Abstract:
Techniques for designing optical devices that can be manufactured in volume are disclosed. In an exemplary an optical assembly, to ensure that all collimators are on one side to facilitate efficient packaging, all collimators are positioned on both sides of a substrate. Thus one or more beam folding components are used to fold a light beam up and down through the collimators on top of the substrate and bottom of the substrate.

Description:
CROSS REFERENCE 
     This application is a continuation-in-part of co-pending U.S. application Ser. No.: 11/669,947 filed Feb. 1, 2007, now U.S. Pat. No.: 7,843,644, and related to U.S. Pat. No.: 11/379,788, commonly assigned, entitled “Optical devices and method for making the same”, now U.S. Pat. No.: 7,224,865. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is generally related to the area of optical devices. In particular, the present invention is related to optical wavelength multiplexing/demultiplexer or add/drop devices with new optical layouts and manufacturing processes. 
     2. The Background of Related Art 
     Optical add/drop and multiplexer/demultiplexer devices are optical components often used in optical systems and networks. These devices using wavelength division multiplexing (WDM) techniques allow a simultaneous transfer of optical signals at different wavelengths or channels through a single optical link such as an optical fiber. In operation, a WDM device or system may need to drop or add a set of channels from or to a transmitting signal. Multiplexer/demultiplexer (Mux/Demux) is often needed for this application. 
       FIG. 1  replicates a WDM device disclosed in U.S. Pat. No. 5,583,683. A multiple wavelength light beam traveling in a fiber is separated into multiple narrow spectral bands, each directed to an individual port. At each of the ports for a channel, a dielectric thin film filter is used to transmit a specified wavelength in the multi-wavelength (collimated) light passed by the port but reflects all other wavelengths. The remaining of the multi-wavelength signal continues to a next channel port, where an in-band signal at a specific wavelength is transmitted and all others are reflected. The remaining of the multi-wavelength signal continues to propagate along an optical path. After multiple bounces, signals at different wavelengths are separated. Compared with a conventional three-port cascading modules, the dimension of the device of  FIG. 1  is small in size as fiber routing in the three-port modules are replaced with collimated beams, thus the routing overhead is saved. 
     It is well known that a fiber is not allowed to bend too small. For example, for the widely used SMF-28e fiber, the minimum bend radius is about 30 mm. When being routed, the fiber roll wastes a specific space, for example, 60 mm in diameter for SMF-28e fiber. Without fiber routing, a WDM device box could be even smaller than a square of 30 mm by 30 mm. 
     Even so, for the prior art device of  FIG. 1 , the fiber input/output (I/O) ports are positioned on both sides of a mechanical box. In the process of fiber handling, due to the minimum radius limitation, the space waste could be doubled as shown in  FIG. 2A . One of the features, objects and advantages of the current invention as will be described below is to have all the I/O ports deposed on one side of a device as shown in  FIG. 2B . For a one-sided device, as the I/O ports are on one side of the device, thus fiber routing could be eliminated. 
     The one-sided optical layout is realized by beam folding components. Prisms or mirrors are commonly used as beam folding components as shown in  FIGS. 3A-3C . These components are all to be used and covered by different embodiments of the present invention. 
       FIG. 4  replicates an optical device of U.S. Pat. No. 6,847,450 using turning prisms to bend light beams from adding channel collimators vertical to the main plane (beam cascading plane). Compared with the prior art device of  FIG. 1 , the length of the device of  FIG. 4  is reduced by a collimator length, but it is at the cost of the height as the cascading optics is now along with the height dimension of the device of  FIG. 4 . 
       FIG. 5  replicates a device of U.S. Pat. No. 7,068,880 that is similar to that of  FIG. 4 . The major difference is that in U.S. Pat. No. 7,068,880, the beam bending is at the collimator lens while in U.S. Pat. No. 6,847,450 the bending occurs after collimators. In either case, the beams are bent by 90 degrees. The common problem is that the height of the device is now big. As will be described below, the beams are also turned twice to reduce the height of a resulting device. Further unlike these prior art devices, the beam folding occurs along a zigzag optical path, resulting in the height being smaller, compared with prior art devices of  FIG. 4  and  FIG. 5 . As will be appreciated from the disclosure herein, the height of the prior art devices is the width of the zigzagging optics (typically &gt;5 mm) plus two collimator mounting space while the height of a device designed in accordance with the present disclosure is the height of a substrate(typically ˜2 mm) plus two collimator spaces. 
     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 in this section as well as in the abstract and the title may be made to avoid obscuring the purpose of this section, the abstract and the title. Such simplifications or omissions are not intended to limit the scope of the present invention. 
     In general, the present invention pertains to improved designs of optical devices, particularly for adding or dropping a selected wavelength or a group of wavelengths as well as multiplexing a plurality of signals into a multiplexed signal or demultiplexing a multiplexed signal into several signals. For simplicity, a group of selected wavelengths or channels will be deemed or described as a selected wavelength hereinafter. According to one aspect of the present invention, an assembly is described. To ensure that all collimators are on one side to facilitate efficient packaging, all collimators are positioned on both sides of a substrate. Thus one or more beam folding components are used to fold a light beam up and down through the collimators on top of the substrate and bottom of the substrate. 
     Depending on implementation, different means are provided to ensure that the collimators are securely boned to the substrate. According to one embodiment, wedges are used to hold each of the collimators. Depending on the shape of the collimators, the wedges are designed in different shape to prove a best contact with the collimators. 
     The present invention may be implemented in many ways as a subsystem, a device or a method. According to one embodiment, the present invention is an optical assembly. The optical assembly comprises at least a common collimator; a substrate; an array of channel collimators including an upper set of collimators and a lower set of collimators, wherein the upper set of collimators is mounted on top of the substrate, and the lower set of collimators is mounted on bottom of the substrate; one or more beam folding components mounted near an end of the substrate, wherein the one or more of the beam folding components turn a light beam traveling through the upper set of collimators to the lower set of collimators, or a light beam traveling through the lower set of collimators to the upper set of collimators, wherein all of the collimators and the common collimator are on one side of the beam folding components. 
     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  replicates a WDM device disclosed in U.S. Pat. No. 5,583,683; 
         FIG. 2A  shows that a could be doubled due to the minimum radius limitation; 
         FIG. 2B  shows that all the I/O ports are deposed on one side of a device; 
         FIGS. 3A-3C  shows some exemplary beam folding components; 
         FIG. 4  replicates an optical device of U.S. Pat. No. 6,847,450 using turning prisms to bend light beams from adding channel collimators vertical to the main plane (beam cascading plane); 
         FIG. 5  replicates a device of U.S. Pat. No. 7,068,880 that is similar to that of  FIG. 4 ; 
         FIG. 6A  shows an structure according to one embodiment of the present invention; 
         FIG. 6B  illustrates a ray-tracing plot for the structure of  FIG. 6A ; 
         FIG. 7A  shows an exemplary 4-channel free-space Demux with one prism block; 
         FIG. 7B  shows an exemplary corresponding 4-channel free-space Mux with one prism block; 
         FIG. 8  shows that two halves of a prism can even be mounted to the two horizontal surfaces of the substrate; 
         FIG. 9  shows a structure with two reflection filters or mirrors 
         FIG. 10  shows one embodiment overcoming the slant collimators and uses a prism to redirect the beam so as to keep to keep the collimator parallel 
         FIG. 11  shows another embodiment using a slant mounted retro-reflection prism to send the beam from the common port to the lower level and project to a first channel filter and then a first channel collimator; 
         FIG. 12A  and  FIG. 12B  show respectively filters can be directly bonded with a prisms to avoid the requirement of having a good sidewall of the substrate; 
         FIG. 13  shows a structure with a substrate end for two extruded widgets; 
         FIG. 14A  to  FIG. 14D  show respectively four different mounting means using wedges; 
         FIG. 15A  shows an exemplary structure for mounting two 4-channel devices in one enclosure; 
         FIG. 15B  shows ports of two devices are laid out in a complementary arrangement; 
         FIG. 16A-FIG .  16 D demonstrate respectively four coarse WDM (CWDM) channel plans for Mux/Demux pair (“M” for Mux, “D” for “Demux”); 
         FIG. 17A  and  FIG. 17B  show two more different settings from  FIGS. 16A-16D ; and 
         FIG. 18A  shows an exemplary stacking of three devices; and 
         FIG. 18B  shows an exemplary stacking of four devices. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The detailed description of the present invention is presented largely in terms of procedures, steps, logic blocks, processing, or other symbolic representations that directly or indirectly resemble the operations of optical devices or systems that can be used in optical networks. These descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. 
     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. 
     Referring now to the drawings, in which like numerals refer to like parts throughout the several views.  FIG. 6A  shows an structure  600  according to one embodiment of the present invention. The structure has two levels, an upper level and a lower level, separated by a substrate  602 . A light beam at the upper level is turned vertically by a trapezoid prism  604  vertically mounted and then turned again by the same prism  604  to the lower level. As a result, the beam comes back to the same side of the structure  600 , namely input and output ports can be mounted on one side of the structure  600 . 
       FIG. 6B  illustrates a ray-tracing plot  650  for the structure  600  of  FIG. 6A . The beam from a common collimator at the upper level is folded by a prism to the lower level, then split by a thin film filter through which an in-band signal passes. The passed signal is then coupled out by a collimator, while all other band signals are directed to the same retro-reflecting prism and folded to the upper level again. After several rounds of optical splitting by filters and optical folding by the prism, different band signals in the incoming signal are dropped to respective ports (all on the same side). 
     This kind of splitting propagation produces a Demux device. If the beam travels in a reversed manner, the device works as a combining mode, resulting in a Mux device. It can be appreciated by those skilled in the art that each of the embodiments described herein works in either mode (Mux or Demux).  FIG. 7A  shows an exemplary 4-channel free-space Demux  700  with one prism block  702  while  FIG. 7B  shows an exemplary corresponding 4-channel free-space Mux  720  with one prism block  704 . 
     As shown in  FIG. 7A  and  FIG. 7B , the prism block or prism  702  or  722  is mounted to the end of the substrate. If the prism is cut into two halves as shown in  FIG. 3B , they may be mounted on the end vertical surface of the substrate, just like one-prism design.  FIG. 8  shows that two halves of the prism can even be mounted to the two horizontal surfaces of the substrate. The edges of two prisms are standing on the extended surfaces of the substrate. The substrate may be designed in various forms to support two prisms or two halves of a prism. Any mechanical designs of the substrate that supports two reflection components (prisms, mirrors, or even filters) to make a beam for a U-turn shall be considered within scope of the present invention. 
       FIG. 9  shows a structure  900  with two reflection filters or mirrors. These two mirrors are mounted on one or two slant wedges attached to the substrate to fold a beam. These wedges may be separated with the substrate or be part of the substrate. The beam from a common collimator or a filter hits the mirror above the substrate and is turned to vertical or similar direction. The turned beam hits the other mirror underneath the substrate and is turned again to the reverse direction to the incident direction. After reflected by the filters on the lower level, the beam comes back to the lower mirror that turns it to the upper mirror and then to the upper filter again. Depending on implementation, the mirrors may be exchangeable with optical filters. 
     The design of  FIG. 9  takes the benefit of simplicity. But due to the existence of common collimators being slanted, the fiber I/O is not entirely one-sided as commonly understood. If the incidence angle is large, this angular offset of the common port is serious and may not be acceptable for packaging in some applications. 
       FIG. 10  shows that one embodiment  1000  overcomes the arrangement of having a slanted collimator and uses a prism to redirect the beam so as to keep the collimator in parallel. As a result, a common collimator can be aligned with other channel collimators. 
       FIG. 11  shows another embodiment  1100  using a slant mounted retro-reflection prism to send the beam from the common port to the lower level and project to a first channel filter and then a first channel collimator. Through the reflection of the first filter, the beam enters the cycle of splitting by filters and folding by a second prism. The filters can be bonded to the substrate surfaces. This requires a good sidewall for each of the filters. To avoid the requirement of having a good sidewall of the substrate, these filters can be directly bonded with the prisms as shown in  FIG. 12A  and  FIG. 12B . 
       FIG. 13  shows a structure  1300  with a substrate end for two extruded wegets. Mounting holes are designed in the widgets to hold the collimators. A type of adhesive (e.g., epoxy) is applied to secure the position of the collimators to the widget. The mounting holes are an example to hold the collimators, other means such as V-grooves may be used to hold the collimators as well. 
     Another mounting method is to use flexible bridges or wedges. To mount a collimator to a flat substrate, the bridge block has two touch surfaces: one with the collimator, the other with substrate. Since the substrate is flat, the best contact is a flat surface. But a collimator has a cylindrical or similar outer shape, the contact surface can be more flexible. If this contact surface is also flat, then the bridge block is a wedge.  FIG. 14A  and  FIG. 14B  show two different mounting means using such wedges. 
     If the surface is curved, curved wedges may be used as shown respectively in  FIG. 14C  and  FIG. 14D . Depending on implementation, there are other types of wedges that may be used. The wedges can be used individually, but for better bonding, the wedges are better to be used in pair. With a pair of bridges, four contact surfaces are involved to secure the support between collimators and the substrate. 
     In some network designs, two or more similar devices are required to be mounted at the same location. Mux/Demux pair is a typical setting. In one embodiment, an array of Mux/Demux devices is mounted on one substrate and within one enclosure to save space and cost.  FIG. 15A  shows an exemplary structure for mounting two  4 -channel devices in one enclosure. The ports of two devices are laid out in a complementary manner as shown in  FIG. 15B . 
     For a first device D 1 , there are three ports (“D 1 -COM”, “D 1 -Ch 2 ”, and “D 1 -Ch 4 ”) are on the upper row and two (“D 1 -Ch 1 ” and “D 1 -Ch 3 ”) on the lower row. For a second device, there are two ports (“D 2 -Ch 1 ” and “D 2 -Ch 3 ”) are on the upper row and three ports (“D 2 -COM”,“D 2 -Ch 2 ”, and “D 2 -Ch 4 ”) on the lower row. These two devices operate independently. Two individual optical signal inputs or outputs “D 1 -COM” or “D 2 -COM” port are Demux or Mux, respectively. The drop or add signals are separated via the channel ports (“D 1 -Ch 1 ”,“D 1 -Ch 2 , . . . ). 
     It should be noted that the wavelength band for each port and each device can be allocated in a customizable manner, mostly based on application request. And each device in the shared enclosure may have a different wavelength channel layout.  FIG. 16A-FIG .  16 D demonstrate respectively four coarse WDM (CWDM) channel plans for Mux/Demux pair (“M” for Mux, “D” for “Demux”). It should be also noted that the devices in the array can have the same or different channel count.  FIG. 17A  and  FIG. 17B  show two more different settings. 
     More than two devices may be lined up side by side in a similar fashion and the devices in the array can have the same or different channel count.  FIG. 18A  shows an exemplary stacking of three devices.  FIG. 18B  shows an exemplary stacking of four devices. 
     While the present invention has been described with reference to specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications to the present invention can be made to the preferred embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claim. Accordingly, the scope of the present invention is defined by the appended claims rather than the forgoing description of embodiments.