of the light emitted by the laser and its stability is of critical importance.  
           [0007]    To overcome these limitations of the FP laser, a periodical layer is introduced into the layer structure. This periodic layer functions as a distributed reflective mirror, replacing the end mirrors. This type of periodical reflective mirror is frequency dependent, resulting in single wavelength lasing action. Lasers built in this manner are referred to as distributed feedback lasers or DFB lasers. Nevertheless, once a DFB laser is fabricated, the operating wavelength is fixed and predetermined, except for slow and limited variation that can be obtained by changing the operating temperature.  
           [0008]    In WDM (Wavelength Division Multiplex) telecommunication systems, a plurality of lasers of different wavelengths provide the signal carriers for signal transmission. In such systems, the operating wavelength of each laser element is individually specified, fabricated and adjusted for proper system operation. Thus, in a 16-channel WDM system, 16 lasers, each operating on a separate frequency, wavelength or color must be obtained and incorporated into the system. This process is expensive as individual lasers must be fabricated, tested, inventoried, and correctly incorporated into a typical WDM system. As the number of wavelengths in a WDM system increases, e.g., 128, 256, etc., a significant cost and burden is imposed on the laser manufacturers and system developers to manage the increased number of different lasers needed.  
           [0009]    Tunable lasers, as known in the art, represent one means for reducing the number of different and unique lasers needed in WDM systems. One example of a tunable laser is an intra-cavity multiple-section laser that allows for separate gain and wavelength control. A second example of a tunable laser is the external cavity laser (ECL) that uses an external, frequency selective, reflection surface, such as a reflection grating, outside the gain medium or active region. However, the former is difficult to manufacture and thus has problems with yield. Furthermore, there are problems with current and voltage control. The latter type is bulky and critically dependent on alignment and mechanical stability. In addition, as the ECL uses a frequency selective element as one of the cavity mirrors, it is limited to reflection grating type filters as the wavelength control element. This type of reflection grating has limited efficiency and does not provide a means to control the magnitude of reflection at a given frequency.  
           [0010]    Thus, there is a need for wavelength selective mirrors that may be used to fabricate semiconductor lasers that are selectively operable at one of a plurality of frequencies or wavelengths, which are further tunable, variable in reflectivity, mechanically stable, and may be constructed using both reflective and transmissive adjustable filter configurations. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 illustrates a conventional prior art semiconductor laser;  
         [0012]    [0012]FIG. 2 illustrates a block diagram of a tunable laser in accordance with the principles of the present invention;  
         [0013]    [0013]FIG. 3 a  illustrates one aspect of the present invention using a Mach-Zehnder interferometer;  
         [0014]    [0014]FIG. 3 b  illustrates a second aspect of the present invention using a Mach-Zehnder interferometer;  
         [0015]    [0015]FIGS. 4 a - 4   c  illustrate different optical couplers operable in accordance with the principles of the invention;  
         [0016]    [0016]FIG. 5 illustrates a second aspect of the present invention using a reflective filter in a Michelson interferometer configuration;  
         [0017]    [0017]FIG. 6 a  illustrates a third aspect of the present invention using a non-reflective filter;  
         [0018]    [0018]FIG. 6 b  illustrates another aspect of the present invention using a non-reflective filter;  
         [0019]    [0019]FIG. 7 illustrates a graph of the experimental wavelength output of a tunable laser illustrated in FIG. 6 b  as a function of displacement that adjusts the a filter tilt angle; and  
         [0020]    [0020]FIG. 8 illustrates a graph of experimental results output power spectra of a tunable laser as shown in FIG. 6 b.   
     
    
       [0021]    [0021]FIGS. 1 through 8 and the accompanying detailed description contained herein are to be used as an illustrative embodiment of the present invention and should not be construed as the only manner of practicing the invention. It is to be understood that these drawings are for purposes of illustrating the concepts of the invention and are not to scale. It will be appreciated that the same reference numerals, possibly supplemented with reference characters where appropriate, have been used throughout to identify corresponding parts.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    [0022]FIG. 2 illustrates a block diagram of a generalized tunable laser  200  in accordance with the principles of the invention. In this generalized configuration, gain material  210  includes highly-reflective (HR) surface  222  and a clear or an anti-reflective (AR) surface (not shown). Anti-reflective coating is preferred as it prevents reflection back into gain material  120 . Also, the channel guiding the light in a semiconductor type gain medium can be formed at an angle with respect to the material facet to further reduce reflection from the surface.  
         [0023]    Light  205  generated by gain material  210  is applied to a first input port of 2×2 coupler  230 , wherein light  205  is split in known levels associated with each output port. The light exiting each of the outputs of coupler  230  is then applied to phase adjustment modules  240   a ,  240   b , respectively, wherein a known level of phase is introduced. The phase adjusted light is next applied to wavelength-selective device  250 , which is operable to return back at least one predetermined, selected or desired wavelength. Hence, the wavelength subsequently returned to gain medium  220  for continued amplification and a portion of the applied light energy emerges from the second coupler input port as laser light  260 . As will be explained further, the selected wavelength may be returned to gain material  210  either by reflection or transmission.  
         [0024]    [0024]FIG. 3 a  illustrates one aspect of the present invention wherein a Mach-Zehnder interferometer  310  (MZI) is used as 2×2 cross-coupling switch  230 . In this illustrated aspect, light energy  205  generated in gain material  210  is applied to port  332  of Mach-Zehnder interferometer  310 . Light  205  is split in a first input coupling stage  334 , phase shifted in phase shifter stage  336  and then split again in second output coupling stage  338 . Mach-Zehnder interferometers are well known in the art and need not be discussed in detail.  
         [0025]    Associated known levels of light exiting MZI  310  at correpsondign output ports are then applied to phase control elements  240   a ,  240   b , through an optical path that can be made using an optical fiber or an embedded waveguiding channel. Phase control elements  240   a ,  240   b  apply phase values φ 1 , φ 2 , respectively to the phase value of the light portions passing therethrough. Phase values φ 1 , φ 2 , as will be appreciated, can be identical in magnitude and opposite in sign, i.e., φ 1 =−φ 2 =φ or can have other values, such as φ 1 =0 and φ 2 =φ. In addition, phase control elements  240   a ,  240   b  may be incorporated into or may be monolithically integrated with the Mach-Zehnder interferometer  310 . The incorporation of the phase control elements  240  is advantageous as it does not increase the cost of the interferometer  310  as the electrodes for the phase control elements  240   a ,  240   b  may be fabricated at the same time the phase electrodes of the MZI  310  are fabricated. It would also be appreciated that the comparable phase difference relation may be achieved using only one phase control unit, either  240   a  or  240   b , represented as  240 .  
         [0026]    The phase adjusted outputs are applied to opposite ends of a filter unit  250 , which in this illustrated aspect is a frequency/time dependent filter possessing a characteristic represented as T(ω,t). Filter  250 , for example, may be a partial reflective/partial transmission filter, such as tunable Fabry-Perot filter that transmits a narrow linewidth about a single frequency within a given frequency range, known as the Free Spectral Range (FSR), and reflects all other frequencies. Similarly, filter  250 , may be a fully reflective filter, such as a Fiber Bragg Grating (FBG) or a fully transmissive filter, such as multi-layered dielectric tilt filter.  
         [0027]    The equations governing the relationship between the input electric field E i  and the reflected electric field E r  and the transmitted electric field Et, of the illustrated variable mirror of FIG. 3 a , can be shown to be:  
                   E   r       E   i       =          jϕ          [         t   f          sin        (     2      ψ     )                 j                 Δ                 ϕ         -       r   f          (         sin   2        ψ     +            j2                 Δϕ            cos   2        ψ       )         ]         ,   and           (   1   )                     E   t       E   i       =     -          jϕ          [         -     r   f          sin                 ψ                 cos                   ψ        (     1   -          j                 2                 Δ                 ϕ         )         +         t   f          (         cos   2        ψ     -         sin                2        ψ       )                            j                 Δϕ           ]           ,           (   2   )                               
 
         [0028]    where Δφ=φ 2 −φ 1 ;  
         [0029]    φ=φ 1 +φ 2 ;  
         [0030]    t f  and r f  are the field transmission and reflection of the filter unit, respectively; and  
         [0031]    ψ is the phase angle of the MZI.  
         [0032]    In one aspect, when φ 1 =φ 2 =0 and Δφ=0, then equations 1 and 2 are represented as:  
                   E   r       E   i       =         t   f          sin        (     2                 ψ     )         -     r   f         ,              and           (   3   )                   E   t       E   i       =       t   f            cos        (     2                 ψ     )       .               (   4   )                               
 
         [0033]    In this case, the reflected field is comprised of a portion of the field transmitted by the filter unit, i.e., t f  sin(2ψ), and the full value of the field reflected by the filter unit, i.e., r f . It will also be understood that in many circumstances mixing the transmission with the reflection, as given by equation 3, is undesirable as it prevents frequency discrimination of the reflection field based on only a single frequency characteristic provided by either the reflection or the transmission of the filter unit.  
         [0034]    Incorporation of at least one phase control unit  240   a ,  240   b  to introduce phase angle values φ 1  and φ 2  respectively, into the path length allows for the adjustment of the phase value in the fiber loop to be tuned to a known value. In one aspect, the fiber loop phase value may be tuned such that a substantially 90 degree phase shift, i.e.,  
           Δ                 ϕ     =     π   2       ,                         
 
         [0035]    exists between the upper and lower halves of the fiber loop. In this case, the field reflection and field transmission ratios, from equations 1 and 2, are represented as:  
                   E   r       E   i       =          jϕ          [         jt   f          sin        (     2      ψ     )         +       r   f        cos                   (     2      ψ     )         ]         ,   and           (   5   )                   E   t       E   i       =     -          jϕ          [         -     r   f            sin        (     2                 ψ     )         +       jt   f                     cos        (     2                 ψ     )           ]                 (   6   )                               
 
         [0036]    In this case, the reflection and transmission of the variable mirror may be substantially controlled with an appropriately selected phase value of the MZI  310 . For example, when the phase of MZI  310  is 45 degrees, i.e.,  
       ψ   =     π   4                           
 
         [0037]    then equations 5 and 6 are represented as::  
                 E   r       E   i       =           jt   f             jϕ       -&gt;     and                     E   t       E   i           =         jr   f               j                 ϕ         -&gt;               (   7   )                               
 
         [0038]    The intensities of the transmitted and reflected signals may then be determined as:  
                        E   r       E   i            2     =                t   f          2                   and                            E   t       E   i            2       =            r   f          2               (   8   )                               
 
         [0039]    Hence, the overall reflection of the electrical field is a function of only the filter transmission value and the overall transmission of the electrical field is a function of only the filter reflection value.  
         [0040]    On the other hand, if the phase value of MZI  310  is set to 90 degrees, i.e.,  
         ψ   =     π   2       ,                         
 
         [0041]    then equations 5 and 6 are represented as::  
                 E   r       E   i       =         -     r   f               jϕ                   and                     E   t       E   i         =       jt   f               j                 ϕ                   (   9   )                               
 
         [0042]    The corresponding intensities then may be determined as:  
                        E   r       E   i            2     =                r   f          2                   and                            E   t       E   i            2       =            t   f          2               (   10   )                               
 
         [0043]    In this case, the overall reflection of the electrical field is a function of only the filter reflection value and the overall transmission of the electrical field is a function of only the filter transmission value.  
         [0044]    Accordingly, in this aspect of the invention, the phase, ψ, of MZI  310 , may be used to determine any combination of the filter reflection (r f ) and/or transmission (t f ) that is reflected back into gain material  210 . Hence, the fiber loop responds as a partially transmissive/partially reflective external second mirror to the gain material that allows a known amount of reflective energy to be returned to gain material  210  at a given frequency determined as by the filter characteristics.  
         [0045]    As the transmission or reflection characteristics of filter  250  may be selectively chosen to specific spectral characteristics, a laser fabricated in accordance with the external fiber loop mirror shown in FIG. 3 a  may be operated in a single frequency mode. In this case, filter  250  may be tuned to a designated lasing frequency or wavelength, while control of the phase values ψ of the MZI and Δφ in the fiber loop allows known level of reflection energy to be returned to the gain medium  210  to achieve lasing operation at maximum output power.  
         [0046]    MZI  310  is a preferred device for a 2×2 coupler  230 , as its phase, ψ, may be electrically controlled and adjusted as shown in FIG. 3 b . In this case, the MZI  310  may have two electrodes that provide control to the resultant phase value, ψ. One control  380  may be used to provide a substantially constant or slowly varying phase change for biasing the MZI  310  to a known value, while the second electrode  375  may be used to apply a fast varying radio frequency (RF) signal. In this case, a modulation signal may be applied to the RF electrode  375  and may be used to either apply information on the laser light or enable the laser to operate in a mode-locked fashion, generating high-repetition-rate pulse train.  
         [0047]    Although MZI  310  is shown operable as coupler  230 , it will be appreciated that other devices have been contemplated and considered to be applicable for use as coupler  230 . For example, coupler  230  may be a fixed ratio directional coupler, a side-polished sliding variable optical fiber coupler, which provides an output split ratio as a function of a position between two fibers, a multi-mode interference (MMI) coupler, or an overcoupled directional coupler, which provides a variable output split ratio as a function of wavelength.  
         [0048]    [0048]FIG. 4 a  illustrates a second embodiment of the present invention, wherein a 3 dB coupler  405  is utilized as 2×2 switch coupler  230 . In this case, light  205  entering coupler  230  is equally split such that one-half the light energy is associated with each leg of fiber  320 . In this illustrated embodiment a phase difference, Δφ, may be introduced in fiber  320  by phase device  240 . In this case, filter  250  in one aspect may be a reflection type filter as described herein.  
         [0049]    [0049]FIG. 4 b  illustrates a third embodiment of the present invention, wherein a variable optical splitter  410  is utilized as coupler  230 . In this embodiment, splitter  410  may split input light  205  such that known percentages of light energy are associated with each leg of fiber  320 . In this illustrated example, splitter  410  splits input light  205  such that 90% of the light energy is directed in one leg of fiber  320  and the remaining 10% of the input light energy is directed in the second leg of fiber  320 . As would be appreciated variable splitter  410  may also be an optical tap with fixed level of optical diversion.  
         [0050]    [0050]FIG. 4 c  illustrates a fourth embodiment of the present invention, wherein an optical over-coupled directional coupler (ODC)  415  is utilized as coupler  230 . In this embodiment, ODC  415  determines the amount of energy transmitted in each fiber leg based on the length of the fiber coupling (L) and a coupling factor (κ). ODC  415  may also isolate a single frequency or wavelength from input light  340  such that a known percentage of the isolated wavelength of light energy is transmitted in each leg of fiber  320 .  
         [0051]    [0051]FIG. 5 illustrates an exemplary second aspect of the present invention  500 , wherein a reflective filter is utilized as filter  250 . In this case reflective filter may be Bragg Grating Filter (BGF) that reflects a single wavelength, represented as λ 1 , while allowing other wavelengths, represented as ≠λ 1 , to be transmitted outside fiber  320 . In this illustrated case, each leg of fiber  320  includes a Bragg Grating Filter  510   a ,  510   b  having a reflectivity represented as r 1 , r 2 , respectively.  
         [0052]    In this exemplary second aspect the field reflection and field transmission ratios may be determined as:  
                   E   r       E   i       =       1   2                 j2        φ   _              (         r   1               -   jΔφ         -       r   2             jΔφ         )           ;   and           (   11   )                     E   t       E   i       =       1   2                 j2        φ   _              (         r   1               -   jΔφ         +       r   2             jΔφ         )                     where            
                  φ   _     =         φ   1     +     φ   2       2                 Δφ   =       φ   2     -     φ   1                       (   12   )                               
 
         [0053]    Δ 100  =φ 2 −φ 1    
         [0054]    Further, when the reflectivity of each filter  510 ,  510   b  is substantially equal, then r 1 =r 2 =r f  and the field reflection and field transmission ratios may be determined as:  
                 E   r       E   i       =              j2        φ   _              r   f          sin        (   Δφ   )                     and                     E   t       E   i         =            j2        φ   _              r   f          cos        (   Δφ   )                   (   13   )                               
 
         [0055]    The reflective and transmission signal intensities may then be determined as:  
                        E   r       E   i            2     =         r   f   2            sin   2          (   Δφ   )                     and                            E   tr       E   i            2       =       r   f   2            cos   2          (   Δφ   )                     (   14     }                               
 
         [0056]    If r f  describes the reflectivity at a known wavelength, λ 1 , with negligible reflectivity at other wavelengths, then the illustrated variable mirror will reflect back to the gain material at λ 1  with a split ratio determined by the the phase change Δφ as described by equation 14.  
         [0057]    However, when the spectral characteristics of filters  510   a  and  510   b  are different such that at λ 1  filter  510   a  exhibitsthe same reflectivity. i.e., r 1 =r 2 ≡r f , while at λ 2  filter  510   a  exhibits reflectivity r 1 =r f  and filter  510   b  exhibits reflectiveity r 2 =0, then the reflective and transmission signal intensities at X 1  are determined using equation 14, and at λ 2  the reflective and transmission signal intensities may be determined from equations 11 and 12 as:  
                        E   r       E   i            2     =           r   f   2     4                   and                            E   t       E   i            2       =       r   f   2     4               (   15   )                               
 
         [0058]    Hence, the configuration illustrated in FIG. 5 may be used as a wavelength selectable tuning element with two different reflective grating filters providing:  
               sin                 Δφ     ≥     1   2             (   16   )                               
 
         [0059]    [0059]FIG. 6 a  illustrates still another aspect  600  of the present invention wherein a non-reflective filter  610  is utilized as filter  250 . In this aspect, light energy  205  generated by gain material  210  is channeled to the two legs of fiber  320  by the illustrated MZI  310 , as previously described. The phase of light in each leg of fiber  320  is then phase adjusted by phase controllers  240   a ,  240   b , respectively. The phase adjusted light  625 ,  625 ′ is next applied to non-reflective filter  610 . In this illustrative example, light  625 , represented as λ, is that light energy traversing fiber  320  in a clockwise direction and light  625 ′ is that light energy traversing fiber  320  in a counterclockwise direction.  
         [0060]    Within filter  610 , light  625  is applied to a partially transmissive, non-reflective assembly, such as mirror  620 . Mirror  620  is operable to select at least one wavelength, λ 1 ,  635 , to pass through and continue in fiber  320 , while causing each other wavelength, i.e., ≠λ 1 ,  630 , to be reflected away and removed from fiber  320 . Mirror  620  is similarly operable on light  625 ′ traversing fiber  320  in a counterclockwise direction so that at least one selected wavelength,  635 ′ remains within fiber  320  and all other wavelengths,  630 ′ are reflected and removed from fiber  320   
         [0061]    As would be appreciated, at least one wavelength may be selected based on the angle of incidence of light  625 ,  625 ′ with regard to mirror  620 . In a preferred embodiment, an angle is selected such that a desired single wavelength or narrow band of wavelengths is maintained in fiber  320  and all others wavelengths are removed from the fiber.  
         [0062]    [0062]FIG. 6 b  illustrates another embodiment of the present invention using a variable coupler  410  and non-reflective filter  610 . Phase controllers  240  contribute a zero phase and, hence, need not depicted. In this embodiment, the field reflection and field transmission ratios may be determined as:  
                   E   r       E   i       =       -     j2cos        (     κ                 L     )              sin        (     κ                 L     )            t   f         ;   and           (   16   )                   E   t       E   i       =       (         cos   2        κ                 L     -       sin   2        κ                 L       )          t   f               (   17   )                               
 
         [0063]    where K is the coefficient of coupling;  
         [0064]    L is the length of coupling; and  
         [0065]    t f  is the filter field transmission coefficient at filter center frequency.  
         [0066]    The signal intensities may then be determined as:  
                        E   r       E   i            2     =         t   f   2            sin   2          (     2      κ                 L     )                     and                            E   t       E   i            2       =       t   f   2            cos   2          (     2      κ                 L     )                   (   18   )                               
 
         [0067]    [0067]FIG. 7 illustrates a graph  700  of experimental results demonstrating a tunable laser in accordance with the embodiment shown in FIG. 6 b . In this graph, wavelengths in the range of 1510-1570 nanometers (nm) may be uniquely achieved by altering a displacement value of a mechanically tunable tilt filter that alters the angle of mirror  620  with regard to the incident angle of light  625 ,  625 ′.  
         [0068]    [0068]FIG. 8 illustrates a composite graph of output power for each lasing wavelength achieved using a tunable laser configuration shown in FIG. 6 b . As would be appreciated, output power is relatively constant in the range of 1530-1570 nm.  
         [0069]    While there has been shown, described, and pointed out, fundamental novel features of the present invention, it will be understood that various omissions and substitutions and changes in the apparatus described, in the form and details of the devices disclosed, and in their operation, may be made by those skilled in the art without departing from the spirit of the present. For example, the present invention has been described with regard to discrete optical components, however, it would be understood that the present invention may be operated using Integrated Photonic devices and hence are considered within the scope of the invention. Hence, other forms of optical waveguides would be understood to be used in place of optical fibers for transporting light from one device to another. It is further expressly intended that all combinations of those elements which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated.