Abstract:
A method of performing eye safety measurements on laser devices is disclosed. The laser is contained within a housing having a central bore. The method uses an optical detector having at least two zones to make separate measurements of both a direct power coming from the laser and an indirect power reflected off of the central bore. The first zone measuring the direct power is smaller than the second zone measuring the indirect power. The measurement of the first power is then used to adjust the power of the laser to be within a specified optical standard, such as the class 1 standard. In one exemplary embodiment, the laser is an 850 nanometer Vertical Cavity Surface Emitting Laser (VCSEL).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. The Field of the Invention  
         [0003]     Exemplary embodiments of the present invention relate to the field of laser devices. More specifically, the exemplary embodiments relate to a segmented detector for performing eye safety measurements on a laser device.  
         [0004]     2. The Relevant Technology  
         [0005]     Laser devices are used in a variety of applications. For example, laser devices are used as data transmitters in optical networks, providing very high bandwidth and data carrying capabilities. Regardless of the specific application, every application that uses a laser device must conform to some level of eye safety. Ideally, the laser falls within the safest category, which is known as Class 1. Typical fiber optic transceivers are designed to have maximum optical output power levels which meet Class 1 eye safety limits, and are thus safe for unprotected viewing without precautions. This Class 1 eye safety limit must be met under all conditions, including all reasonable single fault conditions, which are defined as reasonable failures of a single component or connection. The specific details of the Class 1 standard are specified in International Electrotechnical Commission (IEC) 60825-1:1993+A1:1997+A2:2001, “Safety of laser products-Part 1: Equipment classification, requirements and user&#39;s guide”, Edition 1:1993 with amendments 1:1997 and 2:2001. In order to ensure that this standard is met, the laser output power must be measured using appropriate measuring equipment.  
         [0006]     In general, prior art designs ensure eye safety by one of two methods. In the simplest case, the laser and optical system is fundamentally eye safe because the maximum power the device can emit is less than the eye safety limit. This is often the case in longer wavelength lasers that operate in the 1310-1550 nanometer (mu) bands. In other cases, particularly those involving shorter wavelength 850 nm lasers, the eye safety limit is ensured by redundant electrical circuits that monitor either the laser current or, more directly, monitor the laser output power through a monitor photodiode. Redundant systems are required, because the overall monitoring system must continue to function in the event of the failure of a single electrical component or connection.  
         [0007]     Unfortunately, the design of short wavelength optical transceivers is often complicated by the fact that the desired normal operating power is often quite close to, if not just below, the eye safety limit. This is true because the maximum data transmission rates for optoelectronic devices occur at the maximum power output. Therefore, designing a system to reliably distinguish between normal and unsafe levels of laser power is challenging. In fact, the standards for acceptable output power are often defined by a minimum value for communications reliability and a maximum which corresponds to the eye safety limit. The desire to have the largest usable output power range will thus tend to make the problem of eye safety more difficult.  
         [0008]     One example of a portion of an exemplary laser device package that may require monitoring for eye safety is shown in  FIG. 1  and designated generally as reference numeral  10 . Package  10  schematically illustrates a cross section of a laser emitter  12  in a housing  14 . Housing  14  defines a cylindrical central bore  16  having a first end  13  immediately adjacent laser emitter  12 , and a second end  20  located distally from laser emitter  12 . Second end  20  can have a flared portion  18  that has an increasing diameter when going from end  13  towards end  20 .  
         [0009]     Laser emitter  12  has an optical axis  24  that also corresponds to the axis of central bore  16 . The central bore  16  is sized and configured to accept a ferrule (not shown) containing, for example, an optical fiber capable of transmitting optical signals from emitter  12  to some remote location. In this example, laser emitter  12  is a vertical cavity surface emitting laser (VCSEL) that operates according to the 10 gigabit per second (Gb/s) standard form factor pluggable (XFP) standard. Bore  16  can then accept a standard plug, such as an LC connector plug. Other types of emitters, data speeds, and plugs are also possible.  
         [0010]     Laser emitter  12  transmits a laser beam at a point  25 . While, in this embodiment, laser emitter  12  is shown as being contained within housing  14 , and transmitting a laser beam at point  25 , this need not be the case. Laser emitter  12  can be located at any point behind housing  14 , and the laser beam focused to point  25  using, for example, one or more lenses. In either case, point  25  is the apparent source for the laser beam that enters bore  16 .  
         [0011]     While the laser beam that is transmitted from point  25  is actually one coherent beam, it is perceived by a viewer looking at bore  16 , represented by an arrow A, as being divided into two parts. A first part  26  is transmitted directly from point  25  to a point external to bore  16 , while a second part  28  is reflected off of an inside wall  16   a  of bore  16 . Unfortunately, this makes it somewhat problematic to measure the output power of laser emitter  12  to verify whether the eye safety limits for Class 1 devices, or any other eye safety limits, are being met.  
         [0012]     First part  26  will be generally shaped like a cone. When viewed perpendicularly, this cone will appear as a circle having a specific area. One way to calculate the area of this circle is to use a measurement of the numerical aperture that is defined as the sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system or element, multiplied by the refractive index of the medium in which the vertex of the cone is located. The vertex angle is represented in  FIG. 1  as angle “B”. In this embodiment, the refractive index of the air is 1. Using standard formulas known to those of skill in the art, the numerical aperture for one example geometric configuration can then be calculated as 0.18.  
         [0013]     The problem of measuring the output power of both components of the beam is shown generally in  FIG. 2  (not to scale).  FIG. 2  illustrates the view looking into the barrel of device 10 from about 100 mm away. Beam  26 , which comes directly from point  25 , is directed to a point  42  having a subtense of approximately 0.3 milli-radians (mrad). Beam  28 , which is reflected off of inside wall  16   a , has a subtense of approximately 12.5-12.9 mrad, which is illustrated by the hatched portion of the circular representation of the beams  26  and  28 , depending on whether the reflection, and therefore the apparent source, is from end  18  or end  20 . To make an accurate determination of eye safety, it is desirable to measure the intensity or optical power of both beam  26  and beam  28  separately.  
         [0014]     Currently, making an accurate measurement of both optical powers requires an operator to use expensive optical characterization equipment. Additionally, using such equipment to make the measurements requires a significant amount of time. This corresponds directly to a significant amount of money expended to make these measurements.  
       BRIEF SUMMARY OF THE EXEMPLARY EMBODIMENTS  
       [0015]     It would, therefore, be a great improvement in the art if some device or method could be developed that provided for separate measurements of the optical power of both the direct laser beam and the reflected laser beam. These measurements could then be used to calculate the maximum optical power that could be produced by a particular device and still stay within the Class 1 eye safety limits. Exemplary embodiments of the present invention provide a segmented detector for simultaneously measuring both components of laser optical power in a single device.  
         [0016]     In one embodiment, a printed circuit board (PCB) is disposed within a housing. The PCB can include a dual, co-planar, laser power detector that can separately measure both the direct and indirect optical power from a given laser. A first portion of the detector can be a circular area with a first diameter for measuring the direct optical power of the laser. A second portion of the detector can be a second area with a second diameter larger than the first diameter for measuring the reflected optical power.  
         [0017]     In some embodiments, the PCB can also include one or more standard connections to facilitate the connection of external monitors or other equipment to the PCB/detector. In some embodiments, these connectors can include an eight position Molex connector, a twenty-six pin ribbon connector, and/or other standard or non-standard connectors known to those of skill in the art. The PCB can have a multi-layered trace structure providing connections between components.  
         [0018]     In one method, the detector is used to measure both components of the optical power; first component transmitted directly to the sensor and second component reflected from a surface before being incident to the sensor. These measurements are then used to assure that the optical power is below the Class 1 eye safety limit. The amount of power being generated by a laser is measured as a function of the area over which the components of the beam are spread. For example, in most laser applications, the first component includes most of the power of the laser. The second component is measured over a much wider area. In one test configuration, using a laser transmitting at 850 nanometers, the first component can have a power of about −1.09 decibel milliwatts (dBm), while the corresponding second component can have a power of about +7.9 dBm. Since the first component is measured over an area smaller than the second component, and since in general the corresponding power of the second component is much less than the power of the first component, the measure of the first component can be used to adjust the power of the laser until the first component, by itself, is just below the Class 1 eye safety limit. Since some of the optical power is contained in the second component, this method allows the laser to run at a higher power, and therefore be more efficient.  
         [0019]     The method of measuring the laser power described above allows separation of the power of the laser that actually needs to be considered for the eye safety measurement from the power that need not be. This provides a distinct advantage over systems that measure the total power as one measurement. Specifically, using the exemplary embodiment of the method described above, the laser can now be operated at a slightly higher and therefore more efficient power level while remaining as a Class 1 laser.  
         [0020]     These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
         [0022]      FIG. 1  illustrates a cross-sectional view of an exemplary laser device package;  
         [0023]      FIG. 2  shows the view looking into the laser device of  FIG. 1  along the lines  2 - 2 , from 100 millimeters away;  
         [0024]      FIG. 3  illustrates an exploded perspective view of one exemplary segmented detector according to the present invention;  
         [0025]      FIG. 4  illustrates a cross-sectional side view of the assembled segmented detector of  FIG. 3 ;  
         [0026]      FIGS. 5A through 5F  illustrate one exemplary construction of the printed circuit board used in the segmented detector of  FIGS. 3 and 4 ;  
         [0027]      FIG. 6A  illustrates one case that can be considered when measuring an optical power of the laser device of  FIG. 1 ;  
         [0028]      FIG. 6B  illustrates an alternate case that can be considered when measuring an optical power of the laser device of  FIG. 1 ;  
         [0029]      FIG. 6C  illustrates a third alternate case that can be considered when measuring an optical power of the laser device of  FIG. 1 ; and  
         [0030]      FIG. 7  illustrates one exemplary embodiment of a test geometry for the dual zone optical detector shown in  FIGS. 3-5F .  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0031]     Embodiments of the present invention provide a detector, such as a segmented detector, for simultaneously measuring the optical power of both the direct component and the reflected component of a laser beam for a test device. These measurements can then be used to calculate the maximum optical power that can be produced by the device and still stay within desired eye safety limits. Exemplary embodiments of the present invention provide a device and methods that measure both components of laser optical power, and use these measurements to maximize the amount of power that can be emitted from the laser device without exceeding a predetermined maximum.  
         [0032]     Following is a discussion of the testing device used to determine the optical power levels of different components of a laser beam. Thereafter, a discussion of the method using the testing device to maximize the power level of the laser to increase the efficiency of the laser, while maintaining the power level below a predetermined threshold above which the classification of the laser changes. For instance, the method can be used to maximize the power level of a Class 1 laser.  
         [0033]     One exemplary embodiment of the device for testing laser eye safety is shown in  FIGS. 3 and 4 , and designated generally as reference numeral  100 . This device  100  can be a segmented detector, although other detectors are possible. The detector  100  can include a cylindrical housing  102 , a printed circuit board (PCB)  104  disposed within housing  102 , and a cover plate  106 . The housing  102  can include one or more fastener holes  103  that accommodate one or more fasteners  105 . These fasteners  105  can be used to secure PCB  104  to housing  102  via one or more screw holes  107 . Cover plate  106  can include one or more holes  108  that can accommodate one or more mechanical fasteners  109 . The fasteners  108  can be used to secure cover plate  106  to housing  102  via one or more fastener holes  110 .  
         [0034]     In exemplary embodiments, cover plate  106  can have a circular lip  111  ( FIG. 4 ) extending around the inside surface. The lip  111  can have an outside diameter that is just slightly smaller than the inside diameter of housing  102 , thus facilitating a more secure fit for cover plate  106 . Alternately, cover plate  106  can be secured to a top surface  112  of housing  102  using, by way of example and not limitation, chemical fasteners, threads, or any other system or method know to those of skill in the art for fixing one part to another.  
         [0035]     Housing  102  can also have one or more apertures  122  through an outside surface  124 . The apertures  122  extend into an inner cavity  126  having an inside surface  128 . Apertures  122  provide access to PCB  104  so that various wires or other attachments can be connected to PCB  104 . An annular ring  130  can also be connected to inside surface  128  of housing  102 . Annular ring  130  provides a support platform to attach PCB  104  to housing  102 . As with cover plate  106 , PCB  104  can be attached to annular ring  130  using chemical or mechanical fasteners. Alternately PCB  104  can attach directly to housing  102 . Annular ring  130  also includes a window  132  that exposes a surface of PCB  104  during laser testing. This surface area of PCB  104   
         [0036]     contains the photodetectors that perform the actual power measurements. The specific structure of PCB  104  will be discussed below with reference to  FIGS. 5A through 5  G.  
         [0037]     Corresponding to window  132  is an opening  134  in the bottom of housing  102 . This opening  134  allows passage of the laser beams to be measured. In exemplary embodiments, opening  134  is configured to fit over, for example, laser housing  14  of laser device package  10  ( FIG. 1 ). In alternate embodiments, opening  134  is configured to receive a ferrule containing one end of a fiber optic cable. The other end of the fiber optic cable can be inserted into, by way of example and not limitation, central bore  16  of laser device package  10 . In some embodiments, opening  134  can include threads on an inside surface  133 . The threads can facilitate a more secure fit to attach the laser device being tested. In other alternate embodiments, surface  133  can have a light absorbing coating applied to it or some other light absorbing material attached to it.  
         [0038]     While the embodiment of housing  102  shown in  FIGS. 3 and 4  has a cylindrical shape, this need not be the case. Housing  102  can have any shape that provides sufficient structure to securely hold PCB  104 , and that functions to fix the position of photodetectors on PCB  104  with respect to an optoelectronic device to be tested. Such shapes can include, by way of example and not limitation, oval, square, rectangular, and other polygonal shapes. Likewise, housing  102  can be made from metal or a metal alloy. In this exemplary embodiment, housing  102  is made from an anodized aluminum. However, other materials are also possible, including, but not limited to, plastics, composites, synthetics, or any other material having sufficient rigidity and that functions to fix the photodetectors on PCB  102  with respect to a laser emitter.  
         [0039]      FIGS. 5A-5F  illustrate one embodiment of PCB  104  constructed in accordance with the present invention.  FIG. 5A  illustrates a schematic view of a top layer  150  of PCB  104 . Top layer  150  includes a top surface  152 . A plurality of plated through holes  154  and electrical traces  156  can be disposed on top surface  152 . The plated through holes  154  enable electrical conductivity between layers, while the electrical traces  156  connect various points on a single layer. One or more eight position Molex connectors  158  and one or more twenty-six pin ribbon cable connectors  160  can also be disposed on top surface  152 . In some embodiments, a plurality of jumpers  161  can be disposed on top surface  150  to allow an operator to configure the connectors  160 ,  162  as desired. Other types of connectors and cables can also be used.  
         [0040]      FIGS. 5B-5E  illustrate exemplary embodiments of mid layers  1  through  4 , respectively, designated generally as reference numerals  170 ,  172 ,  174 , and  176 , respectively. While this exemplary embodiment employs a six layer structure, any other number of layers can also be used. For instance, in some exemplary embodiments, only a top and bottom layer is present. In other embodiments many more layers can be used, depending on the complexity and electrical functionality of the circuits involved. As with top layer  150 , each of layers  1  through  4  can include one or more plated through holes  154 , and one or more electrical traces  156  connecting through holes  154 .  
         [0041]      FIG. 5F  illustrates one exemplary bottom layer  180  of PCB  104 . Bottom layer  180  includes a surface  182 . As with the other layers, surface  182  includes the plurality of plated through holes  154  and electrical traces  156 . Additionally, surface  182  can include a laser detector  184 . Laser detector  184  can be constructed from silicon, gallium arsenide, or any other semiconductor with sensitivity appropriate for the  
         [0042]     wavelength of the laser to be tested. In exemplary embodiments, laser detector  184  can include multiple detection areas. For example, in one configuration, connector  160  and jumpers  161  can be configured such that twenty-four of the individual leads on the connector each correspond to one of the twenty-four individual areas on detector  184 . These areas can be aggregated as desired into two or more detection zones, that can be used to separately detect the power in first beam  26  and second beam  28  ( FIG. 1 ). For instance, as shown in  FIG. 5F , the detector  184  can include a first zone  186  and a second zone  188 . These zones will be discussed in more detail with reference to  FIGS. 6A-7 . Alternatively, the power level detected at each of the twenty-four individual areas can be measured and used during the testing process.  
         [0043]     Specific construction techniques for printed circuit boards are well known in the art. The underlying substrate can be made from, by way of example and not limitation, plastics, polymers, composite compounds, glass, etc. As many layers as desired can be joined together, with the plated through holes passing through all of the layers and sealing the layers to each other. Alternately, some of the plated through holes can pass through some of the layers, while others pass through different layers.  
         [0044]     It is understood that  FIGS. 5A-5F  illustrate one exemplary configuration of the various electrical traces, components and connectors. The electrical traces illustrated provide electrical connectivity to the illustrated components. However, many other patterns of traces and components can be used. The invention is therefore not limited to the exemplary embodiment of the PCB shown. Any detector providing for a measurement of two different optical powers on one planar surface is contemplated to fall within the scope of the exemplary embodiments.  
         [0045]     There are three different scenarios for testing whether or not a laser, such as VCSEL in  FIG. 1 , complies with the eye safety requirements of a Class 1 laser. The laser should meet criteria from all three scenarios, which effectively means that compliance is based on whichever of the three is most restrictive for a given case. Following hereinafter is a discussion of the three possible scenarios and methods of using the detector  100  to measure the power level of the laser beam to verify that the laser meets the criteria for a Class 1 safety categorization. These exemplary scenarios are illustrated schematically in  FIGS. 6A-6C  for the exemplary laser shown in  FIG. 1 .  
         [0046]     In a first scenario, shown in  FIG. 6A , the divergence of laser beam  26  is low and all of the optical power of the laser beam  26  exits the barrel  16  without reflection. According to the IEC standards, the acceptable exposure limit (AEL) of laser beam  26  can be provided by the following equation: 
 
 AEL =3.9×10 −4    C   4   C   7    (1) 
 
         [0047]     C 7  is a standard constant having a value of 1. C 4  can be defined by the following equation: 
 
 C   4 =10 0.002(λ−700)    (2) 
 
 where λ is the wavelength of the laser to be tested. Using equation 2, the value of C 4  for an 850 nm laser can be 1.995. Consequently, to comply with the requirements for a Class 1 laser, the AEL of an 850 nm laser, as measured by a detector having a diameter of 50 mm at a distance of 100 mm from the VCSEL, should not exceed −1.09 decibel milliwatts (dBm). In this first scenario, however, only emissions within a numerical aperture (NA) of 0.18, which is the maximum NA of a ray that could exit the barrel  16  of the laser  10  without reflection, need be considered. 
 
         [0048]     Although testing can be performed with detectors having the above-identified diameter and position, the standards allow for use of substitute test methods so long as they use the same numerical aperture to measure the power level of the beam  26  that exits the barrel  16  without reflection. Consequently, it is also possible to test a VCSEL using a detector having a diameter of 7.11 mm at a distance of 19.3 mm and a numerical aperture of 0.18.  
         [0049]     In a second scenario, shown in  FIG. 6B , some divergence of the laser beam takes place. This results in both direct beam component  26  and reflected beam  28  component exiting the barrel  16 . According to the IEC standards, the AEL generated by both beam  26  and beam  28  can be provided by the following equation: 
 
 AEL =7×10 −4   C   4   C   6   C   7   T   2   −0.25    (3) 
 
 where,  
               C   6     =       α     α   min       ⁢   and             (   4   )             
 
 and  
               T   2     =     10   ×     10     [       (     α–α   min     )     98.5     ]                 (   5   )             
 
 α is either (i) the angle of the beam reflected at the near end of the barrel  16  or (ii) the angle of the beam reflected at the far end of the barrel  16 . A beam having the smaller angle between the above would be more focused and so damage an eye more quickly. The smaller of the two angles, therefore, is used to determine the AEL. In this exemplary configuration, the value of α can be about 12.5 mrad, while α min  is the minimum angle of the non-reflected beam exiting from the barrel  16 . The value of α min  can be about 1.5 mrad. Resultantly, in one configuration C 4  can be 1.995, C 6  can be 8.33, C 7  can be 1 and T 2  can be 12.93. 
 
         [0050]     To comply with the requirements for a Class 1 laser, therefore, a total power level of both the direct beam component  26  and the reflected beam  28  of a 850 nm laser, measured by a detector having a diameter of 50 mm at a distance of 100 mm from the VCSEL, must not exceed +7.88 dBm, from Equations 3-5. Since the actual measured power is a function of the area of the detector, the allowable power level is much higher than the power of the direct beam  26 . With this configuration, i.e., 50 mm diameter detector positioned 100 mm from the laser, the numerical aperture is 0.243. Again, it is possible to substitute detectors having other diameters and other locations relative to the laser so long as the numerical aperture is at least 0.243.  
         [0051]     Finally, in a third scenario, shown in  FIG. 6C , a ferrule can be used to abut an optical fiber to the laser transmitter. In this scenario, it is assumed that all of the available power, even above the 0.18 NA, couples to the fiber. However, since approximately 4% of the power reflects from each end of the fiber, the power exiting the output end of the fiber, i.e., the end away from the laser transmitter, is no more than 92% of the open bore power, i.e., −0.36 dB. Therefore, in this scenario, the actual measured power at the VCSEL without the fiber in place can be no more than −1.09+0.36=−0.73 dBm, however the measured power at the output end of the fiber can be no more than −1.09 dBm.  
         [0052]     To comply with the eye safety requirements associated with a Class 1 categorization, it is desirable that a tested laser simultaneously comply with all three of the above-described limits. Keeping these three scenarios in mind, exemplary embodiments of the present invention provide a laser detector that is capable of measuring the power of both components of the laser beam, the direct beam and the reflected beam, to verify that a tested VCSEL meets the Class 1 laser specification described by the three scenarios above. With the AELs calculated, i.e., detected power within 0.18 NA less than −1.09 dBm and detected power within 0.243 NA less than +7.9 dBm, it is possible to use the detector  184  to validate these AELs.  
         [0053]     One exemplary configuration of detector  184  of  FIG. 5F  is shown in  FIG. 7 . Detector  184  is divided into a first zone  186  specifically sized to measure only the direct laser beam  26  coming from the laser being tested and a second zone  188  sized to detect all of the reflected beam  28  coming from the sides of, for example, central bore  16  ( FIG. 1 ). As indicated above, detectors having differing diameters and positioned at differing distances from the test laser can be chosen, so long as the measured power level is equivalent to that measured by a detector having a 50 mm diameter positioned 100 mm from the laser. To accommodate this, in one configuration, a two zone detector having the first zone  186  is sized and positioned a distance from the laser such that the measured power level has to be less than −1.09 dBm. This results in the first zone  186  having a diameter of approximately 7.11 mm and being positioned from the laser a distance of about 19.3 mm. This corresponds to a 0.18 NA for the first zone  186 .  
         [0054]     Turning to the second zone  186 , which measures the reflected beam  28 , it is not necessary to detect all the power generated by the laser. However, if desired, that can be achieved. Rather, it is desirable for the second zone  186  to detect the same power that would have fallen onto a detector having 50 mm diameter and located at a distance of 100 mm from the test laser. This results in a numerical aperture of 0.243. In one illustrative embodiment, the diameter is approximately 10.67 mm, resulting in the second zone  188  having a numerical aperture of 0.266. This is greater than the 0.243 NA, thereby allowing an accurate measurement of the total power.  
         [0055]     More generally, in this exemplary embodiment, the size of the detection zones, and the offset distance between the laser source and the detector, are determined by the physical characteristics of the concentric detection circles or rings on detector  184 . It is understood that these measurements are for the specific hardware discussed above. However, other physical layouts for the detector, and position of the detector relative to the laser being tested, are also possible. In addition, the formulas used in the standard can be used with any other physical detector design to calculate specific offset distances. Therefore, detectors having a first zone with a diameter greater or lesser than 7.11 mm are possible. Similarly, detectors having a second zone with a diameter greater or lesser than 10.67 mm are possible. Further, detectors having one or more zones are also possible. In addition, the position of the detector relative to the laser being tested can be greater or lesser than 19.33 mm, based upon the particular diameter of the detector zones.  
         [0056]     With the measured power levels detected, the power of the laser can be adjusted using typical methods until the power of the direct beam is just below the Class 1 eye safety limit, i.e., −1.09 dBm for a 0.18 NA. This method allows slightly more power to emanate from the laser and still stay within the eye safety limit. As discussed above, the higher the power of the laser, the better the ac performance. Consequently, the present invention provides methods for detecting the output power level of a laser and increasing ac performance through adjusting the laser power level so that the power of the direct beam is just below the Class 1 eye safety limit, i.e., −1.09 dBm for a 0.18 NA.  
         [0057]     In an alternate embodiment, if it is assumed that beam components  26  and  28  coming from laser  12  are symmetrical, then the actual detection zones can be smaller. For example, one could measure the power in each zone in a semicircular area and multiply the measured power by a factor of two to determine total power in each of the zones. Alternately, one could measure the power in a single quadrant and multiply by a factor of four to determine the total power.  
         [0058]     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.