Abstract:
An optical bench for processing laser light in a laser system, including an optical bench housing, steering optics mounted within the optical bench housing for directing the laser light in a path from a laser light input to an output, and a first mechanism for monitoring power output of the laser light regardless of shifts in wavelength of the laser light. The steering optics includes a sampling filter mounted to the optical bench housing and positioned in the path of the laser light, wherein a first portion of the laser light is reflected to the output and a second portion of the laser light is transmitted to the first mechanism. The first mechanism further includes a correction filter for receiving the second laser light portion from the sampling filter, wherein a third portion of the laser light transmitted therethrough is adjusted to compensate for the wavelength shifts, and a power detector for receiving the third laser light portion and providing a signal representative of a detected power output of the laser light. The optical bench also may include a second mechanism for maintaining the power output of the laser light at a desired power output level.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an optical bench for a laser system and, more particularly, to a mechanism for monitoring power output of laser light being processed in an optical bench regardless of shifts in wavelength and fluctuations in diode temperature.  
           [0002]    It is well known that energy generators in the form of laser systems have been utilized to treat many disease states through surgical procedures. Such laser systems typically have a control loop provided therein to monitor and control the output power thereof since the Federal Drug Administration requires that power control accuracy be within 20% of the value displayed by the instrument. In performing this task, a small portion of light energy (approximately 1%) is typically removed from the laser beam by means of a beamsplitter or similar device so as to maximize the usable energy of the laser beam.  
           [0003]    It will be appreciated that many laser systems utilize diodes to produce the desired laser beam and an optical bench for coupling the laser energy into a treatment fiber. Laser diodes have a characteristic, however, which can create differences between the monitored output power of the laser light and the output power actually produced therefrom. More specifically, such laser diodes emit light in a wavelength that varies with the temperature thereof. Since diode-based laser systems are known to be relatively inefficient in converting electrical energy into optical power, the system loses energy in the form of heat. This heat is generally pumped away from the laser diode by using active cooling and a heat sink, for example, but some residual heat causes the diode junction temperature to vary from the time of start-up to steady state operation.  
           [0004]    The aforementioned beamsplitter, in turn, may vary in its transmission and reflection percentages of light impinging on it as a function of the wavelength for such light. Due to the small percentage of light used for power monitoring, the percentage change of transmitted light becomes very sensitive to wavelength fluctuations so that even small variations in wavelength can cause changes in transmitted light to become greatly amplified. For example, a wavelength shift that causes only a 0.5% change in the reflected light from a beamsplitter (i.e., from 99% to 99.5%) causes a fifty percent drop in the transmitted light energy (i.e., from 1% to 0.5%). This can obviously have a drastic effect on the output power detected within the optical bench even though the actual output power of the laser beam is unaffected.  
           [0005]    In light of the foregoing concerns, as well as the continued need for monitoring and controlling output power in laser treatment systems, it would be advantageous to have a mechanism which automatically compensates for shifts in wavelength experienced by a laser beam, such as by temperature fluctuations of the diode providing such laser beam, so that a signal representative of the detected power output from a sampled portion of such laser beam is accurately provided and a desired power output of such system is able to be maintained. Moreover, such a mechanism would preferably have the ability to be adjusted or tuned in each optical bench, thereby permitting wider specifications on the device so that it can be fabricated more easily and less expensively.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    In accordance with a first aspect of the present invention, an optical bench for processing laser light in a laser system is disclosed as including an optical bench housing, steering optics mounted within the optical bench housing for directing the laser light in a path from a laser light input to an output, and a first mechanism for monitoring power output of the laser light regardless of shifts in wavelength of the laser light. The steering optics includes a sampling filter mounted to the optical bench housing and positioned in the path of the laser light, wherein a first portion of the laser light is reflected to the output and a second portion of the laser light is transmitted to the first mechanism. The first mechanism further includes a correction filter for receiving the second laser light portion from the sampling filter, wherein a third portion of the laser light transmitted therethrough is adjusted to compensate for the wavelength shifts, and a power detector for receiving the third laser light portion and providing a signal representative of a detected power output for the laser light. Alternatively, the first mechanism further may include a correction filter for receiving the laser light, wherein an amount of the laser light transmitted therethrough is adjusted to compensate for shifts in wavelength of the laser light, a sampling filter mounted to the optical bench housing and positioned in the path of the transmitted laser light, wherein a first portion of the transmitted laser light is reflected to the output and a second portion of the transmitted laser light is transmitted through the sampling filter, and a power detector for receiving the second transmitted laser light portion and providing a signal representative of a detected power output for the laser light. The optical bench also may include a second mechanism for maintaining the power output of the laser light at a desired power output level.  
           [0007]    In accordance with a second aspect of the present invention, a laser system is disclosed as including a diode for producing laser light, an optical fiber in optical communication with the laser light, an optical bench for directing the laser light from a laser light input to the optical fiber, and a first mechanism for monitoring power output of the laser light provided to the optical fiber regardless of fluctuations in temperature of the diode. The first mechanism further includes a sampling filter positioned in a path of the laser light, wherein the laser light is separated into a first portion and a second portion as a function of diode temperature, a correction filter for receiving the second laser light portion from the sampling filter, wherein a third portion of the laser light transmitted therethrough is adjusted to compensate the diode temperature fluctuations, and a power detector for receiving the third laser light portion and providing a signal representative of a detected power output for the laser light. The correction filter is preferably positioned at an angle of incidence other than 90° with an optical axis running longitudinally through the second laser light portion, but is movable with respect to the optical axis to adjust the angle of incidence therewith. The laser system further includes a second mechanism for maintaining the power output of the laser light provided to the optical fiber at a desired power output.  
           [0008]    In accordance with a third aspect of the present invention, a method of monitoring power output of a laser beam in an optical system regardless of shifts in wavelength for the laser beam is disclosed as including the following steps: sampling a portion of the laser beam; adjusting the sampled laser beam portion to automatically compensate for any wavelength shifts of the laser beam; directing the adjusted sampled laser beam portion onto a power detector; and, providing a signal representative of a detected power output for the laser beam. The method may also include the step of maintaining the power output of the laser beam at a desired power output by providing a signal representative of the desired power output for the laser beam, supplying a power in response to the desired power output signal to a diode providing the laser beam, determining any difference between the desired power output signal and the detected power output signal, and modifying the power supplied to the diode in accordance with any difference between the desired power output signal and the detected power output signal.  
           [0009]    In accordance with a fourth aspect of the present invention, an apparatus for monitoring power output of a laser beam in an optical system is disclosed as including a sampling filter positioned in a path of the laser beam, wherein the laser beam is separated into a first portion and a second portion as a function of a wavelength for the laser beam, a correction filter for receiving the second laser beam portion from the sampling filter, wherein a third portion of the laser beam transmitted therethrough is adjusted to compensate for fluctuations in the wavelength, and a power detector for receiving the third laser light portion and providing a signal representative of a detected power output for the laser beam. The apparatus may also include a mechanism for maintaining the power output of the laser beam provided by the optical system at a desired power output.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the same will be better understood from the following description taken in conjunction with the accompanying drawings in which:  
         [0011]    [0011]FIG. 1 is an isometric view of a laser treatment system in accordance with the present invention having an optical fiber connectable thereto;  
         [0012]    [0012]FIG. 2 is an isometric view of the laser treatment system of FIG. 1, where the cover has been removed so as to expose a controller board and the exterior of an optical bench therein;  
         [0013]    [0013]FIG. 3 is a section view of the optical bench depicted in FIGS.  2 , where the steering optics therein are in a normal operating position so as to allow a laser beam used for medical treatment procedures to pass through the optical bench and into the optical fiber;  
         [0014]    [0014]FIG. 4 is an isometric view of the optical bench depicted in FIGS. 2 and 3, where a connect block and a printed circuit board are shown as being attached thereto; and  
         [0015]    [0015]FIG. 5 is a schematic block diagram of circuitry in the laser treatment system utilized to monitor and control the power output of the treatment laser in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Referring now to the drawings in detail, wherein identical numerals indicate the same elements throughout the figures, FIG. 1 depicts a laser treatment system  10  for transferring energy to human tissue by means of light from an optical fiber  20 . A first laser diode  12  is provided in laser treatment system  10  (see FIG. 5) to produce a first laser beam  14  having a predetermined power (preferably in a range of approximately 2-20 watts) and a predetermined wavelength (preferably in a range of approximately 800-850 nanometers) useful for the medical treatment of disease. As further seen in FIG. 1, a connect block  16  is located within a front portion of a housing  18  for laser treatment system  10 . Connect block  16  assists first laser beam  14  to be optically linked with a first end  22  of optical fiber  20  via a connector  24  so that first laser beam  14  can be transmitted from a second end (or tip)  26  of optical fiber  20 .  
         [0017]    [0017]FIG. 2 depicts laser treatment system  10  with housing  18  removed so as to expose an optical bench, identified generally by reference numeral  34 , in order to direct first laser beam  14  into optical communication with optical fiber first end  22  during normal operation. A controller board  28  is also shown that includes, among other components, a main processor  30  for receiving and processing electronic signals to control the operation of laser treatment system  10 . Among other functions, main processor  30  operates to provide a desired power output signal  141  in a control loop described in greater detail herein.  
         [0018]    With regard to the operation of optical bench  34 , it will be seen from FIGS. 3 and 4 that the path of first laser beam  14  enters optical bench  34  from an optical fiber  13  in optical communication with first laser diode  12 . Optical fiber  13  is positioned within a connector  35  in optical bench  34  to assure proper alignment. First laser beam  14  is transmitted through a beam collimator  54  containing a lens  56  and is preferably directed toward a total internal reflection (TIR) prism  58  mounted to a housing  60  for optical bench  34 . First laser beam  14  preferably reflects off TIR prism  58  and is received by a first beamsplitter  62 , which reflects first laser beam  14  toward a second beamsplitter  64 . First laser beam  14  is then reflected from second beamsplitter  64  through an output beam lens assembly  66  and an output lens  68  so as to place first laser beam  14  in optical communication with optical fiber first end  22  via connector  24 .  
         [0019]    Similarly, a second laser diode  80  preferably provides a second laser beam  82 , also known herein as a marker laser beam, to optical bench  34  by means of an optical fiber  81 . Optical fiber  81  is positioned within a connector  85  in optical bench  34  to assure proper alignment. Second laser beam  82  is transmitted through a marker beam collimator  84 , a marker lens  86 , and a marker filter  87  attached to optical bench housing  60 . Marker laser beam  82  preferably has a predetermined power (preferably in a range of approximately 0.5-2 milliwatts) and a predetermined wavelength (preferably in a range of approximately 600-650 nanometers). It will be appreciated that marker laser beam  82  is preferably used as the light source to optically stimulate a fluorescent slug in optical fiber  20  so as to generate a desired optical fluorescent response therefrom. In order to place marker laser beam  82  in optical communication with optical fiber first end  22  via connector  24 , it is directed toward a first laser turning mirror  88  which reflects it to a second laser turning mirror  90 . Marker laser beam  82  then impacts first beamsplitter  62 , which transmits most of marker laser beam  82  (as a function of its wavelength) so that it passes therethrough to second beamsplitter  64 . Marker laser beam  82  then reflects off second beamsplitter  64  and through output beam lens assembly  66  and output lens  68 . Accordingly, both first (treatment) laser beam  14  and second (marker) laser beam  82  are routed from first beamsplitter  62  to second beamsplitter  64 , as indicated by reference numeral  92 , into first end  22  of optical fiber  20  during normal operation of laser treatment system  10 .  
         [0020]    It will be appreciated that marker laser beam  82  provides an optical stimulus to the fluorescent slug in optical fiber second end  26 , which absorbs the energy of marker laser beam  82  and fluoresces in response thereto. The time delay from stimulation of the fluorescent slug by marker laser beam  82  to the fluorescence of such fluorescent slug is a function of the temperature of optical fiber second end  26  and can be measured and used to calculate such temperature. The optical fluorescent response, indicated by reference numeral  94 , is transmitted back through optical fiber  20  and out optical fiber first end  22  into optical bench  34 . Optical fluorescent response  94  preferably has extremely low power (in a range of approximately 5-100 nanowatts) and has a preferred wavelength of approximately 680-780 nanometers. Optical fluorescent response  94  then passes through output lens  68  and output beam lens assembly  66  to second beamsplitter  64 . Second beamsplitter  64  is constructed so that optical fluorescent response  94  is transmitted therethrough to a signal filter set  96 , which functions to block any reflected marker and treatment light. The remaining signal, filtered to pass only the fluorescent and blackbody wavelengths, passes through a signal lens  98  and signal collimator  99  into a fluorescence/blackbody detector  100 . It will be understood that the blackbody radiation returns along the same path as optical fluorescence signal  94 , but is passed in a fourth waveband (approximately greater than 1500 nanometers) at extremely low power (in a range of approximately 0-100 nanowatts) through second beamsplitter  64 . Florescence/blackbody detector  100  thus captures and analyzes this signal as a secondary temperature mechanism for a fail-safe mode, where blackbody radiation indicating a temperature too high for proper operation will shut down power to laser diode  12 .  
         [0021]    It will be appreciated that a small percentage (preferably on the order of 1%) of first laser beam  14  identified by reference numeral  15  is transmitted by first beamsplitter  62  (also known herein as a sampling filter) to a laser power detector  70  by means of a turning mirror  72  so that the power output of first laser beam  14  can be monitored and controlled. It will be understood that the percentage of first laser beam  14  transmitted by first beamsplitter  62  varies in a predictable fashion as a function of the wavelength of light being transmitted. This is due to the dielectric layers coated on first beamsplitter  62 , as understood by one of ordinary skill in the art. Since the temperature of first laser diode  12  can vary between start-up and steady state operation of laser treatment system  10 , the wavelength of first laser beam  14  will experience fluctuations or shifts corresponding thereto.  
         [0022]    In order to account for diode temperature fluctuations and wavelength shifts, it is preferred that a correction filter  76  be mounted to optical bench housing  60  by a filter mount  77 . The spectral response of correction filter  76  is preferably designed to complement that of first beamsplitter  62  so that the portion of first laser beam  14  transmitted therethrough to laser power detector  70  is a predetermined, substantially constant amount (indicated by reference numeral  79  as a third portion of first laser beam  14 ) with respect to the current wavelength therefor. The power output of laser light  79  detected by power laser detector  70  will therefore vary only with respect to the actual intensity of first laser diode  12  producing first laser beam  14 . It will also be understood that the amount of laser light  79  transmitted through correction filter  76  is a function of the amount of laser light  15  transmitted by first beamsplitter  62  (and, therefore, indirectly of the wavelength for first laser beam  14  and the temperature of first laser diode  12 ).  
         [0023]    It will also be appreciated that correction filter  76  is preferably positioned at an angle of incidence θ with respect to an optical axis  75  running longitudinally through laser light  15 . In order to tune correction filter  76  in each optical bench  34 , it is preferred that it be movable with respect to optical axis  75  to adjust angle of incidence θ with laser light  15 . Accordingly, filter mount  77  may be repositioned by merely loosening a cap screw  83  holding filter mount  77  in place. It will be understood that correction filter  76  is preferably positioned at a non-normal angle of incidence θ (i.e., other than 90°) with respect to optical axis  75 , whereby the degree of wavelength compensation may be adjusted either higher or lower by exposing such laser light  15  to a lesser or greater thickness of coating on correction filter  76 .  
         [0024]    A neutral density filter  78  is preferably provided between correction filter  76  and laser power detector  70 . Filter  78  functions to diminish the intensity of laser light  79  in order to avoid overloading laser power detector  70 .  
         [0025]    It will be seen that a sensor board  102  is provided adjacent optical bench housing  60  so as to interface with fluorescence/blackbody detector  100  and laser detector  70 . Circuitry on sensor board  102  is connected to and communicates with controller board  28  and main processor  30 , as well as certain components located on a driver board  101 . As seen in FIG. 5, main processor  30  provides a signal  141  to a summing device  143  on driver board  101  representative of a desired output power to be provided first laser diode  12 . Summing device  143  also receives a signal  145  from laser power detector  70  representative of the detected output power from laser light  79 . Accordingly, a signal  147  taking into account any difference or error between signals  141  and  145  is provided to a power amplifier  104 , which then supplies the corresponding output power (i.e., drive current) to first laser diode  12 . In this way, the power output of first laser beam  14  is able to be maintained at the desired level.  
         [0026]    An alternate embodiment of correction filter  76  could also be employed if the laser light intensity transmitted to optical fiber  20  is not constant with wavelength, but varies with a known function. If, for example, beamsplitter  62  possessed a transmissibility versus wavelength function where the transmissibility varied considerably with wavelength, and the transmissibility was appreciable compared to the total light impinging upon it, the transmissibility versus wavelength function of the actual laser light transmitted through to optical fiber  20  would not be substantially constant. Accordingly, a substantially constant intensity versus wavelength M(λ) transmitted through to laser power detector  70  would not be preferred, but an M(λ) proportional to the intensity of light versus wavelength function R b (λ) that is reflected from first beamsplitter  62  into optical fiber  20  is desirable. When laser power detector  70  receives light having an intensity versus wavelength function proportional to the function of the light sent to optical fiber  20 , the proper power output to optical fiber  20  can accurately be maintained.  
         [0027]    When a function R b (λ) is reflected into optical fiber  20 , the function T b (λ)=1-R b (λ) is transmitted through to correction filter  76 . In order to ensure the function M(λ) impinging upon laser power detector  70  accurately represents power to optical fiber  20 , M(λ) should be proportional to T b (λ). This proportionality yields M(λ)=K*T b (λ). The correction function T c (λ) can then be calculated by knowing that the correction function T c (λ) times the function transmitted to correction filter  76  T b (λ) should be proportional to the light intensity to the optical fiber, R b (λ), or R b (λ)=K*T c (λ)*T b (λ). The function for correction filter  76  can then be specified as T c (λ)=R b (λ)/(K*T b (λ)).  
         [0028]    It will be noted that K is a constant and thus can be evaluated at any wavelength. For example, a nominal wavelength λ n  may be chosen so that K can be evaluated at a given λ n , or K=R b (λ n )/[T c (λ n )*T b (λ n )], where T c (λ n ) represents the transmissibility of correction filter  76  at the nominal wavelength. In this way, T c (λ n ) can be chosen to create a practical, producable function T c (λ) for correction filter  76 .  
         [0029]    It should be noted that if light intensity directed into optical fiber  20  as a function of wavelength R b (λ) is substantially constant, the function for correction filter  76  degenerates into T c (λ)=1/K*T b (λ). Assuming M(λ) to be substantially constant, this expression for T c (λ) describes the special case disclosed hereinabove.  
         [0030]    Using methods and devices disclosed, a person of ordinary skill in the art could specify any desired wavelength versus intensity function and not necessarily a function that is substantially proportional to the function of the light traveling to connector  24 . This function could correct for waveband shifts and tolerances in many optical and electrical parts within laser treatment system  10 , such as, but not limited to, filters, laser diodes, detectors, or other electronic parts. In this way, correction filter  76  could modify the wavelength of light to correct for shifts caused by variables other than the temperature of first laser diode  12 . Correction filter  76  may possess any wavelength versus intensity function to modify light in the beampath so that the calculations of main processor  30  correlate to intensity and power of the output laser light.  
         [0031]    It will be recognized that equivalent structures may be substituted for the structures illustrated and described herein and that the described embodiment of the invention is not the only structure that may be employed to implement the claimed invention. In particular, correction filter  76  may be positioned in the path of first laser beam  14  prior to transmittance by first beamsplitter  62 . This embodiment causes the amount of first laser beam  14  to be transmitted by correction filter  76  to be pre-adjusted according to the spectral response of first beamsplitter  62 . Nevertheless, the amount of first laser beam  14  provided to laser power detector  70  has been calibrated for any shift in wavelength thereof. It will also be appreciated that the beampath of optical bench  34  may be arranged so that first beamsplitter  62  transmits light into optical fiber  20  and uses reflected light instead of transmitted light to monitor laser intensity. In this case, where optical fiber  20  receives transmitted light instead of reflected light, a similar derivation yields T c (λ)=T b (λ)/R b (λ)*K.  
         [0032]    As a further example of equivalent structures, if losses elsewhere in laser treatment system  10  modify the intensity versus wavelength function directed to optical fiber  20 , correction filter  76  may also be modified accordingly to create an intensity versus wavelength function of light received by laser power detector  70 . Multiple correction filters may be used, if desired, and may alternatively be placed in the laser output beampath rather than in the path of laser light traveling to laser power detector  70 .  
         [0033]    While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.