Abstract:
Several embodiments of an apparatus for remote amplification of seismic sensor fiber optical signals from seismic sensor arrays are disclosed. The seismic sensor fiber optical signals are transmitted using FDM/WDM and TDM/WDM techniques. Embodiments of the invention allow for modular structure of the seismic sensor arrays, wherein the excess of the pumped optical energy is used to amplify another module of the sensor arrays. The sensor arrays can be arranged in serial and/or parallel configuration. An embodiment of the invention allows for repeated amplification of the seismic sensor fiber optical signals using pumped optical energy from a single source. In another aspect of the invention, systems corresponding to the apparatus and methods of using the systems are disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to optical amplifiers and specifically to fiber optic telemetry systems and methods.  
           [0002]    In a typical configuration for an optical amplifier, an optical signal feeds a piece of doped optical fiber, the dopant ions in the fiber being excited by a pump signal into the fiber. As the signal enters the amplifier, the energy from the excited dopant ions is transferred into photons at the signal wavelength. In addition, in many typical configurations the signal for the optical amplifiers is sent with circulators integral to the amplifier. In such amplifier configurations, however, individual pump diodes are resident at each optical amplifier.  
           [0003]    Seismic sensor arrays typically extend over long distances, sometimes several miles. An economic approach to sensing the seismic arrays is through fiber optic telemetry schemes. Many times, however, the optical loss associated with these telemetry schemes is excessive and results in a problem regarding optical signal attenuation. That is, optical signal attenuation may become significant over long distances, and the signal requires optical amplifiers to make up for the propagation signal loss. Multiple stages of amplification are added to accommodate all of the fibers in an array along the signal path in order to increase the signal to noise ratio. In addition, to achieve multiple amplifications, conventional practice requires an individual pump diode resident at each amplifier.  
           [0004]    Accordingly, there is a need for a system and method for amplifying a signal that avoids the need for individual pump diodes at each optical amplifier. It is an object of the present invention to address the above-described needs.  
         SUMMARY OF THE INVENTION  
         [0005]    The above needs are addressed, according to one example embodiment of the invention, by providing an amplification method and system that uses remote optical pumping of multiple stages of amplification with a single pump line. In some embodiments, a single pump fiber is used with multiple amplifiers on many telemetry lines. In other embodiments, multiple amplifiers are used on a single telemetry line.  
           [0006]    In one aspect of the invention, a method is provided for amplifying optical sensor signals, the method comprising: pumping a first optical amplifier, located in a seismic cable, with a pumping source; feeding a first optical signal to the first optical amplifier; pumping a second optical amplifier, located in the seismic cable, with the pumping source; and feeding a second optical signal to the second optical amplifier.  
           [0007]    In another of the invention, a system is provided for amplifying optical sensor signals, the system comprising: means for pumping a first optical amplifier, located in a seismic cable, with a pumping source; means for feeding a first optical signal to the first optical amplifier; means for pumping a second optical amplifier, located in the seismic cable, with the pumping source; and means for feeding a second optical signal to the second optical amplifier.  
           [0008]    In a further aspect of the invention, an apparatus for remote amplification of at least one optical sensor signal is provided. In one example embodiment, the apparatus comprises at least one amplification section, wherein the at least one amplification section comprises a first wavelength-selective coupler having a first coupler first side and a first coupler second side, the first coupler first side further comprising an optical pump input port adapted to receive an optical pump input, and a signal output port adapted to output an amplified optical sensor signal, and the first coupler second side having a first coupler optical amplifier connection port. The apparatus further comprises an optical amplifier having an amplifier first port and an amplifier second port, wherein the amplifier first port is coupled to the first coupler optical amplifier connection port. Further still, the apparatus comprises a second wavelength-selective coupler having a second coupler first side and a second coupler second side, the second coupler first side optically coupled to the amplifier second port, and the second coupler second side further comprising a second coupler signal input port and an optical pump tap out port, wherein the second coupler signal input port is adapted to receive one of the at least one optical sensor signal input, and the optical pump tap out port is adapted to output an excess optical pump energy to another amplification section.  
           [0009]    According to another aspect of the present invention, an apparatus for remote multistage amplification of a optical sensor signal is provided. In one example embodiment, the apparatus comprises a first wavelength-selective coupler having a first coupler first side and a first coupler second side, wherein the first coupler first side further comprising a first coupler optical pump input port adapted to receive an optical pump input, and a first coupler signal output port adapted to output an amplified optical sensor signal, and the first coupler second side having a first coupler optical amplifier connection port; a first optical amplifier having a first amplifier first port and a first amplifier second port, wherein the first amplifier first port is coupled to the first coupler optical amplifier connection port. The apparatus further comprises a second wavelength-selective coupler having a second coupler first side and a second coupler second side, wherein the second coupler first side is optically coupled to the first amplifier second port, and the second coupler second side further comprising a second coupler signal input port and a second coupler optical pump output port, wherein the second coupler signal input port is adapted to receive an amplified optical sensor signal input, and the second coupler optical pump output port is adapted to output a first excess optical pump energy. The apparatus further comprises a third wavelength-selective coupler having a third coupler first side and a third coupler second side, wherein the third coupler first side further comprising a third coupler signal output port, and a third coupler optical pump energy input port, and wherein the third coupler optical pump energy input port optically coupled to the second coupler optical pump output port, and the third coupler second side further comprising a third coupler signal input port; a second optical amplifier having a second amplifier first port and a second amplifier second port, wherein the second amplifier first port is coupled to the third coupler signal input port. Further still, the apparatus comprises a fourth wavelength-selective coupler having a fourth coupler first side and a fourth coupler second side, wherein the fourth coupler first side is optically coupled to the second amplifier second port, and the fourth coupler second side further comprising a fourth coupler signal input port and a fourth coupler optical pump output port, wherein the fourth coupler signal input port is adapted to receive a optical sensor signal input, and the fourth coupler optical pump output port is adapted to output a second excess optical pump energy.  
           [0010]    According to still another aspect of the present invention, an apparatus for remote amplification a plurality of optical sensor signals in a parallel configuration using an optical pump is provided. In an example embodiment, the apparatus comprises: a first wavelength-selective coupler having a first coupler first side and a first coupler second side, wherein the first coupler first side further comprising a first coupler optical pump input port coupled to an optical pump, and a first coupler signal output port adapted to output a first amplified optical sensor signal, and the first coupler second side having a first coupler optical amplifier connection port. The apparatus further comprises a first optical amplifier having a first amplifier first port and a first amplifier second port, wherein the first amplifier first port is coupled to the first coupler optical amplifier connection port, and the first amplifier second port adapted to receive a first optical sensor signal input. The apparatus further still comprises a second wavelength-selective coupler having a second coupler first side and a second coupler second side, wherein the second coupler first side further comprising a second coupler optical pump input port coupled to the optical pump, and a second coupler signal output port adapted to output a second amplified optical sensor signal, and the second coupler second side having a second coupler optical amplifier connection port; and a second optical amplifier having a second amplifier first port and a second amplifier second port, wherein the second amplifier first port is coupled to the second coupler optical amplifier connection port, and the second amplifier second port adapted to receive a second optical sensor signal input, wherein a second amplified optical sensor signal results.  
           [0011]    In a still another aspect of the invention, a method of amplifying optical sensor signals is provided. The method comprises pumping a first optical amplifier, located in a seismic cable, with a pumping source, and feeding a first optical signal to the first optical amplifier. The method further comprises pumping a second optical amplifier, located in the seismic cable, with the same pumping source, and feeding a second optical signal to the second optical amplifier.  
           [0012]    In another aspect of the invention, a system for amplifying optical sensor signals is provided. The system comprises a means for pumping a first optical amplifier, located in a seismic cable, with a pumping source, and a means for feeding a first optical signal to the first optical amplifier. The system further comprises a means for pumping a second optical amplifier, located in the seismic cable, with the same pumping source, and a means for feeding a second optical signal to the second optical amplifier.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 shows an example embodiment of the present invention for an apparatus having remote optical signal amplification in a series configuration.  
         [0014]    [0014]FIG. 2 shows an example embodiment of the present invention for an apparatus having remote multistage optical signal amplification.  
         [0015]    [0015]FIG. 3 shows an example embodiment of the present invention for an apparatus having remote optical signal amplification in parallel configuration.  
         [0016]    [0016]FIG. 4 shows example embodiments of the present invention for systems involving amplifying optical sensor signals with the same pump source.  
         [0017]    [0017]FIG. 5 shows example embodiments of the present invention for systems involving amplifying optical sensor signals with telemetry lines feeding optical signals from seismic arrays to optical amplifiers.  
         [0018]    [0018]FIG. 6 shows example embodiments of the present invention for systems involving splitting a pump signal before amplifying optical sensor signals with the same pump source.  
         [0019]    [0019]FIG. 7 shows example embodiments of the present invention for systems involving feeding optical signals through separate lines to optical amplifiers, that is, a one to one ratio between lines and amplifiers.  
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0020]    Referring now to FIG. 1, an example embodiment of the invention is seen in which an apparatus  10  for remote amplification of at least one optical sensor signal  15  is provided. Applications of embodiments include seismic sensing, down-hole logging, and many other applications as will occur to those of skill in the art. According to the illustrated embodiment, the apparatus  10  comprises at least one amplification section  20 , wherein the at least one amplification section  20  comprises: a first wavelength-selective coupler  25  having a first coupler first side  30  and a first coupler second side  35 , the first coupler first side  30  further comprising an optical pump input port  40 , adapted to receive an optical pump input  45 , and a signal output port  50  adapted to output an amplified optical sensor signal  55 . The first coupler second side  35  includes a first coupler optical amplifier connection port  60  and an optical amplifier  65  having an amplifier first port  70  and an amplifier second port  75 , wherein the amplifier first port  70  is coupled to the first coupler optical amplifier connection port  60 . A second wavelength-selective coupler  80  is also seen, having a second coupler first side  85  and a second coupler second side  90 . The second coupler first side  85  is optically coupled to the amplifier second port  75 .  
         [0021]    The second coupler second side  90  further comprises a second coupler signal input port  95  and an optical pump tap out port  100 , wherein the second coupler signal input port  95  is adapted to receive at least one optical sensor signal  15  inputs, and the optical pump tap out port  100  is adapted to output an excess optical pump energy  105  to another amplification section  110 .  
         [0022]    Still referring to the example embodiment of FIG. 1, the at least one amplification section  20  comprises a plurality of amplification sections coupled to each other in a cascaded manner, wherein each amplification section  20  is adapted to receive one optical sensor signal input  15 , output one optical sensor signal output  55 , and output one excess optical pump energy  105  to an adjacent amplification section  110 . In another embodiment, the first wavelength-selective coupler  25  comprises a WDM coupler. In a still another embodiment, the second wavelength-selective coupler  80  comprises a WDM coupler. In a still further embodiment, the optical amplifier  65  comprises an erbium doped optical amplifier. In a yet another embodiment, the second coupler signal input port further comprises an optical isolator  115 . In a still another embodiment, the optical isolator  115  is integral to the second coupler signal input port  95 .  
         [0023]    In additional specific embodiments, the excess optical pump energy  105  is used to provide optical pump energy to the optical pump input port of a next amplification section  110 . Similarly, the process of providing left over optical pump energy to the adjacent amplification section is continued. Design of the apparatus  10  provides unique advantage of modular construction of seismic sensor arrays in which the amplification sections are connected serially according to the requirements in the field and provided with remote optical pumping from a single optical pump.  
         [0024]    Now referring to FIG. 2, another example embodiment of the invention is seen in which an apparatus  200  is provided for remote multistage amplification of a optical sensor signal  210 . According to the illustrated embodiment, the apparatus  200  comprises: a first wavelength-selective coupler  215  having a first coupler first side  220  and a first coupler second side  225 , wherein the first coupler first side  220  further comprises a first coupler optical pump input port  230  adapted to receive an optical pump input  235 , and a first coupler signal output port  240  adapted to output an amplified optical sensor signal  245 . The first coupler second side  225  includes a first coupler optical amplifier connection port  250  and a first optical amplifier  255 , having a first amplifier first port  260  and a first amplifier second port  265 , wherein the first amplifier first port  260  is coupled to the first coupler optical amplifier connection port  250 . A second wavelength-selective coupler  270  is provided having a second coupler first side  275  and a second coupler second side  280 , wherein the second coupler first side  275  is optically coupled to the first amplifier second port  265 . The second coupler second side  280  further comprises a second coupler signal input port  285  and a second coupler optical pump output port  290 , wherein the second coupler signal input port  285  is adapted to receive an amplified optical sensor signal  295  input. Further, the second coupler optical pump output port  290  is adapted to output a first excess optical pump energy  300 . A third wavelength-selective coupler  305  includes a third coupler first side  310  and a third coupler second side  315 , wherein the third coupler first side  310  further comprises a third coupler signal output port  320 , and a third coupler optical pump energy input port  325 . The third coupler optical pump energy input port  325  is optically coupled to the second coupler optical pump output port  290 , and the third coupler second side  315  further comprises a third coupler signal input port  330 . A second optical amplifier  335  is provided and includes a second amplifier first port  340  and a second amplifier second port  345 , wherein the second amplifier first port  340  is coupled to the third coupler signal input port  330 . Fourth wavelength-selective coupler  350  has a fourth coupler first side  355  and a fourth coupler second side  360 , wherein the fourth coupler first side  355  is optically coupled to the second amplifier second port  345 , and the fourth coupler second side  360  further comprises a fourth coupler signal input port  365  and a fourth coupler optical pump output port  370 . The fourth coupler signal input port  365  is adapted to receive a optical sensor signal  210  input, and the fourth coupler optical pump output port  370  is adapted to output a second excess optical pump energy  375 .  
         [0025]    Again referring to FIG. 2, in one of the embodiments of the invention, the first wavelength-selective coupler  215  comprises a WDM coupler. In another embodiment, the first optical amplifier comprises  255  an erbium doped optical amplifier. In a still another embodiment, the second wavelength-selective coupler  270  comprises a WDM coupler. In a still further embodiment, the second coupler signal input port  285  further comprises a first optical isolator  380 . In a yet still further embodiment, the first optical isolator  380  is integral to the second coupler signal input port  285 . In a yet further embodiment, the third wavelength-selective coupler  305  comprises a WDM coupler. In a still other embodiment, the second optical amplifier  335  comprises an erbium doped optical amplifier. In another aspect of the embodiment, the fourth wavelength-selective coupler  350  comprises a WDM coupler. In a yet another aspect of the embodiment, the fourth coupler signal input port  365  further comprises a second optical isolator  385 . In a still yet another aspect of the embodiment, the second optical isolator  385  is integral to the fourth coupler signal input port  365 .  
         [0026]    Note that the second excess optical pump energy  375  is used, in some embodiments, to provide optical pump energy to the optical pump input port of a next signal amplification module that is similar to the apparatus  200 . Likewise, the process of providing left over optical pump energy to the adjacent amplification module that is similar to the apparatus  200  is continued in other embodiments. Design of the apparatus  200  provides unique advantage of modular construction of seismic sensor arrays in which the amplification modules can be connected serially according to the requirements in the field and provided with remote optical pumping from a single optical pump.  
         [0027]    Referring now to FIG. 3, another example embodiment of the apparatus  400  for remote amplification of a plurality of optical sensor signals  410  and  415  in a parallel configuration using an optical pump  420  is seen. Here, the apparatus  400  comprises: a first wavelength-selective coupler  425  having a first coupler first side  430  and a first coupler second side  435 , wherein the first coupler first side  430  further comprises a first coupler optical pump input port  440  coupled to an optical pump  420 , and a first coupler signal output port  445  adapted to output a first amplified optical sensor signal  450 . The first coupler second side  435  has a first coupler optical amplifier connection port  450 . First optical amplifier  455  includes a first amplifier first port  460  and a first amplifier second port  465 , wherein the first amplifier first port  460  is coupled to the first coupler optical amplifier connection port  450 , and the first amplifier second port  465  adapted to receive a first optical sensor signal  410  input. Second wavelength-selective coupler  470  comprises a second coupler first side  475  and a second coupler second side  480 , wherein the second coupler first side  475  further comprises a second coupler optical pump input port  485  coupled to the optical pump  420 , and a second coupler signal output port  490  adapted to output a second amplified optical sensor signal  495 , and the second coupler second side  480  has a second coupler optical amplifier connection port  500 . Second optical amplifier  505  includes a second amplifier first port  510  and a second amplifier second port  515 , wherein the second amplifier first port  510  is coupled to the second coupler optical amplifier connection port  500 , and the second amplifier second port  515  adapted to receive a second optical sensor signal  415  input.  
         [0028]    Referring still to FIG. 3, in one embodiment of the invention, the first wavelength-selective coupler  425  comprises a WDM coupler. In another embodiment, the first optical amplifier  455  comprises an erbium doped optical amplifier. In a yet another embodiment, the first amplifier second port  465  further comprises a first optical isolator  520 . In a still yet another embodiment, the first optical isolator  520  is integral to the first amplifier second port  465 . In a further yet another embodiment, the second wavelength-selective coupler  470  comprises a WDM coupler. In a still another embodiment, the second optical amplifier  505  comprises an erbium doped optical amplifier. In another aspect of the embodiment, the second amplifier second port  515  further comprises a second optical isolator  525 . In a still another aspect of the embodiment, the second optical isolator  525  is integral to the second amplifier second port  515 .  
         [0029]    Note that in embodiments of FIG. 3, any number of branches, within the of capabilities of the hardware used, are arranged in a parallel configuration to remotely amplify optical sensor signals using a single optical pump, wherein branches in the parallel configuration provide a modular structure of the apparatus  400 .  
         [0030]    Referring now to FIG. 4, further example embodiments of the invention are depicted, wherein a system  600  for amplifying optical sensor signals  610   a ,  610   b  is disclosed. The system  600  comprises a means  620  for pumping a first optical amplifier  622   a , located in a seismic cable  605 , with a pumping source  615 , and a means  625  for feeding a first optical signal  610   a  to the first optical amplifier  622   a . The system  600  further comprises a means  630  for pumping a second optical amplifier  622   b , located in the seismic cable  605 , with the pumping source  615 , and a means  635  for feeding a second optical signal  610   b  to the second optical amplifier  622   b . The pumping of the optical amplifiers  622   a ,  622   b  with a pump signal  622  from the pump source  615  shared by all optical amplifiers  622   a ,  622   b  excites the ions in the optical amplifiers  622   a ,  622   b . Typically, the ions are erbium ions in the doped fiber coils of the optical amplifiers  622   a ,  622   b , and the pump source  615  exciting these erbium ions is sent through cabling, telemetry lines, or the like, as is seen in FIG. 5.  
         [0031]    Turning to FIG. 5 then, another example embodiment of the invention is the system  600  previously described, wherein the means (FIG. 4, reference  625 ) for feeding the first optical signal  610   a  comprises means for feeding the first optical signal  610   a  through a first telemetry line  642 , and the means (FIG. 4, reference  635 ) for feeding the second optical signal  610   b  comprises feeding the second optical signal  610   b  through a second telemetry line  652 . Other methods and means for feeding optical signals will occur to those of skill in the art that do not depart from the spirit of the claimed invention.  
         [0032]    Referring to FIG. 6, another example embodiment of the invention is the system  600  previously described and further comprising a means  660  for splitting a pump signal  662  from the pumping source  615  before the means  620  for pumping the first optical amplifiers  622   a  and before the means  630  for pumping the second optical amplifier  622   b . Rather than using the described method and system in a series configuration, whether a cascading or in-line series configuration, splitting the pump signal  662  is ideal for use of the disclosed methods and systems in a parallel configuration. Joining two separate telemetry lines ( 642 ,  652  on FIG. 5), wherein each telemetry line ( 642 ,  652  on FIG. 5) has its own input optical signals ( 610   a ,  610   b  on FIG. 5), is a coupler, such as a WDM coupler. But even before the WDM coupler, a pump demultiplexer  660  splits out the pump signal  662  from the same pump source  615  so that each telemetry line  620 ,  630  has its own pump signal  662  to excite an optical amplifier  622   a ,  622   b , and thereby, produce amplified optical signals.  
         [0033]    Turning back to FIG. 5, another example embodiment of the invention is seen, wherein the system  600  further comprises a means  670  for receiving the first optical signal  610   a  from a first seismic sensor array  672 , and means  675  for receiving the second optical signal  610   b  from a second seismic sensor array  678 . For example, methods and means  670 ,  675  for receiving optical signals  610   a ,  610   b  from arrays  672 ,  678  include through cabling, lines or the like.  
         [0034]    Referring to FIG. 4 again, more example embodiments of the invention are shown. In one example embodiment, the system  600  further comprises a means  680  for pumping additional optical amplifiers  622  with the pumping source  615 . That is, the previously described methods and systems are not limited to two optical amplifiers  622   a ,  622   b , two optical signals  610   a ,  610   b , and so forth. Rather, the invention is remote amplification of many optical signals  610  using the same pump source  615  for multiple amplifiers  622 . In still another example embodiment, the system  600  further comprises a means  690  for feeding additional optical signals  610  to additional optical amplifiers  622 . And in FIG. 7, another example embodiment is illustrated, wherein the means ( 690  on FIG. 4) for feeding additional optical signals  610  comprises through separate telemetry lines  705 . That is, for example, a method or system employing twenty optical amplifiers  622 , then twenty telemetry lines  705  are used wherein each telemetry line  705  is connected to its own optical amplifier  622 , feeds its own optical amplifier  622 , but all twenty optical amplifiers  622  share the same pump source ( 615  on FIG. 4) for exciting the fibers of the optical amplifiers  622 .  
         [0035]    The various means described in reference to the later Figures will be understood and will occur to those of ordinary skill in the art from a review of the earlier disclosure, and the specific examples of the various drawings.  
         [0036]    Having thus described exemplary embodiments of the invention, it will be apparent that various alterations, modifications and improvements will readily occur to those skilled in the art. Such obvious alterations, modifications and improvements, though not expressly described above, are nevertheless intended to be implied and are within the spirit and scope of the invention. Accordingly, the foregoing discussion is intended to be illustrative only, and not limiting; the invention is limited and defined by the following claims and equivalents thereto.