Abstract:
A system and method for controlling an electrochromic device is provided. The system comprises a light source that produces an input light signal, and an electrochromic window configured to attenuate the input light signal by a certain amount and transmit a resulting attenuated light signal. An optical detector is configured to detect an optical property of the attenuated light signal, and a power module is connected to the electrochromic window and the detector. The power module generates a pulse-width modulated power signal and inputs the power signal to the electrochromic window. The power signal is modulated by an amount based on the detected optical property of the attenuated light signal. A control circuit for an electrochromic device is also disclosed.

Description:
This application claims the benefit of priority to U.S. Provisional Application No. 60/422,824, filed on Oct. 30, 2002, the disclosure of which is herein incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to the field of optical attenuation devices for use in optical systems. In particular, the present invention relates to a control system for an electrochromic device. 
   2. Background Technology 
   Fiber optics are increasingly used for transmitting voice and data signals. As a transmission medium, light provides a number of advantages over traditional electrical communication techniques. For example, light signals allow for extremely high transmission rates and very high bandwidth capabilities. Also, light signals are resistant to electromagnetic interference that would otherwise interfere with electrical signals. Light also provides a more secure signal because it does not emanate the type of high frequency components often experienced with conductor-based electrical signals. Light also can be conducted over greater distances without the signal loss typically associated with electrical signals on a copper conductor. 
   Many conventional electrical networks are being upgraded to optical networks to take advantage of increased speed and efficiency. Optical communication networks use lasers to create light which is then modulated to convey information. One of the many components of an optical communications network is an optical attenuator. Optical attenuators control the intensity of one or more wavelengths of light within an optical system. One use for optical attenuators is in combination with an optical receiver having a photodetector and a preamplifier. The optical attenuator can be used to attenuate the incoming optical signal if the intensity of the signal exceeds a specified threshold. In this manner, the intensity of the incoming signal is brought in line with the dynamic range of the components of the optical receiver, and avoids the need of using more expensive receivers that would have larger dynamic operating ranges. 
   In addition to the foregoing use of optical attenuators, it is sometimes necessary to recalibrate or replace one or more of the lasers generating light in the system. To avoid data corruption, it is necessary to completely extinguish the laser&#39;s light from the optical system before recalibration or replacement. Optical attenuators are capable of extinguishing the laser&#39;s light by blocking it from entering the remainder of the optical system. There are numerous general methods of attenuating or completely extinguishing light, including polarization, reflection, diffusion, etc. In addition, it is often necessary to control the intensity of a particular wavelength or channel of light entering a fiber. Although it is possible to simply adjust the electrical current feeding a laser to adjust the output intensity, this is not desirable because this method of attenuation will affect the bandwidth capabilities of the laser. Therefore, it is necessary to use a variable optical attenuator to attenuate or adjust the output intensity of a particular laser. 
   One type of attenuator uses an electrochromic (EC) window to attenuate light that is transmitted through the window. An EC window attenuates the amount of light that is allowed to transmit through the window as a function of the input voltage that is applied to the window. This type of attenuator does not use moving parts nor does it change the polarization in any way to attenuate the incoming light. An EC window utilizes a particular crystalline structure that reflects and refracts light in such a way as to attenuate the light when a voltage is applied across the window. Many applications for EC windows require them to maintain a particular attenuation level for a long period of time. One of the difficulties associated with controlling the attenuation provided by an electrochromic attenuation device is that the attenuation is exponentially related to the voltage applied to the attenuation device. Accordingly, achieving an accurate and prolonged level of attenuation has been difficult using conventional approaches. Moreover, conventional attenuation techniques involve applying a particular voltage to the EC window for the entire duration of active operation of the EC window in order to maintain the proper attenuation level. 
   Therefore, there is a need in the industry for an EC control circuit that minimizes the amount of power that must be expended in order to maintain a particular attenuation level. In addition, the control circuit should be relatively easy to manufacture and implementable in a wide variety of applications. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a system and method for controlling an electrochromic device. The system comprises a light source such as a laser device that produces an input light signal, and an electrochromic window configured to attenuate the input light signal by a certain amount and transmit a resulting attenuated light signal. An optical detector is configured to detect an optical property of the attenuated light signal, and a power module is connected to the electrochromic window and the detector. The power module generates a pulse-width modulated power signal and inputs the modulated power signal to the electrochromic window. 
   In a method of controlling an electrochromic device according to the invention, a light source produces an input light signal that is directed to an electrochromic window configured to attenuate the light signal. The attenuated light signal is transmitted from the electrochromic window to an optical detector configured to detect an optical property of the attenuated light signal. A pulse-width modulated power signal is directed to the electrochromic window. The power signal is modulated by an amount based on the detected optical property of the attenuated light signal. 
   One embodiment of a control circuit for an electrochromic device comprises a substrate having an upper surface, a preamp integrated circuit on the upper surface of the substrate, and an insulator on the upper surface of the substrate and adjacent to the preamp integrated circuit. One or more conductive posts are electrically connected to the preamp integrated circuit. An electrochromic window is interposed between first and second layers of a transparent material. The electrochromic window is in electrical communication with the preamp integrated circuit. 
   These and other 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 
     In order to illustrate the manner in which the advantages and features of the invention are obtained, a description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore 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: 
       FIG. 1  illustrates a functional block diagram of one embodiment of an electrochromic control system that utilizes a pulse-width modulation (PWM) circuit in order to minimize the power required to operate an electrochromic window; 
       FIG. 2  illustrates the electrical signal generated by the PWM circuit in FIG.  1  and the reflectivity response of the electrochromic window; 
       FIG. 3  illustrates a particular optimum power range for use in an optical communication system; and 
       FIG. 4  illustrates one embodiment of an electrochromic control circuit mounted on a transistor outline can for use in an optical or electrical application. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In general, the present invention relates to an electrochromic (EC) control system that minimizes the amount of power required to operate an electrochromic window for use in attenuating light. The control system capitalizes on the slow response time of an electrochromic window by using a pulse-width modulation (PWM) to drive the EC window rather than a standard constant signal. By modulating the input signal at a rate that is just fast enough to maintain the required light attenuation of the EC window, the power transferred to the EC window is minimized. Also, while embodiments of the present invention are described in the context of optical attenuation for optical networking, it will be appreciated that the teachings of the present invention are applicable to other applications as well. For example, EC windows are commonly used in place of traditional glass windows to attenuate sunlight at particular times of the day or in response to temperature. 
   Reference will now be made to the drawings to describe presently preferred embodiments of the invention. It is to be understood that the drawings are diagrammatic and schematic representations of the embodiments, and are not limiting of the present invention, nor are they necessarily drawn to scale. 
     FIG. 1  is a functional block diagram illustrating one embodiment of an electrochromic control system  100  that utilizes pulse-width modulation (PWM) in order to minimize the power required to operate the electrochromic window. The illustrated control system  100  configuration is designed for use in optical communication systems. The control system  100  includes a light source such as a laser  105 , an EC window  110 , an optical detector  115 , and a power module that includes a PWM circuit  125  and a power supply  120 . The laser  105  generates a light signal that digitally encodes information in one or more wavelength channels. The laser  105  can be any laser source, including gas and semiconductor based lasers. The light signal is transmitted from the laser  105  into the EC window  110 . The EC window  110  attenuates the light signal by a specified amount in order to lower the overall power or irradiance of the light signal. This does not affect the digital information that is encoded within the light signal&#39;s channels, since attenuation involves blocking a certain percentage of the overall light signal&#39;s power as opposed to blocking or filtering specific wavelengths of the light signal. The EC window  110  attenuates the light signal by an amount mathematically related to the amount of voltage applied upon it from the PWM circuit  125 . The higher the voltage applied upon the EC window  110 , the larger the amount of attenuation generated by the EC window  110  with respect to the light signal. An example of this relationship is represented in the graph of FIG.  1 B. 
   The unattenuated portion of the light signal transmits through the EC window  110  onto the detector  115 . The detector is an optical device, such as a charge-coupled device (CCD) array, that measures the power of the light signal over a one or two-dimensional area. Alternatively, the light signal may also be transmitted to another location in addition to the detector  115 . The power measurement made by the detector  115  is then electrically communicated or transferred to the PWM circuit  125 . The PWM circuit  125  controls the distribution of electricity from the power supply  120  to the EC window  110  in such a way as to minimize the power used by the EC window. The PWM circuit  125  modulates the voltage from the power supply  120  in a pulse-width modulated manner such that the modulation rate is faster than the total decay rate of the EC window  110 . In other words, the period between pulses in the voltage is selected to be less than the time that it takes for the attenuation activity of the EC window to significantly decay. By continually pulsing the voltage onto the EC window  110  in this manner, the overall attenuation level of the EC window  110  can be maintained around a particular value. Moreover, the use of pulse-width modulation of the voltage signal with the feedback provided by detector  115  enables the attenuation level to be controlled more accurately than the conventional technique of using a constant voltage, since the attenuation level is an exponential function of the voltage. 
   Reference is next made to  FIG. 2 , which illustrates the electrical signal generated by the PWM circuit in FIG.  1  and the reflectivity or attenuation response of the electrochromic window, designated generally at  200 . The graph  200  includes a PWM input signal  210  and a reflectivity or attenuation response  220 . The PWM input signal  210  is the electrical voltage signal generated by the PWM circuit  125  versus time. As described above, the PWM circuit  125  modulates the input signal at a rate that is faster than the decay rate of the electrochromic window  110 . The decay rate of the EC window is based on its ion mobility and diffusion rates. The modulation of the input signal can be done in many ways, including simply switching on and off the electrical connection between the power supply  120  and the electrochromic window  110 . The PWM input signal  210  includes sections where the voltage is at a value V 1  and other sections where the voltage is 0. The reflectivity or attenuation response  220  is the reflectivity or attenuation level of the electrochromic window  110  versus time. Reflectivity is the percentage of light that is reflected or attenuated by the electrochromic window  110 . The remainder of the light that is not reflected or attenuated is transmitted through the electrochromic window  110 . 
   The PWM input signal  210  and the reflectivity or attenuation response  220  are aligned in time to illustrate the affect the PWM input signal  210  has on the reflectivity or attenuation response  220 . When the PWM input signal  210  is generating a voltage V 1 , the reflectivity or attenuation response  220  increases in a logarithmic manner to a reflectivity R 2 . Whereas, when the PWM input signal  210  is not generating any voltage, the reflectivity or attenuation response  220  decreases in a logarithmic manner to a reflectivity of R 1 . Therefore, by modulating the PWM input signal  210  at a certain rate, the reflectivity or attenuation can be maintained within a certain range between R 1  and R 2  without having to maintain a constant electrical voltage on the electrochromic window. The faster the modulation of the PWM input signal  210 , the smaller the range between reflectivity values R 1  and R 2 . 
   Reference is next made to  FIG. 3 , which illustrates one example of the range of power of an input optical signal that is received by an optical receiver. Chart  300  of  FIG. 3  shows how an optical attenuator operated according to the invention can be used to reduce the power of an incoming optical signal to a level that is compatible with the optimal dynamic operating range of the optical receiver. While  FIG. 3  illustrates one example of the reduction of the power of an optical signal to a specified range, it is to be understood that the principles of the invention can be used to arbitrarily attenuate the power of an optical signal as needed to comply with the operating requirements of an optical receiver or for other reasons. The chart  300  illustrates a range of power levels commonly used in optical attenuators. The chart  300  further includes an input power range  310 , a fixed attenuation range  320 , and a variable attenuation range  330 . The input power range  310  represents a typical power level associated with an incoming optical signal that is received by the EC window. In this example, the input power range  310  is between −3 dBm and +8 dBm. The input power is then attenuated into either the fixed attenuation range  320  or the variable attenuation range  330 , depending on whether the electrochromic window is used for fixed or variable attenuation. The fixed attenuation range  320  is between −4 dBm and −15 dBm, and the variable attenuation range  330  is between −6 dBm and −10 dBm. 
   Reference is next made to  FIG. 4  which illustrates one embodiment of a electrochromic control circuit  400  mounted on an upper surface of a substrate such as a transistor outline (TO) can  405  for use in an optical or electrical application, such as in an optical receiver or transmitter. The control circuit  400  of  FIG. 4  includes a preamp integrated circuit  413 , an insulator  420 , a conductive post  410 , layers of transparent material  425  and  430  and an electrochromic window sandwiched between the layers of transparent material  425  and  430 . This structure enables the electrochromic window to operate in a controlled environment. The electrochromic window is in electrical communication with the preamp integrated circuit which includes a PWM circuit. 
   The electrochromic control system of the present invention is more efficient than existing EC control circuits in that the level of attenuation can be more easily controlled. In contrast, conventional EC windows are operated using a fixed voltage, which makes it difficult to control the level of attenuation, which is related exponentially to the voltage. 
   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.