Abstract:
A monolithic optical module of injection-molded high temperature polymeric resin combines an optical turn of typically 90 degrees together with dual or triple beam paths. No additional piece parts are necessary for achieving the optical turn, since this occurs by total internal reflection (TIR), and no additional piece parts are necessary for dual monitoring, which is realized by means of an air-gap functioning as a dual beam-splitter plate. The monolithic optical module further includes integrally surfaces for accurate alignment of the module with external optical elements, and can additionally include integral optical elements, for example lenses and thin film coatings.

Description:
TECHNICAL FIELD 
     The present invention relates to optical devices and particularly to small form factor all-polymer optical devices with integrated dual beam paths based on a total internal reflection optical turn. 
     BACKGROUND OF THE INVENTION 
     A tilted partial reflective mirror in path of vertical cavity surface emitting laser (VCSEL) for monitoring introduces complex assemblies having various piece parts. Silicon optical benches with built-in optical turn mirrors are expensive, even in large volumes. A monitoring path used in one prior art micro-photonics transmitter device involves individually mounted separate piece optical components (see Fisher et al., U.S. Pat. No. 5,937,114, issued Aug. 10, 1999). 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to a system and method which combine an optical turn of typically 90 degrees together with dual or triple beam paths using a monolithic optical module of injection-molded high temperature resin, for example, polyetherimide, polyimide or polysulfone high-temperature resistant optical polymer. No additional piece parts are necessary for achieving the optical turn, since this occurs by optical total internal reflection (TIR), and no additional piece parts are necessary for dual monitoring, which is realized by means of an air-gap functioning as a dual beam-splitter plate. The monolithic optical module further includes integral surfaces for accurate alignment of the module with external optical elements, and can additionally include integral optical elements, for example lenses and thin film optical coatings. 
     Among the technical problems addressed by the invention are: Enabling a 90-degree optical turn permitting active optoelectronic devices, for example vertical cavity surface emitting lasers (VCSELs) and optical detectors, to be surface mounted on a substrate orthogonal and at a desired offset distance relative to a transmitter fiber port; minimizing use of diverse materials and/or mounting techniques and separated optical elements to reduce cost when such a optical turn is realized; and providing an integrated single or dual laser monitoring path using an air-gap integrated beam-splitter, thereby further minimizing use of diverse components, materials, separated optical elements, and/or mounting techniques, and consequently reducing cost. Dual path laser monitoring further allows wavelength locking using two detectors with a narrow band optical filter or etalon in the beam path of one of them. Embodiments of the invention allow open fiber control and/or dual direction communication across a single optical fiber. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  is a schematic diagram illustrating the structure and functionality of a small form factor all-polymer integrated optical module, in accordance with embodiments of the present invention; 
         FIG. 2  is a flow diagram  200  depicting the operation of optical assembly  100 , in accordance with embodiments of the present invention; 
         FIGS. 3A-3B  depict two alternative configurations for generating an output beam offset and parallel relative to the input beam axis; 
         FIG. 4  depicts optical module  410  configured for bi-directional transmitting/receiving; 
         FIG. 5  depicts optical module  510 , providing a TIR transmitted beam path with partial internal reflection at two wedge-like features; and 
         FIG. 6  depicts optical module  610 , providing a TIR transmitted beam path in which a TIR interface has curvature that simultaneously focuses the reflected beam in addition to only reflecting the collimated beam. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic diagram illustrating the structure and functionality of a small form factor all-polymer monolithic optical module, in accordance with embodiments of the present invention. Optical module  110  can integrally incorporate among other optical elements any combination of the following: total internal reflection interface  111  capable of redirecting an optical beam, e.g. through a 90-degree turn; wedge air/polymer/air multiple-interface beam splitter  112  capable of creating a multiple beam path and redirecting the beam path; focusing lenses  116 ,  117  capable, for example, of focusing a light beam on a detector; fiber facing lens  118  capable of focusing a light beam into an optical fiber; and collimating lens  119  capable of transforming a diverging light beam, for example a laser output beam, to a collimated beam. In addition to the above optical elements which meet optical dimensional and surface finish tolerances, integrated optical module  110  includes non-optical structural walls, for example structural surfaces  131 - 140 , which provide mechanical integrity to the optical elements and can include alignment interfaces with other system components, and which may have opaque or diffuse optical properties. 
     Integrated optical module  110  is formed of high temperature resin, e.g., polyetherimide, polyimide or polysulfone high-temperature resistant optical polymer by a high-precision polymer fabrication technique, using for example a polymer injection molding process similar to that commonly employed for contact lenses, intraocular lenses, or other ophthalmic elements. All of the optical elements of integrated optical module  110  are formed simultaneously and monolithically from the same material with integrated optical module  110 , thereby substantially reducing the cost and complexity of fabrication and enhancing the compactness, alignment precision, and mechanical integrity of optical alignment. 
     For ease of understanding, in  FIG. 1  integrated optical module  110  is depicted as part of optical assembly  100 , which also includes optical base or substrate  101  providing attachment for active optical components, for example Vertical Cavity Surface Emitting Laser (VCSEL)  102  and optical detectors  103  and  104 ; and optical transmitting/receiving fiber  105 . 
       FIG. 2  is a flow diagram  200  depicting the operation of optical assembly  100 , in accordance with embodiments of the present invention. At step  201 , VCSEL  102  and optical detectors  103 ,  104  are attached, typically using surface mounting technology, to substrate  101 , e.g. a PCB (printed circuit board), which at step  202  is fastened in precise alignment with integrated optical module  110  using for example alignment interfaces on structural surfaces  131 - 140 . In surface mounting technology, components such as capacitors, resistors and ICs (Integrated Circuits) are commonly placed on a surface, e.g., a PCB substrate, by pick-and-place manipulators in a perpendicular placing action and are attached to the surface by use of an epoxy, solder, or other adhesive. At step  203 , optical fiber  105  is aligned with optical module  110  using for example a self-aligning fiber port connector integral with optical module  110 . 
     At step  204 , VCSEL  102  emits diverging beam  120 , which at step  205  is collimated by collimating lens  119  to form collimated beam  121  propagating within the medium of integrated optical module  110 . At step  206 , collimated beam  121  is turned through an angle by total internal reflection (TIR) from interface  111  to form totally reflected beam  122 . This angle can measure 90 degrees, but it can also be larger or smaller depending, e.g., on beam divergence of laser source  102  and/or other properties of a specific embodiment. It is well known in the optical art that light is totally internally reflected when it is incident at an angle greater than or equal to a “critical angle” onto an interface between an incident medium having a refractive index n=n p  and an external medium having a refractive index n=n 0 , where n p &gt;n 0 . Since for most optical polymers, n p  is in the range of 1.43 to 1.73, it is convenient for the external medium to be air or inert gas, which has a refractive index n 0  near unity. 
     Reflected beam  122  then propagates through the polymer medium of integrated optical module  110  and strikes internal/external interface  113  of multiple-interface beam splitter  112 , where at step  207  it is split into partially reflected beam  123  into the internal medium and partially refracted beam  125  into the external medium. Partially reflected beam  123  is focused at step  208  by focusing lens  116  to form converging beam  124 , which, for example, is captured by optical detector  103 . Partially refracted beam  125  propagates through the external medium and at step  209  strikes external/internal interface  114  of multiple-interface beam splitter  112 , where it is further split into external reflected beam  126  and internal refracted beam  129 . The orientations of interfaces  113  and  114  in combination with the orientation of surface  111  assure that the chief ray of beam  129  impinges perpendicularly onto prealigned optical fiber  105  at step  211 , after being focused by fiber facing lens  118  at step  210  to form fiber facing beam  130 . External reflected beam  126  propagates through the external medium and at step  212  strikes external/internal interface  115  of multiple-interface beam splitter  112 , where it is partially refracted into internal refracted beam  127 , which is then focused at step  213  by focusing lens  117  into converging beam  128 , which, for example, is captured at step  214  by optical detector  104 . 
     The purposes of dual/multiple detectors  103 ,  104  include monitoring the intensity of the light signal as emitted by laser source  102 ; providing for bi-directional communication across single optical fiber  105 ; and wavelength locking of laser source  102 . For the latter purpose, two detectors  103 ,  104  are utilized, one having a narrow-band (half width passband typically &lt;0.5 nm) interference filter or an etalon in its path, for example internal refracted beam path  127 . The signals generated by both detectors provide a measure of the wavelength of laser source  102  and stabilize the transmitter to a desired wavelength by changing its operating conditions (e.g., drive current) and/or external environment conditions, for example laser temperature. 
     Embodiments of the present invention are not limited to the optical beam path shown in  FIG. 1 , but include alternative configurations which embody the principles of the present invention, including TIR optical turn and means to tap and monitor the transmitted signal beam by using the reflections from a slanted, parallel, or wedged air/polymer interface.  FIGS. 3A-3B  depict two alternative configurations for generating an output beam offset and parallel relative to the input beam axis, i.e. 90-degree turn at surface  311  or non-90-degree turn at surface  341  compensated by refraction at surfaces  343  and  344 . In module  310  depicted in  FIG. 3A , VCSEL source  102  emits diverging beam  120 , which is collimated by collimating lens  119  integral to module  310  to form collimated beam  121 . Beam  121  in turn is reflected at a 90-degree angle  312  by TIR at interface  311 , forming horizontal beam  322 . Air gap beam splitter  315  includes parallel partially reflective interface surfaces  313 ,  314 , which are disposed diagonally relative to horizontal beam  322 , which is then refracted upward at first interface surface  313  to form refracted beam  325  and is refracted again at second interface surface  314  to form offset beam  329  parallel to horizontal beam  322 . Module  310  has been configured and oriented to insure that offset beam  329  is at an appropriate height to be focused accurately onto optical fiber  105  by integral fiber facing lens  118 . 
     Similarly, in module  340  of  FIG. 3B , VCSEL source  102  emits diverging beam  120 , which is collimated by collimating lens  119  integral to module  340  to form collimated beam  121 . Beam  121  in turn is reflected at a non-90 degree angle  342  by TIR at interface  341 , forming diagonal beam  352 . Wedged air gap beam splitter  345  includes non-parallel partially reflective interface surfaces  343 ,  344 , which are disposed such that horizontal beam  352  is refracted upward at first interface surface  343  to form refracted beam  355  and is refracted again at second interface surface  344  to form offset beam  359  aligned and parallel to the axis of optical fiber  105 . Module  340  has been configured and oriented such that offset beam  329  is focused accurately onto optical fiber  105  by integral fiber facing lens  118 . In general module  310  in  FIG. 3A  is advantageous relative to module  340  in  FIG. 3B  because of optical performance as well as manufacturability. 
       FIGS. 4 ,  5 , and  6  illustrate various configurations for generating multiple beam paths. 
       FIG. 4  depicts optical module  410  configured for bi-directional transmitting/receiving. VCSEL  102  emits diverging beam  120 , which is collimated by integral lens  419  to form collimated beam  421 . Beam  421  is reflected at a non-90-degree angle by TIR interface  411  to form downward slanted beam  422 . At wedge interface  413  of air gap beam splitter  412 , beam  422  is partially reflected to form beam  423  and partially refracted to form beam  426 , which propagates through interface  415  to form output beam  429  that is focused by fiber facing lens  118  onto optical fiber  105  in integral port connector  405 . Partially reflected beam  423  is reflected at TIR interface  414  to form monitor beam  424 , which propagates through interface  416  onto monitor detector  404 . Received beam from optical fiber  105  is collimated by integral fiber facing lens  118  and retraces the paths of beams  429  and  426 . At interface  413 , the received beam is partially reflected to form beam  430 , which is then detected by transceiver detector  403 , and is partially refracted to retrace the paths of beams  422  and  421  through TIR turn at interface  411  and then through collimating lens  419  onto monitor diode  402  situated behind VCSEL source  102 . 
     Alternatively, on interface  413  is a thin film optical coating which has two functions: (1) attenuate the received signal beam to a desired power level; (2) produce a second monitoring beam, which can be detected by a photodiode mounted under it. A single optical communication fiber is utilized to transport information both to and from transceiver module  410 . Embodiments of the present invention can also be used when the transmitted path carries a signal into the optical fiber, is monitored through a dual path, and a received signal is guided along a triple path. If the received signal is at a distinctly different wavelength from the transmitted wavelength, optical module  410  is part of a dual transceiver, e.g., sending at 1550 nm and receiving at 1310 nm, operating in a bi-directional communication mode. The information of the two signals, transmitted and received, can pass through the same optical fiber without interfering, because they occur at different wavelengths. The incoming signal is guided to the desired detector by use of thin film coating on interface  413 , which, e.g., reflects 1310 nm but transmits 1550 nm. 
     Open fiber control is a technology that allows a communication system to detect if an optical communication channel has been established, i.e., if a closed link from transmitter to receiver is present. By use of open fiber control, the light power launched into an optical fiber can be increased, thus allowing longer communication distances and/or improved signal quality, while still meeting eye safety requirements. One way to implement open fiber control is by use of transceiver pairs, such that the transmitter of a first transceiver is connected to the receiver of a second transceiver, while at the same time the transmitter of the second transceiver is connected to the receiver of the first transceiver. The configurations of the first and second transceivers can be similar but are not necessarily limited to that of optical module  410  shown in FIG.  4 . 
       FIG. 5  depicts optical module  510 , providing a TIR transmitted beam path with partial internal reflection at two wedge-like features, which (1) attenuate the transmitted beam to a desired level; (2) generate a monitoring path; and (3) offset the transmitted beam to a desired fiber port height above or below the input beam axis. VCSEL  102  emits diverging beam  120 , which is collimated by integral lens  519  to form collimated beam  521 . Beam  521  is reflected in a 90-degree turn by TIR interface  511  to form horizontal reflected beam  522 . At first wedge interface  512 , beam  522  is partially refracted to form output beam  524  (which is discarded in the present example) and partially reflected to form internal beam  523 . At second wedge interface  513 , internal beam  523  is partially refracted to form monitoring beam  525  incident on monitor detector  503  and is partially reflected to form horizontal output beam  529 , which is then focused by integral fiber facing lens  118  onto optical transmitting fiber  105  in integral port connector  405 . Horizontal output beam  529  propagates parallel to but offset from horizontal reflected beam  522 . 
       FIG. 6  depicts optical module  610 , providing a TIR transmitted beam path in which a TIR interface has curvature that simultaneously focuses the reflected beam in addition to only reflecting the collimated beam as illustrated in FIG.  1  through FIG.  5 . VCSEL  102  emits diverging beam  120 , which at interface  612  is partially refracted to form diverging beam  621  and partially reflected to form monitoring beam  620  incident on monitor detector  603 . Diverging beam  621  is simultaneously reflected and focused by curved TIR interface  611 , forming output beam  622 , which is focused onto optical transmitting fiber  105  in integral port connector  405 . At interface  613 , a portion of output beam  622  is reflected to form sampling beam  623 , which is reflected at TIR interface  614  to form monitoring beam  624 , which propagates through interface  615  to form monitoring beam  625  incident on monitor detector  604 . 
     The single block, all-polymer, molded, implementation allows port connector  405 , which can include a variety of connectors, to be molded in one piece integral with optical module  410 ,  510 ,  610 . In surface mounting technology, components such as capacitors, resistors and ICs (Integrated Circuits) are placed on a surface, e.g., a PCB substrate, by pick-and-place manipulators in a perpendicular placing action and are attached to the surface by use of an epoxy, solder, or other adhesive. The provision of structural surfaces and alignment features also included in optical module  410 ,  510 ,  610  allows the lens to be mounted on the surface of a printed circuit board as explained above. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.