Abstract:
Designs of optical devices for attenuating a light signal are disclosed. According to embodiment, an attenuator includes a screw and a light blocker, wherein the light blocker has only translational movements when the screw is screwed in or out. To facilitate the light signal in and out, a first collimator to receive a light beam, and a second collimator to output the light beam, wherein the light beam is attenuated by the light blocker when the light is transmitted from the first collimator to the second collimator.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is generally related to the area of optical communications. In particular, the invention is related to a method and apparatus for regulating optical channel signals with specified wavelengths. 
   2. The Background of Related Art 
   The future communication networks demand ever increasing bandwidths and flexibility to different communication protocols. DWDM (Dense Wavelength Division Multiplexing) is one of the key technologies for such optical fiber communication networks. DWDM employs multiple wavelengths or channels in a single fiber to transmit in parallel different communication protocols and bit rates. Transmitting several channels in a single optical fiber at different wavelengths can multi-fold expand the transmission capacity of the existing optical transmission systems, and facilitating many functions in optical networking. 
   In general, each of the channel signals comes from a different source and may have transmitted over different mediums, resulting in a different power level. Without equalizing the power levels of the channel signals that are to be combined or multiplexed, some channels in a multiplexed signal may be distorted as a result of various stages of processing the multiplexed signal. On the other hand, many optical devices or systems would not function optimally when incoming signals are beyond a predetermined signal level range. In fact, the power of the incoming signals shall not be too low, neither too high. To ensure that all optical devices or systems receive proper levels of optical signals, attenuation devices are frequently used to adjust the optical signals before they reach an optical device. 
   Many existing optical attenuation devices lack accuracy and have high feedback noise. For example, screws are often used to intrude in an optical path to disrupt or cause to reflect some of the energy in a light beam not to reach a destination so that the light beam may be attenuated. However, in practical application, it is noticed that such attenuation is hard to be controlled. Because every time, a screw is rotated either upwards or downwards, the attenuation is not monotonically changed. This is particularly related to the surface changes of the screw. Unless the tip of a screw is made perfect, the circumambiency of the tip of the screw often has some variances, which resulting in non-monotonic changes in attenuation when the screw is caused to move up and down. Although a perfect screw may be made, the eventual cost of the attenuator may not be practical. Therefore there is a need for cost-effective attenuators with monotonic attenuation. 
   SUMMARY OF THE INVENTION 
   This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions may be made to avoid obscuring the purpose of the section. Such simplifications or omissions are not intended to limit the scope of the present invention. 
   The present invention is related to designs of optical devices and methods for attenuating a light signal. According to one aspect of the present invention, an attenuator includes a screw and a light blocker, wherein the light blocker has only translational movements when the screw is screwed in or out. To facilitate the light signal in and out, a first collimator to receive a light beam, and a second collimator to output the light beam, wherein the light beam is attenuated by the light blocker when the light is transmitted from the first collimator to the second collimator. 
   According to another aspect of the present invention, the light blocker has a tip that is so shaped that a portion of the light beam, when hit by the tip, will reflect to a direction other than either one of the collimators. 
   There are numerous benefits, features, and advantages in the present invention. One of them is the monotonic change in attenuation when adjusting the attenuation. Another one of the benefits, features, and advantages in the present invention is that attenuators made in accordance with the present invention possess the characteristics of simple structure, good performance, high reliability and low cost. 
   Other objects, features, and advantages of the present invention will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1  shows an optical device, also referred to as attenuator, for attenuating channel signals, according to one embodiment of the invention; 
       FIG. 2  shows a diagram of an attenuating means used in  FIG. 1 , according to one embodiment of the present invention; and 
       FIG. 3  shows is an illustration of how the attenuating means attenuates light signals between two collimators. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will become obvious to those skilled in the art that the present invention may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the present invention. 
   Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention. 
   Embodiments of the present invention are discussed herein with reference to  FIGS. 1-3 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments. 
     FIG. 1  shows an optical device, also referred to as attenuator  100 , for attenuating channel signals according to one embodiment of the invention. The optical device  100  is utilized to attenuate the signal strengths of channel signals received at one end and output attenuated channel signals at another end. In particular,  FIG. 1  shows the attenuator  100  is an integrated device. The attenuator  100  is housed in a solid housing  102 . The material of the block is preferably solid, such as stainless steel, aluminum, copper or other metal or material that has reasonably good thermal characteristics and mechanical strengths to support the components used to achieve the attenuation. In addition, it is preferable that the material can withstand the fiber straight pulling, side pulling, vibration, and mechanical shocks, and has good bounding characteristics to epoxies. 
   As shown in  FIG. 1 , the components in the housing  102  include a means  104  for attenuating signals, and two collimators  106  and  108 , both are respectively positioned on both ends of the housing  102 . In addition, external hardware is provided to couple two respective fibers with the two collimators  106  and  108 . As a result, a light beam coming from a fiber is projected onto the collimator  106 , attenuated by the attenuating means  104 , if necessary, and is then collected by the collimator  108  for output through another fiber. According to one embodiment, the collimators  106  and  108  are respectively fixed to the housing  102  by thermal epoxy, in situ, after a proper alignment of the collimators  106  and  108  to achieve a minimum loss. 
     FIG. 2  shows a diagram of the attenuating means  104  according to one embodiment of the present invention. As illustrated, the attenuating means  104  includes an attenuation setting screw  202 , a light blocker  204  and a spring  206 , all encapsulated in a screw mating tube  208  and a spring stop washer  210 . Instead of having a screw directly attenuate a light beam, the light blocker  204  is used to attenuate a light beam. The light blocker  204  is pushed downwards by the screw  202  when the screw  202  is screwed in and upwards by the spring  206  when the screw  202  is screwed out. One of the advantages, benefits and features of the embodiment shown in  FIG. 2  is that the light blocker  204  is always moved along a line or translationally. 
   The purely translational moving of the light blocker  204  is achieved by turning in the attenuation setting screw  202 . While the locked position of the light blocker is attained by the spring  206  that is placed between the light blocker  204  and a spring stop that is attached to the screw mating tube. The spring stop can be made as part of the mating tube, or can be made separately and attached to the mating tube  208  afterward, as shown in  FIG. 2 . 
     FIG. 3  shows is an illustration of how the attenuating means  104  attenuates light signals between two collimators  106  and  108 . The light blocker  204  has a tip  302  that is preferably so shaped that a portion of the light signals, when hit the tip  302 , will reflect to a direction other than the collimator  106 . With the introduction of the tip in the optical path, the attenuation to the signal is realized. 
   In con junction with  FIG. 2 , it can be appreciated that the motion of the tip  302  is translational. Even if there is some dirt on the tip  302 , because there is no rational motion thereof, the dirt just contributes to the attenuation. The amount of the attenuation is steadily controllable. 
   Given the description herein, those skilled in the art can appreciate that the optical attenuators made in accordance with the present invention can also resist to drastic environmental temperature variations and high humidity working condition. 
   The present invention has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of embodiments.